A unified model for the long and high jump

A simple model based on the maximum energy that an athlete can produce in a small time interval is used to describe the high and long jump. Conservation of angular momentum is used to explain why an athlete should run horizontally to perform a vertical jump. Our results agree with world records.Comment: Accepted for publication in Am. J. Phy

Many-body interactions in a quantum wire in the integer quantum Hall regime: suppression of exchange-enhanced g factor

The collapse of Hall gaps in the integer quantum Hall liquid in a quantum wire is investigated. Motivated by recent experiment [Pallecchi et al. PRB 65, 125303 (2002)] previous approaches are extended to treat confinement effects and the exchanged enhanced g-factor in quantum wires. Two scenarios for the collapse of the $\nu =1$ state are discussed. In the first one the $\nu =1$ state becomes unstable at $B_{cr}^{(1)}$, due to the exchange interaction and correlation effects, coming from the edge-states screening. In the second scenario, a transition to the $\nu =2$ state occurs at $B_{cr}^{(2)}$, with a smaller effective channel width, caused by the redistribution of the charge density. This effect turns the Hartree interaction essential in calculating the total energy and changes $B_{cr}^{(2)}$ drastically. In both scenarios, the exchange enhanced g-factor is suppressed for magnetic fields lower than $B_{cr}$. Phase diagrams for the Hall gap collapse are determined. The critical fields, activation energy, and optical $g$-factor obtained are compared with experiments. Within the accuracy of the available data, the first scenario is most probable to be realized.Comment: 11 pages, 10 figure

Edge helicons and repulsion of fundamental edge magnetoplasmons in the quantum Hall regime

A quasi-microscopic treatment of edge magnetoplasmons (EMP) is presented for very low temperatures and confining potentials smooth on the scale of the magnetic length $\ell_{0}$ but sufficiently steep at the edges such that Landau level (LL) flattening can be discarded. The profile of the unperturbed electron density is sharp and the dissipation taken into account comes only from electron intra-edge and intra-LL transitions due to scattering by acoustic phonons. For wide channels and filling factors $\nu =1$ and 2, there exist independent EMP modes spatially symmetric and antisymmetric with respect to the edge. Some of these modes, named edge helicons, can propagate nearly undamped even when the dissipation is strong. Their density profile changes qualitatively during propagation and is given by a rotation of a complex vector function. For $\nu >2,$ the Coulomb coupling between the LLs leads to a repulsion of the uncoupled fundamental LL modes: the new modes have very different group velocities and are nearly undamped. The theory accounts well for the experimentally observed plateau structure of the delay times as well as for the EMP's period and decay rates.Comment: 12 pages, 6 figure

Models for the Observable System Parameters of Ultraluminous X-ray Sources

We investigate the evolution of the properties of model populations of ultraluminous X-ray sources (ULXs) consisting of a black-hole accretor in a binary with a donor star. We have computed models corresponding to three different populations of black-hole binaries; two invoke stellar-mass (~10 Msun) black hole accretors, and the third utilizes intermediate-mass (~1000 Msun) black holes (IMBHs). For each of the three populations, we computed 30,000 binary evolution sequences using a full Henyey stellar evolution code. The optical flux from the model ULXs includes contributions from the accretion disk, due to x-ray irradiation as well as intrinsic viscous heating, and that due to the donor star. We present "probability images" for the ULX systems in planes of color-magnitude, orbital period vs. X-ray luminosity, and luminosity vs. evolution time. Estimates of the numbers of ULXs in a typical galaxy as functions of time and of X-ray luminosity are also presented. Our model CMDs are compared with six ULX counterparts that have been discussed in the literature. Overall, the observed systems seem more closely related to model systems with very high-mass donors (> ~25 Msun) in binaries with IMBH accretors. However, significant difficulties remain with both the IMBH and stellar-mass black hole models.Comment: 15 pages, 8 figures, submitted to ApJ on Oct 05, 200

Neurospora crassa chromosome walks

Chromosome walks have been executed for all seven chromosomes of N. crassa, but the amount of coverage varies greatly, from less than 3% (LG V) to about 25% (LG VII). Overall, about 10% of the genome has been covered by chromosome walks (Table 1). All chromosome walks are shown with respect to the position on the chromosome, oriented from the left telomere to the right. The standard nomenclature for these genomic libraries is followed: pSV50 (Vollmer and Yanofsky 1986 Proc. Natl. Acad. Sci. USA 83:4869-4873), pMOcosX (Orbach 1994 Gene 150:159-162), EMBL3 (Yeadon and Catcheside 1995 Curr. Genet. 28:155-163), pCRD103 (Davis et al. 1994 Genetics 136:1297-1306), CBM1 (Cabibbo et al. 1991 Fungal Genet. Newsl. 38:68-70), CBM2 (Ballario et al. 1996 EMBO J. 15:1650-1657) and yeast artificial chromosome (YAC; Centola et al. 1994 Fungal Genet. Newsl. 41:23-33). For precise map positions of the cited alleles, refer to Perkins et al.(1982 Microbiol. Rev. 46:426-570) and Perkins (1992 Fungal Genet. Newsl. 39:61-70)

Deranged calcium signaling and neurodegeneration in spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is an autosomal-dominant neurodegenerative disorder caused by a polyglutamine expansion in ataxin-3 (SCA3, MJD1) protein. In biochemical experiments we demonstrate that mutant SCA3exp specifically associated with the type 1 inositol 1,4,5-trisphosphate receptor (InsP3R1), an intracellular calcium (Ca2+) release channel. In electrophysiological and Ca2+ imaging experiments we show that InsP3R1 are sensitized to activation by InsP3 in the presence of mutant SCA3exp. We found that feeding SCA3-YAC-84Q transgenic mice with dantrolene, a clinically relevant stabilizer of intracellular Ca2+ signaling, improved their motor performance and prevented neuronal cells loss in pontine nuclei and substantia nigra regions. Our results indicate that deranged Ca2+ signaling may play an important role in SCA3 pathology and that Ca2+ signaling stabilizers such as dantrolene may be considered as potential therapeutic drugs for treatment of SCA3 patients

Translational Correlations in the Vortex Array at the Surface of a Type-II Superconductor

We discuss the statistical mechanics of magnetic flux lines in a finite-thickness slab of type-II superconductor. The long wavelength properties of a flux-line liquid in a slab geometry are described by a hydrodynamic free energy that incorporates the boundary conditions on the flux lines at the sample's surface as a surface contribution to the free energy. Bulk and surface weak disorder are modeled via Gaussian impurity potentials. This free energy is used to evaluate the two-dimensional structure factor of the flux-line tips at the sample surface. We find that surface interaction always dominates in determining the decay of translational correlations in the asymptotic long-wavelength limit. On the other hand, such large length scales have not been probed by the decoration experiments. Our results indicate that the translational correlations extracted from the analysis of the Bitter patterns are indeed representative of behavior of flux lines in the bulk.Comment: 23 pages, 1 figure (not included), harvmac.tex macro needed (e-mail requests to [email protected] SU-CM-92-01

Study and development of acoustic treatment for jet engine tailpipes

A study and development program was accomplished to attenuate turbine noise generated in the JT3D turbofan engine. Analytical studies were used to design an acoustic liner for the tailpipe. Engine ground tests defined the tailpipe environmental factors and laboratory tests were used to support the analytical studies. Furnace-brazed, stainless steel, perforated sheet acoustic liners were designed, fabricated, installed, and ground tested in the tailpipe of a JT3D engine. Test results showed the turbine tones were suppressed below the level of the jet exhaust for most far field polar angles

Probabilistic computer model of optimal runway turnoffs

Landing delays are currently a problem at major air carrier airports and many forecasters agree that airport congestion will get worse by the end of the century. It is anticipated that some types of delays can be reduced by an efficient optimal runway exist system allowing increased approach volumes necessary at congested airports. A computerized Probabilistic Runway Turnoff Model which locates exits and defines path geometry for a selected maximum occupancy time appropriate for each TERPS aircraft category is defined. The model includes an algorithm for lateral ride comfort limits