A new experimental procedure for characterizing quantum effects in small magnetic particle systems

A new experimental procedure is discussed, which aims at separating thermal from quantum behavior independently of the energy barrier distribution in small particle systems. Magnetization relaxation data measured between 60 mK and 5 K on a sample of nanoparticles is presented. The comparison between experimental data and numerical calculations shows a clear departure from thermal dynamics for our sample, which was not obvious without using the new procedure presented here.Comment: LaTeX source, 6 pages, 5 PostScript figure

Market dynamics associated with credit ratings: a literature review.

Credit ratings produced by the major credit rating agencies (CRAs) aim to measure the creditworthiness, or more specifically the relative creditworthiness of companies, i.e. their ability to meet their debt servicing obligations. In principle, the rating process focuses on the fundamental long-term credit strength of a company. It is typically based on both public and private information, except for unsolicited ratings, which focus only on public information. The basic rationale for using ratings is to achieve information economies of scale and solve principal-agent problems. Partly for the same reasons, the role of credit ratings has expanded significantly over time. Regulators, banks and bondholders, pension fund trustees and other fiduciary agents have increasingly used ratings-based criteria to constrain behaviour. As a result, the influence of the opinions of CRAs on markets appears to have grown considerably in recent years. One aspect of this development is its potential impact on market dynamics (i.e. the timing and path of asset price adjustments, credit spreads, etc.), either directly, as a consequence of the information content of ratings themselves, or indirectly, as a consequence of the “hardwiring” of ratings into regulatory rules, fund management mandates, bond covenants, etc. When considering the impact of ratings and rating changes, two conclusions are worth highlighting. – First, ratings correlate moderately well with observed credit spreads, and rating changes with changes in spreads. However, other factors, such as liquidity, taxation and historical volatility clearly also enter into the determination of spreads. Recent research suggests that reactions to rating changes may also extend beyond the immediately-affected company to its peers, and from bond to equity prices. Furthermore, this price reaction to rating changes seems to be asymmetrical, i.e. more pronounced for downgrades than for upgrades, and may be more significant for equity prices than for bond prices. – Second, the hardwiring of regulatory and market rules, bond covenants, investment guidelines, etc., to ratings may influence market dynamics, and potentially lead to or magnify threshold effects. The more that different market participants adopt identical ratings-linked rules, or are subject to similar ratings-linked regulations, the more “spiky” the reaction to a credit event is likely to be. This reaction may include, in some cases, the emergence of severe liquidity pressures. Efforts have recently been made, notably with support from the rating agencies themselves, to encourage a more systematic disclosure of rating triggers and to renegotiate and smooth the possibly more destabilising forms of rating triggers. However, the lack of a clear disclosure regime makes it difficult to assess how far this process has evolved. Questions also remain as to the extent to which ratings-based criteria introduce a fundamentally new element into market behaviour, or, conversely, the extent to which they are simply a va riant of more traditional contractual covenants. Rating agencies strive to provide credit assessments that remain broadly stable through the course of the business cycle (rating “through the cycle”). Agencies and other analysts frequently contrast the fundamental credit analysis on which ratings are based with market sentiment — measured for example by bond spreads — which is arguably subject to more short-term influences. Agencies are adamant that they do not directly incorporate market sentiment into ratings (although they may use market prices as a diagnostic tool). On the contrary, they make every effort to exclude transient market sentiment. However, as reliance on ratings grows, CRAs are being increasingly expected to satisfy a widening range of constituencies, with different, and even sometimes conflicting, interests: issuers and “traditional” asset managers will look for more than a simple statement of near-term probability of loss, and will stress the need for ratings to exhibit some degree of stability over time. On the other hand, mark-to-market traders, active investors and risk managers may seek more frequent indications of credit changes. Hence, in the wake of major bankruptcies with heightened credit stress, rating agencies have been under considerable pressure to provide higher-frequency readings of credit status, without loss of quality. So far, they have responded to this challenge largely by adding more products to their traditional range, but also through modifications in the rating process. The rating process and the range of products offered by rating agencies have thus evolved over time, with, for instance, an increasing emphasis on the analysis of liquidity risks, a new focus on the hidden liabilities of companies and an increased use of market-based tools. It is too early, however, to judge whether these changes should simply be regarded as a refinement of the agencies’ traditional methodology or whether they suggest a more fundamental shift in the approach to credit risk measurement. For the same reason, it is not possible to draw any firm conclusions about changes in the effects of credit ratings on market dynamics.

Physical occupational exposures and health expectancies in a French occupational cohort.

OBJECTIVES: To examine the relationships of strenuous and hazardous working conditions and rotating shifts that involve night working with life expectancy in good perceived health and life expectancy without chronic disease. METHODS: The sample contained male gas and electricity workers from the French GAZEL cohort (n=13 393). Six measures of physical working conditions were examined: Self-reports from 1989 and 1990 of ergonomic strain, physical danger, rotating shifts that involve night working and perceived physical strain; company records of workplace injuries and a job-exposure matrix of chemical exposures. Partial healthy life expectancies (age 50-75) relating to (1) self-rated health and (2) chronic health conditions, obtained from annual questionnaires (1989-2014) and company records, were estimated using multistate life tables. The analyses were adjusted for social class and occupational grade. RESULTS: Participants with physically strenuous jobs and who had experienced industrial injuries had shorter partial life expectancy. More physically demanding and dangerous work was associated with fewer years of life spent in good self-rated health and without chronic conditions, with the exception of shift work including nights, where the gradient was reversed. CONCLUSIONS: Strenuous and hazardous work may contribute to lost years of good health in later life, which has implications for individuals' quality of life as well as healthcare use and labour market participation

SearchCal: a Virtual Observatory tool for searching calibrators in optical long baseline interferometry. I: The bright object case

In long baseline interferometry, the raw fringe contrast must be calibrated to obtain the true visibility and then those observables that can be interpreted in terms of astrophysical parameters. The selection of suitable calibration stars is crucial for obtaining the ultimate precision of interferometric instruments like the VLTI. We have developed software SearchCal that builds an evolutive catalog of stars suitable as calibrators within any given user-defined angular distance and magnitude around the scientific target. We present the first version of SearchCal dedicated to the bright-object case V<=10; K<=5). Star catalogs available at the CDS are consulted via web requests. They provide all the useful information for selecting of calibrators. Missing photometries are computed with an accuracy of 0.1 mag and the missing angular diameters are calculated with a precision better than 10%. For each star the squared visibility is computed by taking the wavelength and the maximum baseline of the foreseen observation into account.} SearchCal is integrated into ASPRO, the interferometric observing preparation software developed by the JMMC, available at the address: http://mariotti.fr

Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. II. Concept validation with ZELDA on VLT/SPHERE

Warm or massive gas giant planets, brown dwarfs, and debris disks around nearby stars are now routinely observed by dedicated high-contrast imaging instruments on large, ground-based observatories. These facilities include extreme adaptive optics (ExAO) and state-of-the-art coronagraphy to achieve unprecedented sensitivities for exoplanet detection and spectral characterization. However, differential aberrations between the ExAO sensing path and the science path represent a critical limitation for the detection of giant planets with a contrast lower than a few $10^{-6}$ at very small separations (<0.3\as) from their host star. In our previous work, we proposed a wavefront sensor based on Zernike phase contrast methods to circumvent this issue and measure these quasi-static aberrations at a nanometric level. We present the design, manufacturing and testing of ZELDA, a prototype that was installed on VLT/SPHERE during its reintegration in Chile. Using the internal light source of the instrument, we performed measurements in the presence of Zernike or Fourier modes introduced with the deformable mirror. Our experimental and simulation results are consistent, confirming the ability of our sensor to measure small aberrations (<50 nm rms) with nanometric accuracy. We then corrected the long-lived non-common path aberrations in SPHERE based on ZELDA measurements. We estimated a contrast gain of 10 in the coronagraphic image at 0.2\as, reaching the raw contrast limit set by the coronagraph in the instrument. The simplicity of the design and its phase reconstruction algorithm makes ZELDA an excellent candidate for the on-line measurements of quasi-static aberrations during the observations. The implementation of a ZELDA-based sensing path on the current and future facilities (ELTs, future space missions) could ease the observation of the cold gaseous or massive rocky planets around nearby stars.Comment: 13 pages, 12 figures, A&A accepted on June 3rd, 2016. v2 after language editin

Searching for faint companions with VLTI/PIONIER. I. Method and first results

Context. A new four-telescope interferometric instrument called PIONIER has recently been installed at VLTI. It provides improved imaging capabilities together with high precision. Aims. We search for low-mass companions around a few bright stars using different strategies, and determine the dynamic range currently reachable with PIONIER. Methods. Our method is based on the closure phase, which is the most robust interferometric quantity when searching for faint companions. We computed the chi^2 goodness of fit for a series of binary star models at different positions and with various flux ratios. The resulting chi^2 cube was used to identify the best-fit binary model and evaluate its significance, or to determine upper limits on the companion flux in case of non detections. Results. No companion is found around Fomalhaut, tau Cet and Regulus. The median upper limits at 3 sigma on the companion flux ratio are respectively of 2.3e-3 (in 4 h), 3.5e-3 (in 3 h) and 5.4e-3 (in 1.5 h) on the search region extending from 5 to 100 mas. Our observations confirm that the previously detected near-infrared excess emissions around Fomalhaut and tau Cet are not related to a low-mass companion, and instead come from an extended source such as an exozodiacal disk. In the case of del Aqr, in 30 min of observation, we obtain the first direct detection of a previously known companion, at an angular distance of about 40 mas and with a flux ratio of 2.05e-2 \pm 0.16e-2. Due to the limited u,v plane coverage, its position can, however, not be unambiguously determined. Conclusions. After only a few months of operation, PIONIER has already achieved one of the best dynamic ranges world-wide for multi-aperture interferometers. A dynamic range up to about 1:500 is demonstrated, but significant improvements are still required to reach the ultimate goal of directly detecting hot giant extrasolar planets.Comment: 11 pages, 6 figures, accepted for publication in A&

Occupational and educational inequalities in exit from employment at older ages: evidence from seven prospective cohorts

OBJECTIVES: Past studies have identified socioeconomic inequalities in the timing and route of labour market exit at older ages. However, few studies have compared these trends cross-nationally and existing evidence focuses on specific institutional outcomes (such as disability pension and sickness absence) in Nordic countries. We examined differences by education level and occupational grade in the risks of work exit and health-related work exit. METHODS: Prospective longitudinal data were drawn from seven studies (n=99 164). Participants were in paid work at least once around age 50. Labour market exit was derived based on reductions in working hours, changes in self-reported employment status or from administrative records. Health-related exit was ascertained by receipt of health-related benefit or pension or from the reported reason for stopping work. Cox regression models were estimated for each study, adjusted for baseline self-rated health and birth cohort. RESULTS: There were 50 003 work exits during follow-up, of which an average of 14% (range 2–32%) were health related. Low level education and low occupational grade were associated with increased risks of health-related exit in most studies. Low level education and occupational grade were also associated with an increased risk of any exit from work, although with less consistency across studies. CONCLUSIONS: Workers with low socioeconomic position have an increased risk of health-related exit from employment. Policies that extend working life may disadvantage such workers disproportionally, especially where institutional support for those exiting due to poor health is minimal

Milli-arcsecond astrophysics with VSI, the VLTI spectro-imager in the ELT era

Nowadays, compact sources like surfaces of nearby stars, circumstellar environments of stars from early stages to the most evolved ones and surroundings of active galactic nuclei can be investigated at milli-arcsecond scales only with the VLT in its interferometric mode. We propose a spectro-imager, named VSI (VLTI spectro-imager), which is capable to probe these sources both over spatial and spectral scales in the near-infrared domain. This instrument will provide information complementary to what is obtained at the same time with ALMA at different wavelengths and the extreme large telescopes.Comment: 8 pages. To be published in the proceedings of the ESO workshop "Science with the VLT in the ELT Era", held in Garching (Germany) on 8-12 October 2007, A. Moorwood edito

Work Disability among Employees with Diabetes: Latent Class Analysis of Risk Factors in Three Prospective Cohort Studies

BACKGROUND: Studies of work disability in diabetes have examined diabetes as a homogeneous disease. We sought to identify subgroups among persons with diabetes based on potential risk factors for work disability. METHODS: Participants were 2,445 employees with diabetes from three prospective cohorts (the Finnish Public Sector study, the GAZEL study, and the Whitehall II study). Work disability was ascertained via linkage to registers of sickness absence and disability pensions during a follow-up of 4 years. Study-specific latent class analysis was used to identify subgroups according to prevalent comorbid disease and health-risk behaviours. Study-specific associations with work disability at follow-up were pooled using fixed-effects meta-analysis. RESULTS: Separate latent class analyses for men and women in each cohort supported a two-class solution with one subgroup (total n = 1,086; 44.4%) having high prevalence of chronic somatic diseases, psychological symptoms, obesity, physical inactivity and abstinence from alcohol and the other subgroup (total n = 1,359; 55.6%) low prevalence of these factors. In the adjusted meta-analyses, participants in the 'high-risk' group had more work disability days (pooled rate ratio = 1.66, 95% CI 1.38-1.99) and more work disability episodes (pooled rate ratio = 1.33, 95% CI 1.21-1.46). These associations were similar in men and women, younger and older participants, and across occupational groups. CONCLUSIONS: Diabetes is not a homogeneous disease in terms of work disability risk. Approximately half of people with diabetes are assigned to a subgroup characterised by clustering of comorbid health conditions, obesity, physical inactivity, abstinence of alcohol, and associated high risk of work disability; the other half to a subgroup characterised by a more favourable risk profile

VSI: the VLTI spectro-imager

The VLTI Spectro Imager (VSI) was proposed as a second-generation instrument of the Very Large Telescope Interferometer providing the ESO community with spectrally-resolved, near-infrared images at angular resolutions down to 1.1 milliarcsecond and spectral resolutions up to R=12000. Targets as faint as K=13 will be imaged without requiring a brighter nearby reference object. The unique combination of high-dynamic-range imaging at high angular resolution and high spectral resolution enables a scientific program which serves a broad user community and at the same time provides the opportunity for breakthroughs in many areas of astrophysic including: probing the initial conditions for planet formation in the AU-scale environments of young stars; imaging convective cells and other phenomena on the surfaces of stars; mapping the chemical and physical environments of evolved stars, stellar remnants, and stellar winds; and disentangling the central regions of active galactic nuclei and supermassive black holes. VSI will provide these new capabilities using technologies which have been extensively tested in the past and VSI requires little in terms of new infrastructure on the VLTI. At the same time, VSI will be able to make maximum use of new infrastructure as it becomes available; for example, by combining 4, 6 and eventually 8 telescopes, enabling rapid imaging through the measurement of up to 28 visibilities in every wavelength channel within a few minutes. The current studies are focused on a 4-telescope version with an upgrade to a 6-telescope one. The instrument contains its own fringe tracker and tip-tilt control in order to reduce the constraints on the VLTI infrastructure and maximize the scientific return.Comment: 12 pages, to be published in Proc. SPIE conference 7013 "Optical and Infrared Interferometry", Schoeller, Danchi, and Delplancke, F. (eds.). See also http://vsi.obs.ujf-grenoble.f