887 research outputs found
General Relativistic Effect of Gravitomagnetic Charge on Pulsar Magnetosphere and Particle Acceleration in a Polar Cap
We study magnetospheric structure surrounding rotating magnetized neutron
star with nonvanishing NUT (Newman-Tamburino-Unti) parameter. For the
simplicity of calculations Goldreich-Julian charge density is analyzed for the
aligned neutron star with zero inclination between magnetic field,
gravitomagnetic field and rotation axis. From the system of Maxwell equations
in spacetime of slowly rotating NUT star, second-order differential equation
for electrostatic potential is derived. Analytical solution of this equation
indicates the general relativistic modification of an accelerating electric
field and charge density along the open field lines by the gravitomagnetic
charge. The implication of this effect to the magnetospheric energy loss
problem is underlined. In the second part of the paper we derive the equations
of motion of test particles in magnetosphere of slowly rotating NUT star. Then
we analyze particle motion in the polar cap and show that NUT parameter can
significantly change conditions for particle acceleration.Comment: 21 pages, 6 figures, accepted for publication in Ap
Quantum Interference Effects in Slowly Rotating NUT Space-time
General relativistic quantum interference effects in the slowly rotating NUT
space-time as the Sagnac effect and the phase shift effect of interfering
particle in neutron interferometer are considered. It was found that in the
case of the Sagnac effect the influence of NUT parameter is becoming important
due to the fact that the angular velocity of the locally non rotating observer
must be larger than one in the Kerr space-time. In the case of neutron
interferometry it is found that due to the presence of NUT-parameter an
additional term in the phase shift of interfering particle emerges. This term
can be, in principle, detected by sensitive interferometer and derived results
can be further used in experiments to detect the gravitomagnetic charge.
Finally, as an example, we apply the obtained results to the calculation of the
UCN (ultra-cold neutrons) energy level modification in the slowly rotating NUT
space-time.Comment: 11 pages, 1 figure, accepted for publication in Int. J. Mod. Phys. D;
added reference
External Electromagnetic Fields of a Slowly Rotating Magnetized Star with Gravitomagnetic Charge
We study Maxwell equations in the external background spacetime of a slowly
rotating magnetized NUT star and find analytical solutions for the exterior
electric fields after separating the equations of electric field into angular
and radial parts in the lowest order approximation. The star is considered
isolated and in vacuum, with dipolar magnetic field aligned with the axis of
rotation. The contribution to the external electric field of star from the NUT
charge is considered in detail.Comment: 6 pages, 2 figures, accepted for publication in Astrophysics and
Space Scienc
Volume of the quantum mechanical state space
The volume of the quantum mechanical state space over -dimensional real,
complex and quaternionic Hilbert-spaces with respect to the canonical Euclidean
measure is computed, and explicit formulas are presented for the expected value
of the determinant in the general setting too. The case when the state space is
endowed with a monotone metric or a pull-back metric is considered too, we give
formulas to compute the volume of the state space with respect to the given
Riemannian metric. We present the volume of the space of qubits with respect to
various monotone metrics. It turns out that the volume of the space of qubits
can be infinite too. We characterize those monotone metrics which generates
infinite volume.Comment: 17 page
Plasma Magnetosphere Formation Around Oscillating Magnetized Neutron Stars
The notion of death line of rotating pulsars is applied to model of
oscillating neutron stars. It is shown that the magnetosphere of typical
non-rotating oscillating stars may not contain secondary plasma to support the
generation of radio emission in the region of open field lines of plasma
magnetosphere.Comment: Accepted for publication in Astrophysics & Space Scienc
Observation of the Early Structural Changes Leading to the Formation of Protein Superstructures.
Formation of superstructures in protein aggregation processes has been indicated as a general pathway for several proteins, possibly playing a role in human pathologies. There is a severe lack of knowledge on the origin of such species in terms of both mechanisms of formation and structural features. We use equine lysozyme as a model protein, and by combining spectroscopic techniques and microscopy with X-ray fiber diffraction and ab initio modeling of Small Angle X-ray Scattering data, we isolate the partially unfolded state from which one of these superstructures (i.e., particulate) originates. We reveal the low-resolution structure of the unfolded state and its mechanism of formation, highlighting the physicochemical features and the possible pathway of formation of the particulate structure. Our findings provide a novel detailed knowledge of such a general and alternative aggregation pathway for proteins, this being crucial for a basic and broader understanding of the aggregation phenomena.This is the author's accepted manuscript and will be under embargo until the 3rd of September 2015. The final version is published by ACS in The Journal of Physical Chemistry Letters here: http://pubs.acs.org/doi/abs/10.1021/jz501614e
Magnetized Particle Capture Cross Section for Braneworld Black Hole
Capture cross section of magnetized particle (with nonzero magnetic moment)
by braneworld black hole in uniform magnetic field is considered. The magnetic
moment of particle was chosen as it was done by \citet{rs99} and for the
simplicity particle with zero electric charge is chosen. It is shown that the
spin of particle as well as the brane parameter are to sustain the stability of
particles circularly orbiting around the black hole in braneworld i.e. spin of
particles and brane parameter try to prevent the capture by black hole.Comment: 7 pages, 4 figures, Accepted for publication in Astrophysics & Space
Scienc
Towards a representative reference for MRI-based human axon radius assessment using light microscopy
Non-invasive assessment of axon radii via MRI bears great potential for clinical and neuroscience research as it is a main determinant of the neuronal conduction velocity. However, there is a lack of representative histological reference data at the scale of the cross-section of MRI voxels for validating the MRI-visible, effective radius (reff). Because the current gold standard stems from neuroanatomical studies designed to estimate the bulk-determined arithmetic mean radius (rarith) on small ensembles of axons, it is unsuited to estimate the tail-weighted reff. We propose CNN-based segmentation on high-resolution, large-scale light microscopy (lsLM) data to generate a representative reference for reff. In a human corpus callosum, we assessed estimation accuracy and bias of rarith and reff. Furthermore, we investigated whether mapping anatomy-related variation of rarith and reff is confounded by low-frequency variation of the image intensity, e.g., due to staining heterogeneity. Finally, we analyzed the error due to outstandingly large axons in reff. Compared to rarith, reff was estimated with higher accuracy (maximum normalized-root-mean-square-error of reff: 8.5 %; rarith: 19.5 %) and lower bias (maximum absolute normalized-mean-bias-error of reff: 4.8 %; rarith: 13.4 %). While rarith was confounded by variation of the image intensity, variation of reff seemed anatomy-related. The largest axons contributed between 0.8 % and 2.9 % to reff. In conclusion, the proposed method is a step towards representatively estimating reff at MRI voxel resolution. Further investigations are required to assess generalization to other brains and brain areas with different axon radii distributions
Bures volume of the set of mixed quantum states
We compute the volume of the N^2-1 dimensional set M_N of density matrices of
size N with respect to the Bures measure and show that it is equal to that of a
N^2-1 dimensional hyper-halfsphere of radius 1/2. For N=2 we obtain the volume
of the Uhlmann 3-D hemisphere, embedded in R^4. We find also the area of the
boundary of the set M_N and obtain analogous results for the smaller set of all
real density matrices. An explicit formula for the Bures-Hall normalization
constants is derived for an arbitrary N.Comment: 15 revtex pages, 2 figures in .eps; ver. 3, Eq. (4.19) correcte
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