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S Saha

Publications and source records attributed to S Saha.

At least 19 recordsLinked to original sources
PubMed1992

Structure of sp-9-hydroxy-9-pivaloylfluorene, product of base-catalyzed autoxidation of ap-9-pivaloylfluorene.

1-(9-Hydroxyfluoren-9-yl)-2,2-dimethyl-1-propanone, C18H18O2, M(r) = 266.34, orthorhombic, Pbcn, a = 18.917 (10), b = 11.843 (8), c = 13.177 (7) A, V = 2952 (5) A3, Z = 8, Dx = 1.198 g cm-3, lambda(Mo K alpha) = 0.71069 A, mu = 0.72 cm-1, F(000) = 1136, T = 296 K, R = 0.044 for 1042 unique observed reflections. Conversion of ap-9-pivaloylfluorene, ap-(I), into lithiated (I)-9-anion followed by the addition of MeOH, then H2O, led to unexpected hydroxylation to provide 20-40% of sp-9-hydroxy-9-pivaloyfluorene, sp-(II), and 60-80% recovery of ap-(I). The singular sp conformation of (II) in solution suggested by NMR was confirmed in the crystalline state by X-ray diffraction which showed the O(1)-C(9)-C(10)-O(2) torsion angle approximately 0 degrees and the C(10) = O(2)...H(9)-O(1) non-bonding distance 1.95 (4) A, suggesting strong intramolecular hydrogen bonding in this conformation.

Chemical Phenomena↗
PubMed1992

Comparison of the effects of dietary fish oils with different n-3 polyunsaturated fatty acid compositions on plasma and liver lipids in rats.

The effects of dietary fish oils with different n-3 polyunsaturated fatty acid compositions on plasma lipid profiles in rats have been studied. Forty-eight male rats, previously maintained on a cholesterol-free diet for 15 days, were fed for 60 days with diets supplemented with 10% fat of either marine hilsa fish (Hilsa ilisa, family clupeidae) or fresh-water chital fish (Notopterus chitala, family notopteridae). The diets had similar levels of total saturated (35-41%), monounsaturated (43-47%) and n-3 polyunsaturated (9-10%) fatty acids. Cholesterol contents of the diets were adjusted to 0.85%; gamma-linolenic acid (3.3%) in chital oil and eicosapentaenoic acid (4.9%) in hilsa oil diets were the major n-3 contributors. The percentage of eicosapentaenoic acid in the chital oil diet was 0.57 times that of the hilsa oil diet, but the eicosapentaenoic (EPA) to arachidonic acid (AA) ratio in the latter (4.08) was 3.2 times that of the former (1.27). Sixty days of hilsa oil diet feeding decreased the levels of cholesterol (53.3 +/- 2.9 to 50.0 +/- 1.1 mg/dL), triacylglycerol (75.7 +/- 3.8 to 64.3 +/- 2.6 mg/dL) and phospholipid (55.8 +/- 1.5 to 51.7 +/- 3.1 mg/dL) in rat plasma. Similar treatment with chital oil diet elevated the plasma cholesterol level (53.3 +/- 2.9 to 62.3 +/- 7.6 mg/dL) while triacylglycerol and phospholipid contents remained unaltered. Both the dietary treatments decreased the levels of linoleic and arachidonic acids in liver but only under the hilsa oil diet did the eicosapentaenoic acid percentage increase markedly (0.8 +/- 0.06% to 5.5 +/- 0.06%) at the expense of arachidonic acid.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Electric and dielectric properties of wet human cortical bone as a function of frequency.

In this paper, the electrical and dielectric properties of wet human cortical bone from a distal tibia were examined as a function of frequency and direction. The resistance and capacitance of the cortical bone specimens were measured at near 100% relative humidity. The measurements were made in all three orthogonal directions at discrete frequencies ranging from 120 Hz to 10 MHz using an LCR meter. At a frequency of 100 kHz, the mean resistivity and specific capacitance for the ten cortical bone specimens were 1.55 k omega-cm and 33.81 pF/cm in the axial direction, 15.79 k omega-cm and 9.98 pF/cm in the circumferential direction, and 21.5 k omega-cm and 9.83 pF/cm in the radial direction. All electrical and dielectric properties except the resistivity and the specific impedance were highly frequency dependent for the frequency range tested. However, the resistivity and specific impedance were relatively less frequency dependent. All electrical and dielectric properties were also transversely isotropic in nature, the values for the axial direction being different from the values obtained for the two transverse directions.

Adult↗
PubMed1992

The biomechanical evaluation of intramedullary nails in distal femoral shaft fractures.

The biomechanical parameters (torsional rigidity and compressive strength) for three different intramedullary femoral nails, Küntscher (K), Brooker-Wills (BW), and Küntscher Interlocking (KI) were compared in this study. Fractures were created in the femoral shaft distal to the isthmus with sections removed so that pure torsional rigidity and resistance to compression could be measured. The standard K nail provided no torsional rigidity and only minimal resistance to longitudinal compression. The KI was significantly more rigid under compression than either the BW or the K. In torsional resistance the K nail was significantly weaker than either the BW or KI. The K nail does not provide significant resistance to compression or torsion for use in oblique or comminuted fractures. The BW nail probably provides enough resistance to rotation for use in distal fractures, but probably does not provide enough resistance to compression for use in fractures that are prone to shortening.

Biomechanical Phenomena↗
PubMed1991

Carbachol has opposite effects to glucose in raising the sodium content of pancreatic islets.

Integrating flame photometry was used for measuring sodium in single pancreatic islets from ob/ob mice. Exposure to 100 microM carbachol resulted in a 25-40% increase in sodium without any effect on potassium during incubation with 0-5 mM glucose in media deficient or not in Ca2+. This action of carbachol was abolished by 10 microM atropine or by raising the glucose concentration to 20 mM. A minor increase of the steady state content of sodium occurred in the presence of 200 microM ATP or 10 nM tetradecanoylphorbol 13-acetate (TPA). Carbachol differed from TPA in markedly stimulating sodium accumulation after ouabain inhibition of the Na/K pump. The results indicate that muscarinic receptor activation has opposite effects to glucose in inducing a rise of the islet content of sodium. It is suggested that the cholinergic control of the endocrine pancreas involves entry of Na+ in addition to the Na+ entry mediated by protein kinase C activation of Na+/H+ countertransport.

Adenosine Triphosphate↗
PubMed1991

Quantitative analysis and postsynaptic targets of GABA-immunoreactive boutons within the rat trigeminal motor nucleus.

We have used the post-embedding immunogold labelling method using antibodies to gamma-aminobutyric acid (GABA) to obtain quantitative data on the distribution, frequency, postsynaptic targets and ultrastructural characteristics of GABA-immunoreactive (GABA-IR) boutons in the trigeminal motor nucleus of rats. We have also combined this method with horseradish peroxidase tracing to obtain specific evidence for termination of some GABA-IR boutons onto identified jaw-elevator motoneurones. Twenty-eight percent of all synapses in the motor nucleus involved GABA-IR boutons. Seventy-three percent of the GABA-IR boutons formed axo-dendritic synapses, 13% axo-somatic synapses and 14% axo-axonic synapses. Ninety-three percent of GABA-IR boutons formed symmetrical synapses. Overall, 58% of all boutons contained only flattened vesicles, while 26% contained round vesicles and 16% a mixture of vesicle types. Measurements of bouton cross sectional area, apposition length, and active zone length were obtained from serial reconstructions of 15 GABA-IR boutons and 30 unlabelled boutons. In each case mean values for GABA-IR boutons were significantly smaller than those for nonlabelled boutons.

Animals↗
PubMed1991

Light and electron microscopical localisation of 5-HT-immunoreactive boutons in the rat trigeminal motor nucleus.

We have used pre-embedding EM immunohistochemical methods to obtain quantitative data on the frequency and post-synaptic targets of 5-hydroxytryptamine-immunoreactive (5-HT-IR) boutons within the rat V motor nucleus. Thirteen percent (69/531) of all synaptic contacts in the motor nucleus involved 5-HT-IR boutons. Seventy-four percent of 5-HT-IR boutons made axo-dendritic contacts, 20% axo-somatic contacts, and 6% axo-axonic contacts. We conclude that a significant fraction of boutons in the motor nucleus are 5-HT-IR and most contribute to postsynaptic rather than presynaptic effects on trigeminal motoneurones.

Animals↗
PubMed1991

Post-transcriptional regulation of tubulin mRNA in developing rat brain.

The transcriptional activity of tubulin genes during synaptogenesis in developing rat brain has been examined by 'nuclear run off assay'. For both alpha and beta tubulin genes, the relative rates of transcription were found to be high during the early phase of synaptogenesis (postnatal days 1-5) and declined 20-50% by the end of synaptogenesis (postnatal days 15-20). Comparison of the developmental alterations in the rates of transcription of both alpha and beta tubulin mRNA with the level of polysomal tubulin mRNA shows that the age related decline (70-80%) in the level of polysomal tubulin mRNA during synaptogenesis is much too large compared to the 20-25% decline in their transcription rates suggesting that tubulin mRNA levels in developing rat brain are regulated post-transcriptionally.

Aging↗
PubMed1991

Recovery of injured Campylobacter jejuni cells after animal passage.

Sixteen freeze-thaw-injured nonculturable stocks of Campylobacter jejuni were passed through rat gut, and seven were reisolated. These reisolated strains were converted to toxin producers, as they were before preservation, following consecutive passages through rat gut. This observation indicated the existence of an injured, viable, but nonresuscitated form of C. jejuni which can be resuscitated to a culturable and fully virulent form by passaging the organism through a susceptible host.

Animals↗
PubMed1991

Effect of dietary fish oil on platelet aggregability: comparison between two oils with different eicosapentaenoic to arachidonic acid ratio.

Rats, acclimatized on a control diet, were fed for 60 days with diets, supplemented with 10% fat of either marine Hilsa fish (Hilsa ilisa) or fresh-water Chital fish (Notopterus chitala). The percentage of eicosapentaenoic acid in chital oil diet was 0.57 times that of the hilsa oil diet, but the eicosapentaenoic to arachidonic acid ratio in the latter (4.08) was 3.2 times that of the former (1.27). Otherwise these two diets were comparable in respect to total saturated, monounsaturated and n-3 polyunsaturated fatty acid contents. Results showed that of the two only hilsa oil diet could significantly lower platelet aggregability and in vitro thromboxane production, through replacement of arachidonic acid in platelet phospholipid by eicosapentaenoic acid. The antithrombic criteria of the oil seems to be a combination of low arachidonic acid content and high eicosapentaenoic to arachidonic acid ratio.

Animals↗
PubMed1979

Cement line motion in bone.

Compact bovine bone subjected to constant torsional load for long periods of time exhibits large anelastic effects. Displacements occur at the cement lines and are responsible for part or all of the long-term deformation. The absence of an asymptotic creep strain is consistent with an interpretation of the cement line as a viscous interface.

Animals↗
PubMed1979

Bending properties of wire-reinforced bone cement for applications in spinal fixation.

PMMA beam specimens were tested in four-point bending to determine if the bending strength of acrylic bone cement, as used in posterior spinal fusion, could be improved by metal-wire reinforcement. The result showed that the load-carrying capacities of 1- and 0.5-mm diam stainless-steel-wire-reinforced PMMA specimens in bending were significantly higher than similar unreinforced normal PMMA samples. On an average, steel reinforcement comprising approximately 1% of the cross-sectional area of the PMMA specimens caused a 15% increase in bending strength. Even after the cement fractured, the reinforcing wires still sustained an appreciable amount of bending moment, thus preventing catastrophic failure of cement alone.

Bone Cements↗
PubMed1977

Relations between tensile impact properties and microstructure of compact bone.

Standardized human and beef femoral compact bone specimens were tested in tensile impact and the dynamic mechanical properties were determined. The microstructure of 45 beef and 47 human bone specimens were examined histologically to determine if there is a structural basis to account for strength differences in the bone samples. Strong negative correlations were obtained between the maximum stress and the percentage area of secondary osteons in each specimen. For human bone samples, the energy absorption capacity and the modulus of elasticity were also found to have strong negative correlations with the percentage area of secondary osteons present in each specimen. Linear regression equations were obtained describing the impact strength properties in terms of the percentage areas of secondary osteons and cavities in the samples. Fracture surfaces of the tested bone specimens were examined in a scanning electron microscope. Most surfaces exhibited a fairly rough texture indicating a quasi-cleavage type of failure. Fractographic analysis of bone fracture surface was helpful in understanding the micromechanics of bone fracture.

Animals↗