Showing papers by "Tata Institute of Fundamental Research published in 1983"

Sensilla on the tarsal segments and mouthparts of adult Drosophila melanogaster meigen (Diptera : Drosophilidae)

Abstract: Sensilla on the tarsal segments of legs and on the external and internal mouthparts of adult Drosophila melanogaster Meigen (Diptera : Drosophilidae) were studied by light and electron microscopy. Tarsi are invested with bracteate and bractless bristles. Ethanolic silver nitrate stain distinguishes dendrite-containing bristles from other hairs on the tarsi. Stained bristles are bractless. Males have more silver-staining bristles than females on the I st 4 tarsal segments of prothoracic legs. There are 33 – 34 taste bristles on each half of the labellum. Many of them are 2-pronged. Both prongs have a pore at the tip, but chemosensory dendrites enter only in one of them. The taste bristles in the 2 medial rows on each half of the labellum are predominantly associated with 4 chemosensory neurons and the peripheral bristles usually contain 2 chemosensory neurons each. Five groups of paired sense organs are known to exist on the internal mouthparts. Amongst 9 sensilla present in the labral sense organ, electron microscopy shows that sensilla numbers 1 – 6 have one mechanosensory neuron each. Sensillum number 7 has 8 neurons with dendrites arranged in 3 groups: 2 triplets and a pair. Sensilla 8 and 9 have 2 neurons each. The ventral cibarial sense organ (VCSO) has 2 sensilla, one with 2 and the other with 4 neurons. Rows of hollow satellite bristles forming 2 sensory systems, dorsal and ventral to the VCSO have one mechanosensory neuron each. The dorsal cibarial sense organ has 2 sensilla on either side of the midline, each containing 3 neurons. The paper describes the fine structural morphology of taste receptors and enumerates axons of all the prominent nerves of mouthparts at different levels. An external nerve loop connecting directly 2 regions of the brain, the tritocerebrum and suboesophageal ganglion, is reported.

Projection patterns of different types of antennal sensilla in the antennal glomeruli of Drosophila melanogaster

Abstract: Cobalt fills from small, defined regions of the antenna in D. melanogaster show that the three types of sensilla on the third segment, the flagellum, and a fourth sensillum located in the arista, project into the glomeruli of the antennal lobe. We have identified 19 glomeruli in each lobe, according to their location, shape, and size. At least ten of these represent major projection areas of flagellar or aristal sensilla. The large majority of glomeruli is innervated from both antennae, but a small group of five receive exclusively ipsilateral input. A particular sensory fiber appears to terminate only in one specific glomerulus, either in the ipsilateral or in both lobes. Fills from flagellar regions bearing a single type of sensillum, yield a specific pattern of glomeruli containing stained terminals. Aristal projections remain strictly ipsilateral, whereas those from the other sensilla consist of an ipsilateral and a bilateral component. When filling from different points in an area bearing one type of sensillum, similar projections are produced, suggesting that projection patterns observed reflect predominantly the type of sensillum rather than its location on the flagellum. Accordingly, individual glomeruli might represent functional units, each receiving antennal input in a characteristic combination.

Exact Solution of a Directed-Site Animals-Enumeration Problem in three Dimensions.

Abstract: An exact equivalence is established between the directed-site animals-enumeration (DSAE) problem in $d$ dimensions and a crystal-growth model defined on the same lattice. In special cases, the latter reduces to the calculation of the free energy of a ($d\ensuremath{-}1$)-dimensional lattice gas with extended hard cores. The author solves a DSAE problem with $d=3$ exactly by using its equivalence to the hard-hexagon problem, and shows that the exponent $\ensuremath{\theta}=\frac{5}{6}$. A new and simpler solution to the DSAE problem on the square and triangular lattices is given.

A new class of algorithms for the processing of parametric curves

Abstract: A new class of algorithms for the processing of parametrically defined curves is presented. All the algorithms are based on the 'divide and conquer' (subdivision) paradigm. An important feature which marks out this class of algorithms from earlier subdivision-based algorithms is that the curve is characterized algebraically and not geometrically. Curve shape properties needed for the processing tasks are derived from the algebraic form of the curve. As long as the necessary properties can be derived, any mathematical from of the curve may be used. In particular this paper considers polynominal curves represented in the rational quadratic, cubic or rational cubic form. Shape properties such as linearity and Euclidean bounds are derived and algorithms for drawing and curve-curve intersection are described.

Deformations of principal bundles on the projective line

Abstract: The study of bundles on IP 1 apparently has a long history (see [22, Chap. I, Sect. 2.4]). Grothendieck proved that any principal bundle on IP~ with a complex reductive Lie groups as structure group admits a reduction of structure group to a maximal torus, unique up to Weyl group action [9]. Harder gave a simple proof of this result which works for IP 1 over arbitrary fields 1-11]. In this paper we study the deformations of principal bundles over IPL Let G be a split reductive group over the field k. By the result of Grothendieck-Harder and Zariski locally trivial G-bundle on IP ~ is associated to the G,,-bundle k Z 0 ~ I P 1 by a 1-PS 2: G,,--,G. Let us denote this G-bundle by E~. Let E-,S • 1 be a G-bundle with an isomorphism Eso=E[s o x lP~---E~. We then call E a deformation of Ex parametrized by S,s o. We say that the Gbundle E' tends or degenerates to the G-bundle E, and write E' ,~E, if there is a deformation E ~ S x l P 1 of E such that in every neighbourhood of the base point socS, (E~o-~E), there is an s such that E ,~ E ' . We prove (Theorem 7.4) that if 2,/~ are dominant 1-PS then E , , ~ E z if and only if # < 2 , i.e. 2 p is a positive integral combination of simple coroots (or, equivalently (2-/~, ~oi)e2g + for every fundamental weight co i. See Sect. 2.5). Note that the set of dominant # such that # < 2 is the same as the set of dominant weights occuring in the indecomposable (or irreducible, if char k=0) representation of the dual group G ~ (see Sect. 2.6) with highest weight 2 (cf. [16, Sect. 21.3]). The deformation theory of G-bundles on IP ~ seems to be much the same as the representation theory of the dual group G ~ (cf. [9, p. 123]). It would be interesting to find a more intrinsic connection between them. The G-bundles E and E" are said to be algebraically equivalent if there is a G-bundle E ~ S x lP 1, with S connected, such that E ~ E s and E ' ~ E s, for some s, s 'eS. We prove (Theorem 7.7) that the algebraic equivalence classes of Zariski locally trivial G-bundles are classified by the fundamental group of G (i.e. the quotient of the lattice of 1-PS of G by the lattice of coroots). This result

On the congruence subgroup problem: determination of the "Metaplectic Kernel"

Abstract: Let F be a global field (i.e. either a number field or a function field in one variable over a finite field) and let oo be the set of its archimedean places. Let G be a finite non-empty set of places of F containing oo. Let o = o ( ~ ) denote the ring of G-integers of F. Let A(~) denote the ring of G-adeles i.e. the restricted direct product of the completions F v for r eG. Let f# be an absolutely simple*, simply connected subgroup of SL, defined over F. Recall that a subgroup F of C#(F) is an G-arithmetic subgroup if FnSL(n, o) has finite index in F as well as in ~(o):=fY(F)c~SL(n,o). An G-arithmetic subgroup F is a ~congruence subgroup if there exists a non-zero ideal a in o (= o(G)) such that

Modeling thermal effects on MOS I-V characteristics

Abstract: The temperature distribution in a MOS transistor caused by power dissipation within the device has been calculated by solving the heat diffusion equation. Using this temperature distribution, IV characteristics of a MOS device as modified by thermal effects are calculated. The predicted behavior matches reported experimental observations; in particular, the negative dynamic resistance seen in the saturation region of devices operating at elevated power densities.

Genetics of yeast glucokinase

Abstract: Mutants of Saccharomyces cerevisiae lacking glucokinase (EC 2.7.1.2) have no discernible phenotypic difference from the wild-type strain; in a hexokinaseless background, however, they are unable to grow on any sugar except galactose. Reversion studies with glucokinase mutants indicate that the yeast S. cerevisiae has no other enzyme for phosphorylating glucose except the two hexokinases, P1 and P2, and glucokinase. Spontaneous revertants of hxk1 hxk2 glk1 strains collected on glucose regain any one of these three enzymes. The majority of glucokinase revertants synthesize species of enzyme activity that are kinetically or otherwise indistinguishable from the wild-type enzyme. In a few cases the reverted enzyme is very perceptibly altered in properties with a K m for glucose two orders of magnitude higher than that of the enzyme from the wild-type parent. These recessive, noncomplementing mutants, thus, define a single structural gene GLK1 of glucokinase. Yeast diploids lacking all of the three enzymes for glucose phosphorylation fail to sporulate. Heterozygosity of either of the hexokinase genes HXK1 or HXK2 , but not GLK1 , restores sporulation. The location of GLK1 on chromosome III was indicated by loss of this chromosome when hexokinaseless diploids heterozygous for glk1 were selected for resistance to 2-deoxyglucose; the homologue of chromosome III carrying GLK1 , the mating-type allele and other nutritional markers on this chromosome was lost. Meiotic mapping of glucokinase executed with heterozygosity of one of the hexokinases indicated that the gene GLK1 defining the structure of glucokinase protein is located on the left arm of chromosome III 24 cM to the left of his4 in the order: leu2—his4—glk1 .—Only two of 206 independent glucokinase mutants are nonsense ochre, both of which map at one end of the gene. In hxk1 only one of 130 isolates is a nonsense mutation, whereas in hxk2 none has been found among 220 independent mutants. These results raise the possibility that the protein products of these genes have some other essential function.—An earlier mapping result for hxk2 has been corrected. The new location is on the left arm of chromosome VII , 17 cM distal to ade5 in the order: lys5—ade5—hxk2 .

Molecular properties of Drosophila acetylcholinesterase.

Abstract: Two distinct classes of acetylcholinesterase (AChE) from the fruit fly Drosophila melanogaster are reported: a soluble species that shows heterogeneity of forms and a particulate species. The subunit composition of the particulate enzyme was studied using the active site label [3H]diisopropylfluorophosphate. Comparison of the electrophoretic patterns on nondenaturing gels using the activity stain and the active site label shows that the label is specific to AChE. The smallest active site-containing subunit of the enzyme is a monomer of approximately 60,000 daltons MW. Two such units are linked by disulphide bonds to produce a dimer of about 110,000 daltons. Another monomeric form of MW approximately 64,000 daltons, although present, does not participate in the dimerisation. The particulate enzyme when solubilised exists as a 9-10S species as determined by sucrose gradient centrifugation. This species has a MW greater than 200,000, as shown by its behaviour on a coarse-bead Sephadex-G200 column. Electrophoretic analysis suggests a MW of nearly 250,000 daltons for this form. Thus, this species is likely to be a tetramer. One possibility is that this tetramer is made up of two units of 64,000 daltons each and a dimer of 110,000 daltons. Preliminary data on mutant enzymes that support such a possibility are also presented.

Magnetic properties of the La1−xYxMn2Si2 system

Abstract: The structural and magnetic properties of the system La1−xYxMn2Si2 (0 ⩽ x ⩽ 1) were investigated Both LaMn2Si2 and YMn2Si2 crystallize in the ThCr2Si2-type tetragonal structure and form a complete solid solution without any change in the crystal structure Magnetization studies suggest that ferromagnetic ordering occurs for x < 02 and antiferromagnetic ordering sets in for x ⪢ 02 Complex magnetic behaviour is indicated for x = 02 The nature of the magnetic ordering in these compounds depends on the Mn-Mn distance

Soft modes and grain size effects in ferroelectric ceramics

Abstract: It is pointed out that the grain size effects on the transition parameters in ferroelectric ceramics can be explained on the basis of size effects on the ferroelectric properties of the constituent grains.

Hyperfine Field Investigations in Some Ru and Rh Based Heusler Alloys

Abstract: The hyperfine fields at 57Fe and at 119Sn doped as a dilute impurity replacing Ge, in the new Heusler alloys Ru2FeGe and Rh2FeGe, are reported. The Mossbauer spectra at 119Sn indicate preferential RGe (R = Ru, Rh) disorder like in other Ru and Rh based Heusler alloys. The hyperfine field value is consistent with recent predictions based on the Blandin and Campbell model. Es werden die Hyperfeinfelder von 57Fe und 119Sn als verdunnte Substitutions-Storstellen fur Ge in den neuen Heuslerlegierungen Ru2FeGe und Rh2FeGe mitgeteilt. Die Mosbauerspektren am 119Sn weisen auf eine bevorzugte RGe-(R = Ru, Rh)Fehlordnung wie in den anderen Heuslerlegierungen auf der Basis von Ru und Rh hin. Der Wert des Hyperfeinfeldes stimmt mit kurzlichen Vorhersagen auf Grund des Blandin- und Campbell-Modells uberein.

Cosmologies with variable gravitational constant

Abstract: In 1937 Dirac presented an argument, based on the socalled large dimensionless numbers, which led him to the conclusion that the Newtonian gravitational constantG changes with epoch. Towards the end of the last century Ernst Mach had given plausible arguments to link the property of inertia of matter to the large scale structure of the universe. Mach's principle also leads to cosmological models with a variable gravitational constant. Three cosmologies which predict a variableG are discussed in this paper both from theoretical and observational points of view.