RESEARCH OF THE RATE OF COOLING AND SELECTION OF THE MATERIAL FORM FOR THE MECHANICAL CHARACTERISTICS OF CAST IRON CASTINGS

The structure and properties of cast iron castings depends not only on the chemical composition of molten cast iron and the technology of its smelting, but also on many other conditions such as cooling and crystallization of castings, especially on further solidification of castings in casting molds. The article presents the established dependences of the influence of the cooling rate of castings on the mechanical properties of the obtained parts, the investigated microstructures of experimental samples from the selected molding materials and it is established that the thermal conductivity of materials affects the structure of graphite in cast iron castings. Computer models of dependencies and regression equations of the processes are proposed.

Vitrifying multiple embryos in different arrangements does not alter the cooling rate

Vitrification is the most common method of cryopreservation of gametes in fertility clinics due to its improved survival rates compared to slow freezing techniques. For the Open Cryotop® vitrification device, the number of oocytes, or embryos, mounted onto a single device can vary. In this work, a mathematical model is developed for the cooling of oocytes, or embryos, that is solved computationally, to investigate whether varying the number of samples mounted onto the Open Cryotop® affects the cooling rates, and therefore survival rates, of vitrified samples. Several realistic spatial arrangements of oocytes/embryos are examined, determining the temperature of the system over time, which highlights the effect of spatial arrangement on the rate of cooling. Results indicate that neither spatial arrangement nor the number of mounted oocytes, or embryos, has a large effect on cooling rates, so long as the volume of the cryoprotectant remains minimal. Under the manufacturer's guidelines, clinical decisions regarding the number and arrangement of oocytes or embryos placed on a device can be varied, whilst maintaining rapid cooling.

Isolation of intact extracellular vesicles from cryopreserved samples

Extracellular vesicles (EVs) have emerged as promising candidates in biomarker discovery and diagnostics. Protected by the lipid bilayer, the molecular content of EVs in diverse biofluids are protected from RNases and proteases in the surrounding environment that may rapidly degrade targets of interests. Nonetheless, cryopreservation of EV-containing samples to -80°C may expose the lipid bilayer to physical and biological stressors which may result in cryoinjury and contribute to changes in EV yield, function, or molecular cargo. In the present work, we systematically evaluate the effect of cryopreservation at -80°C for a relatively short duration of storage (up to 12 days) on plasma- and media-derived EV particle count and/or RNA yield/quality, as compared to paired fresh controls. On average, we found that the plasma-derived EV concentration of stored samples decreased to 23% of fresh samples. Further, this significant decrease in EV particle count was matched with a corresponding significant decrease in RNA yield whereby plasma-derived stored samples contained only 47–52% of the total RNA from fresh samples, depending on the extraction method used. Similarly, media-derived EVs showed a statistically significant decrease in RNA yield whereby stored samples were 58% of the total RNA from fresh samples. In contrast, we did not obtain clear evidence of decreased RNA quality through analysis of RNA traces. These results suggest that samples stored for up to 12 days can indeed produce high-quality RNA; however, we note that when directly comparing fresh versus cryopreserved samples without cryoprotective agents there are significant losses in total RNA. Finally, we demonstrate that the addition of the commonly used cryoprotectant agent, DMSO, alongside greater control of the rate of cooling/warming, can rescue EVs from damaging ice formation and improve RNA yield.

Unbalanced exchange flow and its implications for the night cooling of buildings by displacement ventilation

Passive ventilation of buildings at night forms an essential part of a low-energy cooling strategy, enabling excess heat that has accumulated during the day to self-purge and be replaced with cooler night air. Instrumental to the success of a purge are the locations and areas of ventilation openings, and openings positioned at low and at high levels are a common choice as there is then the expectation that a buoyancy-driven displacement flow will establish and persist. Desirable for their efficiency, displacement flows guide excess heat out through high-level openings and cooler air in through low-level openings. Herein we show that displacement flow cannot be maintained for the full duration of a purge. Instead, the flow must transition to an ‘unbalanced exchange flow’, whereby the cool inflow of air at low level is maintained but there is now a warm outflow and a cool inflow occurring simultaneously at the high-level opening. The internal redistribution of heat caused by this exchange alters the rate at which heat is self-purged and the time thought necessary to complete a purge. We develop a theoretical model that captures and predicts these behaviours. Our approach is distinct from all others which assume that a displacement flow will persist throughout the purge. Based on this enhanced understanding, and specifically that the transition to unbalanced exchange flow changes the rate of cooling and resultant emptying times, we anticipate that practitioners will be better placed to design passive systems that meet their target specifications for cooling.

Requiem for the Regolith Hypothesis: Sea-Level and Temperature Reconstructions Provide a New Template for the Middle Pleistocene Transition

<p>The Middle Pleistocene Transition (MPT) has been characterized as the transition in temperature and sea level from low-amplitude, 41-kyr variability to high-amplitude, quasi-100-kyr variability in the absence of any orbital forcing between 1.2 and 0.7 Ma. The regolith hypothesis is one of a class of hypotheses developed to explain the MPT in sea level, which has been largely inferred from d<sup>18</sup>O<sub>benthic</sub> records. Here we use a global array of 130 sea-surface temperature (SST) records based on Mg/Ca, alkenone, and faunal proxies to reconstruct global and regional SST change over the last 4.5 Myr. Average global temperature cooled by ~6.5<sup>o</sup>C since ~3.5 Ma, with the MPT represented by a significant increase in the rate of cooling between ~1.4 and 0.8 Ma, and a change from dominant 41-kyr to dominant quasi-100-kyr frequencies at ~1.2 Ma that are well correlated with CO<sub>2</sub> over the last 800 ka (r<sup>2</sup>=0.6). Temperature terminations after 1.2 Ma correspond to skipped obliquity beats and, for the last 800 ka, large increases in CO<sub>2</sub>. We use our global SST reconstruction to remove the temperature signal from the Ahn17 d<sup>18</sup>O<sub>benthic</sub> stack to derive d<sup>18</sup>O<sub>seawater</sub>. Accounting for the influence of changing temperature on the isotopic composition of ice sheets, we use the d<sup>18</sup>O<sub>seawater</sub> record to reconstruct global sea level for the last 4.5 Myr. These results suggest sea-level minima equivalent to or lower than the LGM sea-level low stand (130 m) throughout the Pleistocene. Since inception of Northern Hemisphere glaciation ~3 Ma, sea level varied linearly with obliquity until ~1.2 Ma, when sea-level began to vary nonlinearly with obliquity, with the largest terminations occurring at the same time as temperature terminations that correspond to increasing obliquity and CO<sub>2</sub>. These results suggest that the MPT is largely a temperature phenomenon likely associated with CO<sub>2</sub>. The regolith hypothesis other hypotheses developed to explain a transition from low- to high-amplitude sea level variability during the MPT are no longer required, with the MPT change in sea-level response to obliquity likely due to modulation by CO<sub>2</sub>.</p>

Molecular dynamics simulation of the solidification of AlCoCuFeNi high–entropy alloy nanowire

Molecular dynamics simulation of the solidification behavior of AlCoCuFeNi nanowire was carried out basing on the embedded atom potential with different cooling rates (1∙1011 , 1∙1012, and 1∙1013 K/s). To simulate an infinite nanowire, a periodical boundary condition along the nanowire axis direction was applied. The crystallization of the nanowire was characterized by studying the temperature dependence of the potential energy. The adaptive common neighbor analysis (CNA) was performed and the radial distribution function (RDF) was calculated to determine the structure and lattice parameters of phases of the AlCoCuFeNi nanowire. It has been shown that the final structure of investigated nanoparticle changes from amorphous to crystalline with decreasing of the rate of cooling.

Minimizing Chromium Leaching from Low-Alloy Electric Arc Furnace (EAF) Slag by Adjusting the Basicity and Cooling Rate to Control Brownmillerite Formation

Brownmillerite is connected to chromium leaching when present in steel slags. To prevent chromium leaching, brownmillerite in slag should be prevented. Two methods for decreasing brownmillerite content in low-alloy electric arc furnace (EAF) slag were investigated: decreasing the basicity and increasing the cooling rate. The methods were tried on both laboratory scale and in full-scale production. In the laboratory scale experiments, chromium leaching decreased as the basicity decreased until brownmillerite was no longer present, slower cooling resulted in increased chromium leaching, and faster cooling decreased chromium leaching. In full-scale production, basicity modified single batches, with a basicity below 2.2, generally leached less chromium than slag batches with higher basicity, thus verifying the correlation between basicity and chromium leaching seen in laboratory scale experiments. The cooling process in the full-scale experiments was achieved either by letting the slag cool by itself in the air or by water spraying. The water-sprayed slag, which cooled faster, had less chromium leaching than the air-cooled slag. The full-scale production experiments confirmed that both decreasing basicity below 2.2 and increasing the rate of cooling could be used to decrease chromium leaching.