Effects of fishing on growth traits: a simulation analysis

Abstract—Fisheries often target individuals based on size. Size-selective fishing can create selection differentials on life-history traits and, when those traits have a genetic basis, may cause evolution. The evolution of life history traits affects potential yield and sustainability of fishing, and it is therefore an issue for fishery management. Yet fishery managers usually disregard the possibility of evolution, because little guidance is available to predict evolutionary consequences of management strategies. We attempt to provide some generic guidance. We develop an individual-based model of a population with overlapping generations and continuous reproduction. We simulate model populations under size-selective fishing to generate and quantify selection differentials on growth. The analysis comprises a variety of common life-history and fishery characteristics: variability in growth, correlation between von Bertalanffy growth parameters (K and L∞), maturity rate, natural mortality rate (M), M/K ratio, duration of spawning season, fishing mortality rate (F), maximum size limit, slope of selectivity curve, age at 50% selectivity, and duration of fishing season. We found that each characteristic affected the magnitude of selection differentials. The most vulnerable stocks were those with a short spawning or fishing season. Under almost all life-history and fishery characteristics examined, selection differentials created by realistic fishing mortality rates are considerable.

Síntese de árvores de padrões Fuzzy através de Programação Genética Cartesiana.

Esta dissertação apresenta um sistema de indução de classificadores fuzzy. Ao invés de utilizar a abordagem tradicional de sistemas fuzzy baseados em regras, foi utilizado o modelo de Árvore de Padrões Fuzzy(APF), que é um modelo hierárquico, com uma estrutura baseada em árvores que possuem como nós internos operadores lógicos fuzzy e as folhas são compostas pela associação de termos fuzzy com os atributos de entrada. O classificador foi obtido sintetizando uma árvore para cada classe, esta árvore será uma descrição lógica da classe o que permite analisar e interpretar como é feita a classificação. O método de aprendizado originalmente concebido para a APF foi substituído pela Programação Genética Cartesiana com o intuito de explorar melhor o espaço de busca. O classificador APF foi comparado com as Máquinas de Vetores de Suporte, K-Vizinhos mais próximos, florestas aleatórias e outros métodos Fuzzy-Genéticos em diversas bases de dados do UCI Machine Learning Repository e observou-se que o classificador APF apresenta resultados competitivos. Ele também foi comparado com o método de aprendizado original e obteve resultados comparáveis com árvores mais compactas e com um menor número de avaliações.

The calculation of acoustic shielding of engine noise by the Silent Aircraft Airframe

The Silent Aircraft airframe has a flying wing design with a large wing planform and a propulsion system embedded in the rear of the airframe with intake on the upper surface of the wing. In the present paper, boundary element calculations are presented to evaluate acoustic shielding at low frequencies. Besides the three-dimensional geometry of the Silent Aircraft airframe, a few two-dimensional problems are considered that provide some physical insight into the shielding calculations. Mean flow refraction effects due to forward flight motion are accounted for by a simple time transformation that decouples the mean-flow and acoustic-field calculations. It is shown that significant amount of shielding can be obtained in the shadow region where there is no direct line of sight between the source and observer. The boundary element solutions are restricted to low frequencies. We have used a simple physically-based model to extend the solution to higher frequencies. Based on this model, using a monopole acoustic source, we predict at least an 18 dBA reduction in the overall sound pressure level of forward-propagating fan noise because of shielding.

松嫩平原盐碱化草地模拟模型研究

松嫩平原盐碱化草地是我国著名的天然草场，又是东北西部绿色生态屏障，具有较高的经济价值和重要的生态意义。但是由于各种自然因素和人为因素，致使草地出现退化、沙化和盐渍化，尤其是草地盐渍化加重，生态环境日趋恶化。当地地形条件和气候要素是导致草地原生盐碱化的主要原因。而人类对草地的过度使用，如过度放牧和割草等则是导致草地快速次生盐碱化的主要原因，不仅导致土壤的退化，而且引起草地群落发生次生演替过程。在典型的次生演替过程中，常常可以出现羊革(Aneurolepidium chinense)群落、羊草和一虎尾草(Aneurotepidium chinense＆Chloris virgata)群落、虎尾草(Chloris virgata)群落、碱蓬(Suaeda glauca)群落等演替阶段。 本文试图建立一个过程模型，来模拟草地的生态学过程机理以及人类过度放牧对草地生态系统的影响。本模型包括5个部分：1）主要气候因子的模拟，2)土壤水分动态的模拟，3）土壤盐碱化动态的模拟，4）草地群落生长的模拟，5)不同放牧强度对草地生态系统的影响评价。以下将对各个部分分别描述a 在气候因子模拟子模型中，给出了影响草地生态系统主要气候园子的种类，并重点介绍了如何利用解析法计算太阳辐射，包括平地和坡地的理论可照时间，天文辐射日总量以及总辐射量。利用改进后的Penman式，模拟了全国的潜在蒸散量，与900多个气象站点的水面蒸发观测资料进行了验证，模拟结果很好。 利用面向对象技术，将土壤水分动力学模型与水分平衡模型相结合，建立了土壤水分动态的物理过程模型。模型以ld为步长，可以模拟多种土壤质地的水分动态。利用松嫩平原4中典型土壤（碳酸盐草甸黑钙土、栗钙土、碱化盐土、草甸碱土）1997年土壤湿度观测资料对模型进行了验证，效果根理想。 在水盐平衡模型和动力学模型基础上建立了物理过程模型，来模拟土壤盐碱化动态。模型以ld为步长，适合于模拟异质性强的多层土壤水盐动态。模拟了1997年羊草及碱蓬群落下的土壤盐分、碱化度、pH值动态，并与实验资料进行了比较，模拟结果可以反映土壤盐分和碱化的季节变化规律。 模型将气候要素、土壤湿度、土壤盐分浓度、碱化度和pH值作为影响草地群落生长最重要的环境因子，在土壤水分动态和盐碱化动态模型基础上，建立了过程模型来模拟以羊草(A．chinense)、虎尾草(C.virgata)、星星草(Puccinellialenuiflora)和碱蓬(S. glauca)为建群种的4种植物群落的地上生物量、地下生物量以及枯死生物量变化动态。利用吉林省长岭的气候资料和实验资料，模拟了1991年土壤湿度动态，1991年4种群落土壤盐分、碱化度和pH值变化动态，以及1991年4种群落生长动态，并分另fj利用实验资料进行了验证，模拟效果非常理想。 在此基础上，利用模型对不同放牧强度对土壤水分动态、盐碱化动态的影响进行了评价，并探讨了对群落演替和生长的可能影响。模型选择不放牧、轻牧、重牧、过牧、极牧5种放牧强度，利用模型每15天将地上生物量分别去除0%. 25%、50%、75%和90%，并且相应改变了土壤导水特性来模拟不同的放牧强度。模拟结果表明，重牧、过牧、极牧下土壤湿度显著降低，但在轻牧下土壤温度略有上升。在不放牧时，土壤以脱盐、脱碱过程为主，而轻牧下脱盐、脱碱过程则会变缓：重牧、过牧、极牧下则以盐碱化为主。．不放牧时羊草群落一直占优势，而轻牧下则被羊草一虎尾草群落替代：虎尾草可以忍受轻的盐碱，因此在重牧F取代羊草群落成为优势种;在过牧和极牧下，土壤盐碱化非常迅速，最终只有碱蓬可以忍受强度的盐碱，这时草地变为碱蓬群落或光碱斑。不放牧下草地群落生长良好，生物量最大;轻牧下，草地群落生物量保持在中等水平;而重牧、过牧、极牧下草地生物量迅速减少。通过将每年收割的生物量进行累加，可以发现轻牧下收获的生物量总量是最大的，随着放牧强度的增加，收获的生物量迅速减少，如果同时考虑到适口性的问题，则可以发现轻牧下可 以收获最多的生物量，而过牧和极牧下只能收获极少的适口性非常差的碱蓬。 模拟结果表明，过牧是导致松嫩草地次生盐碱化最重要的原因，它不仅造成草地土壤的退化，而且加速了草地群落的次生演替。适宜的放牧强度对于保护草地免受退化，保持较高的草地生产力水平至关重要。而过牧不仅降低了草地的生产力，而且严重破坏了草地环境，引起草地的迅速退化。

Modelling the evolution of uncertainty levels during design

Design work involves uncertainty that arises from, and influences, the progressive development of solutions. This paper analyses the influences of evolving uncertainty levels on the design process. We focus on uncertainties associated with choosing the values of design parameters, and do not consider in detail the issues that arise when parameters must first be identified. Aspects of uncertainty and its evolution are discussed, and a new task-based model is introduced to describe process behaviour in terms of changing uncertainty levels. The model is applied to study two process configuration problems based on aircraft wing design: one using an analytical solution and one using Monte-Carlo simulation. The applications show that modelling uncertainty levels during design can help assess management policies, such as how many concepts should be considered during design and to what level of accuracy. © 2011 Springer-Verlag.

Shock Propagation and MPT Noise From a Transonic Rotor in Nonuniform Flow

One of the major challenges in high-speed fan stages used in compact, embedded propulsion systems is inlet distortion noise. A body-force-based approach for the prediction of multiple-pure-tone (MPT) noise was previously introduced and validated. In this paper, it is employed with the objective of quantifying the effects of nonuniform flow on the generation and propagation of MPT noise. First-of-their-kind back-to-back coupled aero-acoustic computations were carried out using the new approach for conventional and serpentine inlets. Both inlets delivered flow to the same NASA/GE R4 fan rotor at equal corrected mass flow rates. Although the source strength at the fan is increased by 38 dB in sound power level due to the nonuniform inflow, far-field noise for the serpentine inlet duct is increased on average by only 3.1 dBA overall sound pressure level in the forward arc. This is due to the redistribution of acoustic energy to frequencies below 11 times the shaft frequency and the apparent cut-off of tones at higher frequencies including blade-passing tones. The circumferential extent of the inlet swirl distortion at the fan was found to be two blade pitches, or 1/11th of the circumference, suggesting a relationship between the circumferential extent of the inlet distortion and the apparent cut-off frequency perceived in the far field. A first-principles-based model of the generation of shock waves from a transonic rotor in nonuniform flow showed that the effects of nonuniform flow on acoustic wave propagation, which cannot be captured by the simplified model, are more dominant than those of inlet flow distortion on source noise. It demonstrated that nonlinear, coupled aerodynamic and aero-acoustic computations, such as those presented in this paper, are necessary to assess the propagation through nonuniform mean flow. A parametric study of serpentine inlet designs is underway to quantify these propagation effects. © 2013 American Society of Mechanical Engineers.

Shock propagation and MPT noise from a transonic rotor in non-uniform flow

One of the major challenges in hig4h-speed fan stages used in compact, embedded propulsion systems is inlet distortion noise. A body-force-based approach for the prediction of multiple-pure-tone (MPT) noise was previously introduced and validated. In this paper, it is employed with the objective of quantifying the effects of non-uniform flow on the generation and propagation of MPT noise. First-of-their-kind back-to-back coupled aero-acoustic computations were carried out using the new approach for conventional and serpentine inlets. Both inlets delivered flow to the same NASA/GE R4 fan rotor at equal corrected mass flow rates. Although the source strength at the fan is increased by 45 dB in sound power level due to the non-uniform inflow, farfield noise for the serpentine inlet duct is increased on average by only 3.1 dBA overall sound pressure level in the forward arc. This is due to the redistribution of acoustic energy to frequencies below 11 times the shaft frequency and the apparent cut-off of tones at higher frequencies including blade-passing tones. The circumferential extent of the inlet swirl distortion at the fan was found to be 2 blade pitches, or 1/11th of the circumference, suggesting a relationship between the circumferential extent of the inlet distortion and the apparent cut-off frequency perceived in the far field. A first-principles-based model of the generation of shock waves from a transonic rotor in non-uniform flow showed that the effects of non-uniform flow on acoustic wave propagation, which cannot be captured by the simplified model, are more dominant than those of inlet flow distortion on source noise. It demonstrated that non-linear, coupled aerodynamic and aeroacoustic computations, such as those presented in this paper, are necessary to assess the propagation through non-uniform mean flow. A parametric study of serpentine inlet designs is underway to quantify these propagation effects. Copyright © 2011 by ASME.

Seismic response of submarine slopes

The geological profile of submerged slopes on the continental shelf typically includes soft cohesive soils with thicknesses ranging from a few meters to tens or hundreds of meters. The response of these soils in simple shear tests is largely influenced by the presence of an initial consolidation shear stress, inducing anisotropic stress-strain-strength properties which depend also on the direction of shear. In this paper, a new simplified effective-stress-based model describing the behavior of normally to lightly overconsolidated cohesive soils is used in conjunction with a one-dimensional seismic site response analysis computer code to illustrate the importance of accounting for anisotropy and small strain nonlinearity. In particular, a simple example is carried out to compare results for different slope inclinations. Depth profiling of the maximum shear strains and permanent deformations provide insight into the mechanisms of deformation during a seismic event, and the effects of sloping ground conditions.

Modeling cyclic behavior of lightly overconsolidated clays in simple shear

Assessment of seismic performance and estimation of permanent displacements for submerged slopes require the accurate description of the soil's stress-strain-strength relationship under irregular cyclic loading. The geological profile of submerged slopes on the continental shelf typically consists of normally to lightly overconsolidated clays with depths ranging from a few meters to a few hundred meters and very low slope angles. This paper describes the formulation of a simplified effective-stress-based model, which is able to capture the key aspects of the cyclic behavior of normally consolidated clays. The proposed constitutive law incorporates anisotropic hardening and bounding surface principles to allow the user to simulate different shear strain and stress reversal histories as well as provide realistic descriptions of the accumulation of plastic shear strains and excess pore pressure during successive loading cycles. (C) 2000 Published by Elsevier Science Ltd. | Assessment of seismic performance and estimation of permanent displacements for submerged slopes require the accurate description of the soil's stress-strain-strength relationship under irregular cyclic loading. The geological profile of submerged slopes on the continental shelf typically consists of normally to lightly overconsolidated clays with depths ranging from a few meters to a few hundred meters and very low slope angles. This paper describes the formulation of a simplified effective-stress-based model, which is able to capture the key aspects of the cyclic behavior of normally consolidated clays. The proposed constitutive law incorporates anisotropic hardening and bounding surface principles to allow the user to simulate different shear strain and stress reversal histories as well as provide realistic descriptions of the accumulation of plastic shear strains and excess pore pressures during successive loading cycles.

Catalyst composition and impurity-dependent kinetics of nanowire heteroepitaxy.

The mechanisms and kinetics of axial Ge-Si nanowire heteroepitaxial growth based on the tailoring of the Au catalyst composition via Ga alloying are studied by environmental transmission electron microscopy combined with systematic ex situ CVD calibrations. The morphology of the Ge-Si heterojunction, in particular, the extent of a local, asymmetric increase in nanowire diameter, is found to depend on the Ga composition of the catalyst, on the TMGa precursor exposure temperature, and on the presence of dopants. To rationalize the findings, a general nucleation-based model for nanowire heteroepitaxy is established which is anticipated to be relevant to a wide range of material systems and device-enabling heterostructures.

Prediction and elucidation of the population dynamics of Microcystis spp. in Lake Dianchi (China) by means of artificial neural networks

Lake Dianchi is a shallow and turbid lake, located in Southwest China. Since 1985, Lake Dianchi has experienced severe cyanabacterial blooms (dominated by Microcystis spp.). In extreme cases, the algal cell densities have exceeded three billion cells per liter. To predict and elucidate the population dynamics ofMicrocystis spp. in Lake Dianchi, a neural network based model was developed. The correlation coefficient (R 2) between the predicted algal concentrations by the model and the observed values was 0.911. Sensitivity analysis was performed to clarify the algal dynamics to the changes of environmental factors. The results of a sensitivity analysis of the neural network model suggested that small increases in pH could cause significantly reduced algal abundance. Further investigations on raw data showed that the response of Microcystis spp. concentration to pH increase was dependent on algal biomass and pH level. When Microcystis spp. population and pH were moderate or low, the response of Microcystis spp. population would be more likely to be positive in Lake Dianchi; contrarily, Microcystis spp. population in Lake Dianchi would be more likely to show negative response to pH increase when Microcystis spp. population and pH were high. The paper concluded that the extremely high concentration of algal population and high pH could explain the distinctive response of Microcystis spp. population to +1 SD (standard deviation) pH increase in Lake Dianchi. And the paper also elucidated the algal dynamics to changes of other environmental factors. One SD increase of water temperature (WT) had strongest positive relationship with Microcystis spp. biomass. Chemical oxygen demand (COD) and total phosphorus (TP) had strong positive effect on Microcystis spp. abundance while total nitrogen (TN), biological oxygen demand in five days (BOD5), and dissolved oxygen had only weak relationship with Microcystis spp. concentration. And transparency (Tr) had moderate positive relationship with Microcystis spp. concentration.

Carrier channels of multimodal-sized quantum dots: A surface-mediated adatom migration picture

This paper focuses on the study of carrier channels of multimodal-sized quantum dots formed on patterned substrate by a rate-equation-based model. Surface-mediated indium adatom migration is revealed by a direct comparison between quantum dot wetting layer, which acts as carrier channel, formed on a flat substrate and on a patterned substrate. For the assessment of suitability, the carrier channel of the dot-in-well structure has also been studied by the present model, and the transition energies of the carrier channel (e.g., InGaAs quantum well) obtained from theoretical simulation agree fairly well with those obtained from the reflectance measurements.

基于安全状态域的网络评估模型

将基于攻击图的评估与依赖标准的评估相结合,提出了一种基于安全状态域(security state region,简称SSR)的网络安全评估模型(security-state-region-based evaluation model,简称SSREM).该模型将攻击的影响分为攻击能力改变和环境改变,通过两者之间的因果关系建立数学模型,提出了安全状态域趋向指数的概念,借助Matlab进行攻击趋势的曲面拟合,进而进行安全状态域的划分和网络的安全性评估.实验结果表明,依据SSREM进行的评估能够通过安全状态城和安全状态域趋向指数反映网络进入不同状态的难易程度,对网络安全性量化评估具有借鉴意义.

基于移动代理的网格计算系统体系结构研究

本文针对物理链路可靠性低、容错性要求高、实体异构程度高的基础设施网格化需求，在系统分析当前主流的网格体系结构的基础上，研究了移动代理（PVM）系统的特性，根据移动代理的特点，提出了基于移动代理的四层网格计算模型MAGC(Mobile Agent Based Grid Computing)，描述了MAGC模型的层次结构，给出了MAGC模型的一个设计方案，分析了MAGC模型的特点，最后介绍了在Aglet平台下实现的原型系统。本文取得的成果主要包括： 第二章提出了基于移动代理的四层网格计算模型(MAGC)，说明了模型中每个层次的功能和层次之间的依赖关系。MAGC模型基于代码迁移，可以解决网络环境恶劣的条件下，网格系统的运行与部署问题。设计了MAGC模型的两个重要基础结构：作业机制和消息机制。设计了移动代理平台抽象层，使网格系统独立于具体的移动代理平台，从而具有一定的可移植性。 第三章在MAGC模型的基础上，进一步给出了MAGC模型的一个实现方案，阐述了MAGC模型中四个子层的功能和组件划分，对每层所包含的组件和组件实现的功能进行了描述，说明了系统的启动方式。 第四章基于MAGC模型构建了一个原型系统，原型系统以IBM开发的Aglets移动代理软件包为基础，实现了作业机制、消息机制和MAGC模型中的移动代理平台抽象层、系统服务层、API层、应用作业层四个子层。