899 research outputs found
Experimental Study of the Cloud Architecture Selection for Effective Big Data Processing
Big data dictate their requirements to the hardware and software. Simple
migration to the cloud data processing, while solving the problem of increasing
computational capabilities, however creates some issues: the need to ensure the
safety, the need to control the quality during data transmission, the need to
optimize requests. Computational cloud does not simply provide scalable
resources but also requires network infrastructure, unknown routes and the
number of user requests. In addition, during functioning situation can occur,
in which you need to change the architecture of the application - part of the
data needs to be placed in a private cloud, part in a public cloud, part stays
on the client
GRBs with optical afterglow and known redshift: a statistical study
We present a correlation between two intrinsic parameters of GRB optical
afterglows. These are the isotropic luminosity at the maximum of the light
curve (Lpeak) and the time-integrated isotropic energy (Eiso) radiated after
the observed maximum. We test the correlation between the logarithms of (Eiso)
and (Lpeak) and finally we value the effect of the different samples of GRBs in
according with the first optical observation reduced to proper time.Comment: To be published in the proceedings of the conference "SWIFT and GRBs:
Unveiling the Relativistic Universe", Venice, June 5-9, 200
The Effect of Surface Roughness on the Universal Thermal Conductance
We explain the reduction of the thermal conductance below the predicted
universal value observed by Schwab et al. in terms of the scattering of thermal
phonons off surface roughness using a scalar model for the elastic waves. Our
analysis shows that the thermal conductance depends on two roughness
parameters: the roughness amplitude and the correlation length .
At sufficiently low temperatures the conductance decrease from the universal
value quadratically with temperature at a rate proportional to .
Values of equal to 0.22 and equal to about 0.75 of the width of
the conduction pathway give a good fit to the data.Comment: 10 pages, 5 figures. Ref. added, typo correcte
Evolutionary Status of Long-Period Radio Pulsars
We analyze the evolutionary status of recently discovered long-period radio
sources PSR J0901-4046, GLEAM-X J1627-52, and GPM J1839-10. We discuss the
hypothesis that all three sources are radio pulsars. In the framework of
standard scenarios, it is often accepted that the pulsar mechanism is switched
off when an external matter can penetrate the light cylinder. If the matter is
stopped outside the light cylinder then the neutron star is at the ejector
stage. We demonstrate that for realistic parameters of the interstellar medium,
the 76-second pulsar PSR J0901-4046 might be at this stage. However, sources
GLEAM-X J1627-52 and GPM J1839-10 with periods s can be ejectors
only in the case of unrealistically large dipolar fields G.
Also, we show that neutron stars with spin periods s and dipolar
magnetic fields G cannot be ejectors in a typical
interstellar medium. Thus, we predict that long-period pulsars with standard
fields will not be discovered.Comment: 7 pages, 2 figures, accepted to Astronomy Letters, translation by the
author
Early Accretion Onset in Long-Period Isolated Pulsars
We model long-term magneto-rotational evolution of isolated neutron stars
with long initial spin periods. This analysis is motivated by the recent
discovery of young long-period neutron stars observed as periodic radio
sources: PSR J0901-4046, GLEAM-X J1627-52, and GPM J1839-10. Our calculations
demonstrate that for realistically rapid spin-down during the propeller stage
all isolated neutron stars with velocities km s are able
to reach the stage of accretion from the interstellar medium within a few
billion years. If neutron stars with long initial spin periods form a
relatively large fraction of all Galactic neutron stars then the number of
isolated accretors is sufficiently larger than it has been predicted by
previous studies.Comment: 12 pages, 2 figures, submitted to PAS
MV3: A new word based stream cipher using rapid mixing and revolving buffers
MV3 is a new word based stream cipher for encrypting long streams of data. A
direct adaptation of a byte based cipher such as RC4 into a 32- or 64-bit word
version will obviously need vast amounts of memory. This scaling issue
necessitates a look for new components and principles, as well as mathematical
analysis to justify their use. Our approach, like RC4's, is based on rapidly
mixing random walks on directed graphs (that is, walks which reach a random
state quickly, from any starting point). We begin with some well understood
walks, and then introduce nonlinearity in their steps in order to improve
security and show long term statistical correlations are negligible. To
minimize the short term correlations, as well as to deter attacks using
equations involving successive outputs, we provide a method for sequencing the
outputs derived from the walk using three revolving buffers. The cipher is fast
-- it runs at a speed of less than 5 cycles per byte on a Pentium IV processor.
A word based cipher needs to output more bits per step, which exposes more
correlations for attacks. Moreover we seek simplicity of construction and
transparent analysis. To meet these requirements, we use a larger state and
claim security corresponding to only a fraction of it. Our design is for an
adequately secure word-based cipher; our very preliminary estimate puts the
security close to exhaustive search for keys of size < 256 bits.Comment: 27 pages, shortened version will appear in "Topics in Cryptology -
CT-RSA 2007
Tevatron Beam Halo Collimation System: Design, Operational Experience and New Methods
Collimation of proton and antiproton beams in the Tevatron collider is
required to protect CDF and D0 detectors and minimize their background rates,
to keep irradiation of superconducting magnets under control, to maintain
long-term operational reliability, and to reduce the impact of beam-induced
radiation on the environment. In this article we briefly describe the design,
practical implementation and performance of the collider collimation system,
methods to control transverse and longitudinal beam halo and two novel
collimation techniques tested in the Tevatron.Comment: 25 p
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