417,163 research outputs found
Resonant Interactions in Rotating Homogeneous Three-dimensional Turbulence
Direct numerical simulations of three-dimensional (3D) homogeneous turbulence
under rapid rigid rotation are conducted to examine the predictions of resonant
wave theory for both small Rossby number and large Reynolds number. The
simulation results reveal that there is a clear inverse energy cascade to the
large scales, as predicted by 2D Navier-Stokes equations for resonant
interactions of slow modes. As the rotation rate increases, the
vertically-averaged horizontal velocity field from 3D Navier-Stokes converges
to the velocity field from 2D Navier-Stokes, as measured by the energy in their
difference field. Likewise, the vertically-averaged vertical velocity from 3D
Navier-Stokes converges to a solution of the 2D passive scalar equation. The
energy flux directly into small wave numbers in the plane from
non-resonant interactions decreases, while fast-mode energy concentrates closer
to that plane. The simulations are consistent with an increasingly dominant
role of resonant triads for more rapid rotation
Hybrid power semiconductor
The voltage rating of a bipolar transistor may be greatly extended while at the same time reducing its switching time by operating it in conjunction with FETs in a hybrid circuit. One FET is used to drive the bipolar transistor while the other FET is connected in series with the transistor and an inductive load. Both FETs are turned on or off by a single drive signal of load power, the second FET upon ceasing conductions, rendering one power electrode of the bipolar transistor open. Means are provided to dissipate currents which flow after the bipolar transistor is rendered nonconducting
Quasimodularity and large genus limits of Siegel-Veech constants
Quasimodular forms were first studied in the context of counting torus
coverings. Here we show that a weighted version of these coverings with
Siegel-Veech weights also provides quasimodular forms. We apply this to prove
conjectures of Eskin and Zorich on the large genus limits of Masur-Veech
volumes and of Siegel-Veech constants.
In Part I we connect the geometric definition of Siegel-Veech constants both
with a combinatorial counting problem and with intersection numbers on Hurwitz
spaces. We introduce modified Siegel-Veech weights whose generating functions
will later be shown to be quasimodular.
Parts II and III are devoted to the study of the quasimodularity of the
generating functions arising from weighted counting of torus coverings. The
starting point is the theorem of Bloch and Okounkov saying that q-brackets of
shifted symmetric functions are quasimodular forms. In Part II we give an
expression for their growth polynomials in terms of Gaussian integrals and use
this to obtain a closed formula for the generating series of cumulants that is
the basis for studying large genus asymptotics. In Part III we show that the
even hook-length moments of partitions are shifted symmetric polynomials and
prove a formula for the q-bracket of the product of such a hook-length moment
with an arbitrary shifted symmetric polynomial. This formula proves
quasimodularity also for the (-2)-nd hook-length moments by extrapolation, and
implies the quasimodularity of the Siegel-Veech weighted counting functions.
Finally, in Part IV these results are used to give explicit generating
functions for the volumes and Siegel-Veech constants in the case of the
principal stratum of abelian differentials. To apply these exact formulas to
the Eskin-Zorich conjectures we provide a general framework for computing the
asymptotics of rapidly divergent power series.Comment: 107 pages, final version, to appear in J. of the AM
Network support for integrated design
A framework of network support for utilization of integrated design over the Internet has been developed. The techniques presented also applicable for Intranet/Extranet. The integrated design system was initially developed for local application in a single site. With the network support, geographically dispersed designers can collaborate a design task through out the total design process, quickly respond to clientsâ requests and enhance the design argilty. In this paper, after a brief introduction of the integrated design system, the network support framework is presented, followed by description of two key techniques involved: Java Saverlet approach for remotely executing a large program and online CAD collaboration
Positivity Of Equivariant GromovâWitten Invariants
We show that the equivariant GromovâWitten invariants of a projective homogeneous space G/P exhibit Graham-positivity: when expressed as polynomials in the positive roots, they have nonnegative coefficients
Local molecular field theory for effective attractions between like charged objects in systems with strong Coulomb interactions
Strong short ranged positional correlations involving counterions can induce
a net attractive force between negatively charged strands of DNA, and lead to
the formation of ion pairs in dilute ionic solutions. But the long range of the
Coulomb interactions impedes the development of a simple local picture. We
address this general problem by mapping the properties of a nonuniform system
with Coulomb interactions onto those of a simpler system with short ranged
intermolecular interactions in an effective external field that accounts for
the averaged effects of appropriately chosen long ranged and slowly varying
components of the Coulomb interactions. The remaining short ranged components
combine with the other molecular core interactions and strongly affect pair
correlations in dense or strongly coupled systems. We show that pair
correlation functions in the effective short ranged system closely resemble
those in the uniform primitive model of ionic solutions, and illustrate the
formation of ion pairs and clusters at low densities. The theory accurately
describes detailed features of the effective attraction between two equally
charged walls at strong coupling and intermediate separations of the walls. New
analytical results for the minimal coupling strength needed to get any
attraction and for the separation where the attractive force is a maximum are
presented.Comment: 8 pages, 5 figures. To be published in PNA
Equivariant Quantum Schubert Polynomials
We establish an equivariant quantum Giambelli formula for partial flag varieties. The answer is given in terms of a specialization of universal double Schubert polynomials. Along the way, we give new proofs of the presentation of the equivariant quantum cohomology ring, as well as Graham-positivity of the structure constants in equivariant quantum Schubert calculus. (C) 2013 Elsevier Inc. All rights reserved
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Machine learning phases in statistical physics
Conventionally, the study of phases in statistical mechan- ics is performed with the help of random sampling tools. Among the most powerful are Monte Carlo simulations consisting of a stochastic importance sampling over state space and evaluation of estimators for physical quantities. The ability of modern machine learning techniques to classify, identify, or in- terpret massive data sets provides a complementary paradigm to the above approach to analyze the exponentially large number of states in statistical physics. In this report, it is demonstrated by application on Ising-type models that deep learning has potential wide applications in solving many-body statis- tical physics problems. In application of supervised learning, we showed that the feed-forward neural network can identify phases and phase transitions in the ferromagnetic Ising model and the convolutional neural network (CNN) is extremely powerful in classifying T = 0 and T = â phases in the Ising gauge model; In application of unsupervised learning, we illustrated that a deep auto-encoder constructed by stacked restricted Boltzmann machines (RBM)
is closely related to the renormalization group (RG) method well understood in modern physics and our reconstruction of Ising spin configurations in the ferromagnetic Ising model is similar to the hand-written digits reconstruction.Statistic
Rare-earth ions doped transparent oxyfluoride glass-ceramics
In recent years, rare-earth ions doped transparent oxyfluoride glass-ceramics have attracted great attentions for their low phonon energy environments of fluoride nanocrystals and high chemical and mechanical stabilities of oxide glassy matrix. In this chapter, firstly, the crystallization behaviors of the transparent glass ceramics containing CaF2 nanocrystals are presented to demonstrate the controllable microstructure evolution of nano-composites. Secondly, the optical properties of the newly developed transparent glass-ceramics containing ÎČ-YF3 nanocrystals are systematically reviewed. The rare-earth ions are inclined to partition into the YF3 nanocrystals after crystallization. Through variation of the rare-earth doping and control of the microstructures, the glass-ceramics could exhibit high-stimulated emission cross-section, broadband near infrared emission, high efficient ultraviolet upconversion emission and bright white light emission, indicating their potential multifunctional applications in solid state laser, upconversion, optical amplifier, three-dimensional display, and so on
Symmetries and Lie algebra of the differential-difference Kadomstev-Petviashvili hierarchy
By introducing suitable non-isospectral flows we construct two sets of
symmetries for the isospectral differential-difference Kadomstev-Petviashvili
hierarchy. The symmetries form an infinite dimensional Lie algebra.Comment: 9 page
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