771 research outputs found
Dephasing time and magnetoresistance of two-dimensional electron gas in spatially modulated magnetic fields
The effect of a spatially modulated magnetic field on the weak localization
phenomenon in two-dimensional electron gas (2DEG) is studied. Both the
dephasing time and magnetoresistance are shown to reveal a nontrivial
behavior as functions of the characteristics of magnetic field profiles. The
magnetic field profiles with rather small spatial scales and modulation
amplitudes such that are characterized by the
dephasing rate . The increase in the flux value
results in a crossover to a standard linear dependence
. Applying an external homogeneous magnetic field
one can vary the local dephasing time in the system and affect the resulting
average transport characteristics. We have investigated the dependence of the
average resistance vs the field for some generic systems and predict a
possibility to observe a positive magnetoresistance at not too large
values. The resulting dependence of the resistance vs should reveal a peak
at the field values .Comment: 12 pages, 5 figure
Nova Sagittarii 1994 #1 (V4332 Sagittarii): The Discovery and Evolution of an Unusual Luminous Red Variable Star
We report photometry and spectroscopy of the evolution of Nova Sagittarii
1994 #1 (V4332 Sagittarii) during outburst. We compare the photometric and
spectral evolution of this outburst to known classes of outbursts -- including
classical novae and outbursts occurring on symbiotic stars -- and find this
object does NOT conform to any known class of outburst. The closest match to
the behavior of this unusual object is M31 RV, an extremely luminous and red
variable object discovered in the bulge of M31 in 1988. However, the temporal
behavior and maximum luminosity of the two events differ by several orders of
magnitude, requiring substantial intrinsic variation if these two events are
members the same type of outburst.
Our model of the spectroscopic evolution of this outburst shows that the
effective temperature cooled from 4400 K to 2300 K over the three month span of
our observations. In combination with line diagnostics in our later spectra,
including [OI] lambda 5577 and the dramatic increase in the Halpha to Hbeta
ratio, we infer the existence of a cool, dense (N_e ~ 10^{8-9} cm^{-3})
envelope that is optically thick in the Hydrogen Balmer recombination lines
(case C). We suggest that a nuclear event in a single star, in which a slow
shock drove the photosphere outwards, can power the observed luminosity
evolution and the emission spectrum.Comment: Accepted for publication in AJ. 24 pages including 8 embedded
postscript figures. Also available at
http://www.astronomy.ohio-state.edu/~martini/pub
Hadronic Regge Trajectories: Problems and Approaches
We scrutinized hadronic Regge trajectories in a framework of two different
models --- string and potential. Our results are compared with broad spectrum
of existing theoretical quark models and all experimental data from PDG98. It
was recognized that Regge trajectories for mesons and baryons are not straight
and parallel lines in general in the current resonance region both
experimentally and theoretically, but very often have appreciable curvature,
which is flavor-dependent. For a set of baryon Regge trajectories this fact is
well described in the considered potential model. The standard string models
predict linear trajectories at high angular momenta J with some form of
nonlinearity at low J.Comment: 15 pages, 9 figures, LaTe
Hubble Space Telescope Imaging of the Outburst Site of M31 RV
M31 RV is a luminous red variable star that appeared for several months in
the bulge of M31 during 1988. Unlike classical novae, M31 RV was cool
throughout its outburst. Interest in this object has revived recently because
of its strong resemblance to V838 Mon, a luminous Galactic variable star that
appeared in 2002 and is illuminating a spectacular light echo, and has evolved
to ever-cooler surface temperatures. V4332 Sgr is a third object which was also
a red supergiant throughout its eruption.
We have examined archival Hubble Space Telescope (HST) images of the site of
M31 RV, obtained fortuitously in 1999 with the WFPC2 camera in parallel mode
during spectroscopic observations of the nucleus of M31. We located the site of
M31 RV in the HST frames precisely through astrometric registration with
ground-based CCD images, including several taken during the outburst. No light
echo is seen at the M31 RV site, implying that M31 RV is not surrounded by
circumstellar (or interstellar) dust similar to that around V838 Mon, or that
its extent is less than ~1.7 pc.
The stellar population at the outburst site consists purely of old red
giants; there is no young population, such as seen around V838 Mon. There are
no stars of unusual color at the site, suggesting that M31 RV had faded below
HST detectability in the 11 years since outburst, that it is an unresolved
companion of one of the red giants in the field, or that it is one of the red
giants. We suggest future observations that may help decide among these
possibilities.Comment: 16 pages, 3 figures, 2 tables; AJ accepte
Apoptosis in differentiating C2C12 muscle cells selectively targets Bcl-2-deficient myotubes
Muscle cell apoptosis accompanies normal muscle development and regeneration, as well as
degenerative diseases and aging. C2C12 murine myoblast cells represent a common model to
study muscle differentiation. Though it was already shown that myogenic differentiation of C2C12
cells is accompanied by enhanced apoptosis in a fraction of cells, either the cell population
sensitive to apoptosis or regulatory mechanisms for the apoptotic response are unclear so far. In
the current study we characterize apoptotic phenotypes of different types of C2C12 cells at all
stages of differentiation, and report here that myotubes of differentiated C2C12 cells with low
levels of anti-apoptotic Bcl-2 expression are particularly vulnerable to apoptosis even though they
are displaying low levels of pro-apoptotic proteins Bax, Bak and Bad. In contrast, reserve cells
exhibit higher levels of Bcl-2 and high resistance to apoptosis. The transfection of proliferating
myoblasts with Bcl-2 prior to differentiation did not protect against spontaneous apoptosis
accompanying differentiation of C2C12 cell but led to Bcl-2 overexpression in myotubes and to
significant protection from apoptotic cell loss caused by exposure to hydrogen peroxide. Overall,
our data advocate for a Bcl-2-dependent mechanism of apoptosis in differentiated muscle cells.
However, downstream processes for spontaneous and hydrogen peroxide induced apoptosis are
not completely similar. Apoptosis in differentiating myoblasts and myotubes is regulated not
through interaction of Bcl-2 with pro-apoptotic Bcl-2 family proteins such as Bax, Bak, and Bad
Diastereoselective reduction of protein-bound methionine sulfoxide by methionine sulfoxide reductase
AbstractMethionine sulfoxide (MetSO) in calmodulin (CaM) was previously shown to be a substrate for bovine liver peptide methionine sulfoxide reductase (pMSR, EC 1.8.4.6), which can partially recover protein structure and function of oxidized CaM in vitro. Here, we report for the first time that pMSR selectively reduces the D-sulfoxide diastereomer of CaM-bound L-MetSO (L-Met-D-SO). After exhaustive reduction by pMSR, the ratio of L-Met-D-SO to L-Met-L-SO decreased to about 1:25 for hydrogen peroxide-oxidized CaM, and to about 1:10 for free MetSO. The accumulation of MetSO upon oxidative stress and aging in vivo may be related to incomplete, diastereoselective, repair by pMSR
Particular features of interrelation of motivation, values and sense of life’s meaning as subjective factors of individualizing trajectory in the system of continuous education
The relevance of the problem under study is based on the fact that, as regards methodological and theoretical aspects, the problem of value and motivational sphere is poorly elaborated regarding the interrelation between professional education and professional activity and on the empirical level there is no clear understanding of how the sense of purpose of life and own professional values is related to the professional motivation. The aim of the article is to identify the specific features of the interrelation and effects of meaning of life to the professional values and motivation. The leading method of research is questionnaire method which makes it possible to identify the following: level of sense of life’s purpose – method of life-meaning orientations, specific features of professional motivation – method “Motivation of professional activity” and method “Level of correlation between value and availability of value”. The article presents and discusses the results of empirical study of the interrelation between professional values, professional motivation and life-meaning orientations, as well as the effects of the level of life’s meaning on professional motivation. The practical value is the possibility to use the results of the research in developing programs for correcting and increasing professional motivation, as well as for developing technologies of psychology-pedagogical assistance to sense-making and professional self-identification in projecting and implementing individual educational trajectories in the continuous vocational education system. The article can be useful for specialists in professiology, teachers of technical subjects and professional consultants for forecasting professional development of a person. © 2016 Zavodchikov et al
- …