965 research outputs found
A search for strong, ordered magnetic fields in Herbig Ae/Be stars
The origin of magnetic fields in intermediate-mass and high-mass stars is
fundamentally a mystery. Clues toward solving this basic astrophysical problem
can likely be found at the pre-main sequence (PMS) evolutionary stage. With
this work, we perform the largest and most sensitive search for magnetic fields
in pre-main sequence Herbig Ae/Be (HAeBe) stars. Sixty-eight observations of 50
HAeBe stars have been obtained in circularly polarised light using the FORS1
spectropolarimeter at the ESO VLT. An analysis of both Balmer and metallic
lines reveals the possible presence of weak longitudinal magnetic fields in
photospheric lines of two HAeBe stars, HD 101412 and BF Ori. The intensity of
the longitudinal fields detected in HD 101412 and BF Ori suggest that they
correspond to globally-ordered magnetic fields with surface intensities of
order 1 kG. Monte Carlo simulations of the longitudinal field measurements of
the undetected stars allow us to place an upper limits of about 300 G on the
general presence of aligned magnetic dipole magnetic fields, and of about 500 G
on perpendicular dipole fields. We find that the observed bulk incidence of
magnetic HAeBe stars in our sample is 8-12%, in good agreement with that of
magnetic main sequence stars of similar masses. We also find that the rms
longitudinal field intensity of magnetically-detected HAeBe stars is similar to
that of Ap stars and consistent with magnetic flux conservation during stellar
evolution. These results are all in agreement with the hypothesis that the
magnetic fields of main sequence Ap/Bp stars are fossils, which already exist
within the stars at the pre-main sequence stage. Finally, we explore the
ability of our new magnetic data to constrain magnetospheric accretion in
Herbig Ae/Be stars.Comment: Accepted by Monthly Notices of the Royal Astronomical Society, 2007
January 11. Received 2007 January 11; in original form 2006 August 18. The
paper contains 18 pages, 11 figures and 2 table
Investigation of the magnetic field characteristics of Herbig Ae/Be stars: Discovery of the pre-main sequence progenitors of the magnetic Ap/Bp stars
We are investigating the magnetic characteristics of pre-main sequence Herbig
Ae/Be stars, with the aim of (1) understanding the origin and evolution of
magnetism in intermediate-mass stars, and (2) exploring the influence of
magnetic fields on accretion, rotation and mass-loss at the early stages of
evolution of A, B and O stars. We have begun by conducting 2 large surveys of
Herbig Ae/Be stars, searching for direct evidence of photospheric magnetic
fields via the longitudinal Zeeman effect. From observations obtained using
FORS1 at the ESO-VLT and ESPaDOnS at the Canada-France-Hawaii Telescope, we
report the confirmed detection of magnetic fields in 4 pre-main sequence A- and
B-type stars, and the apparent (but as yet unconfirmed) detection of fields in
2 other such stars. We do not confirm the detection of magnetic fields in
several stars reported by other authors to be magnetic: HD 139614, HD 144432 or
HD 31649. One of the most evolved stars in the detected sample, HD 72106A,
shows clear evidence of strong photospheric chemical peculiarity, whereas many
of the other (less evolved) stars do not. The magnetic fields that we detect
appear to have surface intensities of order 1 kG, seem to be structured on
global scales, and appear in about 10% of the stars studied. Based on these
properties, these magnetic stars appear to be pre-main sequence progenitors of
the magnetic Ap/Bp stars.Comment: v2: Include comment regarding publication source To appear in the
proceedings of "Solar Polarisation 4", held in Boulder, USA, Sept. 200
Influence of the substrate-induced strain and irradiation disorder on the Peierls transition in TTF-TCNQ microdomains
The influence of the combined effects of substrate-induced strain, finite
size and electron irradiation-induced defects have been studied on individual
micron-sized domains of the organic charge transfer compound
tetrathiafulvalene-tetracyanoquinodimethane (TTF-TCNQ) by temperature-dependent
conductivity and current-voltage measurements. The individual domains have been
isolated by focused ion beam etching and electrically contacted by focused ion
and electron beam induced deposition of metallic contacts. The
temperature-dependent conductivity follows a variable range hopping behavior
which shows a crossover of the exponent as the Peierls transition is
approached. The low temperature behavior is analyzed within the segmented rod
model of Fogler, Teber and Shklowskii, as originally developed for a
charge-ordered quasi one-dimensional electron crystal. The results are compared
with data obtained on as-grown and electron irradiated epitaxial TTF-TCNQ thin
films of the two-domain type
Method for fabricating submicron silicide structures on silicon using a resistless electron beam lithography process
Abstract : A novel resistless lithography process using a conventional electron beam system is presented. Metallic lines with widths of less than 50 nm were produced on silicon substrates. The process is based on localized heating with a focused electron beam of thin platinum layers deposited on silicon. It is demonstrated that silicide formation occurs at the Pt-Si interface. By using a dilute solution of aqua regia, it is possible to obtain a sufficient difference in etch rates between exposed and unexposed regions of the platinum thin film to selectively remove only the unexposed areas
Validation of the Aura Microwave Limb Sounder HNOmeasurements
We assess the quality of the version 2.2 (v2.2) HNO3 measurements from the Microwave Limb Sounder (MLS) on the Earth Observing System Aura satellite. The MLS HNO3 product has been greatly improved over that in the previous version (v1.5), with smoother profiles, much more realistic behavior at the lowest retrieval levels, and correction of a high bias caused by an error in one of the spectroscopy files used in v1.5 processing. The v2.2 HNO3 data are scientifically useful over the range 215 to 3.2 hPa, with single-profile precision of ∼0.7 ppbv throughout. Vertical resolution is 3–4 km in the upper troposphere and lower stratosphere, degrading to ∼5 km in the middle and upper stratosphere. The impact of various sources of systematic uncertainty has been quantified through a comprehensive set of retrieval simulations. In aggregate, systematic uncertainties are estimated to induce in the v2.2 HNO3 measurements biases that vary with altitude between ±0.5 and ±2 ppbv and multiplicative errors of ±5–15% throughout the stratosphere, rising to ∼±30% at 215 hPa. Consistent with this uncertainty analysis, comparisons with correlative data sets show that relative to HNO3 measurements from ground-based, balloon-borne, and satellite instruments operating in both the infrared and microwave regions of the spectrum, MLS v2.2 HNO3 mixing ratios are uniformly low by 10–30% throughout most of the stratosphere. Comparisons with in situ measurements made from the DC-8 and WB-57 aircraft in the upper troposphere and lowermost stratosphere indicate that the MLS HNO3 values are low in this region as well, but are useful for scientific studies (with appropriate averaging)
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Dairy consumption and cardiometabolic diseases: systematic review and updated meta-analyses of prospective cohort studies
Purpose of Review Dairy products contain both beneficial and harmful nutrients in relation to cardiometabolic diseases. Here, we
provide the latest scientific evidence regarding the relationship between dairy products and cardiometabolic diseases by
reviewing the literature and updating meta-analyses of observational studies.
Recent Findings We updated our previous meta-analyses of cohort studies on type 2 diabetes, coronary heart disease (CHD), and
stroke with nine studies and confirmed previous results. Total dairy and low-fat dairy (per 200 g/d) were inversely associated with
a 3–4% lower risk of diabetes. Yogurt was non-linearly inversely associatedwith diabetes (RR = 0.86, 95%CI: 0.83–0.90 at 80 g/
d). Total dairy and milk were not associated with CHD (RR~1.0). An increment of 200 g of daily milk intake was associated with
an 8% lower risk of stroke.
Summary The latest scientific evidence confirmed neutral or beneficial associations between dairy products and risk of cardiometabolic
diseases
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Low-Multiplicity Burst Search At The Sudbury Neutrino Observatory
Results are reported from a search for low-multiplicity neutrino bursts in the Sudbury Neutrino Observatory. Such bursts could indicate the detection of a nearby core-collapse supernova explosion. The data were taken from Phase I (1999 November-2001 May), when the detector was filled with heavy water, and Phase II (2001 July-2003 August), when NaCl was added to the target. The search was a blind analysis in which the potential backgrounds were estimated and analysis cuts were developed to eliminate such backgrounds with 90% confidence before the data were examined. The search maintained a greater than 50% detection probability for standard supernovae occurring at a distance of up to 60 kpc for Phase I and up to 70 kpc for Phase II. No low-multiplicity bursts were observed during the data-taking period.Natural Sciences and Engineering Research Council, CanadaIndustry Canada, CanadaNational Research Council, CanadaNorthern Ontario Heritage Fund, CanadaAtomic Energy of Canada, Ltd., CanadaOntario Power Generation, CanadaHigh Performance Computing Virtual Laboratory, CanadaCanada Foundation for Innovation, CanadaCanada Research Chairs, CanadaDepartment of Energy, USNational Energy Research Scientific Computing Center, USAlfred P. Sloan Foundation, USScience and Technology Facilities Council, UKFundacao para a Ciencia e a Technologia, PortugalAstronom
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Searches For High-Frequency Variations In The B-8 Solar Neutrino Flux At The Sudbury Neutrino Observatory
We have performed three searches for high-frequency signals in the solar neutrino flux measured by the Sudbury Neutrino Observatory, motivated by the possibility that solar g-mode oscillations could affect the production or propagation of solar B-8 neutrinos. The first search looked for any significant peak in the frequency range 1-144 day(-1), with a sensitivity to sinusoidal signals with amplitudes of 12% or greater. The second search focused on regions in which g-mode signals have been claimed by experiments aboard the Solar and Heliospheric Observatory satellite, and was sensitive to signals with amplitudes of 10% or greater. The third search looked for extra power across the entire frequency band. No statistically significant signal was detected in any of the three searches.Natural Sciences and Engineering Research Council, CanadaIndustry Canada, CanadaNational Research Council, CanadaNorthern Ontario Heritage Fund, CanadaAtomic Energy of Canada, Ltd., CanadaOntario Power Generation, CanadaHigh Performance Computing Virtual Laboratory, CanadaCanada Foundation for InnovationDept. of Energy, USNational Energy Research Scientific Computing Center, USScience and Technologies Facilities Council, UKAstronom
Low Multiplicity Burst Search at the Sudbury Neutrino Observatory
Results are reported from a search for low-multiplicity neutrino bursts in
the Sudbury Neutrino Observatory (SNO). Such bursts could indicate detection of
a nearby core-collapse supernova explosion. The data were taken from Phase I
(November 1999 - May 2001), when the detector was filled with heavy water, and
Phase II (July 2001 - August 2003), when NaCl was added to the target. The
search was a blind analysis in which the potential backgrounds were estimated
and analysis cuts were developed to eliminate such backgrounds with 90%
confidence before the data were examined. The search maintained a greater than
50% detection probability for standard supernovae occurring at a distance of up
to 60 kpc for Phase I and up to 70 kpc for Phase II. No low-multiplicity bursts
were observed during the data-taking period.Comment: 11 pages, 4 figures, submitted to Ap
Combined Analysis of all Three Phases of Solar Neutrino Data from the Sudbury Neutrino Observatory
We report results from a combined analysis of solar neutrino data from all
phases of the Sudbury Neutrino Observatory. By exploiting particle
identification information obtained from the proportional counters installed
during the third phase, this analysis improved background rejection in that
phase of the experiment. The combined analysis resulted in a total flux of
active neutrino flavors from 8B decays in the Sun of (5.25 \pm
0.16(stat.)+0.11-0.13(syst.))\times10^6 cm^{-2}s^{-1}. A two-flavor neutrino
oscillation analysis yielded \Deltam^2_{21} = (5.6^{+1.9}_{-1.4})\times10^{-5}
eV^2 and tan^2{\theta}_{12}= 0.427^{+0.033}_{-0.029}. A three-flavor neutrino
oscillation analysis combining this result with results of all other solar
neutrino experiments and the KamLAND experiment yielded \Deltam^2_{21} =
(7.41^{+0.21}_{-0.19})\times10^{-5} eV^2, tan^2{\theta}_{12} =
0.446^{+0.030}_{-0.029}, and sin^2{\theta}_{13} =
(2.5^{+1.8}_{-1.5})\times10^{-2}. This implied an upper bound of
sin^2{\theta}_{13} < 0.053 at the 95% confidence level (C.L.)
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