Sound radiation from a high speed axial flow fan due to the inlet turbulence quadrupole interaction

A formula is obtained for the total acoustic power spectra radiated out the front of the fan as a function of frequency. The formula involves the design parameters of the fan as well as the statistical properties of the incident turbulence. Numerical results are calculated for values of the parameters in the range of interest for quiet fans tested at the Lewis Research Center. As in the dipole analysis, when the turbulence correlation lengths become equal to the interblade spacing, the predicted spectra exhibit peaks around the blade passing frequency and its harmonics. There has recently been considerable conjecture about whether the stretching of turbulent eddies as they enter a stationary fan could result in the inlet turbulence being the dominant source of pure tones from nontranslating fans. The results of the current analysis show that, unless the turbulent eddies become quite elongated, this noise source contributes predominantly to the broadband spectrum

Vortex pinning and stability in the low field, superconducting phases of UPt_3

We use an array of miniature Hall probe magnetometers to probe the entry and flow of flux in a single crystal torus or the heavy fermion superconductor UPt_3. Local measurements over the hole are exquisitely sensitive to vortex motion anywhere in the torus, and they permit us to detect avalanches restricted to and with a sharp onset in the lower temperature superconducting phase. Computer simulations support a mechanism dependent upon the degenerate nature of the superconducting order parameter

Quantum spin glass in anisotropic dipolar systems

The spin-glass phase in the \LHx compound is considered. At zero transverse field this system is well described by the classical Ising model. At finite transverse field deviations from the transverse field quantum Ising model are significant, and one must take properly into account the hyperfine interactions, the off-diagonal terms in the dipolar interactions, and details of the full J=8 spin Hamiltonian to obtain the correct physical picture. In particular, the system is not a spin glass at finite transverse fields and does not show quantum criticality.Comment: 6 pages, 2 figures, to appear in J. Phys. Condens. Matter (proceedings of the HFM2006 conference

Baby-Step Giant-Step Algorithms for the Symmetric Group

We study discrete logarithms in the setting of group actions. Suppose that $G$ is a group that acts on a set $S$. When $r,s \in S$, a solution $g \in G$ to $r^g = s$ can be thought of as a kind of logarithm. In this paper, we study the case where $G = S_n$, and develop analogs to the Shanks baby-step / giant-step procedure for ordinary discrete logarithms. Specifically, we compute two sets $A, B \subseteq S_n$ such that every permutation of $S_n$ can be written as a product $ab$ of elements $a \in A$ and $b \in B$. Our deterministic procedure is optimal up to constant factors, in the sense that $A$ and $B$ can be computed in optimal asymptotic complexity, and $|A|$ and $|B|$ are a small constant from $\sqrt{n!}$ in size. We also analyze randomized "collision" algorithms for the same problem

Inference with interference between units in an fMRI experiment of motor inhibition

An experimental unit is an opportunity to randomly apply or withhold a treatment. There is interference between units if the application of the treatment to one unit may also affect other units. In cognitive neuroscience, a common form of experiment presents a sequence of stimuli or requests for cognitive activity at random to each experimental subject and measures biological aspects of brain activity that follow these requests. Each subject is then many experimental units, and interference between units within an experimental subject is likely, in part because the stimuli follow one another quickly and in part because human subjects learn or become experienced or primed or bored as the experiment proceeds. We use a recent fMRI experiment concerned with the inhibition of motor activity to illustrate and further develop recently proposed methodology for inference in the presence of interference. A simulation evaluates the power of competing procedures.Comment: Published by Journal of the American Statistical Association at http://www.tandfonline.com/doi/full/10.1080/01621459.2012.655954 . R package cin (Causal Inference for Neuroscience) implementing the proposed method is freely available on CRAN at https://CRAN.R-project.org/package=ci

Experimental Observation of Continuous Melting into a Hexatic Phase

This paper reports the results of an x-ray diffuse scattering study of the melting transition of monolayer xenon on the surface of single crystals of exfoliated graphite. It is found that the two-dimensional xenon solid melts into an orientationally ordered liquid (or hexatic) phase. The temperature dependence of the orientational correlations suggests that the hexatic phase exists as a consequence of the continuous melting process, not the substrate

Test-retest reliability of the Italian version of the M-BACK questionnaire to assess the barriers, attitudes, confidence, and knowledge of mental health staff regarding metabolic health of psychiatric patients

OBJECTIVES:The Metabolic-Barriers, Attitudes, Confidence, and Knowledge Questionnaire (M-BACK) was developed to determine the barriers, attitudes, confidence, and knowledge of mental health practitioners regarding the metabolic health of patients in order to determine the efficacy of targeted training interventions. This study aimed to validate the Italian version of M-BACK questionnaire (M-BACK-IT) and to determine the test-retest reliability. METHODS:The M-BACK questionnaire was translated into Italian and back-translated using an established protocol. In order to determine the test-retest reliability of the instrument, mental health professionals were recruited from a private psychiatric hospital located in northeast Italy and completed the questionnaire on two separate occasions, seven days apart. Intraclass correlation coefficients (ICC) were calculated for the total score, as well as each of the four M-BACK domains. RESULTS:Thirty mental health professionals (4 psychiatrists, 9 psychologists, 12 nurses, and 5 exercise specialists) completed the M-BACK-IT. ICCs ranged from 0.58 to 0.94. CONCLUSIONS:The test-retest reliability of the M-BACK-IT demonstrated comparable results to the English version. The M-BACK-IT is a reliable measure to assess key elements of practitioners' perceptions of the barriers, their knowledge, attitudes, and confidence regarding metabolic monitoring and intervention in people with mental illness

PLANTAR PRESSURE MEASUREMENTS IN A SOCCER SHOE: CHARACTERIZATION OF SOCCER SPECIFIC MOVEMENTS AND EFFECTS AFTER SIX WEEKS OF AGING

The purposes of the study were (i) to characterize in-shoe pressure distribution (PD) measurements during soccer specific movements, (ii) to describe the changes on (PD) after six weeks of aging. 21 experienced male subjects participated in the study. Four different movements (run, cut, sprint and goal shot) were measured on a red cinder surface before and after six weeks of aging. Results showed specific loading characteristics for each movement: Compared to running, the medial part of the foot in cutting, the forefoot in sprinting and the lateral part in kicking were predominantly loaded. Peak pressures increased over 10% after six weeks of use in some high-load areas. Attention should be paid to sprinting and cutting with respect to overuse injuries. Sockliners should be exchanged on a regular basis to maintain a certain amount of cushioning

Quantum Barkhausen Noise Induced by Domain Wall Co-Tunneling

Most macroscopic magnetic phenomena (including magnetic hysteresis) are typically understood classically. Here, we examine the dynamics of a uniaxial rare-earth ferromagnet deep within the quantum regime, so that domain wall motion, and the associated hysteresis, is dominated by large-scale quantum tunneling of spins, rather than classical thermal activation over a potential barrier. The domain wall motion is found to exhibit avalanche dynamics, observable as an unusual form of Barkhausen noise. We observe non-critical behavior in the avalanche dynamics that only can be explained by going beyond traditional renormalization group methods or classical domain wall models. We find that this ``quantum Barkhausen noise'' exhibits two distinct mechanisms for domain wall movement, each of which is quantum-mechanical, but with very different dependences on an external magnetic field applied transverse to the spin (Ising) axis. These observations can be understood in terms of the correlated motion of pairs of domain walls, nucleated by co-tunneling of plaquettes (sections of domain wall), with plaquette pairs correlated by dipolar interactions; this correlation is suppressed by the transverse field. Similar macroscopic correlations may be expected to appear in the hysteresis of other systems with long-range interactions.Comment: 11 pages, 4 figure