B-field Determination from Magnetoacoustic Oscillations in kHz QPO Neutron Star Binaries: Theory and Observations

We present a method for determining the B-field around neutron stars based on observed kHz and viscous QPO frequencies used in combination with the best-fit optical depth and temperature of a Comptonization model. In the framework of the transition layer QPO model, we analyze magnetoacoustic wave formation in the layer between a neutron star surface and the inner edge of a Keplerian disk. We derive formulas for the magnetoacoustic wave frequencies for different regimes of radial transition layer oscillations. We demonstrate that our model can use the QPO as a new kind of probe to determine the magnetic field strengths for 4U 1728-42, GX 340+0, and Sco X-1 in the zone where the QPOs occur. Observations indicate that the dependence of the viscous frequency on the Keplerian frequency is closely related to the inferred dependence of the magnetoacoustic wave frequency on the Keplerian frequency for a dipole magnetic field. The magnetoacoustic wave dependence is based on a single parameter, the magnetic moment of the star as estimated from the field strength in the transition layer. The best-fit magnetic moment parameter is about (0.5-1)x 10^{25} G cm^3 for all studied sources. From observational data, the magnetic fields within distances less 20 km from neutron star for all three sources are strongly constrained to be dipole fields with the strengths 10^{7-8} G on the neutron star surface.Comment: 10 pages, 1 figure, accepted for the Astrophysical Journal Letter

Performance of a tandem-rotor/tandem-stator conical-flow compressor designed for a pressure ratio of 3

A conical-flow compressor stage with a large radius change through the rotor was tested at three values of rotor tip clearance. The stage had a tandem rotor and a tandem stator. Peak efficiency at design speed was 0.774 at a pressure ratio of 2.613. The rotor was tested without the stator, and detailed survey data were obtained for each rotor blade row. Overall peak rotor efficiency was 0.871 at a pressure ratio of 2.952

An Initial Exploration of Improved Numerics within the Guidelines of the Negative Spalart-Allmaras Turbulence Model

A simple modification to the negative Spalart-Allmaras turbulence model is suggested so that when the turbulence working variable, ~v, is negative, diagonal dominance is increased, as is the tendency for the time-advancement scheme to push e toward positive values. Owing to the fact that the modification is only active when ~v is less than zero, the physical model is left unchanged. Using the proposed modification with a strong implicit solver based on Newton's method, convergence rates can be somewhat improved, with typical reductions in iterations and computer time on the order of 15-50%. The benefits are realized primarily when second- or higher-order accuracy is used for discretizing the convective terms in the turbulence model because of large overshoots that can occur with these schemes at the edges of boundary layers and wakes. For flowfields with few regions of negative ~v, or on very fine meshes where ~v is always greater than zero, little or no benefits should be expected

An evlauation of the three-dimensional split-film anemometer for measurements of atmospheric turbulence

A three-dimensional split-film anemometer was tested in turbulent, as well as in nonturbulent flow downstream from a wind tunnel turbulence grid. The data obtained with this probe in the turbulence behind the grid, indicated that the measured turbulence intensities were somewhat lower than the intensity measured with the conventional hot-wire anemometry; a result of the finite dimensions of the sensor arrays. The probe yaw angle was determined to be accurate within three degrees. Statistical averages, determined by mean-wind direction and vertical and lateral directions were computed on the basis of the probe yaw angle

Robot-Mediated Interviews with Children : What do potential users think?

Luke Wood, Hagen Lehmann, Kerstin Dautenhahn, Ben Robins, Austen Rayner, and Dag Syrdal, ‘Robot-Mediated Interviews with Children: What do potential users think?’, paper presented at the 50th Annual Convention of the Society for the Study of Artificial Intelligence and the Simulation of Behaviour, 1 April 2014 – 4 April 2014, London, UK.When police officers are conducting interviews with children, some of the disclosures can be quite shocking. This can make it difficult for an officer to maintain their composure without subtly indicating their shock to the child, which can in turn impede the information acquisition process. Using a robotic interviewer could eliminate this problem as the behaviours and expressions of the robot can be consciously controlled. To date research investigating the potential of Robot-Mediated Interviews has focused on establishing whether children will respond to robots in an interview scenario and if so how well. The results of these studies indicate that children will talk to a robot in an interview scenario in a similar way to which they talk to a human interviewer. However, in order to test if this approach would work in a real world setting, it is important to establish what the experts (e.g. specialist child interviewers) would require from the system. To determine the needs of the users we conducted a user panel with a group of potential real world users to gather their views of our current system and find out what they would require for the system to be useful to them. The user group we worked with consisted of specialist child protection police officers based in the UK. The findings from this panel suggest that a Robot-Mediated Interviewing system would need to be more flexible than our current system in order to respond to unpredictable situations and paths of investigation. This paper gives an insight into what real world users would need from a Robot-Mediated Interviewing system

The platinum nuclei: concealed configuration mixing and shape coexistence

The role of configuration mixing in the Pt region is investigated. For this chain of isotopes, the nature of the ground state changes smoothly, being spherical around mass $A\sim 174$ and $A\sim 192$ and deformed around the mid-shell N=104 region. This has a dramatic effect on the systematics of the energy spectra as compared to the systematics in the Pb and Hg nuclei. Interacting Boson Model with configuration mixing calculations are presented for gyromagnetic factors, $\alpha$-decay hindrance factors, and isotope shifts. The necessity of incorporating intruder configurations to obtain an accurate description of the latter properties becomes evident.Comment: Accepted in Physical Review

Mixing with the radiofrequency single-electron transistor

By configuring a radio-frequency single-electron transistor as a mixer, we demonstrate a unique implementation of this device, that achieves good charge sensitivity with large bandwidth about a tunable center frequency. In our implementation we achieve a measurement bandwidth of 16 MHz, with a tunable center frequency from 0 to 1.2 GHz, demonstrated with the transistor operating at 300 mK. Ultimately this device is limited in center frequency by the RC time of the transistor's center island, which for our device is ~ 1.6 GHz, close to the measured value. The measurement bandwidth is determined by the quality factor of the readout tank circuit.Comment: Submitted to APL september 200

Fermi LAT Gamma-ray Detections of Classical Novae V1369 Centauri 2013 and V5668 Sagittarii 2015

We report the Fermi Large Area Telescope (LAT) detections of high-energy (>100 MeV) gamma-ray emission from two recent optically bright classical novae, V1369 Centauri 2013 and V5668 Sagittarii 2015. At early times, Fermi target-of-opportunity observations prompted by their optical discoveries provided enhanced LAT exposure that enabled the detections of gamma-ray onsets beginning ~2 days after their first optical peaks. Significant gamma-ray emission was found extending to 39-55 days after their initial LAT detections, with systematically fainter and longer duration emission compared to previous gamma-ray detected classical novae. These novae were distinguished by multiple bright optical peaks that encompassed the timespans of the observed gamma rays. The gamma-ray light curves and spectra of the two novae are presented along with representative hadronic and leptonic models, and comparisons to other novae detected by the LAT are discussed.Comment: 13 pages, 6 figures, 4 tables, ApJ accepte