23,078 research outputs found
On the constrained structure of duality symmetric Maxwell theory
The constrained structure of the duality invariant form of Maxwell theory is
considered in the Hamiltonian formulation of Dirac as well as from the
symplectic viewpoint. Compared to the former the latter approach is found to be
more economical and elegant. Distinctions from the constrained analysis of the
usual Maxwell theory are pointed out and their implications are also discussed.Comment: Latex, 12 page
Magnetic glass in Shape Memory Alloy : Ni45Co5Mn38Sn12
The first order martensitic transition in the ferromagnetic shape memory
alloy Ni45Co5Mn38Sn12 is also a magnetic transition and has a large field
induced effect. While cooling in the presence of field this first order
magnetic martensite transition is kinetically arrested. Depending on the
cooling field, a fraction of the arrested ferromagnetic austenite phase
persists down to the lowest temperature as a magnetic glassy state, similar to
the one observed in various intermetallic alloys and in half doped manganites.
A detailed investigation of this first order ferromagnetic austenite (FM-A) to
low magnetization martensite (LM-M) state transition as a function of
temperature and field has been carried out by magnetization measurements.
Extensive cooling and heating in unequal field (CHUF) measurements and a novel
field cooled protocol for isothermal MH measurements (FC-MH) are utilized to
investigate the glass like arrested states and show a reverse martensite
transition. Finally, we determine a field -temperature (HT) phase diagram of
Ni45Co5Mn38Sn12 from various magnetization measurements which brings out the
regions where thermodynamic and metastable states co-exist in the HT space
clearly depicting this system as a 'Magnetic Glass'.Comment: Magnetic field tunes kinetic arrest and CHUF shows devitrification
and melting of Magnetic glas
Second generation planet formation in NN Serpentis?
In this paper, we study the general impact of stellar mass-ejection events in
planetary orbits in post-common envelope binaries with circumbinary planets
like those around NN Serpentis. We discuss a set of simple equations that
determine upper and lower limits for orbital expansion and investigate the
effect of initial eccentricity. We deduce the range of possible semi-major axes
and initial eccentricity values of the planets prior to the common-envelope
event. In addition to spherically-symmetric mass-ejection events, we consider
planetary dynamics under the influence of an expanding disk. In order to have
survived, we suggest that the present planets in NN Ser must have had
semi-major axes AU and high eccentricity values which is
in conflict with current observations. Consequently, we argue that these
planets were not formed together with their hosting stellar system, but rather
originated from the fraction of matter of the envelope that remained bound to
the binary. According to the cooling age of the white dwarf primary of
yr, the planets around NN Ser might be the youngest known so far and open up a
wide range of further study of second generation planet formation.Comment: 4 pages, 2 figure
Towards QCD thermodynamics using exact chiral symmetry on lattice
The thermodynamics of massless ideal gas of overlap quarks has been
investigated numerically for both zero and nonzero baryon chemical potential
. While the parameter M has been shown to be irrelevant in the continuum
limit, it is shown numerically that the continuum limit can be reached with
relatively coarser lattices for certain range of M. Numerical limitation of the
existing method of introduction of chemical potential in the overlap formalism
is discussed. We have also studied the energy density of free domain wall
fermions in the absence of and estimated the extent of lattice in the
fifth dimension for which the overlap results are recovered.
Interestingly, this value of is also minimum for the same range of M
found in the overlap case.Comment: 5 pages, 4 figures, to appear in the proceedings of the 20th
International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions:
Quark Matter 2008 (QM2008
Anomalies at finite density and chiral fermions
Using perturbation theory in the Euclidean (imaginary time) formalism as well
as the non-perturbative Fujikawa method, we verify that the chiral anomaly
equation remains unaffected in the presence of nonzero chemical potential,
. We extend our considerations to fermions with exact chiral symmetry on
the lattice and discuss the consequences for the recent Bloch-Wettig proposal
for the Dirac operator at finite chemical potential. We propose a new simpler
method of incorporating and compare it with the Bloch-Wettig idea.Comment: 12 pages, 3 figures,some typos corrected, a better proof for the \mu
independence of anomaly is given in section IIB, v4: the published versio
Peak effect in laser ablated DyBa2Cu3O7-d films at microwave frequencies at subcritical currents
In this paper we report the observation of a peak in the microwave surface
resistance (at frequencies ~10GHz) of laser ablated DyBa2Cu3O7-d films in
magnetic field ranging from 2 to 9kOe (||c) close to the superconducting
transition temperature (Tc(H)). The exact nature of peak is sample dependent
but it follows a general behaviour. The peak shifts to lower temperature when
the magnetic field is increased. It has strong frequency dependence and the
peak is pronounced at frequencies close to the depinning frequency of the flux
line lattice. From the observed temperature and field dependence we argue that
this peak is associated with the order disorder transition of the flux line
lattice close to Tc(H).Comment: 8 pages, 2 pages (accepted for publication in JAP, Intermag symposium
proceeding
Supercooling and Nucleation in Phase Transitions of the Early Universe -
The three phase transitions - the GUT, the electro-weak and the quark-hadron,
which the universe is assumed to have undergone produce very important physical
effects if they are assumed to be of first order. It is also important that
enough supercooling is produced at these transitions so that the rate of
nucleation of the lower temperature phase out of the higher temperature phase
is large.
We argue on the basis of finite-size scaling theory that for the quark-hadron
and the electro-weak transitions the universe does nor supercool enough to
produce sizeable nucleation rates. Only for the GUT transition nucleation
probability seems to be significant.Comment: 10 pages, REVTEX 3.0, TIFR-TH-93-4
A method for increasing the surface area of perovskite-type oxides
A method based on hydrothermal treatments is described for increasing the surface area of sintered ABO3-type perovskite oxides. Influence of hydrothermal treatments, such as water treatment at 125-300°C under autogeneous pressure and steam treatment at 350-800°C, to low surface area (or sintered) LaCoO3 and LaMnO3 perovskite oxides on their surface properties (viz. surface area, crystal size and morphology and surface La/(Co or Mn) ratio) and also catalytic activity in complete combustion of methane at different temperatures (450-600°C) has been thoroughly investigated. The hydrothermal treatments result in the activation of the perovskite oxides by increasing their surface area very markedly
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