Slow Temperature Variations Research Articles

Thermal characterization of polyethylene glycol 600 in liquid and solid phase and across the phase transition

The polyethylene glycol (PEG) is characterized by experimental means in both solid and liquid phase. Main thermal properties inherent to the phase transition are also provided. More specifically, we focus on PEG 600, whose average molar mass is 600 g mol−1 and melting temperature transition is around 283–298 K. The phase change does not occur at a given temperature but rather over a range of temperature, highlighting the complexity of the material. Several methodologies have been developed and calibrated in order to obtain, in both phases, the density and the thermal conductivity. A temperature dependence fit is proposed for the density in liquid phase. The relative density variation from the liquid to solid phase is significant as it can reach about 35%, meaning a quite large volume shrinkage. Differential Scanning Calorimetry (DSC) has been used for measuring the heat capacity of solid and liquid phase and the effective heat capacity at the transition states. The latent heat of fusion and solidification converge to a value of around 128 kJ kg−1. Undercooling effects are mitigated by performing DSC with slow temperature variation rates. Lastly, we have also observed several exothermic peaks during the solidification process that are related to structural reorganizations of the material.

Real-time Estimation of Temperature Time Derivative in Inertial Measurement Unit by Finite-Impulse-Response Exponential Regression on Updates.

We present a filtering technique that allows estimating the time derivative of slowly changing temperature measured via quantized sensor output in real time. Due to quantization, the output may appear constant for several minutes in a row with the temperature actually changing over time. Another issue is that measurement errors do not represent any kind of white noise. Being typically the case in high-grade inertial navigation systems, these phenomena amid slow variations of temperature prevent any kind of straightforward assessment of its time derivative, which is required for compensating hysteresis-like thermal effects in inertial sensors. The method is based on a short-term temperature prediction represented by an exponentially decaying function, and on the finite-impulse-response Kalman filtering in its numerically stable square-root form, employed for estimating model parameters in real time. Instead of using all of the measurements, the estimation involves only those received when quantized sensor output is updated. We compare the technique against both an ordinary averaging numerical differentiator and a conventional Kalman filter, over a set of real samples recorded from the inertial unit.

Thermodynamic Geometry of Microscopic Heat Engines.

We develop a general framework to describe the thermodynamics of microscopic heat engines driven by arbitrary periodic temperature variations and modulations of a mechanical control parameter. Within the slow-driving regime, our approach leads to a universal trade-off relation between efficiency and power, which follows solely from geometric arguments and holds for any thermodynamically consistent microdynamics. Focusing on Lindblad dynamics, we derive a second bound showing that coherence as a genuine quantum effect inevitably reduces the performance of slow engine cycles regardless of the driving amplitudes. To show how our theory can be applied in practice, we work out a specific example, which lies within the range of current solid-state technologies.

Development of a SiPM-based CsI(Tl) spectrometer with gain stabilization designs for rapid temperature variations

Abstract A spectrometer employing a silicon photomultiplier (SiPM) based scintillation detector has spectrum drift issues under temperature variations. Although some temperature-dependent compensation methods are reported, spectrum distortions under rapid temperature fluctuations have received little attention. We have developed a SiPM-based CsI(Tl) spectrometer and proposed gain stabilization designs to settle this problem. A temperature sensor was coupled to the SiPM in the detector and wrapped with a thermal insulation foam material to acquire the temperature of the SiPM. Meanwhile, a temperature correction module was applied in the field-programmable gate array (FPGA) within a custom multichannel analyzer (MCA). The effectiveness of the temperature correction module in the FPGA and a specialized detector design were studied and verified under slow and rapid temperature variations. The results prove that the spectrum drifts of the SiPM-based CsI(Tl) spectrometer under rapid temperature variations can be significantly constrained with the proposed gain stabilization designs.

A Phenomenological Model of the Screen-Printed, Silver Paste Contact to Si Substrate

A phenomenological model of screen-printed silver contact to an n-doped, p-type multi-crystalline Si wafer, based on extensive electrical, morphological, and compositional evaluations, has been developed. Rapid and quasi steady state heating configurations over broad (150–925°C) temperature ranges were investigated. Conventional rapid thermal annealing (RTA) with a conveyor belt was used for a rapid and custom-designed three-zone quartz tube furnace (QTF) for slow temperature variations. Lowest contact resistivity at 0.15 mΩ cm2 was observed in RTA horizontal configuration which was 25 times smaller than the same in QTF. RTA contact resistivity measurements revealed a minimum at 870°C while linear reduction in contact resistance was observed for the QTF configuration. The silver/silicon contact was based on three physical mechanisms: (1) migration of Si into glass and silver regions of the paste, (2) intermixing of silver and silicon (nano- and micrometer scale), and (3) epitaxial growth of silver/silicon crystallites. Experimental evidence of silicon migration was supported through extensive phosphorous concentration measurements from silicon and silver/silicon regions. The glass film with a colloidal distribution of randomly-distributed silver/silicon crystallites leads to lower contact resistance. Rapid temperature fluctuations facilitate development of Ag/Si crystallites. The higher contact resistance in quasi steady state thermal configuration was attributed to glass films with reduced density of Ag/Si crystallites. This disadvantage may be eliminated through post-contact, forming gas annealing at lower temperatures.

Software-defined reconfigurable VCSEL-based transmission.

We propose and demonstrate a programmable and self-adaptive VCSEL-based transponder for short-reach applications that is easily extensible up to access and metro scenarios. The transponder presents a monitoring system that feeds the transponder controller in order to maintain the proper transmission performance. The emerging NETCONF protocol including the YANG model controls and manages the transponder. NETCONF messages are reported for two reference scenarios - uncooled and cooled systems - together with performance at varying environment conditions. For the uncooled scenario heating processes on the board are emulated with various dynamics, the effect on the performance of a 25 Gbps WDM channel is checked through optical power monitoring and the control plane reacts so as to optimize the performance by suitably controlling the bias current. For slow temperature variations the system is able to avoid service outage whereas for variations faster than 1.3 °C/s outage occurs and corresponding notifications are opportunely triggered. For the cooled scenario, an optical power loss is emulated with consequent service outage, leading to a reconfiguration of the transponder data rate from 25 to 10 Gbps, so as to recover successful transmission.

Compensation of thermal strain induced polarization nonreciprocity in dual-polarization fiber optic gyroscope.

Dual-polarization interferometric fiber optic gyroscope (IFOG) is a novel scheme in which the polarization nonreciprocal (PN) phase error of the two orthogonal polarizations can be optically compensated. In this work, we investigate the effective of PN phase error compensation under varying temperature. It is proved that, the thermally induced strain deforms the fiber, and results in perturbations on the birefringence and polarization cross coupling which degrades the IFOG's stability. A wave propagation model and analytical expressions of PN phase error are derived by using coupled-wave equation and Jones matrix. We theoretically and experimentally verify that, although the single-mode (SM) and polarization-maintaining (PM) fiber coils behave different owing to their intrinsic properties of wave propagation, the thermal strain induced PN phase error can still be compensated under slow and adiabatic temperature variations. This could be a promising feature to overcome the temperature fragility of IFOG.

Dynamic Switching of Helical Microgel Ribbons.

We report on a microscopic poly(N-isopropylacrylamide) hydrogel ribbon, coated by a thin gold layer, that shows helical coiling. Confined swelling and shrinkage of the hydrogel below and above its characteristic volume phase transition leads to a temperature actuated reversal of the sense of the helix. The extent and the shape of the winding are controlled by the dimensions and mechanical properties of the bilayer ribbon. We focus on a cylindrical helix geometry and monitor the morphing under equilibrium and nonequilibrium conditions, that is, when the temperature changes faster than the volume (millisecond range). For slow temperature variations, the water release and uptake follow the equilibrium transition trajectory determined by the time needed for the diffusion of water into and out of the microscopic gel. Much faster variations of the temperature are accomplished by internal heating of embedded gold nanorods by IR-light irradiation. This causes elastic stresses that strongly affect the motions. This method enables well-reproducible deviations from the equilibrium transition path and allows us to control rather precisely the spatiotemporal transformation in a cyclic repetitive process. Actuation and response are sensitive to small variations of temperature and composition of the aqueous sol in which the gel is immersed. The principle as described may be used to detect specific analytes that bind either to the surface of the gold layer or within the gel and can modify the interaction between the water and the gel. The reported nonequilibrium morphing implies that the system dissipates energy and may also be able to perform work as required for a microscopic motor.

Annealing Effects on Magnetic Properties of Co/Cu Multilayered Nanowires

Co/Cu nanowires were fabricated by electrodeposition using anodic alumina templates, with 100nm diameter nanopores. The thickness of Co and Cu layer was about 45nm and 5nm, respectively. The magnetic properties have been studied before and after simple and magnetic field annealing. For simple annealing an increase in coercivity and squareness along easy axis of magnetization has been observed. For comparison, the magnetic field annealing effect on magnetic properties has been studied by using fast and slow temperature variations. The corresponding change in saturation magnetization, coercivity, remanent squareness, and the shape of hysteresis loops has been investigated.

Magnetic Field Annealing Effects on Magnetic Properties of Electrodeposited Co/Cu Multilayered Nanowires

Co/Cu nanowires were fabricated by electrodeposition using anodic alumina templates, with 100 nm diameter nanopores. The thickness of Co and Cu layer was about 45 and 5 nm, respectively. The magnetic properties of multilayered nanowires have been studied before and after simple and magnetic field (MF) annealing. For simple annealing, an increase in coercivity and squareness (SQ) along easy axis of magnetization has been observed. Magnetic field annealing has been done under MF of 1 T. For comparison, the MF annealing effect on magnetic properties has been studied using fast and slow temperature variations. The corresponding change in saturation magnetization, coercivity, remanent SQ, and the shape of hysteresis loops has been investigated. The coercivity Hc decreases in case of MF annealing with fast temperature variation, whereas it increases in case of MF annealing with slow temperature variation, as compared with as deposited. The enhanced magnetic anisotropy has been observed by slow MF annealing (SMFA), whereas magnetic anisotropy attenuated a little by fast MF annealing. Annealing without MF has also shown the enhanced magnetic anisotropy. SMFA and annealing without MF is likely to improve the interface of Co/Cu.

Thermal energy conversion by coupled shape memory and piezoelectric effects

This work gives experimental evidence of a promising method of thermal-to-electric energy conversion by coupling shape memory effect (SME) and direct piezoelectric effect (DPE) for harvesting quasi-static ambient temperature variations. Two original prototypes of thermal energy harvesters have been fabricated and tested experimentally. The first is a hybrid laminated composite consisting of TiNiCu shape memory alloy (SMA) and macro fiber composite piezoelectric. This composite comprises 0.1 cm3 of active materials and harvests 75 µJ of energy for each temperature variation of 60 °C. The second prototype is a SME/DPE ‘machine’ which uses the thermally induced linear strains of the SMA to bend a bulk PZT ceramic plate through a specially designed mechanical structure. The SME/DPE ‘machine’ with 0.2 cm3 of active material harvests 90 µJ over a temperature increase of 35 °C (60 µJ when cooling). In contrast to pyroelectric materials, such harvesters are also compatible with both small and slow temperature variations.

Three-dimensional numerical modeling of vertical ground heat exchangers: Domain decomposition and state model reduction

Modeling of vertical ground heat exchangers is relatively complex because of the three-dimensional transient nature of the problem inside the borehole and in the surrounding ground. Furthermore, the system is characterized by various time scales with rapid changes inside the borehole and slow variations of ground temperature far away from the borehole. Most existing numerical models require important computational resources to adequately represent the short time-scale heat transfer occurring in the immediate vicinity of the borehole, which warrant their use for annual energy simulations. In this article, a three-dimensional reduced model (3D-RM), based on domain decomposition and state model reduction techniques, is proposed to reduce computation time and computer memory. Domain decomposition is used to sub-structure the domain and to vary the time-step values in each sub-domain, and state model reduction is applied to each resulting sub-zone. A comparison with a complete three-dimensional dynamic model indicates that the proposed 3D-RM model reduces computational time by a factor of about 30 without loss of accuracy. A comparison with experimental results shows that the relatively fast transients occurring in the borehole are well predicted by the 3D-RM model not only for the outlet fluid temperature but also for the tube wall temperatures at different depths.

About climate-seismicity coupling from correlation analysis

Abstract. We have analyzed together the slow climate temperature variations in the near-equatorial Pacific Ocean area (SSTOI indices) and crustal seismic activity in the same region during 1973–2008 time period using correlation analysis and found similarity in seismic and ENSO periodicities (the latter with time lag about 1.5 years). Trends of the processes are also similar showing about 2 times increase in average seismic energy release during the whole period of analysis and conventional 0.1 °C/(10 years) increase in SSTOI index anomalies. Our major conclusion is on real credibility of climate-seismicity coupling. It is rather probable that at least partially climate ENSO oscillations and temperature anomaly trends are induced by similar variation in seismicity.

Semi-analytical calculation of the impedance of a differential sensor for eddy current non-destructive testing

In this contribution, we aim at the modelling of the impedance of a differential sensor in eddy-current non-destructive testing. This mode of control is very common in the detection of abrupt geometrical and electromagnetic variations, disturbances generated by slow variations of dimensions and temperature being in particular not observed. We develop a direct semi-analytical model of a voltage-excited system. The formulation is based upon the use of coupled electric circuits. It provides a particular form of the differential impedance, which clarifies the role of the electromagnetic and geometric characteristics. This form of impedance will allow the investigation of non-destructive testing by means of differential sensors and will facilitate the development of real-time inversion procedures. The model is validated by results published in the literature. We exploit it in order to study various electric and geometrical parameters of the control system.

Climate change and the effect of temperature backlashes causing frost damage in Picea abies

In boreal and nemoboreal forests, tree frost hardiness is modified in reaction to cues from day length and temperature. The dehardening processes in Norway spruce, Picea abies, could be estimated to start when the daily mean temperature is above 5 °C for 5 days. Bud burst will occur approximately after 120–170 degree-days above 5 °C, dependent on genetic differences among provenances. A reduced cold hardiness level during autumn and spring and an advanced onset of bud burst are expected impacts of projected future global warming. The aim of this study was to test if this will increase the risk for frost damage caused by temperature backlashes. This was tested for Sweden by comparing output from the Hadley Centre regional climate model, HadRM3H, for the period 1961–1990 with future IPCC scenario SRES A2 and B2 for 2070–2099. Different indices for calculating the susceptibility to frost damage were used to assess changes in frost damage risk. The indices were based on: (1) the start of dehardening; (2) the severity of the temperature backlash; (3) the timing of bud burst; and (4) the cold hardiness level. The start of dehardening and bud burst were calculated to occur earlier all over the country, which is in line with the overall warming in both climate change scenarios. The frequency of temperature backlashes that may cause frost damage was calculated to increase in the southern part, an effect that became gradually less pronounced towards the north. The different timing of the onset of dehardening mainly caused this systematic latitudinal pattern. In the south, it occurs early in the year when the seasonal temperature progression is slow and large temperature variations occur. In the north, dehardening will occur closer to the spring equinox when the temperature progression is faster.

Lagrangian effective material constants for the modeling of thermal behavior of acoustic waves in piezoelectric crystals. I. Theory.

After some necessary recalls on the nonlinear theory of thermoelectroelasticity in piezoelectric crystals, asserting the need of constitutive equations which derive from a rotationally invariant energy function, this paper presents the governing equations for a small vibration superimposed on a bias originated by a slow and homogeneous temperature variation from a well-defined reference state. Thereafter, the authors define the effective coefficients appearing in the linearized incremental dynamic balance equations for linear momentum and electrical charge in Lagrange configuration, not omitting associated boundary conditions. The main features of these coefficients are discussed and explicit relations with more conventionally defined coefficients are given. Determination of numerical values of the proposed effective coefficients and examples of their use in the higher order modeling of static frequency-temperature characteristics of either bulk acoustic wave or surface acoustic wave devices are given in a companion paper.

Lagrangian effective material constants for the modeling of thermal behavior of acoustic waves in piezoelectric crystals. II. Applications and numerical values for quartz.

This paper presents a set of numerical values of temperature derivatives of Lagrangian effective elastic coefficients suitable for the modeling of small vibrations in quartz devices submitted to slow and homogeneous temperature variations. After a short description of the proper writing of vibration problems in practical applications with the help of this kind of coefficient, we determine the proposed set of numerical values from the frequency-temperature characteristics of an heterogeneous set of bulk and surface acoustic wave devices.

Influence of thermal and osmotic stresses on the viability of the yeast Saccharomyces cerevisiae

This work studies the effect of thermal and dehydration kinetics on the viability of Saccharomyces cerevisiae. The influence of the rate of temperature ( T) and osmotic pressure ( Π) increases are first investigated. Results showed that yeast viability is preserved by slow variations of temperature or osmotic pressure in a precise range of T or Π. The influence of a previous thermal stress on the resistance to a hyperosmotic stress is also studied. Temperatures equal to or lower than 10°C allowed the preservation of viability after an osmotic stress whereas temperatures above 10°C did not preserve yeast survival.

Differential sensitivity analysis and multi-variant simulation of formation pressure and temperature in heterogeneous media

Methodology of differential sensitivity analysis and sensitivity-based aggregate simulation for formation pressure, temperature and fluid flow is developed here. It is aimed at estimation of variations of formation pressure, temperature and velocity field for fluid flow due to variations in the properties of the medium and fluids in the pores. It includes the use of the so-called “sensitivity functions” defined as partial derivatives of the formation pressure and temperature with respect to parameters of the rock and fluids in the pores. It is shown that the sensitivity functions are defined by the same system of equations as formation pressure and temperature fields with the right-hand side of the equations dependent on the type of sensitivity function.There are several important applications of the differential sensitivity analysis and sensitivity functions:(1)Sensitivity functions allow to estimate, under certain conditions, the magnitude of variation of formation pressure and temperature fields1(2)Using sensitivity function-based technique, it is possible to partially decouple the system of equations for formation pressure and temperature fields under conditions of slow variations of temperature or pressure in time.(3)Differential sensitivity analysis may serve as a basis for calculation of multiple versions (aggregate simulation) of formation pressure and temperature fields due to various changes in the parameters of the medium and pore fluids.

A test of water vapor radiometer‐based troposphere calibration using very long baseline interferometry observations on a 21‐km baseline

Simultaneous very long baseline interferometry (VLBI) and water vapor radiometer (WVR) measurements on a 21‐km baseline showed that calibration by WVRs removed a significant fraction of the effect of tropospheric delay fluctuations for these experiments. From comparison of the residual delay variations within scans and between scans, the total tropospheric contribution to the delay residuals for each of the three 5–20 hour sessions was estimated as 1%, 17%, and 10%, with the first value being very uncertain. The observed improvement in rms residual delay from WVR calibration during these three sessions was 4%, 16%, and 2%, respectively. The improvement is consistent with the estimated 2–3 mm path delay precision of current WVRs. The VLBI measurements of natural radio sources were conducted in April and May 1993 at Goldstone, California. Dual‐frequency (2.3 and 8.4 GHz) observations were employed to remove the effects of charged particles from the data. Measurements with copointed WVRs, located within 50 m of the axis of each antenna, were performed to test the ability of the WVRs to calibrate line‐of‐sight path delays. Factors which made WVR performance assessment difficult included the facts that (1) the level of tropospheric fluctuations was smaller than is typical for Goldstone during these experiments, and (2) VLBI delay variations on longer timescales (i.e., over multiple scans) contained uncalibrated instrumental effects (probably a result of slow temperature variations in the VLBI hardware) that were larger than the tropospheric effects.