7,166 research outputs found
Toward Open-Closed String Theoretical Description of Rolling Tachyon
We consider how the time-dependent decay process of an unstable D-brane
should be described in the full (quantum) open-closed string theory. It is
argued that the system, starting from the unstable D-brane configuration, will
evolve in time into the time-independent open string tachyon vacuum
configuration which we assume to be finite, with the total energy conserved. As
a concrete realization of this idea, we construct a toy model describing the
open and closed string tachyons which admits such a time-dependent solution.
The structure of our model has some resemblance to that of open-closed string
field theory.Comment: 1+10 pages, 6 figures. v2: a reference adde
Parallel Imaging with RASER using Multiband Frequency-modulated Excitation Pulses
The many advantages of the recently proposed RASER sequence have been demonstrated. Hence, RASER holds great promises for functional MRI (fMRI), particularly for studies of the orbital-frontal cortex and other brain regions near air cavities, which cause distortion and signal loss in conventional EPI methods. However, the single-shot RASER sequence implemented so far inherently presents a set of temporal and spatial limitations that hinders it feasibility and full potential for fMRI applications. It is believed that parallel imaging will help overcome such restrictions. In this work, the RASER acquisition and reconstruction scheme is extended for parallel imaging using tailored pulses for simultaneous multi-band excitation
Tropical climate–vegetation–fire relationships: multivariate evaluation of the land surface model JSBACH
The interactions between climate, vegetation and fire can strongly influence
the future trajectories of vegetation in Earth system models. We evaluate the
relationships between tropical climate, vegetation and fire in the global
vegetation model JSBACH, using a simple fire scheme and the complex fire
model SPITFIRE with the aim to identify potential for model improvement. We
use two remote-sensing products (based on MODIS and Landsat) in different
resolutions to assess the robustness of the obtained observed relationships.
We evaluate the model using a multivariate comparison that allows us to focus
on the interactions between climate, vegetation and fire and test the
influence of land use change on the modelled patterns.
Climate–vegetation–fire relationships are known to differ between
continents; we therefore perform the analysis for each continent separately.The observed relationships are
similar in the two satellite data sets, but maximum tree cover is reached at
higher precipitation values for coarser resolution. This shows that the
spatial scale of models and data needs to be consistent for meaningful
comparisons. The model captures the broad spatial patterns with regional
differences, which are partly due to the climate forcing derived from an
Earth system model. Compared to the simple fire scheme, SPITFIRE strongly
improves the spatial pattern of burned area and the distribution of burned
area along increasing precipitation. The correlation between precipitation
and tree cover is higher in the observations than in the largely climate-driven vegetation model, with both fire models. The multivariate comparison
identifies excessive tree cover in low-precipitation areas and a too-strong relationship between high fire occurrence and low tree cover for the
complex fire model. We therefore suggest that drought effects on tree cover
and the impact of burned area on tree cover or the adaptation of trees to
fire can be improved.The observed variation in the relationship between precipitation and maximum
tree cover between continents is higher than the simulated one. Land use
contributes to the intercontinental differences in fire regimes with SPITFIRE
and strongly overprints the modelled multimodality of tree cover with
SPITFIRE.The multivariate model–data comparison used here has several
advantages: it improves the attribution of model–data mismatches to model
processes, it reduces the impact of biases in the meteorological forcing on
the evaluation and it allows us to evaluate not only a specific target variable
but also the interactions.</p
D-brane States and Disk Amplitudes in OSp Invariant Closed String Field Theory
We construct solitonic states in the OSp invariant string field theory, which
are BRST invariant in the leading order of regularization parameter .
We calculate the disk amplitudes using these solitonic states and show that
they describe D-branes and ghost D-branes.Comment: 37 pages, 8 figure
Driving offences and risk of subsequent crash in novice drivers: the DRIVE cohort study 12-year follow-up
Background Penalties are a key component to improve road user safety, but previous studies suggested that they might not be successful in reducing crashing in offending drivers. However, these studies were not able to consider important crash risk factors in the analysis that might confound the results. Using data from a large prospective cohort study of young drivers in New South Wales, Australia, we explored if novice drivers with driving offences have a higher rates of car crash and if these differences are explained by established crash risk factors. Methods We used data from a 2003/2004 Australian survey of young drivers, linked to police reported offence and crash data, hospital data and deaths data up to 2016. We used Poisson regression models adjusted for confounders to estimate the association between driving offences during 2003–2006 with car crash during 2007–2016. Results The study cohort comprised 20 781 young drivers of whom 7860 drivers (37.8%) had at least one driving offence and 2487 (12.0%) were involved in at least one crash. After adjusting for confounders in the regression model, drivers with three or more driving offences had 2.25 (95% CI 1.98 to 2.57), 2.87 (95% CI 1.60 to 5.17) and 3.28 (95% CI 2.28 to 4.72) times higher rates of any crash, crashes that resulted in hospital admission or death and single vehicle crashes compared with drivers with no driving offences. Conclusion Measures that successfully mitigate the underlying risk factors for both, crashes and offences, have the potential to improve road safety
The Schrodinger Wave Functional and Closed String Rolling Tachyon
In this short note we apply Schrodinger picture description of the
minisuperspace approach to the closed string tachyon condensation. We will
calculate the rate of produced closed string and we will show that the density
of high massive closed string modes reaches the string density in time of order
one in string units.Comment: 12 page
Emitter-site selective photoelectron circular dichroism of trifluoromethyloxirane
The angle-resolved inner-shell photoionization of R-trifluoromethyloxirane,
C3H3F3O, is studied experimentally and theoretically. Thereby, we investigate
the photoelectron circular dichroism (PECD) for nearly-symmetric O 1s and F 1s
electronic orbitals, which are localized on different molecular sites. The
respective dichroic and angular distribution parameters
are measured at the photoelectron kinetic energies from 1 to 16 eV by using
variably polarized synchrotron radiation and velocity map imaging spectroscopy.
The present experimental results are in good agreement with the outcome of ab
initio electronic structure calculations. We report a sizable chiral asymmetry
of up to about 9% for the K-shell photoionization of oxygen atom.
For the individual fluorine atoms, the present calculations predict asymmetries
of similar size. However, being averaged over all fluorine atoms, it drops down
to about 2%, as also observed in the present experiment. Our study demonstrates
a strong emitter- and site-sensitivity of PECD in the one-photon inner-shell
ionization of this chiral molecule
Ionization dynamics in expanding clusters studied by XUV pump probe spectroscopy
he expansion and disintegration dynamics of xenon clusters initiated by the ionization with femtosecond soft x ray extreme ultraviolet XUV pulses were studied with pump probe spectroscopy using the autocorrelator setup of the Free Electron LASer in Hamburg FLASH facility. The ionization by the first XUV pulse of 92 eV photon energy 8 1012 W cm amp; 8722;2 leads to the generation of a large number of quasi free electrons trapped by the space charge of the cluster ions. A temporally delayed, more intense probe 4 1013 W cm amp; 8722;2 pulse substantially increases a population of nanoplasma electrons providing a way of probing plasma states in the expanding cluster by tracing the average charge of fragment ions. The results of the study reveal a timescale for cluster expansion and disintegration, which depends essentially on the initial cluster size. The average charge state of fragment ions, and thus the cluster plasma changes significantly on a timescale of 1 3 p
Association of Pathogen Load in Pigs with Retail Pork Contamination.
Salmonella and Campylobacter are estimated to cause 3.9 million illnesses annually in the United States, and most of these illnesses are food-related. Pigs can be sub-clinically infected with these pathogens and fecal contamination of meat during processing is a food safety risk. Quantitative measures of foodborne safety risk are rarely reported and are a critical data gap for development of quantitative risk assessments. The goal of this study was to determine the association between the concentration of Salmonella and Campylobacter in porcine feces and hide with concentrations in meat
Disk Partition Function and Oscillatory Rolling Tachyons
An exact cubic open string field theory rolling tachyon solution was recently
found by Kiermaier et. al. and Schnabl. This oscillatory solution has been
argued to be related by a field redefinition to the simple exponential rolling
tachyon deformation of boundary conformal theory. In the latter approach, the
disk partition function takes a simple form. Out of curiosity, we compute the
disk partition function for an oscillatory tachyon profile, and find that the
result is nevertheless almost the same.Comment: 17 pages, 2 figures. v4: discussion clarified, appendix added,
conclusions unchanged; version to appear in J.Phys.
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