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N Menon

Publications and source records attributed to N Menon.

At least 19 recordsLinked to original sources
PubMed2000

Velocity fluctuations in a homogeneous 2D granular gas in steady state

We have measured the spectrum of velocity fluctuations in a granular system confined to a vertical plane and driven into a homogeneous, steady state by strong vertical vibration. The distribution of horizontal velocities is not Maxwell-Boltzmann and is given by P(v) = Cexp[-beta(|v|/sigma)(alpha)] where alpha = 1.55+/-0.1 at all frequencies and amplitudes investigated, and also for varying boundary conditions. The deviation from Maxwell-Boltzmann statistics occurs in the absence of spatial clustering and does not result from an inhomogeneous average over regions of varying local density. Surprisingly, P(v) has the same shape over a wide range of densities.

Journal Article↗
PubMed2000

Two-body B meson decays to eta and eta('): observation of B --> eta K*.

In a sample of 19 x 10(6) produced B mesons, we have observed the decays B-->eta K(*) and improved our previous measurements of B-->eta'K. The branching fractions we measure for these decay modes are B(B+-->eta K(*+)) = (26.4(+9.6)(-8.2)+/-3.3)x10(-6), B(B(0)-->eta K(*0)) = (13.8(+5.5)(-4.6)+/-1.6)x10(-6), B(B(+)-->eta'K(+) = (80(+10)(-9)+/-7)x10(-6), and B(B(0)-->eta'K0) = (89(+18)(-16)+/-9)x10(-6). We have searched with comparable sensitivity for related decays and report upper limits for these branching fractions.

Journal Article↗
PubMed2000

Measurement of charge asymmetries in charmless hadronic B meson decays.

We search for CP-violating charge asymmetries (alpha(CP)) in the B meson decays to K(+/-)pi(-/+), K(+/-)pi(0), K(0)(S)pi(+/-), K(+/-)eta('), and omega pi(+/-). Using 9.66 million upsilon(4S) decays collected with the CLEO detector, the statistical precision on alpha(CP) is in the range of +/-0.12 to +/-0.25 depending on decay mode. While CP-violating asymmetries of up to +/-0.5 are possible within the standard model, the measured asymmetries are consistent with zero in all five decay modes studied.

Journal Article↗
PubMed2000

Hysteresis and packing in gas-fluidized beds

The packing fraction and the pressure drop across gas-fluidized beds of granular media exhibit hysteresis as the gas-flow rate is cycled up and down across the fluidization transition. Presumably this is due to contact forces and transfer of stress to the surrounding walls, and hence should vary nontrivially with the aspect ratio of the sample. Here we present systematic measurements of the variation of hysteresis with particle size and aspect ratio of the sample. Remarkably, the hysteresis scales in a trivial way with these parameters, showing no evidence of long-range effects of the wall. Our measurements also show that the packing fraction becomes 0. 590+/-0.004, independent of particle size and container shape, when the fluidizing flow of gas flow is slowly removed.

Journal Article↗
PubMed1998

The acute effects of prostacyclin on pulmonary hemodynamics in patients with pulmonary hypertension secondary to systemic sclerosis.

OBJECTIVE: To determine whether patients with isolated pulmonary hypertension secondary to systemic sclerosis (SSc) have a pulmonary vasculature that is responsive to treatment with vasodilators. METHODS: Seven SSc patients with pulmonary hypertension underwent right heart catheterization. Pulmonary pressures and cardiac output were measured before and during a systemic intravenous infusion of prostacyclin. RESULTS: Both pulmonary arterial mean pressure and pulmonary vascular resistance decreased significantly with prostacyclin infusion (median decrease 11% and 32%, respectively), with a concomitant increase in cardiac output (median increase 26%). No adverse hemodynamic effects were noted during the infusion. CONCLUSION: Vasospasm contributes to the pulmonary hypertension complicating SSc. This feature may be amenable to treatment with vasodilators.

Adult↗
PubMed1997

Diffusing-Wave Spectroscopy of Dynamics in a Three-Dimensional Granular Flow

Diffusing-wave spectroscopy was used to measure the microscopic dynamics of grains in the interior of a three-dimensional flow of sand. The correlation functions show that minutely separated grains fly from collision to collision with large random velocities. On a time scale 10(3) to 10(4) times longer than the average time between collisions, the grains displayed slow, collective rearrangements, which, at the long-time limit, produced diffusive dynamics.

Journal Article↗
PubMed1992

Structure-function relationships among the nickel-containing hydrogenases.

The enzymology of the heterodimeric (NiFe) and (NiFeSe) hydrogenases, the monomeric nickel-containing hydrogenases plus the multimeric F420-(NiFe) and NAD(+)-(NiFe) hydrogenases are summarized and discussed in terms of subunit localization of the redox-active nickel and non-heme iron clusters. It is proposed that nickel is ligated solely by amino acid residues of the large subunit and that the non-heme iron clusters are ligated by other cysteine-rich polypeptides encoded in the hydrogenase operons which are not necessarily homologous in either structure or function. Comparison of the hydrogenase operons or putative operons and their hydrogenase genes indicate that the arrangement, number and types of genes in these operons are not conserved among the various types of hydrogenases except for the gene encoding the large subunit. Thus, the presence of the gene for the large subunit is the sole feature common to all known nickel-containing hydrogenases and unites these hydrogenases into a large but diverse gene family. Although the different genes for the large subunits may possess only nominal general derived amino acid homology, all large subunit genes sequenced to date have the sequence R-X-C-X-X-C fully conserved in the amino terminal region of the polypeptide chain and the sequence of D-P-C-X-X-C fully conserved in the carboxyl terminal region. It is proposed that these conserved motifs of amino acids provide the ligands required for the binding of the redox-active nickel. The existing EXAFS (Extended X-ray Absorption Fine Structure) information is summarized and discussed in terms of the numbers and types of ligands to the nickel and the various redox species of nickel defined by EPR spectroscopy. New information concerning the ligands to nickel is presented based on site-directed mutagenesis of the gene encoding the large subunit of the (NiFe) hydrogenase-1 of Escherichia coli. Based on considerations of the biochemical, molecular and biophysical information, ligand environments of the nickel in different redox states of the (NiFe) hydrogenase are proposed.

Amino Acid Sequence↗
PubMed1990

Posterior mediastinal teratoma with abdominal extension.

Posterior mediastinal benign teratomas are uncommon neoplasms in infancy; nine cases have been reported so far. A one month old baby was found to have a benign posterior mediastinal teratoma infiltrating the lower oesophagus from the level of the carina through the oesophageal hiatus into the upper abdomen. Partial oesophagectomy provided a successful outcome.

Abdominal Neoplasms↗
PubMed1990

Pressure-induced contractions in bovine pulmonary artery preparations.

Experiments were conducted in a superfusion bioassay system in which the effluent of a bovine main pulmonary artery (generator) was allowed to superfuse a spirally cut precontracted bovine arterial strip (detector), which had been deprived of endothelium. Effluents of endothelium-intact generator relaxed the precontracted detector by an average of 22 +/- 4.1%. Following removal of endothelium of the generator, the relaxing effect of the effluent was only 1%. A rapid increase of transmural pressure in the generator to about 40 mm Hg for 3 min induced contraction of the detector (8.4 +/- 2%) above the histamine-induced tension. In the absence of endothelium, smaller contractions were obtained from the pressurized generator (4.9 +/- 1.8%). This effect was reversible after pressure release. Effluents of endothelium-deprived generator showed no significant vasoactivity. NG-Mono-methyl-L-arginine (L-NMMA, 3.3 x 10(-5) mol/l), a specific inhibitor of nitric oxide (NO), also depressed endothelium-dependent relaxation and caused a 10.5% increase in contraction of the endothelial effluent. When the endothelium-intact generator was exposed to both pressure and L-NMMA, an additive effect was noted. Based on these observations, it was concluded that transient increase of transmural pressure in bovine main pulmonary arteries depresses the endothelium-dependent relaxation and unmasks a small but significant contractile activity of the endothelial effluent.

Animals↗
PubMed1987

Identification of three classes of hydrogenase in the genus, Desulfovibrio.

A comparison of amino-terminal amino acid sequences from the large and small subunits of hydrogenases from Desulfovibrio reveals significant differences. These results, in conjunction with antibody analyses, clearly indicate that the iron, iron + nickel, and iron + nickel + selenium containing hydrogenases represent three distinct classes of hydrogenase in Desulfovibrio.

Amino Acid Sequence↗