Perishable inventory systems with impatient demands

An inventory system for perishable commodities (PIS) with finite shelf size and finite waiting room for demands is studied; the maximum shelf life and the maximum waiting time of a demand are assumed to be either constant or exponentially distributed, and the arrival rates for items and for demands are state-dependent. We determine the stationary distribution of the system and derive various kinds of cost functionals that are useful to evaluate the efficiency of the PIS.     

Isoscattering Schottky manifolds

We exhibit pairs of infinite-volume, hyperbolic three-manifolds that have the same scattering poles and conformally equivalent boundaries, but which are not isometric. The examples are constructed using Schottky groups and the Sunada construction. Submitted: October 1998, Final version: June 1999.     

Repair systems with exchangeable items and the longest queue mechanism

We consider a repair facility consisting of one repairman and two arrival streams of failed items, from bases 1 and 2. The arrival processes are independent Poisson processes, and the repair times are independent and identically exponentially distributed. The item types are exchangeable, and a failed item from base 1 could just as well be returned to base 2, and vice versa. The rule according to which backorders are satisfied by repaired items is the longest queue rule: At the completion of a service (repair), the repaired item is delivered to the base that has the largest number of failed items. We point out a direct relation between our model and the classical longer queue model. We obtain simple expressions for several probabilities of interest, and show how all two-dimensional queue length probabilities may be obtained. Finally, we derive the sojourn time distributions.     

Photophysical studies of uranyl complexes: VIII. Luminescence spectra of UO2SO4 · 312H2O and two polymorphs of bis(urea) uranyl sulfate

The photoluminescence spectra of hydrated and anhydrous uranyl sulfates have been studied under conditions of high resolution at cryogenic temperatures. All uranyl sulfate systems were found to yield nonequivalent spectra: the energies for the electronic and vibronic origins were found to vary with the system, and certain uranyl vibrational frequencies exhibited a dependence on environment. These differences must reflect the various ways in which the uranyl centers are linked by the bridging sulfate groups, as this linking is the main difference between the various structures.     

Robust antimicrobial compounds and polymers derived from natural resin acids

We report novel robust resin acid-derived antimicrobial agents that exhibit excellent antimicrobial activities against a broad spectrum of bacteria (6 Gram-positive and 7 Gram-negative) with selective lysis of microbial membranes over mammalian membranes. Our results indicate that hydrophobicity and unique structures of resin acids can be determining factors in dictating the antimicrobial activity.     

Proton grease: an acid accelerated molecular rotor

A molecular rotor was designed that rotates 7 orders of magnitude faster upon protonation. The quinoline rotor is based on a rigid N-arylimide framework that displays restricted rotation due to steric interaction between the quinoline nitrogen and imide carbonyls. At rt (23 °C), the rotor rotates slowly (t(1/2) = 26 min, ΔG(?) = 22.2 kcal/mol). However, upon addition of 3.5 equiv of acid the rotor rotates rapidly (t(1/2) = 2.0 × 10(-4) s, ΔG(?) = 12.9 kcal/mol). Mechanistic studies show that this dramatic acid catalyzed change is due to stabilization of the planar transition state by the formation of an intramolecular hydrogen bond between the protonated quinoline nitrogen (N(+)-H) and an imide carbonyl (O═C). The acid catalyzed acceleration is reversible and can be stopped by addition of base.     

Reference phase shift determination in phase shifting interferometry

The phase shifting technique has recently seen application to many types of interferometers, including holographic, speckle and moiré systems for strain analysis. In these applications, close control of the phase shifts may be impossible due to the effect of mechanical vibrations, and this presents difficulties when extracting the phase information, since the reference phase shifts are generally assumed to be known. In this work, several approaches to the problem of determining the reference phase shifts in a perturbing environment are critically evaluated using computer simulations. The analyses provide a general relationship between precision and reference phase shift errors and demonstrate the performance of each method as certain idealised fringe pattern error parameters are varied. A practical example confirms the predictions of the numerical simulations and demonstrates the feasibility of using reference phase shift estimates to improve data reduction procedures.     

Measuring the effects of knowledge in military campaigns

A particularly difficult problem in command and control is that of identifying the relationship between intelligence, decision and combat outcome. The problem centres on three things: (1) an adequate representation of the situation confronting the commander on the battlefield; (2) an adequate measure of combat outcome; and (3) an appropriate metric linking knowledge of the first to the second. In this paper, we focus on the third of these by developing a measure of the knowledge possessed by the commander at the time he takes his decision and by relating this to combat outcomes. Combat outcomes are represented using traditional attrition-based metrics and the combat situation is simply the size, location and identity of enemy units. Therefore, the possible number of identified enemy units arrayed against the friendly commander constitutes the set of hypotheses on alternative situations. Surveillance assets provide the commander with evidence that is used to update the probability distribution. Knowledge if then represented as the product of two components: residual knowledge, the knowledge gained from the updated probability distribution, and detection knowledge, the knowledge from the detection itself. Information entropy was used to develop a metric that reflects the degree to which the commander understands the situation confronting him. The metric was applied in a UK Ministry of Defence study of a proposed Airborne STand-Off Radar (ASTOR) to measure the effects of improved surveillance on combat outcomes.     

Magneto-photoluminescence studies of manganese acceptors in GaAs/AlGaAs multiple quantum wells

We have investigated the photoluminescence associated with residual manganese acceptors in n-type, modulation doped, GaAs/AlGaAs multiple quantum wells. In a magnetic field the luminescence breaks into discrete lines attributed to transitions between conduction band Landau levels and manganese acceptor states. The polarization of the luminescence was studied as function of magnetic field. A simple model based on the spin exchange interaction between the holes and the manganese ions successfully describes the polarization data.     

Jahn-Teller phase transitions in TbcGd1−cVO4

The temperatures at which the cooperative Jahn-Teller phase transitions occur in Tb_cGd_1?cVO₄ have been determined from Raman and optical birefringence measurements. Over a narrow range of c there are two transition temperatures; between these temperatures the crystal is distorted, but a higher and lower temperatures the crystal has the same undistorted structure. This unusual behaviour was predicted earlier, and is accurately described by molecular field theory.