The Darkies\u27 Cradle Song

https://digitalcommons.library.umaine.edu/mmb-vp/4649/thumbnail.jp

Temporal Ordering in Quantum Mechanics

We examine the measurability of the temporal ordering of two events, as well as event coincidences. In classical mechanics, a measurement of the order-of-arrival of two particles is shown to be equivalent to a measurement involving only one particle (in higher dimensions). In quantum mechanics, we find that diffraction effects introduce a minimum inaccuracy to which the temporal order-of-arrival can be determined unambiguously. The minimum inaccuracy of the measurement is given by dt=1/E where E is the total kinetic energy of the two particles. Similar restrictions apply to the case of coincidence measurements. We show that these limitations are much weaker than limitations on measuring the time-of-arrival of a particle to a fixed location.Comment: New section added, arguing that order-of-arrival can be measured more accurately than time-of-arrival. To appear in Journal of Physics

Letters between W. J. Kerr and G. C. Wheeler

Letters concerning filling Professor Dryden\u27s position at the Utah Agricultural College

A Liquid Model Analogue for Black Hole Thermodynamics

We are able to characterize a 2--dimensional classical fluid sharing some of the same thermodynamic state functions as the Schwarzschild black hole. This phenomenological correspondence between black holes and fluids is established by means of the model liquid's pair-correlation function and the two-body atomic interaction potential. These latter two functions are calculated exactly in terms of the black hole internal (quasilocal) energy and the isothermal compressibility. We find the existence of a ``screening" like effect for the components of the liquid.Comment: 20 pages and 6 Encapsulated PostScript figure

Cerebrospinal fluid levels of extracellular heat shock protein 72: A potential biomarker for bacterial meningitis in children

Extracellular heat shock protein 72 (Hsp72) is an endogenous danger signal and potential biomarker for critical illness in children. We hypothesized that elevated levels of extracellular Hsp72 in the cerebrospinal fluid (CSF) of children with suspected meningitis could predict bacterial meningitis. We measured extracellular Hsp72 levels in the CSF of 31 critically ill children with suspected meningitis via a commercially available enzyme-linked immunosorbent assay. Fourteen had bacterial meningitis based on CSF pleocytosis and bacterial growth in either blood or CSF culture. Seventeen children with negative cultures comprised the control group. CSF Hsp72 was significantly elevated in children with bacterial meningitis compared to controls. Importantly, CSF Hsp72 levels did not correlate with the CSF white blood cell count. On receiver operator characteristic analysis, using a cut-off of 8.1 ng/mL, CSF Hsp72 has a sensitivity of 79% and a specificity of 94% for predicting bacterial meningitis. We therefore conclude that CSF extracellular Hsp72 levels are elevated in critically ill children with bacterial meningitis versus controls. Hsp72 potentially offers clinicians improved diagnostic information in distinguishing bacterial meningitis from other processes

Heavy ion beam lifetimes at relativistic and ultrarelativistic colliders

The effects of higher order corrections in ultra-relativistic nuclear collisions are considered. It is found that higher order contributions are small at low energy, large at intermediate energy and small again at very high energy. An explanation for this effect is given. This means that the Weizsacker-Williams formula is a good approximation to use in calculating cross sections and beam lifetimes at energies relevant to RHIC and LHC.Comment: 10 pages, 2 tables, 4 figure

Finite-time quantum-to-classical transition for a Schroedinger-cat state

The transition from quantum to classical, in the case of a quantum harmonic oscillator, is typically identified with the transition from a quantum superposition of macroscopically distinguishable states, such as the Schr\"odinger cat state, into the corresponding statistical mixture. This transition is commonly characterized by the asymptotic loss of the interference term in the Wigner representation of the cat state. In this paper we show that the quantum to classical transition has different dynamical features depending on the measure for nonclassicality used. Measures based on an operatorial definition have well defined physical meaning and allow a deeper understanding of the quantum to classical transition. Our analysis shows that, for most nonclassicality measures, the Schr\"odinger cat dies after a finite time. Moreover, our results challenge the prevailing idea that more macroscopic states are more susceptible to decoherence in the sense that the transition from quantum to classical occurs faster. Since nonclassicality is prerequisite for entanglement generation our results also bridge the gap between decoherence, which appears to be only asymptotic, and entanglement, which may show a sudden death. In fact, whereas the loss of coherences still remains asymptotic, we have shown that the transition from quantum to classical can indeed occur at a finite time.Comment: 9+epsilon pages, 4 figures, published version. Originally submitted as "Sudden death of the Schroedinger cat", a bit too cool for APS policy :-

Phase field modeling of electrochemistry II: Kinetics

The kinetic behavior of a phase field model of electrochemistry is explored for advancing (electrodeposition) and receding (electrodissolution) conditions in one dimension. We described the equilibrium behavior of this model in [J. E. Guyer, W. J. Boettinger, J.A. Warren, and G. B. McFadden, ``Phase field modeling of electrochemistry I: Equilibrium'', cond-mat/0308173]. We examine the relationship between the parameters of the phase field method and the more typical parameters of electrochemistry. We demonstrate ohmic conduction in the electrode and ionic conduction in the electrolyte. We find that, despite making simple, linear dynamic postulates, we obtain the nonlinear relationship between current and overpotential predicted by the classical ``Butler-Volmer'' equation and observed in electrochemical experiments. The charge distribution in the interfacial double layer changes with the passage of current and, at sufficiently high currents, we find that the diffusion limited deposition of a more noble cation leads to alloy deposition with less noble species.Comment: v3: To be published in Phys. Rev. E v2: Attempt to work around turnpage bug. Replaced color Fig. 4a with grayscale 13 pages, 7 figures in 10 files, REVTeX 4, SIunits.sty, follows cond-mat/030817