Low Temperature Part Research Articles

Thermally assisted photo transfer OSL from deep traps in Al2O3:C grains exhibiting different TL peak shapes

The present work studies the thermally assisted photo transfer OSL (TAPT OSL) signal in the case of Al2O3:C samples showing double-structured main dosimetric TL peaks. The measurement signal provides indirect experimental evidence regarding the presence of deep traps along with one transfer mechanism extremely powerful and efficient. The experimental features of this signal are presented along with those yielded for samples with narrow TL peaks for the sake of comparison. In the framework of a dosimetric characterization, the straightforward relation observed between the TAPT OSL integrated intensity and the dose, even if non-linear, implies that this signal could be effectively used towards dosimetry purposes in the high dose region up to 250Gy. Furthermore, the study on the influence of the annealing temperature on the TL glow curve shape on Al2O3:C grains is attempted. The variety of glow curve shapes reported especially in the case of single grains is not affected by high temperature annealing, since its effect is dominant even after heating at 1085°C. Thus, this variety should not be correlated to the different deep trap occupancies, but rather be attributed to a possible structural defect. The main dosimetric TL peak af all grains is considered to be a composite of two unambiguously different traps of non-first-order kinetics. The low temperature part of these traps, reaching a maximum at ∼190°C is an electron trap and the high temperature part with maximum at ∼250°C is a hole trap. TL dose response of Al2O3:C grains presenting double peak structures is presented for the first time in literature, suggesting the usefulness on the applicability of Al2O3:C in the dose regime up to 100Gy.

Heat Capacity of Compounds in the CaO-SiO2 System—A Review

In this work, we will be reviewing and assessing the heat capacity of CaO-SiO2 compounds at constant pressure (Cp) as a function of temperature. While there is a large amount of literature available for CaSiO3 high and low temperature compounds, literature for the remaining compounds Ca3Si2O7, Ca2SiO4 and Ca3SiO5 is scarce. Whereas most of the reports in the literature concerning the heat capacities (Cp) of CaSiO3 are in agreement, some of them do deviate (e.g., for the liquid). Experimental determinations of the heat capacities of the Ca3Si2O7 and Ca3SiO5 phases are particularly scarce. Most of the data were therefore taken from thermodynamic assessments. For Ca2SiO4 there are experimental and modelling results which show some slight deviation in the low temperature part. This review provides the current status of the research on heat capacity of compounds in the CaO-SiO2 system.

Investigation of HTS Current Leads Under Pulsed Operation for JT-60SA

The test of two Wendelstein 7-X (W7-X) prototype high temperature superconductor (HTS) current leads (CL) was extended to dynamic operation, in order to evaluate AC losses in parts of the CL. Trapezoidal and triangular current cycles up to a maximum current of 20 kA with different ramp rates between 0.5 kA/s and 10 kA/s were performed. Temperature changes at the warm end of the HTS-module and the influence on the heat load at the cold end of the CL were studied. Additionally, a DC operation that generates a power loss equivalent to the triangular pulsing run was investigated. AC losses in the low temperature part of the CL are estimated by simplified models and compared to the experimental results of the heat load measurements. The effect of the AC losses on the CL performance is discussed.

Exergy Analysis of Cascade Ethylene-Propane Rankine Cycle with Cold Energy Recovery of LNG

Cascade Rankine power cycle is suitable for cold recovery in a CCHP system which uses LNG as the primary energy. It has the advantages of low operating pressure and high energy efficiency. Exergy analysis of a typical cascade ethylene-propane Rankine power cycle is conducted. The results show that the exergy losses mainly occur in the low temperature part of the cycle. The exergy loss in the LNG-ethylene heat exchanger could reach about 46% of the total exergy loss. Therefore, the reduction of the exergy losses in the low temperature is important for the improvement of the performance of cascade power cycle.

Use BP Neural Network Set up the Corrosion Prediction Model of Low Temperature Parts of Atmospheric Pressure Device

In research of the low temperature parts of atmospheric pressure device, by using BP neural network, the connection of PH value, Cl-, H2S and Fe+2 was setup which can predict Fe+2 content accurately, and obtain the requirement accuracy, hence more accurate corrosion can be predicted and providing more suggests for corrosion protection.

Chemical energy storage using reversible solid/gas-reactions (CWS) – results of the research project

Within a four year joint research project the technical feasibility of thermo-chemical heat storage for solar thermal applications and the achievable advantages compared to conventional storage technologies have been investigated. The project, directed to applied research, was divided into a high temperature (> 300°C) and a low temperature part (< 100°C). In the low temperature part the main focus was on the development of a compact seasonal heat store for single or multifamily houses. Concerning high temperature applications thermo-chemical energy stores show high potential for improving energy efficiency of power plants and for recovery of process heat.The investigations have been carried out by a close cooperation of the Institute of Thermodynamics and Thermal Engineering (ITW) of the University of Stuttgart, specialised for solar thermal heating in the building sector and the Institute of Technical Thermodynamics (ITT) of the German Aerospace Center (DLR) as a specialist on solar thermal power plants.The project started in 2008 and runs until end of June 2012. This paper will focus on the low temperature part of the project, discuss important experiences and recent experimental results of the project and will report the very latest developments. Moreover the paper will summarise the important improvements achieved for temperature thermo- chemical heat storage. Finally recommendations for future activities will be given.

Corrosion–erosion test of SS316L grain boundary engineering material (GBEM) in lead bismuth flowing loop

To evaluate the lifetime of structural materials utilized in a spallation neutron source, corrosion tests in lead–bismuth eutectic (LBE) have been done at JAEA. Austenitic steels are preferable as the structural material for ADS. However, previous studies have revealed that austenitic steel SS316 shows severe corrosion–erosion in LBE because of LBE penetration through grain boundaries and separation of grains. So it was considered that GBE (grain-boundary engineered) materials may be effective to improve the corrosion resistance of austenitic steels in LBE. In this study, the results of corrosion tests on austenitic steel SS316L-BM (base metal) and SS316L-GBEM (grain-boundary-engineered material) under flowing LBE conditions will be reported. The corrosion test was performed using the JAEA lead–bismuth material corrosion loop (JLBL-1). The experimental conditions were as follows: The high and low temperature parts of the loop were 450°C and 350°C, respectively. The flow velocity at the test specimens was about 0.7m/s. The oxygen concentration in LBE was not controlled and was estimated to have been very low. After the 3600h of operation, macroscopic, SEM, and SIM observations and EDX analysis were carried out. The results showed that the corrosion depth and LBE penetration through the grain boundaries of the 316SS-GBEM were smaller than those of the 316SS-BM.

Systematic study of structural, transport, and magnetic properties of Ni52+xMn26−xAl22 (1 ≤ x ≤ 5) melt-spun ribbons

Structural, magnetic, and transport properties of Ni52+xMn26−xAl22 (1 ≤ x ≤ 5) melt-spun ribbons have been characterized by a variety of experimental techniques. As the composition changed from x = 1 to x = 5, the martensitic transition temperature T0 [ = (Ms + Af)/2] was found to increase from 277 K to 446 K which was attributed to an increase in the valence electron concentration e/a. In the martensitic state, all the samples demonstrate an anomalous semiconducting behavior of electrical resistivity ρ. This uncommon feature of the transport properties has been ascribed to the existence of a gap (Eg ∼ 0.1 eV) at the Fermi level. A crossover from semiconducting to metallic behavior of ρ observed in the martensitic state of Ni57Mn21Al22 is presumably related to a spin-density wave formation at the Neel temperature TN ≈ 300 K. Analysis of a low-temperature (T &amp;lt; 60 K) part of the resistivity curves and comprehensive magnetic measurements of a Ni57Mn21Al22 (x ≤ 5) sample provide grounds for the conclusion that the splitting of zero-field cooling and field cooling magnetization curves observed at low temperatures is due to a spin-glass state that is formed below the freezing temperature Tf.

Elastic properties and heat capacity of opal matrices and related 3D-nanocomposite materials

The elastic properties of opal matrices and related 3D-nanocomposites, as well as their heat capacity, have been investigated. The velocities and attenuation coefficients of longitudinal and transverse waves have been measured at room temperature. The Debye temperature has been calculated from the velocities of ultrasound. The temperature dependence of the heat capacity of the opal matrix has been studied. It has been shown that the low-temperature part of this dependence contains contributions proportional to the first and third powers of the temperature. It has been found that the Debye temperatures determined from the velocities of ultrasound and those obtained from the heat capacity differ significantly.

Influence of the Top Chamber Window Temperature on the STI Etch Process

During shallow trench isolation etching it was found that etch stop appears at the center of a 300 mm wafer as the temperature of the top quartz window of the etch chamber exceeds 85°C. We attributed the etch stop to redeposition of some low-volatile SiOxCly etch products. At low quartz window temperature part of the products are deposited on it, but as the window temperature rises well above the wafer temperature (which is constant at 60°C), the products primarily are deposited on the wafer causing the etch stop.

Ab initioprediction of low-temperature parts of the phase diagram for theMSb-M′Sb(M, M′=Al, Ga, or In) and AlSb-GaSb-InSb systems

The low-temperature parts of phase diagrams for the quasibinary and quasiternary semiconductors of ${\text{A}}^{\text{III}}{\text{B}}^{\text{V}}$ type in the Al/Ga/In/Sb system were calculated based on the ab initio calculations without employing any experimental information. Via global exploration of the enthalpy landscapes for many different compositions in these systems, candidates for crystalline solid-solution phases were identified. Next, their free enthalpies were computed on ab initio level and the respective low-temperature phase diagram was derived. The miscibility gap of the quasiternary system was calculated based not only on the data of the corresponding binaries but also on additional information about enthalpies of formation of quasiternary compositions.

CFD analysis of thermodynamic cycles in a pulse tube refrigerator

The objectives of this paper are to study the thermodynamic cycles in an inertance tube pulse tube refrigerator (ITPTR) by means of CFD method. The simulation results show that gas parcels working in different parts of ITPTR undergo different thermodynamic cycles. The net effects of those thermodynamic cycles are pumping heat from the low temperature part to the high temperature part of the system. The simulation results also show that under different frequencies of piston movement, the gas parcels working in the same part of the system will undergo the same type of thermodynamic cycles. The simulated thermal cycles are compared with those thermodynamic analysis results from a reference. Comparisons show that both CFD simulations and theoretical analysis predict the same type of thermal cycles at the same location. However, only CFD simulation can give the quantitative results, while the thermodynamic analysis is still remaining in quality.

Multi-step relaxations in the Glauber dynamics of a bond-diluted Ising model on a Bethe lattice

The Glauber dynamics of a bond-diluted Ising model on a Bethe lattice (a random graph with fixed connectivity) is investigated by an approximate theory which provides exact results for equilibrium properties. The time-dependent solutions of the dynamical system derived by this method are in good agreement with the results obtained by Monte Carlo simulations in almost all situations. Furthermore, the derived dynamical system exhibits a remarkable phenomenon that the magnetization shows multi-step relaxations at intermediate time scales in a low-temperature part of the Griffiths phase without bond percolation clusters.

Fe concentration dependent transport properties of LiI–AgI–B 2O 3 glass system

LiI–AgI–B 2O 3 glasses mixed with different concentrations of Fe 2O 3 (ranging from 0 to 2.0 mol%) were prepared. DC conductivity and dielectric properties over a range of temperature and also optical absorption and ESR spectral studies have been investigated. The optical absorption and ESR studies have indicated that iron ions do exist in both Fe 2+ and Fe 3+ states and the reduction ratio is the highest in the samples containing 0.9 mol% of Fe 2O 3. The analysis of the results of DC conductivity has indicated that T > θ D/2, the small polaron hopping model seems to be fit and the conduction is adiabatic in nature. These results further indicated that there is a mixed conduction (both ionic and electronic) and the ionic conduction seems to prevail over polaron hopping in the glasses containing Fe 2O 3 more than 0.9 mol% of Fe 2O 3. The variations of dielectric constant and loss with temperature have been analyzed on the basis of space charge polarization. The low temperature part of AC conductivity is explained based on the quantum mechanical tunneling model.

On the OSL curve shape and preheat treatment of electronic components from portable electronic devices

The shape of the OSL decay curve and the effect of longer time delays between accidental exposure and readout of alumina-rich electronic components from portable electronic devices are investigated. The OSL decay curve follows a hyperbolic decay function, which is interpreted as an approximation of several closely spaced or even a continuous distribution of single trap OSL decay functions. Longer time delays between exposure and readout lead to a rising dose vs. OSL integration time plot, when applying a low preheat. Supplementary TL investigations indicate a distribution in activation energies for the main dosimetric (190 °C) peak and that the lower temperature part could fade with a higher rate than the higher temperature part. Consequences for the applied preheat treatment prior to dose measurement are discussed.

Ab initio prediction of low-temperature phase diagrams in the Al–Ga–In–As system, MAs–M′As (M, M′ = Al, Ga or In) and AlAs–GaAs–InAs, via the global study of energy landscapes

Traditionally, the determination of phase diagrams has followed the inductive paradigm, where experimental observations provide the phase boundaries in more or less detail and phenomenological and semi-phenomenological models are employed to interpolate between the experimental data points, and by extrapolation to predict the shape of the phase boundaries in experimentally inaccessible regions. Over the past fifteen years, a new methodology has been developing, the aim of which is the prediction, determination and validation of phase diagrams in chemical systems without any recourse to experimental information. The foundation stone of this deductive approach is the global study of the energy landscape of the chemical system. In this study, we present an application of this approach to the prediction of the low-temperature part of the phase diagram of the quasi-ternary semiconductors (Al, Ga, In)As.

10.1007/s11451-008-1020-5

The effect of external fields (dc electric field, light illumination) on the memory effect of the incommensurate phase in the ferroelectric-semiconductor TlGaSe2 is studied using the measured dielectric constant. The results obtained are discussed. It is shown for the first time that the effect of external fields on the anomaly related to the memory effect in TlGaSe2 can be reduced to the following universal empirical rule: when a sample is held for many hours at a constant temperature T 0 in the temperature range of the incommensurate phase in a dc electric field, the deflection amplitude in the low-temperature part of the anomaly in the temperature dependence of the relative change in the dielectric constant Δɛ/ɛ increases (the deflection in the high-temperature part of the Δɛ/ɛ anomaly disappears) as compared to this segment in the dependence obtained during isothermal annealing of this sample at the same temperature without an electric field. The crystal remembers its thermal history at a temperature that is several kelvins higher than T 0. Light illumination increases the deflection amplitude in the high-temperature part of the Δɛ/ɛ(T) anomaly and shifts the temperature at which the crystal remembers its thermal history toward lower temperatures with respect to T 0.

Electrical conduction and other related properties of silver ion doped LiF–V 2O 5–P 2O 5 glass system

LiF–V 2O 5–P 2O 5 glasses mixed with different concentrations of Ag 2O (ranging from 0 to 1.5 mol%) were prepared. The DSC studies of these glasses indicated that the glass forming ability is the highest for the glass doped with 0.6 mol% of Ag 2O. D.C. conductivity and dielectric properties over a range of temperature and also optical absorption, ESR, IR and magnetic susceptibility studies have been investigated. The optical absorption, ESR and magnetic susceptibility studies have indicated that the reduction ratio of V 4+–V 5+ ions is higher in the samples containing higher concentrations of Ag 2O. The analysis of the results of d.c. conductivity has indicated that T> θ D/2, the small polaron hopping model seems to be fit and the conduction is adiabatic in nature. These results further indicated that there is a change over of conduction mechanism from electronic to ionic at about 0.6 mol% of Ag 2O. The variations of dielectric constant and loss with temperature have been explained on the basis of space charge polarization. The low temperature part of a.c. conductivity is explained based on the quantum mechanical tunneling model.

Spin-peierls transition in dimerized stacks of anion-radical salt (N-Me-2,5-di-Me-Pz)(TCNQ) 2, (Pz is pyrazine)

An anion-radical salt (ARS) (N-Me-2,5-di-Me-Pz)(TCNQ) 2, where Pz is pyrazine, was synthesized and its crystal structure was resolved. X-ray diffraction experiments on single crystals were performed. Heat capacity was measured in the temperature range from 2 to 300 K. Magnetisation and magnetic susceptibility were measured in the temperature range from 2 to 300 K and the low-temperature part was measured in magnetic fields from 5 mT to 5 T. The experimental results were explained in terms of dimerized Heisenberg spin 1 2 chain model. Numerical calculations were performed and compared with experimental data.

Ag concentration dependent transport properties of LiF–MoO3–P2O5 glasses

Abstract LiF–MoO3–P2O5 glasses mixed with different concentrations of Ag2O (ranging from 0 to 1.0 mol%) was prepared. D.C. conductivity and dielectric properties over a range of temperature have been investigated. The analysis of the results of d.c. conductivity has indicated that T>θD/2, the small polaron hoping model seems to be fit and the conduction is adiabatic in nature. These results further indicated that there is a change over of conduction mechanism from electronic to ionic at about 0.4 mol% of Ag2O. The low temperature part of a.c. conductivity is explained based on quantum mechanical tunneling model. The quantitative analysis of these results is further extended with the aid of the data on optical absorption, ESR and IR spectral studies.