2,677 research outputs found
Comment on "Material Evidence of a 38 MeV Boson"
In the recent preprint 1202.1739 it was claimed that preliminary data
presented by COMPASS at recent conferences confirm the existence of a resonant
state of mass 38 MeV decaying to two photons. This claim was made based on
structures observed in two-photon mass distributions which however were shown
only to demonstrate the purity and mass resolution of the {\pi}0 and {\eta}
signals. The additional structures are understood as remnants of secondary
interactions inside the COMPASS spectrometer. Therefore, the COMPASS data do
not confirm the existence of this state.Comment: 2 pages, 7 figure
Topological analysis of polymeric melts: Chain length effects and fast-converging estimators for entanglement length
Primitive path analyses of entanglements are performed over a wide range of
chain lengths for both bead spring and atomistic polyethylene polymer melts.
Estimators for the entanglement length N_e which operate on results for a
single chain length N are shown to produce systematic O(1/N) errors. The
mathematical roots of these errors are identified as (a) treating chain ends as
entanglements and (b) neglecting non-Gaussian corrections to chain and
primitive path dimensions. The prefactors for the O(1/N) errors may be large;
in general their magnitude depends both on the polymer model and the method
used to obtain primitive paths. We propose, derive and test new estimators
which eliminate these systematic errors using information obtainable from the
variation of entanglement characteristics with chain length. The new estimators
produce accurate results for N_e from marginally entangled systems. Formulas
based on direct enumeration of entanglements appear to converge faster and are
simpler to apply.Comment: Major revisions. Developed near-ideal estimators which operate on
multiple chain lengths. Now test these on two very different model polymers
Angular Correlations in Internal Pair Conversion of Aligned Heavy Nuclei
We calculate the spatial correlation of electrons and positrons emitted by
internal pair conversion of Coulomb excited nuclei in heavy ion collisions. The
alignment or polarization of the nucleus results in an anisotropic emission of
the electron-positron pairs which is closely related to the anisotropic
emission of -rays. However, the angular correlation in the case of
internal pair conversion exhibits diverse patterns. This might be relevant when
investigating atomic processes in heavy-ion collisions performed at the Coulomb
barrier.Comment: 27 pages + 6 eps figures, uses revtex.sty and epsf.sty,
tar-compressed and uuencoded with uufile
Storage Capacity of Two-dimensional Neural Networks
We investigate the maximum number of embedded patterns in the two-dimensional
Hopfield model. The grand state energies of two specific network states,
namely, the energies of the pure-ferromagnetic state and the state of specific
one stored pattern are calculated exactly in terms of the correlation function
of the ferromagnetic Ising model. We also investigate the energy landscape
around them by computer simulations. Taking into account the qualitative
features of the phase diagrams obtained by Nishimori, Whyte and Sherrington
[Phys. Rev. E {\bf 51}, 3628 (1995)], we conclude that the network cannot
retrieve more than three patterns.Comment: 13pages, 7figures, revtex
Effect of the spin-orbit interaction and the electron phonon coupling on the electronic state in a silicon vacancy
The electronic state around a single vacancy in silicon crystal is
investigated by using the Green's function approach. The triply degenerate
charge states are found to be widely extended and account for extremely large
elastic softening at low temperature as observed in recent ultrasonic
experiments. When we include the LS coupling on each Si
atom, the 6-fold spin-orbital degeneracy for the state with the valence
+1 and spin 1/2 splits into doublet groundstates and
quartet excited states with a reduced excited energy of . We also consider the effect of couplings between electrons and
Jahn-Teller phonons in the dangling bonds within the second order perturbation
and find that the groundstate becomes quartet which is responsible
for the magnetic-field suppression of the softening in B-doped silicon.Comment: 4 pages, 2 figure
On the Geometry of Supersymmetric Quantum Mechanical Systems
We consider some simple examples of supersymmetric quantum mechanical systems
and explore their possible geometric interpretation with the help of geometric
aspects of real Clifford algebras. This leads to natural extensions of the
considered systems to higher dimensions and more complicated potentials.Comment: 18 page
Synthesis and physicochemical properties of spherical catalysts based on TiO2-SiO2/MxOy, where M - Co, Cr
Catalysts TiO2-SiO2 composition in the form of hollow spheres modified cobalt and chromium was obtained. Spatial structure of spherical samples after heat treatment was study by method of 3D microtomography. Status cations of transition elements and titanium was characterized by UV-Vis DRS. The catalysts were tested in the oxidation reaction of heptane
An Unusual Suspect in Cocaine Addiction
Development of drug addiction is extremely complex, but its initiation can be as simple as the flip-flop of glutamatergic receptor subtypes triggered by an “unusual” type of NMDA receptors, as suggested by Yuan et al. (2013) in this issue of Neuron
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