Free-flight measurements of stagnation-point convective heat transfer at velocities to 41,000 ft/sec

Free flight measurements of stagnation point convective heat transfer in air at hypersonic speed

Analytic and Numerical Study of Preheating Dynamics

We analyze the phenomenon of preheating,i.e. explosive particle production due to parametric amplification of quantum fluctuations in the unbroken case, or spinodal instabilities in the broken phase, using the Minkowski space $O(N)$ vector model in the large $N$ limit to study the non-perturbative issues involved. We give analytic results for weak couplings and times short compared to the time at which the fluctuations become of the same order as the tree level,as well as numerical results including the full backreaction.In the case where the symmetry is unbroken, the analytic results agree spectacularly well with the numerical ones in their common domain of validity. In the broken symmetry case, slow roll initial conditions from the unstable minimum at the origin, give rise to a new and unexpected phenomenon: the dynamical relaxation of the vacuum energy.That is, particles are abundantly produced at the expense of the quantum vacuum energy while the zero mode comes back to almost its initial value.In both cases we obtain analytically and numerically the equation of state which turns to be written in terms of an effective polytropic index that interpolates between vacuum and radiation-like domination. We find that simplified analysis based on harmonic behavior of the zero mode, giving rise to a Mathieu equation forthe non-zero modes miss important physics. Furthermore, analysis that do not include the full backreaction do not conserve energy, resulting in unbound particle production. Our results do not support the recent claim of symmetry restoration by non-equilibrium fluctuations.Finally estimates of the reheating temperature are given,as well as a discussion of the inconsistency of a kinetic approach to thermalization when a non-perturbatively large number of particles is created.Comment: Latex file, 52 pages and 24 figures in .ps files. Minor changes. To appear in Physical Review D, 15 December 199

Database Search Strategies for Proteomic Data Sets Generated by Electron Capture Dissociation Mass Spectrometry

Large data sets of electron capture dissociation (ECD) mass spectra from proteomic experiments are rich in information; however, extracting that information in an optimal manner is not straightforward. Protein database search engines currently available are designed for low resolution CID data, from which Fourier transform ion cyclotron resonance (FT-ICR) ECD data differs significantly. ECD mass spectra contain both z-prime and z-dot fragment ions (and c-prime and c-dot); ECD mass spectra contain abundant peaks derived from neutral losses from charge-reduced precursor ions; FT-ICR ECD spectra are acquired with a larger precursor m/z isolation window than their low-resolution CID counterparts. Here, we consider three distinct stages of postacquisition analysis: (1) processing of ECD mass spectra prior to the database search; (2) the database search step itself and (3) postsearch processing of results. We demonstrate that each of these steps has an effect on the number of peptides identified, with the postsearch processing of results having the largest effect. We compare two commonly used search engines: Mascot and OMSSA. Using an ECD data set of modest size (3341 mass spectra) from a complex sample (mouse whole cell lysate), we demonstrate that search results can be improved from 630 identifications (19% identification success rate) to 1643 identifications (49% identification success rate). We focus in particular on improving identification rates for doubly charged precursors, which are typically low for ECD fragmentation. We compare our presearch processing algorithm with a similar algorithm recently developed for electron transfer dissociation (ETD) data

Resumming the large-N approximation for time evolving quantum systems

In this paper we discuss two methods of resumming the leading and next to leading order in 1/N diagrams for the quartic O(N) model. These two approaches have the property that they preserve both boundedness and positivity for expectation values of operators in our numerical simulations. These approximations can be understood either in terms of a truncation to the infinitely coupled Schwinger-Dyson hierarchy of equations, or by choosing a particular two-particle irreducible vacuum energy graph in the effective action of the Cornwall-Jackiw-Tomboulis formalism. We confine our discussion to the case of quantum mechanics where the Lagrangian is $L(x,\dot{x}) = (1/2) \sum_{i=1}^{N} \dot{x}_i^2 - (g/8N) [ \sum_{i=1}^{N} x_i^2 - r_0^2 ]^{2}$. The key to these approximations is to treat both the $x$ propagator and the $x^2$ propagator on similar footing which leads to a theory whose graphs have the same topology as QED with the $x^2$ propagator playing the role of the photon. The bare vertex approximation is obtained by replacing the exact vertex function by the bare one in the exact Schwinger-Dyson equations for the one and two point functions. The second approximation, which we call the dynamic Debye screening approximation, makes the further approximation of replacing the exact $x^2$ propagator by its value at leading order in the 1/N expansion. These two approximations are compared with exact numerical simulations for the quantum roll problem. The bare vertex approximation captures the physics at large and modest $N$ better than the dynamic Debye screening approximation.Comment: 30 pages, 12 figures. The color version of a few figures are separately liste

Improvement of Shelf Life for Space Food Through a Hurdle Approach

The processed and prepackaged spaceflight food system is a critical human support system for manned space flights. As missions extend longer and farther from Earth over the next 20 years, strategies to stabilize the nutritional and sensory quality of food must be identified. For a mission to Mars, the space foods themselves must maintain quality for up to 5 years to align with cargo prepositioning scenarios. Optimizing the food system to achieve a 5-year shelf life mitigates the risk of an inadequate food system during extended missions. Because previous attempts to determine a singular pathway to a 5-year shelf life for food were unsuccessful, this investigation combines several approaches, based on science, technological advancement, and past empirical evidence, that will define the prepackaged food system for long duration missions. This study supports the Advanced Food Technology strategic planning process by identifying food processing, packaging, and storage technologies that will be required for exploration missions and the extent that they must be implemented to achieve a 5-year shelf life for the entire food system

Time evolution of the chiral phase transition during a spherical expansion

We examine the non-equilibrium time evolution of the hadronic plasma produced in a relativistic heavy ion collision, assuming a spherical expansion into the vacuum. We study the $O(4)$ linear sigma model to leading order in a large-$N$ expansion. Starting at a temperature above the phase transition, the system expands and cools, finally settling into the broken symmetry vacuum state. We consider the proper time evolution of the effective pion mass, the order parameter $\langle \sigma \rangle$, and the particle number distribution. We examine several different initial conditions and look for instabilities (exponentially growing long wavelength modes) which can lead to the formation of disoriented chiral condensates (DCCs). We find that instabilities exist for proper times which are less than 3 fm/c. We also show that an experimental signature of domain growth is an increase in the low momentum spectrum of outgoing pions when compared to an expansion in thermal equilibrium. In comparison to particle production during a longitudinal expansion, we find that in a spherical expansion the system reaches the ``out'' regime much faster and more particles get produced. However the size of the unstable region, which is related to the domain size of DCCs, is not enhanced.Comment: REVTex, 20 pages, 8 postscript figures embedded with eps

Gauge Fields Out-Of-Equilibrium: A Gauge Invariant Formulation and the Coulomb Gauge

We study the abelian Higgs model out-of-equilibrium in two different approaches, a gauge invariant formulation, proposed by Boyanovsky et al. \cite{Boyanovsky:1996dc} and in the Coulomb gauge. We show that both approaches become equivalent in a consistent one loop approximation. Furthermore, we carry out a proper renormalization for the model in order to prepare the equations for a numerical implementation. The additional degrees of freedom, which arise in gauge theories, influence the behavior of the system dramatically. A comparison with results in the 't Hooft-Feynman background gauge found by us recently, shows very good agreement.Comment: 32 pages, 8 figure

Equilibrium and nonequilibrium properties associated with the chiral phase transition at finite density in the Gross-Neveu Model

We study the dynamics of the chiral phase transition at finite density in the Gross-Neveu (GN) model in the leading order in large-N approximation. The phase structure of the GN model in this approximation has the property that there is a tricritical point at a fixed temperature and chemical potential separating regions where the chiral transition is first order from that where it is second order. We consider evolutions starting in local thermal and chemical equilibrium in the massless unbroken phase for conditions pertaining to traversing a first or second order phase transition. We assume boost invariant kinematics and determine the evolution of the order parameter $\sigma$, the energy density and pressure as well as the effective temperature, chemical potential and interpolating number densities as a function of the proper time $\tau$. We find that before the phase transition, the system behaves as if it were an ideal fluid in local thermal equilibrium with equation of state $p=\epsilon$. After the phase transition, the system quickly reaches its true broken symmetry vacuum value for the fermion mass and for the energy density. The single particle distribution functions for Fermions and anti-Fermions go far out of equilibrium as soon as the plasma traverses the chiral phase transition. We have also determined the spatial dependence of the "pion" Green's function $<\bar{\psi}(x) \gamma_5 \psi(x) \bar{\psi}(0) \gamma_5 \psi(0)>$ as a function of the proper time.Comment: 39 pages, 23 figure

Hydrodynamic scaling from the dynamics of relativistic quantum field theory

Hydrodynamic behavior is a general feature of interacting systems with many degrees of freedom constrained by conservation laws. To date hydrodynamic scaling in relativistic quantum systems has been observed in many high energy settings, from cosmic ray detections to accelerators, with large particle multiplicity final states. Here we show first evidence for the emergence of hydrodynamic scaling in the dynamics of a relativistic quantum field theory. We consider a simple scalar $\lambda \phi^4$ model in 1+1 dimensions in the Hartree approximation and study the dynamics of two colliding kinks at relativistic speeds as well as the decay of a localized high energy density region. The evolution of the energy-momentum tensor determines the dynamical local equation of state and allows the measurement of the speed of sound. Hydrodynamic scaling emerges at high local energy densities.Comment: 4 pages, 4 color eps figures, uses RevTex, v2 some typos corrected and references adde