基于分段常滑翔角的长航时纵向远程滑翔飞行方程近似解

提出用包含地球旋转效应的n个常滑翔角飞行段近似实际滑翔飞行轨迹的方法。基于该方法推导了长航时纵向远程滑翔飞行轨迹近似解，并给出了各段常滑翔角、滑翔时间的求解方法及整个滑翔轨迹近似计算步骤。文中算例结果表明，该近似求解方法计算得到的滑翔航程和滑翔时间与实际值相差很小，航程误差率约为0．7％，时间误差率约为0．6％，因此该方法在近似小初始滑翔角的长航时远程纵向滑翔飞行时是有效的、可行的，尤其针对航程在地球半圈以上的滑翔飞行轨迹。

Domains beyond the grain boundary

Thin films of inorganic materials are used in diverse applications, typically in polycrystalline form due to their relatively simple production. We have used enhanced piezoresponse force microscopy to investigate the domain distribution within neighbouring grains in thin polycrystalline films of the ferroelectric-ferroelastic system lead zirconate titanate (PZT). We demonstrate that domains are organized into areas with a correlated alignment of the ferroelastic and ferroelectric domains, spanning multiple grain boundaries. We present five typical arrangements of such structures: azimuthal, radial, gradient, and short- and long- range linear domain organizations. Moreover, we discuss the mechanical and electrical constraints that dictate these structures. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Directly synthesized strong, highly conducting, transparent single-walled carbon nanotube films

We report the direct synthesis of strong, highly conducting, and transparent single-walled carbon nanotube (SWNT) films. Systematically, tests reveal that the directly synthesized films have superior electrical and mechanical properties compared with the films made from a solution-based filtration process: the electrical conductivity is over 2000 S/cm and the strength can reach 360 MPa. These values are both enhanced by more than 1 order. We attribute these intriguing properties to the good and long interbundle connections. Moreover, by the help of an extrapolated Weibull theory, we verify the feasibility of reducing the interbundle slip by utilizing the long-range intertube friction and estimate the ultimate strength of macroscale SWNTs without binding agent.

助推-远程滑翔三维飞行的热流峰值分析

为简便分析助推-远程滑翔弹道三维情况下的热流特性,基于远程滑翔三维飞行动力学模型和热力学基本公式,根据助推-远程滑翔弹道的两类飞行弹道（平衡滑翔弹道和跳跃滑翔弹道）的特点,推导建立了两类弹道三维情况下平均热流和驻点热流计算的解析公式。详尽分析了再入角、再入速度、升阻比、滚转角和翼载荷对两类弹道热流峰值的影响规律。由分析可知在远程滑翔三维飞行情况下,滚转角对其热流峰值有显著影响;升阻比大于1,滚转角控制在60度以内,其热流峰值能够得到有效降低。

Species and size relationships within schools of yellowfin and skipjack tuna as indicated by catches in the Eastern Tropical Pacific Ocean

ENGLISH: Yellowfin tuna, Neothunnus macropterus, and skipjack tuna, Katsuwonus pelamis, are fished intensively off the west coast of the Americas in an area from about the California-Mexico border in the north to the Peru-Chile border in the south. The historical development of this fishery, and its expansion by the long-range California fleets of bait and purse-seine vessels, are well documented by Godsil (1938), Scofield (1951) and Shimada and Sehaefer (1956). The quarterly distribution of the tuna catches within this area has been reported for some recent years by Alverson (1959). SPANISH: Los atunes aleta amarilla, Neothunnus macropterus, y barrilete, Katsuwonus pelamis, son pescados con intensidad frente a la costa occidental del continente americano, en un área comprendida más o menos entre la frontera California-México en el norte y el límite Perú-Chile en el sur. El desarrollo histórico de esta pesquería y la expansión que le han dado las flotas californianas de largo radio de acción, formadas por los barcos de carnada y rederos, están bien documentados por Godsil (1938), Scofield (1951) y Shimada y Schaefer (1956). La distribución trimestral de las pescas de atún dentro de esta área ha sido tratada por Alverson (1959) con referencia a años recientes.

Size- And Temperature-Dependent Thermal Expansion Coefficient Of A Nanofilm

The thermal expansion coefficient (TEC) of an ideal crystal is derived by using a method of Boltzmann statistics. The Morse potential energy function is adopted to show the dependence of the TEC on the temperature. By taking the effects of the surface relaxation and the surface energy into consideration, the dimensionless TEC of a nanofilm is derived. It is shown that with decreasing thickness, the TEC can increase or decrease, depending on the surface relaxation of the nanofilm.

A unified guide to two opposite size effects in nano elastic materials

The microstructural variation near surface of nano elastic materials is analyzed based on different potentials. The atomic/molecular mechanism underlying the variation and its effect on elastic modulus are such that the nature of long-range interactions (attractive or repulsive) in the atomic/molecular potentials essentially governs the variation near surface (looser or tighter) and results in two opposite size effects (decreasing or increasing modulus) with decreasing size.

Mechanisms underlying two kinds of surface effects on elastic constants

ABSTRACT Recently, people are confused with two opposite variations of elastic modulus with decreasing size of nano scale sample: elastic modulus either decreases or increases with decreas- ing sample size. In this paper, based on intermolecular potentials and a one dimensional model, we provide a unified understanding of the two opposite size effects. Firstly, we analyzed the mi- crostructural variation near the surface of an fcc nanofilm based on the Lennard-Jones potential. It is found that the atomic lattice near the surface becomes looser in comparison with the bulk, indicating that atoms in the bulk are located at the balance of repulsive forces, resulting in the decrease of the elastic moduli with the decreasing thickness of the film accordingly. In addition, the decrease in moduli should be attributed to both the looser surface layer and smaller coor- dination number of surface atoms. Furthermore, it is found that both looser and tighter lattice near the surface can appear for a general pair potential and the governing mechanism should be attributed to the surplus of the nearest force to all other long range interactions in the pair po- tential. Surprisingly, the surplus can be simply expressed by a sum of the long range interactions and the sum being positive or negative determines the looser or tighter lattice near surface re- spectively. To justify this concept, we examined ZnO in terms of Buckingham potential with long range Coulomb interactions. It is found that compared to its bulk lattice, the ZnO lattice near the surface becomes tighter, indicating the atoms in the bulk located at the balance of attractive forces, owing to the long range Coulomb interaction. Correspondingly, the elastic modulus of one- dimensional ZnO chain increases with decreasing size. Finally, a kind of many-body potential for Cu was examined. In this case, the surface layer becomes tighter than the bulk and the modulus increases with deceasing size, owing to the long range repulsive pair interaction, as well as the cohesive many-body interaction caused by the electron redistribution.

远程超低飞行轨道分析

研究了一种新的远程导弹飞行轨道的可行性,它的最大飞行高度约100 km.这种超低弹道,借鉴卫星模式,利用离心力抵抗重力.与卫星轨道运行不同的是,超低弹道周围的稀薄空气影响至关重要,必须考虑.计算和分析结果表明,在相同载荷条件和射程条件下,超低弹道和经典的最小能量弹道对于火箭动力的需求大致相当,射程10000km以上基本相同,头部半径为5cm的轴对称外形,沿超低弹道飞行时,其驻点热流在高度26km左右达到最大值50MW/m~2,约为最小能量弹道驻点热流最大值的50%.由于超低弹道对升力没有要求,飞行过程中的气动加热问题,沿用成熟方法如烧蚀防热即可解决.总体而言,超低弹道对于火箭动力与外形气动力/热要求,现有技术容易满足,因此利用它增强远程导弹的突防能力是现实可能的.

Dissipative particle dynamics simulation of wettability alternation phenomena in the chemical flooding process

Wettability alternation phenomena is considered one of the most important enhanced oil recovery (EOR) mechanisms in the chemical flooding process and induced by the adsorption of surfactant on the rock surface. These phenomena are studied by a mesoscopic method named as dissipative particle dynamics (DPD). Both the alteration phenomena of water-wet to oil-wet and that of oil-wet to water-wet are simulated based on reasonable definition of interaction parameters between beads. The wetting hysteresis phenomenon and the process of oil-drops detachment from rock surfaces with different wettability are simulated by adding long-range external forces on the fluid particles. The simulation results show that, the oil drop is liable to spread on the oil-wetting surface and move in the form of liquid film flow, whereas it is likely to move as a whole on the water-wetting surface. There are the same phenomena occuring in wettability-alternated cases. The results also show that DPD method provides a feasible approach to the problems of seepage flow with physicochemical phenomena and can be used to study the mechanism of EOR of chemical flooding.

San Francisco Bay regional sediment management strategy development

The San Francisco Bay Conservation and Development Commission (BCDC), in continued partnership with the San Francisco Bay Long Term Management Strategies (LTMS) Agencies, is undertaking the development of a Regional Sediment Management Plan for the San Francisco Bay estuary and its watershed (estuary). Regional sediment management (RSM) is the integrated management of littoral, estuarine, and riverine sediments to achieve balanced and sustainable solutions to sediment related needs. Regional sediment management recognizes sediment as a resource. Sediment processes are important components of coastal and riverine systems that are integral to environmental and economic vitality. It relies on the context of the sediment system and forecasting the long-range effects of management actions when making local project decisions. In the San Francisco Bay estuary, the sediment system includes the Sacramento and San Joaquin delta, the bay, its local tributaries and the near shore coastal littoral cell. Sediment flows from the top of the watershed, much like water, to the coast, passing through rivers, marshes, and embayments on its way to the ocean. Like water, sediment is vital to these habitats and their inhabitants, providing nutrients and the building material for the habitat itself. When sediment erodes excessively or is impounded behind structures, the sediment system becomes imbalanced, and rivers become clogged or conversely, shorelines, wetlands and subtidal habitats erode. The sediment system continues to change in response both to natural processes and human activities such as climate change and shoreline development. Human activities that influence the sediment system include flood protection programs, watershed management, navigational dredging, aggregate mining, shoreline development, terrestrial, riverine, wetland, and subtidal habitat restoration, and beach nourishment. As observed by recent scientific analysis, the San Francisco Bay estuary system is changing from one that was sediment rich to one that is erosional. Such changes, in conjunction with increasing sea level rise due to climate change, require that the estuary sediment and sediment transport system be managed as a single unit. To better manage the system, its components, and human uses of the system, additional research and knowledge of the system is needed. Fortunately, new sediment science and modeling tools provide opportunities for a vastly improved understanding of the sediment system, predictive capabilities and analysis of potential individual and cumulative impacts of projects. As science informs management decisions, human activities and management strategies may need to be modified to protect and provide for existing and future infrastructure and ecosystem needs. (PDF contains 3 pages)

Structural and mechanistic study of monoalkyl diazenes. Synthesis, characterization, and reactivity of 1,6-didehydro[10]annulene

Methodology for the preparation of allenes from propargylic hydrazine precursors under mild conditions is described. Oxidation of the propargylic hydrazines, which can be readily prepared from propargylic alcohols, with either of two azo oxidants, diethyl azodicarboxylate (DEAD) or 4-methyl 1,2-triazoline-3,5-dione (MTAD), effects conversion to the allenes, presumably via sigmatropic rearrangement of a monoalkyl diazene intermediate. This rearrangement is demonstrated to proceed with essentially complete stereospecificity. The application of this methodology to the preparation of other allenes, including two that are notable for their reactivity and thermal instability, is also described.

The structural and mechanistic study of a monoalkyl diazene intermediate in the oxidative transformation of propargylic hydrazines to allenes is described. The use of long-range heteronuclear NMR coupling constants for assigning monoalkyl diazene stereochemistry (E vs Z) is also discussed. Evidence is presented that all known monoalkyl diazenes are the E isomers, and the erroneous assignment of stereochemistry in the previous report of the preparation of (Z)-phenyldiazene is discussed.

The synthesis, characterization, and reactivity of 1,6-didehydro[10]annulene are described. This molecule has been recognized as an interesting synthetic target for over 40 years and represents the intersection of two sets of extensively studied molecules: nonbenzenoid aromatic compounds and molecules containing sterically compressed π-systems.The formation of 1,5-dehydronaphthalene from 1 ,6-didehydro[10]annulene is believed to be the prototype for cycloaromatizations that produce 1,4-dehydroaromatic species with the radical centers disposed anti about the newly formed single bond. The aromaticity of this annulene and the facility of its cycloaromatization are also analyzed.

Dynamics of cell–matrix mechanical interactions in three dimensions

The forces cells apply to their surroundings control biological processes such as growth, adhesion, development, and migration. In the past 20 years, a number of experimental techniques have been developed to measure such cell tractions. These approaches have primarily measured the tractions applied by cells to synthetic two-dimensional substrates, which do not mimic in vivo conditions for most cell types. Many cell types live in a fibrous three-dimensional (3D) matrix environment. While studying cell behavior in such 3D matrices will provide valuable insights for the mechanobiology and tissue engineering communities, no experimental approaches have yet measured cell tractions in a fibrous 3D matrix.

This thesis describes the development and application of an experimental technique for quantifying cellular forces in a natural 3D matrix. Cells and their surrounding matrix are imaged in three dimensions with high speed confocal microscopy. The cell-induced matrix displacements are computed from the 3D image volumes using digital volume correlation. The strain tensor in the 3D matrix is computed by differentiating the displacements, and the stress tensor is computed by applying a constitutive law. Finally, tractions applied by the cells to the matrix are computed directly from the stress tensor.

The 3D traction measurement approach is used to investigate how cells mechanically interact with the matrix in biologically relevant processes such as division and invasion. During division, a single mother cell undergoes a drastic morphological change to split into two daughter cells. In a 3D matrix, dividing cells apply tensile force to the matrix through thin, persistent extensions that in turn direct the orientation and location of the daughter cells. Cell invasion into a 3D matrix is the first step required for cell migration in three dimensions. During invasion, cells initially apply minimal tractions to the matrix as they extend thin protrusions into the matrix fiber network. The invading cells anchor themselves to the matrix using these protrusions, and subsequently pull on the matrix to propel themselves forward.

Lastly, this thesis describes a constitutive model for the 3D fibrous matrix that uses a finite element (FE) approach. The FE model simulates the fibrous microstructure of the matrix and matches the cell-induced matrix displacements observed experimentally using digital volume correlation. The model is applied to predict how cells mechanically sense one another in a 3D matrix. It is found that cell-induced matrix displacements localize along linear paths. These linear paths propagate over a long range through the fibrous matrix, and provide a mechanism for cell-cell signaling and mechanosensing. The FE model developed here has the potential to reveal the effects of matrix density, inhomogeneity, and anisotropy in signaling cell behavior through mechanotransduction.

Femtosecond pulse laser-induced self-organized nanostructures on the surface of ZnO crystal

This paper reports self-organized nanostructures observed on the surface of ZnO crystal after irradiation by a focused beam of a femtosecond Ti:sapphire laser with a repetition rate of 250 kHz. For a linearly polarized femtosecond laser, the periodic nanograting structure on the ablation crater surface was promoted. The period of self-organization structures is about 180 nm. The grating orientation is adjusted by the laser polarization direction. A long range Bragg-like grating is formed by moving the sample at a speed of 10 mu m/s. For a circularly polarized laser beam, uniform spherical nanoparticles were formed as a result of Coulomb explosion during the interaction of near-infrared laser with ZnO crystal.

Crystal Coulomb energies: I. Organic donor-acceptor complexes--a review. II. Classical Ewald calculations of the Coulomb binding energy of four donor-acceptor crystals and Wurster's blue perchlorate. III. A rapid-convergence quantum-mechanical formalism for crystal electronic energies

Chapter I

Theories for organic donor-acceptor (DA) complexes in solution and in the solid state are reviewed, and compared with the available experimental data. As shown by McConnell et al. (Proc. Natl. Acad. Sci. U.S., 53, 46-50 (1965)), the DA crystals fall into two classes, the holoionic class with a fully or almost fully ionic ground state, and the nonionic class with little or no ionic character. If the total lattice binding energy 2ε₁ (per DA pair) gained in ionizing a DA lattice exceeds the cost 2ε_o of ionizing each DA pair, ε₁ + ε_o less than 0, then the lattice is holoionic. The charge-transfer (CT) band in crystals and in solution can be explained, following Mulliken, by a second-order mixing of states, or by any theory that makes the CT transition strongly allowed, and yet due to a small change in the ground state of the non-interacting components D and A (or D⁺ and A^-). The magnetic properties of the DA crystals are discussed.

Chapter II

A computer program, EWALD, was written to calculate by the Ewald fast-convergence method the crystal Coulomb binding energy E_C due to classical monopole-monopole interactions for crystals of any symmetry. The precision of E_C values obtained is high: the uncertainties, estimated by the effect on E_C of changing the Ewald convergence parameter η, ranged from ± 0.00002 eV to ± 0.01 eV in the worst case. The charge distribution for organic ions was idealized as fractional point charges localized at the crystallographic atomic positions: these charges were chosen from available theoretical and experimental estimates. The uncertainty in E_C due to different charge distribution models is typically ± 0.1 eV (± 3%): thus, even the simple Hückel model can give decent results.

E_C for Wurster's Blue Perchl orate is -4.1 eV/molecule: the crystal is stable under the binding provided by direct Coulomb interactions. E_C for N-Methylphenazinium Tetracyanoquino- dimethanide is 0.1 eV: exchange Coulomb interactions, which cannot be estimated classically, must provide the necessary binding.

EWALD was also used to test the McConnell classification of DA crystals. For the holoionic (1:1)-(N,N,N',N'-Tetramethyl-para- phenylenediamine: 7,7,8,8-Tetracyanoquinodimethan) E_C = -4.0 eV while 2ε_o = 4.6₅ eV: clearly, exchange forces must provide the balance. For the holoionic (1:1)-(N,N,N',N'-Tetramethyl-para- phenylenediamine:para-Chloranil) E_C = -4.4 eV, while 2ε_o = 5.0 eV: again EC falls short of 2ε₁. As a Gedankenexperiment, two nonionic crystals were assumed to be ionized: for (1:1)-(Hexamethyl- benzene:para-Chloranil) E_C = -4.5 eV, 2ε_o = 6.6 eV; for (1:1)- (Napthalene:Tetracyanoethylene) E_C = -4.3 eV, 2ε_o = 6.5 eV. Thus, exchange energies in these nonionic crystals must not exceed 1 eV.

Chapter III

A rapid-convergence quantum-mechanical formalism is derived to calculate the electronic energy of an arbitrary molecular (or molecular-ion) crystal: this provides estimates of crystal binding energies which include the exchange Coulomb inter- actions. Previously obtained LCAO-MO wavefunctions for the isolated molecule(s) ("unit cell spin-orbitals") provide the starting-point. Bloch's theorem is used to construct "crystal spin-orbitals". Overlap between the unit cell orbitals localized in different unit cells is neglected, or is eliminated by Löwdin orthogonalization. Then simple formulas for the total kinetic energy Q^(XT)_λ, nuclear attraction [λ/λ]^XT, direct Coulomb [λλ/λ'λ']^XT and exchange Coulomb [λλ'/λ'λ]^XT integrals are obtained, and direct-space brute-force expansions in atomic wavefunctions are given. Fourier series are obtained for [λ/λ]^XT, [λλ/λ'λ']^XT, and [λλ/λ'λ]^XT with the help of the convolution theorem; the Fourier coefficients require the evaluation of Silverstone's two-center Fourier transform integrals. If the short-range interactions are calculated by brute-force integrations in direct space, and the long-range effects are summed in Fourier space, then rapid convergence is possible for [λ/λ]^XT, [λλ/λ'λ']^XT and [λλ'/λ'λ]^XT. This is achieved, as in the Ewald method, by modifying each atomic wavefunction by a "Gaussian convergence acceleration factor", and evaluating separately in direct and in Fourier space appropriate portions of [λ/λ]^XT, etc., where some of the portions contain the Gaussian factor.