Showing papers by "Tata Institute of Fundamental Research published in 1977"
246 citations
TL;DR: In a 7-year follow-up study of 107 cases of oral epithelial dysplastic precancerous lesions in Indian villagers, 6.6 per cent were found to develop into carcinomas and clinical spontaneous regression occurred in 14.8 per cent.
135 citations
TL;DR: The gluconeogenic requirement of a growing culture of E. coli was shown to be one-twentieth of its total catabolic and anabolic needs, which countered to a large extent the severe repression of beta-galactosidase synthesis that glucose caused in these mutants.
Abstract: Physiological properties of mutants of Escherichia coli defective in glyceraldehyde 3-phosphate dehydrogenase, glycerate 3-phosphate kinase, or enolase are described. Introduction of a lesion in any one of the reversible steps catalyzed by these enzymes impaired both the glycolytic and gluconeogenic capabilities of the cell and generated an obligatory requirement for a source of carbon above the block (gluconeogenic) and one below (oxidative). A mixture of glycerol and succinate supported the growth of these mutants. Mutants lacking glyceraldehyde 3-phosphate dehydrogenase and glycerate 3-phosphate kinase could grow also on glycerol and glyceric acid, and enolase mutants could grow on glycerate and succinate, whereas double mutants lacking the kinase and enolase required l-serine in addition to glycerol and succinate. Titration of cell yield with limiting amounts of glycerol with Casamino Acids in excess, or vice versa, showed the gluconeogenic requirement of a growing culture of E. coli to be one-twentieth of its total catabolic and anabolic needs. Sugars and their derivatives inhibited growth of these mutants on otherwise permissive media. The mutants accumulated glycolytic intermediates above the blocked enzyme on addition of glucose or glycerol to resting cultures. Glucose inhibited growth and induced lysis. These effects could be substantially overcome by increasing the osmotic strength of the growth medium and, in addition, including 5 mM cyclic adenosine 3',5'-monophosphate therein. This substance countered to a large extent the severe repression of beta-galactosidase synthesis that glucose caused in these mutants.
104 citations
TL;DR: In this paper, it was shown that the moduli of vector bundles V on X, endowed with additional structures, namely flags at the fibres of V at PeS, can be interpreted algebraically.
Abstract: Let H be the upper half plane and F a discrete subgroup of AutH. When H mo d F is compact, one knows that the moduli space of unitary representations of F has an algebraic interpretation (cf. [7] and [10]); for example, if moreover F acts freely on H, the set of isomorphism classes of unitary representations of F can be identified with the set of equivalence classes of semi-stable vector bundles of degree zero on the smooth projective curve H modF, under a certain equivalence relation. The initial motivation for this work was to extend these considerations to the case when H m od F has finite measure. Suppose then that H modF has finite measure. Let X be the smooth projective curve containing H modF as an open subset and S the finite subset of X corresponding to parabolic and elliptic fixed points under F. Then to interpret algebraically the moduli of unitary representation of F, we find that the problem to be considered is the moduli of vector bundles V on X, endowed with additional structures, namely flags at the fibres of V at PeS. We call these quasi parabolic structures of V at S and, if in addition we attach some weights to these flags, we call the resulting structures parabolic structures on V at S (cf. Definition 1.5). The importance of attaching weights is that this allows us to define the notion of a parabolic degree (generalizing the usual notion of the degree of a vector bundle) and consequently the concept of parabolic semi-stable and stable vector bundles (generalizing Mumford's definition of semi-stable and stable vector bundles). With these definitions one gets a complete generalization of the results of [7, 10, 12] and in particular an algebraic interpretation of unitary representations of F via parabolic semi-stable vector bundles on X with parabolic structures at S (cf, Theorem 4.1). The basic outline of proof in this paper is exactly the same as in [12], however, we believe, that this work is not a routine generalization. There are some new aspects and the following are perhaps worth mentioning. One is of course the idea of parabolic structures; this was inspired by the work of Weil (cf. [16], p. 56). The second is a technical one but took some time to arrive at, namely when one
103 citations
TL;DR: Two independent isolates of Saccharomyces cerevisiae lacking hexokinase activity are described, and genetic analysis suggests that these two unlinked genes hxk1 and hxK2 determine, independently of each other, the synthesis ofhexokinase isozymes P1 and P2, respectively.
Abstract: Two independent isolates of Saccharomyces cerevisiae lacking hexokinase activity (EC 2.7.1.1) are described. Both mutant strains grow on glucose but are unable to grow on fructose, and contain two mutant genes hxk1 and hxk2 each. The mutations are recessive and noncomplementing. Genetic analysis suggests that these two unlinked genes hxk1 and hxk2 determine, independently of each other, the synthesis of hexokinase isozymes P1 and P2, respectively. hxk1 is located on chromosome VIR distal to met10, and hxk2 is on chromosome IIIR distal to MAL2. Of four hexokinase-positive spontaneous reversions, one is very tightly linked to hxk1 and the other three to the hxk2 locus. The reverted enzymes are considerably more thermolabile than the respective wild-type enzymes, and in one case show altered immunological properties. Data are presented which suggest that the hxk1 and hxk2 mutations are missense mutations in the structural genes of hexokinase P1 and hexokinase P2, respectively. These are presumably the only enzymes that allow S. cerevisiae to grow on fructose.
100 citations
TL;DR: Starting with a mutant of Saccharomyces cerevisiae lacking glucokinase and both the hexokinase isozymes P1 and P2, strains were constructed, by genetic crosses, that carry single glucose-phosphorylating enzymes.
82 citations
TL;DR: In this paper, the lifetime of neutrinos for radiative decay divided by the rest mass was shown to exceed 10.17$ sec/eV for x-ray, optical, and radio frequencies.
Abstract: Astronomical observations at the x-ray, optical, and radio frequencies are used to show that the lifetime of neutrinos for radiative decay divided by the rest mass, $\frac{{\ensuremath{\tau}}_{0}}{{m}_{\ensuremath{
u}}}$, exceeds ${10}^{17}$ sec/eV. If one makes the further assumption that ${m}_{\ensuremath{
u}}g{10}^{\ensuremath{-}3}$ eV, then ${\ensuremath{\tau}}_{0}g~{10}^{19}$ sec. If there are other competing decays of neutrinos, it is then shown that $\frac{{\ensuremath{\Gamma}}_{{\ensuremath{
u}}_{e}}({\ensuremath{
u}}_{e}\ensuremath{\rightarrow}x+\ensuremath{\gamma})}{{\ensuremath{\Gamma}}_{{\ensuremath{
u}}_{e}}(\mathrm{total})}l~{10}^{\ensuremath{-}15}$ and $\frac{{\ensuremath{\Gamma}}_{{\ensuremath{
u}}_{\ensuremath{\mu}}}({\ensuremath{
u}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}x+\ensuremath{\gamma})}{{\ensuremath{\Gamma}}_{{\ensuremath{
u}}_{\ensuremath{\mu}}}(\mathrm{total})}l~3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$.
63 citations
TL;DR: There appears to be neither a common genetic regulator controlling two or more of these glucose-phosphorylating enzymes nor a sugar carrier that can be dispensed with.
Abstract: When strains of Saccharomyces cerevisiae carrying a single glucose-phosphorylating enzyme such as hexokinase Pl or hexokinase P2 or glucokinase, are subjected to the selection pressure against the toxic sugar 2-deoxyglucose, the majority of survivors are mutants lacking the respective enzymes. All the 2-deoxyglucose-resistant segregants recovered from backcrosses of these mutants to a wild type strain are glucose-negative and all the sensitive ones are glucose-positive. The hexokinase mutations are located in the same complementation groups as defined by the structural genes of hexokinase P1 and hexokinase P2. No interallelic complementation has been observed either in hexokinase P1 or in hexokinase P2 amongst a total of 4 X 64, and 5 X 60 different combinations of independent mutants at the hxk1 and hxk2 loci respectively. There appears to be neither a common genetic regulator controlling two or more of these glucose-phosphorylating enzymes nor a sugar carrier that can be dispensed with.
58 citations
01 Apr 1977
TL;DR: In this article, the lifetime of neutrinos for radiative decay divided by the rest mass was shown to exceed 10.17$ sec/eV for x-ray, optical, and radio frequencies.
Abstract: Astronomical observations at the x-ray, optical, and radio frequencies are used to show that the lifetime of neutrinos for radiative decay divided by the rest mass, $\frac{{\ensuremath{\tau}}_{0}}{{m}_{\ensuremath{
u}}}$, exceeds ${10}^{17}$ sec/eV. If one makes the further assumption that ${m}_{\ensuremath{
u}}g{10}^{\ensuremath{-}3}$ eV, then ${\ensuremath{\tau}}_{0}g~{10}^{19}$ sec. If there are other competing decays of neutrinos, it is then shown that $\frac{{\ensuremath{\Gamma}}_{{\ensuremath{
u}}_{e}}({\ensuremath{
u}}_{e}\ensuremath{\rightarrow}x+\ensuremath{\gamma})}{{\ensuremath{\Gamma}}_{{\ensuremath{
u}}_{e}}(\mathrm{total})}l~{10}^{\ensuremath{-}15}$ and $\frac{{\ensuremath{\Gamma}}_{{\ensuremath{
u}}_{\ensuremath{\mu}}}({\ensuremath{
u}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}x+\ensuremath{\gamma})}{{\ensuremath{\Gamma}}_{{\ensuremath{
u}}_{\ensuremath{\mu}}}(\mathrm{total})}l~3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$.
52 citations
TL;DR: In this paper, a mechanism for the formation of superparamagnetic grains in basalts and its implications to palaeomagnetism is presented, which can account for the observed variation in their magnetic stability.
48 citations
TL;DR: It appears that this mutation interferes with a step leading to normal wing-notum compartmentation of the wing disk, and therefore mutations in this gene can be autonomous in mosaics.
Abstract: The properties of the mutation wingless discovered by Sharma are discussed. It appears that this mutation interferes with a step leading to normal wing-notum compartmentation of the wing disk. From the study of mutational mosaics in the wingless locus we conclude that mutations in this gene can be autonomous in mosaics.
TL;DR: Palatal keratosis was very stable, whereas red areas changed into nonpigmented areas, and Epithelial dysplasia was found in 23% of the 101 biopsies, the highest being in the red areas.
TL;DR: From the protonema of the moss Funaria hygrometrica (L.) Sibth, a factor indistinguishable from cyclic adenosine 3':5'-monophosphate (cAMP) has been isolated, which stimulated the activity of protein kinase from rabbit skeletal muscle and co-chromatographed with authentic cAMP in two solvent systems.
Abstract: From the protonema of the moss Funaria hygrometrica (L.) Sibth, a factor indistinguishable from cyclic adenosine 3′:5′-monophosphate (cAMP) has been isolated. The factor stimulated the activity of protein kinase from rabbit skeletal muscle and co-chromatographed with authentic cAMP in two solvent systems. Its ability to stimulate protein kinase activity was completely abolished by 3′:5′-cyclic nucleotide phosphodiesterase, the rate of inactivation being similar to that of authentic cAMP. Based on these properties, this factor is identified as 3′,5′-cAMP. Cyclic AMP could be readily removed from the cells and washing the cells with water reduced the endogenous level of cAMP by 2- to 3-fold. A comparison of cAMP levels by protein kinase and Gilman assays was made. The intracellular levels determined by protein kinase assay were about 7-fold lower than the values obtained by Gilman assay. This discrepancy was due to the presence of unidentified compounds which were completely degraded by 3′:5′-cyclic nucleotide phosphodiesterase. Although these displaced labeled cAMP in the Gilman assay, they did not stimulate the protein kinase activity. The protonema may contain cyclic nucleotides other than cAMP; these will not be detected in the protein kinase assay due to the specificity of this reaction. The crude extracts were found to be unsuitable for assaying cAMP by either method.
TL;DR: In this article, it was shown that the presence of Ga in the top contact prevents micro-alloying to take place during heat treatment and thus prevents degradation of the diode behavior.
Abstract: It is shown that unlike AuGaAs Schottky diodes, a Schottky barrier made on GaAs using an evaporated film of AuGa eutectic alloy does not degrade on heat treatment. It is shown that the presence of Ga in the top contact prevents micro-alloying to take place during heat treatment and thus prevents degradation of the diode behaviour.
TL;DR: In this paper, the conformally invariant theory of Hoyle and Narlikar is applied to two astrophysical scenarios, and the existence of zero mass surfaces in the four-dimensional manifold in this theory can lead to black holes and white holes.
TL;DR: In this paper, a study of the inclusive production of π −, η, ϱ 0, ω ad f mesons in p p annihilation at 0.7 GeV/c is presented.
TL;DR: The majority of single-step spontaneous revertants on glucose regain the enzyme activity fully and this activity appears to be due to the same enzyme present in the wild type, which is believed to involve some regulatory element in the synthesis of pyruvate kinase.
Abstract: Mutants of Saccharomyces cerevisiae lacking pyruvate kinase (EC 2.7.1.40) are described. These have less than 0.5% of the pyruvate kinase activity of the wild type. All the other glycolytic enzymes are present in normal amounts in these mutants. The mutation is recessive and segregates in diploids as a single gene. Five alleles examined fail to complement one another. Tetrad analysis and mitotic recombination data place the mutation on the left arm of chromosome I distal to cys 1. The majority of single-step spontaneous revertants on glucose regain the enzyme activity fully and this activity appears, by a number of criteria, to be due to the same enzyme present in the wild type. Some of these revertants become nuclear petites. The mutants do neither grow on nor ferment sugars but do grow on ethyl alcohol or pyruvate. Glucose addition to cultures growing on alcohol arrests growth until glucose is exhausted. The steady state rate of glucose utilization is slower than in the wild type. This is associated with the accumulation of as much as 5 micronmoles P-enolpyruvate per g wet weight of cells and proportional amounts of 2-P-glyceric and 3-P glyceric acids. The mutation is believed to involve some regulatory element in the synthesis of pyruvate kinase.
TL;DR: In this article, anomalous Mossbauer lineshapes are attributed to ionic spin fluctuations, either due to the motion of individual spins, or due to collective motion of large number of spins in a small region of material.
Abstract: Mossbauer measurements show that an incomplete annealing of the magnetically ordered Ga2O3–Fe2O3 system gives rise to anomalous Mossbauer spectra which are characterised by an enhancement in the intensity (or percentage absorption) of their central portions as compared to the intensity of outer absorption peaks. Measurements carried out in an external magnetic field confirm that the observed anomalous Mossbauer lineshapes are due to ionic spin fluctuations (either due to the motion of individual spins, i.e. electronic relaxation effects, or due to the collective motion of large number of spins in a small region of material, i.e. superparamagnetic effects) and are not a result of any distribution of hyperfine field or the presence of critical superparamagnetism in the incompletely annealed solid solutions.
Mosbauermessungen zeigen, das eine unvollstandige Temperung des magnetisch geordneten Ga2O3–Fe2O3-Systems Anlas zu anomalen Mosbauerspektren gibt, die durch eine Erhohung der Intensitat (oder der relativen Absorption) in ihren zentralen Teilen im Vergleich zur Intensita t der auseren Absorptionsmaxima charakterisiert sind. Messungen in einem aseren Magnetfeld bestatigen, das die beobachteten anomalen Masbauerlinienformen von den ionaren Spin-Fluktuationen herruhren (entweder von der Bewegung der individuellen Spins, d. h. elektronischen Relaxationseffekten, oder durch die kollektive Bewegung einer grosen Anzahl von Spins in einem kleinen Bereich des Materials, d. h. superparamagnetischen Effekten) und nicht das Ergebnis einer Verteilung der Hyperfeinfelder oder des Vorhandenseins von kritischem Superparamagnetismus in den unvollstandig getemperten Mischsystemen sind.
TL;DR: In this article, an investigation involving an application of resonance fluorescence theory to C2 was presented, taking into account all important electronic transitions which determine the population distribution of the lowest energy states.
Abstract: Swan-band emission from the C2 molecule provides important information for a study of the physical processes occurring in comets It is, therefore, a disturbing factor that many quantitative Swan-band observations are in clear contradiction of predictions of resonance fluorescence excitation of the Swan bands A description is presented of an investigation involving an application of resonance fluorescence theory to C2 The investigation takes into account all important electronic transitions which determine the population distribution of the lowest energy states It is found that the previous discrepancy for the brighter band sequences disappears
TL;DR: In this paper, the authors show an exact equivalence between the partition function of a d-dimensional model of electrons with short range interactions and a (d + 1)-dimensional classical problem.
TL;DR: In this paper, a sum rule relating the masses of the four charmonium levels, for each L ⩾ 1, which is valid for a wide class of potentials, was derived.
TL;DR: In this paper, the structure and properties of ions in magnetic fields with strengths of the order of 10 − 9 − 10 − 10 G have been studied by means of a variational method.
Abstract: The structure and properties of ${\mathrm{H}}_{3}^{+}$ ions in magnetic fields with strengths of the order of ${10}^{9}$-${10}^{10}$ G have been studied by means of a variational method. It is found that there is a rapid change in the configuration of the ${\mathrm{H}}_{3}^{+}$ ion from its equilateral triangular structure to a linear chain, around a magnetic field ${B}_{c}=2.35\ifmmode\times\else\texttimes\fi{}{10}^{9}$ G. The exchange contribution increases with the magnetic field, and its effect on ${B}_{c}$ is to lower its value. The vibrational frequencies of ${\mathrm{H}}_{3}^{+}$, about its ground-state structure increase with the field strength and undergo a rapid change near ${B}_{c}$. The oscillator strengths for the electronic transition stay nearly constant in the range 0-4.7 \ifmmode\times\else\texttimes\fi{} ${10}^{10}$ G of the magnetic field strength studied.
TL;DR: The positions of three celestial X-ray sources were measured with the rotating modulation collimators (RMC) on SAS-3 during a survey of the galactic plane and are precise to ≤ 25″ as mentioned in this paper.
Abstract: THE positions of three celestial X-ray sources were measured with the rotating modulation collimators (RMC) on SAS-3 during a survey of the galactic plane1 and are precise to ≤ 25″ (ref. 2). One of these sources, Cir X-1 (ref. 3), is a highly variable X-ray source often compared with the black-hole candidate, Cyg X-1. Another, TrA X-1 = A1524–61, is a 1974 X-ray nova4, and the third, 3U1626–67 (ref. 5), is a 7.68-s X-ray pulsar6. The results reported here support recently proposed optical and radio identifications7–9 of these three sources. In two cases (TrA X-1 and 3U1626–67), they have been instrumental in bringing about the proposed identifications. Cir X-1 exhibits a binary periodicity10 of 16.6 d, extreme aperiodic variability on timescales of > 0.1s (refs 11, 12) and 1–3 s (ref. 13), and flaring14,15 with time constants of a few ms. This variability and the absence of a shorter (spin) period13,15 have led to suggestions11,13–15 that this object may be similar to Cyg X-1. The absence of a compelling optical or radio counterpart, however, has prevented the further exploration of this hypothesis.
TL;DR: In this paper, hyperfine fields measured by NMR at various nuclear sites in ferromagnetic cobalt-based Heusler alloys Co 2 TSn (T=Ti, Zr, Hf, Nb, V) and Co 2 VGa are reported.
Abstract: Hyperfine fields measured by NMR at various nuclear sites in ferromagnetic cobalt-based Heusler alloys Co 2 TSn (T=Ti, Zr, Hf, Nb), Co 2 TAl (T=Ti, Zr, Hf, V) and Co 2 VGa are reported.
TL;DR: A mutation pgi1 in the yeast Saccharomyces cerevisiae conferring deficiency of the glycolytic enzyme glucose 6-phosphate isomerase is characterised genetically and can be suppressed intragenically giving revertants that have an unstable enzyme.
Abstract: A mutation pgi1 in the yeast Saccharomyces cerevisiae conferring deficiency of the glycolytic enzyme glucose 6-phosphate isomerase is characterised genetically. The mutation segregates 2+:2- in tetrads from diploids heterozygous for the mutant phenotype. The mutation is semi-dominant and is located on the right arm of chromosome II in the order: tsm134-lys2-pgi1-tyr1 approximately 15 map units from tyr1. The mutation pgi1 defines the structural gene of glucose 6-phosphate isomerase and can be suppressed intragenically giving revertants that have an unstable enzyme. In one temperature-sensitive revertant no enzyme activity in excess of the mutant level could be detected although fructose 6-phosphate was converted to glucose 6-phosphate in vivo. The suppressor locus in this revertant is dominant and is unlinked to the pgi1 locus.
TL;DR: In this article, the positions, error radii, and intensities of six X-ray sources located in the galactic bulge were determined using the SAS-3 rotating modulation collimators.
Abstract: PRECISE (20–25″) positions of six X-ray sources located in the galactic bulge, GX1+4, GX9+9, GX3+1, GX+1, G%13+1 and GX17+2 are reported here. The data were taken as part of the survey of the galactic plane performed with the SAS-3 rotating modulation collimators1–4. Previously proposed optical counterparts for three of these sources (GX1+4, GX9+9, and GX17+2) lie within our error circles. The positions, error radii, and intensities (2–11 keV) determined for the sources are given in Table 1. We compare our results with those determined with previous sounding rocket and satellite experiments in Fig. 1. Proposed optical and radio candidates are also included. Finding charts for the six sources are given in Fig. 2.
TL;DR: In this article, precise positions for three steady X-ray sources that have been identified recently as Xray burst sources: 4U (MXB) 1636-53, 4U 1728-33, and 4U 1635-44 were obtained from data obtained with the SAS 3 rotating modulation collimators during a survey of the galactic plane.
Abstract: Precise (20-30 arcsec) positions are reported for three steady X-ray sources that have been identified recently as X-ray burst sources: 4U (MXB) 1636-53, 4U 1728-33 (MXB 1728-34), and 4U (MXB) 1735-44. The positions were derived from data obtained with the SAS 3 rotating modulation collimators during a survey of the galactic plane. Possible optical counterparts are noted.
TL;DR: The data from a recently completed survey of the galactic plane with the SAS-3 modulation collimators provided precise (20 to 60 arcsec) celestial positions of galactic X-ray sources as mentioned in this paper.
Abstract: The data from a recently completed survey of the galactic plane with the SAS-3 modulation collimators provide precise (20 to 60 arcsec) celestial positions of galactic X-ray sources. Preliminary positions of 60-arcsec precision are reported for five sources. One of these led to the identification of the star, Gamma Cas, as an X-ray source, and the others lend substantial confidence to previously proposed optical identifications: 3U 0352+30 = X Per, 3U 1145-61 = HEN 715, GX301-2 = WRA977, and GX304-1 = MMV star. These identifications seem to establish the existence of a previously suggested class of Be-star X-ray emitters.