Large non-adiabatic hole polarons and matrix element effects in the angle-resolved photoemission spectroscopy of dielectric cuprates

It has been made an extention of the conventional theory based on the assumption of the well isolated Zhang-Rice singlet to be a first electron-removal state in dielectric copper oxide. One assumes the photohole has been localised on either small (pseudo)Jahn-Teller polaron or large non-adiabatic polaron enclosed one or four to five $CuO_4$ centers, respectively, with active one-center valent $(^{1}A_{1g}-{}^{1,3}E_{u})$ manifold. In the framework of the cluster model we have performed a model microscopic calculation of the ${\bf k}$-dependence of the matrix element effects and photon polarization effects for the angle-resolved photoemission in dielectric cuprate like $Sr_{2}CuO_{2}Cl_{2}$. We show that effects like the ''remnant Fermi surface'' detected in ARPES experiment for $Ca_{2}CuO_{2}Cl_{2}$ may be, in fact, a reflection of the matrix element effects, not a reflection of the original band-structure Fermi surface, or the strong antiferromagnetic correlations. The measured dispersion-like features in the low-energy part of the ARPES spectra may be a manifestation of the complex momentum-dependent spectral line-shape of the large PJT polaron response, not the dispersion of the well-isolated Zhang-Rice singlet in antiferromagnetic matrix.Comment: 16 pages, TeX, 9 eps figures adde

Recombination dramatically speeds up evolution of finite populations

We study the role of recombination, as practiced by genetically-competent bacteria, in speeding up Darwinian evolution. This is done by adding a new process to a previously-studied Markov model of evolution on a smooth fitness landscape; this new process allows alleles to be exchanged with those in the surrounding medium. Our results, both numerical and analytic, indicate that for a wide range of intermediate population sizes, recombination dramatically speeds up the evolutionary advance

Hypermutable Non-Synonymous Sites Are under Stronger Negative Selection

Mutation rate varies greatly between nucleotide sites of the human genome and depends both on the global genomic location and the local sequence context of a site. In particular, CpG context elevates the mutation rate by an order of magnitude. Mutations also vary widely in their effect on the molecular function, phenotype, and fitness. Independence of the probability of occurrence of a new mutation's effect has been a fundamental premise in genetics. However, highly mutable contexts may be preserved by negative selection at important sites but destroyed by mutation at sites under no selection. Thus, there may be a positive correlation between the rate of mutations at a nucleotide site and the magnitude of their effect on fitness. We studied the impact of CpG context on the rate of human–chimpanzee divergence and on intrahuman nucleotide diversity at non-synonymous coding sites. We compared nucleotides that occupy identical positions within codons of identical amino acids and only differ by being within versus outside CpG context. Nucleotides within CpG context are under a stronger negative selection, as revealed by their lower, proportionally to the mutation rate, rate of evolution and nucleotide diversity. In particular, the probability of fixation of a non-synonymous transition at a CpG site is two times lower than at a CpG site. Thus, sites with different mutation rates are not necessarily selectively equivalent. This suggests that the mutation rate may complement sequence conservation as a characteristic predictive of functional importance of nucleotide sites

The limits of normal approximation for adult height

Adult height inspired the first biometrical and quantitative genetic studies and is a test-case trait for understanding heritability. The studies of height led to formulation of the classical polygenic model, that has a profound influence on the way we view and analyse complex traits. An essential part of the classical model is an assumption of additivity of effects and normality of the distribution of the residuals. However, it may be expected that the normal approximation will become insufficient in bigger studies. Here, we demonstrate that when the height of hundreds of thousands of individuals is analysed, the model complexity needs to be increased to include non-additive interactions between sex, environment and genes. Alternatively, the use of log-normal approximation allowed us to still use the additive effects model. These findings are important for future genetic and methodologic studies that make use of adult height as an exemplar trait

Large Non-Adiabatic Hole Polarons and Matrix Element Effects in the Angle-Resolved Photoemission Spectroscopy of Dielectric Cuprates

We propose a generalization of the conventional theory based on the assumption of the well-isolated Zhang-Rice 1A1g singlet to be a first electron-removal state in insulating copper oxide. The photohole is assumed to be localized on either small (pseudo) Jahn-Teller (PJT) polaron or large non-adiabatic polaron-enclosed one or four to five CuO4 centers, respectively, with active one-center valent (1A1g-1,3Eu) manifold. In the framework of the cluster model we have performed the model microscopic calculation of the k-dependence of the matrix element effects and photon polarization effects for the angle-resolved photoemission (ARPES) in insulating cuprates like Sr2CuO2Cl2. We show that effects like the "remnant Fermi surface" detected in the ARPES experiment for Ca2CuO2Cl2 may be, in fact, the manifestation of the matrix element effects rather than of the original band-structure Fermi surface or strong antiferromagnetic correlations. The measured dispersion-like features in the low-energy part of the ARPES spectra may be the manifestation of the complex momentum-dependent spectral line shape of the large PJT polaron response, in addition to the dispersion effect for the well-isolated Zhang-Rice singlet in antiferro-magnetic matrix. © 2002 Elsevier Science B.V. All rights reserved.We wish to thank S.-L. Drechsler and R. Hayn for valuable discussions. The research described in this publication was made possible in part by Award No. REC-005 of the US Civilian Research & Development Foundation for the Independent States of the Former Soviet Union (CRDF). The authors acknowledge a partial support from the Russian Ministry of Education, Grant E00-3.4-280, and Russian Foundation for Basic Researches, Grant 01-02-96404

Cliques and duplication-divergence network growth

A population of complete subgraphs or cliques in a network evolving via duplication-divergence is considered. We find that a number of cliques of each size scales linearly with the size of the network. We also derive a clique population distribution that is in perfect agreement with both the simulation results and the clique statistic of the protein-protein binding network of the fruit fly. In addition, we show that such features as fat-tail degree distribution, various rates of average degree growth and non-averaging, revealed recently for only the particular case of a completely asymmetric divergence, are present in a general case of arbitrary divergence.Comment: 7 pages, 6 figure

Optimizing the regimes of Advanced LIGO gravitational wave detector for multiple source types

We develop here algorithms which allow to find regimes of signal-recycled Fabry-Perot--Michelson interferometer (for example, Advanced LIGO), optimized concurrently for two (binary inspirals + bursts) and three (binary inspirals + bursts + millisecond pulsars) types of gravitational waves sources. We show that there exists a relatevely large area in the interferometer parameters space where the detector sensitivity to the first two kinds of sources differs only by a few percent from the maximal ones for each kind of source. In particular, there exists a specific regime where this difference is ~0.5 for both of them. Furthermore we show that even more multipurpose regimes are also possible, that provide significant sensitivity gain for millisecond pulsars with only minor sensitivity degradation for binary inspirals and bursts.Comment: 10 pages, 14 figures, 3 tables. Minor corrections in main text are done in version 2 and two plots and one table are added for the sake of clarity of the obtained result

Методика выбора оптимальной степени повышения давления в вентиляторе по эффективным параметрам силовой установки

Nowadays, civilian aircrafts occupy the major share of global aviation industry market. As to medium and long - haul aircrafts, turbofans with separate exhaust streams are widely used. Here, fuel efficiency is the main criterion of this engine. The paper presents the research results of the mutual influence of fan pressure ratio and bypass ratio on the effective specific fuel consumption. Shows the increasing bypass ratio to be a rational step for reducing the fuel consumption. Also considers the basic features of engines with a high bypass ratio. Among the other working process parameters, fan pressure ratio and bypass ratio are the most relevant for consideration as they are the most structural variables at a given level of technical excellence. The paper presents the dependence of the nacelle drag coefficient on the engine bypass ratio. For computation were adopted the projected parameters of prospective turbofans to be used in the power plant of the 180-seat medium-haul aircraft. Computation of the engine cycle was performed in Mathcad using these data, with fan pressure ratio and bypass ratio being varied. The combustion chamber gas temperature, the overall pressure ratio and engine thrust remained constant. Pressure loss coefficients, the efficiency of the engine components and the amount of air taken for cooling also remained constant. The optimal parameters corresponding to the minimum effective specific fuel consumption were found as the result of computation. The paper gives recommendations for adjusting optimal parameters, depending on the considered external factors, such as weight of engine and required fuel reserve. The obtained data can be used to estimate parameters of future turbofan engines with high bypass ratio.В настоящее время основную долю мирового рынка авиационной промышленности занимают гражданские самолеты. Для средне - и дальнемагистральных самолетов наибольше распространение получили двухконтурные турбореактивные двигатели с раздельным истечением потоков. При этом основным критерием оценки двигателя является его экономичность. В данной работе представлены результаты исследования взаимного влияния степени повышения давления в вентиляторе и степени двухконтурности на эффективный удельный расход топлива. Была показана рациональность повышения степени двухконтурности с целью уменьшения удельного расхода топлива, а также рассмотрены основные особенности двигателей со сверхвысокими степенями двухконтурности. Степень повышения давления в вентиляторе и степень двухконтурности являются наиболее актуальными к рассмотрению параметрами рабочего процесса, т.к. являются по большей части конструктивными на заданном уровне технического совершенства. В работе приведена зависимость коэффициента сопротивления мотогондолы двигателя от степени двухконтурности. Для расчета были приняты прогнозируемые параметры перспективных двухконтурных турбореактивных двигателей, ориентированных на использование в силовой установке среднемагистрального самолета в классе 180 мест. По этим данным в системе Mathcad был произведен расчет цикла двигателя. При этом варьировались степень повышения давления в вентиляторе и степень двухконтурности. Температура газа в камере сгорания, суммарная степень повышения давления в компрессоре и тяга двигателя оставались постоянными. Также неизменными принимались коэффициенты сохранения полного давления, КПД узлов, величина отбора воздуха на охлаждение. В результате расчета были получены оптимальные параметры, соответствующие минимуму эффективного удельного расхода топлива. Были даны рекомендации по корректировке оптимальных параметров, в зависимости от рассматриваемых внешних факторов, таких как масса двигателя и потребный запас топлива. Полученные данные могут использоваться для предварительной оценки параметров перспективных двухконтурных турбореактивных двигателей со сверхвысокими степенями двухконтурности