3,818 research outputs found
Distribution of the time at which the deviation of a Brownian motion is maximum before its first-passage time
We calculate analytically the probability density of the time
at which a continuous-time Brownian motion (with and without drift) attains its
maximum before passing through the origin for the first time. We also compute
the joint probability density of the maximum and . In the
driftless case, we find that has power-law tails: for large and for small . In
presence of a drift towards the origin, decays exponentially for large
. The results from numerical simulations are in excellent agreement with
our analytical predictions.Comment: 13 pages, 5 figures. Published in Journal of Statistical Mechanics:
Theory and Experiment (J. Stat. Mech. (2007) P10008,
doi:10.1088/1742-5468/2007/10/P10008
Wave function-dependent mobility and suppression of interface roughness scattering in a strained SiGe p-channel field-effect structure
The 4 K Hall mobility has been measured in a top-gated, inverted, modulation-doped Si/Si0.8Ge0.2 structure having a Si:B doping layer beneath the alloy. From comparisons with theoretical calculations, we argue that, unlike an ordinary enhancement-mode SiGe p-channel metalâoxideâsemiconductor structure, this configuration leads to a decrease of interface roughness scattering with increasing sheet carrier density. We also speculate on the nature of the interface charge observed in these structures at low temperature
Adapting to the digital age: a narrative approach
The article adopts a narrative inquiry approach to foreground informal learning and exposes a collection of stories from tutors about how they adapted comfortably to the digital age. We were concerned that despite substantial evidence that bringing about changes in pedagogic practices can be difficult, there is a gap in convincing approaches to help in this respect. In this context, this project takes a âbottom-upâ approach and synthesises several life-stories into a single persuasive narrative to support the process of adapting to digital change. The project foregrounds the small, every-day motivating moments, cultural features and environmental factors in people's diverse lives which may have contributed to their positive dispositions towards change in relation to technology enhanced learning. We expect that such narrative approaches could serve to support colleagues in other institutions to warm up to ever-changing technological advances
Do selective cyclo-oxygenase-2 inhibitors and traditional non-steroidal anti-inflammatory drugs increase the risk of atherothrombosis? Meta-analysis of randomised trials
Objective: To assess the effects of selective cyclo-oxygenase-2 (COX 2) inhibitors and traditional non-steroidal anti-inflammatory drugs (NSAIDs) on the risk of vascular events. Design: Meta-analysis of published and unpublished tabular data from randomised trials, with indirect estimation of the effects of traditional NSAIDs. Data sources: Medline and Embase (January 1966 to April 2005); Food and Drug Administration records; and data on file from Novartis, Pfizer, and Merck. Review methods: Eligible studies were randomised trials that included a comparison of a selective COX 2 inhibitor versus placebo or a selective COX 2 inhibitor versus a traditional NSAID, of at least four weeks' duration, with information on serious vascular events (defined as myocardial infarction, stroke, or vascular death). Individual investigators and manufacturers provided information on the number of patients randomised, numbers of vascular events, and the person time of follow-up for each randomised group. Results: In placebo comparisons, allocation to a selective COX 2 inhibitor was associated with a 42% relative increase in the incidence of serious vascular events (1.2%/year v 0.9%/year; rate ratio 1.42, 95% confidence interval 1.13 to 1.78; P = 0.003), with no significant heterogeneity among the different selective COX 2 inhibitors. This was chiefly attributable to an increased risk of myocardial infarction (0.6%/year v 0.3%/year; 1.86, 1.33 to 2.59; P = 0.0003), with little apparent difference in other vascular outcomes. Among trials of at least one year's duration (mean 2.7 years), the rate ratio for vascular events was 1.45 (1.12 to 1.89; P = 0.005). Overall, the incidence of serious vascular events was similar between a selective COX 2 inhibitor and any traditional NSAID (1.0%/year v 0.9/%year; 1.16, 0.97 to 1.38; P = 0.1). However, statistical heterogeneity (P = 0.001) was found between trials of a selective COX 2 inhibitor versus naproxen (1.57, 1.21 to 2.03) and of a selective COX 2 inhibitor versus non-naproxen NSAIDs (0.88, 0.69 to 1.12). The summary rate ratio for vascular events, compared with placebo, was 0.92 (0.67 to 1.26) for naproxen, 1.51 (0.96 to 2.37) for ibuprofen, and 1.63 (1.12 to 2.37) for diclofenac. Conclusions: Selective COX 2 inhibitors are associated with a moderate increase in the risk of vascular events, as are high dose regimens of ibuprofen and diclofenac, but high dose naproxen is not associated with such an excess
Growth pattern to the end of the mating period influences the reproductive performance of Merino ewe lambs mated at 7 to 8 months of age
The reproductive performance of Merino ewe lambs is highly variable and generally poor in comparison to older ewes. In this study, we determined the impacts of growth pattern to the end of the mating period and sire genetics on the reproductive performance of Merino ewe lambs. Five hundred ewe lambs with full pedigree records were managed under commercial conditions from weaning and weighed 43.5âkg at the start of the mating period with an average age of 224 days. The ewe lambs were offered a moderate or high feed allowance to achieve target growth rates of 100 or 200âg/day during a 46-day mating period. They were then recombined and scanned for pregnancy status 60 days after the mating period. At the individual animal level, a 5âkg greater live weight at the start of the mating period increased reproductive rate (foetuses per 100 ewes joined) by about 20% (Pâ<â0.001). Regardless of their live weight at the start of the mating period, gaining an extra 100âg/day of live weight during the mating period further increased their reproductive rate by about 20% (Pâ<â0.001). Ewe lambs from sires with higher Australian Sheep Breeding Values for fat measured post-weaning achieved a higher fertility (Pâ<â0.05) and reproductive rate (Pâ<â0.01) regardless of feed allowance treatment. The effects of sire fatness was significant even when the sire breeding values for live weight measured post-weaning were included in the model. The effects of managing growth pattern and sire genetics were additive, so improving the reproductive performance of Merino ewe lambs mated at 7 to 8 months of age requires improving their feed allowance and rate of live weight gain until the end of the mating period and using sires with higher breeding values for fatness
Assessment-schedule matching in unanchored indirect treatment comparisons of progression-free survival in cancer studies
Background
The timing of efficacy-related clinical events recorded at scheduled study visits in clinical trials are interval censored, with the interval duration pre-determined by the study protocol. Events may happen any time during that interval but can only be detected during a planned or unplanned visit. Disease progression in oncology is a notable example where the time to an event is affected by the schedule of visits within a study. This can become a source of bias when studies with varying assessment schedules are used in unanchored comparisons using methods such as matching-adjusted indirect comparisons.
Objective
We illustrate assessment-time bias (ATB) in a simulation study based on data from a recent study in second-line treatment for locally advanced or metastatic urothelial carcinoma, and present a method to adjust for differences in assessment schedule when comparing progression-free survival (PFS) against a competing treatment.
Methods
A multi-state model for death and progression was used to generate simulated death and progression times, from which PFS times were derived. PFS data were also generated for a hypothetical comparator treatment by applying a constant hazard ratio (HR) to the baseline treatment. Simulated PFS times for the two treatments were then aligned to different assessment schedules so that progression events were only observed at set visit times, and the data were analysed to assess the bias and standard error of estimates of HRs between two treatments with and without assessment-schedule matching (ASM).
Results
ATB is highly affected by the rate of the event at the first assessment time; in our examples, the bias ranged from 3 to 11% as the event rate increased. The proposed method relies on individual-level data from a study and attempts to adjust the timing of progression events to the comparatorâs schedule by shifting them forward or backward without altering the patientsâ actual follow-up time. The method removed the bias almost completely in all scenarios without affecting the precision of estimates of comparative effectiveness.
Conclusions
Considering the increasing use of unanchored comparative analyses for novel cancer treatments based on single-arm studies, the proposed method offers a relatively simple means of improving the accuracy of relative benefits of treatments on progression times
Direct evidence for a piezoelectriclike effect in coherently strained SiGe/Si heterostructures
A hybrid acoustic spectroscopy technique has been used to demonstrate the (reversible) conversion of high frequency electric fields into longitudinal acoustic waves within a modulation-doped pseudomorphic Si/Si0.88Ge0.12/Si heterostructure. This provides compelling evidence for the existence of a piezoelectriclike coupling within such structures
Polynomial kernels for 3-leaf power graph modification problems
A graph G=(V,E) is a 3-leaf power iff there exists a tree T whose leaves are
V and such that (u,v) is an edge iff u and v are at distance at most 3 in T.
The 3-leaf power graph edge modification problems, i.e. edition (also known as
the closest 3-leaf power), completion and edge-deletion, are FTP when
parameterized by the size of the edge set modification. However polynomial
kernel was known for none of these three problems. For each of them, we provide
cubic kernels that can be computed in linear time for each of these problems.
We thereby answer an open problem first mentioned by Dom, Guo, Huffner and
Niedermeier (2005).Comment: Submitte
Phonon-drag effects on thermoelectric power
We carry out a calculation of the phonon-drag contribution to the
thermoelectric power of bulk semiconductors and quantum well structures for the
first time using the balance equation transport theory extended to the weakly
nonuniform systems. Introducing wavevector and phonon-mode dependent relaxation
times due to phonon-phonon interactions, the formula obtained can be used not
only at low temperatures where the phonon mean free path is determined by
boundary scattering, but also at high temperatures. In the linear transport
limit, is equivalent to the result obtained from the Boltzmann equation
with a relaxation time approximation. The theory is applied to experiments and
agreement is found between the theoretical predictions and experimental
results. The role of hot-electron effects in is discussed. The importance
of the contribution of to thermoelectric power in the hot-electron
transport condition is emphasized.Comment: 8 pages, REVTEX 3.0, 7 figures avilable upon reques
The Thermopower of Quantum Chaos
The thermovoltage of a chaotic quantum dot is measured using a current
heating technique. The fluctuations in the thermopower as a function of
magnetic field and dot shape display a non-Gaussian distribution, in agreement
with simulations using Random Matrix Theory. We observe no contributions from
weak localization or short trajectories in the thermopower.Comment: 4 pages, 3 figures, corrected: accidently omitted author in the
Authors list, here (not in the article
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