Cold Strain Research Articles

Temperature effect on production of hydrogen and oxygen byChlamydomonas cold strain CCMP1619 and wild-type 137c

Photosynthetic water splitting for hydrogen and oxygen production is a promising biological process that converts sunlight into useful chemical energy. In green algae, this process becomes active when hydrogenase is induced. In this process, water is split into molecular oxygen, protons, and electrons by photosystem II (PSII). The electrons acquired from water splitting are transferred through PSII to photosystem I (PSI). At PSI, these electrons are further energized by the PSI photochemical reaction. The energized electrons emergent from the reducing side of PSI are transferred to hydrogenase via ferredoxin (Fd), and thereby utilized in a hydrogenase-catalyzed reaction, the reduction of protons and production of molecular hydrogen. The protons consumed in the reduction reaction are derived ultimately from water splitting. The net result of this process is cleavage of water to molecular hydrogen and oxygen. Hydrogenase is a key enzyme in the photoproduction of hydrogen. In multicellular algae and higher plants, this enzyme is lost or no longer inducible for photoproduction of hydrogen. This enzyme is, however, inducible for photoevolution of hydrogen in certain microscopic algae such as Chlamydomonas. However, not all species of Chlamydomonas have an inducible enzyme to produce hydrogen in the light. In the work described in thismore » article, a Chlamydomonas cold strain, CCMP1619, was assayed for its potential hydrogenase activity by measuring anaerobically induced production of dark- and light-dependent hydrogen. This cold strain was originally isolated from Lake Bonney (ice-covered), Antarctica, and known to grow at low temperatures. The effect of temperature on hydrogen production by CCMP1619 was compared with the wild-type Chlamydomonas st rain 137c. The results indicated that 137c and CCMP1619 contain inducible hydrogenase, and that temperature had a significant effect on the rates of hydrogenase induction and on the kinetics of hydrogen production.« less

Dynamic Reerystallization of Magnesium at Ambient Temperature

This paper is concerned with structural changes taking place in pure magnesium subjected to cold straining under heavy loading. It was shown that at T = 0.3 T[sub m] (melting point), low temperature dynamic recrystallization (LTDR) developed in the material. During LTDR, the size of dynamically recrystallized grains was found to be strain dependent. A certain relationship was established between this dependence and the dominating deformation mechanisms. The causes of the strain dependence of the dynamic recrystallization parameters in magnesium are discussed. (orig.)

Manufacturing and fabrication of thermomechanically rolled heavy plates

The development of heavy plates for constructional steelwork, shipbuilding and line pipes is characterized by a reduction of the carbon equivalent values. At the same time the strength and toughness properties are improved. Significant progress has been made by application of modern TM-rolling processes including accelerated cooling. Process control has been optimized to produce a homogeneity comparable to normalized plates. Strength and hardness profiles demonstrate the actual homogeneity. The properties after cold forming and strain aging have been evaluated. The weldability, in particular welding without preheating, is shown as a function of the H 2 -content of the weld metal. Flame straightening of TM-rolled plates is possible and is demonstrated for different types of flame straightening procedures

Effect of aging and plastic strain on the mechanical properties of high manganese steel

1. Aging of high-manganese 110G13L steel at temperatures from 200 to 400°C permits to increase its ultimate strength without changing the yield stress, while plastic properties, and the semibrittleness temperature T50 slightly decrease. Aging at temperatures above 400°C leads to sharp reduction of σB, ψ, δ and T50. 2. After fractional loading of the 110G13L steel at temperatures of 20–250°C an increase of σ0.2 and σB is achieved; the plastic properties decrease in cold strain while in thermal strain they do not change. 3. The process of plastic strain of the 110G13L steel with subsequent aging causes an increase of strength properties without reducing plasticity. Apparently this takes place on account of the separation during aging of dispersed particles along the slip planes, produced by preliminary deformation.

Chest Symptoms in Chimney Sweeps and Postmen—A Comparative Survey

The purpose of this survey was to study the association between a number of chronic diseases and occupational exposure to soot and smoke. The problem was illustrated by comparing chimney sweeps and postmen with regard to self-reported occurrence of symptoms. Data were obtained by means of a postal questionnaire. Potential confounding was controlled by matching and stratified analysis. Compared to postmen, the chimney sweeps experienced a significantly increased risk of long-term coughing with expectorate (Prevalence Rate Ratio (PRR) = 1.74), dyspnoea from fast walking (PRR = 1.46), dyspnoea from ordinary walking (PRR = 1.79), dyspnoea when dressing (PRR = 2.29) and substernal oppression from exposure to cold or physical strain (PRR = 1.41). It seems likely that the chimney sweep's inhalation of soot particles and locally irritating flue gases may have contributed to the increased occurrence of chest symptoms in this occupational group.

Interaction of Different Strains of Entamoeba histolytica with Target Cells: Characterization of Electrophysiological and Morphological Features

Two strains of Entamoeba histolytica with pathogenic zymodemes (SFL3, HK9), one strainwith non-pathogenic zymodeme (≪Bru≫) and one non-pathogenic Entamoeba sp. strain (≪cold strain≫), were investigated with respect to their interaction with target cells. Three test systems were used: 1) direct microscopical observation and qualitative as well asquantitative evaluation of contact and binding events with MDCK cells as targets, 2) kinetics of cytotoxic activity as measured by means of chromium release from 51Cr-labelled K562 cells, and 3) electrophysiological observations with freshly prepared mouse liver cells. We observed that the non-pathogenic cold strain interacted only shortly with target cells(statistical events, interaction type ≪I≫), but did not induce morphological changes, chromium release or depolarization of targets. Non-pathogenic and avirulent strain ≪ Bru≫ showed, apart from type ≪I≫-binding, the ability to establish tight (type ≪II≫) and long-lasting contact (type ≪-III≫) with targets, but again without cytotoxic effects. The pathogenic but avirulent strain HK9 tightly interacted (type ≪II≫) and sometimes long-lasting with target cells, but morphological changes and chromium release were of a moderate degree during the first 20 min, and depolarization was only a rare event. In contrast, strain SFL3 produced tight and long-lasting contacts (type ≪III≫ binding), leading to cell death in 83 % (type ≪IV≫ interaction) within 20 min, substantial chromium release within 10 min and rapid depolarization (≪electric collapse≫) of target cells.

Modified live Sendai virus vaccine diluted by passage through incubated culture medium for providing a cold strain

Modified live Sendai virus vaccine diluted by passage through incubated culture medium for providing a cold strain

Microstructure Development in a High Current Density NbTi Superconducting Composite

Several features of the metallurgy of superconducting composites of Nb-Ti in a Cu matrix are of interest. The cold drawing strains are generally of order 8-10, producing a very fine grain structure of diameter 30-50 nm. Heat treatments of as little as 3 hours at 300 C (∼ 0.27 TM) produce a thin (1-3 nm) Ti-rich grain boundary film, the precipitate later growing out at triple points to 50-100 nm dia. Further plastic deformation of these larger a-Ti precipitates by strains of 3-4 produces an elongated ribbon morphology (of order 3 x 50 nm in transverse section) and it is the thickness and separation of these precipitates which are believed to control the superconducting properties. The present paper describes initial attempts to put our understanding of the metallurgy of these heavily cold-worked composites on a quantitative basis. The composite studied was fabricated in our own laboratory, using six intermediate heat treatments. This process enabled very high critical current density (Jc) values to be obtained. Samples were cut from the composite at many processing stages and a report of the structure of a number of these samples is made here.

Straining phenomena of POY revealed by thermal retraction and other techniques

AbstractPartially oriented polyesters yarns (POY) were strained at different strain rates (0.03–12.00 min−1) and temperatures above and below Tg (3–92°C). Thermal retraction, density, DSC, and WAXS techniques show that strain‐induced crystallization takes place by straining at temperatures above as well as below Tg. Above Tg, depending upon the strain rate, two regimes are observed: Below the strain rate of 1.5 min−1, the flow regime; the degree of crystallinity is reduced as the strain rate increases. Above the strain rate of 1.5 min−1, the strain‐induced crystallization regime; the degree of crystallinity increases as the strain rate increases. Thermal retraction, stress–relaxation, and sonic modulus techniques indicate that, upon cold straining, instead of the original Tg at 65–69°C, two glass transitions occur: an upper Tg (u) and a lower Tg (l). For POY strained at 3°C and at a strain rate of 10 min−1, the values are 78°C and 37°C, respectively. The higher the strain rate and the lower the straining temperature, the large the difference between Tg (u) and Tg (l).

Organ cultures in evaluation of antiviral drugs

Human embryonic trachea explants were the only organized tissue in which virus strains, causing colds in man, could be grown and in which the effect of antiviral drugs against cold virus strains can perhaps be assessed. Dog trachea explants could be readily infected with influenza viruses and parainfluenza 1 (Sendai) virus both by conventional methods or by virus aerosols. They can provide a suitable organ culture system for evaluation of antiviral drugs, especially against recent influenza A2 strains. Ferret trachea explants can be employed for antiviral drug evaluation against some influenza A and B or Sendai virus strains but variation in sensitivity between trachea explants from different ferrets is to be expected. Respiratory tissue explants from vervet monkeys, pigs, hamsters, rats and mice can provide tools for studies on the specific virus-cell interaction in organized tissue but did not meet the requirements presented as essential for antiviral drug testing in organ cultures.

Resistive Transition and Current Density Characteristics in Superconducting Niobium Containing Dissolved Gases

Oxygen and nitrogen as interstitial solutes in niobium cause the metal in transverse field to exhibit anomalous resistance minima or critical current maxima (peak effect). The anomaly appears at ${H}_{c2}$, the upper critical field of these Type II superconductors. The resistance in the mixed state is decreased by exceeding the solubility limit, by cold working and by strain aging at 170\ifmmode^\circ\else\textdegree\fi{}C, masking out the anomaly. Rapidly quenching from the solution temperature decreases the anomaly. The results suggest that the anomaly is strongest at some intermediate stage of the process of segregation and precipitation at dislocations. Resistance in the mixed state is increased by introducing more solute, by quenching, and by etching. Structural changes brought about by cold working, strain aging, and rapid quenching responsible for large changes in ${J}_{c}(H)$ or $R(H)$ in the mixed state also cause changes in the region ${H}_{c2}lHl{H}_{c3}$. In this latter region, field orientation effects and observed $\frac{{H}_{c3}}{{H}_{c2}}$ ratios are roughly consistent with the concept of a superconducting surface sheath as recently proposed by Saint-James and de Gennes. Pure niobium, however, tends to exhibit consistently higher ratios.