1,943 research outputs found
Azimuth axis optical alignment system Final report
Azimuth axis optical alignment system to monitor and measure attitude or angular position of remote object about azimuth axis using phase information imposed on returning beam of ligh
Unbiased computation of transition times by pathway recombination
In many systems, the time scales of the microscopic dynamics and macroscopic
dynamics of interest are separated by many orders of magnitude. Examples
abound, for instance nucleation, protein folding, and chemical reactions. For
these systems, direct simulation of phase space trajectories does not
efficiently determine most physical quantities of interest. The last decade has
seen the advent of methods circumventing brute force simulation. For most
dynamical quantities, these methods all share the drawback of systematical
errors. We present a novel method for generating ensembles of phase space
trajectories. By sampling small pieces of these trajectories in different phase
space domains and piecing them together in a smart way using equilibrium
properties, we obtain physical quantities such as transition times. This method
does not have any systematic error and is very efficient; the computational
effort to calculate the first passage time across a free energy barrier does
not increase with the height of the barrier. The strength of the method is
shown in the Ising model. Accurate measurements of nucleation times span almost
ten orders of magnitude and reveal corrections to classical nucleation theory.Comment: 8 pages, 4 figure
A systematically coarse-grained model for DNA, and its predictions for persistence length, stacking, twist, and chirality
We introduce a coarse-grained model of DNA with bases modeled as rigid-body
ellipsoids to capture their anisotropic stereochemistry. Interaction potentials
are all physicochemical and generated from all-atom simulation/parameterization
with minimal phenomenology. Persistence length, degree of stacking, and twist
are studied by molecular dynamics simulation as functions of temperature, salt
concentration, sequence, interaction potential strength, and local position
along the chain, for both single- and double-stranded DNA where appropriate.
The model of DNA shows several phase transitions and crossover regimes in
addition to dehybridization, including unstacking, untwisting, and collapse
which affect mechanical properties such as rigidity and persistence length. The
model also exhibits chirality with a stable right-handed and metastable
left-handed helix.Comment: 30 pages, 20 figures, Supplementary Material available at
http://www.physics.ubc.ca/~steve/publications.htm
Sampling Time Effects for Persistence and Survival in Step Structural Fluctuations
The effects of sampling rate and total measurement time have been determined
for single-point measurements of step fluctuations within the context of
first-passage properties. Time dependent STM has been used to evaluate step
fluctuations on Ag(111) films grown on mica as a function of temperature
(300-410 K), on screw dislocations on the facets of Pb crystallites at 320K,
and on Al-terminated Si(111) over the temperature range 770K - 970K. Although
the fundamental time constant for step fluctuations on Ag and Al/Si varies by
orders of magnitude over the temperature ranges of measurement, no dependence
of the persistence amplitude on temperature is observed. Instead, the
persistence probability is found to scale directly with t/Dt where Dt is the
time interval used for sampling. Survival probabilities show a more complex
scaling dependence which includes both the sampling interval and the total
measurement time tm. Scaling with t/Dt occurs only when Dt/tm is a constant. We
show that this observation is equivalent to theoretical predictions that the
survival probability will scale as Dt/L^z, where L is the effective length of a
step. This implies that the survival probability for large systems, when
measured with fixed values of tm or Dt should also show little or no
temperature dependence.Comment: 27 pages, 10 figure
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Effective elements of cognitive behaviour therapy for psychosis: results of a novel type of subgroup analysis based on principal stratification
Background. Meta-analyses show that cognitive behaviour therapy for psychosis (CBT-P) improves distressing positive symptoms. However, it is a complex intervention involving a range of techniques. No previous study has assessed the delivery of the different elements of treatment and their effect on outcome. Our aim was to assess the differential effect of type of treatment delivered on the effectiveness of CBT-P, using novel statistical methodology.
Method. The Psychological Prevention of Relapse in Psychosis (PRP) trial was a multi-centre randomized controlled trial (RCT) that compared CBT-P with treatment as usual (TAU). Therapy was manualized, and detailed evaluations of therapy delivery and client engagement were made. Follow-up assessments were made at 12 and 24 months. In a planned analysis, we applied principal stratification (involving structural equation modelling with finite mixtures) to estimate intention-to-treat (ITT) effects for subgroups of participants, defined by qualitative and quantitative differences in receipt of therapy, while maintaining the constraints of randomization.
Results. Consistent delivery of full therapy, including specific cognitive and behavioural techniques, was associated with clinically and statistically significant increases in months in remission, and decreases in psychotic and affective symptoms. Delivery of partial therapy involving engagement and assessment was not effective.
Conclusions. Our analyses suggest that CBT-P is of significant benefit on multiple outcomes to patients able to engage in the full range of therapy procedures. The novel statistical methods illustrated in this report have general application to the evaluation of heterogeneity in the effects of treatment
Anomalous Behavior of Ru for Catalytic Oxidation: A Theoretical Study of the Catalytic Reaction CO + 1/2 O_2 --> CO_2
Recent experiments revealed an anomalous dependence of carbon monoxide
oxidation at Ru(0001) on oxygen pressure and a particularly high reaction rate.
Below we report density functional theory calculations of the energetics and
reaction pathways of the speculated mechanism. We will show that the
exceptionally high rate is actuated by a weakly but nevertheless well bound
(1x1) oxygen adsorbate layer. Furthermore it is found that reactions via
scattering of gas-phase CO at the oxygen covered surface may play an important
role. Our analysis reveals, however, that reactions via adsorbed CO molecules
(the so-called Langmuir-Hinshelwood mechanism) dominate.Comment: 5 pages, 4 figures, Phys. Rev. Letters, Feb. 1997, in prin
A comparison of the Thunderbeat and standard electrocautery devices in head and neck surgery:a prospective randomized controlled trial
PURPOSE: New energy-based sutureless vessel ligation devices, such as the Thunderbeat (Olympus Medical Systems Corp., Tokyo, Japan), could reduce operative time and limit blood loss in head and neck surgery; however, efficacy and safety in major head and neck surgery have not been investigated in a prospective, randomized study. METHODS: This prospective, double-arm, randomized controlled trial consisted of two parts: total laryngectomy (TL) and neck dissection (ND). Thirty patients planned for TL were randomized in two groups. For the ND part, forty-two operative sides were likewise randomized. In both parts, Thunderbeat was used in addition to the standard instrumentation in the intervention groups, while only standard instrumentation was used in the control groups. Primary outcome values were blood loss, operative time and complication rate. RESULTS: For the TL part there was no difference in mean blood loss (p = 0.062), operative time (p = 0.512) and complications (p = 0.662) between both hemostatic techniques. For the neck dissection part, there was a reduction in blood loss (mean 210 mL versus 431 mL, p = 0.046) and in operative time (median 101 (IQR 85-130) minutes versus 150 (IQR 130-199) minutes, p = 0.014) when Thunderbeat was used. There was no difference in complication rate between both hemostatic systems (p = 0.261). CONCLUSION: The Thunderbeat hemostatic device significantly reduces operative blood loss and operative time for neck dissections, without increase in complications. In TL, blood loss using Thunderbeat was comparable with the standard technique, but the operative time tended to be shorter. TRIAL REGISTRATION: UMCG Research Register, Reg. no. 201700041, date of registration: 18/1/2017
Gut-microbe derived TMAO and its association with more progressed forms of AF:Results from the AF-RISK study
Introduction: The importance of gut microbiome in cardiovascular disease has been increasingly recognized. Trimethylamine N-oxide (TMAO) is a gut microbe-derived metabolite that is associated with cardiovascular disease, including atrial fibrillation (AF). The role of TMAO in clinical AF progression however remains unknown. Methods and results: In this study we measured TMAO and its precursor (betaine, choline, and L- carnitine) levels in 78 patients using plasma samples from patients that participated in the AF-RISK study. 56 patients suffered from paroxysmal AF and 22 had a short history of persistent AF. TMAO levels were significantly higher in patients with persistent AF, as compared to those with paroxysmal AF (median [IQR] 5.65 [4.7–9.6] m/z versus 4.31 [3.2–6.2] m/z, p < 0.05), while precursor levels did not differ. In univariate analysis, we observed that for every unit increase in TMAO, the odds for having persistent AF increased with 0.44 [0.14–0.73], p < 0.01. Conclusion: These results suggest that higher levels of TMAO are associated with more progressed forms of AF. We therefore hypothesize that increased TMAO levels may reflect disease progression in humans. Larger studies are required to validate these preliminary findings.Trial Registration number: Clinicaltrials.gov NCT01510210
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