9,480 research outputs found
Fluid dynamics and low gravity effects of chemical vapor deposition
Based on the comparison between experimental data and numerical results for the growth of GaAs from TMGa, it was shown that 3D simulations are necessary to simulate rectangular CVD reactors even when operated under subcritical (Ra) conditions. The important points found are summarized in the three attached reprints. The experimental studies of mixed convection in horizontal channels have shown three regimes of high Ra (22,220) number flows. At Re = 18.5, the rolls develop very quickly, significantly modulating the axial velocity even before it reaches the beginning of the hot plate. A few centimeters downstream, the velocities become asymmetric about the vertical centerplane and at x = 12 cm, become unsteady. These asymmetries were predicted theoretically, but experimental evidence has not been published prior to this work. At Re = 36, the axial velocity is only slightly modified at x = 0. Although the flow remains steady and symmetric about the vertical centerplane, there is a small spatial oscillation in the velocities over the length of the channel. The period of this oscillation was around 5 cm. At Re = 54, the longitudinal rolls developed smoothly over a length of 30 cm, with no asymmetries, unsteadiness, or spatial oscillations. Comparison of numerical simulations of these flows to experiments has revealed the importance and difficulty of setting proper thermal boundary conditions on the sidewalls. Calculated flows and experimentally measured flows showed very similar profiles, but at different axial locations, with the rolls developing more rapidly in the experiments. This is directly attributable to partially conducting sidewalls of the apparatus being hotter in the entrance section than the adiabatic walls of the simulations. A thorough comparison of the experimental data and numerical results for a variety of sidewall boundary conditions is in preparation
Novel protein crystal growth technology: Proof of concept
A technology for crystal growth, which overcomes certain shortcomings of other techniques, is developed and its applicability to proteins is examined. There were several unknowns to be determined: the design of the apparatus for suspension of crystals of varying (growing) diameter, control of the temperature and supersaturation, the methods for seeding and/or controlling nucleation, the effect on protein solutions of the temperature oscillations arising from the circulation, and the effect of the fluid shear on the suspended crystals. Extensive effort was put forth to grow lysozyme crystals. Under conditions favorable to the growth of tetragonal lysozyme, spontaneous nucleation could be produced but the number of nuclei could not be controlled. Seed transfer techniques were developed and implemented. When conditions for the orthorhombic form were tried, a single crystal 1.5 x 0.5 x 0.2 mm was grown (after in situ nucleation) and successfully extracted. A mathematical model was developed to predict the flow velocity as a function of the geometry and the operating temperatures. The model can also be used to scaleup the apparatus for growing larger crystals of other materials such as water soluble non-linear optical materials. This crystal suspension technology also shows promise for high quality solution growth of optical materials such as TGS and KDP
A matrix product algorithm for stochastic dynamics on networks, applied to non-equilibrium Glauber dynamics
We introduce and apply a novel efficient method for the precise simulation of
stochastic dynamical processes on locally tree-like graphs. Networks with
cycles are treated in the framework of the cavity method. Such models
correspond, for example, to spin-glass systems, Boolean networks, neural
networks, or other technological, biological, and social networks. Building
upon ideas from quantum many-body theory, the new approach is based on a matrix
product approximation of the so-called edge messages -- conditional
probabilities of vertex variable trajectories. Computation costs and accuracy
can be tuned by controlling the matrix dimensions of the matrix product edge
messages (MPEM) in truncations. In contrast to Monte Carlo simulations, the
algorithm has a better error scaling and works for both, single instances as
well as the thermodynamic limit. We employ it to examine prototypical
non-equilibrium Glauber dynamics in the kinetic Ising model. Because of the
absence of cancellation effects, observables with small expectation values can
be evaluated accurately, allowing for the study of decay processes and temporal
correlations.Comment: 5 pages, 3 figures; minor improvements, published versio
Adaptive Survival Trials
Mid-study design modifications are becoming increasingly accepted in
confirmatory clinical trials, so long as appropriate methods are applied such
that error rates are controlled. It is therefore unfortunate that the important
case of time-to-event endpoints is not easily handled by the standard theory.
We analyze current methods that allow design modifications to be based on the
full interim data, i.e., not only the observed event times but also secondary
endpoint and safety data from patients who are yet to have an event. We show
that the final test statistic may ignore a substantial subset of the observed
event times. Since it is the data corresponding to the earliest recruited
patients that is ignored, this neglect becomes egregious when there is specific
interest in learning about long-term survival. An alternative test
incorporating all event times is proposed, where a conservative assumption is
made in order to guarantee type I error control. We examine the properties of
our proposed approach using the example of a clinical trial comparing two
cancer therapies.Comment: 22 pages, 7 figure
The Financial System in the Czech Republic, Hungary and Poland after a Decade of Transition
The Czech Republic, Hungary and Poland (CEEC-3) have undertaken substantial efforts to build a new financial system under the constraints of their legacies from central planning. In this study, first we look at the banking sector. Then we give a description of bond and stock markets. These topics are complemented by an analysis of the structure of funding for the private and public sector, of the financial sector's vulnerability and of the legal conditions for external finance as well as for banking supervision. We find that the financial sector and financial intermediation are internationally integrated already to a large extent. This implies, inter alia, a non-negligible exposure of the corporate sector to exchange rate risk. While funding via equity markets remained modest, local currencydenominated debt issues are important for public financing. Our analysis shows that the legal, supervisory and regulatory infrastructure of the financial system is formally well developed, but suffers from enforcement problems. -- Polen, die Tschechische Republik und Ungarn unternahmen, ausgehend vom Erbe der zentralen Planwirtschaft, substanzielle Anstrengungen zur Errichtung neuer Finanzsysteme. Aufbauend auf einer Untersuchung des Bankensektors sowie der Kapitalmärkte erfolgt eine Analyse der Finanzierungsstruktur des privaten und des öffentlichen Sektors, der Krisenanfälligkeit des Finanzsektors sowie der rechtlichen Regelungen für externe Unternehmensfinanzierung und Bankenaufsicht. Finanzsektoren und -intermediation sind bereits in hohem Maße international integriert. Dies impliziert u.a., dass der Unternehmenssektor einem beachtlichen Wechselkursrisiko ausgesetzt ist. Während die Finanzierung über den Aktienmarkt gering ist, sind in nationaler Währung denominierte Schuldtitel für die Finanzierung des öffentlichen Sektors wichtig. Unsere Analyse zeigt, dass der rechtliche und aufsichtsrechtliche Rahmen der Finanzsysteme formal gut entwickelt ist. Es gibt jedoch Mängel bei der praktischen Umsetzung dieser Standards.Financial System in Czech Republic,Hungary and Poland,Financial Sector Transition,Transition Economics
Software-Defined Networks Supporting Time-Sensitive In-Vehicular Communication
Future in-vehicular networks will be based on Ethernet. The IEEE
Time-Sensitive Networking (TSN) is a promising candidate to satisfy real-time
requirements in future car communication. Software-Defined Networking (SDN)
extends the Ethernet control plane with a programming option that can add much
value to the resilience, security, and adaptivity of the automotive
environment. In this work, we derive a first concept for combining
Software-Defined Networking with Time-Sensitive Networking along with an
initial evaluation. Our measurements are performed via a simulation that
investigates whether an SDN architecture is suitable for time-critical
applications in the car. Our findings indicate that the control overhead of SDN
can be added without a delay penalty for the TSN traffic when protocols are
mapped properly.Comment: To be published at IEEE VTC2019-Sprin
Simulation of Mixed Critical In-vehicular Networks
Future automotive applications ranging from advanced driver assistance to
autonomous driving will largely increase demands on in-vehicular networks. Data
flows of high bandwidth or low latency requirements, but in particular many
additional communication relations will introduce a new level of complexity to
the in-car communication system. It is expected that future communication
backbones which interconnect sensors and actuators with ECU in cars will be
built on Ethernet technologies. However, signalling from different application
domains demands for network services of tailored attributes, including
real-time transmission protocols as defined in the TSN Ethernet extensions.
These QoS constraints will increase network complexity even further.
Event-based simulation is a key technology to master the challenges of an
in-car network design. This chapter introduces the domain-specific aspects and
simulation models for in-vehicular networks and presents an overview of the
car-centric network design process. Starting from a domain specific description
language, we cover the corresponding simulation models with their workflows and
apply our approach to a related case study for an in-car network of a premium
car
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