Interpretation of the angular dependence of the de Haas-van Alphen effect in MgB_2

We present detailed results for the amplitude and field dependence of the de Haas-van Alphen (dHvA) signal arising from the electron-like $\pi$ sheet of Fermi surface in MgB_2. Our data and analysis show that the dip in dHvA amplitude when the field is close to the basal plane is caused by a beat between two very similar dHvA frequencies and not a spin-zero effect as previously assumed. Our results imply that the Stoner enhancement factors in MgB_2 are small on both the Sigma and Pi sheets.Comment: 4 pages with figures. Submitted to PR

A systematic review of the impact of psychosocial factors on immunity: Implications for enhancing BCG response against tuberculosis.

Background: Tuberculosis (TB) remains an urgent global public health priority, causing 1.5 million deaths worldwide in 2018. There is evidence that psychosocial factors modulate immune function; however, how this may influence TB risk or BCG vaccine response, and whether this pathway can be modified through social protection, has not been investigated. This paper aims to: a) systematically review evidence of how psychosocial factors influence the expression of biomarkers of immunity, and b) apply this general evidence to propose plausible TB-specific pathways for future study. Methods: Papers reporting on the impact of psychosocial stressors on immune biomarkers in relation to infectious disease risk were identified through a search of the databases MEDLINE, PsycINFO, Global Health and PsycEXTRA alongside reference list and citation searching of key papers. Data extraction and critical appraisal were carried out using a standardised form. The findings were tabulated and synthesised narratively by infectious disease category, and used to propose plausible mechanisms for how psychosocial exposures might influence immune outcomes relevant to TB and BCG response. Results: 27,026 citations were identified, of which 51 met the inclusion criteria. The literature provides evidence of a relationship between psychosocial factors and immune biomarkers. While the direction and strength of associations is heterogenous, some overarching patterns emerged: adverse psychosocial factors (e.g. stress) were generally associated with compromised vaccine response and higher antibody titres to herpesviruses, and vice versa for positive psychosocial factors (e.g. social support). Conclusions: The evidence identifies pathways linking psychosocial factors and immune response: co-viral infection and immune suppression, both of which are potentially relevant to TB and BCG response. However, the heterogeneity in the strength and nature of the impact of psychosocial factors on immune function, and lack of research on the implications of this relationship for TB, underscore the need for TB-specific research

A population and harvest intensity estimate for Sooty Shearwater, Puflinus griseus, on Taukihepa (Big South Cape), New Zealand

We estimated the total number of burrow entrances, chicks and total population size of the Sooty Shearwater, Puffinusgriseus, colony on Taukihepa (Big South Cape), the largest of the 36 Titi Islands where Titi (Sooty Shcarwater chicks) are harvested. Between 1999 and 2005 we surveyed six manu (family birded areas) as well as a colony in the interior forested region on the island, measuring entrance density and burrow occupancy and habitat variables, as well as recording birders' harvest intensity. We found little support for any relationship between habitat variables and entrance density on the surveyed manu. Therefore we used a detailed aerial image to map areas and extrapolate these estimates to island totals and a simple population model, incorporating known demographic parameters to calculate the total population size. We estimated that the island contains 1.67 million (95% CI: 1.47-1.88) burrow entrances and 1.12 million (0.959-1.28) breeding pairs, equating to a total of 5.31 million (95% CI: 3.98-6.77) juveniles, pre-breeders and adults associated with the island. Assuming the harvest intensity on the surveyed manu 0.18% (0.16-0.21) was similar elsewhere on the unsurveyed but harvested region of the island, we estimated that ofthe 807000 (712000-901 000) fledging chicks on the island, 137000 (105000-173000) are harvested each year. These findings highlight the importance of the island both in terms of total Sooty Shearwater population in New Zealand and to the Rakiura Maori who harvest the Titi

Development and Use of Color Standards for Egg Yolks

Abstract FOR SOME YEARS poultry scientists have been engaged in nutrition studies on the effects of various grains fed to laying birds. Some of these studies have been concerned with the effect of grain or combinations of grains in determining yolk color. The desired yolk color for home use varies with the geographical location and customs of the people, but in general a fairly light color is preferred. On the other hand users of yolks such as noodle manufacturers and cake bakers pay premium prices for dark colored yolk. It is therefore more profitable for the egg producer if he accurately maintains the yolk color within the desired range for his particular market. Since verbal color descriptions are ambiguous it is necessary to have standards for egg yolk colors in recording and communicating the results of poultry diet research. The only color chart available in Canada was one which had been

The Physicist's Guide to the Orchestra

An experimental study of strings, woodwinds (organ pipe, flute, clarinet, saxophone and recorder), and the voice was undertaken to illustrate the basic principles of sound production in music instruments. The setup used is simple and consists of common laboratory equipment. Although the canonical examples (standing wave on a string, in an open and closed pipe) are easily reproduced, they fail to explain the majority of the measurements. The reasons for these deviations are outlined and discussed.Comment: 11 pages, 10 figures (jpg files). Submitted to European Journal of Physic

Anomalous superfluid density in quantum critical superconductors

When a second-order magnetic phase transition is tuned to zero temperature by a non-thermal parameter, quantum fluctuations are critically enhanced, often leading to the emergence of unconventional superconductivity. In these `quantum critical' superconductors it has been widely reported that the normal-state properties above the superconducting transition temperature $T_c$ often exhibit anomalous non-Fermi liquid behaviors and enhanced electron correlations. However, the effect of these strong critical fluctuations on the superconducting condensate below $T_c$ is less well established. Here we report measurements of the magnetic penetration depth in heavy-fermion, iron-pnictide, and organic superconductors located close to antiferromagnetic quantum critical points showing that the superfluid density in these nodal superconductors universally exhibit, unlike the expected $T$-linear dependence, an anomalous 3/2 power-law temperature dependence over a wide temperature range. We propose that this non-integer power-law can be explained if a strong renormalization of effective Fermi velocity due to quantum fluctuations occurs only for momenta $\bm{k}$ close to the nodes in the superconducting energy gap $\Delta(\bm{k})$. We suggest that such `nodal criticality' may have an impact on low-energy properties of quantum critical superconductors.Comment: Main text (5 pages, 3 figures) + Supporting Information (3 pages, 4 figures). Published in PNAS Early Edition on February 12, 201

Plasmonic Resonances and Electromagnetic Forces Between Coupled Silver Nanowires

We compute the electromagnetic response and corresponding forces between two silver nanowires. The wires are illuminated by a plane wave which has the electric field vector perpendicular to the axis of the wires, insuring that plasmonic resonances can be excited. We consider a nontrivial square cross section geometry that has dimensions on the order of $0.1 \lambda$, where $\lambda$ is the wavelength of the incident electromagnetic field. We find that due to the plasmonic resonance, there occurs great enhancement of the direct and mutual electromagnetic forces that are exerted on the nanowires. The Lippman-Schwinger volume integral equation is implemented to obtain solutions to Maxwell's equations for various $\lambda$ and separation distances between wires. The forces are computed using Maxwell's stress tensor and numerical results are shown for both on and off resonant conditions

de Haas-van Alphen effect investigation of the electronic structure of Al substituted MgB_2

We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al doped crystals of MgB$_2$. We have measured crystals with $\sim 7.5$% Al which have a $T_c$ of 33.6 K, ($\sim 14$% lower than pure MgB$_2$). dHvA frequencies for the $\sigma$ tube orbits in the doped samples are lower than in pure MgB$_2$, implying a $16\pm2$ reduction in the number of holes in this sheet of Fermi surface. The mass of the quasiparticles on the larger $\sigma$ orbit is lighter than the pure case indicating a reduction in electron-phonon coupling constant $\lambda$. These observations are compared with band structure calculations, and found to be in excellent agreement.Comment: 4 pages with figure

Investigating the Magnetospheres of Rapidly Rotating B-type Stars

Recent spectropolarimetric surveys of bright, hot stars have found that ~10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (~kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA's XMM-Newton space telescope, we observed 5 rapidly rotating B-type stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.Comment: IAUS Conference Proceeding

Transverse Magnetoresistance of GaAs/AlGaAs Heterojunctions in the Presence of Parallel Magnetic Fields

We have calculated the resistivity of a GaAs\slash AlGaAs heterojunction in the presence of both an in--plane magnetic field and a weak perpendicular component using a semiclassical Boltzmann transport theory. These calculations take into account fully the distortion of the Fermi contour which is induced by the parallel magnetic field. The scattering of electrons is assumed to be due to remote ionized impurities. A positive magnetoresistance is found as a function of the perpendicular component, in good qualitative agreement with experimental observations. The main source of this effect is the strong variation of the electronic scattering rate around the Fermi contour which is associated with the variation in the mean distance of the electronic states from the remote impurities. The magnitude of the positive magnetoresistance is strongly correlated with the residual acceptor impurity density in the GaAs layer. The carrier lifetime anisotropy also leads to an observable anisotropy in the resistivity with respect to the angle between the current and the direction of the in--plane magnetic field.Comment: uuencoded file containing a 26 page RevTex file and 14 postscript figures. Submitted to Phys. Rev.