6,111 research outputs found
Baby-Step Giant-Step Algorithms for the Symmetric Group
We study discrete logarithms in the setting of group actions. Suppose that
is a group that acts on a set . When , a solution
to can be thought of as a kind of logarithm. In this paper, we study
the case where , and develop analogs to the Shanks baby-step /
giant-step procedure for ordinary discrete logarithms. Specifically, we compute
two sets such that every permutation of can be
written as a product of elements and . Our
deterministic procedure is optimal up to constant factors, in the sense that
and can be computed in optimal asymptotic complexity, and and
are a small constant from in size. We also analyze randomized
"collision" algorithms for the same problem
Strange Quarks Nuggets in Space: Charges in Seven Settings
We have computed the charge that develops on an SQN in space as a result of
balance between the rates of ionization by ambient gammas and capture of
ambient electrons. We have also computed the times for achieving that
equilibrium and binding energy of the least bound SQN electrons. We have done
this for seven different settings. We sketch the calculations here and give
their results in the Figure and Table II; details are in the Physical Review
D.79.023513 (2009).Comment: Six pages, one figure. To appear in proceedings of the 2008 UCLA
coference on dark matter and dark energ
Inference with interference between units in an fMRI experiment of motor inhibition
An experimental unit is an opportunity to randomly apply or withhold a
treatment. There is interference between units if the application of the
treatment to one unit may also affect other units. In cognitive neuroscience, a
common form of experiment presents a sequence of stimuli or requests for
cognitive activity at random to each experimental subject and measures
biological aspects of brain activity that follow these requests. Each subject
is then many experimental units, and interference between units within an
experimental subject is likely, in part because the stimuli follow one another
quickly and in part because human subjects learn or become experienced or
primed or bored as the experiment proceeds. We use a recent fMRI experiment
concerned with the inhibition of motor activity to illustrate and further
develop recently proposed methodology for inference in the presence of
interference. A simulation evaluates the power of competing procedures.Comment: Published by Journal of the American Statistical Association at
http://www.tandfonline.com/doi/full/10.1080/01621459.2012.655954 . R package
cin (Causal Inference for Neuroscience) implementing the proposed method is
freely available on CRAN at https://CRAN.R-project.org/package=ci
A VIDA URBANA SOB A ĂTICA DO FANTĂSTICO:potĂȘncias do estranhamento na produção de subjetividades
Este trabalho busca um olhar para a vida na cidade inspirado no gĂȘnero literĂĄrio nomeado realismo fantĂĄstico. Parte de conceituaçÔes do termo fantĂĄstico fora do campo da literatura, compreendendo-o como uma sensação de estranhamento que pode se fazer presente na vida urbana contemporĂąnea, e propĂ”e utilizĂĄ-lo como fio condutor para urdir tramas sobre modos de vida urbanos.
Temos, portanto, um levantamento teĂłrico sobre o que se entende por modo de vida urbano e seu papel na produção de subjetividades e sobre o fantĂĄstico entendido como sensação que extrapola a literatura, utilizando conexĂ”es hibridas: acadĂȘmicos de campos do saber diversos, cineastas, mĂșsicos, escritores de ficção e o saber popular, o saber das pessoas. Como desenvolvimento da pesquisa de campo realizada na cidade de VitĂłria, temos relatos de situaçÔes urbanas tramadas com fios de fantĂĄstico, a fim de ensaiar modos diferentes de pensar, viver e escrever. Espera-se que esse olhar sobre a vida na cidade potencialize o questionamento acerca de um modo como temos vivido no espaço urbano: automatizado, acelerado, individual, anestesiado de sentidos e funcional. TambĂ©m experimentamos as tramas fantĂĄsticas como um truque ou estratĂ©gia de resistĂȘncia ao cansaço, adoecimento e desencanto que esse modo nos tĂȘm causado, desnaturalizando-o. A convergĂȘncia entre essa proposição polĂtica de resistĂȘncia e sua experimentação no cotidiano constitui a fonte, por assim dizer, desta pesquis
Conductivity of Metallic Si:B near the Metal-Insulator Transition: Comparison between Unstressed and Uniaxially Stressed Samples
The low-temperature dc conductivities of barely metallic samples of p-type
Si:B are compared for a series of samples with different dopant concentrations,
n, in the absence of stress (cubic symmetry), and for a single sample driven
from the metallic into the insulating phase by uniaxial compression, S. For all
values of temperature and stress, the conductivity of the stressed sample
collapses onto a single universal scaling curve. The scaling fit indicates that
the conductivity of si:B is proportional to the square-root of T in the
critical range. Our data yield a critical conductivity exponent of 1.6,
considerably larger than the value reported in earlier experiments where the
transition was crossed by varying the dopant concentration. The larger exponent
is based on data in a narrow range of stress near the critical value within
which scaling holds. We show explicitly that the temperature dependences of the
conductivity of stressed and unstressed Si:B are different, suggesting that a
direct comparison of the critical behavior and critical exponents for stress-
tuned and concentration-tuned transitions may not be warranted
IR Kuiper Belt Constraints
We compute the temperature and IR signal of particles of radius and
albedo at heliocentric distance , taking into account the
emissivity effect, and give an interpolating formula for the result. We compare
with analyses of COBE DIRBE data by others (including recent detection of the
cosmic IR background) for various values of heliocentric distance, ,
particle radius, , and particle albedo, . We then apply these
results to a recently-developed picture of the Kuiper belt as a two-sector disk
with a nearby, low-density sector (40<R<50-90 AU) and a more distant sector
with a higher density. We consider the case in which passage through a
molecular cloud essentially cleans the Solar System of dust. We apply a simple
model of dust production by comet collisions and removal by the
Poynting-Robertson effect to find limits on total and dust masses in the near
and far sectors as a function of time since such a passage. Finally we compare
Kuiper belt IR spectra for various parameter values.Comment: 34 pages, LaTeX, uses aasms4.sty, 11 PostScript figures not embedded.
A number of substantive comments by a particularly thoughtful referee have
been addresse
The Hopf Algebra of Renormalization, Normal Coordinates and Kontsevich Deformation Quantization
Using normal coordinates in a Poincar\'e-Birkhoff-Witt basis for the Hopf
algebra of renormalization in perturbative quantum field theory, we investigate
the relation between the twisted antipode axiom in that formalism, the Birkhoff
algebraic decomposition and the universal formula of Kontsevich for quantum
deformation.Comment: 21 pages, 15 figure
PLANTAR PRESSURE MEASUREMENTS IN A SOCCER SHOE: CHARACTERIZATION OF SOCCER SPECIFIC MOVEMENTS AND EFFECTS AFTER SIX WEEKS OF AGING
The purposes of the study were (i) to characterize in-shoe pressure distribution (PD) measurements during soccer specific movements, (ii) to describe the changes on (PD) after six weeks of aging. 21 experienced male subjects participated in the study. Four different movements (run, cut, sprint and goal shot) were measured on a red cinder surface before and after six weeks of aging. Results showed specific loading characteristics for each movement: Compared to running, the medial part of the foot in cutting, the forefoot in sprinting and the lateral part in kicking were predominantly loaded. Peak pressures increased over 10% after six weeks of use in some high-load areas. Attention should be paid to sprinting and cutting with respect to overuse injuries. Sockliners should be exchanged on a regular basis to maintain a certain amount of cushioning
SPECIFIC TRAINING CAN IMPROVE SENSORIMOTOR CONTROL IN TYPE 2 DIABETIC PATIENTS
Diabetes mellitus often is associated with proprioceptive and sensory deficits as a result of distal diabetic polyneuropathy (DPN). The aim of this prospective controlled longitudinal trial was to evaluate a specific sport intervention program regarding sensorimotor capabilities in type 2 diabetic patients compared to healthy controls. A higher incidence of fall-related injuries is given in the literature (Allet et al.2008; Allet et al 2009)
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