Showing papers by "Tata Institute of Fundamental Research published in 1975"
TL;DR: In this paper, a radiating device is adapted to be installed upon any size flue pipe extending from a furnace to a chimney to transmit flue heat to the surrounding atmosphere, and a plurality of outwardly disposed radiating fins circularly positioned about said mounting base and extending outwardly therefrom.
Abstract: A radiator device adapted for attachment to a radiator pipe, comprising a mounting base wrapped about the radiator pipe and secured thereto by wire fastenings; a plurality of outwardly disposed radiating fins circularly positioned about said mounting base and extending outwardly therefrom. This radiating device is adapted to be installed upon any size flue pipe extending from a furnace to a chimney to transmit flue pipe heat to the surrounding atmosphere.
411 citations
TL;DR: In this paper, a form of quantum electrodynamics is developed which allows us to treat a number of problems involving dielectric and conducting surfaces, the presence of which leads to new observable effects.
Abstract: A form of quantum electrodynamics is developed which allows us to treat a number of problems involving dielectric and conducting surfaces, the presence of which leads to a number of new observable effects. A number of suitably defined response functions play a basic role in the present approach, as these in conjunction with the fluctuation-dissipation theorem lead to electromagnetic field correlation functions, which describe physical effects such as lifetimes, frequency shifts of the excited states, dispersion forces, etc. The quantization of the electromagnetic field is only implicitly used. A large part of the present paper is devoted to the calculation of the response functions involving different geometries and various types of dielectrics. Both spatially dispersive and spatially nondispersive dielectrics are considered. The response functions are calculated using Maxwell's equations and the usual boundary conditions at the interface adjoining the two mediums. As a first application of the present approach, the black-body fluctuations in finite geometries and the influence of surfaces on its temporal and spatial coherence are studied. An interesting theorem is also proved which enables us to calculate the normally ordered (antinormally ordered) correlation functions from the symmetrized correlation functions.
237 citations
TL;DR: In this article, a quantum-electrodynamic theory of spontaneous emission in presence of dielectrics and conductors is developed, which makes use of the master-equation techniques and the response function formalism.
Abstract: A quantum-electrodynamic theory of spontaneous emission in presence of dielectrics and conductors is developed. The theory makes use of the master-equation techniques and the response-function formalism of part I of this series of papers. Various observable entities such as damping coefficients (lifetimes), Lamb shifts, and frequency shifts are related to the appropriate surface-dependent response functions. The results are valid for arbitrary geometries (involving linear dielectrics) and naturally contain, as a special case, the usual results of spontaneous emission in free space. As explicit examples we consider a two-level atom (also the multilevel atom) in presence of a plane dielectric interface and between two conducting plates. Formulas for the shifts and widths are given and their asymptotic behavior for large and short distances is discussed. The behavior when the atom is embedded inside the dielectric is different than when the atom is outside the dielectric. The origin of coherence in the present model is discussed and the coherence effects in this model are contrasted with those in Dicke's model. The results are also compared with those obtained by the image method. Exact expressions for the operator radiation-reaction fields are obtained in terms of the atomic polarization operators and response functions. Approximate results for such fields are also given. The far-zone behavior of the radiation fields is obtained in terms of response functions and the polarization operators. Some of the normally ordered correlation functions are also calculated. The connection of some of the theoretical results with a recent experimental work of Carniglia, Mandel, and Drexhage is discussed. The effect of anisotropy of the dielectric function on the lifetimes as well as on the far-field correlation functions is also considered. Finally the contribution to the shifts and widths due to the excitation of surface polariton modes is computed and the results are compared with those obtained by the quantization of surface polariton field. It is found that such surface modes contribute significantly to widths.
150 citations
TL;DR: In this article, the authors show that the stable vector bundles of the coarse moduli scheme of isomorphism classes of stable vector bundle of rank n and determinant isomorphic to an lFq-rational line bundle L of degree d are precisely the same as the stable vectors on X defined over a finite field Fq with q elements.
Abstract: §1. In this note, we indicate a few improvements to [3]. Let X be an irreducible, non-singular projective algebraic curve defined over a finite field Fq with q elements, of characteristic p. Let SL(n, d) be the coarse moduli scheme of isomorphism classes of stable vector bundles of rank n and determinant isomorphic to an lFq-rational line bundle L of degree d. [We will assume that (n, d) = 1.] By replacing lFq by a finite extension if necessary, we may assume that SL(n, d) is defined over IFq. As one might expect, it is then indeed true that the IFq-rational points of SL(n, d) are precisely the stable vector bundles on X defined over IFq (see [3]). By the Weil conjectures, it is easy to write down the Poincar6 polynomials of SL(n, d) once the number of its lFq-rational points is known. In order to compute the latter, one first notices that the fact that the Tamagawa number of SL(n) is 1 can be interpreted as follows.
94 citations
TL;DR: In this paper, an exact expression for the interaction energy in a system of harmonic oscillators interacting with a second-quantized radiation field is obtained in terms of appropriate response functions.
Abstract: The different kinds of response functions introduced in a previous paper are used to calculate the dispersion forces. An exact expression for the interaction energy in a system of harmonic oscillators interacting with a second-quantized radiation field is obtained in terms of appropriate response functions. The radiation field may be either the field appropriate to entire free space or the field altered by the presence of the dielectric. The result is valid for arbitrary geometries involving dielectric and conducting surfaces. An expansion of our result in powers of ${e}^{2}$ leads to the results of other authors. The calculation of the dispersion force for the case of excited states is also briefly discussed. Next the problem of the dispersion force between macroscopic bodies is considered. Lifshitz's expression for the dispersion force is rederived using the response functions and the two methods are compared. The role of surface modes in the determination of dispersion force is discussed. Finally the dispersion force between a spatially dispersive and spatially nondispersive dielectric is calculated exactly. When the spatial dispersion is weak, then it is found that the first-order term is repulsive in nature, in contrast to the zeroth-order term which is attractive. As a by-product of our analysis, surface-polariton dispersion relations are obtained.
93 citations
TL;DR: In this paper, the surface-dependent correction terms for the case of a small blackbody bounded by two plane conducting surfaces are derived and a straightforward perturbation theory is used to obtain one-photon transition probabilities in terms of the surfacedependent response functions.
Abstract: In this paper the physical entities such as transition probabilities and the density of states are related to appropriate electromagnetic-field correlation functions and to appropriate response functions. Such response functions have already been computed in a previous paper and therefore these can be used to obtain surface-dependent corrections. It is shown how the density of states and hence Planck's law depends on the presence of surfaces. I explicitly calculate the correction terms for the case of a small blackbody bounded by two plane conducting surfaces. An appreciable correction occurs if the linear dimensions of the blackbody are of the order of a wavelength. Next electric-dipole-type transitions in atomic systems are considered and a straightforward perturbation theory is used to obtain one-photon transition probabilities in terms of the surface-dependent response functions. As an illustration of the surface-dependent terms, the transitions in presence of a conducting surface are considered. The transition probabilities show a marked increase or decrease depending on whether the dipole transition is parallel or perpendicular to the surface. Both stationary and nonstationary fields are considered. As a special case of nonstationary fields, the transitions in a coherent field are considered in detail. It is also shown how the coherent radiation field in presence of dielectrics can be realized. It is found that if the radiation field, in arbitrary geometries, is initially in vacuum state then at later times it would be found in a coherent state if perturbed by an external ($c$-number) electromagnetic field.
74 citations
TL;DR: In this article, a perturbative treatment of the Ewald-Oseen extinction theorem is used for the analysis of scattering and extinction cross-sections of rough surfaces, including Smith-Purcell radiation, Wood anomalies and reflectance drops at rough surfaces.
58 citations
TL;DR: In this article, the concentrations of the radionuclides, 10Be, 230Th and 232Th have been measured in four gravity cores from the Pacific and one piston core from the Indian Ocean.
54 citations
TL;DR: In this article, the ac conductivity in evaporated amorphous germanium films has been measured as a function of annealing and has been found to obey the ω 0.8 law, in accordance with the hopping model.
Abstract: The ac conductivity in evaporated amorphous germanium films has been measured as a function of annealing and has been found to obey the ω 0.8 law, in accordance with the hopping model. The dc conductivity measurements on the same samples show a T 1 4 law behaviour. The densities of localized states near the Fermi level g ( E F ), obtained from both experiments are in reasonable agreement with each other. Both the measurements show a reduction by about a factor of 2 in g ( E F ) when a freshly prepared film is fully annealed. High-temperature substrate films also show the ω 0.8 behaviour. This suggests that the frequency dependence of the ac conductivity is not caused by voids alone. Other possible explanations of our results are also discussed.
45 citations
45 citations
TL;DR: In three districts of India where an oral precancer registry comprising 30,000 individuals was established in 1967, regular follow-up surveys have been conducted, age-adjusted annual incidence rates for oral cancer were found to be 33 and 22 per 100,000 respectively.
Abstract: In three districts of India where an oral precancer registry comprising 30,000 individuals was established in 1967, regular follow-up surveys have been conducted. This paper discusses the results of a 7-year follow-up study. In Bhavnagar district only one case or oral cancer was reported in this study. In the districts of Ernakulam and Srikakulam, age-adjusted annual incidence rates for oral cancer were found to be 33 and 22 per 100,000 respectively. The significance of tobacco habits and oral submucous fibrosis as etiologic factors is discussed.
TL;DR: In this article, the diffuse component of cosmic soft gamma rays in the energy range 0.1 −4 MeV was measured with a balloon-borne telescope and it was shown that the spectrum gradually steepens from E−2.3 to E −2.8 as the energy increases from 100 to 500 keV and becomes less steep thereafter.
Abstract: IN this paper we present new measurements on the diffuse component of cosmic soft gamma rays in the energy range 0.1–4 MeV obtained with a balloon-borne telescope. These measurements show that the energy spectrum gradually steepens from E−2.3 to E−2.8 as the energy increases from 100 to 500 keV and becomes less steep thereafter, consistent with the presence of a hump in the MeV region.
TL;DR: In this article, the authors considered the galactic model of cosmic ray confinement in an in-depth theoretical investigation of the cosmic ray propagation in the Galaxy, with consideration also given to the interpretation of observed data, and the necessary data concerning the interstellar medium were summarized in order to form a basis for the theoretical formulation of the propagation of cosmic rays.
Abstract: The galactic model of cosmic ray confinement is assumed in an in-depth theoretical investigation of cosmic ray propagation in the Galaxy, with consideration also given to the interpretation of observed data. The necessary data concerning the interstellar medium are summarized in order to form a basis for the theoretical formulation of the propagation of cosmic rays, which are assumed to be in a state of equilibrium and homogeneously distributed in the residence volume. The interaction of cosmic rays with the attenuated gases, weak magnetic fields, and radiation fields of the interstellar medium is examined. Many of these interactions lead to the production of radiations ranging the entire electromagnetic spectrum. The possible roles played by cosmic rays in some aspects of galactic dynamics such as the hydrostatic equilibrium of interstellar gas, gravitational instability and formation of clouds, and heating of interstellar gas, are also studied.
TL;DR: In this paper, the authors considered deep inelastic weak and electromagnetic processes within the parton framework taking the partons to be integrally charged quarks and coloured gluons.
Abstract: Deep inelastic weak and electromagnetic processes are considered within the parton framework taking the partons to be integrally charged quarks and coloured gluons. Despite the participation of the spin-one gluons in these processes, scaling is shown to be maintained by treating the problem in a unified gauge model based on the groupSU (3)colour⊗SUL (2)⊗U(1). This is a consequence of the vector-dominance type of couplings between the gluons and the weak or electromagnetic vector bosons which are induced by the spontaneous breakdown of gauge symmetry. As a further consequence it is found that in the asymptotic region far above the gluon masses the colour octet parts of the weak and electromagnetic currents of the quarks are damped so that, in particular, the integrally charged quarks behave as fractionally charged quarks in this region.
TL;DR: In this paper, the vanadyl ion was analyzed in paramagnetically dilute form in K2Zn(SO4)2·6H2O and K2Mg(SO 4)2 ·6H 2O at room temperature at X-band.
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TL;DR: In this paper, the grade of a module M over a noetherian local ring R is defined to be the length of a maximal R -sequence contained in the annihilator of M. If M has finite projective dimension, it is known that grade M ≤ proj. dim M.
Abstract: All rings that occur in this note will be assumed to be commutative with unity and all modules will be finitely generated and unitary. The grade of a module M over a noetherian local ring R is defined to be the length of a maximal R -sequence contained in the annihilator of M. If M has finite projective dimension it is well-known that grade M ≤ proj. dim M . We can say more when R is a regular local ring.
TL;DR: In this paper, the authors describe the strong fluctuations in the intensity of radio source PKS 2025-15, observed at 327 MHz, during its occultation by comet Kohoutek (1973f) in 1974, January 5.
Abstract: This paper describes the strong fluctuations in the intensity of radio source PKS 2025-15, observed at 327 MHz, during its occultation by comet Kohoutek (1973f) in 1974, January 5. Possible mechanisms which could produce the observed fluctuations are examined. It is difficult to explain the fluctuations in terms of scintillation produced due to the passage of radio waves through the irregular cometary plasma. No detectable radio emission was observed from the comet at 327 MHz.
TL;DR: In this paper, high fluences (i.e., the integrated fluxes) of C, N, O group of nuclei and some of the heavier ones, in the energy interval 10−25 MeV/amu, have been identified in a Lexan polycarbonate detector assembly exposed on the exterior of the Skylab for 73 days.
Abstract: High fluences (i.e. the integrated fluxes) of C, N, O group of nuclei and some of the heavier ones, in the energy interval 10–25 MeV/amu, have been identified in a Lexan polycarbonate detector assembly exposed on the exterior of the Skylab for 73 days. The existence of large flux of low energy nuclei in the Skylab orbit is surprising since the minimum geomagnetic cut-off energy for fully stripped nuclei (A/Z=2) is ≃50 MeV/amu at the orbit of the satellite, and the period of exposure was a ‘quiet’ one, free from significant solar particle events. We have considered two sources for these particles: (i) partly ionized interplanetary ions accelerated within the magnetosphere and (ii) heavy nuclei trapped in the Earth's radiation belt. The flux and composition of the nuclei observed by us seem to be significantly different from those in the trapped radiation as known at present; hence it seems likely that the major part of the observed flux may be interpreted, in terms of partly ionized interplanetary ions that are further accelerated in the magnetosphere.
TL;DR: In this article, the results of nuclear magnetic resonance (NMR) and magnetic susceptibility measurements in CeSn3 are presented together with other available data, which suggest a sizeable 4f occupation near the Fermi level in Csn3.
Abstract: The results of nuclear magnetic resonance (NMR) and magnetic susceptibility measurements in CeSn3 are presented together with other available data. The magnetic susceptibility of CeSn3 shows a broad maximum around 135 K and a rapid rise below 30 K. The 119Sn Knight shift in CeSn3 in the temperature region 1.2 t o 300 K is not proportional to the bulk susceptibility. The electrical resistivity of CeSn3 shows a T2 term at low temperatures as expected in localised spin fluctuation systems, and the coefficient of the electronic specific heat is also very large. These results suggest sizeable 4f occupation near the Fermi level in CeSn3.
Nous allons presenter ici quelques resultats sur la resonance magnetique nucleaire et sur la mesure de susceptibilite dans CeSn3 avec aussi des autres resultats disponibles sur ces composes. La susceptibilite magnetique de CeSn3 montre un maximum assez large au voisinage de 135 K et une croissance rapide au-dessous de 30 K. Le deplacement de Knight de 119Sn dans CeSn3 dans la region de temperature 1,2 a 300 K n'est pas proportionel a la susceptiblite. La resistivite electrique de CeSn3 montre un T2 terme dans les temperatures bas, semblable au systeme de fluctuation spineure localisee et la coefficient de electronique chaleur specifique est aussi tres large. Ces resultats nous suggissent que une'occupation considerable 4f au voisinage du niveau de Fermi dans CeSn3.
TL;DR: In this article, the authors studied the effect of acetic and trifluoroacetic acid dimers on the thermodynamic parameters (ΔH and ΔS) and monomer and dimer chemical shifts.
TL;DR: The cosmic microwave background may be explained on the basis of absorption and reemission of the light from galaxies by graphite whiskers of length ≤ 0.1-1 mm as discussed by the authors.
Abstract: The cosmic microwave background may be explained on the basis of absorption and reemission of the light from galaxies by graphite whiskers of lengthsl≃0.1-1 mm. The mass density of such particles required is of the order of 10−34 g cm−3.
TL;DR: In this article, the authors present evidence based on 5 events recorded in cosmic ray experiments deep underground, for the production of new, massive (⪆ 2 GeV) and long lived (τ ∼ −9 sec) particles in neutrino with rock nuclei.
TL;DR: The role of exploding objects in high-energy astrophysics is discussed in this article, where a simple case of the canonical white hole which explodes from a singularity and consists of pressure-free matter in the comoving frame of reference General relativity is used for calculating the dynamical results.
Abstract: The role of exploding objects in high-energy astrophysics is discussed Quantitative results are obtained for the simple case of the canonical white hole which explodes from a singularity and consists of pressure-free matter in the comoving frame of reference General relativity is used for calculating the dynamical results Applications to X-ray background, transient X-ray sources, γ-ray bursts and high energy cosmic rays are considered White holes of more general types are discussed in a qualitative manner
TL;DR: The proposed model provides explanations to a number of dynamic and static properties of phospholipids, in particular to the observed NMR coupling constants, 1 H and 13 C relaxation times, studies based on ESR spin labels and the observed X-ray diffraction results on model compounds.
TL;DR: In this paper, the quadratic mass formula for the amplitude of the (3*, 3) \ensuremath{\bigoplus} (3, 3*) model of chiral-symmetry breaking was used to find a satisfactory fit to the data.
Abstract: Using the simple model that the amplitude for ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\pi}$ is dominated by the $\ensuremath{\delta}(970)$ resonance we find a satisfactory fit to the data. The quadratic mass formula for $\ensuremath{\eta}\ensuremath{-}{\ensuremath{\eta}}^{\ensuremath{'}}$ mixing with a positive mixing angle (i.e. reduction of $s\overline{s}$ content in the physical $\ensuremath{\eta}$ state) is preferred in agreement with the requirement for ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}2\ensuremath{\gamma}$. Failure of the current-algebra calculation for ${\ensuremath{\eta}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\eta}\ensuremath{\pi}\ensuremath{\pi}$ is explained and is shown not to be evidence against the (3*, 3) \ensuremath{\bigoplus} (3, 3*) model of chiral-symmetry breaking.
TL;DR: In this paper, a special class of events has been observed, at present 6 in number, characterised by several, (in general 3), charged particles arising from a vertex, either in air or in the thin material of the detectors, with large opening angles; the vertex is at a distance of around 70-100 cms from the rock wall.
Abstract: In the cosmic ray experiments deep underground in the Kolar Gold Mines, a special class of events has been observed, at present 6 in number, characterised by several, (in general 3), charged particles arising from a vertex, either in air or in the thin material of the detectors, with large opening angles; the vertex is at a distance of around 70–100 cms from the rock wall. The most plausible interpretation of these events is that they are due to the decay of new, massive and long-lived particles produced in neutrino collisions inside rock, or through hitherto unknown processes.
TL;DR: The lifetime of 239U compound nuclei formed in 238U(n, f) reactions has been measured at three neutron energies, 1.7, 2.3, and 3.6 MeV, by the crystal-blocking lifetime technique as mentioned in this paper.
TL;DR: In this paper, the existence of two chemically equivalent but physically non equivalent sites in a unit cell of trisarcosine calcium bromide (TSCBr) has been investigated.
Abstract: Electron paramagnetic resonance of Mn 2+ in a single crystal of tris-sarcosine calcium bromide (TSCBr), as a function of temperature and orientation, has been studied. These studies suggest the existence of two chemically equivalent but physically non equivalent Mn 2+ site in a unit cell of TSCBr. Of the two space groups determined by neutron diffraction studies, Pnma and Pn2 1 a, EPR studies are in conformity with the space group Pnma. The dielectric constant measurements in TSCBr do not show any anomaly in the temperature interval 300–100 K. Tris-sarcosine calcium chloride (TSCC, space group Pnma in the paraelectric phase) undergoes a ferroelectric phase transition at 127 K. Replacement of Cl by Br is expected to introduce changes in the N-H..X bond (X=Cl, Br) and hence, we believe, protons in the N-H..Cl bond may be playing an important role in the mechanism of ferroelectricity in TSCC.