There have been two runs at the LHC with lead ion collisions at 2.76 TeV per nucleon pair : the first at the end of 2010 (November-December) and the second at the end of 2011 (November- December). In what follows there is a compilation of the most spectacular results from these runs. Often comparison is done with the corresponding results from RHIC, the Relativistic Heavy Ion Collider at Brookhaven, where the energy is ~ 14 times lower. Calibrating at the LHC The interactions between heavy ions are complex and for their interpretation the knowledge of the initial conditions of the fireball at the instant after the collision is essential. The multiplicity, that is, the total number of particles produced in a collision, tells us a lot about how the quarks and gluons of the incoming nuclei transform into particles (pions, kaons etc) observed in the detectors; also about the energy density reached within the collision and the temperature of the fireball. The number of generated particles is correlated with the distance between centres of the colliding nuclei (impact parameter). Head-on (central) collisions (small impact parameter), when the largest number of incoming protons and neutrons participate in the collision, generate most particles. The charged particle multiplicity per colliding nucleon pair measured by ALICE for the most central collisions is double that measured at RHIC, where the collision energy is factor 14 lower, fig.1. This shows that the system created at LHC has much higher energy density and is at least 30% hotter that at RHIC. Fig. 2 shows the charged particle multiplicity as a function of the number of participants. Figure 1 (left). Charged particle multiplicity per colliding nucleon pair versus number of nucleons participating in the collision. Figure 2 (right). Charged particle multiplicity per colliding nucleon pair as a function of the collision energy. A perfect liquid at the LHC An interesting observable used for the study of the quark gluon plasma is flow: it provides information on the equation of state and the transport properties of matter created in heavy-ion collisions. Multiple interactions between the constituents of the created matter and initial asymmetries in the spatial geometry of non-central collisions result in an azimuthal anisotropy in particle production. The measured azimuthal distribution of particles in momentum space can be decomposed into Fourier coefficients. The second Fourier coefficient of this azimuthal asymmetry is known as elliptic flow. Its magnitude depends strongly on the friction in the created matter, characterized be the ratio η/s, where η is the shear viscosity and s the entropy. For a good fluid such as water the value of η/s is small. For a thick liquid such as honey η/s has large values. Measurements of the elliptic flow at RHIC had revealed that the hot matter created in heavy ion collisions flows like a fluid with little friction, with η/s close to the lower limit for a perfect fluid. At LHC this observation was confirmed, with values of the elliptic flow higher by 30% with respect to those at RHIC. Elliptic Flow The size of the fireball A technique called Bose-Einstein or HBT Interferometry allows us to measure the size and lifetime of the fireball created in heavy-ion collisions. This method is devised by the pioneering work of Hanbury, Brown and Twiss in astronomy and looks at pairs of particles (two-pion correlation functions). In hadron and ion collisions, there is enhanced production of bosons close together in phase space, due to Bose Einstein statistics. This leads to an excess of pairs at low relative momentum. The width of the excess region is inversely proportional to the size of the system at decoupling, at the point when most particles stop interacting. The quark gluon plasma behaves as a fluid, with strong collective motions described well by hydrodynamic equations. The collective flow makes the size of the system appear smaller as the pair momentum increases. The radius of the pion source is measured in three dimensions : along the beam axis, Rlong; along the transverse momentum of the pair, Rout; and in a direction perpendicular to these two, Rside, show in in Fig. 1. The similarity between Rout and Rside indicates a short duration of the emission – explosive emission. The time when the emission reaches its maximum, with respect to the first encounter, is found to be 10-11 fm/c, significantly longer than at RHIC. The product of the three radii – an estimate of the homogeneity volume of the system at decoupling - is twice as large as at RHIC. The conclusion is that at LHC the fireball formed in heavy ion collisions is hotter, lives longer and expands to a larger size that at lower energies. Partonic energy loss – Jet Quenching When the fast partons (quarks and gluons) produced from heavy ion collisions propagate through the dense medium of the fireball, they lose energy via gluon radiation or elastic scattering. The amount of radiated energy depends on the density of the medium and distance travelled by the parton in the medium, as well as the flavour of the parton. These partons become observable as jets of hadrons when they hadronize and the energy loss becomes evident in a phenomenon known as “jet quenching”. Instead of two jets going back-to-back and having similar energies, a striking imbalance is observed, one jet being almost absorbed by the medium. This is demonstrated in the following figure. One way of studying nuclear effects of the medium is by looking at the nuclear modification factor, RAA. This is the ratio of the charged particle pT spectrum in lead-lead collisions, normalized to the number of binary collisions , divided by the corresponding spectrum from proton-proton collisions. Direct photons and measurement of the QGP temperature One of the classic signals expected for a quark–gluon plasma (QGP) is the radiation of "thermal photons", with a spectrum reflecting the temperature of the system. With a mean-free path much larger than nuclear scales, these photons leave the reaction zone created in a nucleus–nucleus collision unscathed. So, unlike hadrons, they provide a direct means to examine the early hot phase of the collision. However, thermal photons are produced throughout the entire evolution of the reaction and also after the transition of the QGP to a hot gas of hadrons. In the PbPb collisions at the LHC, thermal photons are expected to be a significant source of photons at low energies (transverse momenta, pT, less than around 5 GeV/c). The experimental challenge in detecting them comes from the huge background of photons from hadron decays, predominantly from the two-photon decays of neutral pions and ? mesons. Direct photons are defined as photons not coming from decays of hadrons, so photons from initial hard parton-scatterings (prompt photons and photons produced in the fragmentation of jets) – i.e. processes already present in proton–proton collisions – contribute to the signal. Indeed, for pT greater than around 4 GeV/c, the measured spectrum agrees with that for photons from initial hard scattering obtained in a next-to-leading-order perturbative QCD calculation. For lower pT, however, the spectrum has an exponential shape and lies significantly above the expectation for hard scattering, as the figure shows. The inverse slope parameter measured by ALICE, TLHC = 304 ± 51 (stat.+syst.) MeV, is larger than the value observed in gold–gold collisions at √s = 0.2 TeV at Brookhaven’s Relativistic Heavy-Ion Collider (RHIC), TRHIC = 221 ± 19 (stat.) ± 19 (syst.) MeV. In typical hydrodynamic models, this parameter corresponds to an effective temperature averaged over the time evolution of the reaction. The measured values suggest initial temperatures well above the critical temperature of 150–160 MeV (approx. 1.8 × 1012 K) at which the transition between ordinary hadronic matter and the QGP occurs. The ALICE measurement also indicates that the LHC has produced the hottest piece of matter ever formed in a laboratory. Strangeness enhancement Ordinary matter around us is made of protons and neutrons, which in turn are composed of up (u) and down (d) quarks. The next quark that can be liberated from the sea of quark-anti-quark pairs that populate the vacuum is the strange quark (s-quark). It is heavier than u and d, yet close enough in mass to undergo production and modification processes in similar manner. That, and the relative abundance of the strange quark in high-energy interactions, make the s-quark a very useful study tool for proton-proton and heavy nucleus collisions. Strange particles, K-mesons (Kaons, made up of a strange and a non-strange quark pair), Lambda (uds), Xi (dss), and Omega (sss) baryons have an appreciable lifetime before they decay into ordinary matter. These decays have a characteristic geometrical configuration, which allows an effective reconstruction of strange particles. The strangeness data obtained in pp collisions are particularly important to improve the overall modeling of those collisions. PYTHIA is a software package that is able to generate events from a model. The model parameterizes the low-momentum processes taking place in elementary collisions, and calculates the higher energy processes up to the next to leading order perturbative term in the perturbative QCD expansion. The latest PYTHIA versions describe the general properties of real collisions fairly closely, but significantly underestimate the yields of strange particles: the more the strangeness content of the particle, the worse is the discrepancy. One of the recent PYTHIA versions, PYTHIA Perugia-2011, made significant modifications to its s-quark cross-section, and as a result came very close to reproducing the yields of baryons with multiple strange quarks, especially at higher transverse momentum. ALICE is the only experiment at the LHC to have measured Omega baryon yields in pp collisions. In addition, the pp measurement serves as a baseline for the measurements in Pb-Pb collisions, where we expect to produce the Quark-Gluon-Plasma (QGP). An enhancement in the production of particles with strange quarks has long been thought to be a signature of extra degrees of freedom available in the QGP. Indeed, this enhancement has been seen at lower energies as well: the larger the volume of the collision, the more the number of Lambda, Xi and Omega baryons increases with respect to the baseline (a pp or a Be-Be collision). This is also observed at 2.76 TeV Pb-Pb collisions, however, with a caveat: the enhancement is smaller than that at lower energies! We think this is due to the complexity of our baseline: at these high energies, pp collisions to which we compare are more complex and produce much more strangeness than events at lower energies. Enhancement in the production of particles with strange quarks ALICE and the charm of heavy-ion collisions The ALICE collaboration has measured the production of the charmed mesons D0 and D+ in lead–lead collisions at the LHC. In central (head-on) collisions they find a large suppression with respect to expectations at large transverse momentum, pt, indicating that charm quarks undergo a strong energy loss in the hot and dense state of QCD matter formed at the LHC. This is the first time that D meson suppression has been measured directly in central nucleus–nucleus collisions. Heavy-flavour particles are recognized as effective probes of the highly excited system (medium) formed in nucleus–nucleus collisions; they are expected to be sensitive to its energy density, through the mechanism of in-medium energy loss. The nuclear modification factor RAA – the ratio of the yield measured in nucleus–nucleus collisions to that expected from proton–proton collisions – is well established as a sensitive observable for the study of the interaction of hard partons with the medium. Because of the QCD nature of parton energy-loss, quarks are predicted to lose less energy than gluons (which have a higher colour charge); in addition, the so-called "dead-cone" effect and other mechanisms are expected to reduce the energy loss of heavy partons with respect to light ones. Therefore, there a pattern of gradually decreasing RAA suppression should emerge when going from the mostly gluon-originated light-flavour hadrons (e.g. pions) to the heavier D and B mesons: RAA( ) RAA(D) RAA(B). The measurement and comparison of these different probes provides, therefore, a unique test of the colour-charge and mass dependence of parton energy-loss. Experiments at the Relativistic Heavy Ion Collider at Brookhaven measured the suppression of heavy flavour hadrons indirectly in gold–gold collisions at 200 GeV through the RAA of the inclusive decay electrons. Using data from the first lead–lead run at the LHC (?sNN = 2.76 TeV), the ALICE collaboration has measured the production of prompt D mesons via the reconstruction of the decay vertex in the channels D0?K–p+ and D+?K–p+p+. The results show a suppression of a factor 4–5, as large as for charged pions, above 5 GeV/c (see figure). At lower momenta, there is an indication of smaller suppression for D than for mesons. Data with higher statistics, expected from the 2011 lead–lead run, will allow the collaboration to study this region with more precision and address this intriguing mass-dependence in QCD energy-loss. The result implies a strong in-medium energy loss for heavy quarks, as also suggested by the suppression measured by the ALICE collaboration for electrons and muons from heavy flavour decays, and by the CMS collaboration for J/ψ particles from B meson decays. The mystery of the J/Psi The J/ψ is composed of a heavy quark–antiquark pair with the two objects orbiting at a relative distance of about 0.5 fm, held together by the strong colour interaction. However, if such a state were to be placed inside a QGP, it turns out that its binding could be screened by the huge number of colour charges (quarks and gluons) that make up the QGP freely roaming around it. This causes the binding of the quark and antiquark in the J/ψ to become weaker so that ultimately the pair disintegrates and the J/ψ disappears – i.e. it is "suppressed". Theory has shown that the probability of dissociation depends on the temperature of the QGP, so that the observation of a suppression of the J/ψ can be seen as a way to place a "thermometer" in the medium itself. Such a screening of the colour interaction, and the consequent J/ψ suppression, was first predicted by Helmut Satz and Tetsuo Matsui in 1986 and was thoroughly investigated over the following years in experiments with heavy-ion collisions. In particular, Pb–Pb interactions were studied at CERN’s Super Proton Synchrotron (SPS) at a centre-of-mass energy, √s, of around 17 GeV per nucleon pair and then Au–Au collisions were studied at √s=200 GeV at Brookhaven’s Relativistic Heavy-Ion Collider (RHIC). As predicted by the theory, a suppression of the J/ψ yield was observed with respect to what would be expected from a mere superposition of production from elementary nucleon–nucleon collisions. However, the experiments also made some puzzling observations. In particular, the size of the suppression (about 60–70% for central, i.e. head-on nucleus–nucleus collisions) was found to be approximately the same at the SPS and RHIC, despite the jump in the centre-of-mass energy of more than one order of magnitude, which would suggest higher QGP temperatures at RHIC. Ingenious explanations were suggested but a clear-cut explanation of this puzzle proved impossible. At the LHC, however, extremely interesting developments are expected. In particular, a much higher number of charm–anticharm pairs are produced in the nuclear interaction, thanks to the unprecedented centre-of-mass energies. As a consequence, even a suppression of the J/ψ yield in the hot QGP phase could be more than counter-balanced by a statistical combination of charm–anticharm pairs happening when the system, after expansion and cooling, finally crosses the temperature boundary between the QGP and a hot gas of particles. If the density of heavy quark pairs is large enough, this regeneration process may even lead to an enhancement of the J/ψ yield – or at least to a much weaker suppression with respect to the experiments at lower energies. The observation of the fate of the J/ψ in nuclear collisions at the LHC constitutes one of the goals of the ALICE experiment and was among its main priorities during the first run of the LHC with lead beams in November/December 2010. The ALICE experiment is particularly suited to observing a J/ψ regeneration process. For simple kinematic reasons, regeneration can be more easily observed for charm quarks with low transverse-momentum. Contrary to the other LHC experiments, both detector systems where the J/ψ detection takes place – the central barrel (where the J/ψ→e+e– decay is studied) and the forward muon spectrometer (for J/ψ→μ+μ–) – can detect J/ψ particles down to zero transverse momentum. As the luminosity of the LHC was still low during its first nucleus–nucleus run, the overall J/ψ statistics collected in 2010 were not huge, of the order of 2000 signal events. Nevertheless, it was possible to study the J/ψ yield as a function of the centrality of the collisions in five intervals from peripheral (grazing) to central (head-on) interactions. Clearly, suppression or enhancement of a signal must be established with respect to a reference process. And for such a study, the most appropriate reference is the J/ψ yield in elementary proton–proton collisions at the same energy as in the nucleus–nucleus data-taking. However, in the first proton run of the LHC the centre-of-mass energy of 7 TeV was more than twice the energy of 2.76 TeV per nucleon–nucleon collision in the Pb–Pb run. To provide an unbiased reference, the LHC was therefore run for a few days at the beginning of 2011 with lower-energy protons and J/ψ production was studied at the same centre-of-mass energy of Pb–Pb interactions. The Pb–Pb and p–p results are compared using a standard quantity, the nuclear modification factor RAA. This is basically a ratio between the J/ψ yield in Pb–Pb collisions, normalized to the average number of nucleon–nucleon collisions that take place in the interaction of the two nuclei and the proton–proton yield. Values smaller than 1 for RAA therefore indicate a suppression of the J/ψ yield, while values larger than 1 represent an enhancement. Fig. 1. A comparison of the J/ψ suppression between RHIC (PHENIX) and the LHC (ALICE). The ALICE results show a strikingly smaller suppression, in particular for head-on collisions (large Npart), despite the much larger centre-of-mass energy. The results from the first ALICE run are rather striking, when compared with the observations from lower energies (figure 1). While a similar suppression is observed at LHC energies for peripheral collisions, when moving towards more head-on collisions – as quantified by the increasing number of nucleons in the lead nuclei participating in the interaction – the suppression no longer increases. Therefore, despite the higher temperatures attained in the nuclear collisions at the LHC, more J/ψ mesons are detected by the ALICE experiment in Pb–Pb with respect to p–p. Such an effect is likely to be related to a regeneration process occurring at the temperature boundary between the QGP and a hot gas of hadrons (T≈160 MeV). The picture arises from these observations is consistent with the formation, in Pb–Pb collisions at the LHC, of a deconfined system (QGP) that can suppress the J/ψ meson, followed by a hadronic system in which a fraction of the charm–anticharm pairs coalesce and ultimately give a J/ψ yield larger than that observed at lower energies. This picture should be clarified by the Pb–Pb data that were collected in autumn 2011. Thanks to an integrated luminosity for such studies that was 20 times larger than in 2010, a final answer on the fate of the J/ψ inside the hot QGP produced at the LHC seems to be within reach. 原文见 http://aliceinfo.cern.ch/Public/en/Chapter1/results.html
http://scienceblog.com/ Efforts to mitigate climate change must target energy efficiency Study brings a doubted exoplanet ‘back from the dead’ Scientists sharing space: Proximity breeds collaboration Scientists deepen genetic understanding of MS New genes discovered for body mass levels Robots in the Home: Will Older Adults Roll Out the Welcome Mat? Exercise boosts satisfaction with life Changing the balance of bacteria in drinking water to benefit consumers Bushmeat pushes African species to the brink Antibacterial Triclosan needs to be monitored
http://scienceblog.com/ Mug handles could help hot plasma give lower-cost, controllable fusion energy Who was TV’s first anchorman? Poor UK summers may arise from global warming and Arctic ice loss Relaxing immigration could generate billions for global economy Angry? Sad? Ashamed? Depressed people can’t tell difference Nearby super-Earth likely a diamond planet Prospective Alzheimer’s drug builds new brain cell connections The Marshmallow Study Revisited Soft-shelled turtles urinate through mouth
For normal spin polarized calculations, and if lorbit=11, the general layout for the procar file is: spin up{ k-point: i kx ky kz weight { band 1: energy: E1 { atom1: s py pz px dxy dyz dz2 dxz dx2 total (all atoms) total ..... } {all bands} } {all kpoints} } {spin down} to view it with a normal data plotter ( i. e. gnuplot, origin, etc) you need to parse these data into a table arranged like this (or watever you find useful) for every band: (kpoint distance) Energy (s py pz px dxy dyz dz2 dxz dx2)_totals This layout changes a little if you perform spin-orbit calculations. Instead of having spin up and spin down datablocks, for each band you have four blocks with m_tot, m_x, m_y and m_z contributions for all atoms. Hope This helps! if this is wrong, I will also be grateful to anyone who can point me to the section in the manual where this is clearly explained! About p4v, it is a great tool if you can make it run in your system, so I recommend you to try!
Raman spectroscopy determination of the Debye temperature and atomic cohesive energy of CdS, CdSe, Bi 2 Se 3 , and Sb 2 Te 3 nanostructures \JPA 112, 083508 (2012)\ We have formulated the size and temperature dependence of the phonon relaxation dynamics for CdS, CdSe, Bi 2 Se 3 and Sb 2 Te 3 nanostructures based on the framework of bond order–length–strength (BOLS) correlation and the local bond averaging (LBA) approach. The Raman shifts are correlated directly to the identities (nature, order, length, and energy) of the representative bond of the specimen without needing involvement of the Grüneisen parameters or considering the processes of phonon decay or multi-phonon resonant scattering. Quantitative information of the Debye temperature, the atomic cohesive energy, the reference frequencies from which the Raman shifts proceed, and the effective coordination numbers of the randomly sized particles, as well as the length and energy of the representative bond has been obtained. It is clarified that the size-induced phonon softening arises intrinsically from the cohesive weakening of the undercoordinated atoms in the skin up to three atomic layers and the thermally-derived phonon softening results from the thermally lengthening and weakening of bonds. Developed approach empowers the Raman technique in deriving quantitative and direct information regarding bond stiffness relaxation with applied stimuli such as coordination, mechanical, thermal and chemical environment, which are crucial to practical applications.
http://www.nationmaster.com/compare/Singapore/United-States/Energy ps. I tried to read a little about Singapore before I started my first trip to this mega city. We all know that the weather in Singapore is too warm for being outdoors all the time during the day. One can retreat to a place with a/c easily here: a shopping mall, an MRT station, etc. Since the a/c is used so widely in Singapore, I wanted to know where the energy is coming from. When I could not find the answer from talking to people, I google...
Liu Zh., Liang S., Geng Y., Xue B., Xi F., Pan Y., Zhang T., Fujita T.. Features, trajectories and driving forces for energy-related GHG emissions from Chinese mega cites: The case of Beijing, Tianjin, Shanghai and Chongqing . ENERGY, 2012, 37(1): 245-254. -------------------------------------------------------------------------------- Abstract ： With China’s rapid economic development and urbanization process, cities are facing great challenges for tackling anthropogenic climate change. In this paper we present features, trajectories and driving forces for energy-related greenhouse gas (GHG) emissions from four Chinese mega-cities (Beijing, Tianjin, Shanghai and Chongqing) during 1995–2009. First, top-down GHG inventories of these four cities, including direct emissions (scope 1) and emissions from imported electricity (scope 2) are presented. Then, the driving forces for the GHG emission changes are uncovered by adopting a time serial LMDI decomposition analysis. Results indicate that annual GHG emission in these four cities exceeds more than 500 million tons and such an amount is still rapidly growing. GHG emissions are mainly generated from energy use in industrial sector and coal-burning thermal power plants. The growth of GHG emissions in four mega-cities during 1995–2009 is mainly due to economic activity effect, partially offset by improvements in carbon intensity. Besides, the proportion of indirect GHG emission from imported energy use (scope 2) keeps growing, implying that big cities are further dependent on energy/material supplies from neighboring regions. Therefore, a comprehensive consideration on various perspectives is needed so that different stakeholders can better understand their responsibilities on reducing total GHG emissions. Highlights: ► We present features, trajectories and driving forces on greenhouse gas (GHG) emission in four Chinese mega-cities. ► All four cities experienced a rapid growth of GHG emission due to economic activity effect. ► Different industrial structure and development stage result in different GHG emission scenarios. ► Mitigation policies should be differentiated in different cities, based upon local realities.
全名：2007-06A systems approach towards high energy laser implementation aboard navy ships 共63页。 免费网盘下载地址： http://www.ctdisk.com/file/4335497 论坛下载地址： http://radarew.5d6d.com/thread-589-1-1.html
The devastating earthquake and tsunami off the coast of Japan in March 2011 will have a significant impact on the future of nuclear energy. The ultimate outcome of the Fukushima Daiichi accident will influence public opinion and government decisions about the future development of nuclear power worldwide. And the lessons we learn from the crisis will inform future decisions about nuclear fuel storage, appropriate safety standards and accountability measures, and emergency preparedness. However, our ability to respond effectively to the challenges presented by the Fukushima Daiichi accident has been, in large part, predicated on research, practices, and policies developed over the last three decades. What additional events or developments might surprise us in the future that could affect the spread of nuclear energy? How can we better anticipate such surprises so that we can more effectively mitigate the impacts of negative develop ments and maximize the impact of positive developments? Toward this end, in August 2010 the American Academy, as part of its Global Nuclear Future Initiative, cosponsored a meeting with the Center for International Security and Cooperation (CISAC) at Stanford University on Game Changers for Nuclear Energy. The conference brought together a small group of representatives from diverse energy backgrounds—including government, industry, NGOs, national laboratories, and academia—for an in-depth discussion of variables that could affect the future of nuclear power. These include reactor and fuel cycle technology and regulation, accidents and security incidents, climate change, and relevant politics. The purpose of the workshop was to explore what events, foreseen or not, could change the presently foreseen nuclear power “game.” What follows is the resulting paper from this meeting. This Occasional Paper is part of the American Academy’s Global Nuclear Future Initiative, which examines the safety, security, and nonproliferation implications of the global spread of nuclear energy and is develop ing pragmatic recommendations for managing the emerging nuclear order. The Global Nuclear Future Initiative is supported by generous grants from Carnegie Corporation of New York; the William and Flora Hewlett Foundation; the Alfred P. Sloan Foundation; the Flora Family Foundation; and Fred Kavli and the Kavli Foundation. The American Academy is grateful to the principal investigators of the Global Nuclear Future Initiative—Steven Miller, Scott Sagan, Robert Rosner, and Stephen Goldberg—for contributing their time, experience, and expertise to the work of the Initiative. CISAC would like to thank the Flora Family Foundation and the John D. and Catherine T. MacArthur Foundation for supporting the scholars’ work on this project. We would like to thank Thomas Isaacs, Michael May, and Kate Marvel for organizing a substantive meeting and the participants for their thoughtful contributions at the meeting and to this paper. We are grateful to Michael and Kate for bringing their knowledge and insight to bear on this important issue. Leslie Berlowitz President and William T. Golden Chair American Academy of Arts and Sciences Scott D. Sagan Caroline S.G. Munro Professor of Political Science Codirector, Center for International Security and Cooperation, Stanford University 原文见 http://www.amacad.org/pdfs/book_game_changers.pdf
EXECUTIVE SUMMARY Water as a Factor in the Energy Supply Chain Water and energy are closely linked. The water industry is energy-intensive, consuming electricity for desalination, pumping, and treatment of wastewater. The energy industry is also water-intensive, which is the focus of this report. Water is used for resource extraction (oil, gas, coal, biomass etc.), energy conversion (refining and processing), transportation and power generation. Energy accounts for 27% of all water consumed in the United States outside the agricultural sector (Electric Power Research Institute 2008). Water, like energy, is a commodity but with very different characteristics. Water is almost always local where energy tends to be more of a global sector, linked to fungible commodities. Constraints on water availability often influence the choice of technology, sites, and types of energy facilities. For instance, water has always been a potential constraint for thermal electricity generation, given the large volumes of water typically required for cooling. Water availability is thus of paramount importance when deciding on a suitable location of a power plant. This paper provides an overview of water consumption for different sources of energy, including extraction, processing and conversion of resources, fuels, and technologies. The primary focus of is consumptive use of water for different sources of energy. Where appropriate, levels of water withdrawals are also discussed, especially in the context of cooling of thermoelectric power plants. The most comprehensive review of water consumption and energy production is a December 2006 report to Congress by the U.S. Department of Energy (DOE), titled “Energy Demands on Water Resources” (U.S. Department of Energy 2006). The DOE report was the starting point for this research effort, with additional sources used to increase the coverage of fuels (notably improved estimates for biofuels and shale gas production), additional processing technologies (coal-to-liquids and gas-to-liquids), and a more extensive review of water use in electricity from renewable sources, and carbon capture and sequestration (CCS). The data compiled in this analysis is based on an extensive review of available literature for the U.S. market, with particular emphasis on capturing recent trends where there may have been significant changes (e.g., biofuels, shale gas, and solar technology) and further studies completed. To the best of the authors’ knowledge, there are no individual reports that have integrated information of resource extraction, processing, and conversion since the 2006 DOE report. 原文见 http://belfercenter.ksg.harvard.edu/files/ETIP-DP-2010-15-final-4.pdf
暗能量综述 2011年4月3日 http://limiao.net/2789 感谢李淼教授同意转载！ 从去年年底，一直致力于写暗能量综述，这篇文章很长，达到176页，应该是暗能量综述里最长的文章。作者除了我，还有王一，李霄栋和王爽。 文章： Dark Energy 这篇文章正文151页，文献目录就有20多页，文章贴出后很快收到十几封信要求引用他们的文章。文章分两大部分，第一部分总结理论模型和想法，有83页，其余是总结观测暗能量手段，未来观测计划，以及数值工作。 第一部分是理论部分，先大致回顾了Weinberg在他的著名综述文章中的分类（Rev. Mod. Phys. 61 (1989) 1）。这篇文章比暗能量的发现早了大约10年，这篇文章目前被引了1900次。即使在1998年前，宇宙学常数一直是个重要的理论问题，所以Weinberg的文章每年大约也有25次引用左右。而在1998年之后，被引了1600次左右。当然，这个引用数目并不吓人，因为我想Weinberg不会去特意写信让大家去引他。1998年Riess等人的文章被引了五千次了。 Weinberg的分类是：1、超对称和超弦。2、人择原理。3、调节机制。4、修改引力理论。5、量子宇宙学。 我们将98年以后的新模型新想法分成8类，前五类和Weinberg的一样，只是将第一类变成了对称性。新增的3类是：6、全息原理。7、引力的反作用。8、唯象理论。 其实第8类包含的quintessence也早就了。第8类最大，几乎所有不带理论想法的模型都是唯象模型。 对称性除了超对称外，还有’t Hooft等人的坐标延拓，共形对称性，还有每个量子场和其ghost partner之间的对称性。人择原理则有不少弦论界中的人相信，例如Susskind和Polchinski。调节机制则增加了高维中的调节机制，例如通过膜与bulk中的标量场的耦合来调节。第4类，修改引力，也许在唯象模型之外发表文章最多的一类了。我们将f(R)理论，MOND及其相对论性推广，DGP理论都归在这一类。第五类，主要是Hartle-Hawking的无界波函数理论，其实这一类研究的人最少，也缺乏理论基础。 毫无疑问，我自己对第6类最感兴趣，我自己的理论研究基本只在这一类中。你要让我打赌，我会将赌注押在这一类上。在研究全息暗能量之外，过去两年我还研究了Casimir energy以及熵力与暗能量的关系。我坚信暗能量是有限尺度效应，即暗能量的“总能”与宇宙某个宏观尺度成正比，能量密度与该尺度的平方成反比。那么，暗能量或宇宙学常数的紫外发散是怎么解决的？我倾向于严格抵消。当然，我们在文章中没有强调我个人的观点。 对暗能量的探测手段，李霄栋和王爽认真地调研了几个月。 暗能量的探测手段首先是IA型超新星。宇宙加速膨胀就是用超新星的Hubble图发现的。在超新星之外，最常用的手段就是CMB和BAO了，前者是微波背景辐射，后者是重子声学振荡。目前，CMB有用的数据点不多，BAO也 不多。也许在未来，BAO的数据会越来越多。 在以上三大主要手段外，还有：弱引力透镜；星系团计数；伽玛暴；X射线气体；Hubble参数的直接观测；古老星体的年龄；密度涨落的成长因子。 接着是综述暗能量的探测计划，这是根据2006年暗能量Task Force的分类，分为四个阶段。第一阶段已经结束了，第二阶段正在进行中，第三阶段即将实施，第四阶段是未来10年左右要实施的。从暗能量的两个简单参数（ ）来看，第三、第四阶段提高的精度都是3倍左右。当然如果考虑更多的参数，提高还是蛮多的。后来一些计划进化了，例如JDEM进化成了WFIRST。 ————————补充 ———————— （1）李淼老师等的论文 ，在《Dark Energy》，Cosmology and Extragalactic Astrophysics （arXiv:1103.5870v2 ）： http://arxiv.org/abs/1103.5870 （2）一些读者评论摘录如下（陆续补充中）： 2011年4月3日17:08:47 李老师,正在拜读您的大作. 关于暗能量的探测方法, 还有下面的: In 1986, Schutz found that the luminosity distance of the binary neutron stars (or black hole) can be independently determined by observing the gravitational wa ves generated by this system. If we can also find the electricmagnetic counterpart, the redshift can also be determined. Thus the dL-z relation can be used to study the evolution of universe. This is the so-called: standard sires. (Schutz,Nature,1986)。 最近有很多人讨论利用LISA能探测到的超大质量双黑洞,或者用Einstein Telescope能探测到的双中子星系统来探测暗能量: B. Schutz, Nature (London) 323, 310 (1986). D. E. Holz and S. A. Hughes, Astrophys. J 629, 15 (2005). K. G. Arun, B. R. Iyer, B. S. Sathyaprakash, S. Sinha, and C. Van Den Broeck, Phys. Rev. D 76, 104016 (2007); B. S. Sathyaprakash, B. F. Schutz, and C. Van Den Broeck, Classical Quantum Gravity 27, 215006 (2010). W. Zhao, C. Van Den Broeck, D. Baskaran, and T. G. F. Li PRD 83, 023005 (2011) 2011年4月7日11:26:21 any one see this? http://www.nytimes.com/2011/04/06/science/06particle.html?_r=1ref=science and the paper: http://arxiv.org/abs/1104.0699
水循环过程中，除了自然力驱动的水的自然水循环，还包括社会力所驱动的社会水循环。在社会水循环过程中，内在驱动力是水的经济社会效益，而外在的物化表现则是电力驱动的水泵。 Vast amounts of energy are needed for the transportation, distribution and treatment of water. Pumping it over mountain ranges or from deep underground aquifers also requires a significant amount of energy. But the largest share of energy use comes from individual customers who heat water to bathe, cook and run businesses. 研究结果正如上面所说， 能源消耗最大的位于用水终端的个体水消费者。 Results： （1）In the sector of water extraction and delivery, only 23% of electricity requirements are used for water pumping out, purification, and distribution. Energy costs varydepending on the pumping distance, water quality, water pipelines, and water source. Groundwater pumping can increase energy use 30% over surface water sources. (2) End use: In this sector, up to 73% electricity requirements are needed in water cycle by homes, farms, and businesses. It is reported that household appliance such as washing machine, dishwasher, water heaters, and dryers use the largest amount of electricity in water cycle, 28%. (3) Waste water management just costs only 4% energy, which not only reveals waste treatment currently need less energy but shows there is lot of potentiality we can clean much moredischargedwater again. So far, only 4% electricity was used for water cleaning before it is discharged to water source. However, with the population growth and increasingly stringent treatment standards, more and more energy is needed, which could soon lead to increased wastewater management costs. Discussion Based on the results above, I suggest we should shift our eyes from water to energy and water together. How to do some comprehensive research on water cycle driven by energy requirements should be the focus of water cycle research in the future.
欢迎大家补充！众人拾柴火焰高呀！ 2011 1. Thermal and Materials Nanoscience and Nanotechnology, May 29 June 3, 2011, Antalya, Turkey; http://www.ichmt.org/tmnn-2011/ 2. 7th International Conference on Computational Heat and Mass Transfer , 18-22 July, 2011, ?stanbul, TURKEY 3. 9th International Fuel Cell Science, Engineering Technology Conference , 07-10 August, 2011, Washington DC, USA 4. The third IEEE Energy Conversion Congress and Exposition, Phoenix, Arizona, 17-22 September, 2011. 5. 19th European Conference on Thermophysical Properties, August 28 - September 1, 2011, Thessaloniki, Greece, Nicolaos Germanos Conference Center, HELEXPO http://19ectp.cheng.auth.gr/ 6. ICTA 2011 : International Conference on Thermophysics and Aeromechanics Paris, France , July 27-29, 2011. http://www.waset.org/conferences/2011/paris/icta/index.php 7. ASME-JSME 8th Thermal Engineering Joint Conference (AJTEC2011), March 13 - 17, 2011, Waikiki Beach Marriott Resort Spa, Honolulu, Hawaii, USA. https://www.asmeconferences.org/AJTEC2011/ 8.42nd AIAA Thermophysics Conference, 27 - 30 Jun 2011, Sheraton Waikiki and the Hawaii Convention Center Honolulu, Hawaii http://www.aiaa.org/content.cfm?pageid=230lumeetingid=2223viewcon=submit 9. 31th International Thermal Conductivity Conference (ITCC) and 19th International Thermal Expansion Symposium (ITES),June 26 - 30, 2011 Saguenay, Qc, CANADA http://www.thermalconductivity.org/ 10.INCOTEE 2011 - International Conference on Thermal Energy and Environment, India, March 24 - 26, 2011, www.kalasalingam.ac.in/mech/incotee2011.html
David Bradwell, 28 MIT Cheap, reliable batteries to store renewable energy Liquid battery: An early prototype battery has been sawed in half to reveal its electrodes and electrolyte, which are liquid during operation. Credit: Joshua Scott In the fall of 2007, David Bradwell, an MIT grad student, created a new kind of battery--one that might eventually be used to store massive amounts of solar and wind energy for use at night or when the wind isn't blowing. Unlike existing batteries, it has active components that are liquid, which enables it to handle high currents without fracturing (the battery is kept at 700 degrees Celcius with the help of insulation). Last year Bradwell's research attracted a total of about $11 million from the U.S. Department of Energy's new Advanced Research Projects Agency-Energy (ARPA-E) and the French oil company Total. Bradwell's battery is based on an electrolyte that can dissolve a compound consisting of two metals, such as magnesium and antimony. Applying a current in one direction splits the compound, and the two metals are deposited onto opposite electrodes. When no electricity is delivered, a voltage difference between the electrodes drives a current in the other direction. That generates electricity and causes the metals to recombine in the electrolyte. The system could eventually cost less than $100 per kilowatt-hour for a new installation--about the same as pumping water up a hill to be released later to spin a turbine (the cheapest conventional approach for large-scale energy storage), says Arun Majumdar, the director of ARPA-E. The battery, however, would have the advantage of working in places without hills or large amounts of water, where many renewable power resources are located. --Kevin Bullis from:http://www.technologyreview.com/TR35/Profile.aspx?Cand=TTRID=972
After months of behind the scenes negotiations, Senators John Kerry (D-MA) and Joe Lieberman (I-VT) unveiled their climate and energy bill, the American Power Act (APA), on May 12. The draft bill aims to reduce carbon emissions by 17 percent by 2020 and by over 80 percent in 2050 through a cap and refund regime, which would return two-thirds of revenues not dedicated to reducing the nations deficit back to consumers with the rest spent on ensuring a smooth transition for American businesses and investing in projects and technologies to reduce emissions and advance our energy security. Below is a summary of APA provisions of interest to the research community. ------------------------------------------- Energy Provisions The APA was drafted to try to bridge the differences within the Senate in realization that at least 60 votes would be needed to pass energy and climate change legislation. As such, the APA includes provisions to promote the development of a U.S. nuclear industry; to allow offshore oil and gas exploration and drilling (modified in view of the unprecedented BP oil spill in the Gulf of Mexico); to enable the use of domestic coal resources by facilitating a national strategy to develop and deploy carbon capture and sequestration technologies; to accelerate large-scale deployment of renewable energy technologies and energy efficiency by establishing a Clean Energy Technology Fund; and to promote workforce development in clean energy technologies. The APA is not a complete companion bill to the House-passed American Clean Energy and Security Act (H.R. 2454), also known as the Waxman-Markey bill that passed the House of Representatives on June 26, 2009. Many of the provisions of interest to the academic and research communities are addressed in a separate Senate bill, S. 1462, the American Clean Energy Leadership Act of 2009 authored by Sen. Jeff Bingaman (D-NM), that has been pending before the Senate since last July. These provisions include the authorization of the Energy Innovation Hubs, improvements to ARPA-E (Advanced Research Projects Agency-Energy), and establishment of a Clean Energy Deployment Administration. The Senate Energy and Natural Resources Committee recently approved a package of bipartisan amendments to S. 1462 that align more closely with the Waxman-Markey bill (a separate report will be prepared on S. 1462). The APA and S. 1462 are envisioned to be combined into one bill if the Senate considers climate change and energy legislation this year. The American Power Act includes the following energy-related provisions of interest to universities: Nuclear Energy Research Initiative The Senate bill requires the Secretary of Energy to develop and publish a schedule that contains an outline of a five-year strategy to conduct research to lower the cost of nuclear reactors, including research regarding modular and small-scale reactors; balance-of-plant issues; cost-efficient manufacturing and construction; licensing issues; and enhanced proliferation controls. The bill authorizes $50 million per year for each of fiscal years (FY) 2011 through 2015 for this program and would need to be funded through the Congressional appropriations process. The House (Waxman-Markey) bill does not include such a program. National Strategy for Carbon Capture and Sequestration The Senate bill tasks federal agencies, including the Environmental Protection Agency (EPA), Department of Energy (DOE), Department of Interior (DOI), and other agencies the President may designate with reporting to Congress on the key legal, regulatory, and other barriers to the commercial-scale deployment of carbon capture and storage (CCS) technology. The Administrator of EPA is charged with establishing a task force composed of experts, including academic researchers, to study existing laws, regulatory frameworks, and private sector mechanisms to assess their applicability to risk management, financial responsibilities, and environmental liabilities associated with CCS. The House bill does not include this initiative. Carbon Capture and Sequestration Program Technical Advisory Committee APA establishes a special funding program for the development and deployment of carbon capture, sequestration and conversion technologies that would be funded by a special assessment on electric utilities for all fossil fuel-based electricity. This program would be governed by a Carbon Capture and Sequestration Program Partnership Council that would appoint a technical advisory committee, whose membership could include universities and independent research institutions, to provide independent scientific review of applications for grants, contracts, cooperative agreements and other transactions funded under the special funding program. The House bill includes provisions to establish a Carbon Storage Research Corporation that would invest $10 billion in carbon capture and storage technologies. Electric Vehicle Infrastructure APA authorizes the Secretary of Energy to work with stakeholders that could include universities to develop a National Transportation Low-Emission Energy Plan and a Pilot Program. The plan would assess the near- and long-term need for and location of electric drive vehicle refueling infrastructure across the nation and identify the infrastructure and standardization needs for electricity providers, infrastructure providers, vehicle manufacturers, and consumers necessary to deploy electric vehicles by January 2020. The proposed pilot projects in different regions of the country would demonstrate the electric drive vehicles and infrastructure. These initiatives are subject to future appropriations. The House bill would direct $20 billion to electric and other advanced technology vehicles. Clean Energy Technology Fund The Senate bill establishes a Clean Energy Technology Fund to support programs that enhance the economic, energy, and environmental security of the United States through the development of clean energy technologies and the development and deployment of advanced energy technologies. The fund would be capitalized by allowances distributed by the Secretary of Energy on a competitive basis to institutions of higher education, companies, research foundations, trade and industry research collaborations, or consortia of such entitles to support research and development of clean energy technology, including nuclear energy, energy transmission and storage technology, energy efficiency improvements, the Smart Grid, and energy efficiency improvements for transportation. There is no estimate for the amounts that would be available from the allowances. The House bill would allocate approximately one and a half percent of cap and trade allowances to specifically fund the Energy Innovation Hubs and ARPA-E. The House bill would also direct $20 billion to electric and other advanced technology vehicles, and $20 billion to basic RD activities for clean energy and energy efficiency programs largely focused on industry. The House bill would establish a Clean Energy Deployment Administration to support private investment in clean energy technologies, including nuclear power. Greenhouse Gas Emission Reduction and Sequestration Advisory Committee APA authorizes the Secretary of Energy and Administrator of EPA to establish an independent advisory committee composed of scientists and other experts to provide scientific and technical advice on the establishment and implementation of the offset credit program for domestic Greenhouse Gas reductions, including methodologies and types of projects or activities to be funded. There is no comparable advisory committee in the House bill. International Offsets Integrity Advisory Committee APA provides for the establishment of an independent International Offset Integrity Advisory Committee to provide scientific and technical advice on establishing and implementing the international offsets program authorized in the bill. The advisory committee will also provide recommendations on offset project eligibility, scientific uncertainty, quantification methodologies and related issues. There is no comparable advisory committee in the House bill. Clean Energy Technology and Jobs The Senate bill authorizes three initiatives related to developing the clean energy workforce. The Secretary of Education is authorized to award competitive grants to partnerships to develop programs of study focused on emerging careers and jobs in the fields of clean energy, renewable energy, energy efficiency, climate change mitigation, and climate change adaptation. The Secretary is to consult with the Secretary of Labor and the Secretary of Energy in developing these funding solicitations. An eligible partnership includes a post-secondary education institution, a local education agency, and representatives of businesses, labor, and industry. The Senate bill also authorizes these three agencies to develop an Internet-based clearinghouse to aid career education and job training programs for the renewable energy sectors. The Secretary of Labor is to solicit information from universities, businesses, career and technical schools, and community colleges in crafting the clearinghouse. APA also authorizes a clean energy construction careers demonstration project to promote vocational training and workforce development in the green energy sector. The House bill includes provisions to direct cap and trade revenues toward programs to train the energy workforce and to establish a vocational education and job training clearinghouse. Low-Carbon Industrial Technologies RD The Senate bill authorizes the Secretary of Commerce to establish a federally funded research and development center (FFRDC)to support development and demonstration of technology to improve the competitiveness and job creation in the domestic manufacturing sector. The FFRDC is to be known as the National Industrial Innovation Institute and is to be located in a facility owned and operated by a nongovernmental, nonprofit organization selected by the Secretary.The Institute is to collaborate with research universities and other research and technology entities as well as industry and manufacturers. This initiative is subject to funding through the Congressional appropriations process. The House bill has no comparable provision.
http://www.nytimes.com/2010/02/13/opinion/13herbert.html?em Op-Ed Columnist Watching China Run function getSharePasskey() { return 'ex=1423803600&en=f22c2b7bf78070a5&ei=5124';} function getShareURL() { return encodeURIComponent('http://www.nytimes.com/2010/02/13/opinion/13herbert.html'); } function getShareHeadline() { return encodeURIComponent('Watching China Run'); } function getShareDescription() { return encodeURIComponent('China has nothing comparable to the research, industrial and economic resources of the United States. Yet the Chinese are blowing us away in the race to the future.'); } function getShareKeywords() { return encodeURIComponent('United States Economy,Greenhouse Gas Emissions,Energy and Power,Alternative and Renewable Energy,United States,China'); } function getShareSection() { return encodeURIComponent('opinion'); } function getShareSectionDisplay() { return encodeURIComponent('Op-Ed Columnist'); } function getShareSubSection() { return encodeURIComponent(''); } function getShareByline() { return encodeURIComponent('By BOB HERBERT'); } function getSharePubdate() { return encodeURIComponent('February 13, 2010'); } By BOB HERBERT Published: February 13, 2010 It was primarily a symbolic gesture. Way back in 1979, in the midst of an energy crisis, Jimmy Carter had solar panels installed on the roof of the White House. They were used to heat water for some White House staffers. Skip to next paragraph Bob Herbert Go to Columnist Page Related Times Topics: Solar Energy | China Readers' Comments Readers shared their thoughts on this article. Read All Comments (240) A generation from now, said Mr. Carter, this solar heater can either be a curiosity, a museum piece, an example of a road not taken, or it can be a small part of one of the greatest and most exciting adventures ever undertaken by the American people, harnessing the power of the sun to enrich our lives as we move away from our crippling dependence on foreign oil. Ronald Reagan had the panels taken down. We missed the boat then, and lord knows were missing it now. Two weeks ago, as I was getting ready to take off for Palo Alto, Calif., to cover a conference on the importance of energy and infrastructure for the next American economy, The Timess Keith Bradsher was writing from Tianjin, China, about how the Chinese were sprinting past everybody else in the world, including the United States, in the race to develop clean energy. That we are allowing this to happen is beyond stupid. China is a poor country with nothing comparable to the tremendous research, industrial and economic resources that the U.S. has been blessed with. Yet theyre blowing us away at least for the moment in the race to the future. Our esteemed leaders in Washington cant figure out how to do anything more difficult than line up for a group photo. Put Americans back to work? You must be kidding. Health care? Weve been working on it for three-quarters of a century. Infrastructure? Dont ask. But, as Mr. Bradsher tells us, China vaulted past competitors in Denmark, Germany, Spain and the United States last year to become the worlds largest maker of wind turbines and is poised to expand even further this year. China also has become the worlds largest manufacturer of solar panels and is pushing hard on other clean energy advances. As Mr. Bradsher wrote: These efforts to dominate renewable energy technologies raise the prospect that the West may someday trade its dependence on oil from the Mideast for a reliance on solar panels, wind turbines and other gear manufactured in China. Were in the throes of an awful and seemingly endless employment crisis, and China is the country moving full speed ahead on the development of the worlds most important new industries. Id like one of the Washington suits to step away from the photo-op and explain the logic of that to me. The truth, of course, is that there is no reason at all for this to be happening. The United States, in many ways, is very well prepared to move ahead on clean energy. It could and should be the worlds leader. Many, if not most, of the innovations in this area were developed right here. But much of that know-how, as we are seeing in China (and have been seeing in Germany and other places), is being implemented overseas. The conference that I attended in Palo Alto spotlighted the need to move to a low-carbon economy in the U.S. and exemplified some of the resources available to make it happen. It was sponsored by the Brookings Institution and Lazard, the investment banking advisory firm. The participants included the leaders of and major investors in companies that are making great strides in the alternative energy industry. But much of their business is done overseas because right now in Americas wacky, dysfunctional public sector there is no clear vision of a viable clean-energy economy, and, thus, no clue about how to get there. The network of world-class universities and advanced research institutions in the U.S. is by far the most impressive in the world: think Harvard and Stanford and Berkeley and M.I.T. and on and on. If you add to that the venture capital community in the U.S. with its vast experience and the willingness of investors to take risks, and the sheer entrepreneurial talent of the American business community, you end up with an array of resources fully capable of moving the U.S. into a low-carbon, high-growth and extraordinarily productive economy that would be the envy of the world. But for that to happen as Bruce Katz, a Brookings executive who was one of the organizers of the conference, pointed out Americas corporate, civic and political leaders will have to articulate whats really at stake here. And whats at stake is the future of the American economy. The low-carbon era is coming. We can be dragged into that newer, greener world by leading countries like China; or we can take up the challenge and become the worlds leader ourselves. Sign in to Recommend Next Article in Opinion (2 of 28) A version of this article appeared in print on February 13, 2010, on page A23 of the New York edition.
Ultrafast vibrational dynamics of interfacial water Avishek Ghosh a, Marc Smits a, Maria Sovago a, Jens Bredenbeck a,1, Michiel Mu ller b, Mischa Bonn a,* Chemical Physics 350 (2008) 2330 摘要 We report investigations of the vibrational dynamics of water molecules at the waterair and at the waterlipid interface. Following vibrational excitation with an intense femtosecond infrared pulse resonant with the OH stretch vibration of water, we follow the subsequent relaxation processes using the surface-specific spectroscopic technique of sum frequency generation. This allows us to selectively follow the vibrational relaxation of the approximately one monolayer of water molecules at the interface. Although the surface vibrational spectra of water at the interface with air and lipids are very similar, we find dramatic variations in both the rates and mechanisms of vibrational relaxation. For water at the waterair interface, very rapid exchange of vibrational energy occurs with water molecules in the bulk, and this intermolecular energy transfer process dominates the response. For membrane-bound water at the lipid interface, intermolecular energy transfer is suppressed, and intramolecular relaxation dominates. The difference in relaxation mechanism can be understood from differences in the local environments experienced by the interfacial water molecules in the two different systems. 正文 本文作者利用IR pump VSFG Probe的方法研究了waterair和waterlipid界面水分子的OH伸缩振动的弛豫动力学。实验技术是通过add to the VSFG scheme an additional 'pump', or excitation, pulse, which excites a significant fraction of OH groups to their first vibrationally excited state 。 The femtosecond time-resolved SFG study presented here allows to selectively probe the lifetime dynamics (T1) of the OH stretch vibration and provides new insights in the structure and dynamics of interfacial water. Comparing the waterair interface and the waterlipid interface , pronounced differences of the mechanism and timescale of interfacial vibrational energy flow are found. 实验结果发现，waterair界面的水分子振动弛豫中有两个timescales而waterlipid界面水分子只有一个timescales。所以waterair界面的水分子的弛豫动力学中包含了一个中间态，而waterlipid界面水分子则是不包含中间态的一个单指数的过程。 For the waterair interface (Fig. 3A), two timescales seem apparent: a fast (200 fs) relaxation time corresponding to the recovery of the pump-induced bleach signal (most clearly evident at m = 3500 cm1, and a slower (500 fs) timescale by which the final SFG level is reached (most apparent at m = 3200 cm1). Such dynamics are reminiscent of previous observations for bulk water and observations for water at the waterquartz interface . Hence, it is clear that the hydrogen-bonded network vibrational dynamics at the waterair interface are dominated by ultrafast vibrational energy transfer processes. This also explains the similarity between the dynamics at the waterair interface and those at the hydrophilic and hydrophobic silica/water interface recently reported using SFG in total internal reflection (TIR) geometry . For the latter interface, McGuire and Shen reported somewhat slower dynamics, with T1 = 300 fs and Tthermalization = 700 fs. The rigid silica surface (required for TIR-SFG) has been shown to induce order in the interfacial water compared to water at the waterair interface . The effect of the increased order on the vibrational dynamics is limited due to the ultrafast energy transfer processes that dominate the observed relaxation behavior. Remarkably, Fig. 3B reveals that the behavior of water at the waterlipid interface is very different from that at the waterair interface. Unlike the waterair interface, the data can be described very well by a single exponential decay, with distinct time constants at different probe frequencies within the hydrogen-bonded regime. Reference: J.A. McGuire, Y.R. Shen, Science 313 (2006) 1945. M. Smits, A. Ghosh, M. Sterrer, M. Muller, M. Bonn, Phys. Rev. Lett. 98 (2007) 4. A. Ghosh, M. Smits, J. Bredenbeck, M. Muller, M. Bonn, J. Am. Chem. Soc. 129 (2007) 9608.
标签: Energy
