207 research outputs found
Parameter estimation for alpha-fractional bridges
Let alpha,T>0. We study the asymptotic properties of a least squares
estimator for the parameter alpha of a fractional bridge defined as
dX_t=-alpha*X_t/(T-t)dt+dB_t, with t in [0,T) and where B is a fractional
Brownian motion of Hurst index H>1/2. Depending on the value of alpha, we prove
that we may have strong consistency or not as t tends to T. When we have
consistency, we obtain the rate of this convergence as well. Also, we compare
our results to the (known) case where B is replaced by a standard Brownian
motion W.Comment: 21 pages. To appear in the Festschrift in Honor of David Nualart, a
volume to be published by Springer in the Proceedings in Mathematics Serie
Spin transport in graphene nanostructures
Graphene is an interesting material for spintronics, showing long spin
relaxation lengths even at room temperature. For future spintronic devices it
is important to understand the behavior of the spins and the limitations for
spin transport in structures where the dimensions are smaller than the spin
relaxation length. However, the study of spin injection and transport in
graphene nanostructures is highly unexplored. Here we study the spin injection
and relaxation in nanostructured graphene with dimensions smaller than the spin
relaxation length. For graphene nanoislands, where the edge length to area
ratio is much higher than for standard devices, we show that enhanced spin-flip
processes at the edges do not seem to play a major role in the spin relaxation.
On the other hand, contact induced spin relaxation has a much more dramatic
effect for these low dimensional structures. By studying the nonlocal spin
transport through a graphene quantum dot we observe that the obtained values
for spin relaxation are dominated by the connecting graphene islands and not by
the quantum dot itself. Using a simple model we argue that future nonlocal
Hanle precession measurements can obtain a more significant value for the spin
relaxation time for the quantum dot by using high spin polarization contacts in
combination with low tunneling rates
Spin transport in high quality suspended graphene devices
We measure spin transport in high mobility suspended graphene (\mu ~ 10^5
cm^2/Vs), obtaining a (spin) diffusion coefficient of 0.1 m^2/s and giving a
lower bound on the spin relaxation time (\tau_s ~ 150 ps) and spin relaxation
length (\lambda_s=4.7 \mu m) for intrinsic graphene. We develop a theoretical
model considering the different graphene regions of our devices that explains
our experimental data.Comment: 22 pages, 6 figures; Nano Letters, Article ASAP (2012)
(http://pubs.acs.org/doi/abs/10.1021/nl301050a
Very low-calorie diet in candidates for bariatric surgery: change in body composition during rapid weight loss
OBJECTIVE: To analyze the changes in the body composition of morbidly obese patients induced by a very lowcalorie diet. METHODS: We evaluated 120 patients selected from a university hospital. Body composition was assessed before and after the diet provided during hospitalization, and changes in weight, body mass index, and neck, waist and hip circumferences were analyzed. Bioimpedance was used to obtain body fat and fat-free mass values. The data were categorized by gender, age, body mass index and diabetes diagnosis. RESULTS: The patients consumed the diet for 8 days. They presented a 5% weight loss (without significant difference among groups), which represented an 85% reduction in body fat. All changes in body circumference were statistically significant. There was greater weight loss and a greater reduction of body fat in men, but the elderly showed a significantly higher percentage of weight loss and greater reductions in body fat and fat-free mass. Greater reductions in body fat and fat-free mass were also observed in superobese patients. The changes in the diabetic participants did not differ significantly from those of the non-diabetic participants. CONCLUSIONS: The use of a VLCD before bariatric surgery led to a loss of weight at the expense of body fat over a short period, with no significant differences in the alteration of body composition according to gender, age, body mass index and diabetes status
New benzene absorption cross sections in the VUV, relevance for Titan’s upper atmosphere
This is a pre-print (pre-peer review) manuscript. It is moderately different from the accepted manuscript and from the published article. Citation of published article: Fernando J. Capalbo, Yves Bénilan, Nicolas Fray, Martin Schwell, Norbert Champion, Et-touhami Es-sebbar, Tommi T. Koskinen, Ivan Lehocki, Roger V. Yelle. Icarus, vol. 265, p. 95 - 109. February 2016. doi: 10.1016/j.icarus.2015.10.006.International audienceBenzene is an important molecule in Titan’s atmosphere because it is a potential link between the gas phase and the organic solid phase. We measured photoabsorption in the ultraviolet by benzene gas at temperatures covering the range from room temperature to 215 K. We derived benzene absorption cross sections and analyzed them in terms of the transitions observed. No significant variation with measurement temperature was observed. We discuss the implications of our measurements for the derivation of benzene abundance profiles in Titan’s thermosphere, by the Cassini/Ultraviolet Imaging Spectrograph (UVIS). The use of absorption cross sections at low temperature is recommended to avoid small systematic uncertainties in the profiles. We used our measurements, together with absorption cross sections from other molecules, to analyze four stellar occultations by Titan, measured by UVIS during flybys T21, T41, T41_II, and T53. We derived and compared benzene abundance profiles in Titan’s thermosphere between approximately 530 and 1000 km, for different dates and geographical locations. The comparisons of our benzene profiles with each other, and with profiles from models of the upper atmosphere, point to a complex behavior that is not explained by current photochemical models
Searching for Exoplanets Using a Microresonator Astrocomb
Detection of weak radial velocity shifts of host stars induced by orbiting
planets is an important technique for discovering and characterizing planets
beyond our solar system. Optical frequency combs enable calibration of stellar
radial velocity shifts at levels required for detection of Earth analogs. A new
chip-based device, the Kerr soliton microcomb, has properties ideal for
ubiquitous application outside the lab and even in future space-borne
instruments. Moreover, microcomb spectra are ideally suited for astronomical
spectrograph calibration and eliminate filtering steps required by conventional
mode-locked-laser frequency combs. Here, for the calibration of astronomical
spectrographs, we demonstrate an atomic/molecular line-referenced,
near-infrared soliton microcomb. Efforts to search for the known exoplanet HD
187123b were conducted at the Keck-II telescope as a first in-the-field
demonstration of microcombs
individual participant data meta-analysis of randomised trials study protocol
Introduction Parenteral anticoagulants may improve outcomes in patients with
cancer by reducing risk of venous thromboembolic disease and through a direct
antitumour effect. Study-level systematic reviews indicate a reduction in
venous thromboembolism and provide moderate confidence that a small survival
benefit exists. It remains unclear if any patient subgroups experience
potential benefits. Methods and analysis First, we will perform a
comprehensive systematic search of MEDLINE, EMBASE and The Cochrane Library,
hand search scientific conference abstracts and check clinical trials
registries for randomised control trials of participants with solid cancers
who are administered parenteral anticoagulants. We anticipate identifying at
least 15 trials, exceeding 9000 participants. Second, we will perform an
individual participant data meta-analysis to explore the magnitude of survival
benefit and address whether subgroups of patients are more likely to benefit
from parenteral anticoagulants. All analyses will follow the intention-to-
treat principle. For our primary outcome, mortality, we will use multivariable
hierarchical models with patient-level variables as fixed effects and a
categorical trial variable as a random effect. We will adjust analysis for
important prognostic characteristics. To investigate whether intervention
effects vary by predefined subgroups of patients, we will test interaction
terms in the statistical model. Furthermore, we will develop a risk-prediction
model for venous thromboembolism, with a focus on control patients of
randomised trials. Ethics and dissemination Aside from maintaining participant
anonymity, there are no major ethical concerns. This will be the first
individual participant data meta-analysis addressing heparin use among
patients with cancer and will directly influence recommendations in clinical
practice guidelines. Major cancer guideline development organisations will use
eventual results to inform their guideline recommendations. Several knowledge
users will disseminate results through presentations at clinical rounds as
well as national and international conferences. We will prepare an evidence
brief and facilitate dialogue to engage policymakers and stakeholders in
acting on findings. Trial registration number PROSPERO CRD4201300352
Chlamydia trachomatis growth inhibition and restoration of LDL-receptor level in HepG2 cells treated with mevastatin
Elliptic flow of charged particles in Pb-Pb collisions at 2.76 TeV
We report the first measurement of charged particle elliptic flow in Pb-Pb
collisions at 2.76 TeV with the ALICE detector at the CERN Large Hadron
Collider. The measurement is performed in the central pseudorapidity region
(||<0.8) and transverse momentum range 0.2< < 5.0 GeV/. The
elliptic flow signal v, measured using the 4-particle correlation method,
averaged over transverse momentum and pseudorapidity is 0.087 0.002
(stat) 0.004 (syst) in the 40-50% centrality class. The differential
elliptic flow v reaches a maximum of 0.2 near = 3
GeV/. Compared to RHIC Au-Au collisions at 200 GeV, the elliptic flow
increases by about 30%. Some hydrodynamic model predictions which include
viscous corrections are in agreement with the observed increase.Comment: 10 pages, 4 captioned figures, published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/389
- …