Observation of unusual surface ordering in a uniaxial Sm-A phase formed by a highly biaxial compound

We have studied one banana-shaped compound using null-transmission ellipsometry. By studying free-standing films of various thicknesses we confirm that this compound exhibits the Sm-A phase. This is the first banana-shaped compound with a relatively small bend angle (approximately 140 degrees) in which a uniaxial phase has been observed. At the lower temperature end of the Sm-A phase we observe unusual ordering at the surface of the film.     

Balancing families of sets

Given k finite sets S₁,…,S_k, to what extent is it possible to partition their union into two parts A and B in such a way that, for each j, S_j ∩ A and S_j ∩ B contain approximately the same number of elements? Bounds are found for this and similar questions.     

Step structures on III-V phosphide (001) surfaces: how do steps and Sb affect CuPt ordering of GaInP2?

The observation of III-V phosphide (001)-(2 x 2) surfaces makes it possible to solve a long standing mystery of step structures. First-principles calculations show that a bulklike type-B step on a hydrogenated 2 x 2 surface is more stable than a rebonded one by 1.1 eV/unit step. In contrast, this energy difference for a H-free beta(2 x 4) surface is only 0.5 eV/unit step. The large difference explains why the CuPt ordering of GaInP is stronger in metal-organic chemical vapor deposition than in molecular beam epitaxy. However, a minute amount of Sb will preferentially attach to the 2 x 2 surface steps and induce additional step structures that cause ordering disruption.     

Nonoccupational noise: exposures associated with routine activities

Efforts to characterize nonoccupational noise exposures have focused primarily on infrequent, episodic events. Few studies have assessed noise levels resulting from routine daily activities. In the current study, 112 construction workers wore datalogging noise dosimeters and simultaneously completed activity logs during two phases of data collection. The 81 subjects monitored in phase 1 received logs listing numerous preselected occupational and nonoccupational activities, while the 31 subjects monitored in phase 2 used free-field logs and reported nonoccupational activities in greater detail. Nearly all of the 221,439 1-min intervals of nonoccupational L(eq) level and activity reporting were below 70 dBA; only a small percentage exceeded 80 dBA. The primary contributor to nonoccupational noise exposure was traveling in a car or bus, while time at home contributed the least. One hundred seventy 24-h L(eq) levels were computed from the 1-min noise level data. The percentage of phase 2 workday L(eq(24)) levels which exceeded 80 dBA was higher than that of the nonworkday levels. The mean L(eq(24)) level of phase 2 workdays was higher than that of nonworkdays, and the difference was statistically significant. Routine nonoccupational noise exposures contributed much less to total noise dose than occupational exposures in the subjects evaluated.     

A nonmusical paradigm for identifying absolute pitch possessors

The ability to identify and reproduce sounds of specific frequencies is remarkable and uncommon. The etiology and defining characteristics of this skill, absolute pitch (AP), have been very controversial. One theory suggests that AP requires a specific type of early musical training and that the ability to encode and remember tones depends on these learned musical associations. An alternate theory argues that AP may be strongly dependent on hereditary factors and relatively independent of musical experience. To date, it has been difficult to test these hypotheses because all previous paradigms for identifying AP have required subjects to employ knowledge of musical nomenclature. As such, these tests are insensitive to the possibility of discovering AP in either nonmusicians or musicians of non-Western training. Based on previous literature in pitch memory, a paradigm is presented that is intended to distinguish between AP possessors and nonpossessors independent of the subjects' musical experience. The efficacy of this method is then tested with 20 classically defined AP possessors and 22 nonpossessors. Data from these groups strongly support the validity of the paradigm. The use of a nonmusical paradigm to identify AP may facilitate research into many aspects of this phenomenon.     

Intracochlear pressure measurements related to cochlear tuning

Pressure in turn one of the scala tympani (s.t.) was measured close to the basilar membrane (b.m.) and at additional positions as the pressure sensor approached and/or withdrew from the b.m. The s.t. pressure measured within about 100 microm of the b.m. varied rapidly in space at frequencies around the region's best frequency. Very close to the b.m. the s.t. pressure was tuned and scaled nonlinearly with sound level. The scala vestibuli (s.v.) pressure was measured at one position close to the stapes within seconds of the s.t. pressure and served primarily as a reference pressure. The driving pressure across the organ of Corti and the b.m. velocity were derived from the pressure data. Both were tuned and nonlinear. Therefore, their ratio, the specific acoustic impedance of the organ of Corti complex, was relatively untuned, and only subtly nonlinear. The impedance was inspected specifically for negative resistance (amplification) and resonance. Both were detected in some instances; taken as a whole, the current results constrain the possibilities for these qualities.     

Moving Wigner glasses and smectics: dynamics of disordered Wigner crystals

We examine the dynamics of driven classical Wigner solids interacting with quenched disorder from charged impurities. For strong disorder, the initial motion is plastic, in the form of crossing winding channels. For increasing drive, there is a reordering into a moving Wigner smectic with the electrons moving in separate 1D channels. These different dynamic phases can be related to the conduction noise and I(V) curves. For strong disorder, we show criticality in the voltage onset just above depinning. We obtain the dynamic phase diagram for driven Wigner solids and demonstrate a finite threshold of force for transverse sliding, recently observed experimentally.     

Directed flow of lambda hyperons in (2-6 )A GeV Au+Au collisions

Directed flow measurements for Lambda hyperons are presented and compared to those for protons produced in the same Au+Au collisions (2A, 4A, and 6A GeV; b<5-6 fm). The measurements indicate that Lambda hyperons flow consistently in the same direction but with smaller magnitudes. A strong positive flow [for Lambdas] has been predicted in calculations which include the influence of the Lambda-nucleon potential. The experimental flow ratio Lambda/p is in qualitative agreement with expectations (approximately 2/3) from the quark counting rule at 2A GeV but is found to decrease with increasing beam energy.     

Static and dynamic coupling transitions of vortex lattices in disordered anisotropic superconductors

We use three-dimensional molecular dynamics simulations of magnetically interacting pancake vortices to study vortex matter in disordered, highly anisotropic materials such as BSCCO. We observe a sharp 3D-2D transition from vortex lines to decoupled pancakes as a function of relative interlayer coupling strength, with an accompanying large increase in the critical current reminiscent of a second peak effect. We find that decoupled pancakes, when driven, simultaneously recouple and order into a crystalline-like state at high drives. We construct a dynamic phase diagram and show that the dynamic recoupling transition is associated with a double peak in dV/dI.