bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical Diffusion in Nickel Oxide
Authors: NOWOTNY J. , SADOWSKI A.
Published: October 2006

The chemical diffusion coefficient was measured for undoped, single‐crystalline NiO at 900° to 1200°C and within an oxygen partial pressure of 10−5 to 0.21 atm. Electrical conductivity was used to monitor the reequilibration kinetics after the oxygen pressure was suddenly changed over the initially equilibrated NiO crystal. The chemical diffusion coefficient was calculated vs the reequilibration degree indicating the most stable range of investigations. The chemical diffusion coefficient value is virtually the same for the oxidation and reduction experiments, giving, respectively: Dchem.=(1.64 × 10−2) exp[‐(22,480±800)/RT] Dchem.=(9.68 × exp[‐(21,430±2600)/RT] It has been stated that chem is independent of the oxygen pressure and thus of oxide composition. The electrical conductivity depends on the oxygen partial pressure in the power (l/n) = (1/5.45), indicating that doubly ionized cation vacancies are the predominant defects. Deviation from the linear dependence of log α vs logpo2 was observed at <10−5 atm, indicating formation of anion vacancies of interstitials.
Retardation of Tricalcium Aluminate Hydration by Calcium Sulfate
Authors: COLLEPARDI MARIO , BALDINI GIORGIO , PAURI MARCO , CORRADI MARIO
Published: October 2006

The influence of calcium sulfate on the hydration of 3CaO· Al2O3 in the presence of Ca(OH)2 was studied using conduction calorimetry, differential thermogravimetry, and X‐ray diffraction. Sodium sulfate was also used instead of calcium sulfate. A substantial retardation of tricalcium aluminate hydration in the presence of sulfate occurs only when calcium sulfate is used and enough ettringite is formed. When ettringite disappears due to the consumption of gypsum, tricalcium aluminate hydration is renewed. Sodium sulfate does not significantly retard this hydration. The results confirm the hypothesis that ettringite formation is essential for coating 3CaO·Al2O3 grains and then retarding their hydration.
Phase Relations in the System Na2O‐TiO2‐SiO2
Authors: GLASSER F. P. , MARR J.
Published: October 2006

Liǵuid us and subsolidus phase relations were studied using the quenching technique. The system contains four ternary compounds stable to liquidus temperatures: Na2TiSi4O11, Na2TiSi2O7, Na2TiSiO5, and Na2Ti2Si2O9. Six eutectics, eight peritecties, and eight thermal maxima were located and a region of liquid immiscibility was delineated. X‐ray powder data are given for the stable and metastable crystalline phases. Glass‐transition temperatures were determined by thermal analysis. The relation between physical properties of melts and glasses and the configuration of the liquidus is discussed.
Recent Progress in Understanding Die Compaction of Powders
Authors: STRIJBOS S. , van GROENOU A. BROESE , VERMEER P. A.
Published: October 2006

Experiments on the mechanical behavior of powders are briefly described. A triaxial cell is used for σ1= 160 MPa and σ2=σ3= 40 MPa for the bulk behavior and a wall‐test apparatus gives information on the influence of wall parameters, such as hardness and roughness. Based on these data, finit‐element calculations were made of the stresses in a die‐pressed sample; there was fair agreement with the wall stresses obtained in earlier experimental work on iron oxide powder. The important result is that powder densification occurs before failure.
The Trident Seal—A Rapid and Accurate Expansion Differential Test
Authors: HAGY H. E.
Published: October 2006

A simple glass‐to‐glass seal is used to measure expansion differential by residual stress measurement using optical bench techniques. Since only uniaxial stresses are produced, Poisson strain corrections are not required, thus overcoming a shortcoming in conventional seals. Sensitivity and reproducibility are greater than with direct dilatometry. Glass‐to‐ceramic and glass‐to‐metal differentials can also be measured.
Strength Degradation of Glass Impacted with Sharp Particles: I, Annealed Surfaces
Authors: WIEDERHORN S. M. , LAWN B. R.
Published: October 2006

The strength characteristics of annealed brittle surfaces impacted with sharp particles were studied. A theory of the degradation process is constructed in three steps: (1) A sharp particle delivers an impulsive load to the target surface via a plastic contact; (2) the contact loading initiates and propagates median cracks in the surface; (3) the cracks thus induced reduce the strength of the material. Static indentation tests provide essential contact parameters for the degradation equations, thereby allowing for prediction of strengths under in‐service conditions. Strength tests on soda‐lime glass laths impacted with SIC grit confirm basic predictions of the theory. Higher toughness and lower hardness are the main material requirements for improved resistance to degradation. Initial flaw population in the target surface and projectile geometry are not important factors in the damage process. The study shows that impact energy is the important service variable in determining the extent of strength loss.
Some Effects of Cavities on the Fracture of Ceramics: I, Cylindrical Cavities
Authors: EVANS A. G. , BISWAS D. R. , FULRATH R. M.
Published: October 2006

The problem of fracture from cylindrical cavities in brittle materials was analyzed. The analysis is based on the conditions required to extend cracks that preexist at the cavity surface and involves the combined use of fracture mechanics and statistics solutions for crack extension in the concentrated stress field around the cavity. The pertinence of the approach is substantiated by experimental studies of fracture from cavities in polycrystalline alumina.
Electrical Resistivity of Magnetite and Nickel Ferrous Ferrite Above 300°K
Authors: BOTROUS EL BADRAMANY N. M. , MINA E. F. , MERCHANT H. D. , ARAFA S. , POPLAWSKY R. P.
Published: October 2006

The electrical resistivity of Fe2+0.95Fe3+2.05O2+4, Ni2+0.51Fe2+0.46Fe1.95,3+O2−4, and Ni0.89,2+Fe2+0.13Fe3+2.11O2−4 single crystals was determined at >300°K. The dc resistivity up to 800°K shows a monotonic decrease with increased temperature, with an average activation energy of 0.065 eV independent of temperature and Fez+ concentration. The ac resistivity, at frequencies of 540 kHz to 34 MHz up to 450°K, shows temperature and frequency dependences of the relative dielectric constant similar to that found when true dielectric relaxation occurs, with the activation energy depending slightly on frequency and ferrous ion content.
Chemical Composition of C‐S‐H Gel Formed in the Hydration of Calcium Silicate Pastes
Authors: BENTUR ARNON , BERGER R. L.
Published: October 2006

The chemical and physical compositions of C‐S‐H formed in paste hydration of C3S cured at 4°, 25°, and 65°C and of C2S and a C3S/C2S blend cured at 25°C were studied using quantitative X‐ray diffraction analysis (QXDA), extraction, and thermal effluent gas analysis (TEGA) to determine the free CH content. The amount of CH determined by extraction is greater than or equal to that determined by QXDA. The difference between the two results increased with the H2O surface area of the paste, indicating the existence of adsorbed CH in the form of Ca2+ and (OH)− ions which cannot be measured by QXDA and suggesting that the extraction method is better for estimating the composition of C‐S‐H.
Formation of Silicon‐Aluminum Spinel
Authors: CHAKRABORTY AKSHOY KUMAR
Published: October 2006

Characterization of the intermediate cubic phase formed during the transformation of coprecipitated SiO2‐Al2O3 gel on heating was studied and X‐ray diffraction methods are reviewed and criticized. Coprecipitated gels of different SiO2/Al2O3 ratios were prepared; all showed a 980°C exotherm followed by crystallization of the cubic phase and liberation of SiO2. Alkali extraction of SiO2 showed two types present in the 980°‐heated product. One variety is free amorphous SiO2 and the other, chemically bonded to alumina in the crystalline cubic phase, was isolated and characterized as Si‐Al spinel with the same composition as mullite. Thus, its formation from the gel of mullite composition shows the highest exotherm and the measured density agrees approximately with the theoretically calculated value.
Fracture and Crack Healing in (U,Pu)C
Authors: SINGH R. N. , ROUTBORT J. L.
Published: October 2006

The fracture stress of several types of (U,Pu)C1+x pellets was measured from 25° to 1200°C at a fixed strain rate. The fracture stress increases with temperature and the fracture is predominantly transgranular up to ≊500°C. At >500°C, the fracture stress decreases as the temperature increases and the fracture becomes increasingly intergranular. The flow stress, σ0.002, decreased rapidly between 1000° and 1600°C. An investigation of the stress dependence and kinetics of crack healing at 1300° to 1600°C indicates that strength may recover by a volume‐diffusion‐controlled mechanism.
Models for Kinetics of Solid State Sintering
Authors: WONG BOON , PASK JOSEPH A.
Published: October 2006

Kinetic equations for the isothermal densification of a single‐phase powder compact are formulated for the initial and intermediate stages of sintering; they are identified as continuous open‐pore stages, with a decreasing number of voids and grains per unit volume accompanied by grain growth in the intermediate stage. Each stage can be represented by an equation based on mass transport along the forming grain boundary to the “neck” region as the rate‐controlling step or by one on movement from the neck to the free surface regions as the rate‐controlling step.
The Reduction of Silica with Carbon and Silicon Carbide
Authors: MILLER PATRICK D. , LEE J. G. , CUTLER IVAN B.
Published: October 2006

In the presence of carbon or silicon carbide, silica can be reacted to form a vapor of silicon monoxide. The rates of these reactions were explored at 1300° to 1550°C. For mixtures of carbon and silica, evidence supported a two‐step reaction: silicon carbide formed prior to reaction between silicon carbide and silica.
Rate and Mechanism of Hydration of β‐Dicalcium Silicate
Authors: FUJII KINJIRO , KONDO WAKICHI
Published: October 2006

The hydration of β‐dicalcium silicate was followed at a fixed w/c ratio of 0.45 and at 10° to 40°C by analyzing the liquid phase in the paste, by determining free lime and combined water, and by electron microscopy. The reaction proceeded from the induction period through a propagative surface nucleation‐growth of the CSH stage and an Overall penetration reaction Sw; the kinetics of these stages are discussed.
Phase Diagram of a Nickel‐Zinc Ferrite of Composition Ni0.685Zn0.177Fe2.138O4+γ
Authors: BRACCONI PIERRE , GALLAGHER P. K.
Published: October 2006

The oxygen content of Ni0.685Zn0.177Fe2.138O4+γ was determined gravimetrically at atmospheric pressure in varying Po2, 3.5 × 10−4 to 1.0 atm at 600° to 1450°C. The phase boundary associated with the precipitation of α‐Fe2O3 was determined from the change in slope of γ vs T plots observed on heating. Metastability is particularly evident for curves observed on cooling. Isacompositional lines (0.002 < γ < 0.045) are shown on a plot of log PO2 vs 1/T. An enthalpy of ‐21.6 kcal/mol is calculated for the oxidation of Fe2+.
Mixed‐Mode Fracture in Soda‐Lime Glass
Authors: FREIMAN S. W. , GONZALEZ A. C. , MECHOLSKY J. J.
Published: October 2006

Soda‐lime‐silica glass was fractured under combined mode I and mode II loading from flaws produced by hardness indentations. Critical stress intensities calculated from K1and K11combined using four analyses, are compared to KICmeasured by a fracture mechanics technique and to values of KICdetermined by measuring fracture‐mirror size. The comparison showed that KICcalculated using a noncoplanar strain‐energy release‐rate analysis gave the best agreement with values obtained by fracture mechanics techniques over the widest range of crack orientations. KICcalculated from mirror sizes was constant regardless of the orientation of the original flaw.
The Effect of Microstructure and Microcracking on the Thermal Conductivity of UO2‐U4O9
Authors: BUYKX W. J.
Published: October 2006

Several microstructures were produced in dense polycrystalline UO2‐U4O9 specimens by cooling UO2+x, solid solutions at different rates. Void formation (intragranular pores, grain‐boundary microcracks) was observed in specimens which had a nonuniform distribution of the U4O9 precipitate; such formation was probably caused by the relief of stresses generated by differential thermal contraction. The microstructures were assessed quantitatively and used to calculate thermal conductivities from theoretical models. The effect of microcracking was calculated. Thermal conductivities were also determined from thermal diffusivity values measured by the laser‐flash method. The thermal conductivity was primarily influenced by the amount of U4O9, present and the occurrence of voids, whereas the effect of U4O9, distribution was minor. Good agreement was obtained between theoretical predictions of thermal conductivity based on microstructure and experimental values.
Mobility of Sodium Ions in Silica Glass of Different OH Content
Authors: SCHAEFFER; H. A. , MECHA J. , STEINMANN J.
Published: October 2006

Using 22Na as a radiotracer, mobilities of sodium ions in various types of SiO2 glasses were measured and found to depend on the OH content in the silica network. Increasing OH content in SiO2 considerably reduces the Na mobility. The effect of immobilization of Na is discussed in terms of an interaction between hydrogen and sodium ions, similar to the “mixed‐alkali effect” in alkali silicate glasses. High OH‐containing SiO2, structures display the lowest diffusivities of either sodium or hydrogen ions, thus indicating properties which are preferential in practice, such as decreasing ionic instabilities in metal‐oxide‐semiconductor devices.
Transformation Enthalpies of the TiO2 Polymorphs
Authors: MITSUHASHI T. , KLEPPA O. J.
Published: October 2006

The enthalpies of transformation of pure, well‐characterized samples of brookite and anatase to rutile were determined by solution calorimetry in a 3Na2O·4MoO3 melt at 971 ±2 K. The experiments gave the following results: brookite→rutile, ΔH°971= ‐0.17±0.09 kcal mol−1; anatase → rutile, ΔH°971= ‐0.78±0.20 kcal mol−1.
Structural Properties of Calcium Silicate Pastes: II, Effect of Curing Temperature
Authors: BENTUR ARNON , BERGER R. L. , KUNG J. H. , MILESTONE N. B. , YOUNG J. F.
Published: October 2006

The chemical and physical properties of C3S pastes cured at 4°, 25°, and 65°C were investigated. The 65°C paste had lower H2O surface area and larger capillary pore volume than the 25°C paste. The structure of the gel in the 4°C paste changes markedly with increased hydration. These changes were reflected in an increase in H2O surface area, decrease in C/S ratio, and decrease in the diameter of the mesopores. The degree of silicate polymerization increased with time and temperature of curing. In addition, the 4°C paste had a significant amount of monomer in the gel, which polymerizes with time.
Viscosity and Microstructure of Phase‐Separated Borosilicate Glasses
Authors: TAKAMORI TAKESHI , TOMOZAWA MINORU
Published: October 2006

The viscosity of a sodium borosilicate glass (SiO2 70, B2O3 23, and Na2O 7 wt%) was measured as a function of heat‐treatment temperature and time for phase separation. The viscosity was shown to approach an equilibrium value unique to the heat‐treatment temperature. The magnitude of the equilibrium viscosity increased as the heat‐treatment temperature decreased. These results, plus electron microscopy of microstructure development, established that the viscosity of phase‐separated borosilicate glasses is primarily controlled by the composition of the continuous, high‐viscosity phase and that the effect, if any, of the microstructure size is small. In contrast to previous reports, the heat‐treatment time required to attain the equilibrium composition was extremely long.
Creep of MgO Containing a Dispersion of Carbon
Authors: SUGARMAN A. C. , BLACHERE J. R.
Published: October 2006

Creep experiments on polycrystalline MgO containing a fine dispersion of carbon are reported. The samples were prepared by hot‐pressing and creep was measured in four‐point bending under stresses of 1000 to 5000 psi at 1000° to 1300° C. Although results for MgO creep without carbon addition are in good agreement with published reports, introducing dispersions of 0.5 to 2 vol% C into MgO modifies its creep behavior. Comparing specimens of the same grain size, the samples containing the carbon dispersion had lower creep rates than those of MgO without addition. This effect increased with increasing carbon additions. The stress exponent remained small (1 to 2) in all cases. The apparent activation energy for creep increased dramatically with the carbon additions. Possible mechanisms for the influence of this dispersion on creep are discussed briefly.
Electronic Conductivity and Related Properties of Amorphous and Crystallized V2O5‐Based Glasses
Authors: LIMB YOUNG , DAVIS ROBERT F.
Published: October 2006

Crystallization of V2O3 from V2O3P2O3, glasses containing 0 to 9 mol% B2O3, during heat treatment in the range 220° to 410°C, caused progressive micro structural changes which dramatically affected the electronic conductivity (γ), the activation energy for conduction (W), and the resistance to chemical attack. All compositions were ≊83% crystalline after heating to 410°C. As a result, the values of γ and W were almost identical to those observed for pure polycrystalline V2O5.
Ionic Conductivity of the System Si‐Al‐O‐N from 850° to 1400°C
Authors: UKYO Y. , GOTO K. S. , INOMATA Y.
Published: October 2006

Electrical conductivity was measured from 850° to 1400°C for β‐sialon and pure X phase as well as for the sintered system Si3N4‐Al2O3, containing β‐sialon, X phase, β‐Si3N4, and glassy phase. Ionic conductivity was measured at >1000°C. The charge carriers were identified by electrolysis. The results showed that pure β‐sialon is ionically conducting because of Si4+ migration for the temperature range studied. Pure X phase shows ionic conduction by Si4+ above 1000°; below 1000°C, it shows electronic conduction because of impurities. The conductivity of the sintered system Si3N4‐Al2O3 containing β‐sialon, β‐Si3N4 X phase, and glassy phase changes as the relative quantities of β ‐sialon and X phase change. The apparent activation energies for the ionic and electronic conductivities are 45 and 20 kcal/mol, respectively.
Optical and NMR Studies on Interdiffusion of Silver in SiO2‐B2O3‐AI2O3‐R2O Glasses
Authors: KOBAYASHI KEIJI
Published: October 2006

Interdiffusion of silver ions in SiO2‐B2O3‐AI2O3‐R2O glasses where R=Na or K was investigated, using optical transmission, ESR, and wet chemical methods to determine concentration and the chemical state of silver, and NMR spectra as a probe of the glass structure. The concentration of silver introduced by ion exchange increased monotonically, as the line widths of27AI NMR spectra decreased. The sharp and narrow features of 27Al line shapes were broadened and the amount of colloidal silver produced by ion exchange decreased, as R2O/B2O3 approached unity with fixed AI2O3. The BO4 to BO3 ratio approached unity and the quadrupole coupling constant of BO3 units varied from 2.70 to 2.96 MHZ, as R2O/AI2O3, approached unity for fixed B2O3. These diverse data suggest a relation between silver diffusion and glass structure, although the phenomena of phase separation and the mixed‐alkali effect could also influence silver‐colloid formation in the glasses studied.
Reactivities of Various Silicates with Calcium Hydroxide and Water
Authors: KONDO RENICHI , OHSAWA SHIGENARI
Published: October 2006

The reactivity of oxides and silicates with alkaline solutions is especially important in cement chemistry and is closely related to the pozzolanic reaction, the alkali‐aggregate reaction, and to glass fiber reinforcement of hardened cement. Thus, the rate of the hydration reaction between several silicates and Ca(OH)2 or portland cement at 20° and 80°C was studied. Results showed that essentially high reactivity in the reaction with Ca(OH)2 was found in Italian pozzolan, metakaolin, and silica gel in which the first two have very high Blaine surface areas. The pozzolanic reaction of typical oxides and silicates was considered from a thermodynamic point of view.
Preparation and Thermal Properties of Dense Polycrystalline Oxyhydroxyapatite
Authors: KIJIMA TSUYOSHI , TSUTSUMI MASAYUKI
Published: October 2006

Solution‐grown crystals of hydroxyapatite were sintered into polycrystalline oxyhydroxyapatite bodies, using the range 1050 to 1450°C. The heat capacity, thermal diffusivity, and thermal conductivity of the sintered bodies were measured by the laser flash method at 130–1000 K. The sintered bodies were 94.4 to 99.4% of theoretical density and 0.8 to 12 μm in grain size. Sintering is accompanied by grain growth and by vacancy formation and cell contraction due to thermal dehydration. Typical values of the heat capacity, thermal diffusivity, and thermal conductivity at room temperature are 0.73 J/g K, 0.0057 cm2/s and 0.013 J/s cm K, respectively. Low‐temperature thermal conductivity increased with increasing temperature, similarly to that of amorphous solids. This odd behavior is discussed in terms of phonon mean free path.
Conductivity Behavior of High‐Silica Glasses with Varied Concentrations of Sodium Ions
Authors: SIMMONS CATHERINE J. , SIMMONS JOSEPH H.
Published: October 2006

The low‐frequency conductivity of silica glasses containing 5% B2O3 and from 0.02 to 6.7% Na2O is extrapolated to dc values and analyzed in terms of temperature and concentration dependence. The concentration dependence of the conductivity occurs exclusively in the activation enthalpy. This prevents an analysis of the number of ions participating in the conduction in all but one sample for which tracer diffusion data gave a correlation factor of unity in the Nernst‐Einstein equation. The concentration dependence of the activation enthalpy was analyzed empirically. The activation enthalpy varies linearly with sodium‐sodium separation or jump distance. This result suggests that, at low Na concentrations, the conducting ions execute several separate motions between nonequilibrium sites before reaching the nearest equivalent site. The empirical equation is shown to fit activation energy data for silica glasses containing from 0.06 to 40% Na2O.
Biaxial and Uniaxial Data for Statistical Comparisons of a Ceramic's Strength
Authors: GIOVAN M. N. , SINES GEORGE
Published: October 2006

The uniaxial and equibiaxial tensile strengths of a brittle material were measured in bending. Equibiaxial tension was attained by concentric ring loading of disks and uniaxial tension by four‐point line loading of plates. The two specimen designs give equal volumes, surface areas, and stress gradients. Ground surfaces and lapped surfaces were tested. The equibiaxial tensile strength of a dense alumina was lower than the uniaxial tensile strengths for both ground and lapped surfaces, 8.5 and 8.1%, respectively. The Batdorf theory of flaw statistics, in which biaxial tensile strengths can be predicted from the statistical distribution of uniaxial tensile strength measurements, agreed with the data.
Epididymal obstruction results in isolated sperm heads in post‐vasectomy rats
Authors: Khaira Herkanwal S. , Schuster Timothy G. , Zhang Wen‐Xiang , Dunn Rodney , Smith Gary D. , Ohl Dana A.
Published: October 2006

The aim of this study was to determine if, following vasectomy, epididymal obstruction resulted in changes in vasal stump fluid using a rat vasectomy model. One hundred and twenty‐two mature male rats underwent bilateral surgical vasectomy and subsequent unilateral epididymal obstruction. Animals were randomly assigned to one of the five cohorts, which determined the time to kill and vasal fluid assessment. Numbers of whole sperm and sperm heads were compared between the obstructed and non‐obstructed sides. Parametric analysis of microscopic vasal fluid findings was performed using a paired t‐test. Whole sperm and sperm heads were detected bilaterally among the initial five cohorts. On the obstructed epididymis side, percentage of whole sperm dropped from 36.9% to less than 1% and sperm heads increased from 63.2 to 99.7% at 12 weeks post‐obstruction (p < 0.05 at each time interval). On the unobstructed side, percentage of whole sperm rose from 66.3 to 89.5% and sperm heads dropped from 33.7 to 10.5% (p < 0.05 at each time interval). At 12 weeks, the difference between the obstructed and non‐obstructed sides for both percentage and quantity of whole sperm and heads was significant with a p value of <0.001. In this rat model, following vasectomy and subsequent epididymal obstruction, testicular vasal stump fluid will contain progressively diminishing numbers of whole sperm and increases in the percentage and absolute numbers of sperm heads.
Peripheral INSL3 concentrations decline with age in a large population of Australian men
Authors: Anand‐Ivell Ravinder , Wohlgemuth Jessica , Haren Matthew T. , Hope Perdita J. , Hatzinikolas George , Wittert Gary , Ivell Richard
Published: October 2006

The novel peptide hormone insulin‐like peptide 3 (INSL3) is a major secretory product of the Leydig cells of the testis, and in adult men is secreted into the blood, giving rise to circulating concentrations ranging from 0.5 to 2.5 ng/mL. We studied a large randomly recruited cohort of 1183 men from South Australia, comparing serum INSL3 concentrations with age, and a variety of endocrine, cognitive and morphological parameters. While INSL3 concentration declines significantly (p < 0.001) and continuously with age from 1.29 ± 0.47 ng/mL in young men (age 35–44 years) to 0.79 ± 0.39 ng/mL in the age group 75–80 years, there is no correlation with testosterone or components of the hypothalamo‐pituitary‐gonadal (HPG) axis, independent of age, nor with any other parameter measured, including thyroid or prostate status and obesity. For men exhibiting normal follicle stimulating hormone (FSH) and high luteinizing hormone (LH) levels, there was a significant inverse correlation with plasma oestradiol. Unilaterally orchidectomized men had INSL3 values intermediate between intact men and anorchid subjects, and showed inverse correlations (p < 0.001) between INSL3 and FSH or LH concentrations, which were independent of age. Taken together, the data show that INSL3 is an independent measure of Leydig cell function (quality and number), which appears to be independent of acute control via the HPG axis. Its decline with age reflects a decline in the properties of the Leydig cell population only, and emphasizes a gonadal component in the age‐related decrease in androgen production.
Reframing birth: a consequence of cesarean section
Authors: Fenwick Jennifer , Gamble Jenny , Hauck Yvonne
Published: October 2006

Aim.  This paper is a report of a study to describe the childbirth expectations, influences and knowledge of a group of Western Australian women who experienced a cesarean section (CS) and would prefer a CS in a subsequent pregnancy.

Background.  Evidence suggests that a previous CS is not an indication for an elective CS in a subsequent pregnancy, but western world data indicate high probability of repeat CS.

Methods.  Community advertisements invited women who had experienced a CS to participate in a telephone interview. The thematic analysis presented in this paper is derived from data collected during 2003/2004 from 49 participants who had initially expected to birth vaginal but had a CS and who had planned a CS in a subsequent pregnancy or stated that they would choose this option in a future pregnancy.

Findings.  Before the first CS most women expected and wanted to give birth normally. After having a CS, however, many reframed vaginal birth as uncertain, unsafe and unachievable. For this group of women, the medical discourse that promoted CS as the safest option was a major influence on their decisions. As a result, they reconstructed CS as an acceptable alternative that was safer for them and their babies, allowed them to be better prepared, and was convenient.

Conclusion.  In the present climate, enabling women to keep birth ‘fear’ in perspective may be an important strategy if we are to improve the uptake of vaginal birth after CS and the quality of care offered to women during the normal, but major, life event of childbirth.
Ovarian Steroids But Not the Locus Coeruleus Regulate Stress‐Induced Prolactin Secretion in Female Rats
Authors: Poletini M. O. , Szawka R. E. , Franci C. R. , Anselmo‐Franci J. A.
Published: October 2006

Stress has been proposed to stimulate prolactin release if its prestress levels are low, or to inhibit it if they are elevated, but the role of ovarian‐steroid fluctuations in the prolactin stress response is not yet clearly understood. Because the noradrenergic nucleus locus coeruleus has been implicated in stress responses and generation of prolactin surges in female rats, the present study aimed to evaluate stress‐induced prolactin secretion under different hormonal conditions, determining the effect of locus coeruleus lesion on each response. Blood samples were withdrawn from a jugular vein catheter 5 and 2 min before and 2, 5, 10, 15 and 30 min after ether stress in male rats, female rats during the oestrous cycle and ovariectomised rats treated with oil (OVX), oestradiol (OVE) or oestradiol plus progesterone (OVEP). Increased Fos immunoreactivity demonstrated locus coeruleus activation following ether stress. Ether stress increased both low (at 16.00 h in males, in OVX and on dioestrous and at 11.00 h on pro‐oestrous and oestrous) and high plasma prolactin (at 16.00 h on oestrous and in OVE), but it decreased elevated prolactin levels during the afternoon on pro‐oestrous and in OVEP. Locus coeruleus lesion prevented prolactin surges during the afternoon on pro‐oestrous, oestrous, OVE and OVEP but did not modify either pattern (i.e. increase or decrease) or degree of prolactin stress response under any condition studied. The present data therefore suggest that oestradiol and progesterone modulate stress‐induced prolactin secretion, regardless of its prestress levels. Moreover, the locus coeruleus is probably not involved in prolactin response to stress and most likely has a specific role in prolactin surges induced by ovarian steroids.
Dimerization of plasmid DNA accelerates selection for antibiotic resistance
Authors: Mazin Alexander V. , Timchenko Tatiana V. , Saparbaev Murat K. , Mazina Olga M.
Published: October 2006

Dimerization of multicopy plasmids is widely assumed to be disadvantageous both for plasmid maintenance and for the host cell. It is known that dimerization causes plasmid instability; dimer‐containing cells grow slower than their monomer‐containing counterparts. However, as we demonstrate here, under conditions of selective stress, dimers provide an advantage for bacteria. Dimers facilitate segregation of mutants from numerous copies of the parental plasmid. Accelerated segregation greatly increases the rate of accumulation of plasmids carrying mutations that are adaptive for bacteria. In contrast, resolution of dimers by site‐specific recombination decreases, 103‐105‐fold, the efficiency of selection of spontaneous reversions in the tet gene of pBR327.
The hmu locus of Yersinia pestis is essential for utilization of free haemin and haem‐protein complexes as iron sources
Authors: Hornung Jan M. , Jones Heather A. , Perry Robert D.
Published: October 2006

Yersinia pestis strains utilize haem and several haem‐protein complexes as sole sources of iron. In this study, the haemin uptake locus (hmu) of Y. pestis KIM6+ was selected from a genomic library by trans‐duction into an Escherichia coli siderophore synthesis (entC) mutant. Recombinant plasmids containing a common 16 kb BamHI insert were isolated that allowed E. coli entC to use haemin as an iron source. An 8.6 kb region of this insert was found to be essential for haemin utilization and encoded at least five proteins with molecular masses of 79/77, 44, 37, 35, and 30/27.5 kDa. A 10.9 kb Clal fragment containing the hmu locus showed varying degrees of homology to genomic DNA from Yersinia pseudotuberculosis, Yersinia enter‐ocolitica, and other genera of Enterobacteriaceae. An E. coli hemA aroB strain harbouring cloned hmu genes used haemin as both an iron and porphyrin source but only on iron‐poor medium, suggesting that haemin uptake is tightly iron regulated. Additionally, haemoglobin and myoglobin were used as iron sources by an E. coli entC (pHMU2.2) strain. Deletion of the hmu locus from Y. pestis KIM6+ chromosome generated a mutant that grew poorly on iron‐depleted medium containing free haemin as well as mammalian haem‐protein complexes including haemoglobin, haemoglobin‐haptoglobin, myoglobin, haem‐haemopexin, and haem‐albumin unless it was complemented with cloned hmu genes.
Dependency of Escherichia coli cell‐division size, and independency of nucleoid segregation on the mode and level of ftsZ expression
Authors: Palacios Pilar , Vicente Miguel , Sánchez Manuel
Published: October 2006

Expression of ftsZ in strain VIP205 is dissociated from its natural promoters, and is under the control of an inducible tac promoter. This abolishes the oscillation in ftsZ transcription observed in the wild type, allowing different levels of ftsZ expression. We demonstrate that this construction does not affect the expression of other genes, and has no effects on replication or nucleoid segregation. A shift in IPTG from 30 μM, that supports division at wild‐type sizes, to lower (6 μM) or higher (100μM) concentrations, indicates that VIP205 cells can divide within a broad range of FtsZ concentrations. Analysis of the morphological parameters during the transition from one IPTG concentration to another suggests that the correct timing of ftsZ expression, and the correct FtsZ concentration, are required for division to occur at normal cell sizes. After a transient division delay during the transition to lower IPTG concentrations, cells in which ftsZ is expressed continuously (yielding 80% of the wild‐type FtsZ levels) divide with the same division time as the wild type, but at the expense of becoming 1.5 times larger. A precise control of ftsZ expression is required for normal division, but the existence of additional regulators to maintain the correct timing during the cell cycle cannot be ruled out.
Differential binding of BvgA to two classes of virulence genes of Bordetella pertussis directs promoter selectivity by RNA polymerase
Authors: Zu Tao , Manetti Riccardo , Rappuoli Rino , Scarlato Vincenzo
Published: October 2006

Transcription of virulence genes of Bordetella pertussis is co‐ordinately regulated by the BvgA and BvgS proteins, which are members of the two‐component family of bacterial signal‐transduction proteins. BvgS is the transmembrane sensor and BvgA the transcriptional regulator. By gel mobility shift assays we demonstrate that phosphorylated BvgA (BvgAP) forms distinct complexes with the filamentous haemag‐glutinin (PFHA) promoter DNA at different BvgAP: DNA ratios. DNase I protection analyses show that phosphorylation of BvgA not only enhances affinity of the protein for the binding sites of the PFH and bvgP1 promoters, but it extends significantly the bound region towards position ‐35 of these promoters. Conversely, a 10‐fold higher amount of BvgAP is required for binding to a large DNA region, from ‐168 to ‐60, of the pertussis toxin (Ptox) promoter sequence. These findings suggest that the molecular interaction of BvgA P with the Ptox promoter is different from its interaction with the PFHA and bvgP1 promoters. The ß70Escherichia coli RNA polymerase (RNP) does not bind to the bug‐regulated promoters. However, following the formation of a BvgAP‐promoter complex, the E. coli RNP specifically recognizes and binds to the bvg‐regulated promoters. Thus, BvgAP exerts its action at the level of promoter recognition by directing promoter selectivity by RNP.
ERA, a novel cis‐acting element required for autoregulation and ethanol repression of PDC1 transcription in Saccharomyces cerevisiae
Authors: Liesen Thomas , Hollenberg Cornelis P. , Heinisch Jürgen J.
Published: October 2006

Yeast pyruvate decarboxylase (Pdc) catalyses the reaction at the branch‐point of fermentation and respiration. In this work we have investigated the mechanisms of its transcriptional regulation in response to glucose and the non‐fermentable carbon source ethanol. For this purpose we studied the function of different promoter fragments of PDC1, encoding the major pyruvate decarboxylase enzyme in wild‐type cells, in the basal CYC1 promoter context. Thus, we identified a sequence mediating the response to ethanol and provide evidence showing that transcription of PDC1 is controlled by ethanol repression rather than by glucose induction. Furthermore, we showed that the same sequence is responsible for an autoregulatory process, leading to increased transcription from both the PDC1 and the PDC5 promoters, in strains in which the genomic copy of PDC1 is deleted. In addition, we have confirmed the role of Rap1 binding and have demonstrated that the Gcr1 protein also acts in transcriptional activation. DNA‐protein interactions at the consensus Rap1 ‐binding site and the newly identified ethanol‐repression sequence (5 ‐AAATGC‐ATA‐3, termed 'ERA') were investigated by gel‐shift and footprint analyses. Both DNA‐binding activities were found in extracts from cells grown in media containing glucose or ethanol as the carbon source, indicating that the capacity to bind is not altered by the carbon source used.
Organizational characteristics and information content of an archaeal genome: 156kb of sequence from Sulfolobus solfataricus P2
Authors: Sensen C. W. , Klenk H.‐P. , Singh R. K. , Allard G. , Chan C. C.‐Y. , Liu Q. Y. , Penny S. L. , Young F. , Schenk M. E. , Gaasterland T. , Doolittle W. F. , Ragan M. A. , Charlebois R. L.
Published: October 2006

We have initiated a project to sequence the 3Mbp genome of the thermoacidophilic archaebacterium Sulfolobus solfataricus P2. Cosmids were selected from a provisional set of minimally overlapping clones, subcloned in pUC18, and sequenced using a hybrid (random plus directed) strategy to give two blocks of contiguous unique sequence, respectively, 100389 and 56105bp. These two contigs contain a total of 163 open reading frames (ORFs) in 26–29 putative operons; 56 ORFs could be identified with reasonable certainty. Clusters of ORFs potentially encode proteins of glycogen biosynthesis, oxidative decarboxylation of pyruvate, ATP‐dependent transport across membranes, isoprenoid biosynthesis, protein synthesis, and ribosomes. Putative promoters occur upstream of most ORFs. Thirty per cent of the predicted strong and medium‐strength promoters can initiate transcription at the start codon or within 10 nucleotides upstream, indicating a process of initial mRNA‐ribosome contact unlike that of most eubacterial genes. A novel termination motif is proposed to account for 15 additional terminations. The two contigs differ in densities of ORFs, insertion elements and repeated sequences; together they contain two copies of the previously reported insertion sequence ISC 1217, five additional IS elements representing four novel types, four classes of long non‐IS repeated sequences, and numerous short, perfect repeats.
Comparison of ion transportation before and after egg hatching in Amphinemura sp. (Plecoptera)
Authors: YOSHIMURA MAYUMI , YAMADA TSUYOSHI
Published: October 2006

Abstract An increase in egg size with embryonic development in stoneflies is believed to result from the uptake of water by osmosis. The present study aims to investigate whether a selective ion transport through egg membranes exists before hatching, and whether ions are released after hatching. Viable and nonviable egg masses are incubated in Petri dishes filled with water, and the concentrations of the ions F−, Cl−, SO42−, NO3−, Na+, K−, Mg2+ and Ca2+ in the water are determined. The ion transport of an egg mass before and after hatching and a nonviable egg mass is then calculated. Before hatching, Cl−, SO42−, NO3−, Na+, Mg2+ and Ca2+ are taken up from the surrounding water into the inner egg. These ions are selectively taken into the egg. After hatching, Cl−, SO42−, Na+, Mg2+ and Ca2+ are released into the surrounding water. The amount of these ions released after hatching is lower than the amount taken up before hatching. Ions that are not released after hatching are considered to be used in embryonic development.
Anti‐TNF Effects on Destructive Fibroblasts Depend on Mechanical Stress
Authors: Lange F. , Härtl S. , Ungethuem U. , Kuban R. J. , Hammerschmidt S. , Faber S. , Morawietz L. , Wirtz H. , Emmrich F. , Krenn V. , Sack U.
Published: October 2006

Joint destruction in rheumatoid arthritis (RA) starts typically at sites of mechanically stressed inserts of the synovial membrane near the cartilage/bone border. In the therapy of RA, tumour necrosis factor (TNF) antagonists have rapidly emerged as a valuable class of anti‐rheumatic agents that reduce joint destruction. The aim of this study was to investigate and profile genes involved in the interaction between articular movement and anti‐TNF therapy in an in vitro model. Murine LS48 cells, an established substitute for invasive RA synovial fibroblasts, were cultured, stretched and/or treated with anti‐TNF‐α antibody for 24 h. RNA was isolated and gene transcript levels were determined using U74Av2 Affymetrix GeneChips to identify transcriptional events. Positive findings were verified by polymerase chain reaction (PCR). We identified 170 differentially regulated genes, including 44 of particular interest. Gene expression fell into different functional groups that can be explained by RA pathogenesis and experimental conditions. For 21 genes of the 44 of particular interest, regulation could be confirmed by real‐time PCR. Remarkably, we found structural as well as functional genes differently regulated between stretched cells, anti‐TNF‐treated cells, and stretched cells treated with anti‐TNF antibody. Additionally, we also found a large number of genes that are apparently not related to the experimental conditions. Mechanical exertion modulates gene expression and subsequently cellular response to anti‐TNF therapy. Results in exerted cells correspond to current knowledge regarding RA pathogenesis and underline the relevance of our experimental approach. Finally, the central function of the interleukin‐18 system in joint destruction could be confirmed by our findings.
Tube weaning according to the Graz Model in two children with Alagille syndrome*
Authors: Burmucic K. , Trabi T. , Deutschmann A. , Scheer P. J. , Dunitz‐Scheer M.
Published: October 2006

Abstract:  Two children were weaned from long‐term tube feeding after liver transplant because of Alagille syndrome. The children were successfully weaned, one in seven days and the other in 13 days, using our standard and highly specialized intensive treatment protocol. Normal feeding behavior and stabilization of body weight were established. Children fed by long‐term enteral tubes can be weaned from enteral feeding even after a long period of treatment. The return to age‐appropriate self‐feeding should be introduced as early as possible. Our weaning program time is brief and effective and can be recommended generally to improve quality of life and withhold unintended side‐effects of enteral nutrition.
Zeocin resistance as a dominant selective marker for transformation and targeted gene deletions in Candida glabrata
Authors: Alderton Alex J. , Burr Ian , Mühlschlegel Fritz A. , Tuite Mick F.
Published: October 2006

Many of the genetic tools used to generate gene knockouts in Candida glabrata exploit auxotrophic markers but this is not suitable for use with clinical strains. Antibiotic resistance markers, however, allow one to target genes to be deleted without any prior genetic manipulation of clinical isolates. Such antibiotic selection markers have been widely reported for the manipulation of Saccharomyces cerevisiae. However, very few antibiotic resistance markers have been shown to be useful in C. glabrata. Here, we report the use of Zeocin resistance (ZeoR), encoded by the ble gene from Streptoalloteichus hindustanus, as a new positive selection marker for the genetic manipulation of C. glabrata including clinical strains that we show are significantly more sensitive to Zeocin than to G418. The potential of the ZeoR marker for targeted gene disruption in C. glabrata was confirmed by constructing deletions of the ADE2 in both a laboratory and a clinical strain of C. glabrata, using both short (90 bp) and long (400 bp) homology cassettes.
Yeast associated with human infections in south‐eastern Nigeria
Authors: Abia‐Bassey L. N. , Utsalo S. J.
Published: October 2006

A total of 1921 specimens from nine clinical sources were examined by direct microscopy and culture to recover yeast associated with human infection. Identification of yeast was based on their carbon assimilation patterns, using API 20C AUX and ID 32 C (bioMérieux, France) commercial kits. A total of 178 specimens (9.3%) were positive for yeast. Most of the yeast isolates were recovered from urine samples and genital swabs. Prevalence was significantly higher in women (14.7%) than in men (1.4%) (P < 0.05). The age group 21–30 years recorded the highest prevalence of yeast infection (65.2%) followed by age group 11–20 years (16.9%) and >40 years (9.0%). When genital samples were considered, prevalence was significantly higher in the age group 21–30 years than that in older ones (P < 0.05). Isolates recovered included seven species of Candida and Trichosporon inkin. C. albicans accounted for the highest number of isolates (128) followed by C. tropicalis (23) and C. parapsilosis (9). Two isolates each of C. famata and C. norvegensis were recorded and are reported for the first time in Nigeria. The two isolates of T. inkin were recovered from perianal lesions and are also reported for the first time from Nigeria. C. albicans, C. glabrata, C. parapsilosis and C. krusei were found to be the most common yeast species that act as agents of human disease in south‐eastern Nigeria.
Tinea capitis among rural school children of the district of Magude, in Maputo province, Mozambique
Authors: Sidat Mohsin M. , Correia Della , Buene Titos P.
Published: October 2006

The study was carried out in two rural primary schools of the District of Magude, the largest district of Maputo Province in 2001. The prevalence of tinea capitis in each school was 11.6% (49/422) and 6.8% (18/263) and affected predominantly male children. The most common dermatophytes isolated from both schools were Microsporum audouinii. However, Trichophyton mentagrophytes was also found to be an important causal agent of tinea capitis in the District of Magude. Although the prevalence of tinea capitis found in our study is relatively high compared to previous cross‐sectional studies carried out in Mozambique, it is still closely related to the prevalence rates reported for African countries. Tinea capitis continues to be an important public health issue in Mozambique, particularly in primary school setting.