Low Temperature Cooling Research Articles

Yield and weight distribution of two potato cultivars grown from seed potatoes of different physiological ages

ABSTRACTAfter seed potatoes (Solanum tuberosum L.) are harvested, they may be stored in sheds, in low temperature coolers or left un-lifted in the ground. This research describes the response of tuber yield and distribution (formed by the weight grade of each potato) of ‘Bondi’ and ‘Fraser’ crops planted from seed potatoes at different physiological ages generated from different combinations of these storage regimes applied in the Early and Late phases of storage. De-sprouting half of the potatoes prior to planting was used to accelerate the rate of physiological ageing, synchronise the planting material and increase the range of treatments. Total yield and number of potatoes produced were unaffected by any of the storage treatments and reflected a constant pattern of canopy development, radiation use efficiency and harvest index. The largest tubers were attained by higher rates of tuber growth which was inversely related to the number of stems per plant.

Yield and weight distribution of two potato cultivars grown from seed potatoes of different physiological ages

ABSTRACTAfter seed potatoes (Solanum tuberosum L.) are harvested, they may be stored in sheds, in low temperature coolers or left un-lifted in the ground. This research describes the response of tuber yield and distribution (formed by the weight grade of each potato) of ‘Bondi’ and ‘Fraser’ crops planted from seed potatoes at different physiological ages generated from different combinations of these storage regimes applied in the Early and Late phases of storage. De-sprouting half of the potatoes prior to planting was used to accelerate the rate of physiological ageing, synchronise the planting material and increase the range of treatments. Total yield and number of potatoes produced were unaffected by any of the storage treatments and reflected a constant pattern of canopy development, radiation use efficiency and harvest index. The largest tubers were attained by higher rates of tuber growth which was inversely related to the number of stems per plant.

Correlation Between Endodontic Broken Instrument and Nickel Level in Urine

This study aims to evaluate the correlation between the presences of separated endodontic instrument inside the dental canal and the nickel (Ni) level in the urine samples of subjected patients. Same-gendered and near-aged participants were selected and were instructed to collect their urine in sterile nickel-free plastic containers. The procedures were carried out in the office, and samples were stored in low-temperature cooler for 1 day and then they were transferred to the laboratory for electrothermal atomic absorption spectrometry. The level of Ni was measured and the correlation coefficient was calculated. Data were analyzed using t tests, Pearson's correlation coefficients, and linear regression analysis, at a level of significance P < 0.05. The statistical analysis has showed significant difference in Ni level between endodontic and control groups (P < 0.05). There was no correlation between Ni level in urine and the age or time period of broken instrument inside the canal; however, Ni level of urine and the age of participants in experimental group has demonstrated a positive correlation. The amount of Ni element can be increased in the urine of patients who have experienced broken endodontic instrument inside the dental canal. However, there is no positive correlation between the remaining pieces of instruments inside the canal and the elevation of nickel amount in urine during the tested time period. This issue suggested that the aging of remaining broken instrument inside the canal does not show any remarkable concern regarding the Ni elevation in the urine excreted by an individual.

How the Performance of a Superconducting Magnet Is Affected by the Connection Between a Small Cooler and the Magnet

As low temperature cryocoolers become more frequently used to cool superconducting magnets, it becomes increasingly apparent that the connection between the cooler and the magnet has an effect on the design and performance of the magnet. In general, the use of small coolers can be considered in two different temperature ranges; 1) from 3.8 to 4.8 K for magnet fabricated with LTS conductor and 2) from 18 to 35 K for magnets fabricated using HTS conductor. In general, both temperature ranges call for the use of a two-stage cooler. The best method for connecting a cooler to the magnet depends on a number of factors. The factors include: 1) whether the cooler must be used to cool down the magnet from room temperature, 2) whether the magnet must have one or more reservoirs of liquid cryogen to keep the magnet cold during a loss of cooling, and 3) constraints on the distance from the cooler cold heads and the magnet and its shield. Two methods for connecting low temperature coolers to superconducting magnets have been studied. The first method uses a cold strap to connect the cold heads directly to the loads. This method is commonly used for cryogen-free magnets. The second method uses a thermal siphon and liquid cryogens to make the connection between the load being cooled and the cold head. The two methods of transferring heat from the magnet to the cooler low temperature cold head are compared for the two temperature ranges given above

Development of a cryogen-free continuous ADR for the constellation-X mission

Constellation-X is a multi-satellite X-ray astronomy mission presently being planned for launch in the 2010 time frame. Each of four identical satellites will contain a telescope and instruments for imaging and spectroscopic analysis of hard and soft X-rays. The X-ray Microcalorimeter Spectrometer (XMS) instrument will use arrays of microcalorimeters to detect X-rays with energies from 0.2 to 6 keV. To achieve the desired energy resolution of 2 eV, the detectors will be cooled to 50 mK. The projected cooling power requirement is approximately 5 μW. In order to meet the mission lifetime requirement of 6 years (with a goal of 10 years), a mechanical cryocooler will be used to provide a heat sink for the low temperature cooler. In this paper we discuss the development of a continuous adiabatic demagnetization refrigerator (CADR) that meets the cooling requirements of the XMS instrument. The four-stage CADR presently being tested can operate continuously at 50 mK using a 4.2 K helium bath as a heat sink. Its cooling power of 6 μW at 50 mK exceeds the XMS requirement, and its peak heat rejection rate is less than 7 mW. Details of the CADR's design and operation, as well as the development program leading up to a flight-qualified instrument, are discussed.

Single Crystals of p -Type Solid Solutions between Bismuth and Antimony Chalcogenides for Cooling to T < 150 K

Sb2Te3–Bi2Te3 crystals (25–60 mol % Bi2Te3) doped with Bi2Se3 and excess Te were studied with the aim of identifying the optimal compositions for the p-legs of low-temperature coolers. The crystals were grown by the floating-crucible technique. Their transport properties were studied in the range 100–400 K. By measuring axial thermopower profiles, it was shown that increasing the Bi2Te3 and Bi2Se3 contents of the crystals has an adverse effect on their homogeneity. Crystals were prepared with a carrier concentration in the range (1–5) × 1019 cm–3 and a thermoelectric power above 200 μV/K at room temperature and the highest thermoelectric figure of merit at temperatures below 200 K. The maximum temperature drops and thermoelectric figures of merit were calculated for low-temperature stages of magnetothermoelectric coolers with hot-junction temperatures of 200 and 170 K and Bi–Sb n-legs.

A low-temperature cooler for protein crystallography

A compact and economical cooling system utilizing thermoelectric modules has been designed and constructed. The cooler is small and light and can be positioned close to the crystal. It is capable of cooling air at 101 min−1 to −15°C (258 K), and can maintain a set temperature to within ± 0.1°C (0.1 K) over long periods.

The preparation and properties of certain technologically important semimetals and semiconductors

During the last twenty years the majority of solid-state device work has been concerned with the utilisation of semiconductors with a band gap (EG ) > 0.7 eV, i.e., large with respect to the thermal-activation energy, kT, at room temperature. The p-n diode, transistor, and, more lately, the integrated circuit have used germanium (0.72 eV) and silicon (I.I eV) as the basic material, while Gunn diodes and semiconducting lasers have depended upon the properties of GaAs with a band gap of I.45 eV. A survey of the literature shows that in recent years a much greater research effort has been put into small-band-gap materials, say, with EG < 0.2 eV and, indeed, into semimetals in which the valence band and conduction band can be considered to overlap at some point in E/k space. The interest in these materials has arisen in two ways. The advent of the laser has made it important to be able to detect radiation in the infrared and the far infrared; for example, the CO2 laser is one of the most powerful available and its emission peak lies at 10.6 μ or 0.12 eV. A small-band-gap semiconductor using intrinsic generation of electron/hole pairs could, in principle, be used in the photoconductive mode to detect such radiation. Another totally different usage has arisen from the work on low-temperature coolers. The Nernst-Ettingshausen effect has been known for over a century but it was not until recently that an effect which was a scientific curiosity was used to produce significant cooling at temperatures below 150 K.

A Novel Microwave Noise Temperature Generator Having an Output Temperature of from below 40 to above 370 K

A variable microwave noise temperature standard having an output from below 40 to above 370 K is described. This temperature standard is unique in that a closed cycle low temperature cooler used in conjunction with a proportional control heater network provides continuously variable low temperatures which are independent of the boiling temperatures of cryogenic liquids and may be readily changed and known with an accuracy of better than 1.0 K. A variable temperature output is obtained without the use of a microwave attenuator thus eliminating the inherent errors associated with the attenuator. The output noise temperature is completely calculable using measured parameters (i.e., thermal temperatures, waveguide insertion loss, and impedance mismatch factors) and as a result may qualify as a primary noise standard.