23,436 research outputs found
Noncontact measurement of high-temperature surface tension and viscosity of bulk metallic glass-forming alloys using the drop oscillation technique
High-temperature surface tension and viscosities for five bulk metallic glass-forming alloys with widely different glass-forming abilities are measured. The measurements are carried out in a high-vacuum electrostatic levitator using the drop oscillation technique. The surface tension follows proportional mathematical addition of pure components' surface tension except when some of the constituent elements have much lower surface tension. In such cases, there is surface segregation of the low surface tension elements. These alloys are found to have orders of magnitude higher viscosity at their melting points compared to the constituent metals. Among the bulk glass-forming alloys, the better glass former has a higher melting-temperature viscosity, which demonstrates that high-temperature viscosity has a pronounced influence on glass-forming ability. Correlations between surface tension and viscosity are also investigated
Quantum field theories on the Lefschetz thimble
In these proceedings, we summarize the Lefschetz thimble approach to the sign
problem of Quantum Field Theories. In particular, we review its motivations,
and we summarize the results of the application of two different algorithms to
two test models.Comment: contributions to 31st International Symposium on Lattice Field Theory
- LATTICE 2013, July 29 - August 3, 2013, Mainz, Germany and QCD-TNT-III, 2-6
September, 2013, European Centre for Theoretical Studies in Nuclear Physics
and Related Areas (ECT*), Villazzano, Trento (Italy
Stability of the Matrix Model in Operator Interpretation
The IIB matrix model is one of the candidates for nonperturbative formulation
of string theory, and it is believed that the model contains gravitational
degrees of freedom in some manner. In some preceding works, it was proposed
that the matrix model describes the curved space where the matrices represent
differential operators that are defined on a principal bundle. In this paper,
we study the dynamics of the model in this interpretation, and point out the
necessity of the principal bundle from the viewpoint of the stability and
diffeomorphism invariance. We also compute the one-loop correction which
possibly yields a mass term for each field due to the principal bundle. We find
that the correction does generate some mass terms with the supersymmetry
broken, while fields in the original IIB matrix model remain massless. The
positivity is not violated as long as the number of bosonic degrees of freedom
is larger than the fermionic counterpart. The generation of mass terms means
that the new mass scale emerges through the loop correction.Comment: 20 pages, 6 figure
Separation of variables for a lattice integrable system and the inverse problem
We investigate the relation between the local variables of a discrete
integrable lattice system and the corresponding separation variables, derived
from the associated spectral curve. In particular, we have shown how the
inverse transformation from the separation variables to the discrete lattice
variables may be factorised as a sequence of canonical transformations,
following the procedure outlined by Kuznetsov.Comment: 14 pages. submitted for publicatio
Spectral analysis of gluonic pole matrix elements for fragmentation
The non-vanishing of gluonic pole matrix elements can explain the appearance
of single spin asymmetries in high-energy scattering processes. We use a
spectator framework approach to investigate the spectral properties of
quark-quark-gluon correlators and use this to study gluonic pole matrix
elements. Such matrix elements appear in principle both for distribution
functions such as the Sivers function and fragmentation functions such as the
Collins function. We find that for a large class of spectator models, the
contribution of the gluonic pole matrix element in fragmentation functions
vanishes. This outcome is important in the study of universality for
fragmentation functions and confirms findings using a different approach.Comment: 9 pages, 4 figures, added reference
Ultracold nonreactive molecules in an optical lattice: connecting chemistry to many-body physics
We derive effective lattice models for ultracold bosonic or fermionic
nonreactive molecules (NRMs) in an optical lattice, analogous to the Hubbard
model that describes ultracold atoms in a lattice. In stark contrast to the
Hubbard model, which is commonly assumed to accurately describe NRMs, we find
that the single on-site interaction parameter is replaced by a
multi-channel interaction, whose properties we elucidate. The complex,
multi-channel collisional physics is unrelated to dipolar interactions, and so
occurs even in the absence of an electric field or for homonuclear molecules.
We find a crossover between coherent few-channel models and fully incoherent
single-channel models as the lattice depth is increased. We show that the
effective model parameters can be determined in lattice modulation experiments,
which consequently measure molecular collision dynamics with a vastly sharper
energy resolution than experiments in an ultracold gas.Comment: 4 pages+refs, 3 figures; 2.5 pages+1 figure Supplemental Materia
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Expert-level detection of acute intracranial hemorrhage on head computed tomography using deep learning.
Computed tomography (CT) of the head is used worldwide to diagnose neurologic emergencies. However, expertise is required to interpret these scans, and even highly trained experts may miss subtle life-threatening findings. For head CT, a unique challenge is to identify, with perfect or near-perfect sensitivity and very high specificity, often small subtle abnormalities on a multislice cross-sectional (three-dimensional [3D]) imaging modality that is characterized by poor soft tissue contrast, low signal-to-noise using current low radiation-dose protocols, and a high incidence of artifacts. We trained a fully convolutional neural network with 4,396 head CT scans performed at the University of California at San Francisco and affiliated hospitals and compared the algorithm's performance to that of 4 American Board of Radiology (ABR) certified radiologists on an independent test set of 200 randomly selected head CT scans. Our algorithm demonstrated the highest accuracy to date for this clinical application, with a receiver operating characteristic (ROC) area under the curve (AUC) of 0.991 ± 0.006 for identification of examinations positive for acute intracranial hemorrhage, and also exceeded the performance of 2 of 4 radiologists. We demonstrate an end-to-end network that performs joint classification and segmentation with examination-level classification comparable to experts, in addition to robust localization of abnormalities, including some that are missed by radiologists, both of which are critically important elements for this application
Adiabatic charge pumping through a dot at the junction of N quantum wires
We study adiabatic charge pumping through a quantum dot placed at the
junction of quantum wires. We explicitly map out the pattern of pumped
charge as a function of the time-varying tunneling parameters coupling the
wires to the dot and the phase between any two time varying parameters
controlling the shape of the dot. We find that with time-independent
well-coupled leads, the maximum pumped charge in the remaining two leads is
strongly suppressed with increasing , leading to the possibility of tuning
of the pumped charge, by modulating the coupling of the leads.Comment: 5 pages, 6 figures, version to be published in PR
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