Heat capacity and magnetoresistance in Dy(Co,Si)2 compounds

Magnetocaloric effect and magnetoresistance have been studied in Dy(Co1-xSix)2 [x=0, 0.075 and 0.15] compounds. Magnetocaloric effect has been calculated in terms of adiabatic temperatue change (Delta Tad) as well as isothermal magnetic entropy change (Delta SM) using the heat capacity data. The maximum values of DeltaSM and DeltaTad for DyCo2 are found to be 11.4 JKg-1K-1 and 5.4 K, respectively. Both DSM and DTad decrease with Si concentration, reaching a value of 5.4 JKg-1K-1 and 3 K, respectively for x=0.15. The maximum magnetoresistance is found to about 32% in DyCo2, which decreases with increase in Si. These variations are explained on the basis of itinerant electron metamagnetism occurring in these compounds.Comment: Total 8 pages of text and figure

Process development for producing fine-grain casting in space

Assessment of grain growth kinetics at temperatures near the melting point and investigation into the use of potential nucleating agents in combination with the naturally occurring BeO led to the definition of critical low-g experiments which would help to determine whether one or both of these possibilities are valid and whether space processing would be able to yield fine grain ingot beryllium

Augmented Superfield Approach To Unique Nilpotent Symmetries For Complex Scalar Fields In QED

The derivation of the exact and unique nilpotent Becchi-Rouet-Stora-Tyutin (BRST)- and anti-BRST symmetries for the matter fields, present in any arbitrary interacting gauge theory, has been a long-standing problem in the framework of superfield approach to BRST formalism. These nilpotent symmetry transformations are deduced for the four (3 + 1)-dimensional (4D) complex scalar fields, coupled to the U(1) gauge field, in the framework of augmented superfield formalism. This interacting gauge theory (i.e. QED) is considered on a six (4, 2)-dimensional supermanifold parametrized by four even spacetime coordinates and a couple of odd elements of the Grassmann algebra. In addition to the horizontality condition (that is responsible for the derivation of the exact nilpotent symmetries for the gauge field and the (anti-)ghost fields), a new restriction on the supermanifold, owing its origin to the (super) covariant derivatives, has been invoked for the derivation of the exact nilpotent symmetry transformations for the matter fields. The geometrical interpretations for all the above nilpotent symmetries are discussed, too.Comment: LaTeX file, 17 pages, journal versio

Wigner's little group and BRST cohomology for one-form Abelian gauge theory

We discuss the (dual-)gauge transformations for the gauge-fixed Lagrangian density and establish their intimate connection with the translation subgroup T(2) of the Wigner's little group for the free one-form Abelian gauge theory in four $(3 + 1)$-dimensions (4D) of spacetime. Though the relationship between the usual gauge transformation for the Abelian massless gauge field and T(2) subgroup of the little group is quite well-known, such a connection between the dual-gauge transformation and the little group is a new observation. The above connections are further elaborated and demonstrated in the framework of Becchi-Rouet-Stora-Tyutin (BRST) cohomology defined in the quantum Hilbert space of states where the Hodge decomposition theorem (HDT) plays a very decisive role.Comment: LaTeX file, 17 pages, Journal-ref. give

Gauge Transformations, BRST Cohomology and Wigner's Little Group

We discuss the (dual-)gauge transformations and BRST cohomology for the two (1 + 1)-dimensional (2D) free Abelian one-form and four (3 + 1)-dimensional (4D) free Abelian 2-form gauge theories by exploiting the (co-)BRST symmetries (and their corresponding generators) for the Lagrangian densities of these theories. For the 4D free 2-form gauge theory, we show that the changes on the antisymmetric polarization tensor e^{\mu\nu} (k) due to (i) the (dual-)gauge transformations corresponding to the internal symmetry group, and (ii) the translation subgroup T(2) of the Wigner's little group, are connected with each-other for the specific relationships among the parameters of these transformation groups. In the language of BRST cohomology defined w.r.t. the conserved and nilpotent (co-)BRST charges, the (dual-)gauge transformed states turn out to be the sum of the original state and the (co-)BRST exact states. We comment on (i) the quasi-topological nature of the 4D free 2-form gauge theory from the degrees of freedom count on e^{\mu\nu} (k), and (ii) the Wigner's little group and the BRST cohomology for the 2D one-form gauge theory {\it vis-{\`a}-vis} our analysis for the 4D 2-form gauge theory.Comment: LaTeX file, 29 pages, misprints in (3.7), (3.8), (3.9), (3.13) and (4.14)corrected and communicated to IJMPA as ``Erratum'

Suppressing Super-Horizon Curvature Perturbations?

We consider the possibility of suppressing superhorizon curvature perturbations after the end of the ordinary slow-roll inflationary stage. This is the opposite of the curvaton limit. We assume that large curvature perturbations are created by the inflaton and investigate if they can be diluted or suppressed by a second very homogeneous field which starts to dominate the energy density of the universe shortly after the end of inflation. We show explicit that the gravitational sourcing of inhomogeneities from the more inhomogeneous fluid to the more homogeneous fluid makes the suppression difficult if not impossible to achieve.Comment: 10 pages, 1 figure. Important revision. Conclusions more negativ

The study of multifragmentation around transition energy in intermediate energy heavy-ion collisions

Fragmentation of light charged particles is studied for various systems at different incident energies between 50 and 1000 MeV/nucleon. We analyze fragment production at incident energies above, below and at transition energies using the isospin dependent quantum molecular dynamics(IQMD) model. The trends observed for the fragment production and rapidity distributions depend upon the incident energy, size of the fragments, composite mass of the reacting system as well as on the impact parameter of the reaction. The free nucleons and light charged particles show continous homogeneous changes irrespective of the transition energies indicating that there is no relation between the transition energy and production of the free as well as light charged particles

Multiple magnetic transitions and magnetocaloric effect in Gd1-xSmxMn2Ge2 compounds

Magnetic and magnetocaloric properties of polycrystalline samples of Gd1-xSmxMn2Ge2 have been studied. All the compounds except GdMn2Ge2 show re-entrant ferromagnetic behavior. Multiple magnetic transitions observed in these compounds are explained on the basis of the temperature dependences of the exchange strengths of the rare earth and Mn sublattices. Magnetocaloric effect is found to be positive at the re-entrant ferromagnetic transition, whereas it is negative at the antiferro-ferromagnetic transition. In SmMn2Ge2, the magnetic entropy change associated with the re-entrant transition is found to decrease with field, which is attributed to the admixture effect of the crystal field levels. The isothermal magnetic entropy change is found to decrease with increase in Sm concentration.Comment: