Generalization of the Van Cittert--Zernike theorem: observers moving with respect to sources

The use of the Van Cittert--Zernike theorem for the formulation of the visibility function in satellite-based Earth observation with passive radiometers does not take into account the relative motion of the observer (the satellite antenna) with respect to sources of the electro-magnetic fields at the surface of the Earth. The motion of the observer leads on the one hand to a more complex signal due to a pixel-dependent Doppler shift that is neglected in the standard derivation of the Van Cittert--Zernike theorem, but on the other hand one may hope that it could be employed for a temporal aperture synthesis, where virtual baselines are created through the motion of the satellite. Here, we generalize the formulation of the aperture synthesis concept to the case of observers moving with respect to the sources, and to the correlation of fields measured at times that differ by the travel time of the observer along a virtual baseline. Our derivation is based on first principles, starting with the wave propagation in the Earth reference frame of electro-magnetic fields arising from incoherent current sources, and Lorentz transforming the fields into the reference frame of the satellite. Our detailed study leads to the remarkable conclusion that the delay time due to observer motion cancels exactly the Doppler effect. This justifies the neglect of the Doppler effect in existing imaging systems based on the standard Van Cittert--Zernike theorem.Comment: 13 pages in IOP MST forma

Two-Dimensional Finite Element Ablative Thermal Response Analysis of an Arcjet Stagnation Test

The finite element ablation and thermal response (FEAtR, hence forth called FEAR) design and analysis program simulates the one, two, or three-dimensional ablation, internal heat conduction, thermal decomposition, and pyrolysis gas flow of thermal protection system materials. As part of a code validation study, two-dimensional axisymmetric results from FEAR are compared to thermal response data obtained from an arc-jet stagnation test in this paper. The results from FEAR are also compared to the two-dimensional axisymmetric computations from the two-dimensional implicit thermal response and ablation program under the same arcjet conditions. The ablating material being used in this arcjet test is phenolic impregnated carbon ablator with an LI-2200 insulator as backup material. The test is performed at the NASA, Ames Research Center Interaction Heating Facility. Spatially distributed computational fluid dynamics solutions for the flow field around the test article are used for the surface boundary conditions

Not all suffering is pain: sources of patients' suffering in the emergency department call for improvements in communication from practitioners

Background Provision of prompt, effective analgesia is rightly considered as a standard of care in the emergency department (ED). However, much suffering is not ‘painful’ and may be under-recognised. We sought to describe the burden of suffering in the ED and explore how this may be best addressed from a patient centred perspective. Methods In a prospective cohort study, we included undifferentiated patients presenting to the ED. We undertook two face to face questionnaires with the first immediately following triage. We asked patients: (a) if they were ‘suffering’; (b) how they were suffering; and (c) what they hoped would be done to ease this. Prior to leaving the ED, we asked patients what had been done to ease their suffering. Data were analysed thematically. Results Of 125 patients included, 77 (61.6%) reported suffering on direct questioning and 92 (73.6%) listed at least one way in which they were suffering. 90 (72.0%) patients had a pain score >0/10 but only 37 (29.6%) reported that pain was causing suffering. Patients reported suffering from both physical symptoms (especially pain, nausea, vomiting and dizziness) and emotional distress (notably anxiety). Treatment (to ease physical and emotional symptoms), information (particularly diagnosis, reassurance and explanation), care (notably friendly staff) and closure (being seen, resolving the problem and going home) were the key themes identified as important for relief of suffering. Conclusions In seeking to ease suffering in the ED, clinicians must focus not only on providing analgesia but on treating Emotional distress, Physical symptoms, providing Information, Care and Closure (EPICC)

Chiral phase transition at finite temperature and conformal dynamics in large Nf QCD

We investigate the chiral phase transition at finite temperature (T) in colour SU(Nc=3) Quantum Chromodynamics (QCD) with six species of fermions (Nf=6) in the fundamental representation by using lattice QCD with improved staggered fermions. By considering lattices with several temporal extensions Nt, we observe asymptotic scaling for Nt > 4. We then extract the dimensionless ratio Tc/Lambda_L (Lambda_L = Lattice Lambda-parameter) for Nf = 6 and Nf = 8, the latter relying on our earlier results. Further, we collect the critical couplings beta^c for the chiral phase transition at Nf = 0 (quenched), and Nf = 4 at a fixed Nt = 6. The results are consistent with enhanced fermionic screening at larger Nf. The Tc/Lambda_L depends very mildly on Nf in the Nf = 0 - 4 region, starts increasing at Nf = 6, and becomes significantly larger at Nf = 8, close to the edge of the conformal window. We discuss interpretations of these results as well as their possible interrelation with preconformal dynamics in the light of a functional renormalization group analysis.Comment: 8 pages, 9 figure

Hadron Resonance Mass Spectrum and Lattice QCD Thermodynamics

We confront lattice QCD results on the transition from the hadronic phase to the quark--gluon plasma with hadron resonance gas and percolation models. We argue that for T < T_c the equation of state derived from Monte--Carlo simulations of (2+1) quark--flavor QCD can be well described by a hadron resonance gas. We examine the quark mass dependence of the hadron spectrum on the lattice and discuss its description in terms of the MIT bag model. This is used to formulate a resonance gas model for arbitrary quark masses which can be compared to lattice calculations. We finally apply this model to analyze the quark mass dependence of the critical temperature obtained in lattice calculations. We show that the value of T_c for different quark masses agrees with lines of constant energy density in a hadron resonance gas. For large quark masses a corresponding contribution from a glueball resonance gas is required.Comment: 18 pages, LaTex2

Nucleon form factors induced by isovector and isoscalar axial-vector currents in QCD

Using the most general form of the baryon current, nucleon form factors, induced by isovector and isoscalar axial-vector currents, are studied in the framework of light cone QCD sum rule approach. Comparison of our results on form factors with the existing results and lattice calculations are presented.Comment: 17 pages, 10 figures, LaTeX formatte

A Mean Field Theory of the Chiral Phase Transition

The recent discussions by Koci\'c and Kogut on the nature of the chiral phase transition are reviewed. The mean-field nature of the transition suggested by these authors is supported in random matrix theory by Verbaarschot and Jackson which reproduces many aspects of QCD lattice simulations. In this paper, we point out physical arguments that favor a mean-field transition, not only for zero density and high temperature, but also for finite density. We show, using the Gross-Neveu model in 3 spatial dimensions in mean-field approximation, how the phase transition is constructed. In order to reproduce the lowering of the $\rho=0$, $T=0$ vacuum evaluated in lattice calculations, we introduce {nucleons} rather than constituent quarks in negative energy states, down to a momentum cut-off of $\Lambda$. We also discuss Brown-Rho scaling of the hadron masses in relation to the QCD phase transition, and how this scaling affects the CERES and HELIOS-3 dilepton experiments.Comment: 23 pages, Latex, no figure

πη\pi\eta pair hard electroproduction and exotic hybrid mesons

We show that hard electroproduction is a promising way to study exotic hybrid mesons, in particular through the hybrid decay channel $H \to \pi\eta$. We discuss the $\pi\eta$ generalized distribution amplitude, calculate the production amplitude and propose a forward-backward asymmetry as a signal for the hybrid meson production.Comment: 4 pages, 1 figure, presented by I.V. Anikin at Xth International Conference "BARYONS'04", Palaiseau, Franc

Aspects of thermal and chemical equilibration of hadronic matter

We study thermal and chemical equilibration in 'infinite' hadron matter as well as in finite size relativistic nucleus-nucleus collisions using a BUU cascade transport model that contains resonance and string degrees-of-freedom. The 'infinite' hadron matter is simulated within a cubic box with periodic boundary conditions. The various equilibration times depend on baryon density and energy density and are much shorter for particles consisting of light quarks then for particles including strangeness. For kaons and antikaons the chemical equilibration time is found to be larger than $\simeq$ 40 fm/c for all baryon and energy densities considered. The inclusion of continuum excitations, i.e. hadron 'strings', leads to a limiting temperature of $T_s\simeq$ 150 MeV. We, furthermore, study the expansion of a hadronic fireball after equilibration. The slope parameters of the particles after expansion increase with their mass; the pions leave the fireball much faster then nucleons and accelerate subsequently heavier hadrons by rescattering ('pion wind'). If the system before expansion is close to the limiting temperature $T_s$, the slope parameters for all particles after expansion practically do not depend on (initial) energy and baryon density. Finally, the equilibration in relativistic nucleus-nucleus collision is considered. Since the reaction time here is much shorter than the equilibration time for strangeness, a chemical equilibrium of strange particles in heavy-ion collisions is not supported by our transport calculations. However, the various particle spectra can approximately be described within the blast model.Comment: 39 pages, LaTeX, including 18 postscript figures, Nucl. Phys. A, in pres

Grenzen und Dysfunktionalitäten des Kassenwettbewerbs in der GKV: Theorie und Empirie der Risikolektion in Deutschland

Eine Funktionsbedingung für Kassenwettbewerb ist, dass Risikoselektion unterbunden wird. Denn Gegenstand des Kassenwettbewerbs sollen nicht bestimmte Merkmale von Versicherten sein (z.B. der Gesundheitszustand), vielmehr sollen die Anreize zur Verbesserung der Qualität und Effizienz der medizinischen Versorgung verstärkt werden. In einem wettbewerblichen Krankenversicherungssystem mit Risikoselektion werder die Interessen schlechter Risiken unzureichend berücksichtigt. Risikoselektion in der gesetzlichen Krankenversicherung (GKV) soll durch den Risikostrukturausgleich (RSA) verhindert werden. Seine Ausgestaltung muss bisher als unzureichend bezeichnet werden. Die Versichertenmerkmale Einkommen und Morbidität werder nicht hinreichend ausgeglichen. Theoretisch bestehen für die Krankenkassen also deutliche Anreize, Risikoselektion zu betreiben, was sich in der Empirie durch zahlreiche Beispiele belegen lässt. -- One of the requirements for the good functioning of competition among sickness funds is the absence of risk selection. Selection by funds has adverse effects which counter the positive effects of competition, to name the improvement of quality and efficiency of medical care. The interests of insured persons with high risks are inadequately accounted for in a competitive health insurance market with risk selection. Risk selection in the German statutory health insurance market is to be preserved by a system of risk equalization payments among German Statutory Sickness Funds. This risk compensation scheme is so far incomplete. The compensation for morbidity and income is inadequate. In theory, there are strong incentives for the sichness funds to select good risks, which can be affirmed by many examples.