OALib Journal期刊

ISSN: 2333-9721




2015 ( 13 )

2014 ( 19 )

2013 ( 30 )

2012 ( 22 )


匹配條件: “Hubertus Hertzberg” ,找到相關結果約172條。
Formaliserade m ten, tidigarelagda val. Reflektioner kring gymnasieutredningens syn p verg ng fr n skola till arbetsmarknad
Fredrik Hertzberg
Utbildning & Demokrati : Tidsskrift f?r Didaktik och Utbildningspolitik , 2008,
Experimental Investigation of Operating Room Air Distribution in a Full-Scale Laboratory Chamber Using Particle Image Velocimetry and Flow Visualization  [PDF]
James McNeill, Jean Hertzberg, Zhiqiang (John) Zhai
Journal of Flow Control, Measurement & Visualization (JFCMV) , 2013, DOI: 10.4236/jfcmv.2013.11005
Abstract: Room air distribution in hospital operating rooms (OR) is critical to the effective functioning of surgical procedures, but the air distribution patterns are governed by complex physics that are currently not well understood. Both qualitative and quantitative flow visualization techniques were used to evaluate the room air distribution in a full-scale chamber designed to simulate a hospital operating room. A laser sheet illumination technique was used to identify key features of the room air distribution, and particle image velocimetry (PIV) was used to measure the velocity field in a plane crossing the surgical site. Hospital operating rooms require the use of ASHRAE Group E diffusers in an array above the surgical table, providing downward, unidirectional, non-aspirating air flow across the sterile region of the room. The supply air jet is characterized by complex physics, including annular shape, impingement, buoyancy, a large jet to room aspect ratio, and recirculation. The large diameter of the jet relative to the room size makes the overall room air distribution highly sensitive to the parameters of the supply air. The air distribution pattern in the room was found to have relatively low velocity and turbulence near the supply air diffuser, but increasing velocity and turbulence in the shear region at the edge of the supply air jet. Flow visualization and PIV methods both demonstrated an angle of the shear layer inwards towards the center of the jet. This flow feature reduces the overall coverage area for the sterile air flow and may pose a risk to the protection of the surgical patient.
Partitioning and Tearing of Networks Applied to Process Flowsheeting
Truls Gundersen,Terje Hertzberg
Modeling, Identification and Control , 1983, DOI: 10.4173/mic.1983.3.2
Abstract: A review of the methods available for identification of the computational sequence in modular process simulators (partitioning and tearing) is followed by the presentation of a new very efficient and close-to-optimal routine for tearing. The problem of partitioning can be solved in computer times that are linear functions of the number of unit modules (vertices in the graph). The algorithm of Johns has been found to execute faster than the later and far better known algorithm of Tarjan. These methods are almost identical in idea but use different techniques in the book-keeping.
Dynamic Simulation of Chemical Engineering Systems by the Sequential Modular Approach
Magne Hillestad,Terje Hertzberg
Modeling, Identification and Control , 1986, DOI: 10.4173/mic.1986.3.1
Abstract: An algorithm for dynamic simulation of chemical engineering systems, using the sequential modular approach, is proposed. The modules are independent simulators, and are integrated over a common time horizon. Interpolation polynomials are used to approximate input variables. These input polynomials are updated before modules are intergrated in order to interpolate output from preceding module(s) and thereby increase coupling and stabilize the computation. Tear stream variables have to be predicted at future time tn+1 and various prediction methods are proposed.
Quality of Researchers' Searches of the ERIC Database
Scott Hertzberg,Lawrence Rudner
Education Policy Analysis Archives , 1999,
Abstract: During the last ten years, end-users of electronic databases have become progressively less dependent on librarians and other intermediaries. This is certainly the case with the Educational Resources Information Center (ERIC) Database, a resource once accessed by passing a paper query form to a librarian and now increasingly searched directly by end-users. This article empirically examines the search strategies currently being used by researchers and other groups. College professors and educational researchers appear to be doing a better job searching the database than other ERIC patrons. However, the study suggests that most end-users should be using much better search strategies.
On Inflation with Non-minimal Coupling
Mark P. Hertzberg
Physics , 2010, DOI: 10.1007/JHEP11(2010)023
Abstract: A simple realization of inflation consists of adding the following operators to the Einstein-Hilbert action: (partial phi)^2, lambda phi^4, and xi phi^2 R, with xi a large non-minimal coupling. Recently there has been much discussion as to whether such theories make sense quantum mechanically and if the inflaton phi can also be the Standard Model Higgs. In this note we answer these questions. Firstly, for a single scalar phi, we show that the quantum field theory is well behaved in the pure gravity and kinetic sectors, since the quantum generated corrections are small. However, the theory likely breaks down at ~ m_pl / xi due to scattering provided by the self-interacting potential lambda phi^4. Secondly, we show that the theory changes for multiple scalars phi with non-minimal coupling xi phi dot phi R, since this introduces qualitatively new interactions which manifestly generate large quantum corrections even in the gravity and kinetic sectors, spoiling the theory for energies > m_pl / xi. Since the Higgs doublet of the Standard Model includes the Higgs boson and 3 Goldstone bosons, it falls into the latter category and therefore its validity is manifestly spoiled. We show that these conclusions hold in both the Jordan and Einstein frames and describe an intuitive analogy in the form of the pion Lagrangian. We also examine the recent claim that curvature-squared inflation models fail quantum mechanically. Our work appears to go beyond the recent discussions.
Quantum Radiation of Oscillons
Mark P. Hertzberg
Physics , 2010, DOI: 10.1103/PhysRevD.82.045022
Abstract: Many classical scalar field theories possess remarkable solutions: coherently oscillating, localized clumps, known as oscillons. In many cases, the decay rate of classical small amplitude oscillons is known to be exponentially suppressed and so they are extremely long lived. In this work we compute the decay rate of quantized oscillons. We find it to be a power law in the amplitude and couplings of the theory. Therefore, the quantum decay rate is very different to the classical decay rate and is often dominant. We show that essentially all oscillons eventually decay by producing outgoing radiation. In single field theories the outgoing radiation has typically linear growth, while if the oscillon is coupled to other bosons the outgoing radiation can have exponential growth. The latter is a form of parametric resonance: explosive energy transfer from a localized clump into daughter fields. This may lead to interesting phenomenology in the early universe. Our results are obtained from a perturbative analysis, a non-perturbative Floquet analysis, and numerics.
Inflation, Symmetry, and B-Modes
Mark P. Hertzberg
Physics , 2014, DOI: 10.1016/j.physletb.2015.04.031
Abstract: We examine the role of using symmetry and effective field theory in inflationary model building. We describe the standard formulation of starting with an approximate shift symmetry for a scalar field, and then introducing corrections systematically in order to maintain control over the inflationary potential. We find that this leads to models in good agreement with recent data. On the other hand, there are attempts in the literature to deviate from this paradigm by invoking other symmetries and corrections. In particular: in a suite of recent papers, several authors have made the claim that standard Einstein gravity with a cosmological constant and a massless scalar carries conformal symmetry. They further claim that such a theory carries another hidden symmetry; a global SO(1,1) symmetry. By deforming around the global SO(1,1) symmetry, they are able to produce a range of inflationary models with asymptotically flat potentials, whose flatness is claimed to be protected by these symmetries. These models tend to give rise to B-modes with small amplitude. Here we explain that these authors are merely introducing a redundancy into the description, not an actual conformal symmetry. Furthermore, we explain that the only real (global) symmetry in these models is not at all hidden, but is completely manifest when expressed in the Einstein frame; it is in fact the shift symmetry of a scalar field. When analyzed systematically as an effective field theory, deformations do not generally produce asymptotically flat potentials and small B-modes, but other types of potentials with B-modes of appreciable amplitude. Such simple models typically also produce the observed red spectral index, Gaussian fluctuations, etc. In short: simple models of inflation, organized by expanding around a shift symmetry, are in excellent agreement with recent data.
Can Inflation be Connected to Low Energy Particle Physics?
Mark P. Hertzberg
Physics , 2011, DOI: 10.1088/1475-7516/2012/08/008
Abstract: It is an interesting question whether low energy degrees of freedom may be responsible for early universe inflation. To examine this, here we present a simple version of Higgs-inflation with minimal coupling to gravity and a quadratic inflationary potential. This quantitatively differs from the popular non-minimally coupled models, although it is qualitatively similar. In all such models, new heavy fields must enter in order for the theory to be well behaved in the UV. We show that in all cases the Higgs self coupling lambda must be quite small in order to integrate out the heavy fields and use the resulting low energy effective field theory of the Higgs to describe inflation. For moderately sized lambda, the UV completion is required and will, in general, determine the inflationary regime. We discuss the important issue of the arbitrariness of the Lagrangians used in all these setups by presenting a new class of such models, including a supergravity version. This suggests that the inflationary potential is disconnected from low energy physics.
Entanglement Entropy in Scalar Field Theory
Mark P. Hertzberg
Physics , 2012, DOI: 10.1088/1751-8113/46/1/015402
Abstract: Understanding the dependence of entanglement entropy on the renormalized mass in quantum field theories can provide insight into phenomena such as quantum phase transitions, since the mass varies in a singular way near the transition. Here we perturbatively calculate the entanglement entropy in interacting scalar field theory, focussing on the dependence on the field's mass. We study lambda phi^4 and g phi^3 theories in their ground state. By tracing over a half space, using the replica trick and position space Green's functions on the cone, we show that space-time volume divergences cancel and renormalization can be consistently performed in this conical geometry. We establish finite contributions to the entanglement entropy up to two-loop order, involving a finite area law. The resulting entropy is simple and intuitive: the free theory result in d=3 (that we included in an earlier publication) Delta S ~ A m^2 ln(m^2) is altered, to leading order, by replacing the bare mass m by the renormalized mass m_r evaluated at the renormalization scale of zero momentum.

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