Showing papers by "Tata Institute of Fundamental Research published in 1979"

Inclusive production ofK *(892) andΣ(1385) in $$\bar p$$ p interactions at 3.6 GeV/c and a test of factorization hypothesis

Abstract: We present a study of the inclusive production ofK *(892) and ∑t+-(1385)+cc at 3.6 GeV/c from $$\bar p$$ p interactions. The sensitivity of the exposure is 35.4 events/μb. Longitudinal and transverse momentum distributions are presented. The indirect production ofK 0 from parentK * and that of Λ's from parent Σ(1385) are studied. The shape of thex distribution of Λ's for $$p\xrightarrow{{\bar p}}\Lambda $$ are calculated from $$p\xrightarrow{p}\Lambda $$ and $$p\xrightarrow{{\pi ^ - }}\Lambda $$ and compared with the experimental distributions. The difference of antiparticle production cross-section ofK 0 in the central region is compared with the expectation from Mueller-Regge formalism.

Geometry of SU(2) gauge fields

Abstract: We studySU(2) Yang-Mills theory onS3×ℝ from the canonical view-point. We use topological and differential geometric techniques, identifying the “true” configuration space as the base-space of a principal bundle with the gauge-group as structure group.

Homogenization of elliptic eigenvalue problems: Part 1

Abstract: The aim of this paper is to study the homogenization of elliptic eigenvalue problems, with a second order homogeneous Dirichlet problem as an example. The main homogenization theorem states that the same operator which serves to homogenize the corresponding static problem works for the eigenvalue problem as well and that the structure of eigenvalues and eigenvectors is in some sense preserved. Formulae for first and second order correctors for eigenvalues are proposed and error estimates are obtained. These results are applied to the case of coefficients with a periodic structure and a simple numerical example is presented. Extensions to other types of boundary conditions and to higher order equations are indicated.

FFT algorithm for both input and output pruning

Abstract: When an input data sequence has a large number of zeros and the number of output samples required to be computed is small, significant time saving can be achieved by a judicious combination of the pruning algorithms for decimation-in-time (DIT) and decimation-in-frequency (DIF). It is shown that the complementary structure of the DIT and the DIF formulations makes possible the application of the pruning algorithms simultaneously at the input, as well as at the output, for either of the formulations. For a given number of input and output points, a choice between the two formulations can be made based on the amount of time saved in each. Also, a simple assembly language modification is shown by which the bit reversal is made significantly faster.

On invariant measures, minimal sets and a lemma of margulis

Abstract: Let G be a semisimple, or more generally a reductive, Lie group and let F be a lattice in G; i.e. G/F admits a finite G-invariant (Borel) measure. Let U be a horospherical subgroup of G; i.e. there exists g e G such that U = {x ~ G I gJx g j ~ e asj ~ 0o } where e is the identity element in G. The action of U on G/F is called a horospherical flow. In [3] the author obtained a classification of all finite invariant measures of a certain class of horospherical flows. In the present paper we show that if F is an 'ar i thmetic ' lattice then every locally finite ergodic invariant measure of the action of any unipotent subgroup (a horospherical subgroup as above is always unipotent) is necessarily finite. The first step is the following theorem.

Homogenization of elliptic eigenvalue problems: Part 2

Abstract: The aim of this paper is to study the homogenization of elliptic eigenvalue problems, with a second order homogeneous Dirichlet problem as an example. The main homogenization theorem states that the same operator which serves to homogenize the corresponding static problem works for the eigenvalue problem as well and that the structure of eigenvalues and eigenvectors is in some sense preserved. Formulae for first and second order correctors for eigenvalues are proposed and error estimates are obtained. These results are applied to the case of coefficients with a periodic structure and a simple numerical example is presented. Extensions to other types of boundary conditions and to higher order equations are indicated.

Compactification of generalised Jacobians

Abstract: The aim of this paper is to show that there is a natural “compactification” of the Picard Scheme of a Family of Curves and to study its properties.

Inhibition of domain wall formation and its effects on the bulk magnetic properties of certain spinels

Abstract: It is shown that hysteresis and susceptibility studies at various temperatures could provide an idea whether a magnetic sample contains multidomain, single-domain or superparamagnetic particles. Our results on titanomagnetites with those of others on cobalt substituted magnesium ferrites suggest that domain wall formation is inhibited in some of them whereby only single-domain or superparamagnetic particles occur irrespective of the physical grain size of such materials. At high concentration of titanium in titanomagnetites, the magnetic behaviour is similar to a spin glass, which we interpret as a transition of optimum single-domains going over to superparamagnetic state.

Waves in the sunspot umbra

Abstract: The magnetoacoustic modes excited in a thermally conducting polytropic fluid layer in the presence of a vertical magnetic field are examined with a view to classify them with the help of phase diagrams. The possibility of identifying the umbral flashes with overstable magnetoacoustic modes is explored.

Moduli for principal bundles

Abstract: A principal bundle E over a space X ( or a G-bundle, for short ) is a space E onwhich G operates (from the right ) and a G-invariant morphism p: E ~ X which is locally trivial in the etale topology, i.e. for every point x of X there is a neighbourhood U of x and an etale covering f: U' ~ U such that there is a G-equivariant isomorphism of f(E) with U'x G over U' where G operates by right translations on the second factor of U' x G.

An oral lesion in tobacco-lime users in Maharashtra, India.

Abstract: The habit of chewing tobacco along with lime in the canine-premolar region of the mandibular groove is widespread (28%) in the rural population of Maharashtra, India. Among individuals with this habit, a thick yellowish-white-to-brown lesion was observed at the site of placement of the mixture. Unlike leukoplakia, this lesion could be scraped off. The prevalence of this lesion among 101,761 Maharashtrian villagers was 2.9% which is four times more common than leukoplakia (0.67%). It is surmised that this particular lesion among the tabacco-lime users is a specific entity with consistent histological features. The diagnosis should be made on the basis of history, clinical features, and consistent histological picture.

Involvement of cyclic adenosine-3', 5'-monophosphate in chloronema differentiation in protonema cultures of Funaria hygrometrica.

Abstract: The role of purine and pyrimidine ribosides, nucleotides and substituted xanthines in the differentiation of chloronema filaments in suspension cultures of protonema of the moss Funaria hygrometrica Hedw. has been examined. Cyclic adenosine-3',5'-monophosphate (cAMP) and mono-and dibutyryl cAMP evoked the maximum response in wild-type protonema. ADP and ATP also enhanced chloronema differentiation but were less active than cAMP; pyrimidine derivatives were completely inactive. Inhibitors of cyclic-nucleotide phosphodiesterase aminophylline, theophylline and ICI 58, 301 (3-acetamido-6-methyl-8-n-propyl-s-triazolo-(4,3a)-pyrazine)-mimicked the effect of cAMP. A leaky, chloronema-repressed mutant was isolated and in this mutant cAMP was much more active than cyclic guanosine monophosphate and ADP in enhancing chloronema differentiation. These results strongly indicate that cAMP is involved in chloronema differentiation in Funaria, and a hypothesis on growth regulation in protonema cell cultures is proposed.

Discovery of IR bursts from Liller I/MXB1730–333

Abstract: THE first detection of IR bursts from the object1 known as Liller I which has been identified2 with the rapid X-ray burster MXB1730–333 is reported here. The rapid burster is the only one of its kind that has been extensively studied in the X-ray region3–5 and some of its known characteristics can be summarised as follows. When it is active it gives several thousand X-ray bursts per day. It operates in two modes: mode I (usually in March and September every year), mode II (usually in April and October every year). In mode I it gives large X-ray bursts with energy in the range 1039–1040 erg and also small bursts with energy in the range of 1038–1039 erg; while in mode II it primarily emits bursts with energy typically close to 1039 erg. These bursts are called type II on the basis of the constant character of their spectrum during the decay phase. The rapid burster occasionally also gives bursts known as type I which are characterised by the softening of the X-ray spectrum during the decay phase. The energy in these bursts is usually in excess of 1039 erg and their frequency is about one every few hours.

Cell-density-dependent Changes in the Metabolism of Chloronema Cell Cultures: I. Relationship between Cell Density and Enzymic Activities.

Abstract: In the growing chloronema cell suspension cultures of the moss Funaria hygrometrica Hedw., activities of several enzymes have been found to be cell-density-dependent. Cyclic nucleotide phosphodiesterase (cNPDE), nitrate reductase (NR), and protein kinase showed highest activity at a low cell density (1 to 2 milligrams per milliliter) while indoleacetic acid (IAA) oxidase and peroxidase were highest at a high cell density (>10 milligrams per milliliter). 3′-Nucleotidase and the glycolytic enzymes (aldolase, hexokinase, phosphofructokinase, phosphoglucoisomerase, pyruvate kinase, and triose phosphate isomerase) showed no significant dependence on the cell density. Alternatively, if the NR and peroxidase activities were determined as a function of time in batch cultures, their levels were maximal 60 to 70 and 320 hours after subculture, respectively, the corresponding cell densities being 1 to 2 and 23 milligrams per milliliter. The relationship between cell density and NR and peroxidase activities is the same, whether these enzymes are measured in batch cultures during a growth cycle or in the cells cultured at different initial inoculum densities for a constant time. Conventionally enzymic changes have been correlated with growth phases; however, it is felt that the pattern of enzymic activities can also be interpreted as cell-density-dependent. In moss protonema, the dependence of cNPDE, IAA oxidase, and peroxidase on cell density may play an important role in modulating the endogenous levels of IAA and cAMP, both of which regulate the differentiation of specific cell types (Johri and Desai 1973 Nature New Biol 245: 223-224; and Handa and Johri 1976 Nature 259: 480-482).

Absorption effects of intergalactic natural graphite whiskers on observations at microwave and radio frequencies

Abstract: An attempt has been made to explain the microwave background within the framework of the steady state theory by invoking thermalizers in the form of long whiskers of semi-metallic grains such as natural graphite. An ad hoc but general method has been sought for the description of a cosmic thermal system in terms of absorption coefficients of such grains in the proper Rayleigh limit. We have found that typically natural graphite grains, having axial ratios of the order of 104 to 105 and a temperature about 4 K, have a broad absorption peak only at decimetre wavelengths and thus cannot adequately thermalize the background. It is also shown that the effects of such an absorbing medium on such radio astronomical tests as the number count test or the angular size test can be very severe, especially in Friedmann cosmologies. These effects are marginal in the steady state theory. The desirable physico-optical properties of such semi-metallic thermalizers have also been investigated.

Quantum fluctuations near the classical space-time singularity

Abstract: The method of path integration is used to study the effects of quantum fluctuations in the space-time geometry near the classical singularity of general relativity. It is shown that in certain special cases explicit Feynman propagators can be constructed which enable us to evaluate these fluctuationsquantitatively. The cases discussed are (i) the gravitational collapse of a uniform dust ball, (ii) the Friedmann cosmologies, (iii) the axisymmetric Bianchi type I cosmological model, and (iv) the general anisotropic Bianchi type I cosmological model. In all cases discussed here the quantum uncertainty grows to infinity as the classical space-time singularity is approached. In this wider regime of quantum gravitation nonsingular solutions can occur with finite probabilities.

25 keV-neutron capture cross-sections

Abstract: By using the filtered beam of 25 keV neutrons from the reactions of the Bhabha Atomic Research Centre, isotopic capture crosssections for 19 nuclides in the mass regionA=51 to 187 have been measured. These measured cross-sections have been discussed in the light of s (slow) process nucleosynthesis.