Controlled Stress Conditions Research Articles

CMS (constant mean stress) VS. UCS (unconfined strength) tests: A tool to reduce core damage effects

An experimental study is presented, where the unconfined strength (UCS) is compared to the strength obtained by a CMS (constant mean stress) path terminating at zero confinement. The CMS values are found to be 20–50% in excess of the UCS values. In this study, we have utilized synthetic sandstones, formed under controlled stress conditions, in order to have a reproducible material. With this technique, we can also estimate the “virgin” strength of the material, which is found to be close to the CMS strength. Experiments with natural sandstones confirm the behaviour seen with the synthetics.

Effects of previous zinc exposure on pH tolerance of periphyton communities

AbstractThe community‐level effects of previous chemical exposure on resistance to a dissimilar subsequent stress were evaluated. Naturally derived periphytic communities on polyurethane‐foam artificial substrates provided colonists for development of new communities under controlled stress conditions in the laboratory. Communities were colonized under three levels of Zn stress: control, low (73 μg/L), and high (172 μg/L). After 21 d, laboratory‐colonized communities were exposed to 5 pH levels (control, 4.5, 4.0, 3.5, 3.0) for 48 h. No significant differences occurred between Zn treatments in response to pH for total biomass, assimilation ratio, respiration to biomass ratio, and net daily metabolism. Response to pH was dependent on Zn treatment for number of protozoan species, algal biomass, gross primary productivity, and community respiration. Number of protozoan species in high Zn was impaired in absence of pH stress. Primary production and community respiration were impaired in absence of pH stress in both low and high Zn. For these three end points, outcome for Zn treatments converged with increasing secondary stress; no differences between Zn treatment groups were observed at pH < 4.0. For several end points, Zn‐stressed communities changed less, relative to their initial state, with subsequent acid shock.

EFFECTS OF PREVIOUS ZINC EXPOSURE ON pH TOLERANCE OF PERIPHYTON COMMUNITIES

The community-level effects of previous chemical exposure on resistance to a dissimilar subsequent stress were evaluated. Naturally derived periphytic communities on polyurethane-foam artificial substrates provided colonists for development of new communities under controlled stress conditions in the laboratory. Communities were colonized under three levels of Zn stress: control, low (73 μg/L), and high (172 μg/L). After 21 d, laboratory-colonized communities were exposed to 5 pH levels (control, 4.5, 4.0, 3.5, 3.0) for 48 h. No significant differences occurred between Zn treatments in response to pH for total biomass, assimilation ratio, respiration to biomass ratio, and net daily metabolism. Response to pH was dependent on Zn treatment for number of protozoan species, algal biomass, gross primary productivity, and community respiration. Number of protozoan species in high Zn was impaired in absence of pH stress. Primary production and community respiration were impaired in absence of pH stress in both low and high Zn. For these three end points, outcome for Zn treatments converged with increasing secondary stress; no differences between Zn treatment groups were observed at pH < 4.0. For several end points, Zn-stressed communities changed less, relative to their initial state, with subsequent acid shock.

Shock-prod burying test in rats: Autonomic and behavioral responses

Heart rate (HR), core temperature (CT) and gross locomotor activity (GLA) were recorded in rats by a computerized telemetry system before, during and after 15-min exposure to a constantly electrified (2mA) or nonelectrified (0mA) prod which was presented through a hole in the home cage with woodshavings on the floor [shock-prod burying (SPB) test]. Measurement of both autonomic and behavioral responses continued up to 60 min after introduction of the prod into the home cage. Twenty-four h after the SPB test, rats were tested for retention. During the SPB test, significant increases in HR, respective to baseline values, were observed in both the 2mA and 0mA group, but the tachycardiac response in the former group significantly outweighed that in the latter group. In shocked rats, HR remained elevated during the entire 45-min posttest period, whereas HR declined immediately after removal of the prod in nonshocked animals. An onset in rise in CT was observed in the 2mA, but not in the 0mA group, during prod exposure time, which eventually resulted in an additional—more than two-fold—increase after termination of the test and outlasted total recording time. Marked behavioral activation was observed in the 2mA group, whereas the 0mA responded to a lesser extent. Approach and exploration of the prod was reduced when the prod was electrified. The total time spent by rats burying the prod was significantly longer in the shocked than in the nonshocked group. When exposed to the nonelectrified prod after 24 h, total burying time was reduced in the 2mA group but still significantly longer than in the 0mA group. On this occasion, shocked rats showed a similar overall pattern in HR, CT and GLA reponses as on day 1, with concomitant behavioral activation up to 1 h after the onset of the retention trial, all increases, however, being less pronounced. Conversely, the 0mA group showed no significant response when tested for retention. However, detailed analysis of the first minute of prod reexposure revealed a tendency towards bradycardia in both groups, with HR deceleration being most marked in the shocked rats. These results demonstrate that a mild novelty stress (0mA) as well as an aversive stimulus (2mA) induces simultaneous changes in autonomic and behavioral responses in rats, the magnitude and duration of which being dependent on the nature of the stimulus. A (conditioned) responding pattern of both autonomic and behavioral parameters, similar to that observed on day 1, was observed during the 24-h retention trial. In the present study, we have demonstrated differential involvement of the ANS in various stress-induced behavioral states in rats. The SPB test, used together with a wireless telemetry system, enables the evaluation of genuine stress responses under well-defined and controlled stress conditions.

Studies on the Influence of Photoperiod and Temperature on Floral Traits in Buckwheat (Fagopyrum esculentum Moench) under Controlled Stress Conditions

AbstractFloral traits of three Japanese and one European buckwheat varieties were studied in a phytotron under three photoperiods (short‐day 10/14 h, long‐day 14/10 h, extreme long‐day 18/6 h) and two thermoperiods (25/20, and 15 °C constant temperature). The Japanese varieties showed a strong delay in flowering under prolonged day length, whereas one European variety reacted almost day‐neutral. Also affected by the photoperiod were the number of flower clusters as well as their sizes. A constant low temperature of 15 °C led to a strong delay in flowering under short‐ and long‐day in all the varieties tested. In particular, the Japanese varieties were sensitive to temperature, developing more flower clusters under high temperature. Furthermore the experiments revealed complex genotype/pliotopenod/thermoperiod interactions. The study, conducted to investigate the causes of low seed‐set observed in buckwheat, offered some suggestions for new breeding strategies. Insensitive genotypes, showing less sensitivity to photoperiod as well as to thermoperiod, should be included in further buckwheat improvement.

Effects of Pore and Confining Pressures on Failure Characteristics of Sedimentary Rocks

Published in Petroleum Transactions, AIME, Volume 216, 1959, pages 26–32. Abstract Triaxial compression tests have been performed to determine the strength characteristics of limestone, sandstone and shale rocks subjected to controlled stress conditions. This control was exercised by varying the liquid pressures within and around a plastic-encased rock specimen. The pressure in the pores of the rock was varied throughout the range from atmospheric to 15,000 psig; the external pressure was changed over the same range with various positive pressure differences between it and the internal pressure. The data show that the rock strength increased and the mode of failure changed as the pressure surrounding the rock became greater than the pressure in the pores of the rock. These observations and the results of microbit drilling experiments indicate that the increased rock strength under pressure may be an important effect in reducing drilling rate, but that other factors are probably of even greater importance. Introduction A large part of the research conducted to reduce the cost of drilling is directed toward improving present drilling technology and developing new drilling methods. In spite of the fact that drilling is essentially the act of making rocks fail, many details of the mechanism of failure are not known. It seems probable, therefore, that continuing studies of the fundamentals of rock failure can lay a foundation for future improvements in drilling technology. One of the factors which affects rock failure is the stress applied to the rock. This effect has been known for many years. As an example, stress studies have been published by engineers concerned with the strength characteristics of concrete in large dams. More recently, a number of investigators have explored the effects of stress on the strength of geologic formations and the geologic implications of their findings. During the last few years some research on rock strengths has also been conducted in an attempt to gain additional insight into the factors which affect rock drillability. In determining the strength characteristics of rocks under different stress conditions, investigators have conventionally used triaxial compression equipment, wherein a jacketed rock cylinder is uniformly loaded from all directions and then compressed longitudinally.

Apparatus for X-Ray Diffraction Studies of Metals under Controlled Stress at Elevated Temperature

A Geiger-counter x-ray spectrometer was constructed for the dynamic study of phase changes and other phenomena in metals under controlled stress conditions at elevated temperatures. Temperature could be controlled from room temperature to the melting point of steel, and stress was independently varied from zero stress to the breaking stress of stainless steel. Applications included isothermal and athermal transformation studies under tensile stress in pearlite, bainite, and martensite.