1,960 research outputs found
Impact Ionization And High-field Effects In Wide-band-gap Semiconductors
No full textImpact ionization is important for electron transport in wide-band-gap semiconductors at high electric fields. We consider a realistic band structure as well as high-field quantum corrections such as the intracollisional field effect in the calculation of the microscopic scattering rate. A pronounced softening of the impact ionization threshold is obtained. This field-dependent impact ionization rate is included within a full-band ensemble Monte Carlo simulation of high-field transport in ZnS. Although the impact ionization rate itself is strongly affected, little effect is observed on measurable quantities such as the impact ionization coefficient. © 2002 Elsevier Science B.V. All rights reserved.3141-45254Ang, W.M., (1995) J. Appl. Phys., 77, p. 2719Reigrotzki, M., Stobbe, M., Redmer, R., Schattke, W., (1995) Phys. Rev. B, 52, p. 1456Reigrotzki, M., (1996) J. Appl. Phys., 80, p. 5054Dür, M., (1998) J. Appl. Phys., 83, p. 3176Reigrotzki, M., (1997) Phys. Stat. Sol. B, 204, p. 528Dür, M., (1999) Physica B, 272, p. 295Quade, W., Schöll, E., Rossi, F., Jacoboni, C., (1994) Phys. Rev. B, 50, p. 7398Redmer, R., (2000) J. Appl. Phys., 87, p. 781Reigrotzki, M., (2001) Int. J. High Speed Electron. Systems, 11, p. 511Reigrotzki, M., (1999) J. Appl. Phys., 86, p. 4458Madureira, J.R., Semkat, D., Bonitz, M., Redmer, R., (2001) J. Appl. Phys., 90, p. 829Bude, J., Hess, K., Iafrate, G.J., (1992) Phys. Rev. B, 45, p. 1095
R Measurement at BESIII
No full textThe R value is measured with a total of 14 data points with the corresponding center-of-mass energy going from 2.2324 to 3.6710 GeV. The statistical uncertainty of the measured R is less than 0.6%. Two different simulation models, the LUARLW and a new Hybrid generator, are used and give consistent detection and initial-state radiation corrections. An accuracy of better than 2.6% below 3.1 GeV and 3.0% above is achieved for the R value. The precise measurement will be an important constraint for precision tests of the Standard Model, such as calculations of the anomalous magnetic moment of the moun and the running of the QED coupling
A strappado for the Diuell /
No full text"A volume founded directly on 'The abuses whipt and stript' of George Wither."--Dict. nat. biog.With reprint of original t.-p.: a Strappado for the Diuell. Epygrams and Satyres alluding to the time, with diuers measures of no lesse Delight ... At London printed by I.B. for Richard Redmer ... 1615.""300 copies only small paper and 50 large.Mode of access: Internet
Using economic indicators in a simple model to predict annual growth in the wind energy industry
No full textClimate change is going to be the main problem this and future generations will face. Wind energy is promising to be one of the industries that could help mitigate this impending crisis. In literature many different models and predictions can be found to describe the possible futures of wind energy. But there is still a lot of uncertainty in this field as to what factors play which role in its development.This research contributes to this challenge by comparing the economic attractiveness of windmills expressed as Net Present Value(NPV) with annual added wind capacity in five countries for 2008 till 2019. The countries used for this research are Germany, Denmark, Canada, Texas and Sweden. This research found an exponential relationship between the NPV and added wind power capacity. A 10% increase in NPV(AC/MWh) found an increase of 15% for the annual added wind capacity(MW/TWh) of added windmill capacity per TWh of electricity produced. The vast amount of data sources used could have lead to a higher uncertainty regarding their uniformity and trustworthiness. Doing a sensitivity analysis yielded no improvements in the results. The simple economic model used was able to describe the growth in wind energy in countries, though there is still a significant spread in the results. A likely explanation for this spread is the lack of several important aspects such as permits, company influences, cultural differences and social-economic challenges which were all not taken into account. This research also makes several recommendations regarding possible policies countries could in order for them to reach their wind or clean energy goals.Management of Technology (MoT
Analysis of evacuation performance of early stage ship designs using a Markov-Decision-Process model
No full textThis thesis research is conducted on behalf of the Delft University of Technology and Bureau Veritas Rotterdam BV, and the goal is to improve ship evacuation by analyzing this aspect early on in the design process. First, this summary will provide a background on the difficulties involved with the ship evacuation process . Next, an explanation is given why this thesis proposes a different model. And lastly, how this model is validated is elaborated upon.A ship evacuation is a highly complex process and it is one of the most important aspects concerning the safety of crew and passengers on-board. This process is affected by various factors, largely by the general arrangement. The layout of a ship varies throughout the design period but the most design freedom occurs during the early stage. An estimated 90% of the decisions which have major impact on final design have been made in this stage. As a result, this stage holds the most potential to improve the ship evacuation performance. This stage is characterized by a lack of detailed layout information available, which results in reduced accuracy in evacuation prediction. As of 1st of July 2020 all passenger ships with more than 36 passengers have to perform an evacuation analysis based on guidelines created by the International Maritime Organization (IMO). The guidelines describe two methods, a simplified method for the early design stage, and an advanced method for the detailed or final design stage. The simplified method translates the ship design to a hydraulic network which in turn results in various method limitations. The goal of an evacuation analysis is, among other things, to provide the designer with information about possible congestion points, identify areas of counter- and cross flows, prove that the escape arrangements are sufficiently flexible, and prove that the evacuation time does not exceed a threshold.Evacuation models capable of performing an evacuation analysis tend to have four general components that define the various aspects influencing the process. The four components are configuration, environmental, procedural, and behavior component. Including evacuee behavior in an evacuation model tends to be difficult due to the complexity and lack of research available. Evacuation models can be categorized using various descriptors however resolution tends to dominate. High resolution models are called macroscopic models whereas low resolution models are called microscopic models. Microscopic models simulate each individual evacuee as an agent with certain attributes, such as walking speed and destination. Most early stage evacuation analysis are macroscopic models and simulate the population as a whole. A different macroscopic approach is proposed by Kana and Singer, which uses probability theory to incorporate the stochastic nature of an evacuation process. This method consists of a Markov-Decision-Process (MDP) to calculate the most probable evacuation routes. Policies are determined for each small geometric area, called a state, in the layout. These policies affect evacuation routes. The evacuation process can then be simulated by using the MDP policies and an initial population distribution. The initial population distributions are defined by the Fire Safety Systems Code. Design variations can be compared based on the calculated optimal routes, the time it takes for the process to converge, and how the population is distributed among the exits. A lack of literature is noticed that investigates the relationship between early stage ship design and the ship evacuation performance. Two different studies were found which can be used to validate the MDP methodology. The first validation study determines which exit configuration is most optimal from an egress perspective. Kurdi et al. defined four different layouts for two population sizes. Having exits on all sides was determined to be the most efficient layout. The MDP model consisted of the same setup as the validation study. The MDP method is able to identify the same exit configuration as most efficient based on the population distributed among the exits and simulation convergence times. The second validation study evaluates two different frigate layouts with varying passageway configuration. One layout has a single passageway throughout the ship. The other layout has a parallel passageway configuration. Casarosa applied a microscopic model to calculate a range of performance metrics for 7 different scenarios. All evacuees were modeled as singular agents with different behavior and objectives. 3 out of 7 scenarios were emergency scenarios, where only 1 scenario corresponds with the MDP assumptions. Discrepancy between models is considered as a result of limited, and confidential, layout information used by Casarosa. The MDP method was able to differentiate between the two layout configurations and can identify critical areas in the layout. However, due to the assumptions, it cannot be determined to what extend the method inputs were similar. Nevertheless, both validation studies showed the potential of using a Markov-Decision-Process based method to evaluate early stage ship designs on evacuation performance.<br/
Using Narrow Reading to Develop Fluency
No full textThe author presents a step-by-step procedure for using narrow reading—“reading several texts about a single, narrow topic”—to promote reading fluency, with examples and suggested variations.補正完
Quanten-Monte-Carlo: Gesamtenergierechnungen zu strukturellen und dynamischen Eigenschaften von Festkörpern
No full textQuantum Monte Carlo (QMC) methods are a stochastic approach to directly tackle the many-body problem in solids. Especially variational quantum Monte Carlo (VMC) calculations using nonlocal ab initio pseudopotentials offer a way to study many-body effects in real materials systematically, safely founded on Ritz' variational principle 'the lower the energy, the better the wave function'. In this work the method is extended to study dynamical and structural aspects in solids and solid surfaces from first principles, with practical calculations for phonons and the electron-phonon coupling in gallium arsenide (GaAs) and relaxation at the (110) surface of GaAs. Within a frozen phonon scheme, the frequency of an optical phonon is determined with an accuracy of a few meV in very good agreement with experiment. An optical deformation potential approach is chosen for the electron-phonon coupling, showing that the interaction between excited states and distortions of the ion lattice is statistically resolvable within the VMC method. As for the surface systems, taking the boundary condition for the simulation from a finite-layer geometry, the Hamiltonian is cast in a layer-resolved form and evaluated with a two-dimensional Ewald summation technique. The exact cancellation of all jellium contributions to the total energy is ensured. In the trial wave function a confinement term is introduced to compensate for the smoothing effect of the Jastrow factor. A realistic surface model of GaAs(110) is compared with the ideal geometry for different system sizes, showing a consistent finite size dependence of the total energy per atom. With the resulting optimal wave function further surface specific information is extracted to further analyze the many-body effects at solid surfaces
Natural History of the Wood Frog (Rana sylvatica) in the Shawnee National Forest, Southern Illinois
No full textI studied several aspects of the natural history and population biology of R. sylvatica in the Shawnee National Forest (SNF) between 1993 and 1997. The primary objective was to conduct the first extensive study of this species in Illinois. The first portion of this study documented the distribution of R. sylvatica in the SNF. Observations of general aspects of natural history (predation, amphibian community associates, and larval period) were also recorded. I then identified and qualitatively characterized types of breeding ponds and woodland habitats in which the species occurs, and recorded the phenology of breeding activity and weather conditions at which they occurred. I then used skeletochronology to estimate individual ages of wood frogs, and compared statistical correlations between age and body length of individuals and female age and body length with clutch size and ovum size
Research Opportunities Featuring Christian Businesses: Case Teaching Notes, Tackling the Hard Part First
No full textWhen conducting research, the author often has a preconceived idea on what is the likely outcome. With basic research, there is generally a stated hypothesis, and the research sets out to either prove or disprove this hypothesis. With applied research, data collection is often used, and there is some expectation on what the results will be. In case studies, a less familiar research area, results can be entirely different than expected for a variety of reasons, some of which could be totally unforeseen by the author. This increased uncertainty can make the research process more enticing or have a severe detrimental impact on the study to the point of curtailing the case study altogether
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