789 research outputs found
Boson-fermion unification, superstrings, and Bohmian mechanics
Bosonic and fermionic particle currents can be introduced in a more unified
way, with the cost of introducing a preferred spacetime foliation. Such a
unified treatment of bosons and fermions naturally emerges from an analogous
superstring current, showing that the preferred spacetime foliation appears
only at the level of effective field theory, not at the fundamental superstring
level. The existence of the preferred spacetime foliation allows an objective
definition of particles associated with quantum field theory in curved
spacetime. Such an objective definition of particles makes the Bohmian
interpretation of particle quantum mechanics more appealing. The superstring
current allows a consistent Bohmian interpretation of superstrings themselves,
including a Bohmian description of string creation and destruction in terms of
string splitting. The Bohmian equations of motion and the corresponding
probabilistic predictions are fully relativistic covariant and do not depend on
the preferred foliation.Comment: 30 pages, 1 figure, revised, to appear in Found. Phy
Quantum Transparency of Anderson Insulator Junctions: Statistics of Transmission Eigenvalues, Shot Noise, and Proximity Conductance
We investigate quantum transport through strongly disordered barriers, made
of a material with exceptionally high resistivity that behaves as an Anderson
insulator or a ``bad metal'' in the bulk, by analyzing the distribution of
Landauer transmission eigenvalues for a junction where such barrier is attached
to two clean metallic leads. We find that scaling of the transmission
eigenvalue distribution with the junction thickness (starting from the single
interface limit) always predicts a non-zero probability to find high
transmission channels even in relatively thick barriers. Using this
distribution, we compute the zero frequency shot noise power (as well as its
sample-to-sample fluctuations) and demonstrate how it provides a single number
characterization of non-trivial transmission properties of different types of
disordered barriers. The appearance of open conducting channels, whose
transmission eigenvalue is close to one, and corresponding violent mesoscopic
fluctuations of transport quantities explain at least some of the peculiar
zero-bias anomalies in the Anderson-insulator/superconductor junctions observed
in recent experiments [Phys. Rev. B {\bf 61}, 13037 (2000)]. Our findings are
also relevant for the understanding of the role of defects that can undermine
quality of thin tunnel barriers made of conventional band-insulators.Comment: 9 pages, 8 color EPS figures; one additional figure on mesoscopic
fluctuations of Fano facto
Preparation and Characterization of Fe<sub>2</sub>O<sub>3</sub>-SiO<sub>2</sub> Nanocomposite for Biomedical Application
The scope of this chapter is to get deeper insight into the correlation between synthesis parameters and magnetic behavior of the nanocomposite materials containing hematite (α-Fe2O3) nanoparticles. Potential applications of nano-hematite in biomedicine are listed in the short overview. Then, basic requirements necessary for synthesis of high-quality nanoparticles for biomedical application are summarized. The next part of the chapter is devoted to the sol-gel synthesis that is recognized as suitable for preparation of the nanocomposite materials containing α-Fe2O3 nanoparticles. Having in mind that sol-gel method considers preparation of hematite nanoparticles via Fe2O3 phase transformations initiated by thermal treatment at high temperatures, coexistence of the other iron oxides (such as ε-Fe2O3) with α-Fe2O3 phase is commented. Special attention is paid on mechanism of the critical field (which is in literature usually denoted as coercivity field) alterations. Diffraction patterns and hysteresis measurements of the chosen samples containing hematite nanoparticles in the silica matrix are represented. Finally, variations in the observed measured critical field values are discussed
Quantum mechanics: Myths and facts
A common understanding of quantum mechanics (QM) among students and practical
users is often plagued by a number of "myths", that is, widely accepted claims
on which there is not really a general consensus among experts in foundations
of QM. These myths include wave-particle duality, time-energy uncertainty
relation, fundamental randomness, the absence of measurement-independent
reality, locality of QM, nonlocality of QM, the existence of well-defined
relativistic QM, the claims that quantum field theory (QFT) solves the problems
of relativistic QM or that QFT is a theory of particles, as well as myths on
black-hole entropy. The fact is that the existence of various theoretical and
interpretational ambiguities underlying these myths does not yet allow us to
accept them as proven facts. I review the main arguments and counterarguments
lying behind these myths and conclude that QM is still a
not-yet-completely-understood theory open to further fundamental research.Comment: 51 pages, pedagogic review, revised, new references, to appear in
Found. Phy
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Development of non-conventional instrument transformers (NCIT) using smart materials
In this paper is presented a novel approach for current measurement using smart materials, magnetic shape memory (MSM) alloys. Their shape change can be controlled by the application of magnetic field or mechanical stress. This gives the possibility to measure currents by correlating the magnetic field produced by the current, shape change in an MSM- based sensor and the voltage output of a Linear Variable Differential Transducer (LVDT) actuated by this shape change. In the first part of the paper is presented a review of existing current measurement sensors by comparing their properties and highlighting their advantages and disadvantages
Structural, chemical and deformation changes in friction welded joint of dissimilar steels
Fundamental principles of friction welding of dissimilar steels (high speed and tempering steel) from the aspect of metallurgical and chemical processes occurring in the joint zone are presented in this paper. Considering that phenomena accompanying the friction welding are interdependent, it was necessary to experimentally determine the process variable parameters, to establish the optimal welding regime. The experiments were set and realized so that all the variables were analyzed as a function of the friction time. The metallographic investigations included analysis of the joint zone microstructure through structural phases and hardness changes, due to influence of the heat treatment - annealing. The experimental work included analysis of the geometry changes, the joint zone structure and the basic mechanical characteristics of the joint realized by the friction welding
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Transcription Factor Activation during Signal-induced Apoptosis of Immature CD4+CD8+ Thymocytes: A Protective Role of c-Fos
Many signals that cause apoptotic cell death operate by inducing transcription and translation of other (presumably death effector) mediators, and it is well established that stimulus-induced apoptosis can often be blocked by inhibiting transcription and translation. Transcriptional regulation of apoptosis, however, is incompletely understood. To gain insight into nuclear events associated with signal-induced apoptosis during T cell development, we studied signal-induced apoptosis of ex vivo isolated immature CD8+4+ double-positive (DP) thymocytes. Stimuli utilizing the T cell receptor (TCR) signaling pathway or its parts (an αCD3/TCR monoclonal antibody, a Ca2+ ionophore, or a protein kinase C-activating phorbol ester) or a stimulus that antagonizes TCR signaling and apoptosis in T cell hybridoma (forskolin, a cyclic AMP-signaling activator) resulted in massive apoptosis of DP thymocytes. At the same time, these stimuli induced qualitatively similar but quantitatively unique patterns of inducible transcription factors (TFs) NF-κB/RelA-p50, AP-1 (Fos-Jun), and NUR-77. We focused our attention on the role of AP-1 (Fos-Jun) complex, which was strongly induced by all of the above stimuli and thus was a candidate for a proapoptotic TF. However, we found that AP-1/c-Fos induction was vital in prolonging DP thymocyte life, as judged by increased spontaneous and induced death of DP cells in Fos−/− mice. In direct support of this hypothesis, experiments with antisense oligonucleotides demonstrated that c-Fos plays an essential role in protecting normal DP thymocytes from Ca2+- and cAMP-induced apoptosis but not from TCR-mediated death. Together, these results demonstrate a physiological role for c-Fos in maintaining longevity of DP thymocytes
Physico-chemical characterization of 90Y-labeled antimony trisulfide colloid and comparison with 99mTc-labeled one
In radionuclide therapy, the importance of 90Y as a beta-emitting radionuclide is increasing rapidly. The properties of the 90Y-labeled antimony trisulfide colloid (Sb2S3) were compared with the 99mTc-labeled one. Labeling efficiencies reached >96% and >97% for 90Y- and 99mTc-labeled colloids respectively. Both preparations were stable for 72 h in saline and 1% albumin solution. Filtration analysis showed that more than 94% of total 90Y radioactivity is associated with the colloidal particles smaller than 20 nm, while more than 90% of 99mTc radioactivity is associated with the particles retained on the filter with a 20 nm pore size. 90Y-labeled colloids showed high labeling efficiency, stability and potency for clinical use.Physical chemistry 2008 : 9th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 24-28 September 200
Two-dimensional fermionic superfluids, pairing instability and vortex liquids in the absence of time reversal symmetry
We consider a generic two-dimensional system of fermionic particles with
attractive interactions and no disorder. If time-reversal symmetry is absent,
it is possible to obtain incompressible insulating states in addition to the
superfluid at zero temperature. The superfluid-insulator phase transition is
found to be second order in type-II systems using a perturbative analysis of
Cooper pairing instability in quantum Hall states of unpaired fermions. We
obtain the pairing phase diagram as a function of chemical potential (density)
and temperature. However, a more careful analysis presented here reveals that
the pairing quantum phase transition is always preempted by another transition
into a strongly correlated normal state which retains Cooper pairing and cannot
be smoothly connected to the quantum Hall state of unpaired fermions. Such a
normal phase can be qualitatively viewed as a liquid of vortices, although it
may acquire conventional broken symmetries. Even if it did not survive at
finite temperatures its influence would be felt through strong quantum
fluctuations below a crossover temperature scale. These conclusions directly
apply to fermionic ultra-cold atom systems near unitarity, but are likely
relevant for the properties of other strongly correlated superfluids as well,
including high temperature superconductors.Comment: 11 pages, 3 figures, published versio
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