18,957 research outputs found

### Optical probes of the quantum vacuum: The photon polarization tensor in external fields

The photon polarization tensor is the central building block of an effective
theory description of photon propagation in the quantum vacuum. It accounts for
the vacuum fluctuations of the underlying theory, and in the presence of
external electromagnetic fields, gives rise to such striking phenomena as
vacuum birefringence and dichroism. Standard approximations of the polarization
tensor are often restricted to on-the-light-cone dynamics in homogeneous
electromagnetic fields, and are limited to certain momentum regimes only. We
devise two different strategies to go beyond these limitations: First, we aim
at obtaining novel analytical insights into the photon polarization tensor for
homogeneous fields, while retaining its full momentum dependence. Second, we
employ wordline numerical methods to surpass the constant-field limit.Comment: 13 pages, 4 figures; typo in Eq. (5) corrected (matches journal
version

### Application of Batch Poisson Process to Random-sized Batch Arrival of Sediment Particles

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchive

### An easy-to-use diagnostic system development shell

The Diagnostic System Development Shell (DSDS), an expert system development shell for diagnostic systems, is described. The major objective of building the DSDS is to create a very easy to use and friendly environment for knowledge engineers and end-users. The DSDS is written in OPS5 and CommonLisp. It runs on a VAX/VMS system. A set of domain independent, generalized rules is built in the DSDS, so the users need not be concerned about building the rules. The facts are explicitly represented in a unified format. A powerful check facility which helps the user to check the errors in the created knowledge bases is provided. A judgement facility and other useful facilities are also available. A diagnostic system based on the DSDS system is question driven and can call or be called by other knowledge based systems written in OPS5 and CommonLisp. A prototype diagnostic system for diagnosing a Philips constant potential X-ray system has been built using the DSDS

### Estimating the central charge from the R\'enyi entanglement entropy

We calculate the von Neumann and R\'enyi bipartite entanglement entropy of
the $O(2)$ model with a chemical potential on a 1+1 dimensional Euclidean
lattice with open and periodic boundary conditions. We show that the
Calabrese-Cardy conformal field theory predictions for the leading logarithmic
scaling with the spatial size of these entropies are consistent with a central
charge $c=1$. This scaling survives the time continuum limit and truncations of
the microscopic degrees of freedom, modifications which allow us to connect the
Lagrangian formulation to quantum Hamiltonians. At half-filling, the forms of
the subleading corrections imposed by conformal field theory allow the
determination of the central charge with an accuracy better than two percent
for moderately sized lattices. We briefly discuss the possibility of estimating
the central charge using quantum simulators.Comment: 10 pages, 8 figures, 3 table

### Vehicular fuel composition and atmospheric emissions in South China: Hong Kong, Macau, Guangzhou, and Zhuhai

International audienceVehicular emission is an important source of air pollutants in urban cities in the Pearl River Delta (PRD) region of South China. In order to study the impact of vehicular fuel on air quality, several commonly used fuel samples were collected in four main cities in the PRD region ? Hong Kong, Guangzhou, Macau and Zhuhai, and analyzed for their volatile organic compounds (VOCs) composition. Source profiles of the vehicular fuels used in these cities were constructed and are believed to be the first reported for the PRD region. The C8?C10 hydrocarbons were the main constituents of diesel. Different from diesel, gasoline used in the PRD region was mainly comprised of lighter C4?C7 hydrocarbons, with toluene and i-pentane being the two most abundant species. The benzene content in the Guangzhou and Zhuhai gasoline samples were higher than that in Hong Kong and Macau and exceeded the maximum benzene levels for Mainland China unleaded gasoline. Liquefied Petroleum Gas (LPG) samples were collected only in Hong Kong and were comprised mainly of n-butane, propane and i-butane. Traffic samples indicated that evaporative loss and vehicular combustion were the primary contributors to elevated VOC levels in roadside atmospheres. Significant i-pentane and toluene concentrations were observed in roadside atmospheres in all four cities. Ratio of i-pentane in gasoline samples to that in roadside samples were calculated and this showed that the degree of evaporative loss was higher in Guangzhou and Zhuhai than that in Hong Kong and Macau. We suggest the difference is due to the better maintenance and more new cars in Hong Kong and Macau. From tunnel samples collected in Hong Kong in two different years, we found that the relative amount of propane, i-butane, and n-butane increased between 2001 to 2003, consistent with the 40% increase in LPG fueled vehicles. Propane to butanes ratios were calculated for LPG and tunnels samples, and the comparable ratios illustrated the LPG leakages from LPG fueled vehicles crossing the tunnel

### Quantum Joule Expansion of One-Dimensional Systems

We investigate the Joule expansion of nonintegrable quantum systems that
contain bosons or spinless fermions in one-dimensional lattices. A barrier
initially confines the particles to be in half of the system in a thermal state
described by the canonical ensemble and is removed at time $t = 0$. We
investigate the properties of the time-evolved density matrix, the diagonal
ensemble density matrix and the corresponding canonical ensemble density matrix
with an effective temperature determined by the total energy conservation using
exact diagonalization. The weights for the diagonal ensemble and the canonical
ensemble match well for high initial temperatures that correspond to negative
effective final temperatures after the expansion. At long times after the
barrier is removed, the time-evolved R\'enyi entropy of subsystems bigger than
half can equilibrate to the thermal entropy with exponentially small
fluctuations. The time-evolved reduced density matrix at long times can be
approximated by a thermal density matrix for small subsystems. Few-body
observables, like the momentum distribution function, can be approximated by a
thermal expectation of the canonical ensemble with strongly suppressed
fluctuations. The negative effective temperatures for finite systems go to
nonnegative temperatures in the thermodynamic limit for bosons, but is a true
thermodynamic effect for fermions, which is confirmed by finite temperature
density matrix renormalization group calculations. We propose the Joule
expansion as a way to dynamically create negative temperature states for
fermion systems with repulsive interactions.Comment: 19 pages, 19 figure

### Weak dipole moment of $\tau$ in $e^+e^-$ collisions with longitudinally polarized electrons

It is pointed out that certain CP-odd momentum correlations in the production
and subsequent decay of tau pairs in $e^+e^-$ collisions get enhanced when the
$e^-$ is longitudinally polarized. Analytic expressions for these correlations
are obtained for the single-pion decay mode of $\tau$ when $\tau^+\tau^-$ have
a ``weak" dipole form factor (WDFF) coupling to $Z$ . For $e^+e^-$ collisions
at the $Z$ peak, a sensitivity of about 1-5$\times 10^{-17}$\mbox{$e$ cm} for
the $\tau$ WDFF can be reached using a {\em single} $\tau^+\tau^-$ decay
channel, with $10^6\, Z$'s likely to be available at the SLC at Stanford with
$e^-$ polarization of 62\%-75\%.Comment: 9 pages, Latex, PRL-TH-93/17 (Revised

### Desilting Efficiency Due to Empty Flushing of Agongdian Reservoir

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchive

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