68 research outputs found
Dynamics of barrier penetration in thermal medium: exact result for inverted harmonic oscillator
Time evolution of quantum tunneling is studied when the tunneling system is
immersed in thermal medium. We analyze in detail the behavior of the system
after integrating out the environment. Exact result for the inverted harmonic
oscillator of the tunneling potential is derived and the barrier penetration
factor is explicitly worked out as a function of time. Quantum mechanical
formula without environment is modifed both by the potential renormalization
effect and by a dynamical factor which may appreciably differ from the
previously obtained one in the time range of 1/(curvature at the top of
potential barrier).Comment: 30 pages, LATEX file with 11 PS figure
Metastability Driven by Soft Quantum Fluctuation Modes
The semiclassical Euclidean path integral method is applied to compute the
low temperature quantum decay rate for a particle placed in the metastable
minimum of a cubic potential in a {\it finite} time theory. The classical path,
which makes a saddle for the action, is derived in terms of Jacobian elliptic
functions whose periodicity establishes the one-to-one correspondence between
energy of the classical motion and temperature (inverse imaginary time) of the
system. The quantum fluctuation contribution has been computed through the
theory of the functional determinants for periodic boundary conditions. The
decay rate shows a peculiar temperature dependence mainly due to the softening
of the low lying quantum fluctuation eigenvalues. The latter are determined by
solving the Lam\`{e} equation which governs the fluctuation spectrum around the
time dependent classical bounce.Comment: Journal of Low Temperature Physics (2008) Publisher: Springer
Netherland
Domain wall roughening in dipolar films in the presence of disorder
We derive a low-energy Hamiltonian for the elastic energy of a N\'eel domain
wall in a thin film with in-plane magnetization, where we consider the
contribution of the long-range dipolar interaction beyond the quadratic
approximation. We show that such a Hamiltonian is analogous to the Hamiltonian
of a one-dimensional polaron in an external random potential. We use a replica
variational method to compute the roughening exponent of the domain wall for
the case of two-dimensional dipolar interactions.Comment: REVTEX, 35 pages, 2 figures. The text suffered minor changes and
references 1,2 and 12 were added to conform with the referee's repor
Quantification of CO2 removal in a large-scale enhanced weathering field trial on an oil palm plantation in Sabah, Malaysia
Modeling studies show that large-scale deployment of enhanced rock weathering on croplands has the potential to reduce levels of atmospheric carbon dioxide by the end of the century. There is, however, a pressing need to verify model predictions through long-term field trials. Here we report results from the first 3 years of an ongoing enhanced weathering field trial, carried out on an oil palm plantation in Sabah, Malaysia. Crushed silicate rock was applied to three hydrologically isolated catchments, and three adjacent (paired) reference catchments were left untreated. The drawdown of atmospheric CO2 was quantified via the export of alkalinity in stream waters and changes in soil carbonate content. The amended and reference catchments were found to have a similar extent of CO2 drawdown via alkalinity export [respectively, 3.8 ± 0.8 (1 SD) and 3.7 ± 0.6 (1 SD) tCO2 ha−1] when all catchments were averaged over the study period (October 2018 to July 2021). However, differences were observed between the different catchment pairs (plots): two of the plots displayed a similar extent of CO2 removal for both the amended and reference catchments, but the third amended catchment had a higher extent of CO2 removal of ~1 tCO2 ha−1 relative to its adjacent reference catchment. The difference in CO2 removal rates determined for this plot can likely be attributed to increased weathering of silicate minerals in the amended catchment. Soil carbonate concentrations were on average < 0.2 wt% CaCO3, but we report a small increase of ~0.03 wt% CaCO3 in the top 30 cm of soil in the amended soils relative to the reference catchments. The magnitude of CO2 drawdown via alkalinity export determined for these agricultural catchments is around an order of magnitude higher than in natural forested catchments in Sabah and similar to that of basaltic catchments. We show that these high weathering rates are primarily driven by weathering of carbonate fertilizers. The data presented from this field trial provide vital contextual information on the real-world efficacy and practicalities associated with the implementation of enhanced weathering for atmospheric CO2 removal that will help to inform further trials as well as wider-scale deployment
Search for Lorentz and CPT violation using sidereal time dependence of neutrino flavor transitions over a short baseline
A class of extensions of the Standard Model allows Lorentz and CPT violations, which can be identified
by the observation of sidereal modulations in the neutrino interaction rate. A search for such modulations
was performed using the T2K on-axis near detector. Two complementary methods were used in this study,
both of which resulted in no evidence of a signal. Limits on associated Lorentz and CPT-violating terms
from the Standard Model extension have been derived by taking into account their correlations in this
model for the first time. These results imply such symmetry violations are suppressed by a factor of more
than 10 20 at the GeV scale
Measurement of coherent production in low energy neutrino-Carbon scattering
We report the first measurement of the flux-averaged cross section for charged current coherent production on carbon for neutrino energies less than 1.5 GeV to a restricted final state phase space region in the T2K near detector, ND280. Comparisons are made with predictions from the Rein-Sehgal coherent production model and the model by Alvarez-Ruso {\it et al.}, the latter representing the first implementation of an instance of the new class of microscopic coherent models in a neutrino interaction Monte Carlo event generator. This results contradicts the null results reported by K2K and SciBooNE in a similar neutrino energy region
The Cholecystectomy As A Day Case (CAAD) Score: A Validated Score of Preoperative Predictors of Successful Day-Case Cholecystectomy Using the CholeS Data Set
Background
Day-case surgery is associated with significant patient and cost benefits. However, only 43% of cholecystectomy patients are discharged home the same day. One hypothesis is day-case cholecystectomy rates, defined as patients discharged the same day as their operation, may be improved by better assessment of patients using standard preoperative variables.
Methods
Data were extracted from a prospectively collected data set of cholecystectomy patients from 166 UK and Irish hospitals (CholeS). Cholecystectomies performed as elective procedures were divided into main (75%) and validation (25%) data sets. Preoperative predictors were identified, and a risk score of failed day case was devised using multivariate logistic regression. Receiver operating curve analysis was used to validate the score in the validation data set.
Results
Of the 7426 elective cholecystectomies performed, 49% of these were discharged home the same day. Same-day discharge following cholecystectomy was less likely with older patients (OR 0.18, 95% CI 0.15–0.23), higher ASA scores (OR 0.19, 95% CI 0.15–0.23), complicated cholelithiasis (OR 0.38, 95% CI 0.31 to 0.48), male gender (OR 0.66, 95% CI 0.58–0.74), previous acute gallstone-related admissions (OR 0.54, 95% CI 0.48–0.60) and preoperative endoscopic intervention (OR 0.40, 95% CI 0.34–0.47). The CAAD score was developed using these variables. When applied to the validation subgroup, a CAAD score of ≤5 was associated with 80.8% successful day-case cholecystectomy compared with 19.2% associated with a CAAD score >5 (p < 0.001).
Conclusions
The CAAD score which utilises data readily available from clinic letters and electronic sources can predict same-day discharges following cholecystectomy
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