Axial motion and scalar transport in stretched spiral vortices

We consider the dynamics of axial velocity and of scalar transport in the stretched-spiral vortex model of turbulent fine scales. A large-time asymptotic solution to the scalar advection-diffusion equation, with an azimuthal swirling velocity field provided by the stretched spiral vortex, is used together with appropriate stretching transformations to determine the evolution of both the axial velocity and a passive scalar. This allows calculation of the shell-integrated three-dimensional spectra of these quantities for the spiral-vortex flow. The dominant term in the velocity (energy) spectrum contributed by the axial velocity is found to be produced by the stirring of the initial distribution of axial velocity by the axisymmetric component of the azimuthal velocity. This gives a k(-7/3) spectrum at large wave numbers, compared to the k(-5/3) component for the azimuthal velocity itself. The spectrum of a passive scalar being mixed by the vortex velocity field is the sum of two power laws. The first is a k(-1) Batchelor spectrum for wave numbers up to the inverse Batchelor scale. This is produced by the axisymmetric component of the axial vorticity but is independent of the detailed radial velocity profile. The second is a k(-5/3) Obukov-Corrsin spectrum for wave numbers less than the inverse Kolmogorov scale. This is generated by the nonaxisymmetric axial vorticity and depends on initial correlations between this vorticity and the initial scalar field. The one-dimensional scalar spectrum for the composite model is in satisfactory agreement with experimental measurement

Memory and rejuvenation in a spin glass

The temperature dependence of the magnetisation of a Cu(Mn) spin glass ($T_g$ $\approx$ 57 K) has been investigated using weak probing magnetic fields ($H$ = 0.5 or 0 Oe) and specific thermal protocols. The behaviour of the zero-field cooled, thermoremanent and isothermal remanent magnetisation on (re-)cooling the system from a temperature (40 K) where the system has been aged is investigated. It is observed that the measured magnetisation is formed by two parts: (i) a temperature- and observation time-dependent thermally activated relaxational part governed by the age- and temperature-dependent response function and the (latest) field change made at a lower temperature, superposed on (ii) a weakly temperature-dependent frozen-in part. Interestingly we observe that the spin configuration that is imprinted during an elongated halt in the cooling, if it is accompanied by a field induced magnetisation, also includes a unidirectional excess magnetisation that is recovered on returning to the ageing temperature.Comment: EPL style; 7 pages, 5 figure

Relationships between lower-body muscle structure and, lower-body strength, explosiveness and eccentric leg stiffness in adolescent athletes

The purpose of the present study was to determine whether any relationships were present between lower-body muscle structure and, lower-body strength, variables measured during a counter-movement jump (CMJ) and squat jump (SJ), and eccentric leg stiffness, in adolescent athletes. Thirty junior male (n = 23) and female (n = 7) surfing athletes (14.8 ± 1.7 y; 1.63 ± 0.09 m; 54.8 ± 12.1 kg) undertook lower-body muscle structure assessment with ultrasonography and performed a; CMJ, SJ and an isomet-ric mid-thigh pull (IMTP). In addition, eccentric leg stiffness was calculated from variables of the CMJ and IMTP. Moderate to very large relationships (r = 0.46-0.73) were identified be-tween the thickness of the vastus lateralis (VL) and lateral gas-trocnemius (LG) muscles, and VL pennation angle and; peak force (PF) in the CMJ, SJ and IMTP. Additionally, moderate to large relationships (r = 0.37-0.59) were found between eccentric leg stiffness and; VL and LG thickness, VL pennation angle, and LG fascicle length, with a large relationship (r = 0.59) also present with IMTP PF. These results suggest that greater thick-ness of the VL and LG were related to improved maximal dy-namic and isometric strength, likely due to increased hypertro-phy of the extensor muscles. Furthermore, this increased thickness was related to greater eccentric leg stiffness, as the associated enhanced lower-body strength likely allowed for greater neuromuscular activation, and hence less compliance, during a stretch-shortening cycle

Memory and superposition in a spin glass

Non-equilibrium dynamics in a Ag(Mn) spin glass are investigated by measurements of the temperature dependence of the remanent magnetisation. Using specific cooling protocols before recording the thermo- or isothermal remanent magnetisations on re-heating, it is found that the measured curves effectively disclose non-equilibrium spin glass characteristics such as ageing and memory phenomena as well as an extended validity of the superposition principle for the relaxation. The usefulness of this "simple" dc-method is discussed, as well as its applicability to other disordered magnetic systems.Comment: REVTeX style; 8 pages, 4 figure

Improving the Sensitivity of Advanced LIGO Using Noise Subtraction

This paper presents an adaptable, parallelizable method for subtracting linearly coupled noise from Advanced LIGO data. We explain the features developed to ensure that the process is robust enough to handle the variability present in Advanced LIGO data. In this work, we target subtraction of noise due to beam jitter, detector calibration lines, and mains power lines. We demonstrate noise subtraction over the entirety of the second observing run, resulting in increases in sensitivity comparable to those reported in previous targeted efforts. Over the course of the second observing run, we see a 30% increase in Advanced LIGO sensitivity to gravitational waves from a broad range of compact binary systems. We expect the use of this method to result in a higher rate of detected gravitational-wave signals in Advanced LIGO data.Comment: 15 pages, 6 figure

RFI Identification and Mitigation Using Simultaneous Dual Station Observations

RFI mitigation is a critically important issue in radio astronomy using existing instruments as well as in the development of next-generation radio telescopes, such as the Square Kilometer Array (SKA). Most designs for the SKA involve multiple stations with spacings of up to a few thousands of kilometers and thus can exploit the drastically different RFI environments at different stations. As demonstrator observations and analysis for SKA-like instruments, and to develop RFI mitigation schemes that will be useful in the near term, we recently conducted simultaneous observations with Arecibo Observatory and the Green Bank Telescope (GBT). The observations were aimed at diagnosing RFI and using the mostly uncorrelated RFI between the two sites to excise RFI from several generic kinds of measurements such as giant pulses from Crab-like pulsars and weak HI emission from galaxies in bands heavily contaminated by RFI. This paper presents observations, analysis, and RFI identification and excision procedures that are effective for both time series and spectroscopy applications using multi-station data.Comment: 12 pages, 9 figures (4 in ps and 5 in jpg formats), Accepted for publication in Radio Scienc

Effect of sine-Gaussian glitches on searches for binary coalescence

We investigate the effect of an important class of glitches occurring in the detector data on matched filter searches of gravitational waves from coalescing compact binaries in the advanced detector era. The glitches, which can be modeled as sine-Gaussians, can produce triggers with significant time delays and thus have important bearing on veto procedures as will be described in the paper. We provide approximated analytical estimates of the trigger SNR and time as a function of the parameters describing the sine-Gaussian (center time, center frequency and Q-factor) and the inspiral waveform (chirp mass). We validate our analytical predictions through simple numerical simulations, performed by filtering noiseless sine-Gaussians with the inspiral matched filter and recovering the time and value of the maximum of the resulting SNR time series. Although we identify regions of the parameter space in which each approximation no longer reproduces the numerical results, the approximations complement each other and together effectively cover the whole parameter space

Social Media Interaction as Informal Science Learning: a Comparison of Message Design in Two Niches

Social media provides science learners opportunities to interact with content-specific messages. However, most science-specific social media content is designed to disseminate information instead of encouraging dialog. In this novel, ex post facto exploratory study of a science social media community, we sought to understand the relationships among community member interaction, design elements of messages, and post type on two digital niches (i.e., Facebook and Twitter). Framed by the theory of symbolic interactionism, we conducted a content analysis of 1370 messages that were systematically created by an informal science learning project and found that usage frequency of messaging elements varied by niche; interaction within each niche differed, varying by messaging element; and differential interaction was found to be associated with post types within Facebook only. This study suggests a pathway for developing and examining social media as an educational component of informal science learning