16,457 research outputs found
Some Spectral and Quasi-Spectral Characterizations of Distance-Regular Graphs
In this paper we consider the concept of preintersection numbers of a graph.
These numbers are determined by the spectrum of the adjacency matrix of the
graph, and generalize the intersection numbers of a distance-regular graph. By
using the preintersection numbers we give some new spectral and quasi-spectral
characterizations of distance-regularity, in particular for graphs with large
girth or large odd-girth
Short-distance and short-time structure of a unitary Fermi gas
We consider the operator product expansions for unitarity fermions. We
compute the dynamic structure factor S(q,w) at large frequency and wavenumber
away from the one-particle peak. The overall normalization of S(q,w) is
determined by Tan's contact parameter, and the dependence on q and w is
obtained in closed analytic form. We also find energy deposited into the system
by small, rapid variations of the inverse scattering length.Comment: 11 pages, 8 figure
Modeling low order aberrations in laser guide star adaptive optics systems
When using a laser guide star (LGS) adaptive optics (AO) system, quasi-static aberrations are observed between the measured wavefronts from the LGS wavefront sensor (WFS) and the natural guide star (NGS) WFS. These LGS aberrations, which can be as much as 1200 nm RMS on the Keck II LGS AO system, arise due to the finite height and structure of the sodium layer. The LGS aberrations vary significantly between nights due to the difference in sodium structure. In this paper, we successfully model these LGS aberrations for the Keck II LGS AO system. We use this model to characterize the LGS aberrations as a function of pupil angle, elevation, sodium structure, uplink tip/tilt error, detector field of view, the number of detector pixels, and seeing. We also employ the model to estimate the LGS aberrations for the Palomar LGS AO system, the planned Keck I and the Thirty Meter Telescope (TMT) LGS AO systems. The LGS aberrations increase with increasing telescope diameter, but are reduced by central projection of the laser compared to side projection
Subgroup analysis in burnout:Relations between fatigue, anxiety, and depression.
Several authors have suggested that burned out patients do not form a homogeneous group and that subgroups should be considered. The identification of these subgroups may contribute to a better understanding of the burnout construct and lead to more specific therapeutic interventions. Subgroup analysis may also help clarify whether burnout is a distinct entity and whether subgroups of burnout overlap with other disorders such as depression and chronic fatigue syndrome. In a group of 113 clinically diagnosed burned out patients, levels of fatigue, depression, and anxiety were assessed. In order to identify possible subgroups, we performed a two-step cluster analysis. The analysis revealed two clusters that differed from one another in terms of symptom severity on the three aforementioned measures. Depression appeared to be the strongest predictor of group membership. These results are considered in the light of the scientific debate on whether burnout can be distinguished from depression and whether burnout subtyping is useful. Finally, implications for clinical practice and future research are discussed
Tight Noise Thresholds for Quantum Computation with Perfect Stabilizer Operations
We study how much noise can be tolerated by a universal gate set before it
loses its quantum-computational power. Specifically we look at circuits with
perfect stabilizer operations in addition to imperfect non-stabilizer gates. We
prove that for all unitary single-qubit gates there exists a tight depolarizing
noise threshold that determines whether the gate enables universal quantum
computation or if the gate can be simulated by a mixture of Clifford gates.
This exact threshold is determined by the Clifford polytope spanned by the 24
single-qubit Clifford gates. The result is in contrast to the situation wherein
non-stabilizer qubit states are used; the thresholds in that case are not
currently known to be tight.Comment: 4 pages, 2 figure
Universal four-component Fermi gas in one dimension
A four-component Fermi gas in one dimension with a short-range four-body
interaction is shown to exhibit a one-dimensional analog of the BCS-BEC
crossover. Its low-energy physics is governed by a Tomonaga-Luttinger liquid
with three spin gaps. The spin gaps are exponentially small in the weak
coupling (BCS) limit where they arise from the charge-density-wave instability,
and become large in the strong coupling (BEC) limit because of the formation of
tightly-bound tetramers. We investigate the ground-state energy, the sound
velocity, and the gap spectrum in the BCS-BEC crossover and discuss exact
relationships valid in our system. We also show that a one-dimensional analog
of the Efimov effect occurs for five bosons while it is absent for fermions.
Our work opens up a very rich new field of universal few-body and many-body
physics in one dimension.Comment: 9 pages, 3 figures; (v2) Efimov effect for 5 bosons in 1D is
discussed; (v3) expanded versio
Searching for magnetic monopoles trapped in accelerator material at the Large Hadron Collider
If produced in high energy particle collisions at the LHC, magnetic monopoles
could stop in material surrounding the interaction points. Obsolete parts of
the beam pipe near the CMS interaction region, which were exposed to the
products of pp and heavy ion collisions, were analysed using a SQUID-based
magnetometer. The purpose of this work is to quantify the performance of the
magnetometer in the context of a monopole search using a small set of samples
of accelerator material ahead of the 2013 shutdown.Comment: 11 page
Simple proof of equivalence between adiabatic quantum computation and the circuit model
We prove the equivalence between adiabatic quantum computation and quantum
computation in the circuit model. An explicit adiabatic computation procedure
is given that generates a ground state from which the answer can be extracted.
The amount of time needed is evaluated by computing the gap. We show that the
procedure is computationally efficient.Comment: 5 pages, 2 figures. v2: improved gap estimates and added some more
detail
Conformality Lost
We consider zero-temperature transitions from conformal to non-conformal
phases in quantum theories. We argue that there are three generic mechanisms
for the loss of conformality in any number of dimensions: (i) fixed point goes
to zero coupling, (ii) fixed point runs off to infinite coupling, or (iii) an
IR fixed point annihilates with a UV fixed point and they both disappear into
the complex plane. We give both relativistic and non-relativistic examples of
the last case in various dimensions and show that the critical behavior of the
mass gap behaves similarly to the correlation length in the finite temperature
Berezinskii-Kosterlitz-Thouless (BKT) phase transition in two dimensions, xi ~
exp(c/|T-T_c|^{1/2}). We speculate that the chiral phase transition in QCD at
large number of fermion flavors belongs to this universality class, and attempt
to identify the UV fixed point that annihilates with the Banks-Zaks fixed point
at the lower end of the conformal window.Comment: 30 pages, 6 figures; v2: typos fixed, references adde
- …