Evaluation of Lignosulfonate Based Retarders for Thickening Time as a Function of Dosage and Temperature

The retardation of class H Portland cement using lignosulfonates was investigated in the temperature range between 54°C and 153°C. Lignosulfonates with varying extent of modification was used in the study, and the optimum retarder dosage and temperature range to achieve desired thickening time was identified for different lignosulfonate types (non-modified, modified and highly modified). In general, a linear thickening response was observed at low retarder dosage, while a near exponential increase in thickening time response was observed at higher dosages. Defining the retarder dosage temperature relationship is essential for proper cement slurry design for securing desired placement of cement slurry. A significant finding is that the thickening time responses trend from near linear at low dosages, transitioning to near exponential at higher dosages. The observed results varied depending on the extent of modification performed on the lignosulfonate retarder. Pure lignosulfonate retarders produce optimal dosage response from 54°C to 97°C. Modified retarders work best in the range of 97°C to 118°C. While highly modified retarders perform best in the range of 118°C to 153°C. Defining the retarder dosage temperature relationship is essential for proper cement slurry design for securing desired placement of cement slurry.

Revisiting the evaluation of central versus peripheral thermoregulatory control in humans

Human thermoregulatory control is often evaluated through the relationship between thermoeffector output and core or mean body temperature. In addition to providing a general indication of whether a variable of interest alters thermoregulatory control, this relationship is often used to determine how this alteration may occur. This latter interpretation relies upon two parameters of the thermoeffector output-body temperature relationship; the onset threshold and thermosensitivity. Traditionally, changes in the onset threshold and thermosensitivity are interpreted as "central" or "peripheral" modulation of thermoregulatory control, respectively. This mini-review revisits the origins of the thermoeffector output-body temperature relationship and its use to interpret "central" or "peripheral" modulation of thermoregulatory control. Against this background, we discuss the strengths and weaknesses of this approach and highlight that "central" thermoregulatory control reflects the neural control of body temperature whereas "peripheral" thermoregulatory control reflects properties specific to the thermoeffector organs. We highlight studies that employed more direct approaches to investigate the neural control of body temperature and peripheral properties of thermoeffector organs. We conclude by encouraging future investigations interested in studying thermoregulatory control to more directly investigate the component of the thermoeffector loop under investigation.

The large-scale, long-term coupling of temperature, hydrology, and water isotopes

The stable isotope ratios of oxygen and hydrogen in polar ice cores are known to record environmental change, and they have been widely used as a paleothermometer. Although it is known to be a simplification, the relationship is often explained by invoking a single condensation pathway with progressive distillation to the temperature at the location of the ice core. In reality, the physical factors are complicated, and recent studies have identified robust aspects of the hydrologic cycle’s response to climate change that could influence the isotope-temperature relationship. In this study, we introduce a new zonal-mean isotope model derived from radiative transfer theory, and incorporate it into a recently developed moist energy balance climate model (MEBM), thus providing an internally consistent representation of the tight physical coupling between temperature, hydrology, and isotope ratios in the zonal-mean climate. The isotope model reproduces the observed pattern of meteoric δ18O in the modern climate, and allows us to evaluate the relative importance of different processes for the temporal correlation between δ18O and temperature at high latitudes. We find that the positive temporal correlation in polar ice cores is predominantly a result of suppressed high-latitude evaporation with cooling, rather than local temperature changes. The same mechanism also explains the difference in the strength of the isotope-temperature relationship between Greenland and Antarctica.