Magneto-resistance in a lithography defined single constrained domain wall spin valve

We have measured domain wall magnetoresistance in a single lithographically constrained domain wall. An H-shaped Ni nano-bridge was fabricated by e-beam lithography with the two sides being single magnetic do- mains showing independent magnetic switching. The connection between the sides constraining the domain wall when the sides line up anti-parallel. The magneto-resistance curve clearly identifies the magnetic con- figurations that are expected from a spin valve-like structure. The value of the magneto-resistance at room temperature is around 0.1% or 0.4 ­. This value is shown to be in agreement with a theoretical formulation based on spin accumulation. Micromagnetic simulations show it is possible to reduce the size of the domain wall further by shortening the length of the bridge

A General Precipitation-Limited L_X-T-R Relation Among Early-Type Galaxies

The relation between X-ray luminosity (L_X) and ambient gas temperature (T) among massive galactic systems is an important cornerstone of both observational cosmology and galaxy-evolution modeling. In the most massive galaxy clusters, the relation is determined primarily by cosmological structure formation. In less massive systems, it primarily reflects the feedback response to radiative cooling of circumgalactic gas. Here we present a simple but powerful model for the L_X-T relation as a function of physical aperture R within which those measurements are made. The model is based on the precipitation framework for AGN feedback and assumes that the circumgalactic medium is precipitation-regulated at small radii and limited by cosmological structure formation at large radii. We compare this model with many different data sets and show that it successfully reproduces the slope and upper envelope of the L_X-T-R relation over the temperature range from ~0.2 keV through >10 keV. Our findings strongly suggest that the feedback mechanisms responsible for regulating star formation in individual massive galaxies have much in common with the precipitation-triggered feedback that appears to regulate galaxy-cluster cores.Comment: Submitted to ApJ, 9 pages, 3 figures (v2 fixes a few small typos

A New Approximate Min-Max Theorem with Applications in Cryptography

We propose a novel proof technique that can be applied to attack a broad class of problems in computational complexity, when switching the order of universal and existential quantifiers is helpful. Our approach combines the standard min-max theorem and convex approximation techniques, offering quantitative improvements over the standard way of using min-max theorems as well as more concise and elegant proofs

Quantitative assessment of prefrontal cortex in humans relative to nonhuman primates

Significance A longstanding controversy in neuroscience pertains to differences in human prefrontal cortex (PFC) compared with other primate species; specifically, is human PFC disproportionately large? Distinctively human behavioral capacities related to higher cognition and affect presumably arose from evolutionary modifications since humans and great apes diverged from a common ancestor about 6–8 Mya. Accurate determination of regional differences in the amount of cortical gray and subcortical white matter content in humans, great apes, and Old World monkeys can further our understanding of the link between structure and function of the human brain. Using tissue volume analyses, we show a disproportionately large amount of gray and white matter corresponding to PFC in humans compared with nonhuman primates.</jats:p

Defect related switching field reduction in small magnetic particle arrays

An array of 42 mum square, 3 mum thick garnet particles has been studied. The strong crystalline uniaxial anisotropy of these particles results in the stable remanent state being single domain with magnetization parallel to the film normal. Magneto-optic measurements of individual particles provide distribution statistics for the easy-axis switching field H-sw, and the in-plane hard-axis effective anisotropy field, H-eff, which induces the formation of a metastable stripe domain structure. Both H-sw and H-eff are much smaller than the crystalline anisotropy field. Micromagnetic simulations show that the small H-sw cannot be attributed to shape anisotropy, but is consistent with smooth, localized reductions in the crystalline anisotropy caused by defects in either the particles or the substrate

A Very Hot, High Redshift Cluster of Galaxies: More Trouble for Omega_0 = 1

We have observed the most distant (z=0.829) cluster of galaxies in the Einstein Extended Medium Sensitivity Survey, with the ASCA and ROSAT satellites. We find an X-ray temperature of 12.3 +3.1/-2.2 keV for this cluster, and the ROSAT map reveals significant substructure. The high temperature of MS1054-0321 is consistent with both its approximate velocity dispersion, based on the redshifts of 12 cluster members we have obtained at the Keck and the Canada-France-Hawaii telescopes, and with its weak lensing signature. The X-ray temperature of this cluster implies a virial mass ~ 7.4 x 10^14 h^-1 solar masses, if the mean matter density in the universe equals the critical value, or larger if Omega_0 < 1. Finding such a hot, massive cluster in the EMSS is extremely improbable if clusters grew from Gaussian perturbations in an Omega_0 = 1 universe. Combining the assumptions that Omega_0 = 1 and that the intial perturbations were Gaussian with the observed X-ray temperature function at low redshift, we show that the probability of this cluster occurring in the volume sampled by the EMSS is less than a few times 10^{-5}. Nor is MS1054-0321 the only hot cluster at high redshift; the only two other $z > 0.5$ EMSS clusters already observed with ASCA also have temperatures exceeding 8 keV. Assuming again that the initial perturbations were Gaussian and Omega_0 = 1, we find that each one is improbable at the < 10^{-2} level. These observations, along with the fact that these luminosities and temperatures of the high-$z$ clusters all agree with the low-z L_X-T_X relation, argue strongly that Omega_0 < 1. Otherwise, the initial perturbations must be non-Gaussian, if these clusters' temperatures do indeed reflect their gravitational potentials.Comment: 20 pages, 4 figures, To appear in 1 Aug 1998 ApJ (heavily revised version of original preprint

No planet for HD 166435

The G0V star HD166435 has been observed by the fiber-fed spectrograph ELODIE as one of the targets in the large extra-solar planet survey that we are conducting at the Observatory of Haute-Provence. We detected coherent, low-amplitude, radial-velocity variations with a period of 3.7987days, suggesting a possible close-in planetary companion. Subsequently, we initiated a series of high-precision photometric observations to search for possible planetary transits and an additional series of CaII H and K observations to measure the level of surface magnetic activity and to look for possible rotational modulation. Surprisingly, we found the star to be photometrically variable and magnetically active. A detailed study of the phase stability of the radial-velocity signal revealed that the radial-velocity variability remains coherent only for durations of about 30days. Analysis of the time variation of the spectroscopic line profiles using line bisectors revealed a correlation between radial velocity and line-bisector orientation. All of these observations, along with a one-quarter cycle phase shift between the photometric and the radial-velocity variationss, are well explained by the presence of dark photospheric spots on HD166435. We conclude that the radial-velocity variations are not due to gravitational interaction with an orbiting planet but, instead, originate from line-profile changes stemming from star spots on the surface of the star. The quasi-coherence of the radial-velocity signal over more than two years, which allowed a fair fit with a binary model, makes the stability of this star unusual among other active stars. It suggests a stable magnetic field orientation where spots are always generated at about the same location on the surface of the star.Comment: 9 pages, 8 figures, Accepted for publication in A&

Direct observation of domain wall structures in curved permalloy wires containing an antinotch

The formation and field response of head-to-head domain walls in curved permalloy wires, fabricated to contain a single antinotch, have been investigated using Lorentz microscopy. High spatial resolution maps of the vector induction distribution in domain walls close to the antinotch have been derived and compared with micromagnetic simulations. In wires of 10 nm thickness the walls are typically of a modified asymmetric transverse wall type. Their response to applied fields tangential to the wire at the antinotch location was studied. The way the wall structure changes depends on whether the field moves the wall away from or further into the notch. Higher fields are needed and much more distorted wall structures are observed in the latter case, indicating that the antinotch acts as an energy barrier for the domain wal

Clinical Feasibility of Noninvasive Visualization of Lymphatic Flow with Principles of Spin Labeling MR Imaging: Implications for Lymphedema Assessment

Purpose To extend a commonly used noninvasive arterial spin labeling magnetic resonance (MR) imaging method for measuring blood flow to evaluate lymphatic flow. Materials and Methods All volunteers (n = 12) provided informed consent in accordance with institutional review board and HIPAA regulations. Quantitative relaxation time (T1 and T2) measurements were made in extracted human lymphatic fluid at 3.0 T. Guided by these parameters, an arterial spin labeling MR imaging approach was adapted to measure lymphatic flow (flow-alternating inversion-recovery lymphatic water labeling, 3 × 3 × 5 mm) in healthy subjects (n = 6; mean age, 30 years ± 1 [standard deviation]; recruitment duration, 2 months). Lymphatic flow velocity was quantified by performing spin labeling measurements as a function of postlabeling delay time and by measuring time to peak signal intensity in axillary lymph nodes. Clinical feasibility was evaluated in patients with stage II lymphedema (three women; age range, 43–64 years) and in control subjects with unilateral cuff-induced lymphatic stenosis (one woman, two men; age range, 31–35 years). Results Mean T1 and T2 relaxation times of lymphatic fluid at 3.0 T were 3100 msec ± 160 (range, 2930–3210 msec; median, 3200 msec) and 610 msec ± 12 (range, 598–618 msec; median, 610 msec), respectively. Healthy lymphatic flow (afferent vessel to axillary node) velocity was 0.61 cm/min ± 0.13 (n = 6). A reduction (P \u3c .005) in lymphatic flow velocity in the affected arms of patients and the affected arms of healthy subjects with manipulated cuff-induced flow reduction was observed. The ratio of unaffected to affected axilla lymphatic velocity (1.24 ± 0.18) was significantly (P \u3c .005) higher than the left-to-right ratio in healthy subjects (0.91 ± 0.18). Conclusion This work provides a foundation for clinical investigations whereby lymphedema etiogenesis and therapies may be interrogated without exogenous agents and with clinically available imaging equipment