11,358 research outputs found
Phase diagrams for quantum Brownian motion models on two-dimensional Bravais lattices
We study quantum Brownian motion (QBM) models for a particle in a dissipative
environment coupled to a periodic potential. We review QBM for a particle in a
one-dimensional periodic potential and extend the study to that for a particle
in two-dimensional (2D) periodic potentials of four Bravais lattice types:
square, rectangular, triangular (hexagonal), and centered rectangular. We
perform perturbative renormalization group analyses to derive the zero
temperature flow diagrams and phase boundaries for a particle in these
potentials, and observe localization behavior dependent on the anisotropy of
the lattice parameters.Comment: 16 pages, 5 figure
The highly connected even-cycle and even-cut matroids
The classes of even-cycle matroids, even-cycle matroids with a blocking pair,
and even-cut matroids each have hundreds of excluded minors. We show that the
number of excluded minors for these classes can be drastically reduced if we
consider in each class only the highly connected matroids of sufficient size.Comment: Version 2 is a major revision, including a correction of an error in
the statement of one of the main results and improved exposition. It is 89
pages, including a 33-page Jupyter notebook that contains SageMath code and
that is also available in the ancillary file
On perturbations of highly connected dyadic matroids
Geelen, Gerards, and Whittle [3] announced the following result: let be a prime power, and let be a proper minor-closed class of
-representable matroids, which does not contain
for sufficiently high . There exist integers
such that every vertically -connected matroid in is a
rank- perturbation of a frame matroid or the dual of a frame matroid
over . They further announced a characterization of the
perturbations through the introduction of subfield templates and frame
templates.
We show a family of dyadic matroids that form a counterexample to this
result. We offer several weaker conjectures to replace the ones in [3], discuss
consequences for some published papers, and discuss the impact of these new
conjectures on the structure of frame templates.Comment: Version 3 has a new title and a few other minor corrections; 38
pages, including a 6-page Jupyter notebook that contains SageMath code and
that is also available in the ancillary file
Moving Toward Non-transcription Based Discourse Analysis in Stable and Progressive Aphasia
Measurement of communication ability at the discourse level holds promise for predicting how well persons with stable (e.g., stroke-induced), or progressive aphasia navigate everyday communicative interactions. However, barriers to the clinical utilization of discourse measures have persisted. Recent advancements in the standardization of elicitation protocols and the existence of large databases for development of normative references have begun to address some of these barriers. Still, time remains a consistently reported barrier by clinicians. Non-transcription based discourse measurement would reduce the time required for discourse analysis, making clinical utilization a reality. The purpose of this article is to present evidence regarding discourse measures (main concept analysis, core lexicon, and derived efficiency scores) that are well suited to non-transcription based analysis. Combined with previous research, our results suggest that these measures are sensitive to changes following stroke or neurodegenerative disease. Given the evidence, further research specifically assessing the reliability of these measures in clinical implementation is warranted
Fast Compact Laser Shutter Using a Direct Current Motor and 3D Printing
We present a mechanical laser shutter design that utilizes a DC electric
motor to rotate a blade which blocks and unblocks a light beam. The blade and
the main body of the shutter are modeled with computer aided design (CAD) and
are produced by 3D printing. Rubber flaps are used to limit the blade's range
of motion, reducing vibrations and preventing undesirable blade oscillations.
At its nominal operating voltage, the shutter achieves a switching speed of
(1.22 0.02) m/s with 1 ms activation delay and 10 s jitter in its
timing performance. The shutter design is simple, easy to replicate, and highly
reliable, showing no failure or degradation in performance over more than
cycles.Comment: 4 pages, 6 figures; supplementary materials for shutter replication
added under "Ancillary files
Optimizing an array of antennas for cellular coverage from a high altitude platform
In a wireless communications network served by a high altitude platform (HAP) the cochannel interference is a function of the antenna beamwidth, angular separation and. sidelobe level. At the millimeter wave frequencies proposed for HAPs, an array of aperture type antennas on the platform is a practicable solution for serving the cells. We present a method for predicting cochannel interference based on curve-fit approximations for radiation patterns of elliptic beams which illuminate cell edges with optimum power, and a means of estimating optimum beamwidths for each cell of a regular hexagonal layout. The method is then applied to a 121 cell architecture. Where sidelobes are modeled As a flat floor at 40-dB below peak directivity, a cell cluster size of four yields carrier-to-interference ratios (CIRs), which vary from 15 dB at cell edges to 27 dB at cell centers. On adopting a cluster size of seven, these figures increase, respectively, to 19 and 30 dB. On reducing the sidelobe level, the. improvement in CIR can be quantified. The method also readily allows for regions of overlapping channel coverage to be shown
A Retrospective Lateral Cephalometric Growth Study of Sagittal Airway Changes
Purpose: This study retrospectively examined the average sagittal dimensions in the pharyngeal airway from skeletal and dental Class I males and females from 7 to 16 years of age utilizing longitudinal data from the American Association of Orthodontists Foundation Craniofacial Growth Legacy Collection. The study evaluated whether average sagittal airway dimensions differed between males and females at each age, and whether the sagittal airway dimension changed with increasing age. Materials and Methods: Sagittal airway dimension based on identifiable anatomical landmarks were digitally traced and measured from the longitudinal lateral cephalograms of 30 females and 32 males from the AAOF Growth Legacy Collection from ages 7 to 16. The distance from the anterior to posterior 2-D limit of the airway along a line perpendicular to Frankfort Horizontal and passing through the anterior nasal spine (ANS) (Measurement 1A-1B), through A-point (Measurement 2A-2B), through upper incisor tip (Measurement 3A-3B), through B-point (Measurement 4A-4B), and throughPogonion (Pog) (Measurement 5A-5B) was measured. Results: ANCOVA showed that males had a statistically significant greater 3A-3B length than females at age 13 (P = 0.02), 15 (P = 0.01), and 16 (P = 0.04). In males, there was a statistically significant increase in 2A-2B length (P = 0.04) and 5A-5B length (P = 0.03) between ages 7 and 16. No other comparisons were statistically significant. Conclusions: No statistically significant difference was found in sagittal airway dimension between males and females. No statistically significant difference was found in change in sagittal airway dimension with increasing age. We were unable to establish normative values
Fidelity of optimally controlled quantum gates with randomly coupled multiparticle environments
This work studies the feasibility of optimal control of high-fidelity quantum
gates in a model of interacting two-level particles. One particle (the qubit)
serves as the quantum information processor, whose evolution is controlled by a
time-dependent external field. The other particles are not directly controlled
and serve as an effective environment, coupling to which is the source of
decoherence. The control objective is to generate target one-qubit gates in the
presence of strong environmentally-induced decoherence and under physically
motivated restrictions on the control field. It is found that interactions
among the environmental particles have a negligible effect on the gate fidelity
and require no additional adjustment of the control field. Another interesting
result is that optimally controlled quantum gates are remarkably robust to
random variations in qubit-environment and inter-environment coupling
strengths. These findings demonstrate the utility of optimal control for
management of quantum-information systems in a very precise and specific
manner, especially when the dynamics complexity is exacerbated by inherently
uncertain environmental coupling.Comment: tMOP LaTeX, 9 pages, 3 figures; Special issue of the Journal of
Modern Optics: 37th Winter Colloquium on the Physics of Quantum Electronics,
2-6 January 200
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