Effects Of Thermal Variations Research Articles

Thermal regime of permafrost at Varandey Settlement along the Barents Sea Coast, North West Arctic Russia

Soil temperature variation is one of the governing factors of mechanical properties of frozen soils and has a large effect on the stability of soil masses in regions affected by permafrost. The understanding of the thermal regime is critical for planning, designing, constructing, and maintaining infrastructure needed to sustain communities and/or industries in these regions. Detailed studies on the effects of thermal variations based on field data measured in permafrost are limited due to the high cost and high risk associated with field investigations in these remote areas. This study will contribute to bridge the current knowledge gap through an investigation of the thermal regime in permafrost at Pesyakov Island in the Varandey settlement along the Barents Sea coast, in northwest Arctic Russia. Samples were collected and thermistor string was installed at a series of 6 boreholes along a 500 m transect. The transect crosses a coastal barrier island from the beach margin through a dune belt to the laida zone. Continuous measurement of the ground temperature over a period of two years reveals a strong correlation between the surface conditions (air temperature, vegetation, snowfall) and the variation of soil temperature above the permafrost. Numerical modelling of the transect, calibrated with the measured soil temperature, shows important features of the thermal profile, including the existence of frozen soil lenses within unfrozen soil masses and vice versa.

Effect of Thermal Variations on Some Nanostructural and Optical Characterizations of Element Oxides Compound (Y2O3/Fe2O3) Prepared Using Laser Ablation

In this study have been synthesis nano oxide composites (Y2O3/Fe2O3) are prepared chemically and affected by Laser Neodymium –YAG ablation by energy (200 mJ), and number of pulses (200 pulses) at two different temperatures (4°C and 65°C) in distilled water. The structural, morphological, and optical properties of synthesized oxides were studied, (XRD) pattern showed that the oxides were highly crystallized in both hot and cold cases with variations in intensity values as they increased in the cold state than in the hot with additional peaks of intermediate compounds [Y(OH)3; PLA], monoclinic and cubic and the two phases (ε-Fe2O3; β-Fe2O3).The (AFM) test indicate the roughness values that increased in the cold state than in the hot state. The results of the (SEM) showed a close approximation in the hot & cold cases in cubic forms, conical sticks (like nanorods, whiskers) as a result of recrystallization. noting that the value of absorbance increased in the cold than in the case of hot. The sample was manufactured in a solar cell, by obtaining a I-V curve under the dark and its illumination. The results showed a significant change in the performance of the solar cell at the values of (Im=42 mA; Vm=0.21 V), when the Iron oxide overlaps with the yttrium oxide with the best conversion efficiency of 7%.

Effects of Temperature in CNTFET-Based Design of Analog Circuits

In this paper we simulate the effects of temperature in CNTFET- based design of analog circuits, enhancing a semi-empirical model of CNTFET, already proposed by us, in which the temperature variation in the drain current equation and in energy bandgap is considered in order to estimate the change in static and dynamic conditions. A short description of the model used to reproduce the I-V characteristics of the device, at different temperatures, is given. Then the effects of thermal variations in the design of a phase shift oscillator, a cascode current sink mirror and an operational trans-conductance amplifier, are illustrated and widely discussed.

Concrete hydration temperatures for the design of crack-width reinforcement in concrete water-retaining structures – design values versus in-situ values

Cracking in concrete can occur due to temperature changes at early ages and exposure to ambient temperature changes in the long term. Design codes and standards allow engineers to design for cracking by quantifying the effects of thermal variations into outputs such as limiting crack widths and reinforcement configurations. Design values given in these codes are however not fully understood by many users, may not be representative of recent developments in concrete materials technology and can potentially result in over-conservative designs. In this paper, concrete hydration temperatures were measured on site using a Thermocouple Data Logger and compared to values used in the project-specific design with the intention of providing a basis on which a database of temperatures representative of mixes commonly used in the South African industry may be compiled. Findings revealed that measured temperature values were around 30 – 50% lower than those given in design codes. Among the reasons identified for this is the fact that readily used design codes for crack-width design of water-retaining concrete structures in South Africa were compiled with data obtained from the use of 42.5 N cements, which may well have been quite different from the now more modern and readily available 52.5 N cements. Furthermore, design codes focus extensively on factors like binder content, binder type and formwork type, while the effects of other factors such as coarse aggregate type, coarse aggregate nominal size and construction sequence (which also play a significant role) are not quantified in the selection process of temperature values. Recommendations for further studies are made which aim to incorporate a wider variety of factors that affect development of thermal properties of concrete. This can allow members of the project team (engineer, contractor) to act during the relevant stages of design/construction of a project to mitigate thermal effects that can incur unwanted cracking.

Performance analysis of junctionless double gate VeSFET considering the effects of thermal variation – An explicit 2D analytical model

The purpose of this paper is to explore junctionless double gate vertical slit field effect transistor (JLDG VeSFET) with reduced short channel effects and to develop an analytical threshold voltage model for the device considering the impact of thermal variations for the very first time. The model has been derived by solving 2D Poisson’s equation and the effects of variation in temperature on various electrical parameters of the device such as Rout, drain current, mobility, subthreshold slope and DIBL has been studied and described in the paper. The model provides a deep physical insight of the device behavior and is also very helpful in contributing to the design space exploration for JLDG VeSFET. The proposed model is verified with simulative analysis at different radii of the device and it has been observed that there is a good agreement between the analytical model and simulation results.

Thermal variation and pressure compensated emitters

A number of factors may contribute to the non-uniformity of an unclogged drip irrigation (DI) system. It is understood that DI emitters respond to the thermal changes in the environment resulting in variable flow-rates. This study investigates the effect of thermal variation (air and water) on the performance of inline pressure compensated (PC) emitters. In order for this, three different types of emitters were subjected to a wide range of continuous heating (eight stages) and cooling (eight stages) cycles inside an enclosed environmental chamber. Both the air and the irrigation water temperature was carefully maintained throughout the experiment. The results showed a general tendency of declining emitter flows during the heating cycles followed by a partial recovery during the cooling cycles. As a result, the variation in flow-rates formed a one-cycle hysteresis loop for all emitter types. Changes in the viscosity of water was shown to have little or no effect on the overall performance of PC emitters. The looped return of emitter flows due to the continuous heating and cooling treatments was explained by the elastic changes in pressure membrane. The results of this study also revealed a transitional temperature range (15–18°C) during which the flow-rate of PC emitters was found to be stable. Hence, this range was taken as a reference temperature in establishing the characteristics of emitter samples. Conducting hydraulic testing of emitters at this range showed promising results compared to the existing recommendation of 23±3°C by the ISO. The overall experience of the study suggests that the potential hydraulic performance of PC emitters can only be achieved at lower temperature levels.

University students' cognitive performance under temperature cycles induced by direct load control events.

As one of the most common strategies for managing peak electricity demand, direct load control (DLC) of air-conditioners involves cycling the compressors on and off at predetermined intervals. In university lecture theaters, the implementation of DLC induces temperature cycles which might compromise university students' learning performance. In these experiments, university students' learning performance, represented by four cognitive skills of memory, concentration, reasoning, and planning, was closely monitored under DLC-induced temperature cycles and control conditions simulated in a climate chamber. In Experiment 1 with a cooling set point temperature of 22°C, subjects' cognitive performance was relatively stable or even slightly promoted by the mild heat intensity and short heat exposure resulting from temperature cycles; in Experiment 2 with a cooling set point of 24°C, subjects' reasoning and planning performance observed a trend of decline at the higher heat intensity and longer heat exposure. Results confirm that simpler cognitive tasks are less susceptible to temperature effects than more complex tasks; the effect of thermal variations on cognitive performance follows an extended-U relationship with performance being relatively stable across a range of temperatures. DLC appears to be feasible in university lecture theaters if DLC algorithms are implemented judiciously.

Flexural response of thermoelastic thin beam resonators due to thermal and mechanical loads

The flexural vibrations of homogeneous, transversely isotropic, generalized (non-Fourier) thermoelastic simply-supported thin beam resonators due to thermal and mechanical loads have been investigated under Euler–Bernoulli hypothesis. The model equation governing the transverse vibrations has been solved by using double Laplace transform technique (LTT) with respect to space and time. A mesh-less computational method, Adomian decomposition method (ADM), has also been employed to solve the model equation in the space domain for the comparison purpose. The inversion of the transformed solution has been carried out by using Durbin׳s technique in order to obtain the results in physical time domain. The natural frequencies and the corresponding mode shapes of the beam have been computed. The effects of thermal variations and other parameters on the deflection and temperature profiles of the thin beam have been studied. The effect of thermal relaxation time (second sound) on the vibration characteristics of beam has also been observed. The results computed by using LTT and ADM have been compared and are found to be in good agreement. It is noticed that ADM is an accurate, computer friendly and provides a unified, systematic powerful mathematical tool for solving the static and dynamic vibration problems for the considered beams.

A physical simulation study of the effect of thermal variations on the secondary dendrite arm spacing in a Ni-based superalloy

The effect of thermal variations on the secondary dendrite arm spacing (SDAS) in a MAR-M247 Ni-based superalloy has been studied by a novel method based on a physical simulation of melting/solidification experiments with a constant cooling rate and variable temperature gradient. The method proved to be effective as it yielded a spread of microstructures corresponding to a range of well-controlled solidification rates in a single melting/solidification experiment. In addition, it has been demonstrated that SDAS is better related to the solidification rate than to the cooling rate in cases when significant variations of thermal parameters during the solidification process occur.

Buffer Sizing and Polarity Assignment in Clock Tree Synthesis for Power/Ground Noise Minimization

In synchronous systems, clock tree causes high peak current at clock edges, increasing power/ground noise significantly, if the clock tree is not carefully designed. This paper addresses the problem of minimizing power/ground noise in the clock tree synthesis. Contrary to the previous approaches which only make use of assigning polarities to clock buffers to reduce power/ground noise, our approach solves a new problem of simultaneous consideration of assigning polarities to clock buffers and determining buffer sizes to fully exploit the effects of buffer sizing together with polarity assignment on the minimization of power/ground noise while satisfying the clock skew constraint. Specifically, the contributions of this paper are: 1) precisely estimating peak currents by clock buffers and reflecting them on the power/ground noise minimization; 2) proposing a pseudo-polynomial time optimal algorithm based on dynamic programming for solving the integrated problem, together with the proof of intractability of the problem; 3) devising a systematic design flow framework for reducing the power/ground noise over the entire chip; and 4) considering the effect of thermal variation on the clock skew bound and the noise minimization.

Latitudinal variation in the aerial/aquatic ratio of oxygen consumption of a supratidal high rocky‐shore crab

AbstractThe colonisation of the terrestrial environment by crustaceans is more apparent in tropical latitudes because of the high diversity of semi‐terrestrial and terrestrial crabs. However, in temperate regions there are also great numbers of crustaceans that inhabit ecological niches at the water–air interface. Grapsidae crabs (Decopoda) are especially important in studies of water‐to‐land transition as the family contains species occupying the intertidal and adjacent regions. A way to evaluate the ability of intertidal invertebrates to breathe air is to measure the aerial/aquatic oxygen consumption ratio. The objective of this study was to test the effect of thermal variation on the aquatic and aerial metabolism. We selected as study model the decopoda crab Cyclograpsus cinereus Dana and utilised five populations of the species spread over 2000 km along the Chilean coast. To determine the compensation capacity in respiration with respect to latitude, we evaluated metabolic rate at the same temperature in a common garden design in the laboratory, to examine the extent to which variation in crab physiology is environmentally determined. Whereas in our study, mb (body mass) varied significantly with latitude, the difference in mass‐independent metabolism both in air and water persisted, indicating that observed differences in MR (Metabolic Rate) were not an effect of differences in body size. We demonstrated that C. cinereus is able to breath oxygen from air and water as expected for an amphibious crab. Almost all the studied populations of C. cinereus show a aerial/aquatic metabolism ratio near 1. The pattern found indicates an increase in metabolic rate, both aerial and aquatic, in low latitudes and therefore does not support the latitudinal compensation hypothesis for temperate habitats. Finally, these kinds of studies are required to make the necessary link between ecological physiology and macroecology and to help develop a global understanding of organismal function in marine systems.

Anisothermal Anodic Bonding: A Method to Control Global Curvature and Residual Stress

The manipulation and characterization of residual stress and wafer curvature in anodically bonded structures is useful in improving the reliability of devices built on silicon on glass substrates. Conventional anodic bonding procedures lead to uncontrolled curvature of the bonded substrates as a result of locked-in residual stresses due to thermal expansion mismatch between silicon and Pyrex. A thermomechanical finite element model is used here to elucidate the effect of thermal variations in wafer temperature during anodic bonding. The results inform the development of an anisothermal recipe to control the resulting residual stresses and post bond wafer curvature and to understand the effects of process control on residual curvature. The model suggests that wafer curvature in anodically bonded substrates can be nearly eliminated by reducing the silicon bonding temperature slightly relative to the Pyrex temperature. A simple quantitative model to predict this effect shows promising agreement with experiments.

Effect of thermal variations on the Knudsen forces in the transitional regime

When objects are maintained at different temperatures and separated by distances of the order of the mean free path of the surrounding host gas molecules, gas kinetic forces called Knudsen forces may be involved. The understanding of this effect may result in some improvements in microelectromechanical devices and measurement systems. We present the thermal dependence of these forces in the transitional regime for different gases. In this mode, the Knudsen effect can be significant and, therefore, become a problem in microscale devices. For this study, a silicon microcantilever, mounted close to a substrate, is used and changes in temperature are observed by measuring bending of the microcantilever.

Heating and Modeling Effects in Tethered Aerocapture Missions

The influence of thermomechanical and tether flexibility effects on tethered aerocapture missions is examined. The focus of these missions is capturing a system, consisting of an orbiter and tether-connected probe, from a hyperbolic to an elliptical orbit via aerodynamic braking. Two temperature-dependent dynamic models of the tether are included: a two-dimensional, straight, massive, extensible tether model derived via Lagrange's equations and a three-dimensional lumped mass model derived via Kane's equations. The dynamics of the aerocapture maneuver are shown to be affected by tether extensibility due to the change in system rotational inertia. If not properly accounted for, this can result in non-capture. The effect of thermal variations on the dynamics of the aerocapture maneuver is shown to be influenced strongly by the thermal properties of the tether material. As a consequence, these thermal variations can decrease the viability of certain proposed tethered aerocapture missions and should be accounted for during design.

Effect of Thermal Variations on Bond Strength of Fusion-Bonded Epoxy-Coated Bars

Abstract Fusion-bonded epoxy coating is extensively used to enhance the corrosion resistance of reinforcing steel. The bond strength between these bars and the concrete is expected to be less than that of the uncoated bars and it may be further impaired due to prolonged exposure to thermal variations. This investigation was conducted to evaluate the effect of thermal variations, simulating the changes in the night to day temperature, on the bond strength of fusion-bonded epoxy-coated steel reinforcement. The pull-out specimens, prepared using bars of two different sizes and two coating thickness, were exposed to thermal cycling. The critical and ultimate bond strength of the fusion-bonded epoxy-coated bars were compared with that of the uncoated bars. The results indicated a reduction in the critical bond strength between concrete and the fusion-bonded coated bars. Furthermore, the difference between the critical bond strength in the coated and uncoated bars decreased with increasing thermal cycles, indicating that thermal variation has a greater effect on bond strength than the coating thickness.

Effect of acclimatization temperatures on incorporation of amino acids into proteins of abdominal muscle from the shrimp Palaemon serratus

The effect of thermal acclimatization on the incorporation of [ 3H]- l-leucine into muscular acid-soluble amino acids, soluble proteins and into the lactate dehydrogenase was studied in the shrimp Palaemon serratus As far as protein synthesis is concerned, a period of time of 10 to 15 days is required for the achievement of the process. During acclimatization to 10° or 20° three periods can be distinguished. During the first 3–4 days the temperature increment exert a direct decreasing or increasing effect on the protein synthesis. The system then tends to reach a new equilibrium respectively below or above the initial level: the synthesis mechanisms were able to partially compensate the effect of thermal variations. The synthesis of LDH follows the general pattern of incorporation of the labelled precursor into the macromolecules

Checking in elastic range of the thrusting monumental structures

The subject is the research of the collapse multiplier of a masonry arch operating even in elastic range. The approach permits the knowledge of the stresses and the failures under the exercise living loads, as well as in the proximity collapse. The effect of thermal variations and seismic loads is emphasized.