对应的C++、C、Fortran、Python、Matlab源码可从 http://geodesy.cn/glonass/index.xml 处下载。 GLONASS Frequency Channels (GFC) are generated using data from official information of GLONASS. This file constains all latest data in the form of a set of date and frequency channels of 24 satellites. All satellites' frequency channels remain unchanged until the date in next set. It's not available if a satellite frequency channel is 99.
Codon usage bias refers to differences in the frequency of occurrence of synonymous codons in coding DNA. A codon is a series of three nucleotides (triplets) that encodes a specific amino acid residue in a polypeptide chain or for the termination of translation (stop codons). There are 64 different codons (61 codons encoding for amino acids plus 3 stop codons) but only 20 different translated amino acids. The overabundance in the number of codons allows many amino acids to be encoded by more than one codon. Because of such redundancy it is said that the genetic code is degenerate. Different organisms often show particular preferences for one of the several codons that encode the same amino acid- that is, a greater frequency of one will be found than expected by chance. How such preferences arise is a much debated area of molecular evolution. It is generally acknowledged that codon preferences reflect a balance between mutational biases and natural selection for translational optimization. Optimal codons in fast-growing microorganisms, like Escherichia coli or Saccharomyces cerevisiae (baker's yeast), reflect the composition of their respective genomic tRNA pool. It is thought that optimal codons help to achieve faster translation rates and high accuracy. As a result of these factors, translational selection is expected to be stronger in highly expressed genes, as is indeed the case for the above-mentioned organisms. In other organisms that do not show high growing rates or that present small genomes, codon usage optimization is normally absent, and codon preferences are determined by the characteristic mutational biases seen in that particular genome. Examples of this are Homo sapiens (human) and Helicobacter pylori. Organisms that show an intermediate level of codon usage optimization include Drosophila melanogaster (fruit fly), Caenorhabditis elegans (nematode worm) or Arabidopsis thaliana (thale cress). The nature of the codon usage-tRNA optimization has been fiercely debated. It is not clear whether codon usage drives tRNA evolution or vice versa. At least one mathematical model has been developed where both codon-usage and tRNA-expression co-evolve in feedback fashion (i.e., codons already present in high frequencies drive up the expression of their corresponding tRNAs, and tRNAs normally expressed at high levels drive up the frequency of their corresponding codons), however this model does not seem to yet have experimental confirmation. Another problem is that the evolution of tRNA genes has been a very inactive area of research. 分析软件：CodonW
Dear Prof. Peiyang: We thought you might enjoy reviewing the most interesting articles for the past month, based on the frequency with which subscribers viewed these in detail. The top 10 appear below. Brian Haynes MD, Editor, Evidence Updates # Article Title 1 Efficacy and safety of dual blockade of the renin-angiotensin system: meta-analysis of randomised trials. BMJ 2 Probiotics for the prevention of Clostridium difficile-associated diarrhea: a systematic review and meta-analysis. Ann Intern Med 3 Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev 4 Effect of ramipril on walking times and quality of life among patients with peripheral artery disease and intermittent claudication: a randomized controlled trial. JAMA 5 Neonatal outcomes after gestational exposure to nitrofurantoin. Obstet Gynecol 6 Effect of corticosteroid injection, physiotherapy, or both on clinical outcomes in patients with unilateral lateral epicondylalgia: a randomized controlled trial. JAMA 7 Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ 8 Prevention of contrast-induced nephropathy with Na/K citrate. Eur Heart J 9 Statins for the primary prevention of cardiovascular disease. Cochrane Database Syst Rev 10 Anti-Diabetic Medications and the Risk of Hepatocellular Cancer: A Systematic Review and Meta-Analysis. Am J Gastroenterol
Pro alpaha_corelate,vx=vx,vr=vr,vo=vo,a_ox,a_ro,a_rx ;+ ;NAME: ; alpaha_corelate ;PURPOSE: ; known two alpaha in order to make sure the third alpaha ;CALLING SEQUENCE: ; alpaha_corelate,vx=vx,vr=vr,vo=vo,a_ox,a_ro,a_rx ;INPUT OUTPUT: ; a_ox ; a_ro ; a_rx ;OPTIONAL KEY INPUT: ; vx --- X-ray frequency ; vr --- Radio frequency ; vo --- Optical frequency ;REVISION HISTORY: ; Original by DL.Wang,May-12-2007 ;- if n_params() lt 2 then begin print,'Syntax - alpaha_corelate,a_ox,,a_ro,a_rx' return endif nox=n_elements(a_ox)1 nro=n_elements(a_ro)1 nrx=n_elements(a_rx)1 a=alog10(vx/vo)/alog10(vx/vr) b=alog10(vo/vr)/alog(vx/vr) ;Check which two parameters are defined, and then determine the other if (nox and nro) then begin a_rx = a * a_ox + b * a_ro endif if (nrx and nro) then begin a_ox = (a_rx - b * a_ro)/ a endif if (nrx and nox) then begin a_ro = (a_rx - a * a_ox)/b endif end
Dear Prof. Peiyang: We thought you might enjoy reviewing the most interesting articles for the past month, based on the frequency with which subscribers viewed these in detail. The top 10 appear below. Brian Haynes MD, Editor, Evidence Updates # Article Title 1 Sequential versus triple therapy for the first-line treatment of Helicobacter pylori: a multicentre, open-label, randomised trial. Lancet 2 Initiation of allopurinol at first medical contact for acute attacks of gout: a randomized clinical trial. Am J Med 3 Reduction versus abrupt cessation in smokers who want to quit. Cochrane Database Syst Rev 4 Beta-blockers for hypertension. Cochrane Database Syst Rev 5 Scores to predict major bleeding risk during oral anticoagulation therapy: a prospective validation study. Am J Med 6 Horse chestnut seed extract for chronic venous insufficiency. Cochrane Database Syst Rev 7 Cognitive behavioural therapy as an adjunct to pharmacotherapy for primary care based patients with treatment resistant depression: results of the CoBalT randomised controlled trial. Lancet 8 Bloodstream infection, venous thrombosis, and peripherally inserted central catheters: reappraising the evidence. Am J Med 9 Vaccines for preventing rotavirus diarrhoea: vaccines in use. Cochrane Database Syst Rev 10 General health checks in adults for reducing morbidity and mortality from disease: Cochrane systematic review and meta-analysis. BMJ
Dear Prof. Peiyang: We thought you might enjoy reviewing the most interesting articles for the past month, based on the frequency with which subscribers viewed these in detail. The top 10 appear below. Brian Haynes MD, Editor, Evidence Updates # Article Title 1 Low sodium versus normal sodium diets in systolic heart failure: systematic review and meta-analysis. Heart 2 Corticosteroids as standalone or add-on treatment for sore throat. Cochrane Database Syst Rev 3 Efficacy and safety of the novel oral anticoagulants in atrial fibrillation: a systematic review and meta-analysis of the literature. Circulation 4 Oestrogen therapy for urinary incontinence in post-menopausal women. Cochrane Database Syst Rev 5 Low-Dose Aspirin for Preventing Recurrent Venous Thromboembolism. N Engl J Med 6 Efficacy of antibiotic therapy for acute exacerbations of mild to moderate chronic obstructive pulmonary disease. Am J Respir Crit Care Med 7 Comparative effectiveness and safety of methods of insulin delivery and glucose monitoring for diabetes mellitus: a systematic review and meta-analysis. Ann Intern Med 8 Incentives for preventing smoking in children and adolescents. Cochrane Database Syst Rev 9 Antibiotics for clinically diagnosed acute rhinosinusitis in adults. Cochrane Database Syst Rev 10 Exenatide once weekly versus liraglutide once daily in patients with type 2 diabetes (DURATION-6): a randomised, open-label study. Lancet
Dear Prof. Peiyang: We thought you might enjoy reviewing the most interesting articles for the past month, based on the frequency with which subscribers viewed these in detail. The top 10 appear below. Brian Haynes MD, Editor, Evidence Updates 1 Does this adult patient with suspected bacteremia require blood cultures?. JAMA 2 Coronary CT angiography versus standard evaluation in acute chest pain. N Engl J Med 3 Intensive and Standard Blood Pressure Targets in Patients With Type 2 Diabetes Mellitus: Systematic Review and Meta-analysis. Arch Intern Med 4 Pharmacotherapy for mild hypertension. Cochrane Database Syst Rev 5 Randomized clinical trial of antibiotics in acute uncomplicated diverticulitis. Br J Surg 6 Long term hormone therapy for perimenopausal and postmenopausal women. Cochrane Database Syst Rev 7 Immunochemical Fecal Occult Blood Testing Is Equally Sensitive for Proximal and Distal Advanced Neoplasia. Am J Gastroenterol 8 Restenosis after carotid artery stenting and endarterectomy: a secondary analysis of CREST, a randomised controlled trial. Lancet Neurol 9 Capsule Endoscopy or Angiography in Patients With Acute Overt Obscure Gastrointestinal Bleeding: A Prospective Randomized Study With Long-Term Follow-Up. Am J Gastroenterol 10 Intravenous immunoglobulin for Guillain-Barre syndrome. Cochrane Database Syst Rev
6.3.4 Radio Frequency (rf) Sputtering At frequencies above 50 kHz , the ions do not have enough mobility to allow establishing a DC diode-like discharge and the applied potential is felt throughout the space between the electrodes . The electrons acquire sufficient energy to cause ionizing collisions in the space between the electrodes and thus the plasma generation takes place throughout the space between the electrodes . When an rf potential, with a large peak-topeak voltage, is capacitively coupled to an electrode, an alternating positive/ negative potential appears on the surface. During part of each halfcycle , the potential is such that ions are accelerated to the surface with enough energy to cause sputtering while on alternate half-cycles , electrons reach the surface to prevent any charge buildup . Rf frequencies used for sputter deposition are in the range of 0.5–30 MHz with 13.56 MHz being a commercial frequency that is often used . Rf sputtering can be performed at low gas pressures (1 mTorr) . Since the target is capacitively coupled to the plasma it makes no difference whether the target surface is electrically conductive or insulating although there will be some dielectric loss if the target is an insulator . If an insulating target material , backed by a metal electrode is used, the insulator should cover the whole of the metal surface since exposed metal will tend to short-out the capacitance formed by the metal-insulator-sheath-plasma . Rf sputtering can be used to sputter electrically insulating materials although the sputtering rate is low . A major disadvantage in rf sputtering of dielectric targets, is that most electrically insulating materials have poor thermal conductivity , high coefficients of thermal expansion, and are usually brittle materials. Since most of the bombarding energy produces heat , this means that large thermal gradients can be generated that result in fracturing the target if high power levels are used. High rate rf sputtering is generally limited to the sputter deposition from targets of silicon dioxide (SiO2) which has a low coefficient of thermal expansion and thus is not very susceptible to thermal shock. In some cases, 48 hours is used to rf sputter-deposit a film of SiO 2 several microns thick.
维基百科，自由的百科全书 TF-IDF （term frequency–inverse document frequency）是一种用于 资讯检索 与 文本挖掘 的常用加权技术。TF-IDF是一种统计方法，用以评估一字词对于一个文件集或一个 语料库 中的其中一份 文件 的重要程度。字词的重要性随着它在文件中出现的次数成 正比 增加，但同时会随着它在语料库中出现的频率成反比下降。TF-IDF加权的各种形式常被 搜索引擎 应用，作为文件与用户查询之间相关程度的度量或评级。除了TF-IDF以外，互联网上的搜寻引擎还会使用基于连结分析的评级方法，以确定文件在搜寻结果中出现的顺序。 目录 1 原理 2 例子 3 在向量空间模型里的应用 4 参考资料 5 外部链接 原理 在一份给定的文件里， 词频 （term frequency，TF）指的是某一个给定的词语在该文件中出现的次数。这个数字通常会被正规化，以防止它偏向长的文件。（同一个词语在长文件里可能会比短文件有更高的词频，而不管该词语重要与否。）对于在某一特定文件里的词语 t i 来说，它的重要性可表示为： 以上式子中 n i , j 是该词在文件 d j 中的出现次数，而分母则是在文件 d j 中所有字词的出现次数之和。 逆向文件频率 （inverse document frequency，IDF）是一个词语普遍重要性的度量。某一特定词语的IDF，可以由总文件数目除以包含该词语之文件的数目，再将得到的商取 对数 得到： 其中 |D|：语料库中的文件总数 ：包含词语 t i 的文件数目（即 的文件数目）如果该词语不在语料库中，就会导致被除数为零，因此一般情况下使用 然后 某一特定文件内的高词语频率，以及该词语在整个文件集合中的低文件频率，可以产生出高权重的TF-IDF。因此，TF-IDF倾向于过滤掉常见的词语，保留重要的词语。 例子 有很多不同的 数学公式 可以用来 计算 TF-IDF。这边的例子以上述的数学公式来计算。词频 (TF) 是一词语出现的次数除以该文件的总词语数。假如一篇文件的总词语数是100个，而词语“母牛”出现了3次，那么“母牛”一词在该文件中的词频就是3/100=0.03。一个计算文件频率 (DF) 的方法是测定有多少份文件出现过“母牛”一词，然后除以文件集里包含的文件总数。所以，如果“母牛”一词在1,000份文件出现过，而文件总数是10,000,000份的话，其逆向文件频率就是 ln(10,000,000 / 1,000)=4。最后的TF-IDF的分数为0.03 * 4=0.12。 在向量空间模型里的应用 TF-IDF权重计算方法经常会和 余弦相似度 （cosine similarity）一同使用于 向量空间模型 中，用以判断两份文件之间的 相似性 。 参考资料 Salton, G. and McGill, M. J. 1983 Introduction to modern information retrieval . McGraw-Hill, ISBN 0-07-054484-0 . Salton, G., Fox, E. A. and Wu, H. 1983 Extended Boolean information retrieval. Commun. ACM 26, 1022–1036. Salton, G. and Buckley, C. 1988 Term-weighting approaches in automatic text retrieval. Information Processing Management 24(5): 513–523. 外部链接 Term Weighting Approaches in Automatic Text Retrieval Robust Hyperlinking ：An application of tf–idf for stable document addressability.
标签: frequency
