Black Hole Monodromy and Conformal Field Theory

The analytic structure of solutions to the Klein-Gordon equation in a black hole background, as represented by monodromy data, is intimately related to black hole thermodynamics. It encodes the "hidden conformal symmetry" of a non-extremal black hole, and it explains why features of the inner event horizon appear in scattering data such as greybody factors. This indicates that hidden conformal symmetry is generic within a universality class of black holes.Comment: 20 pages, v2 minor corrections, updated reference

Mechanical fluidity of fully suspended biological cells

Mechanical characteristics of single biological cells are used to identify and possibly leverage interesting differences among cells or cell populations. Fluidity---hysteresivity normalized to the extremes of an elastic solid or a viscous liquid---can be extracted from, and compared among, multiple rheological measurements of cells: creep compliance vs. time, complex modulus vs. frequency, and phase lag vs. frequency. With multiple strategies available for acquisition of this nondimensional property, fluidity may serve as a useful and robust parameter for distinguishing cell populations, and for understanding the physical origins of deformability in soft matter. Here, for three disparate eukaryotic cell types deformed in the suspended state via optical stretching, we examine the dependence of fluidity on chemical and environmental influences around a time scale of 1 s. We find that fluidity estimates are consistent in the time and the frequency domains under a structural damping (power-law or fractional derivative)model, but not under an equivalent-complexity lumpedcomponent (spring-dashpot) model; the latter predicts spurious time constants. Although fluidity is suppressed by chemical crosslinking, we find that adenosine triphosphate (ATP) depletion in the cell does not measurably alter the parameter, and thus conclude that active ATP-driven events are not a crucial enabler of fluidity during linear viscoelastic deformation of a suspended cell. Finally, by using the capacity of optical stretching to produce near-instantaneous increases in cell temperature, we establish that fluidity increases with temperature---now measured in a fully suspended, sortable cell without the complicating factor of cell-substratum adhesion

The Smith Cloud: HI associated with the Sgr dwarf?

The Smith high velocity cloud (V(LSR) = 98 kms) has been observed at two locations in the emission lines [OIII]5007, [NII]6548 and H-alpha. Both the [NII] and H-alpha profiles show bright cores due to the Reynolds layer, and red wings with emission extending to V(LSR) = 130 kms. This is the first simultaneous detection of two emission lines towards a high velocity cloud, allowing us to form the ratio of these line profiles as a function of LSR velocity. At both cloud positions, we see a clear distinction between emission at the cloud velocity, and the Reynolds layer emission (V(LSR) = 0). The [NII]/H-alpha ratio (=0.25) for the Reynolds layer is typical of the warm ionised medium. At the cloud velocity, this ratio is enhanced by a factor of 3-4 compared to emission at rest with respect to the LSR. A moderately deep upper limit at [OIII] (0.12R at 3-sigma) was derived from our data. If the emission arises from dilute photoionisation from hot young stars, the highly enhanced [NII]/H-alpha ratio, the [OIII] non-detection and weak H-alpha emission (0.24-0.30R) suggest that the Smith Cloud is 26+/-4 kpc from the Sun, at a Galactocentric radius of 20+/-4 kpc. This value assumes that the emission arises from an optically thick slab, with a covering fraction of unity as seen by the ionizing photons, whose orientation is either (a) parallel to the Galactic disk, or (b) such as to maximize the received flux from the disk. The estimated mass and size of the cloud are 4x10^6 Msun and 6 kpc. We discuss a possible association with the much larger Sgr dwarf, at a galactocentric radius of 16+/-2 kpc, which lies within 35 degrees (~12 kpc) of the Smith Cloud.Comment: 18 pages, 14 figures, mn.sty. Our first application of a new method for establishing distances to high velocity clouds. This version matches paper to appear in MNRAS, 299, 611-624 (Sept. 11 issue

Do stiffness and asymmetries predict change of direction performance?

Change of direction speed (CODS) underpins performance in a wide range of sports but little is known about how stiffness and asymmetries affect CODS. Eighteen healthy males performed unilateral drop jumps to determine vertical, ankle, knee and hip stiffness, and a CODS test to evaluate left and right leg cutting performance during which ground reaction force data were sampled. A step-wise regression analysis was performed to ascertain the determinants of CODS time. A two-variable regression model explained 63% (R-2 = 0.63; P = 0.001) of CODS performance. The model included the mean vertical stiffness and jump height asymmetry determined during the drop jump. Faster athletes (n = 9) exhibited greater vertical stiffness (F = 12.40; P = 0.001) and less asymmetry in drop jump height (F = 6.02; P = 0.026) than slower athletes (n = 9); effect sizes were both "large" in magnitude. Results suggest that overall vertical stiffness and drop jump height asymmetry are the strongest predictors of CODS in a healthy, non-athletic population

A Decade Of Starspot Activity On The Eclipsing Short-Period RS Canum Venaticorum Star WY Cancri: 1988-1997

We present optical photometry of the short-period eclipsing RS CVn system WY Cancri for the years 1988–1997. For each light curve, we model the distortion waves in order to study the behavior of starspots in this system. After removing the spot effects f

Lower limb stiffness testing in athletic performance: a critical review

Stiffness describes the resistance of a body to deformation. In regards to athletic performance, a stiffer leg-spring would be expected to augment performance by increasing utilisation of elastic energy. Two-dimensional spring-mass and torsional spring models can be applied to model whole-body (vertical and/or leg stiffness) and joint stiffness. Various tasks have been used to characterise stiffness, including hopping, gait, jumping, sledge ergometry and change of direction tasks. Appropriate levels of reliability have been reported in most tasks, although vary between investigations. Vertical stiffness has demonstrated the strongest reliability across tasks and may be more sensitive to changes in high-velocity running performance than leg stiffness. Joint stiffness demonstrates the weakest reliability, with ankle stiffness more reliable than knee stiffness. Determination of stiffness has typically necessitated force plate analyses, however, validated field-based equations permit determination of whole-body stiffness without force plates. Vertical, leg and joint stiffness measures have all demonstrated relationships with performance measures. Greater stiffness is typically demonstrated with increasing intensity (i.e. running velocity or hopping frequency). Greater stiffness is observed in athletes regularly subjecting the limb to high ground reaction forces (i.e. sprinters). Careful consideration should be given to the most appropriate assessment of stiffness on a team/individual basis

Simple de Sitter Solutions

We present a framework for de Sitter model building in type IIA string theory, illustrated with specific examples. We find metastable dS minima of the potential for moduli obtained from a compactification on a product of two Nil three-manifolds (which have negative scalar curvature) combined with orientifolds, branes, fractional Chern-Simons forms, and fluxes. As a discrete quantum number is taken large, the curvature, field strengths, inverse volume, and four dimensional string coupling become parametrically small, and the de Sitter Hubble scale can be tuned parametrically smaller than the scales of the moduli, KK, and winding mode masses. A subtle point in the construction is that although the curvature remains consistently weak, the circle fibers of the nilmanifolds become very small in this limit (though this is avoided in illustrative solutions at modest values of the parameters). In the simplest version of the construction, the heaviest moduli masses are parametrically of the same order as the lightest KK and winding masses. However, we provide a method for separating these marginally overlapping scales, and more generally the underlying supersymmetry of the model protects against large corrections to the low-energy moduli potential.Comment: 37 pages, harvmac big, 4 figures. v3: small correction