556 research outputs found
Evidance for an Oxygen Diffusion Model for the Electric Pulse Induced Resistance Change Effect in Oxides
Electric pulse induced resistance (EPIR) switching hysteresis loops for
Pr0.7Ca0.7MnO3 (PCMO) perovskite oxide films were found to exhibit an
additional sharp "shuttle peak" around the negative pulse maximum for films
deposited in an oxygen deficient ambient. The device resistance hysteresis loop
consists of stable high resistance and low resistance states, and transition
regions between them. The resistance relaxation of the "shuttle peak" and its
temperature behavior as well as the resistance relaxation in the transition
regions were studied, and indicate that the resistance switching relates to
oxygen diffusion with activation energy about 0.4eV. An oxygen diffusion model
with the oxygen ions (vacancies) as the active agent is proposed for the
non-volatile resistance switching effect in PCMO.Comment: 7 pages, 5 figure
Use of ultrasound densitometry for the assess of structural and functional disorders of bone tissue and prediction of fractures risk
To determine the dependence of lumbar spine compression degree on BMD state and the patients’ age. The relationship of BMD state, the patients’ age and the degree of compression of the vertebrae were studied. Correlation and regression analysis of the relationship between SOS index, score of compression and patients' age have been examined. Results. The data obtained allowed us to develop a mathematical model for predicting BMD reduction and the severity of vertebral compression fractures. Conclusions. Ultrasonic indexes of bone mineral density may be used not only for its screening assessment in general population of different ages, but also in assessing the degree of structural and functional changes of BT, predicting the severity of low-energy osteoporosis fractures. It will help to assign treatment in preclinical stage, and carry out prevention of compression fractures
Search for Millicharged Particles at SLAC
Particles with electric charge q < 10^(-3)e and masses in the range 1--100
MeV/c^2 are not excluded by present experiments. An experiment uniquely suited
to the production and detection of such "millicharged" particles has been
carried out at SLAC. This experiment is sensitive to the infrequent excitation
and ionization of matter expected from the passage of such a particle. Analysis
of the data rules out a region of mass and charge, establishing, for example, a
95%-confidence upper limit on electric charge of 4.1X10^(-5)e for millicharged
particles of mass 1 MeV/c^2 and 5.8X10^(-4)e for mass 100 MeV/c^2.Comment: 4 pages, REVTeX, multicol, 3 figures. Minor typo corrected. Submitted
to Physical Review Letter
Massive Electrodynamics and the Magnetic Monopoles
We investigate in detail the problem of constructing magnetic monopole
solutions within the finite-range electrodynamics (i.e., electrodynamics with
non-zero photon mass, which is the simplest extension of the standard theory;
it is fully compatible with the experiment). We first analyze the classical
electrodynamics with the additional terms describing the photon mass and the
magnetic charge; then we look for a solution analogous to the Dirac monopole
solution. Next, we plug the found solution into the Schr\"{o}dinger equation
describing the interaction between the the magnetic charge and the electron.
After that, we try to derive the Dirac quantization condition for our case.
Since gauge invariance is lost in massive electrodynamics, we use the method of
angular momentum algebra. Under rather general assumptions we prove the theorem
that the construction of such an algebra is not possible and therefore the
quantization condition cannot be derived. This points to the conclusion that
the Dirac monopole and the finite photon mass cannot coexist within one and the
same theory. Some physical consequences of this conclusion are considered. The
case of t'Hooft-Polyakov monopole is touched upon briefly.Comment: 24 pages, revtex, 1 figure appended as a PostScript fil
Experimental implications of mirror matter-type dark matter
Mirror matter-type dark matter is one dark matter candidate which is
particularly well motivated from high energy physics. The theoretical
motivation and experimental evidence are pedagogically reviewed, with emphasis
on the implications of recent orthopositronium experiments, the DAMA/NaI dark
matter search, anomalous meteorite events etc.Comment: about 12 pages lon
How fast is the wave function collapse?
Using complex quantum Hamilton-Jacobi formulation, a new kind of non-linear
equations is proposed that have almost classical structure and extend the
Schroedinger equation to describe the collapse of the wave function as a
finite-time process. Experimental bounds on the collapse time are reported (of
order 0.1 ms to 0.1 ps) and its convenient dimensionless measure is introduced.
This parameter helps to identify the areas where sensitive probes of the
possible collapse dynamics can be done. Examples are experiments with
Bose-Einstein condensates, ultracold neutrons or ultrafast optics.Comment: 9 pages; v2: a shorter version to suit the 4 page limit of
Proceedings of International Conference on Mathematical Modelling in Physical
Sciences, 3-7 September 2012, Budapest, Hungary (IC-MSQUARE 2012
Incrementally Computing Minimal Unsatisfiable Cores of QBFs via a Clause Group Solver API
We consider the incremental computation of minimal unsatisfiable cores (MUCs)
of QBFs. To this end, we equipped our incremental QBF solver DepQBF with a
novel API to allow for incremental solving based on clause groups. A clause
group is a set of clauses which is incrementally added to or removed from a
previously solved QBF. Our implementation of the novel API is related to
incremental SAT solving based on selector variables and assumptions. However,
the API entirely hides selector variables and assumptions from the user, which
facilitates the integration of DepQBF in other tools. We present implementation
details and, for the first time, report on experiments related to the
computation of MUCs of QBFs using DepQBF's novel clause group API.Comment: (fixed typo), camera-ready version, 6-page tool paper, to appear in
proceedings of SAT 2015, LNCS, Springe
Photon mass and electrogenesis
We show that if photon possesses a tiny but non-vanishing mass the universe
cannot be electrically neutral. Cosmological electric asymmetry could be
generated either at an early stage by different evaporation rates of primordial
black holes with respect to positively and negatively charged particles or by
predominant capture of protons in comparison to electrons by heavy galactic
black holes in contemporary universe. An impact of this phenomenon on the
generation of large scale magnetic fields and on the universe acceleration is
considered.Comment: 15 pages, no figures, text added, typos corrected, refs. improve
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