First experimental results of very high accuracy centroiding measurements for the neat astrometric mission

NEAT is an astrometric mission proposed to ESA with the objectives of detecting Earth-like exoplanets in the habitable zone of nearby solar-type stars. NEAT requires the capability to measure stellar centroids at the precision of 5e-6 pixel. Current state-of-the-art methods for centroid estimation have reached a precision of about 2e-5 pixel at two times Nyquist sampling, this was shown at the JPL by the VESTA experiment. A metrology system was used to calibrate intra and inter pixel quantum efficiency variations in order to correct pixelation errors. The European part of the NEAT consortium is building a testbed in vacuum in order to achieve 5e-6 pixel precision for the centroid estimation. The goal is to provide a proof of concept for the precision requirement of the NEAT spacecraft. In this paper we present the metrology and the pseudo stellar sources sub-systems, we present a performance model and an error budget of the experiment and we report the present status of the demonstration. Finally we also present our first results: the experiment had its first light in July 2013 and a first set of data was taken in air. The analysis of this first set of data showed that we can already measure the pixel positions with an accuracy of about 1e-4 pixel.Comment: SPIE conference proceeding

Multipole Ordering and Fluctuations in f-Electron Systems

We investigate effects of multipole moments in f-electron systems both from phenomenological and microscopic viewpoints. First, we discuss significant effects of octupole moment on the magnetic susceptibility in a paramagnetic phase. It is found that even within mean-field approximation, the magnetic susceptibility deviates from the Curie-Weiss law due to interactions between dipole and octupole moments. Next, we proceed to a microscopic theory for multipole ordering on the basis of a j-j coupling scheme. After brief explanation of a method to derive multipole interactions from the $f$-electron model, we discuss several multipole ordered phases depending on lattice structure. Finally, we show our new development of the microscopic approach to the evaluation of multipole response functions. We apply fluctuation exchange approximation to the f-electron model, and evaluate multipole response functions.Comment: 7 pages, 4 figures, Proceedings of ASR-WYP-200

Structure and far-infrared edge modes of quantum antidots at zero magnetic field

We have investigated edge modes of different multipolarity sustained by quantum antidots at zero magnetic field. The ground state of the antidot is described within a local density functional formalism. Two sum rules, which are exact within this formalism, have been derived and used to evaluate the energy of edge collective modes as a function of the surface density and the size of the antidot.Comment: Typeset using Revtex, 8 pages and 6 Postscript figure

Giant ambipolar Rashba effect in a semiconductor: BiTeI

We observe a giant spin-orbit splitting in bulk and surface states of the non-centrosymmetric semiconductor BiTeI. We show that the Fermi level can be placed in the valence or in the conduction band by controlling the surface termination. In both cases it intersects spin-polarized bands, in the corresponding surface depletion and accumulation layers. The momentum splitting of these bands is not affected by adsorbate-induced changes in the surface potential. These findings demonstrate that two properties crucial for enabling semiconductor-based spin electronics -- a large, robust spin splitting and ambipolar conduction -- are present in this material.Comment: 4 pages, 3 figure

A detector interferometric calibration experiment for high precision astrometry

Context: Exoplanet science has made staggering progress in the last two decades, due to the relentless exploration of new detection methods and refinement of existing ones. Yet astrometry offers a unique and untapped potential of discovery of habitable-zone low-mass planets around all the solar-like stars of the solar neighborhood. To fulfill this goal, astrometry must be paired with high precision calibration of the detector. Aims: We present a way to calibrate a detector for high accuracy astrometry. An experimental testbed combining an astrometric simulator and an interferometric calibration system is used to validate both the hardware needed for the calibration and the signal processing methods. The objective is an accuracy of 5e-6 pixel on the location of a Nyquist sampled polychromatic point spread function. Methods: The interferometric calibration system produced modulated Young fringes on the detector. The Young fringes were parametrized as products of time and space dependent functions, based on various pixel parameters. The minimization of func- tion parameters was done iteratively, until convergence was obtained, revealing the pixel information needed for the calibration of astrometric measurements. Results: The calibration system yielded the pixel positions to an accuracy estimated at 4e-4 pixel. After including the pixel position information, an astrometric accuracy of 6e-5 pixel was obtained, for a PSF motion over more than five pixels. In the static mode (small jitter motion of less than 1e-3 pixel), a photon noise limited precision of 3e-5 pixel was reached

A Western-style dietary pattern is associated with cerebrospinal fluid biomarker levels for preclinical Alzheimer's disease-A population-based cross-sectional study among 70-year-olds

Background: Diet may be a modifiable factor for reducing the risk of Alzheimer's disease (AD). Western-style dietary patterns are considered to increase the risk, whereas Mediterranean-style dietary patterns are considered to reduce the risk. An association between diet and AD-related biomarkers have been suggested, but studies are limited. Aim: To investigate potential relations between dietary patterns and cerebrospinal fluid (CSF) biomarkers for AD among dementia-free older adults. Methods: Data were derived from the population-based Gothenburg H70 Birth Cohort Studies, Sweden. A total of 269 dementia-free 70-year-olds with dietary and cerebrospinal fluid (CSF) amyloid beta (Aβ42 and Aβ40), total tau (t-tau), and phosphorylated tau (p-tau) data were investigated. Dietary intake was determined by the diet history method, and four dietary patterns were derived by principal component analysis. A Western dietary pattern, a Mediterranean/prudent dietary pattern, a high-protein and alcohol pattern, and a high-total and saturated fat pattern. Logistic regression models, with CSF biomarker pathology (yes/no) as dependent variables, and linear regression models with continuous CSF biomarker levels as dependent variables were performed. The analyses were adjusted for sex, energy intake, body mass index (BMI), educational level, and physical activity level. Results: The odds ratio for having total tau pathology (odds ratio [OR] 1.43; 95% confidence interval [CI] 1.02 to 2.01) and preclinical AD (Aβ42 and tau pathology; OR 1.79; 95% CI 1.03 to 3.10) was higher among those with a higher adherence to a Western dietary pattern. There were no other associations between the dietary patterns and CSF biomarkers that remained significant in both unadjusted and adjusted models. Discussion: Our findings suggest that higher adherence to a Western dietary pattern may be associated with pathological levels of AD biomarkers in the preclinical phase of AD. These findings can be added to the increasing amount of evidence linking diet with AD and may be useful for future intervention studies investigating dietary intake in relation to AD

Sex differences in CSF biomarkers for neurodegeneration and blood-brain barrier integrity.

INTRODUCTION: As cerebrospinal fluid (CSF) neurofilament light protein (NfL) and the CSF/serum albumin ratio (QAlb) are used in the clinical routine, the impact of demographic factors on these biomarkers is important to understand. METHODS: Participants were derived from two Swedish samples: the population‐based H70 Study (n = 308, age 70) and a clinical routine cohort (CSF NfL, n = 8995, QAlb, n = 39252, age 0 to 95). In the population‐based study, QAlb and NfL were examined in relation to sex, cardiovascular risk factors, and cerebral white matter lesions (WMLs). In the clinical cohort, QAlb and NfL sex differences were tested in relation to age. RESULTS: Men had higher QAlb and NfL concentrations and had higher QAlb and NfL concentrations from adolescence throughout life. NfL was not related to WML, but QAlb correlated positively with WMLs. DISCUSSION: The CSF NfL sex difference could not be explained by vascular pathology. Future studies should consider using different reference limits for men and women