423 research outputs found
Decoupling of superconducting layers in magnetic superconductor RuSr_{2}GdCu_{2}O_{8}
We propose the model for magnetic properties of the magnetic superconductor
RuSrGdCuO, which incorporates the theory of the
superconducting/ferromagnetic multilayers. The transition line , on
which the Josephson coupled superconducting planes are decoupled, i.e. , is calculated as a function of the exchange energy . As the
result of this decoupling a nonmonotonic behavior of magnetic properties, like
the lower critical field , Josephson plasma frequency, etc. is realized
near (or by crossing) the line. The obtained results are used in
analyzing the newly discovered antiferromagnetic ruthenocuprate
RuSrGdCuO with possible weak ferromagnetic order in the RuO
planes.Comment: 12 pages, 3 figs embede
Magnetism and Superconductivity in (RE)Ni2B2C: The Case of TmNi2B2C
The recently reported coexistence of an oscillatory magnetic order with the
wave vector Q=0.241 \AA^{-1} and superconductivity in TmNi2B2C is analyzed
theoretically. It is shown that the oscillatory magnetic order and
superconductivity interact predominantly via the exchange interaction between
localized moments (LM's) and conduction electrons, while the electromagnetic
interaction between them is negligible. In the coexistence phase of the clean
TmNi2B2C the quasiparticle spectrum should have a line of zeros at the Fermi
surface, giving rise to the power law behavior of thermodynamic and transport
properties. Two scenarios of the origin of the oscillatory magnetic order in
TmNi2B2C are analyzed: a) due to superconductivity and b) independently on
superconductivity. Experiments in magnetic field are proposed in order to
choose between them.Comment: 12 pages with 2 PS figures, RevTe
Detecting child grooming behaviour patterns on social media
Online paedophile activity in social media has become a major concern in society as Internet access is easily available to a broader younger population. One common form of online child exploitation is child grooming, where adults and minors exchange sexual text and media via social media platforms. Such behaviour involves a number of stages performed by a predator (adult) with the final goal of approaching a victim (minor) in person. This paper presents a study of such online grooming stages from a machine learning perspective. We propose to characterise such stages by a series of features covering sentiment polarity, content, and psycho-linguistic and discourse patterns. Our experiments with online chatroom conversations show good results in automatically classifying chatlines into various grooming stages. Such a deeper understanding and tracking of predatory behaviour is vital for building robust systems for detecting grooming conversations and potential predators on social media
Supergravity with cosmological constant and the AdS group
It is shown that the supersymmetric extension of the Stelle-West formalism
permits the construction of an action for -dimensional N=1 supergravity
with cosmological constant genuinely invariant under the Since the
action is invariant under the supersymmetric extension of the group, the
supersymmetry algebra closes off shell without the need for auxiliary fields.
The limit case , i.e. -dimensional N=1 supergravity invariant
under the Poincar\'{e} supergroup is also discussed.Comment: 10 page
The NuTeV Anomaly, Neutrino Mixing, and a Heavy Higgs Boson
Recent results from the NuTeV experiment at Fermilab and the deviation of the
Z invisible width, measured at LEP/SLC, from its Standard Model (SM) prediction
suggest the suppression of neutrino-Z couplings. Such suppressions occur
naturally in models which mix the neutrinos with heavy gauge singlet states. We
postulate a universal suppression of the Z-nu-nu couplings by a factor of
(1-epsilon) and perform a fit to the Z-pole and NuTeV observables with epsilon
and the oblique correction parameters S and T. Compared to a fit with S and T
only, inclusion of epsilon leads to a dramatic improvement in the quality of
the fit. The values of S and T preferred by the fit can be obtained within the
SM by a simple increase in the Higgs boson mass. However, if the W mass is also
included in the fit, a non-zero U parameter becomes necessary which cannot be
supplied within the SM. The preferred value of epsilon suggests that the seesaw
mechanism may not be the reason why neutrinos are so light.Comment: 19 pages, REVTeX4, 8 postscript figures. Updated references. Typos
correcte
Edge reconstruction in the fractional quantum Hall regime
The interplay of electron-electron interaction and confining potential can
lead to the reconstruction of fractional quantum Hall edges. We have performed
exact diagonalization studies on microscopic models of fractional quantum Hall
liquids, in finite size systems with disk geometry, and found numerical
evidence of edge reconstruction under rather general conditions. In the present
work we have taken into account effects like layer thickness and Landau level
mixing, which are found to be of quantitative importance in edge physics. Due
to edge reconstruction, additional nonchiral edge modes arise for both
incompressible and compressible states. These additional modes couple to
electromagnetic fields and thus can be detected in microwave conductivity
measurements. They are also expected to affect the exponent of electron Green's
function, which has been measured in tunneling experiments. We have studied in
this work the electric dipole spectral function that is directly related to the
microwave conductivity measurement. Our results are consistent with the
enhanced microwave conductivity observed in experiments performed on samples
with an array of antidots at low temperatures, and its suppression at higher
temperatures. We also discuss the effects of the edge reconstruction on the
single electron spectral function at the edge.Comment: 19 pages, 12 figure
Removing the Big Bang Singularity: The role of the generalized uncertainty principle in quantum gravity
The possibility of avoiding the big bang singularity by means of a
generalized uncertainty principle is investigated. In relation with this
matter, the statistical mechanics of a free-particle system obeying the
generalized uncertainty principle is studied and it is shown that the entropy
of the system has a finite value in the infinite temperature limit. It is then
argued that negative temperatures and negative pressures are possible in this
system. Finally, it is shown that this model can remove the big bang
singularity.Comment: 8 pages, Accepted for publication in Astrophysics & Space Scienc
Gravitation and inertia; a rearrangement of vacuum in gravity
We address the gravitation and inertia in the framework of 'general gauge
principle', which accounts for 'gravitation gauge group' generated by hidden
local internal symmetry implemented on the flat space. We connect this group to
nonlinear realization of the Lie group of 'distortion' of local internal
properties of six-dimensional flat space, which is assumed as a toy model
underlying four-dimensional Minkowski space. The agreement between proposed
gravitational theory and available observational verifications is satisfactory.
We construct relativistic field theory of inertia and derive the relativistic
law of inertia. This theory furnishes justification for introduction of the
Principle of Equivalence. We address the rearrangement of vacuum state in
gravity resulting from these ideas.Comment: 17 pages, no figures, revtex4, Accepted for publication in Astrophys.
Space Sc
Spin light of electron in dense matter
We derive the modified Dirac equation for an electron undergos an influence
of the standard model interaction with the nuclear matter. The exact solutions
for this equation and the electron energy spectrum in matter are obtained. This
establishes a rather powerful method for investigation of different processes
that can appear when electrons propagate in background matter. On this basis we
study in detail the spin light of electron in nuclear matter, a new type of
electromagnetic radiation which can be emitted by an electron moving in dense
matter.Comment: 11 pages in LaTex, 4 figures, typos correcte
Quantum Gravitational Corrections to the Real Klein-Gordon Field in the Presence of a Minimal Length
The (D+1)-dimensional -two-parameter Lorentz-covariant
deformed algebra introduced by Quesne and Tkachuk [C. Quesne and V. M. Tkachuk,
J. Phys. A: Math. Gen. \textbf {39}, 10909 (2006).], leads to a nonzero minimal
uncertainty in position (minimal length). The Klein-Gordon equation in a
(3+1)-dimensional space-time described by Quesne-Tkachuk Lorentz-covariant
deformed algebra is studied in the case where up to first order
over deformation parameter . It is shown that the modified Klein-Gordon
equation which contains fourth-order derivative of the wave function describes
two massive particles with different masses. We have shown that physically
acceptable mass states can only exist for which
leads to an isotropic minimal length in the interval . Finally, we have shown that the above estimation of
minimal length is in good agreement with the results obtained in previous
investigations.Comment: 10 pages, no figur
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