In-flight damping measurement

A new testing technique is described which can be applied in determining the damping coefficient of the critical vibration modes of an airplane in flight. The damping coefficient can be determined in several different ways from the same data using different features of a modified response curve which implies the possibility of checking one value against the other. The method introduces the effect of sweep rate in the driving system. This effect on the frequency response curve of the critical vibration mode and its various characteristics are used in the determination of damping coefficient. A theoretical examination is made of these characteristics for single degree of freedom systems

Reentrant glass transition in a colloid-polymer mixture with depletion attractions

Performing light scattering experiments we show that introducing short-ranged attraction to a colloidal suspension of nearly hard spheres by addition of free polymer produces new glass transition phenomena. We observe a dramatic acceleration of the density fluctuations amounting to the melting of a colloidal glass. Increasing the strength of the attractions the system freezes into another nonergodic state sharing some qualitative features with gel states occurring at lower colloid packing fractions. This reentrant glass transition is in qualitative agreement with recent theoretical predictions.Comment: 14 pages, 3 figure

An algorithm for calculating the Lorentz angle in silicon detectors

Future experiments will use silicon sensors in the harsh radiation environment of the LHC (Large Hadron Collider) and high magnetic fields. The drift direction of the charge carriers is affected by the Lorentz force due to the high magnetic field. Also the resulting radiation damage changes the properties of the drift. In this paper measurements of the Lorentz angle of electrons and holes before and after irradiation are reviewed and compared with a simple algorithm to compute the Lorentz angle.Comment: 13 pages, 7 figures, final version accepted by NIMA. Mainly clarifications included and slightly shortene

Resistance Thermometer for Heat Transfer Measurements in a Shock Tube

This report describes a method for the application of the well-known principle of the resistance thermometer to the problem of measuring surface temperatures and heat transfer rates under highly transient conditions, such as are experienced in a shock tube. By using a thin platinum film sputtered on glass, a resistance thermometer gage is obtained which has a response lag of less than 1 µ sec, a linear output of 2-3 mv/°c, repeatability and durability. The gage preparation, including the sputtering technique, calibration method, and response characteristics are discussed, and some measurements of surface temperatures and heat transfer rates on models in the shock tube are presented in order to illustrate the performance that can be expected from this instrument

The hydrogen atom in an electric field: Closed-orbit theory with bifurcating orbits

Closed-orbit theory provides a general approach to the semiclassical description of photo-absorption spectra of arbitrary atoms in external fields, the simplest of which is the hydrogen atom in an electric field. Yet, despite its apparent simplicity, a semiclassical quantization of this system by means of closed-orbit theory has not been achieved so far. It is the aim of this paper to close that gap. We first present a detailed analytic study of the closed classical orbits and their bifurcations. We then derive a simple form of the uniform semiclassical approximation for the bifurcations that is suitable for an inclusion into a closed-orbit summation. By means of a generalized version of the semiclassical quantization by harmonic inversion, we succeed in calculating high-quality semiclassical spectra for the hydrogen atom in an electric field

Properties of cage rearrangements observed near the colloidal glass transition

We use confocal microscopy to study the motions of particles in concentrated colloidal systems. Near the glass transition, diffusive motion is inhibited, as particles spend time trapped in transient ``cages'' formed by neighboring particles. We measure the cage sizes and lifetimes, which respectively shrink and grow as the glass transition approaches. Cage rearrangements are more prevalent in regions with lower local concentrations and higher disorder. Neighboring rearranging particles typically move in parallel directions, although a nontrivial fraction move in anti-parallel directions, usually from pairs of particles with initial separations corresponding to the local maxima and minima of the pair correlation function $g(r)$, respectively.Comment: 5 pages, 4 figures; text & figures revised in v

Constraints on B--->pi,K transition form factors from exclusive semileptonic D-meson decays

According to the heavy-quark flavour symmetry, the $B\to \pi, K$ transition form factors could be related to the corresponding ones of D-meson decays near the zero recoil point. With the recent precisely measured exclusive semileptonic decays $D \to \pi \ell \nu$ and $D\to K \ell \nu$, we perform a phenomenological study of $B \to \pi, K$ transition form factors based on this symmetry. Using BK, BZ and Series Expansion parameterizations of the form factor slope, we extrapolate $B \to \pi, K$ transition form factors from $q^{2}_{max}$ to $q^{2}=0$. It is found that, although being consistent with each other within error bars, the central values of our results for $B \to \pi, K$ form factors at $q^2=0$, $f_+^{B\to \pi, K}(0)$, are much smaller than predictions of the QCD light-cone sum rules, but are in good agreements with the ones extracted from hadronic B-meson decays within the SCET framework. Moreover, smaller form factors are also favored by the QCD factorization approach for hadronic B-meson decays.Comment: 19 pages, no figure, 5 table

Glasslike Arrest in Spinodal Decomposition as a Route to Colloidal Gelation

Colloid-polymer mixtures can undergo spinodal decomposition into colloid-rich and colloid-poor regions. Gelation results when interconnected colloid-rich regions solidify. We show that this occurs when these regions undergo a glass transition, leading to dynamic arrest of the spinodal decomposition. The characteristic length scale of the gel decreases with increasing quench depth, and the nonergodicity parameter exhibits a pronounced dependence on scattering vector. Mode coupling theory gives a good description of the dynamics, provided we use the full static structure as input.Comment: 14 pages, 4 figures; replaced with published versio

The Effect of Non-specific Response Inhibition Training on Alcohol Consumption: An Intervention

Objective: Excessive alcohol consumption increases the risk of alcohol-related disease and injury. Poor response inhibition; the inability to intentionally override a pre-potent response, has been associated with greater alcohol consumption. The aim of the present study was to clarify if non-specific response inhibition training could improve response inhibition, and reduce alcohol consumption. Method: One hundred and sixty-eight undergraduates were randomly assigned to either an inhibition or active control condition, and completed a stop-signal task once a day for four consecutive days. The inhibition condition comprised a stop-signal task with a high target density (50% stop-signals), while the active control comprised a stop-signal task with a lower target density (25% stop-signals) and the instruction to ignore the signal. Before and after the intervention, participants completed measures of response inhibition, and alcohol consumption. Alcohol consumption was measured again at one month post-training. All parts of the study were completed online. Results: Contrary to the hypotheses, participants in the inhibition condition did not have lower levels of alcohol consumption, nor improved response inhibition after the intervention, compared to participants in the active control condition. Conclusion: It is suggested that response inhibition training needs to be specific to the target behaviour in order to be effective; however, that training did not improve response inhibition itself, calls into question the efficacy of this particular training paradigm. It is recommended that future response inhibition training paradigms consider how training intensity, and the format of administration, influences behavioural outcomes

Photoabsorption spectra of the diamagnetic hydrogen atom in the transition regime to chaos: Closed orbit theory with bifurcating orbits

With increasing energy the diamagnetic hydrogen atom undergoes a transition from regular to chaotic classical dynamics, and the closed orbits pass through various cascades of bifurcations. Closed orbit theory allows for the semiclassical calculation of photoabsorption spectra of the diamagnetic hydrogen atom. However, at the bifurcations the closed orbit contributions diverge. The singularities can be removed with the help of uniform semiclassical approximations which are constructed over a wide energy range for different types of codimension one and two catastrophes. Using the uniform approximations and applying the high-resolution harmonic inversion method we calculate fully resolved semiclassical photoabsorption spectra, i.e., individual eigenenergies and transition matrix elements at laboratory magnetic field strengths, and compare them with the results of exact quantum calculations.Comment: 26 pages, 9 figures, submitted to J. Phys.