Origin of the oscillator strength of the triplet state of a trion in a magnetic field

The dynamics of the spin-triplet trion state, under high magnetic field in a GaAs/AlGaAs quantum well, are studied using time resolved spectroscopy. The oscillator strength of the triplet transition is shown to rise with increasing electron density, in good agreement with a theoretical model where the trion interacts with excess electrons in the quantum well. This analysis suggests that the spin-triplet trion state, which is expected to be an optically "dark" state, is experimentally observable due to the interactions with the excess electrons, demonstrating that X- cannot be regarded as an isolated three particle complex.     

Kondo effect in a quantum antidot

We report Kondo-like behavior in a quantum antidot (a submicron depleted region in a two-dimensional electron gas) in the quantum-Hall regime. When both spins of the lowest Landau level are present all around the antidot, the resonances between extended edge states via antidot bound states show an abnormal feature in alternate Coulomb-blockaded regions. The feature becomes suppressed when the temperature or source-drain bias is raised as for Kondo resonances in quantum dots. Although the exact mechanism is unknown, Kondo-like correlated tunneling may arise from a Skyrmion-type edge reconstruction. This observation demonstrates the generality of the Kondo phenomenon.     

Maximal non- hamilton-laceable graphs

For bipartite graphs the property of being Hamilton laceable is analogous to the property of being Hamilton connected for simple graphs. in this paper it is proven that all of the graphs obtained by deleting fewer than m ? 1 edges from either of the complete bipartite graphs K_{m, m} or K_{m, m+1} are Hamilton laceable. It is also proven that the deletion of m ? 1 edges results in a non-Hamiltonlaceable graph if and only if the graph is either the complement of the star K_1,m?1 in K_{m, m} or K_{m, m+1} or else the complement in K_3,3 of a pair of nonadjacent edges.     

Shock wave interaction with laser-generated single bubbles

The interaction of a lithotripter shock wave (LSW) with laser-generated single vapor bubbles in water is investigated using high-speed photography and pressure measurement via a fiber-optic probe hydrophone. The interaction leads to nonspherical collapse of the bubble with secondary shock wave emission and microjet formation along the LSW propagation direction. The maximum pressure amplification is produced during the collapse phase of the bubble oscillation when the compressive pulse duration of the LSW matches with the forced collapse time of the bubble.     

New class of magnetoresistance oscillations: interaction of a two-dimensional electron gas with leaky interface phonons

We report on a new class of magnetoresistance oscillations observed in a high-mobility two-dimensional electron gas (2DEG) in GaAs-Al(x)Ga(1--x)As heterostructures. Appearing in a weak magnetic field ( B < 0.3 T) and only in a narrow temperature range ( 2 K < T < 9 K), these oscillations are periodic in 1/B with a frequency proportional to the electron Fermi wave vector, k(F). We interpret the effect as a magnetophonon resonance of the 2DEG with leaky interface-acoustic phonon modes carrying a wave vector q = 2k(F). Calculations show a few branches of such modes existing on the GaAs-Al(x)Ga(1--)xAs interface, and their velocities are in quantitative agreement with the observation.     

The acoustic basis for target discrimination by FM echolocating bats

Past experiments show that echolocating bats of the species Myotis lucifugus and Eptesicus fuscus can discriminate among airborne sonar targets presented in the context of pursuit maneuvers for the interception of prey. These bats distinguish between edible mealworms and inedible spheres of various sizes. Myotis can distinguish between disks and mealworms similar enough in size that the bat's performance requires the ability to perceive the acoustic equivalent of target shape. Previously observed small differences in the spectrum of echoes from mealworms and disks appear insufficient to distinguish these targets at the performance levels achieved by bats. We measured the acoustic properties of the targets by broadcasting ultrasonic impulses at mealworms, spheres, and disks and recording their echoes, displaying the results in terms of impulse echo waveforms and the frequency response of targets derived from the target transfer function. The echoes from disks and mealworms at various orientations convey the range-axis profile of the target (number and spacing of reflecting points or glints distributed at different ranges) in terms of the impulse structure of their waveforms and in terms of the locations and spacing of notches or nulls in their spectra. For targets that bats can discriminate and that reflect echoes which do not clearly differ in overall amplitude, the targets appear distinguishable from the acoustic representation of their range profile, which is a feature of targets that bats can perceive with great acuity.     

Visual spatial memory is enhanced in female rats (but inhibited in males) by dietary soy phytoestrogens

Background  

In learning and memory tasks, requiring visual spatial memory (VSM), males exhibit superior performance to females (a difference attributed to the hormonal influence of estrogen). This study examined the influence of phytoestrogens (estrogen-like plant compounds) on VSM, utilizing radial arm-maze methods to examine varying aspects of memory. Additionally, brain phytoestrogen, calbindin (CALB), and cyclooxygenase-2 (COX-2) levels were determined.     

Rayleigh wave study of surface diffusion and stress relaxation in glass

Surface wave propagation on ion-exchanged glass surfaces has been systematically studied. The glass system was an alkali-alumino silicate glass, and the ion-exchange involved the replacement of lithium ions by sodium ions. Accurate velocity measurements were carried out on systems ion-exchanged for various times and at various temperatures. The effects of density and modulus changes on the velocity have been separated. Stress build-up and relaxation have been observed which correlate well with shear viscosity measurements. In addition, the diffusion coefficient for the Na⁺ ? Li⁺ exchange has been determined at a variety of temperatures.