16,936 research outputs found
Universality of modulation length (and time) exponents
We study systems with a crossover parameter lambda, such as the temperature
T, which has a threshold value lambda* across which the correlation function
changes from exhibiting fixed wavelength (or time period) modulations to
continuously varying modulation lengths (or times). We report on a new
exponent, nuL, characterizing the universal nature of this crossover. These
exponents, similar to standard correlation length exponents, are obtained from
motion of the poles of the momentum (or frequency) space correlation functions
in the complex k-plane (or omega-plane) as the parameter lambda is varied. Near
the crossover, the characteristic modulation wave-vector KR on the variable
modulation length "phase" is related to that on the fixed modulation length
side, q via |KR-q|\propto|T-T*|^{nuL}. We find, in general, that nuL=1/2. In
some special instances, nuL may attain other rational values. We extend this
result to general problems in which the eigenvalue of an operator or a pole
characterizing general response functions may attain a constant real (or
imaginary) part beyond a particular threshold value, lambda*. We discuss
extensions of this result to multiple other arenas. These include the ANNNI
model. By extending our considerations, we comment on relations pertaining not
only to the modulation lengths (or times) but also to the standard correlation
lengths (or times). We introduce the notion of a Josephson timescale. We
comment on the presence of "chaotic" modulations in "soft-spin" and other
systems. These relate to glass type features. We discuss applications to Fermi
systems - with particular application to metal to band insulator transitions,
change of Fermi surface topology, divergent effective masses, Dirac systems,
and topological insulators. Both regular periodic and glassy (and spatially
chaotic behavior) may be found in strongly correlated electronic systems.Comment: 22 pages, 15 figure
The Gravity Dual of the Ising Model
We evaluate the partition function of three dimensional theories of gravity
in the quantum regime, where the AdS radius is Planck scale and the central
charge is of order one. The contribution from the AdS vacuum sector can - with
certain assumptions - be computed and equals the vacuum character of a minimal
model CFT. The torus partition function is given by a sum over geometries which
is finite and computable. For generic values of Newton's constant G and the AdS
radius L the result has no Hilbert space interpretation, but in certain cases
it agrees with the partition function of a known CFT. For example, the
partition function of pure Einstein gravity with G=3L equals that of the Ising
model, providing evidence that these theories are dual. We also present
somewhat weaker evidence that the 3-state and tricritical Potts models are dual
to pure higher spin theories of gravity based on SL(3) and E_6, respectively.Comment: 42 page
Parametric study of the polarization dependence of nonlinear Breit-Wheeler pair creation process using two laser pulses
With the rapid development of high-power petawatt class lasers worldwide,
exploring physics in the strong field QED regime will become one of the
frontiers for laser-plasma interactions research. Particle-in-cell codes,
including quantum emission processes, are powerful tools for predicting and
analyzing future experiments where the physics of relativistic plasma is
strongly affected by strong-field QED processes. The spin/polarization
dependence of these quantum processes has been of recent interest. In this
article, we perform a parametric study of the interaction of two laser pulses
with an ultrarelativistic electron beam. The first pulse is optimized to
generate high-energy photons by nonlinear Compton scattering and efficiently
decelerate the electron beam through quantum radiation reaction. The second
pulse is optimized to generate electron-positron pairs by nonlinear
Breit-Wheeler decay of the photons with the maximum polarization dependence.
This may be experimentally realized as a verification of the strong field QED
framework, including the spin/polarization rates.Comment: 16 pages, 13 figure
Parametric phenomena of the particle dynamics in a periodic gravitational wave field
We establish exactly solvable models for the motion of neutral particles,
electrically charged point and spin particles (U(1) symmetry), isospin
particles (SU(2) symmetry), and particles with color charges (SU(3) symmetry)
in a gravitational wave background. Special attention is devoted to parametric
effects induced by the gravitational field. In particular, we discuss
parametric instabilities of the particle motion and parametric oscillations of
the vectors of spin, isospin, and color charge.Comment: 26 pages, to be published in J. Math. Phy
Transport coefficients of multi-particle collision algorithms with velocity-dependent collision rules
Detailed calculations of the transport coefficients of a recently introduced
particle-based model for fluid dynamics with a non-ideal equation of state are
presented. Excluded volume interactions are modeled by means of biased
stochastic multiparticle collisions which depend on the local velocities and
densities. Momentum and energy are exactly conserved locally. A general scheme
to derive transport coefficients for such biased, velocity dependent collision
rules is developed. Analytic expressions for the self-diffusion coefficient and
the shear viscosity are obtained, and very good agreement is found with
numerical results at small and large mean free paths. The viscosity turns out
to be proportional to the square root of temperature, as in a real gas. In
addition, the theoretical framework is applied to a two-component version of
the model, and expressions for the viscosity and the difference in diffusion of
the two species are given.Comment: 31 pages, 8 figures, accepted by J. Phys. Cond. Matte
3D-printed flow cells for aptamer-based impedimetric detection of e. coli crooks strain
Electrochemical spectroscopy enables rapid, sensitive, and label-free analyte detection without the need of extensive and laborious labeling procedures and sample preparation. In addition, with the emergence of commercially available screen-printed electrodes (SPEs), a valuable, disposable alternative to costly bulk electrodes for electrochemical (bio-)sensor applications was established in recent years. However, applications with bare SPEs are limited and many applications demand additional/supporting structures or flow cells. Here, high-resolution 3D printing technology presents an ideal tool for the rapid and flexible fabrication of tailor-made, experiment-specific systems. In this work, flow cells for SPE-based electrochemical (bio-)sensor applications were designed and 3D printed. The successful implementation was demonstrated in an aptamer-based impedimetric biosensor approach for the detection of Escherichia coli (E. coli) Crooks strain as a proof of concept. Moreover, further developments towards a 3D-printed microfluidic flow cell with an integrated micromixer also illustrate the great potential of high-resolution 3D printing technology to enable homogeneous mixing of reagents or sample solutions in (bio-)sensor applications
Fully automated deep learning powered calcium scoring in patients undergoing myocardial perfusion imaging
BACKGROUND
To assess the accuracy of fully automated deep learning (DL) based coronary artery calcium scoring (CACS) from non-contrast computed tomography (CT) as acquired for attenuation correction (AC) of cardiac single-photon-emission computed tomography myocardial perfusion imaging (SPECT-MPI).
METHODS AND RESULTS
Patients were enrolled in this study as part of a larger prospective study (NCT03637231). In this study, 56 Patients who underwent cardiac SPECT-MPI due to suspected coronary artery disease (CAD) were prospectively enrolled. All patients underwent non-contrast CT for AC of SPECT-MPI twice. CACS was manually assessed (serving as standard of reference) on both CT datasets (n = 112) and by a cloud-based DL tool. The agreement in CAC scores and CAC score risk categories was quantified. For the 112 scans included in the analysis, interscore agreement between the CAC scores of the standard of reference and the DL tool was 0.986. The agreement in risk categories was 0.977 with a reclassification rate of 3.6%. Heart rate, image noise, body mass index (BMI), and scan did not significantly impact (p=0.09 - p=0.76) absolute percentage difference in CAC scores.
CONCLUSION
A DL tool enables a fully automated and accurate estimation of CAC scores in patients undergoing non-contrast CT for AC of SPECT-MPI
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