2,004 research outputs found
Automatic programming of simulation models
The objective of automatic programming is to improve the overall environment for describing the program. This improved environment is realized by a reduction in the amount of detail that the programmer needs to know and is exposed to. Furthermore, this improved environment is achieved by a specification language that is more natural to the user's problem domain and to the user's way of thinking and looking at the problem. The goal of this research is to apply the concepts of automatic programming (AP) to modeling discrete event simulation system. Specific emphasis is on the design and development of simulation tools to assist the modeler define or construct a model of the system and to then automatically write the corresponding simulation code in the target simulation language, GPSS/PC. A related goal is to evaluate the feasibility of various languages for constructing automatic programming simulation tools
Automatic programming of simulation models
The concepts of software engineering were used to improve the simulation modeling environment. Emphasis was placed on the application of an element of rapid prototyping, or automatic programming, to assist the modeler define the problem specification. Then, once the problem specification has been defined, an automatic code generator is used to write the simulation code. The following two domains were selected for evaluating the concepts of software engineering for discrete event simulation: manufacturing domain and a spacecraft countdown network sequence. The specific tasks were to: (1) define the software requirements for a graphical user interface to the Automatic Manufacturing Programming System (AMPS) system; (2) develop a graphical user interface for AMPS; and (3) compare the AMPS graphical interface with the AMPS interactive user interface
Dynamical Axion Field in Topological Magnetic Insulators
Axions are very light, very weakly interacting particles postulated more than
30 years ago in the context of the Standard Model of particle physics. Their
existence could explain the missing dark matter of the universe. However,
despite intensive searches, they have yet to be detected. In this work, we show
that magnetic fluctuations of topological insulators couple to the
electromagnetic fields exactly like the axions, and propose several experiments
to detect this dynamical axion field. In particular, we show that the axion
coupling enables a nonlinear modulation of the electromagnetic field, leading
to attenuated total reflection. We propose a novel optical modulators device
based on this principle.Comment: 5 pages, 3 figure
Tunable Multifunctional Topological Insulators in Ternary Heusler Compounds
Recently the Quantum Spin Hall effect (QSH) was theoretically predicted and
experimentally realized in a quantum wells based on binary semiconductor
HgTe[1-3]. QSH state and topological insulators are the new states of quantum
matter interesting both for fundamental condensed matter physics and material
science[1-11]. Many of Heusler compounds with C1b structure are ternary
semiconductors which are structurally and electronically related to the binary
semiconductors. The diversity of Heusler materials opens wide possibilities for
tuning the band gap and setting the desired band inversion by choosing
compounds with appropriate hybridization strength (by lattice parameter) and
the magnitude of spin-orbit coupling (by the atomic charge). Based on the
first-principle calculations we demonstrate that around fifty Heusler compounds
show the band inversion similar to HgTe. The topological state in these
zero-gap semiconductors can be created by applying strain or by designing an
appropriate quantum well structure, similar to the case of HgTe. Many of these
ternary zero-gap semiconductors (LnAuPb, LnPdBi, LnPtSb and LnPtBi) contain the
rare earth element Ln which can realize additional properties ranging from
superconductivity (e. g. LaPtBi[12]) to magnetism (e. g. GdPtBi[13]) and
heavy-fermion behavior (e. g. YbPtBi[14]). These properties can open new
research directions in realizing the quantized anomalous Hall effect and
topological superconductors.Comment: 20 pages, 5 figure
Fluctuation-Induced First Order Transition between the Quantum Hall Liquid and Insulator
We study the phase transition between the quantum Hall liquid state and the
insulating state within the framework of the Chern-Simons-Landau-Ginzburg
theory of the quantum Hall effect. For the transition induced by a background
periodic potential in the absence of disorder, the model is described by a
relativistic scalar field coupled to the Chern-Simons gauge field. For this
system, we show that the transition is of the first order, induced by the
fluctuations of the gauge field, rather than second order, with statistical
angle-dependent scaling exponent.Comment: 5 pages, REVTEX 3.0, two PostScript pictures appended, preprint
SU-ITP-94-
Multi-Receiver Quantum Dense Coding with Non-Symmetric Quantum Channel
A two-receiver quantum dense coding scheme and an -receiver quantum dense
coding scheme, in the case of non-symmetric Hilbert spaces of the particles of
the quantum channel, are investigated in this paper. A sender can send his
messages to many receivers simultaneously. The scheme can be applied to quantum
secret sharing and controlled quantum dense coding.Comment: To appear in Journal of the Korean Physical Societ
Collective excitations in double-layer quantum Hall systems
We study the collective excitation spectra of double-layer quantum-Hall
systems using the single mode approximation. The double-layer in-phase density
excitations are similar to those of a single-layer system. For out-of-phase
density excitations, however, both inter-Landau-level and intra-Landau-level
double-layer modes have finite dipole oscillator strengths. The oscillator
strengths at long wavelengths for the latter transitions are shifted upward by
interactions by identical amounts proportional to the interlayer Coulomb
coupling. The intra-Landau-level out-of-phase mode has a gap when the ground
state is incompressible except in the presence of spontaneous inter-layer
coherence. We compare our results with predictions based on the
Chern-Simons-Landau-Ginzburg theory for double-layer quantum Hall systems.Comment: RevTeX, 21 page
On the Electromagnetic Response of Charged Bosons Coupled to a Chern-Simons Gauge Field: A Path Integral Approach
We analyze the electromagnetic response of a system of charged bosons coupled
to a Chern-Simons gauge field. Path integral techniques are used to obtain an
effective action for the particle density of the system dressed with quantum
fluctuations of the CS gauge field. From the action thus obtained we compute
the U(1) current of the theory for an arbitrary electromagnetic external field.
For the particular case of a homogeneous external magnetic field, we show that
the quantization of the transverse conductivity is exact, even in the presence
of an arbitrary impurity distribution. The relevance of edge states in this
context is analyzed. The propagator of density fluctuations is computed, and an
effective action for the matter density in the presence of a vortex excitation
is suggested.Comment: LaTex file, 27 pages, no figure
Interleukin-23 engineering improves CAR T cell function in solid tumors
Cytokines that stimulate T cell proliferation, such as interleukin (IL)-15, have been explored as a means of boosting the antitumor activity of chimeric antigen receptor (CAR) T cells. However, constitutive cytokine signaling in T cells and activation of bystander cells may cause toxicity. IL-23 is a two-subunit cytokine known to promote proliferation of memory T cells and T helper type 17 cells. We found that, upon T cell antigen receptor (TCR) stimulation, T cells upregulated the IL-23 receptor and the IL-23α p19 subunit, but not the p40 subunit. We engineered expression of the p40 subunit in T cells (p40-Td cells) and obtained selective proliferative activity in activated T cells via autocrine IL-23 signaling. In comparison to CAR T cells, p40-Td CAR T cells showed improved antitumor capacity in vitro, with increased granzyme B and decreased PD-1 expression. In two xenograft and two syngeneic solid tumor mouse models, p40-Td CAR T cells showed superior efficacy in comparison to CAR T cells and attenuated side effects in comparison to CAR T cells expressing IL-18 or IL-15
Landau Quantization of Massless Dirac Fermions in Topological Insulator
The recent theoretical prediction and experimental realization of topological
insulators (TI) has generated intense interest in this new state of quantum
matter. The surface states of a three-dimensional (3D) TI such as Bi_2Te_3,
Bi_2Se_3 and Sb_2Te_3 consist of a single massless Dirac cones. Crossing of the
two surface state branches with opposite spins in the materials is fully
protected by the time reversal (TR) symmetry at the Dirac points, which cannot
be destroyed by any TR invariant perturbation. Recent advances in thin-film
growth have permitted this unique two-dimensional electron system (2DES) to be
probed by scanning tunneling microscopy (STM) and spectroscopy (STS). The
intriguing TR symmetry protected topological states were revealed in STM
experiments where the backscattering induced by non-magnetic impurities was
forbidden. Here we report the Landau quantization of the topological surface
states in Bi_2Se_3 in magnetic field by using STM/STS. The direct observation
of the discrete Landau levels (LLs) strongly supports the 2D nature of the
topological states and gives direct proof of the nondegenerate structure of LLs
in TI. We demonstrate the linear dispersion of the massless Dirac fermions by
the square-root dependence of LLs on magnetic field. The formation of LLs
implies the high mobility of the 2DES, which has been predicted to lead to
topological magneto-electric effect of the TI.Comment: 15 pages, 4 figure
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