High Rayleigh number convection in a one-dimensional model.

A model for one-dimensional convection is proposed by adding a buoyancy term to the Burgers' equation and including an equation for the temperature perturbation. A linear stability analysis shows onset of instability at a critical Rayleigh number. Computation in the unstable region shows steady convection with only one convection cell. Computations up to 10^{5} times the critical Rayleigh number do not show transition to an oscillatory state or to turbulence. Using a large Rayleigh number approximation, closed form solutions for the spectrum and the scaling for the heat transport due to nonlinear convection are obtained up to two orders. These are shown to be in good agreement with numerical results at high Rayleigh number.

Stability of cylindrical Couette flow in the presence of an oscillating axial magnetic field.

The linear stability of cylindrical Couette flow of an electrically conducting fluid in the presence of an axial magnetic field is examined, where the magnetic field has a small oscillatory component imposed on a steady value. The effect of the field modulation on the threshold of instability is studied for different values of gap width, Chandrasekhar number, magnetic Prandtl number, and oscillation frequency. Modulation is found to have a stabilizing effect for low values of the Chandrasekhar number, a destabilizing effect for intermediate values, and again a stabilizing effect for still higher values of the Chandrasekhar number. The effect of modulation is found to be almost independent of the magnetic Prandtl number and the modulation frequency.

Temperature tunability of size in CdS nanoparticles and size dependent photocatalytic degradation of nitroaromatics.

Size tunability of thiophenol capped CdS nanoparticles (NPs) has been achieved by controlling the temperatures in situ. Synthesis at 5 degrees C produced stable particles of smallest size having narrow size distribution and high photoluminescence quantum yield. The photoluminescence of thiophenol capped CdS NPs was quenched by the nitroaromatic compounds. The Stern-Volmer constant of dinitrobenzene was about 15-fold higher than nitrobenzene, which indicates that introduction of nitro groups in the benzene ring increases the quenching efficiency. Further, the as-prepared CdS NPs were found to display size dependent photocatalytic activity towards degradation of nitroaromatics. The catalytic efficiency of CdS quantum particles was quintupled with decrease in particle size from 5.8 to 3.8 nm. An empirical equation has been derived to correlate the catalytic efficiency of the nanoparticles with the twin factors operating in the quantum confinement regime: (i) change in surface to volume ratio and (ii) shift in conduction band edge.

Scaling in magnetohydrodynamic convection at high Rayleigh number.

The theory of Grossmann and Lohse [J. Fluid Mech. 407, 27 (2000)] is extended to include the effect of a magnetic field on convection of an electrically conducting fluid. Different scaling laws are obtained depending on whether the bulk or the boundary layers make the major contribution to the dissipation. Scalings are obtained for both weak and strong magnetic fields. The predictions are shown to be in better agreement with experimental data than earlier theoretical models.

Formation of density waves in traffic flow through intersecting roads.

The formation of density waves in two intersecting roads, with a traffic circle at the intersection, is studied. It is found that, depending on the traffic densities in the two roads, density waves can form in the traffic circle and in one or both of the roads. Depending on the expression chosen for the optimal velocity, either the congestion moves entirely to the traffic circle or the congestion becomes confined to the traffic circle and a part of the road approaching the traffic circle.

Stress-induced reversal of microRNA repression and mRNA P-body localization in human cells.

In metazoa, microRNAs (miRNAs) imperfectly base-pair with the 3'-untranslated region (3'UTR) of mRNAs and prevent protein accumulation by either repressing translation or inducing mRNA degradation. Examples of specific mRNAs undergoing miRNA-mediated repression are numerous, but whether the repression is a reversible process remains largely unknown. Here, we show that cationic amino acid transporter 1 (CAT-1) mRNA and reporters bearing the CAT-1 3'UTR or its fragments can be relieved from the miRNA miR-122-induced inhibition in human hepatoma cells in response to different stress conditions. The derepression of CAT-1 mRNA is accompanied by its release from cytoplasmic processing bodies (P bodies) and its recruitment to polysomes, indicating that P bodies act as storage sites for mRNAs inhibited by miRNAs. The derepression requires binding of HuR, an AU-rich-element-binding ELAV family protein, to the 3'UTR of CAT-1 mRNA. We propose that proteins interacting with the 3'UTR will generally act as modifiers altering the potential of miRNAs to repress gene expression.

Synthesis of CdS nanoparticles in colloidal state and its possible interaction with tyrosine.

The basic objective is to develop a simpler method of preparation of the colloidal CdS nanoparticles with greater stability and to study interaction with tyrosine molecules. Average size of the particles in the colloid is found to be about 3 nm as probed by transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. Effect of both sulfide enriched CdS as well as Cd(2+) enriched CdS on tyrosine is investigated both through absorbance and emission spectroscopy. Quenching of tyrosine emission followed Stern-Volmer relation and was found to be independent of temperature, indicating possible static quenching. However, Forster transfer between tyrosine and CdS can be suspected to mimic static quenching in addition to the charge transfer complexes. In the presence of Cd(2+) enriched CdS nanoparticles, the emission of tyrosine in phosphate buffer shows typical spectral broadening and a long wavelength increase in fluorescence emission. This may be attributed to the sensitized emission of CdS itself.

Different hypotensive responses to intravenous bovine and human thrombin preparations in swine.

BACKGROUND: Accidental intravenous introduction of commercial bovine thrombin (BT) during use of fibrin glue may result in profound hypotension. Commercial human thrombin (HT) is now available. This study compared the effects of intravenous BT versus HT in swine. METHODS: Swine received 30 U/kg BT, 60 U/kg BT, 30 U/kg HT, or 60 U/kg HT intravenously. Mean arterial pressure (MAP) and survival were monitored for 30 minutes. Thrombin purities and in vitro activities were examined. RESULTS: MAP nadir was lower (p < 0.05) after BT, 27.7 +/- 3.3% (mean +/- SEM) of pretreatment MAP, compared with 41.1 +/- 3.7% after HT. Five of six animals died after 60 U/kg BT, whereas all others survived (p < 0.05). Histology suggested more severe disseminated intravascular coagulation after BT. HT was purer than BT. In vitro activities were similar. CONCLUSION: Both BT and HT produced hypotension. HT appeared safer, because of higher purity. Regardless of source and purity, thrombin must be used with caution.

Extraction of metal ions using chemically modified silica gel: a PIXE analysis.

Organic ligand with carboxyhydrazide functional group was immobilised on the surface of silica gel and the metal binding capacity of the ligand-embedded silica was investigated. The functional group was covalently bonded to the silica matrix through a spacer of methylene groups by sequential reactions of silica gel with dibromobutane, malonic ester and hydrazine in different media. Surface area value of the modified silica was determined. The changes in surface area were correlated with the structural change of the silica surface due to chemical modifications. A mixture solution of metal ions [K(I),Cr(III),Co(II),Ni(II),Cu(II),Zn(II),Hg(II) and U(VI)] was treated with the ligand-embedded silica in 10(-3) M aqueous solution. The measurement of metal extraction capacity of the silica based ligand was done by multielemental analysis of the metal complexes thus formed by using Proton Induced X-ray Emission (PIXE) technique.

Mutations in a tRNA import signal define distinct receptors at the two membranes of Leishmania mitochondria.

Nucleus-encoded tRNAs are selectively imported into the mitochondrion of Leishmania, a kinetoplastid protozoan. An oligoribonucleotide constituting the D stem-loop import signal of tRNA(Tyr)(GUA) was efficiently transported into the mitochondrial matrix in organello as well as in vivo. Transfer through the inner membrane could be uncoupled from that through the outer membrane and was resistant to antibody against the outer membrane receptor TAB. A number of mutations in the import signal had differential effects on outer and inner membrane transfer. Some mutants which efficiently traversed the outer membrane were unable to enter the matrix. Conversely, restoration of the loop-closing GC pair in reverse resulted in reversion of transfer through the inner, but not the outer, membrane, and binding of the RNA to the inner membrane was restored. These experiments indicate the presence at the two membranes of receptors with distinct specificities which mediate stepwise transfer into the mitochondrial matrix. The combination of oligonucleotide mutagenesis and biochemical fractionation may provide a general tool for the identification of tRNA transport factors.

Stepwise transfer of tRNA through the double membrane of Leishmania mitochondria.

Import of tRNA into Leishmania mitochondria involves transfer through a double membrane barrier. To examine whether specific sorting mechanisms for individual tRNAs direct them to different mitochondrial compartments, the distribution of tRNA transcripts, internalized in vitro, was examined by suborganellar fractionation. Significant amounts of tRNA(Tyr) were localized in the matrix and on the outer face of the inner mitochondrial membrane. With time, the matrix:membrane ratio increased. Translocation through the inner membrane apparently required the presence of a specific signal in the D arm of tRNA(Tyr), and tRNA(Gln)(CUG), lacking this sequence, was excluded. Hydrolysis of ATP was necessary at both the outer and inner membranes. However, the protonophores carbonylcyanide m-chlorophenylhydrazone and nigericin, the K(+) ionophore valinomycin, and the F(1)F(0) ATPase inhibitor oligomycin had only marginal effects on uptake through the outer membrane but severely inhibited inner membrane translocation, indicating the unusual requirement of both the electrical and chemical components of the electromotive force generated across the inner membrane. The results are consistent with a mechanism involving stepwise transfer of tRNA through distinct outer and inner membrane channels.

Smoke-induced inhalation injury: effects of retinoic acid and antisense oligodeoxynucleotide on stability and differentiated state of the mucociliary epithelium.

Rabbit tracheal explants, exposed to burning pine wood smoke, were cultured in a chemically defined medium with and without retinoic acid (+/- RA). Exposures of 15-20 minute led to RA-independent degeneration of the mucociliary epithelial sheath. In 10 minute exposures tissue integrity was retained, but epithelial morphology changed from normal pseudostratified columnar to the flattened appearance typical of the squamous phenotype. Despite the dramatic shift in morphology, explants exhibited normal RA-dependent mucin gene expression characteristic of the mucociliary phenotype. Furthermore, electron micrographs showed continued presence of both secretory granules and cilia. RA(+) cultures also showed a normal pattern of adherent epithelial cells. In RA(-) cultures, however, there were prominent intercellular spaces indicating an RA dependence for maintaining adhesive contacts following smoke exposure. An 18-mer mucin antisense oligomer that suppressed mucin gene expression also unexpectedly blocked the smoke induced metaplasia in RA(+) cultures, but the sense oligomer had no effect.

Differentiation of respiratory epithelium: the effects of retinoic acid and carcinogens on the expression of mucociliary vs. squamous phenotype.

Changes in ultrastructural characteristics and mucin gene expression were examined in rat tracheal explants cultured in a synthetic medium +/- retinoic acid (RA), benzo[a]pyrene (B[a]P) and N-methyl-N-nitrosourea (NMNU). In the RA(+) cultures, no changes in either ultrastructural features or mucin gene expression were detected after 48 h incubation. After 96 h incubation, however, the ultrastructural features associated with the squamous phenotype were characteristics of cultures containing the two carcinogens and the mucin gene expression was slightly reduced. Thus, in the presence of retinoic acid, the carcinogen induced changes in cytology to the squamous phenotypes were not matched by a marked loss of mucin gene expression. Explants cultured for 48 h without RA and +/- carcinogens showed none of the cytological changes associated with onset of the squamous phenotype. While mucin mRNA was still detected, it was clearly reduced compared to 48 h cultures in RA(+) medium. However, 48 h later, all explants exhibited pronounced squamous metaplasia and the mucin message decreased to trace levels. Thus, the results of these experiments with B[a]P and NMNU in RA(+) and RA(-) media indicates that at least the early carcinogen induced changes may be distinct from those associated with the retinoid pathway controlling expression of the mucin component of the mucociliary epithelium.

Reactions of OH and eaq- adducts of cytosine and its nucleosides or nucleotides with Cu(II) ions in dilute aqueous solutions: a steady-state and pulse radiolysis study.

The reactions of OH and eaq- adducts of cytosine, cytidine and deoxycytidine in the presence of Cu(II) ions have been studied by product analysis and pulse radiolysis. The product analysis studies show that the degradation of the base is enhanced in N2O-saturated conditions in the presence of Cu(II) ions and the major radiolytic products are Cu(I), cytosine glycols and 5(6)-hydroxycytosine. It is also interesting to note that the yields of Cu(I) are equivalent to cytosine degradation yields, which suggests that the interaction of the OH adducts with Cu(II) ions restricts the radical recombination reactions (known to be the major physicochemical repair process) which partly regenerate the parent cytosine. The rate constants of the reactions of cytosine OH adducts with Cu(II) ions determined by pulse radiolysis lie between 10(7) and 10(8) dm3 mol-1 s-1. The growth in the transient absorption spectra of cytosine OH adducts in the range 330-400 nm, observed in the presence of copper(II) ions in free and complexed state, suggests formation of copper radical adduct which decays by water insertion at the copper-carbon bond to give glycol as the major product. Such copper radical adduct formation was also observed in the case of cytidine and deoxycytidine. The protonated electron adducts (at the hetero atoms) of cytosine, cytidine and deoxycytidine transfer electrons to the Cu(II) ions with rate constants of 10(8) and 10(9) dm3 mol-1 s-1. Here no adduct formation is observed. The steady-state results show that such electron transfer reactions regenerate the parent molecules themselves. Hence such electron transfer reactions do not contribute to enhanced base degradation in the presence of copper ions.

Radiosensitization of thymine by copper(II) and nickel(II) complexes of metronidazole.

Aqueous solutions of thymine (10(-3) mol dm(-3)) were irradiated with Co 60 gamma-rays in the absence and presence of metronidazole as well as its Cu(II) and Ni(II) complexes (10(-4) mol dm(-3)) under different conditions. The yields for the loss of thymine and those for the formation of the products of radiolysis were determined by hplc. The degradation of thymine when compared with that in the absence of metronidazole was not significantly altered. However, it increased significantly when the radiolysis of thymine was carried out in the presence of the Cu(II) and Ni(II) complexes of metronidazole. All three compounds were found to promote the formation of thymine glycol although the increase was more significant for the metal complexes than for free metronidazole. The higher radiosensitizing efficiency observed with the metal complexes as compared with that for free metronidazole is due to their higher rate of oxidation of the transient thymine-OH radical adduct. The reduction of the sensitizers results in the formation of the nitro-anion radical which in the case of the Cu(II) complex undergoes intramolecular electron transfer to the metal centre leading to the formation of Cu(I).

Retinoic acid-regulated cellular differentiation and mucin gene expression in isolated rabbit tracheal-epithelial cells in culture.

Rabbit tracheal epithelial cells were cultured in a serum-free and hormone-supplemented medium with and without retinoic acid. The cells showed time-dependent mucin gene expression when cultured in the medium with retinoic acid. In the absence of retinoic acid, however, mucin mRNA was barely detectable in the cells. When retinoic acid was added back to the medium, the mucin message was prominent again. Actinomycin D and cycloheximide did not inhibit mucin gene expression. The mucin message was slightly elevated by cAMP agonists. A mucin antisense oligomer inhibited the retinoic acid-induced mucin mRNA expression and secretion, thus offering an alternate approach in the management of mucus hypersecretion in upper airway respiratory diseases such as chronic bronchitis, asthma, and cystic fibrosis.

Redox reactions of hydrogen adducts of thymine: Comparisons with the reactions of hydroxyl adducts.

Hydrogen atoms form two kinds of adducts with thymine (oxidizing and reducing). Redox reactions of these two kinds, popularly known as 5-hydrogenated-6-thyminyl (reducing) and 6-hydrogenated-5-thyminyl (oxidizing), were investigated where ferric ions (oxidizing) and ferrous ions (reducing) were used as the corresponding redox partners. A steady-state gamma radiolytic system was chosen where hydroxyl radicals were scavenged using t-butyl alcohol in acidic (pH 1.8) solution. It is inferred that the redox potential of oxidizing hydrogenated thyminyl radicals lies between 0.77 and 1.4 V vs. NHE. The reducing hydrogenated thyminyl radical has a redox value less than 0.8 V because it efficiently undergoes electron transfer reaction with Fe(III). A probable range of redox values for hydroxyl adduct of thymine is included for comparison.

Retinoic acid modulation of mucin mRNA in rat tracheal explants: response to actinomycin D, cycloheximide, signal transduction effectors and antisense oligodeoxynucleotide.

Factors affecting the retinoic acid modulated expression of mucin mRNA in rat tracheal cultures were studied. Actinomycin D had no effect on mucin mRNA in cultures grown with retinoic acid (RA+). The usual precipitous drop in mucin mRNA in cultures lacking retinoic acid (RA-) was prevented by actinomycin D. Cycloheximide also had no effect on mucin mRNA in RA+ cultures, but, like actinomycin D, it prevented the precipitous drop in mucin mRNA in RA- cultures. cAMP agonists had some marginal effects on the mucin mRNA, but none as dramatic as those noted by actinomycin D and cycloheximide in the RA- cultures. An antisense oligomer (18 bases) to rat mucin cDNA inhibited the mucin mRNA expression in RA+ cultures.

Effect of retinoic acid on mucin gene expression in rat airways in vitro.

Ultrastructural examination of rat tracheal explants at various times of culture in a serum-free and hormone-supplemented medium containing retinoic acid showed that the cytological characteristics of the epithelium were well preserved for at least 192 h. Hybridization analyses for mucin core protein mRNA in the explants were performed with a 30-base oligonucleotide probe, the design of which was based on the tandem repeat sequence of the rat intestine mucin core protein. The probe reacted with total RNA prepared from trachea, intestine and colon, but not with total RNA obtained from liver or alveolar region of the lung. Type-I keratin expression was observed in the explant grown at different periods of time in a medium with and without retinoic acid. The hybridization probe gave a prominent reaction with RNA preparations obtained from tracheal explants incubated for as long as 192 h in a medium containing retinoic acid. In the absence of retinoic acid, however, the mucin message was evident at the 24 h time point but thereafter decreased to barely detectable levels. When retinoic acid was added at 96 h to the latter cultures, the mucin mRNA was prominent again after additional incubation for 24 and 48 h. Northern-blot analyses of tracheal RNA showed a diffuse band at approx. 7.5 kb. Addition of a variety of chemical and pharmacological agents to explants cultured in the presence of retinoic acid had no dramatic induction or inhibitory effects on the mucin mRNA. Only the steroid prednisolone had a reproducible inhibitory effect.

Tyrosine residues in unirradiated and gamma-irradiated dihydroorotate dehydrogenase: fluorimetric and second-derivative absorption spectrophotometric studies.

The effect of gamma-radiation on tyrosine residues of dihydroorotate dehydrogenase under different conditions was investigated by means of fluorescence spectroscopy and second-derivative spectrophotometry. No change in the fluorescence spectral distribution was observed when unirradiated and irradiated enzyme were denatured in guanidine hydrochloride. However, decreases in fluorescence intensity in irradiated samples indicates a radiation-induced modification of tyrosine residues. The fluorescence intensity at 340 nm decreased exponentially with radiation dose in aerated medium but non-exponentially under argon and nitrous oxide-saturated conditions. The percentage loss of tyrosine fluorescence under different conditions was determined. The number of tyrosine residues left intact following irradiation at a dose for 50% inactivation under different conditions was measured by second-derivative absorption spectrophotometry. The results obtained from both these methods show that the hydroxyl radical is less efficient in inducing radiation damage of tyrosine in aerated conditions compared with that under deoxygenated conditions. This lower efficiency of the hydroxyl radical in aerated medium has been attributed to the protective effect of oxygen and/or the superoxide radical anion.