11,429 research outputs found
Sound velocity and absorption measurements under high pressure using picosecond ultrasonics in diamond anvil cell. Application to the stability study of AlPdMn
We report an innovative high pressure method combining the diamond anvil cell
device with the technique of picosecond ultrasonics. Such an approach allows to
accurately measure sound velocity and attenuation of solids and liquids under
pressure of tens of GPa, overcoming all the drawbacks of traditional
techniques. The power of this new experimental technique is demonstrated in
studies of lattice dynamics, stability domain and relaxation process in a
metallic sample, a perfect single-grain AlPdMn quasicrystal, and rare gas, neon
and argon. Application to the study of defect-induced lattice stability in
AlPdMn up to 30 GPa is proposed. The present work has potential for application
in areas ranging from fundamental problems in physics of solid and liquid
state, which in turn could be beneficial for various other scientific fields as
Earth and planetary science or material research
Effect of picosecond strain pulses on thin layers of the ferromagnetic semiconductor (Ga,Mn)(As,P)
The effect of picosecond acoustic strain pulses (ps-ASP) on a thin layer of
(Ga,Mn)As co-doped with phosphorus was probed using magneto-optical Kerr effect
(MOKE). A transient MOKE signal followed by low amplitude oscillations was
evidenced, with a strong dependence on applied magnetic field, temperature and
ps-ASP amplitude. Careful interferometric measurement of the layer's thickness
variation induced by the ps-ASP allowed us to model very accurately the
resulting signal, and interpret it as the strain modulated reflectivity
(differing for probe polarizations), independently from dynamic
magnetization effects.Comment: 6 pages, 5 figure
How crucial is it to account for the antecedent moisture conditions in flood forecasting? Comparison of event-based and continuous approaches on 178 catchments
This paper compares event-based and continuous hydrological modelling approaches for real-time forecasting of river flows. Both approaches are compared using a lumped hydrologic model (whose structure includes a soil moisture accounting (SMA) store and a routing store) on a data set of 178 French catchments. The main focus of this study was to investigate the actual impact of soil moisture initial conditions on the performance of flood forecasting models and the possible compensations with updating techniques. The rainfall-runoff model assimilation technique we used does not impact the SMA component of the model but only its routing part. Tests were made by running the SMA store continuously or on event basis, everything else being equal. The results show that the continuous approach remains the reference to ensure good forecasting performances. We show, however, that the possibility to assimilate the last observed flow considerably reduces the differences in performance. Last, we present a robust alternative to initialize the SMA store where continuous approaches are impossible because of data availability problems
The evaluation of Education Maintenance Allowance Pilots: three years' evidence: a quantitative evaluation
This is the third report of the longitudinal quantitative evaluation of Education Maintenance Allowance (EMA) pilots and the first since the government announced that EMA is to be rolled out nationally from 2004. The evaluation was commissioned in 1999, by the Department for Education and Skills (DfES) from a consortium of research organisations, led by the Centre for Research in Social Policy (CRSP) and including the National Centre for Social Research, the Institute for Fiscal Studies (IFS) and the National Institute for Careers Education and Counselling (NICEC).
The statistical evaluation design is a longitudinal cohort study involving large random sample surveys of young people (and their parents) in 10 EMA pilot areas and eleven control areas. Two cohorts of young people were selected from Child Benefit records. The first cohort of young people left compulsory schooling in the summer of 1999 and they, and their parents, were interviewed between October 1999 and April 2000 (Year 12 interview). A second interview was carried out with these young people between October 2000 and April 2001 (Year 13 interview). The second cohort left compulsory education the following summer of 2000 and young people, and their parents, were first interviewed between October 2000 and April 2001.
The report uses both propensity score matching (PSM) and descriptive techniques, each of which brings their own particular strengths to the analysis
Image effects in transport at metal-molecule interfaces
We present a method for incorporating image-charge effects into the
description of charge transport through molecular devices. A simple model
allows us to calculate the adjustment of the transport levels, due to the
polarization of the electrodes as charge is added to and removed from the
molecule. For this, we use the charge distributions of the molecule between two
metal electrodes in several charge states, rather than in gas phase, as
obtained from a density-functional theory-based transport code. This enables us
to efficiently model level shifts and gap renormalization caused by
image-charge effects, which are essential for understanding molecular transport
experiments. We apply the method to benzene di-amine molecules and compare our
results with the standard approach based on gas phase charges. Finally, we give
a detailed account of the application of our approach to porphyrin-derivative
devices recently studied experimentally by Perrin et al. [Nat. Nanotechnol. 8,
282 (2013)], which demonstrates the importance of accounting for image-charge
effects when modeling transport through molecular junctions
Translocator protein in late stage Alzheimer\u27s disease and Dementia with Lewy bodies brains
OBJECTIVE: Increased translocator protein (TSPO), previously known as the peripheral benzodiazepine receptor (PBR), in glial cells of the brain has been used as a neuroinflammation marker in the early and middle stages of neurodegenerative diseases, such as Alzheimer\u27s disease (AD) and Dementia with Lewy Bodies (DLB). In this study, we investigated the changes in TSPO density with respect to late stage AD and DLB.
METHODS: TSPO density was measured in multiple regions of postmortem human brains in 20 different cases: seven late stage AD cases (Braak amyloid average: C; Braak tangle average: VI; Aged 74-88, mean: 83 ± 5 years), five DLB cases (Braak amyloid average: C; Braak tangle average: V; Aged 79-91, mean: 84 ± 4 years), and eight age-matched normal control cases (3 males, 5 females: aged 77-92 years; mean: 87 ± 6 years). Measurements were taken by quantitative autoradiography using [
RESULTS: No significant changes were found in TSPO density of the frontal cortex, striatum, thalamus, or red nucleus of the AD and DLB brains. A significant reduction in TSPO density was found in the substantia nigra (SN) of the AD and DLB brains compared to that of age-matched healthy controls.
INTERPRETATION: This distinct pattern of TSPO density change in late stage AD and DLB cases may imply the occurrence of microglia dystrophy in late stage neurodegeneration. Furthermore, TSPO may not only be a microglia activation marker in early stage AD and DLB, but TSPO may also be used to monitor microglia dysfunction in the late stage of these diseases
Characterizing Young Brown Dwarfs using Low Resolution Near-IR Spectra
We present near-infrared (1.0-2.4 micron) spectra confirming the youth and
cool effective temperatures of 6 brown dwarfs and low mass stars with
circumstellar disks toward the Chamaeleon II and Ophiuchus star forming
regions. The spectrum of one of our objects indicates that it has a spectral
type of ~L1, making it one of the latest spectral type young brown dwarfs
identified to date. Comparing spectra of young brown dwarfs, field dwarfs, and
giant stars, we define a 1.49-1.56 micron H2O index capable of determining
spectral type to within 1 sub-type, independent of gravity. We have also
defined an index based on the 1.14 micron sodium feature that is sensitive to
gravity, but only weakly dependent on spectral type for field dwarfs. Our 1.14
micron Na index can be used to distinguish young cluster members (t <~ 5 Myr)
from young field dwarfs, both of which may have the triangular H-band continuum
shape which persists for at least tens of Myr. Using effective temperatures
determined from the spectral types of our objects along with luminosities
derived from near and mid-infrared photometry, we place our objects on the H-R
diagram and overlay evolutionary models to estimate the masses and ages of our
young sources. Three of our sources have inferred ages (t ~= 10-30 Myr)
significantly older than the median stellar age of their parent clouds (1-3
Myr). For these three objects, we derive masses ~3 times greater than expected
for 1-3 Myr old brown dwarfs with the bolometric luminosities of our sources.
The large discrepancies in the inferred masses and ages determined using two
separate, yet reasonable methods, emphasize the need for caution when deriving
or exploiting brown dwarf mass and age estimates.Comment: 11 pages, Accepted to Ap
- …