8,007 research outputs found
Are There Topological Black Hole Solitons in String Theory?
We point out that the celebrated Hawking effect of quantum instability of
black holes seems to be related to a nonperturbative effect in string theory.
Studying quantum dynamics of strings in the gravitational background of black
holes we find classical instability due to emission of massless string
excitations. The topology of a black hole seems to play a fundamental role in
developing the string theory classical instability due to the effect of sigma
model instantons. We argue that string theory allows for a qualitative
description of black holes with very small masses and it predicts topological
solitons with quantized spectrum of masses. These solitons would not decay into
string massless excitations but could be pair created and may annihilate also.
Semiclassical mass quantization of topological solitons in string theory is
based on the argument showing existence of nontrivial zeros of beta function of
the renormalization group.Comment: 12 pages, TeX, requires phyzzx.tex, published in Gen. Rel. Grav. 19
(1987) 1173; comment added on December 18, 199
NN Interaction JISP16: Current Status and Prospect
We discuss realistic nonlocal NN interactions of a new type - J-matrix
Inverse Scattering Potential (JISP). In an ab exitu approach, these
interactions are fitted to not only two-nucleon data (NN scattering data and
deuteron properties) but also to the properties of light nuclei without
referring to three-nucleon forces. We discuss recent progress with the ab
initio No-core Shell Model (NCSM) approach and respective progress in
developing ab exitu JISP-type NN-interactions together with plans of their
forthcoming improvements.Comment: 9 pages, 3 figures, to be published in Proceedings of Few-body 19
conferenc
3D global simulations of a cosmic-ray-driven dynamo in dwarf galaxies
Star-forming dwarf galaxies can be seen as the local proxies of the
high-redshift building blocks of more massive galaxies according to the current
paradigm of the hierarchical galaxy formation. They are low-mass objects, and
therefore their rotation speed is very low. Several galaxies are observed to
show quite strong magnetic fields. These cases of strong ordered magnetic
fields seem to correlate with a high, but not extremely high, star formation
rate. We investigate whether these magnetic fields could be generated by the
cosmic-ray-driven dynamo. The environment of a dwarf galaxy is unfavourable for
the large-scale dynamo action because of the very slow rotation that is
required to create the regular component of the magnetic field. We built a 3D
global model of a dwarf galaxy that consists of two gravitational components:
the stars and the dark-matter halo described by the purely phenomenological
profile proposed previously. We solved a system of magnetohydrodynamic (MHD)
equations that include an additional cosmic-ray component described by the
fluid approximation. We found that the cosmic-ray-driven dynamo can amplify the
magnetic field with an exponential growth rate. The -folding time is
correlated with the initial rotation speed. The final mean value of the
azimuthal flux for our models is of the order of few G and the system
reaches its equipartition level. The results indicate that the
cosmic-ray-driven dynamo is a process that can explain the magnetic fields in
dwarf galaxies.Comment: 6 pages, 4 figures, accepted for publication in A&
Cosmic-ray driven dynamo in the interstellar medium of irregular galaxies
Irregular galaxies are usually smaller and less massive than their spiral,
S0, and elliptical counterparts. Radio observations indicate that a magnetic
field is present in irregular galaxies whose value is similar to that in spiral
galaxies. However, the conditions in the interstellar medium of an irregular
galaxy are unfavorable for amplification of the magnetic field because of the
slow rotation and low shearing rate. We investigate the cosmic-ray driven
dynamo in the interstellar medium of an irregular galaxy. We study its
efficiency under the conditions of slow rotation and weak shear. The star
formation is also taken into account in our model and is parametrized by the
frequency of explosions and modulations of activity. The numerical model
includes a magnetohydrodynamical dynamo driven by cosmic rays that is injected
into the interstellar medium by randomly exploding supernovae. In the model, we
also include essential elements such as vertical gravity of the disk,
differential rotation approximated by the shearing box, and resistivity leading
to magnetic reconnection. We find that even slow galactic rotation with a low
shearing rate amplifies the magnetic field, and that rapid rotation with a low
value of the shear enhances the efficiency of the dynamo. Our simulations have
shown that a high amount of magnetic energy leaves the simulation box becoming
an efficient source of intergalactic magnetic fields.Comment: 9 pages, 6 figure
Prospects for the Application of Nanotechnologies to the Computer System Architecture
Computer system architecture essentially influences the comfort of our everyday living. Developmental
transition from electromechanical relays to vacuum tubes, from transistors to integrated circuits has significantly
changed technological standards for the architecture of computer systems. Contemporary information
technologies offer huge potential concerning miniaturization of electronic circuits. Presently, a
modern integrated circuit includes over a billion of transistors, each of them smaller than 100 nm . Stepping
beyond the symbolic 100 nm limit means that with the onset of the 21 century we have entered a new
scientific area that is an era of nanotechnologies. Along with the reduction of transistor dimensions their
operation speed and efficiency grow. However, the hitherto observed developmental path of classical electronics
with its focus on the miniaturization of transistors and memory cells seems arriving at the limits of
technological possibilities because of technical problems as well as physical limitations related to the appearance
of new nano-scale phenomena as e.g. quantum effects.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2488
Stalling the State: How Digital Platforms Contribute to and Profit From Delays in the Enforcement and Adoption of Regulations
While it is often claimed that the pace of digital transformation is such that its own, often glacial changes do not allow the state to catch up, we argue that technological companies, with the help of some state actors, have been slowing the state down. To capture this phenomenon, we introduce the notion of stalling strategies. We argue that stalling strategies have allowed digital platforms to create time that they have spent generating revenue and accumulating platform power, which later protected them from state actions. Drawing on a case study of Uber in Poland and a number of shadow cases, we distinguish five stalling strategies: reinventing classifications, dragging out court proceedings, stealing the time of street-level bureaucrats, delaying new regulations, and taking time to (not) comply. By analyzing stalling strategies, this article contributes to discussions about the politics of platform capitalism, the temporality of digitalization, and institutional drift.Introduction Theory: Primitive Accumulation of Platform Power and Stalling Strategies Case Selection and Data Stalling Strategies Beyond the Particular Case: Stalling to Accumulate Platform Power, Stalling to Protect It Conclusion: Platform Power as a Fait Accompli Acknowledgements Notes Reference
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