A double-frequency dwarf nova oscillation

We have detected coherent oscillations (``dwarf nova oscillations'') in Hubble Space Telescope spectra of the dwarf nova OY Car. The oscillations were seen towards the end of a superoutburst of OY Car. The oscillations are extraordinary compared to the many other examples in the literature for two reasons. First, their amplitude is large, with a peak-to-peak variation of 8 to 20% of the total flux over the range 1100 to 2500A. However, most remarkably we find that there are two components present simultaneously. Both have periods close to 18sec (equivalent to 4800 cycles/day) but they are separated by 57.7+/-0.5 cycles/day. The lower frequency component of the pair has a strong second harmonic while its companion, which has about twice its amplitude, does not. The oscillation spectra appear hotter than the mean spectrum and approximately follow the continuum distribution of a black-body with a temperature in the range 30,000 to 50,000K. We tentatively suggest that the weaker non-sinusoidal component could represent the rotation of the white dwarf, although we have been unable to recover any such signal in quiescent data.Comment: 9 pages, 9 figure

Quasar Tomography: Unification of Echo Mapping and Photoionisation Models

Reverberation mapping uses time-delayed variations in photoionised emission lines to map the geometry and kinematics of emission-line gas in active galactic nuclei. In previous work, the light travel time delay tau=R(1+cos(theta))/c and Doppler shift v give a 2-d map Psi(tau,v) for each emission line. Here we combine the velocity-delay information with photoionisation physics in a maximum entropy fit to the full reverberating spectrum F_lam(lam,t) to recover a 5-d map of the differential covering fraction f(R,theta,n,N,v), with n and N the density and column density of the gas clouds. We test the method for a variety of geometries (shells, rings, disks, clouds, jets) by recovering a 3-d map f(R,theta,n) from reverberations in 7 uv emission lines. The best test recovers a hollow shell geometry, defining R to 0.15 dex, n to 0.3 dex, and ionisation parameter U ~ 1/(n R^2) to 0.1 dex. The results are sensitive to the adopted distance and luminosity, suggesting that these parameters may be measurable as well.Comment: Accepted 4 Sep 2002 for publication in MNRA

A laser-induced heat flux technique for convective heat transfer measurements in high speed flows

A technique is developed to measure the local convective heat transfer coefficient on a model surface in a supersonic flow field. The technique uses a laser to apply a discrete local heat flux at the model test surface, and an infrared camera system determines the local temperature distribution due to the heating. From this temperature distribution and an analysis of the heating process, a local convective heat transfer coefficient is determined. The technique was used to measure the local surface convective heat transfer coefficient distribution on a flat plate at nominal Mach numbers of 2.5, 3.0, 3.5, and 4.0. The flat plate boundary layer initially was laminar and became transitional in the measurement region. The experimentally determined convective heat transfer coefficients were generally higher than the theoretical predictions for flat plate laminar boundary layers. However, the results indicate that this nonintrusive optical measurement technique has the potential to measure surface convective heat transfer coefficients in high speed flow fields

Conformations of biopolymers in the gas phase: a new mass spectrometric method

A method is developed for measuring collision cross sections of gas-phase biomolecules using a slightly modified commercial triple quadrupole instrument. The modifications allow accurate stopping potentials to be measured for ions exiting the collision region of the instrument. A simple model allows these curves to be converted to cross sections. In order to account for certain poorly defined experimental parameters (exact ion energy, absolute pressure in the collision cell, etc.) variable parameters are included in the model. These parameters are determined on a case by case basis by normalizing the results to the well known cross section of singly charged bradykinin, Two relatively large systems were studied (cytochrome c and myoglobin) so comparisons could be made to literature values. A number of new peptide systems were then studied in the 9 -14 residue range. These included singly and doubly charged ions of luteinizing hormone releasing hormone (LHRH) substance P, and bombesin in addition to bradykinin. The experimental cross sections were in very good agreement with predictions from extensive molecular dynamics modeling. One interesting result was the experimental observation that the cross section of the doubly charged ions of LHRH, substance P, and bombesin were all smaller than those of the corresponding singly charged ions. Molecular dynamics did not reproduce this result, predicting doubly charged cross sections of the same magnitude or slightly larger than for the singly charged species. The experimental results appear to be correct, however. Possible shortcomings in the modeling procedure for multiply charged ions were suggested that might account for the discrepancy

An Empirical Study of a Software Maintenance Process

This paper describes how a process support tool is used to collect metrics about a major upgrade to our own electronic retail system. An incremental prototyping lifecycle is adopted in which each increment is categorised by an effort type and a project component. Effort types are Acquire, Build, Comprehend and Design and span all phases of development. Project components include data models and process models expressed in an OO modelling language and process algebra respectively as well as C++ classes and function templates and build components including source files and data files. This categorisation is independent of incremental prototyping and equally applicable to other software lifecycles. The process support tool (PWI) is responsible for ensuring the consistency between the models and the C++ source. It also supports the interaction between multiple developers and multiple metric-collectors. The first two releases of the retailing software are available for ftp from oracle.ecs.soton.ac.uk in directory pub/peter. Readers are invited to use the software and apply their own metrics as appropriate. We would be interested to correspond with anyone who does so

Reciprocal intronic and exonic histone modification regions in humans.

While much attention has been focused on chromatin at promoters and exons, human genes are mostly composed of intronic sequences. Analyzing published surveys of nucleosomes and 41 chromatin marks in humans, we identified histone modifications specifically associated with 5' intronic sequences, distinguishable from promoter marks and bulk nucleosomes. These intronic marks were spatially reciprocal to trimethylated histone H3 Lys36 (H3K36me3), typically transitioning near internal exons. Several marks transitioned near bona fide exons, but not near nucleosomes at exon-like sequences. Therefore, we examined whether splicing affects histone marking. Even with considerable changes in regulated alternative splicing, histone marks were stable. Notably, these findings are consistent with exon definition influencing histone marks. In summary, we show that the location of many intragenic marks in humans can be distilled into a simple organizing principle: association with 5' intronic or 3' exonic regions

An LDA (Laser-Doppler Anemometry) investigation of three-dimensional normal shock wave boundary-layer interactions

Nonintrusive measurements were made of a normal shock wave/boundary layer interaction. Two dimensional measurements were made throughout the interaction region while 3-D measurements were made in the vicinity of the shock wave. The measurements were made in the corner of the test section of a continuous supersonic wind tunnel in which a normal shock wave had been stabilized. Laser Doppler Anemometry, surface pressure measurement and flow visualization techniques were employed for two freestream Mach number test cases: 1.6 and 1.3. The former contained separated flow regions and a system of shock waves. The latter was found to be far less complicated. The results define the flow field structure in detail for each case

The Presentation

Here am I— The article Of fine coordination— (The sculptor\u27s swish of curtains The little ahs and ohs The flutter of dissection with the slivered tongue)..

Strain and field modulation in bilayer graphene band structure

Using an external electric field, one can modulate the bandgap of Bernal stacked bilayer graphene by breaking A-~B symmetry. We analyze strain effects on the bilayer graphene using the extended Huckel theory and find that reduced interlayer distance results in higher bandgap modulation, as expected. Furthermore, above about 2.5 angstrom interlayer distance, the bandgap is direct, follows a convex relation to electric field and saturates to a value determined by the interlayer distance. However, below about 2.5 angstrom, the bandgap is indirect, the trend becomes concave and a threshold electric field is observed, which also depends on the stacking distance.Comment: 3 pages, 5 figures - v1 and v2 are the same, uploaded twice - v3, some typos fixed and a reference adde