String Effects on Fermi--Dirac Correlation Measurements

We investigate some recent measurements of Fermi--Dirac correlations by the LEP collaborations indicating surprisingly small source radii for the production of baryons in $e^+e^-$-annihilation at the $Z^0$ peak. In the hadronization models there are besides the Fermi--Dirac correlation effect also a strong dynamical (anti-)correlation. We demonstrate that the extraction of the pure FD effect is highly dependent on a realistic Monte Carlo event generator, both for separation of those dynamical correlations which are not related to Fermi--Dirac statistics, and for corrections of the data and background subtractions. Although the model can be tuned to well reproduce single particle distributions, there are large model-uncertainties when it comes to correlations between identical baryons. We therefore, unfortunately, have to conclude that it is at present not possible to make any firm conclusion about the source radii relevant for baryon production at LEP

On marginally outer trapped surfaces in stationary and static spacetimes

In this paper we prove that for any spacelike hypersurface containing an untrapped barrier in a stationary spacetime satisfying the null energy condition, any marginally outer trapped surface cannot lie in the exterior region where the stationary Killing vector is timelike. In the static case we prove that any marginally outer trapped surface cannot penetrate into the exterior region where the static Killing vector is timelike. In fact, we prove these result at an initial data level, without even assuming existence of a spacetime. The proof relies on a powerful theorem by Andersson and Metzger on existence of an outermost marginally outer trapped surface.Comment: 22 pages, 3 figures; 1 reference added, 1 figure changed, other minor change

Time-resolved extinction rates of stochastic populations

Extinction of a long-lived isolated stochastic population can be described as an exponentially slow decay of quasi-stationary probability distribution of the population size. We address extinction of a population in a two-population system in the case when the population turnover -- renewal and removal -- is much slower than all other processes. In this case there is a time scale separation in the system which enables one to introduce a short-time quasi-stationary extinction rate W_1 and a long-time quasi-stationary extinction rate W_2, and develop a time-dependent theory of the transition between the two rates. It is shown that W_1 and W_2 coincide with the extinction rates when the population turnover is absent, and present but very slow, respectively. The exponentially large disparity between the two rates reflects fragility of the extinction rate in the population dynamics without turnover.Comment: 8 pages, 4 figure

Experimentally realizable quantum comparison of coherent states and its applications

When comparing quantum states to each other, it is possible to obtain an unambiguous answer, indicating that the states are definitely different, already after a single measurement. In this paper we investigate comparison of coherent states, which is the simplest example of quantum state comparison for continuous variables. The method we present has a high success probability, and is experimentally feasible to realize as the only required components are beam splitters and photon detectors. An easily realizable method for quantum state comparison could be important for real applications. As examples of such applications we present a "lock and key" scheme and a simple scheme for quantum public key distribution.Comment: 14 pages, 5 figures, version one submitted to PRA. Version two is the final accepted versio

HI Narrow Line Absorption in Dark Clouds

We have used the Arecibo telescope to carry out an survey of 31 dark clouds in the Taurus/Perseus region for narrow absorption features in HI ($\lambda$ 21cm) and OH (1667 and 1665 MHz) emission. We detected HI narrow self--absorption (HINSA) in 77% of the clouds that we observed. HINSA and OH emission, observed simultaneously are remarkably well correlated. Spectrally, they have the same nonthermal line width and the same line centroid velocity. Spatially, they both peak at the optically--selected central position of each cloud, and both fall off toward the cloud edges. Sources with clear HINSA feature have also been observed in transitions of CO, \13co, \c18o, and CI. HINSA exhibits better correlation with molecular tracers than with CI. The line width of the absorption feature, together with analyses of the relevant radiative transfer provide upper limits to the kinetic temperature of the gas producing the HINSA. Some sources must have a temperature close to or lower than 10 K. The correlation of column densities and line widths of HINSA with those characteristics of molecular tracers suggest that a significant fraction of the atomic hydrogen is located in the cold, well--shielded portions of molecular clouds, and is mixed with the molecular gas. The average number density ratio [HI]/[\h2] is $1.5\times10^{-3}$. The inferred HI density appears consistent with but is slightly higher than the value expected in steady state equilibrium between formation of HI via cosmic ray destruction of H$_2$ and destruction via formation of H$_2$ on grain surfaces. The distribution and abundance of atomic hydrogen in molecular clouds is a critical test of dark cloud chemistry and structure, including the issues of grain surface reaction rates, PDRs, circulation, and turbulent diffusion.Comment: 40 pages, 10 figures, accepted by Ap

Quasinormal Modes of Dirty Black Holes

Quasinormal mode (QNM) gravitational radiation from black holes is expected to be observed in a few years. A perturbative formula is derived for the shifts in both the real and the imaginary part of the QNM frequencies away from those of an idealized isolated black hole. The formulation provides a tool for understanding how the astrophysical environment surrounding a black hole, e.g., a massive accretion disk, affects the QNM spectrum of gravitational waves. We show, in a simple model, that the perturbed QNM spectrum can have interesting features.Comment: 4 pages. Published in PR

Hadron attenuation in deep inelastic lepton-nucleus scattering

We present a detailed theoretical investigation of hadron attenuation in deep inelastic scattering (DIS) off complex nuclei in the kinematic regime of the HERMES experiment. The analysis is carried out in the framework of a probabilistic coupled-channel transport model based on the Boltzmann-Uehling-Uhlenbeck (BUU) equation, which allows for a treatment of the final-state interactions (FSI) beyond simple absorption mechanisms. Furthermore, our event-by-event simulations account for the kinematic cuts of the experiments as well as the geometrical acceptance of the detectors. We calculate the multiplicity ratios of charged hadrons for various nuclear targets relative to deuterium as a function of the photon energy nu, the hadron energy fraction z_h=E_h/nu and the transverse momentum p_T. We also confront our model results on double-hadron attenuation with recent experimental data. Separately, we compare the attenuation of identified hadrons (pi^\pm, \pi^0, K^\pm, p and pbar) on Ne and Kr targets with the data from the HERMES Collaboration and make predictions for a Xe target. At the end we turn towards hadron attenuation on Cu nuclei at EMC energies. Our studies demonstrate that (pre-)hadronic final-state interactions play a dominant role in the kinematic regime of the HERMES experiment while our present approach overestimates the attenuation at EMC energies.Comment: 61 pages, 19 figures, version accepted for publication in Phys. Rev.

Joint measurements of spin, operational locality and uncertainty

Joint, or simultaneous, measurements of non-commuting observables are possible within quantum mechanics, if one accepts an increase in the variances of the jointly measured observables. In this paper, we discuss joint measurements of a spin 1/2 particle along any two directions. Starting from an operational locality principle, it is shown how to obtain a bound on how sharp the joint measurement can be. We give a direct interpretation of this bound in terms of an uncertainty relation.Comment: Accepted for publication in Phys. Rev.

Physiological responses and performance factors for double-poling and diagonal-stride treadmill roller-skiing time-trial exercise

Purpose - To compare physiological responses between a self-paced 4-min double-poling (DP) time-trial (TTDP) versus a 4-min diagonal-stride (DS) time-trial (TTDS). The relative importance of peak oxygen uptake (V˙O2peak), anaerobic capacity, and gross efficiency (GE) for projection of 4-min TTDP and TTDS roller-skiing performances were also examined. Methods - Sixteen highly trained male cross-country skiers performed, in each sub-technique on separate occasions, an 8 × 4-min incremental submaximal protocol, to assess individual metabolic rate (MR) versus power output (PO) relationships, followed by a 10-min passive break and then the TTDP or TTDS, with a randomized order between sub-techniques. Results - In comparison to TTDS, the TTDP resulted in 10 ± 7% lower total MR, 5 ± 4% lower aerobic MR, 30 ± 37% lower anaerobic MR, and 4.7 ± 1.2 percentage points lower GE, which resulted in a 32 ± 4% lower PO (all P 2peak and anaerobic capacity were 4 ± 4% and 30 ± 37% lower, respectively, in DP than DS (both P 2 = 0.044). Similar parabolic pacing strategies were used during both TTs. Multivariate data analysis projected TT performance using V˙O2peak, anaerobic capacity, and GE (TTDP, R2 = 0.974; TTDS, R2 = 0.848). The variable influence on projection values for V˙O2peak, anaerobic capacity, and GE were for TTDP, 1.12 ± 0.60, 1.01 ± 0.72, and 0.83 ± 0.38, respectively, and TTDS, 1.22 ± 0.35, 0.93 ± 0.44, and 0.75 ± 0.19, respectively. Conclusions - The results show that a cross-country skier’s “metabolic profile” and performance capability are highly sub-technique specific and that 4-min TT performance is differentiated by physiological factors, such as V˙O2peak, anaerobic capacity, and GE

Critical Field Strength in an Electroclinic Liquid Crystal Elastomer

We elucidate the polymer dynamics of a liquid crystal elastomer based on the time-dependent response of the pendent liquid crystal mesogens. The molecular tilt and switching time of mesogens are analyzed as a function of temperature and cross-linking density upon application of an electric field. We observe an unexpected maximum in the switching time of the liquid crystal mesogens at intermediate field strength. Analysis of the molecular tilt over multiple time regimes correlates the maximum response time with a transition to entangled polymer dynamics at a critical field strength.Comment: 4 pages, 3 figure