188 research outputs found
An Analysis of the First Order Form of Gauge Theories
The first order form of a Maxwell theory and U(1) gauge theory in which a
gauge invariant mass term appears is analyzed using the Dirac procedure. The
form of the gauge transformation which leaves the action invariant is derived
from the constraints present. A non-Abelian generalization is similarly
analyzed. This first order three dimensional massive gauge theory is rewritten
in terms of two interacting vector fields. The constraint structure when using
light-cone coordinates is considered. The relationship between first and second
order forms of the two-dimensional Einstein-Hilbert action is explored where a
Lagrange multiplier is used to ensure their equivalence.Comment: 22 pages, to appear in Canadian Journal of Physics. arXiv admin note:
text overlap with arXiv:hep-th/060922
Giant pulses of pulsar radio emission
Review report of giant pulses of pulsar radio emission, based on our
detections of four new pulsars with giant pulses, and the comparative analysis
of the previously known pulsars with giant pulses, including the Crab pulsar
and millisecond pulsar PSR B1937+21.Comment: Proceedings of the 363. WE-Heraeus Seminar on: Neutron Stars and
Pulsars (Posters and contributed talks) Physikzentrum Bad Honnef, Germany,
May.14-19, 2006, eds. W.Becker, H.H.Huang, MPE Report 291, pp.72-7
Transfer of synthetic human chromosome into human induced pluripotent stem cells for biomedical applications
Alphoid(tetO)-type human artificial chromosome (HAC) has been recently synthetized as a novel class of gene delivery vectors for induced pluripotent stem cell (iPSC)-based tissue replacement therapeutic approach. This HAC vector was designed to deliver copies of genes into patients with genetic diseases caused by the loss of a particular gene function. The alphoid(tetO)-HAC vector has been successfully transferred into murine embryonic stem cells (ESCs) and maintained stably as an independent chromosome during the proliferation and differentiation of these cells. Human ESCs and iPSCs have significant differences in culturing conditions and pluripotency state in comparison with the murine naïve-type ESCs and iPSCs. To date, transferring alphoid(tetO)-HAC vector into human iPSCs (hiPSCs) remains a challenging task. In this study, we performed the microcell-mediated chromosome transfer (MMCT) of alphoid(tetO)-HAC expressing the green fluorescent protein into newly generated hiPSCs. We used a recently modified MMCT method that employs an envelope protein of amphotropic murine leukemia virus as a targeting cell fusion agent. Our data provide evidence that a totally artificial vector, alphoid(tetO)-HAC, can be transferred and maintained in human iPSCs as an independent autonomous chromosome without affecting pluripotent properties of the cells. These data also open new perspectives for implementing alphoid(tetO)-HAC as a gene therapy tool in future biomedical applications
Визначення локальних деформацій в околі зварного шва нікелевого сплаву за даними енергетичних Фур’є спектрів картин Кікучі
A discrete two-dimensional Fourier transform and the power Fourier spectrum are used for determination of average strains near cracks in a welded seam of Ni-Cr-Fe alloy. The alignment of Kikuchi images with the help of genetic algorithms and subtraction of white Gaussian noise made it possible to more fully take into account the influence of instrumental factors on the formation of electron backscatter diffraction patterns.Для визначення значень середніх деформацій в локальних областях поблизу тріщин зварного шва нікелевого сплаву NiCrFe при аналізі картин Кікучі використано методи енергетичного Фур’є спектру та дискретного двомірного Фур’є перетворення. Суміщення зображень Кікучі за допомогою генетичних алгоритмів та виділення білого гаусівського шуму дало можливість більш повно врахувати вплив інструментальних факторів на формування картин дифракції відбитих електронів
Tryptophan hydroxylase-2-mediated serotonin biosynthesis suppresses cell reprogramming into pluripotent state
The monoamine neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) has important functions both in the neural system and during embryonic development in mammals. In this study, we set out to investigate whether and how endogenous serotonin affects reprogramming to pluripotency. As serotonin is synthesized from tryptophan by the rate limiting enzymes tryptophan hydroxylase-1 and -2 (TPH1 and TPH2), we have assessed the reprogramming of TPH1- and/or TPH2-deficient mouse embryonic fibroblasts (MEFs) to induced pluripotent stem cells (iPSCs). The reprogramming of the double mutant MEFs showed a dramatic increase in the efficiency of iPSC generation. In contrast, ectopic expression of TPH2 alone or in conjunction with TPH1 reverted the rate of reprogramming of the double mutant MEFs to the wild-type level and besides, TPH2 overexpression significantly suppressed reprogramming of wild-type MEFs. Our data thus suggest a negative role of serotonin biosynthesis in the reprogramming of somatic cells to a pluripotent state
Diffeomorphism Invariance in the Hamiltonian formulation of General Relativity
It is shown that when the Einstein-Hilbert Lagrangian is considered without
any non-covariant modifications or change of variables, its Hamiltonian
formulation leads to results consistent with principles of General Relativity.
The first-class constraints of such a Hamiltonian formulation, with the metric
tensor taken as a canonical variable, allow one to derive the generator of
gauge transformations, which directly leads to diffeomorphism invariance. The
given Hamiltonian formulation preserves general covariance of the
transformations derivable from it. This characteristic should be used as the
crucial consistency requirement that must be met by any Hamiltonian formulation
of General Relativity.Comment: 13 page
Quasielastic axial-vector mass from experiments on neutrino-nucleus scattering
We analyze available experimental data on the total and differential
charged-current cross sections for quasielastic neutrino and antineutrino
scattering off nucleons, measured with a variety of nuclear targets in the
accelerator experiments at ANL, BNL, FNAL, CERN, and IHEP, dating from the end
of sixties to the present day. The data are used to adjust the poorly known
value of the axial-vector mass of the nucleon.Comment: 27 pages, 19 figures. Typos corrected; tables, figures and references
added, discussion extended; matches published versio
Measurement of (1020) meson leptonic width with CMD-2 detector at VEPP-2M Collider
The (1020) meson leptonic width has been determined from the combined
analysis of 4 major decay modes of the resonance () studied with the CMD-2 detector at
the VEPP-2M collider. The following value has been obtained:
keV.
The meson parameters in four main decay channels have been also
recalculated: , , , .Comment: 14 pages, 3 figure
The Hamiltonian of Einstein affine-metric formulation of General Relativity
It is shown that the Hamiltonian of the Einstein affine-metric (first order)
formulation of General Relativity (GR) leads to a constraint structure that
allows the restoration of its unique gauge invariance, four-diffeomorphism,
without the need of any field dependent redefinition of gauge parameters as is
the case for the second order formulation. In the second order formulation of
ADM gravity the need for such a redefinition is the result of the non-canonical
change of variables [arXiv: 0809.0097]. For the first order formulation, the
necessity of such a redefinition "to correspond to diffeomorphism invariance"
(reported by Ghalati [arXiv: 0901.3344]) is just an artifact of using the
Henneaux-Teitelboim-Zanelli ansatz [Nucl. Phys. B 332 (1990) 169], which is
sensitive to the choice of linear combination of tertiary constraints. This
ansatz cannot be used as an algorithm for finding a gauge invariance, which is
a unique property of a physical system, and it should not be affected by
different choices of linear combinations of non-primary first class
constraints. The algorithm of Castellani [Ann. Phys. 143 (1982) 357] is free
from such a deficiency and it leads directly to four-diffeomorphism invariance
for first, as well as for second order Hamiltonian formulations of GR. The
distinct role of primary first class constraints, the effect of considering
different linear combinations of constraints, the canonical transformations of
phase-space variables, and their interplay are discussed in some detail for
Hamiltonians of the second and first order formulations of metric GR. The first
order formulation of Einstein-Cartan theory, which is the classical background
of Loop Quantum Gravity, is also discussed.Comment: 74 page
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