Enhanced expression of the bgl operon of Escherichia coli in the stationary phase

The bgl operon is silent and uninducible in wild-type strains of Escherichia coli and requires mutational activation for optimal expression. We show that transcription from the wild-type and the activated bgl promoter exhibits a growth phase-dependent enhancement that is highest in the stationary phase. We have assessed the effect of mutations in rpoS, crl, hns, leuO and bglJ, known to regulate bgl expression, on the growth phase-dependent increase in bgl activity. These studies show that this increase is greater in the absence of wild-type rpoS and/or crl. Our studies also indicate that while BglJ has a moderate effect on the expression of the bgl operon in the stationary phase in the absence of rpoS/crl, the modest increase in LeuO concentration in the stationary phase is insufficient to affect transcription from the bgl promoter. Measurements of the fitness of strains carrying the wild type or a null allele of crl showed that, while the strain deleted for crl exhibited a growth advantage over the crl+ strain in an rpoS+ background, it showed a low-level disadvantage in the presence of an rpoS allele that results in attenuated RpoS expression. Possible physiological implications of these results are discussed

Electrical conductivity studies in K<SUB>2</SUB>SO<SUB>4</SUB>-ZnSO<SUB>4</SUB> glasses

The d.c. conductivities of K2SO4-ZnS04 glasses have been measured over a wide range of temperature. It has been found that two different subglassy activation energies are present which may be associated with K+ and Zn++ ions. Also a conductivity maximum occurs as a function of composition. These features have been discussed in the light of the random close packed model of sulphate glasses

Parametrizations of Inclusive Cross Sections for Pion Production in Proton-Proton Collisions

Accurate knowledge of cross sections for pion production in proton-proton collisions finds wide application in particle physics, astrophysics, cosmic ray physics and space radiation problems, especially in situations where an incident proton is transported through some medium, and one requires knowledge of the output particle spectrum given the input spectrum. In such cases accurate parametrizations of the cross sections are desired. In this paper we review much of the experimental data and compare to a wide variety of different cross section parametrizations. In so doing, we provide parametrizations of neutral and charged pion cross sections which provide a very accurate description of the experimental data. Lorentz invariant differential cross sections, spectral distributions and total cross section parametrizations are presented.Comment: 32 pages with 15 figures. Published in Physical Review D62, 094030. File includes 6 tex files. The main file is paper.tex which has include statements refering to the rest. figures are in graphs.di

Mean atomic volume and Tg of Cu-Ge-As-Se glasses

Results of measurements of the mean atomic volume (V), the glass transition temperature (Tg) and the activation energy for glass transition (Et) are reported for 11 glass compositions of the Cu-Ge-As-Se system. The compositions studied can be represented as Cux(Ge0.125As0.25Se0.625)100-x glasses. In the V-x, Tg-x and the Et-x data of these glasses, changes in slope are observed at an x value of approximately 2. The results are consistent with a picture wherein, up to approximately 2 atomic percent (at.%), Cu atoms occupy interlayer positions between the uncorrelated layers of the parent glass matrix without affecting either the medium or the short range ordering of the parent glass. The results also suggest that up to approximately 2 at.%, Cu atoms act as `plasticizers' in the parent glass matrix, reducing its Tg

Density and Tg of glasses of the As-Al-Te system

Results of measurements of the density and the glass transition temperature (Tg) on 25 glass compositions of the As-Al-Te system are reported and discussed. A linear increase of density and a decrease of Tg are seen with increasing As content across the AsAlTe4-As2Te3 tie-line compositions. In the density-composition and mean atomic volume-composition dependences for the AsxAl5Te95-x? AsxAl8Te92-x and AsxAl12Te88-x glasses, a change in slope is seen at the respective tie-line compositions, indicating chemical ordering in these glasses. When he dependence of density on the average coordination number Z are considered, the effects of chemical ordering are obscured; instead, the effects of topological nature emerge, with changes in slope at the topological thresholds of Z ? 2.40 and Z ? 2.67. The results further indicate that the dependence of mean atomic volume v on Z is controlled by the Te content in these glasses. Due to this, the generally observed features in the dependence of v on Z for chalcogenide glasses, namely a minimum in v to Z ? 2.40, a peak in v for Z ? 2.67 and a decrease of v for Z amp;gt; 2.67, are suppressed

Charged defects-controlled conductivity in Ge-In-Se glasses

The variation of the d.c. electrical conductivity, ?, with composition and temperature was investigated for glasses of the Ge-In-Se system. The results indicate a decrease in the activation energy for electrical conductivity, ?E, and an increase in ? on introduction of indium into Ge-Se glasses. The changes in ?E and ? with composition (selenium content in the glasses) are identical for the Gex In5 Se95-x and Gex In8Se92-x families. The results have been traced to the conduction controlled by charged defects in these chalcogenide glasses. The changes in ?E and ? have been explained by a shift in the Fermi level, being brought by the introduction of indium

Ga as an additive in the As2Te3 glass

Results of measurements of the mean atomic volume (V), the glass transition temperature13; (Tg), the activation energy for glass transition (Et) and the d. c. electrical conductivity (x3C3;) are13; reported and discussed for ten glass compositions of the Gax2013;Asx2013;Te system. The glasses13; studied can be represented as Gax(As0.4Te0.6)100x2212;x glasses, with the additive Ga ranging13; from 0 to 12 atomic percent (at.%) in the parent As2Te3 glass. In the Gax(As0.4Te0.6)100x2212;x13; glasses, changes in slope are observed in the V, Tg, Et, x3C3; and other electronic properties, at13; the composition with a Ga content of 2 at.%. The results are compared with those obtained13; on introduction of Ag and Cu to the As2Te3 and the [0.5As2Te3x2013;0.5As2Se3] glasses. Analysis13; of the data suggest formation of GaAs, Ga2Te3 and excess Te structural units (s.u.) in lieu of13; some of the original As2Te3 s.u., for addition of Ga up to 2 at.% to the parent As2Te3 glass;13; for higher Ga contents, formation of GaAs, GaTe and excess Te s.u. are indicated

Pressure induced anomalies in an as-Al-Te glass

The pressure and temperature dependences of the electrical resistance of A34.4AlTe61.6 and As16.mA116.67Te66 66 glasses have been investigated using an opposed anvil setup. The resistance of the glasses exhibit N lo6 fold decrease with increasing pressure up to 7 GPa at 300 K. This hehaviour can be traced to the corresponding changes with pressure of the activation energy for electrical conduction, AE(p).The As34.4A14Te61.6 glass exhibits pressure induced anomalies at 2 GPa in the pressure variation of AE(p) and the pressure coefficient of electrical resistance. Such an anomaly is not seen for the As16.67A116.67Te66.66 glass. The anomalies point to a pressure induced morphological structural transformation in the AS. AIT.glass

Non-isothermal crystallization of As, Se3 glass

The results of non-isothermal crystallization studies performed at different heating rates on batches of As2Se3 glasses prepared iron melts at 4oo'C. 6oo'C and 800'C13; are reported. The peak temperature of crystallization T, the enthalpy of crystallization AH,and the activation energy for crystallization E. are independent of the melt temperature used in the preparation. Bulk nucleation with three-dimensional growth of crystals is indicated for As2Se3. The values of AH6 and E6 are found to be respectively 23.3=09cal/g and 36.5=09 keal/mol for As2Se3

Thermal expansion studies on As-Sb-Se glasses

The results of measurement of thermal expansion coefficient from 50 C to the softening temperature on eight glass composition of the As-Sb-Se system are presented.Measurements have been made on (As, Sb)40Sc60 and As-Sb15 S8 glasses at heating rates of 1quot;C/min and 5quot;C/min. The composition and temperature dependence of the thermal expansion coefficient is discussed in the light of results of other chalcogenide glasses