1,129 research outputs found
Polymer drift in a solvent by force acting on one polymer end
We investigate the effect of hydrodynamic interactions on the non-equilibrium
drift dynamics of an ideal flexible polymer pulled by a constant force applied
at one end of the polymer using the perturbation theory and the renormalization
group method. For moderate force, if the polymer elongation is small, the
hydrodynamic interactions are not screened and the velocity and the
longitudinal elongation of the polymer are computed using the renormalization
group method. Both the velocity and elongation are nonlinear functions of the
driving force in this regime. For large elongation we found two regimes. For
large force but finite chain length the hydrodynamic interactions are
screened. For large chain lengths and a finite force the hydrodynamic
interactions are only partially screened, which in three dimensions results in
unusual logarithmic corrections to the velocity and the longitudinal
elongation.Comment: 6 page
Limit Theorem for Continuous-Time Quantum Walk on the Line
Concerning a discrete-time quantum walk X^{(d)}_t with a symmetric
distribution on the line, whose evolution is described by the Hadamard
transformation, it was proved by the author that the following weak limit
theorem holds: X^{(d)}_t /t \to dx / \pi (1-x^2) \sqrt{1 - 2 x^2} as t \to
\infty. The present paper shows that a similar type of weak limit theorems is
satisfied for a {\it continuous-time} quantum walk X^{(c)}_t on the line as
follows: X^{(c)}_t /t \to dx / \pi \sqrt{1 - x^2} as t \to \infty. These
results for quantum walks form a striking contrast to the central limit theorem
for symmetric discrete- and continuous-time classical random walks: Y_{t}/
\sqrt{t} \to e^{-x^2/2} dx / \sqrt{2 \pi} as t \to \infty. The work deals also
with issue of the relationship between discrete and continuous-time quantum
walks. This topic, subject of a long debate in the previous literature, is
treated within the formalism of matrix representation and the limit
distributions are exhaustively compared in the two cases.Comment: 15 pages, title correcte
Visualization and Interpretation of Attosecond Electron Dynamics in Laser-Driven Hydrogen Molecular Ion using Bohmian Trajectories
We analyze the attosecond electron dynamics in hydrogen molecular ion driven
by an external intense laser field using ab-initio numerical simulations of the
corresponding time-dependent Schr{\"{o}}dinger equation and Bohmian
trajectories. To this end, we employ a one-dimensional model of the molecular
ion in which the motion of the protons is frozen. The results of the Bohmian
trajectory calculations do agree well with those of the ab-initio simulations
and clearly visualize the electron transfer between the two protons in the
field. In particular, the Bohmian trajectory calculations confirm the recently
predicted attosecond transient localization of the electron at one of the
protons and the related multiple bunches of the ionization current within a
half cycle of the laser field. Further analysis based on the quantum
trajectories shows that the electron dynamics in the molecular ion can be
understood via the phase difference accumulated between the Coulomb wells at
the two protons. Modeling of the dynamics using a simple two-state system leads
us to an explanation for the sometimes counter-intuitive dynamics of an
electron opposing the classical force of the electric field on the electron.Comment: 8 pages, 6 figures. The following article has been submitted to The
Journal of Chemical Physics. After it is published, it will be found at
http://jcp.aip.org
Absorption problems for quantum walks in one dimension
This paper treats absorption problems for the one-dimensional quantum walk
determined by a 2 times 2 unitary matrix U on a state space {0,1,...,N} where N
is finite or infinite by using a new path integral approach based on an
orthonormal basis P, Q, R and S of the vector space of complex 2 times 2
matrices. Our method studied here is a natural extension of the approach in the
classical random walk.Comment: 15 pages, small corrections, journal reference adde
Heterogeneity in connectivity of habitat networks saves stable coexistence of competing species
Coexistence of individuals with different species or phenotypes is often
found in nature in spite of competition between them. Stable coexistence of
multiple types of individuals have implications for maintenance of ecological
biodiversity and emergence of altruism in society, to name a few. Various
mechanisms of coexistence including spatial structure of populations,
heterogeneous individuals, and heterogeneous environments, have been proposed.
In reality, individuals disperse and interact on complex networks. We examine
how heterogeneous degree distributions of networks influence coexistence,
focusing on models of cyclically competing species. We show analytically and
numerically that heterogeneity in degree distributions promotes stable
coexistence.Comment: 4 figure
Initial severity of depression and efficacy of cognitive-behavioural therapy: individual-participant data meta-analysis of pill-placebo-controlled trials
BACKGROUND: The influence of baseline severity has been examined for antidepressant medications but has not been studied properly for cognitive-behavioural therapy (CBT) in comparison with pill placebo. AIMS: To synthesise evidence regarding the influence of initial severity on efficacy of CBT from all randomised controlled trials (RCTs) in which CBT, in face-to-face individual or group format, was compared with pill-placebo control in adults with major depression. METHOD: A systematic review and an individual-participant data meta-analysis using mixed models that included trial effects as random effects. We used multiple imputation to handle missing data. RESULTS: We identified five RCTs, and we were given access to individual-level data (n = 509) for all five. The analyses revealed that the difference in changes in Hamilton Rating Scale for Depression between CBT and pill placebo was not influenced by baseline severity (interaction P = 0.43). Removing the non-significant interaction term from the model, the difference between CBT and pill placebo was a standardised mean difference of -0.22 (95% CI -0.42 to -0.02, P = 0.03, I2 = 0%). CONCLUSIONS: Patients suffering from major depression can expect as much benefit from CBT across the wide range of baseline severity. This finding can help inform individualised treatment decisions by patients and their clinicians.R01 MH060998 - NIMH NIH HHS; R34 MH086668 - NIMH NIH HHS; R01 AT007257 - NCCIH NIH HHS; R21 MH101567 - NIMH NIH HHS; K02 MH001697 - NIMH NIH HHS; R01 MH060713 - NIMH NIH HHS; R34 MH099311 - NIMH NIH HHS; R21 MH102646 - NIMH NIH HHS; K23 MH100259 - NIMH NIH HHS; R01 MH099021 - NIMH NIH HH
The Prograde Orbit of Exoplanet TrES-2b
We monitored the Doppler shift of the G0V star TrES-2 throughout a transit of
its giant planet. The anomalous Doppler shift due to stellar rotation (the
Rossiter-McLaughlin effect) is discernible in the data, with a signal-to-noise
ratio of 2.9, even though the star is a slow rotator. By modeling this effect
we find that the planet's trajectory across the face of the star is tilted by
-9 +/- 12 degrees relative to the projected stellar equator. With 98%
confidence, the orbit is prograde.Comment: ApJ, in press [15 pages
Role of per-oral pancreatoscopy in the evaluation of suspected pancreatic duct neoplasia: a 13-year U.S. singlecenter experience
Background and Aims
The role of per-oral pancreatoscopy (POP) in the evaluation of occult pancreatic duct (PD) lesions remains limited to case series. The aim of this study was to evaluate the ability of POP to differentiate malignant from benign diseases of the PD.
Methods
Patients who underwent POP between 2000 and 2013 for the evaluation of indeterminate PD strictures, dilatations, or with suspected or known main duct intraductal papillary mucinous neoplasm were identified. Main outcome measurements were visual impression accuracy, POP tissue sampling, efficacy, and safety of POP.
Results
During the study period, 79 patients who underwent POP for the evaluation of pancreatic stricture or dilatation were identified. Technical success was achieved in 78 (97%). In the PD neoplasia group (n = 33), the final diagnosis was based on index confirmatory POP-guided tissue sampling in 29 (88%). For the detection of PD neoplasia, POP visual impression had a sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of 87%, 86%, 83%, 91%, and 87%, respectively. When combined with POP-guided tissue sampling, the values were 91%, 95%, 94%, 93%, and 94%, respectively. Of 102 POPs performed, adverse events were noted in 12 (12%) cases.
Conclusions
This study demonstrates a high technical success rate, visual impression accuracy, and tissue sampling capability of POP. Examinations were performed by endoscopists with expertise in pancreatoscopy interpretation, and the results may not be generalizable
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