Terms Of Temperature Dependence Research Articles

Dynamic Analysis of a Spring-Asphalt Three-Dimensional Isolation System Based on Cyclic Simple Shear and Shaking Table Tests

Damping is one of the important issues related to isolated structures, including the newly proposed low-cost spring-asphalt isolation system. In this study, the damping properties of the system in terms of displacement dependence, frequency dependence and temperature dependence were studied by a cyclic simple shear experiment. Then, the direct least-square method was used to identify the damping properties from the experimental data. Furthermore, to validate the effectiveness of the damping device, a modal analysis was conducted based on multi-dimensional shaking table tests. The results indicate that (1) the hysteretic curves are similar to an ellipse, which means that the asphalt shows characteristics of viscoelastic materials; (2) the damping properties are positively related to the loading frequency and inversely related to the temperature and displacement; and (3) asphalt can provide adequate damping and reduce the displacements of the superstructure by nearly half. On the basis of the experimental test results, an analysis of the modal information with multi-dimensional input is also presented.

Loading frequency and temperature-dependent damping capacity of NiTiHfPd shape memory alloy

Superelastic shape memory alloys with ultra-high-strength, large mechanical hysteresis, and the ability to recover large deformations are promising materials for damping applications. In this study, the superelastic response and damping capacity of quaternary Ni45·3Ti39.7Hf10Pd5 polycrystalline alloys are investigated in terms of temperature and loading frequency dependency. It is shown that this alloy can show fully recoverable superelastic behavior with strain amplitude of 6–7% from −40 °C to 80 °C after heat treatments. The damping capacity of 550°C-3h aged alloy at 20 °C was 22.5 J/cm3 for quasi-static loading which decreased to 12.5 J/cm3 under 1 Hz loading frequency. At the high temperature of 80 °C the damping capacity was determined 9.2 J/cm3 under quasi-static loading and 4 J/cm3 under 1 Hz loading frequency. The decrease in damping capacity with loading frequency and temperature is linked to: the changes in local temperature of the specimen which significantly increases critical stress for reverse transformation while not affecting the critical stress for forward transformation, improved compatibility of transforming phases, and decrease in the contribution of superelastic strain to the total recovered strain.

Anomalous Auger Recombination in PbSe.

Using first-principles approaches we find that the Auger recombination in PbSe is anomalous in three distinct ways. First, the direct Auger coefficient is 4 orders of magnitude lower than that of other semiconductors with similar band gaps, a result that can be attributed to the lack of involvement of a heavy-hole band. Second, phonon-assisted indirect Auger recombination prevails, contrary to the common belief that direct Auger is dominant in narrow-gap semiconductors. Third, an unexpectedly weak temperature dependence of the Auger coefficient is observed, which we can now attribute to the indirect nature of the Auger process. The widely accepted explanation of this behavior in terms of an unusual temperature dependence of the band gap is only a secondary effect. Our results elucidate the mechanisms underlying the anomalous Auger recombination in IV-VI semiconductors in general, which is critical for understanding and engineering carrier transport.

Development of the New Approach for High Side Current Sensing

Accurate current sensing is critical in many applications including battery management, motor control, and over-current protection. Current can be sensed by either placing a small shunt resistor between the load and ground or between the battery and the load. High-side current sensing has two major advantages over low-side current sensing: it can detect high load current caused by accidental shorts, and it does not increase the resistance in the ground path. However, it does require interface circuits that can handle input common-mode voltages up to the battery voltage, which can be several tens of volts. The first part of this paper consists of a brief review of the existing approaches and methods of current sensing that widely used nowadays. This is followed by researching and development new schematic solution of the high-side current sensing which doesn’t need usage of HV amplifiers, has variable gain and has small gain error in temperature range from – 40 oC to 125 oC. Finally, suggested solution will be discussed and compared to existed ones. In previous current approach was used for high-side current measurement. However, this approach is not appropriative in mass production. So, the task of this work was to find out or come up with new solution, which would have same or better characteristics then previous one and would result in good yield in mass production. In reviewing the literature, several possible solutions were found. First of them is creating virtual ground for low voltage differential-input-single-output amplifier. Second approach is using fully differential system it comprises two main blocks, a differential amplifier, and an instrumentation amplifier. First approach is simple to be implemented and it doesn’t need matched high voltage transistors. However, one unanticipated finding was that it was not easy to create build in offset, so this approach can’t measure bidirectional current. Second approach system has good noise immunity and it is to create build in offset. At the same time, it is complex because of presence of instrumental amplifier in the second stage. Instrumental amplifier is hard to design and to match. As a result, new approach is proposed. This is mixing of differential-input-differential-output amplifier and virtual ground. This finding supports the ideas of previously described solutions. It has fully differential input, which results in high CMRR and PSRR, furthermore, it doesn’t require matched HV transistors because of virtual ground for amplifier. In addition, this schematic can be easily matched in terms of temperature dependence. However, new solution has a drawback, that is relatively big input current.

A New Uniformly Ultimate Boundedness Criterion for Temperature Dependent Average Bristle Deflections

Temperature variation intensively affects parameters of the friction force, particularly the average bristle deflections. In our earlier research work, a temperature dependent friction compensation scheme was developed for serial rigid robot manipulators which was comprised of a temperature dependent viscous friction compensation scheme and a temperature dependent disturbance rejection scheme. In this paper, a new criterion for the uniformly ultimate boundedness of the temperature dependent average bristle deflections is proposed in such a way that the temperature dependent average bristle deflections preserve the property of uniformly ultimately boundedness in a larger region. This is an improvement to our earlier research work. As the result of this improvement, it is shown that the proposed method in our earlier work, is applicable to larger temperature dependent disturbance terms. These two improvements are the main contributions of this paper that augment our earlier research work. The idea is supported by a new theorem.

Anomalous Decay of Quantum Resistance Oscillations of 2D Helical Electrons in Magnetic Field

Shubnikov de Haas resistance oscillations of highly mobile two dimensional helical electrons propagating on a conducting surface of strained HgTe 3D topological insulator are studied in magnetic fields B tilted by angle θ from the normal to the conducting layer. Strong decrease of oscillation amplitude A is observed with the tilt: {boldsymbol{A}}sim {boldsymbol{e}}{boldsymbol{x}}{boldsymbol{p}}(,-,{boldsymbol{xi }}/{boldsymbol{c}}{boldsymbol{o}}{boldsymbol{s}}({boldsymbol{theta }})), where ξ is a constant. Evolution of the oscillations with temperature T shows that the parameter {boldsymbol{xi }} contains two terms: {boldsymbol{xi }}={{boldsymbol{xi }}}_{1}+{{boldsymbol{xi }}}_{2}{boldsymbol{T}}. The temperature independent term, {{boldsymbol{xi }}}_{{bf{1}}}, signals possible reduction of electron mean free path {l}_{q} and/or enhancement of in-homogeneous broadening of the oscillations in magnetic field B. The temperature dependent term, {{boldsymbol{xi }}}_{{bf{2}}}{boldsymbol{T}}, indicates increase of the reciprocal velocity of 2D helical electrons: delta ({v}_{F}^{-1})sim B suggesting modification of the electron spectrum in magnetic fields. Results are found in good agreement with proposed phenomenological model.

Collective transitions of two entangled atoms and the Fulling-Davies-Unruh effect

We calculate respectively, from the viewpoints of an instantaneously/locally inertial observer and a coaccelerated observer, the transition rates of the two-atom system in the symmetric/antisymmetric entangled state [$|{\ensuremath{\psi}}_{\ifmmode\pm\else\textpm\fi{}}⟩$]. The scalar fields to which the atoms are coupled are respectively assumed to be in the vacuum state and a thermal state in the instantaneously inertial frame and in the coaccelerated frame. We show that both the upward transition $|{\ensuremath{\psi}}_{\ifmmode\pm\else\textpm\fi{}}⟩\ensuremath{\rightarrow}|{e}_{A}{e}_{B}⟩$ and the downward transition $|{\ensuremath{\psi}}_{\ifmmode\pm\else\textpm\fi{}}⟩\ensuremath{\rightarrow}|{g}_{A}{g}_{B}⟩$ take place, where $|{g}_{A}{g}_{B}⟩$ and $|{e}_{A}{e}_{B}⟩$ represent two collective eigenstates of the two-atom system with both atoms in their ground state and excited state respectively, and the transition rates observed in the two frames are identical only if there exists a thermal bath at the Fulling-Davies-Unruh temperature in the coaccelerated frame. Though both the downward and upward transition rates are characterized by the Plankian factor, this factor does not show up in the average variation rate of energy of the two-atom system, as a result of the perfect cancellation of the terms in the transition rates in the instantaneously inertial frame multiplied by the Plankian factor which corresponds to the Unruh thermal bath, and the cancellation of the temperature-dependent terms in the transition rates observed in the coaccelerated frame. A comparison of the transition rates of a static two-atom system in interaction with the massless scalar field in a thermal state at an arbitrary temperature with those of a uniformly accelerated two-atom system in interaction with the vacuum massless scalar field shows that the equivalence between the thermal bath and the uniform acceleration, which is well known to be valid for the single atom case, no longer holds for the two-atom system in the symmetric/antisymmetric entangled state. The effect of atomic uniform acceleration in the transition rates of the two-atom system, and the roles of both the downward and the upward transitions in the disentanglement of the two-atom system are also discussed.

Variability in cirrus cloud properties using a Polly<sup>XT</sup> Raman lidar over high and tropical latitudes

Abstract. Measurements of geometrical and optical properties of cirrus clouds, performed with a multi-wavelength PollyXT Raman lidar during the period 2008 to 2016, are analysed. The measurements were performed with the same instrument, during sequential periods, in three places at different latitudes, Gwal Pahari (28.43∘ N, 77.15∘ E; 243 m a.s.l.) in India, Elandsfontein (26.25∘ S, 29.43∘ E; 1745 m a.s.l.) in South Africa and Kuopio (62.74∘ N, 27.54∘ E; 190 m a.s.l.) in Finland. The lidar dataset was processed by an automatic cirrus cloud masking algorithm, developed in the frame of this work. In the following, we present a statistical analysis of the lidar-retrieved geometrical characteristics (cloud boundaries, geometrical thickness) and optical properties of cirrus clouds (cloud optical depth, lidar ratio, ice crystal depolarisation ratio) measured over the three areas that correspond to subtropical and subarctic regions as well as their seasonal variability. The effect of multiple scattering from ice particles to the derived optical products is also considered and corrected in this study. Our results show that cirrus layers, which have a noticeable monthly variability, were observed between 6.5 and 13 km, with temperatures ranging from −72 to −27 ∘C. The observed differences on cirrus clouds' geometrical and optical properties over the three regions are discussed in terms of latitudinal and temperature dependence. The latitudinal dependence of the geometrical properties is consistent with satellite observations, following the pattern observed with CloudSat, with decreasing values towards the poles. The geometrical boundaries have their highest values in the subtropical regions, and overall, our results seem to demonstrate that subarctic cirrus clouds are colder, lower and optically thinner than subtropical cirrus clouds. The dependence of cirrus cloud geometrical thickness and optical properties on mid-cirrus temperatures shows a quite similar tendency for the three sites but less variability for the subarctic dataset. Cirrus clouds are geometrically and optically thicker at temperatures between −45 and −35 ∘C, and a second peak is observed at lower temperatures ∼-70 ∘C for the subarctic site. Lidar ratio values also exhibit a pattern, showing higher values moving toward the poles, with higher mean values observed over the subarctic site. The dependency of the mid-cirrus temperatures on the lidar ratio values and the particle depolarisation values is further examined. Our study shows that the highest values of the cirrus lidar ratio correspond to higher values of cirrus depolarisation and warmer cirrus. The kind of information presented here can be rather useful in the cirrus parameterisations required as input to radiative transfer models and can be a complementary tool for satellite products that cannot provide cloud vertical structure. In addition, ground-based statistics of the cirrus properties could be useful in the validation and improvement of the corresponding derived products from satellite retrievals.

Temperature dependence of the Hall coefficient of sensitive layer materials considered for DEMO Hall sensors

The Hall sensors as a part of the DEMO magnetic diagnostics will perform an absolute measurement of the steady-state magnetic field. However, the magnitude of the Hall coefficients generally depends on the temperature. The paper presents an evaluation of the temperature dependencies of the Hall coefficients of materials considered for the DEMO Hall sensors from room temperature up to 550 °C. The results show that tantalum or molybdenum sensors would be the best in terms of the low temperature dependence of their Hall coefficient. Bismuth and antimony offer a Hall coefficient several orders of magnitude higher than other considered materials, but strongly temperature-dependent, while usability of bismuth is limited by its melting temperature of 271.4 °C. The gold, copper and platinum sensors feature modest temperature dependence of their Hall coefficients which might result in the necessity of dedicated temperature monitoring of these sensors in order to achieve sufficient measurement accuracy, similarly to bismuth and antimony.

Temperature dependent kinetic study of the gas phase reaction of ozone with 1-penten-3-ol, cis-2-penten-1-ol and trans-3-hexen-1-ol: Experimental and theoretical data

C5 and C6 unsaturated alcohols are a family of biogenic volatile organic compounds (BVOC) emitted in the atmosphere from vegetation in response to their injuries. In this work, we report the first temperature dependent rate constants for the reaction of three unsaturated alcohols: 1-penten-3-ol (1P3OL), cis-2-penten-1-ol (c-2P1OL) and tran-3-hexen-1-ol (t-3H1OL) with ozone in a pyrex reactor coupled to a FTIR spectrometer and to a GC/MS at four different temperatures (273, 298, 313 and 333 K), at atmospheric pressure, using a relative method. The Arrhenius expressions obtained are (cm3 molecule−1 s−1):The studied reactions were also explored theoretically using computational methods based on quantum chemical theory characterizing the intermediates, transition states and the subsequent formation of reaction products. The rate constants were calculated at room temperature employing a modified transition-state theory (MTST). Both results obtained experimentally and theoretically, were discussed in terms of structure-reactivity relationships and temperature dependence. Tropospheric lifetimes of the investigated species with respect to ozone are calculated. The obtained results showed that these species are not persistent towards ozonolysis process.

Simulating temperature-dependent biodegradation-induced settlement at a landfill with waste lifts placed under frozen conditions

Instrument bundles placed within the Ste. Sophie landfill (Quebec, Canada) have been collecting temperature and settlement data since January 2010. Previous modelling efforts simulated settlement based on a three-component model to account for primary or instantaneous compression, secondary compression or mechanical creep and time-dependent biodegradation-induced settlement. In northern climates where waste may be placed under frozen conditions, a time-dependent biodegradation-induced settlement term is unable to simulate settlement due to biodegradation as waste temperatures transition from below zero to optimal values for anaerobic degradation. This paper presents a temperature-dependent biodegration-induced settlement model. The model simulates heat generation as a function of temperature and tracks the expended energy as the waste degrades. The ratio of the expended energy to the total potential expended energy is used in the proposed temperature-dependent biodegradation-induced settlement term. The new term better accounts for the delayed biodegradation process observed in wastes placed under frozen conditions. The model was able to simulate the settlement trends observed at the Ste. Sophie landfill. The goal of developing and including a temperature-dependent biodegradation-induced settlement term in the model was to study the effects of operating conditions on waste settlement and stabilization. An optimized waste lift placement strategy could enhance waste stabilization and improve the airspace utilization within a landfill, simultaneously bringing increased revenues to landfill operators while decreasing the post closure environmental burden of landfills.

Experimental and computational study on sintering of ceramic coating layers with complex porous structures

AbstractThis study investigated the sintering behavior of an yttria‐stabilized zirconia coating for thermal barrier coatings (TBCs) with a complicated porous structure via both experiment and simulation using the finite element method for samples with only a coating (free coating) and samples with coating on a substrate (constrained coating). Sintering and grain growth proceeded from the bottom of the coating, and the coating bent convex upward in the free coating. In the constrained coating, sintering and grain growth proceeded in a manner similar to the free coating; however, the degrees of sintering and grain growth were small. Furthermore, sintering and grain growth were delayed because of substrate constraints. As a simulation result, the free coating was bent in a manner similar to the experiment. The experimental results could be reproduced in terms of time dependency and temperature dependency. The decrease in the porosity of the constrained coating was delayed compared with that in the free coating because of substrate constraints. This simulation result was able to reproduce the experimental results. Thus, the sintering behavior for the complex porous structures of TBCs can be predicted by experimental research and simulation, which could aid in the development of a prediction technology for the delamination of coatings (TBC lifetime).

Design of the trinitrotoluene biosensor using polydiacetylene conjugated with peptide receptors coated on GR-FETs with colorimetric response

PurposeSmart biosensors that can perform sensitive and selective monitoring of target analytes are tremendously valuable for trinitrotoluene (TNT) explosive detection. In this research, the pre-developed sensor was integrated with biological receptors in which they enhanced the sensitivity of the sensor. This is due to conjugated polydiacetylene onto a peptide-based molecular recognition element (Trp-His-Trp) for TNT molecules in graphene field-effect transistors (GR-FETs) as biosensor that is capable of responding to the presence of a TNT target with a colorimetric response. The authors confirmed the efficacy of the receptor while being attached to polydiacetylene (PDA) by observing the binding ability between the Trp-His-Trp and TNT to alter the electronic band structure of the PDA conjugated backbones. The purpose of this paper is to demonstrate a modular system capable of transducing small-molecule TNT binding into a detectable signal. The details of the real-time and selective TNT biosensor have been reported.Design/methodology/approachFollowing an introduction, this paper describes the way of fabrication GR-FETs with conventional photolithography techniques and the other processes, which is functionalized by the TNT peptide receptors. The authors first determined the essential TNT recognition elements from UV-visible spectrophotometry spectroscopy for PDA sensor unit fabrication. In particular, the blue percentage and the chromic response were used to characterize the polymerization parameter of the conjugatedpbackbone. A continuous-flow trace vapor source of nitroaromatics (two, four, six-TNT) was designed and evaluated in terms of temperature dependence. The TNT concentration was measured by liquid/gas extraction in acetonitrile using bubbling sequence. The sensor test is performed using a four-point probe and semiconductor analyzer. Finally, brief conclusions are drawn.FindingsBecause of their unique optical and stimuli-response properties, the polydiacetylene and peptide-based platforms have been explored as an alternative to complex mechanical and electrical sensing systems. Therefore, the authors have used GR-FETs with biological receptor-PDAs as a biosensor for achieving high sensitivity and selectivity that can detect explosive substances such as TNT. The transport property changed compared to that of the field-effect transistors made by intrinsic graphene, that is, the Dirac point position moved from positive Vg to negative Vg, indicating the transition of graphene fromp-type ton-type after annealing in TNT, and when the device was tested from RT, the response of the device was found to increase linearly with increasing concentrations. Average shifting rate of the Dirac peak was obtained as 0.1-0.3 V/ppm. The resulting sensors exhibited at the limit ppm sensitivity toward TNT in real-time, with excellent selectivity over various similar aromatic compounds. The biological receptor coating may be useful for the development of sensitive and selective micro and nanoelectronic sensor devices for various other target analytes.Originality/valueThe detection of illegally transported explosives has become important as the global rise in terrorism subsequent to the events of September 11, 2001, and is at the forefront of current analytical problems. It is essential that a detection method has the selectivity to distinguish among compounds in a mixture of explosives. So, the authors are reporting a potential solution with the designing and manufacturing of electrochemical biosensor using polydiacetylene conjugated with peptide receptors coated on GR-FETs with the colorimetric response for real-time detection of TNT explosives specifically.

Growth behavior of the δ-Ni3Nb phase in superalloy 718 and modified KJMA modeling for the transformation-time-temperature diagram

The δ-Ni3Nb phase is indispensable in achieving the uniform microstructure containing refined grains during the hot-forging process of superalloy 718. The growth behavior of the δ-Ni3Nb phase at temperatures ranging from 1213 to 1283 K was investigated. The heat-treatments were performed in the argon atmosphere, and annealing time for the precipitation of the δ-Ni3Nb phase varies from 10.8 to 93.6 ks. The measurement of the δ-Ni3Nb phase was performed on the backscattered electron (BSE) image. The positive influence of small grain size on accelerating the precipitation process of the δ-Ni3Nb phase was confirmed. The δ-Ni3Nb phase was found to nucleate at grain boundary preferentially, and the evaluation of the δ-Ni3Nb phase strongly depends on the grain size. A grain-size-dependent Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation, ξ=1−exp[−K(T)ρlm∫0tnt1n−1(t−t1)32dt1] where ξ is the transformed phase fraction over the equilibrium fraction, K(T) is the temperature-dependent term, ρl is the length of the grain boundary per unit area, m is a constant, t is the time in second, and n is a nucleation index, was used by considering proper nucleation and growth behaviors. The predicted TTT curve agrees well with the reported experimental data. The presently proposed KJMA model and plotted TTT curve provide the valuable information for the microstructure control of superalloy 718, accelerating the development of superalloy 718.

Crossover between Electron-Phonon and Boundary-Resistance Limits to Thermal Relaxation in Copper Films

We observe a crossover from electron-phonon (ep) coupling limited energy relaxation to that governed by thermal boundary resistance (pp) in copper films at sub-kelvin temperatures. Our measurement yields a quantitative picture of heat currents, in terms of temperature dependences and magnitudes, in both ep and pp limited regimes, respectively. We show that by adding a third layer in between the copper film and the substrate, the thermal boundary resistance is increased fourfold, consistent with an assumed series connection of thermal resistances.

Unconventional thermal metallic state of charge-neutral fermions in an insulator

Quantum oscillations in transport and thermodynamic parameters at high magnetic fields are an unambiguous signature of the Fermi surface, the defining characteristic of a metal. Recent observations of quantum oscillations in insulating SmB6 and YbB12, therefore, have been a big surprise—despite the large charge gap inferred from the insulating behaviour of the resistivity, these compounds seemingly host a Fermi surface at high magnetic fields. However, the nature of the ground state in zero field has been little explored. Here, we report the use of low-temperature heat-transport measurements to discover gapless, itinerant, charge-neutral excitations in the ground state of YbB12. At zero field, sizeable linear temperature-dependent terms in the heat capacity and thermal conductivity are clearly resolved in the zero-temperature limit, indicating the presence of gapless fermionic excitations with an itinerant character. Remarkably, linear temperature-dependent thermal conductivity leads to a spectacular violation of the Wiedemann–Franz law: the Lorenz ratio is 104–105 times larger than that expected in conventional metals, indicating that YbB12 is a charge insulator and a thermal metal. Moreover, we find that these fermions couple to magnetic fields, despite their charge neutrality. Our findings expose novel quasiparticles in this unconventional quantum state. Despite being a charge insulator, YbB12 behaves like a thermal metal. Low-temperature heat-transport measurements of this compound showed its gapless, itinerant and charge-neutral excitations.

Biologically sound formal model of Hsp70 heat induction

A proper response to rapid environmental changes is essential for cell survival and requires efficient modifications in the pattern of gene expression. In this respect, a prominent example is Hsp70, a chaperone protein whose synthesis is dynamically regulated in stress conditions. In this paper, we expand a formal model of Hsp70 heat induction originally proposed in previous articles. To accurately capture various modes of heat shock effects, we not only introduce temperature dependencies in transcription to Hsp70 mRNA and in dissociation of transcriptional complexes, but we also derive a new formal expression for the temperature dependence in protein denaturation. We calibrate our model using comprehensive sets of both previously published experimental data and also biologically justified constraints. Interestingly, we obtain a biologically plausible temperature dependence of the transcriptional complex dissociation, despite the lack of biological constraints imposed in the calibration process. Finally, based on a sensitivity analysis of the model carried out in both deterministic and stochastic settings, we suggest that the regulation of the binding of transcriptional complexes plays a key role in Hsp70 induction upon heat shock. In conclusion, we provide a model that is able to capture the essential dynamics of the Hsp70 heat induction whilst being biologically sound in terms of temperature dependencies, description of protein denaturation and imposed calibration constraints.

Band filling and disorder effects on the normal state thermoelectric behavior in MgB2

The goal of this work is providing a comprehensive interpretation framework for the wide and varied experimental phenomenology of the Seebeck effect in MgB2 samples with different levels of doping in either π or σ bands and different levels of disorder, using a combined experimental and theoretical approach. We calculate the temperature dependent diffusive Seebeck coefficient Sdiff(T) with the Boltzmann equation resolved in relaxation time approximation, taking into account the scattering with phonons and impurities, the effect of renormalization and the effect doping in a rigid band approximation. We show that selective disorder has a sizeable effect on the Sdiff magnitude, as it tunes the relative contributions of σ and π bands. Disorder also affects the Sdiff temperature dependences, eventually yielding a linear Sdiff(T) behavior in the dirty limit. We also show that band filling has opposite effects on S, depending on which band dominates transport.In parallel, we carry out the Seebeck effect measurements on neutron-irradiated Mg11B2, and on two series of doped samples Mg1−xAlxB2 and Mg(B1−xCx)2. From comparison of calculated Sdiff(T) and experimental S(T) curves, we demonstrate that diffusive and phonon drag terms give comparable contributions in clean samples, but the phonon drag term is progressively suppressed with increasing disorder.In C and Al doped samples we observe very different experimental behaviors in terms of sign, magnitude and temperature dependence. Indeed, notwithstanding the similar electron doping introduced by both substitutions, C or Al doping yields disorder which mainly affects either σ or π bands, respectively. With the help of our theoretical approach, we are able to disentangle the various effects and prove that the Seebeck coefficient is a very sensitive probe of this kind of disorder.

Passivity‐based adaptive control of a 2‐DOF serial robot manipulator with temperature dependent joint frictions

SummaryMechanical systems are always suffering from the effects of temperature dependent friction forces where the system is operated in a wide range of temperature. Temperature and its variation play an important role in friction force in mechanical systems. If it is not compensated, it will tend to unwanted consequences, including steady‐state errors, limit cycling, and hunting. Therefore, it is necessary to take the temperature effects into account. This has been a strong motivation for the researchers to work on temperature effects on joint friction. In this paper, an adaptive compensation (control) scheme is proposed and applied to a 2‐degree‐of‐freedom serial robot manipulator by taking the temperature effects into account on the joints friction. In the proposed control scheme, the temperature is not required to be sensed. In this paper, joint friction is described by LuGre dynamic model with temperature dependent parameters. These parameters are described by some functions with unknown temperature dependent terms. According to the mathematical and practical concepts, the temperature dependent friction is decomposed into a viscous term and a disturbance term. An adaptive controller is designed to compensate the friction effect and it is shown that the proposed controller relaxes the condition for a priori knowledge about the environment characteristics, including the upper and lower bounds of the environment temperature and the parameters of the functions, describing the temperature dependent joint frictions. The stability and convergence of the joint position and velocity are proved in the sense of Lyapunov and then the proposed method is confirmed by the simulations.

Modeling Degradation Kinetics in Dry Foods Storage under Varying Temperature and Moisture Content—Theoretical Evaluation

The combined effect of temperature and moisture (or water activity) on the rate of nutrients loss and other deteriorative chemical reactions in foods has been primarily studied in relation to drying. In long foods storage, changes in their temperature and/or moisture content are much slower and never as dramatic, but their effect can be similar in kind. Reported degradation reactions in foods mostly followed first- or other fixed-order kinetics. Hence, their progress under dynamic conditions primarily depends on the varying rate constant. Perhaps the most economic way to describe the rate constant’s variations pattern and magnitude is a two-parameter temperature-dependence model whose two coefficients are moisture dependent, each described by another two-parameter model, which brings the total number of adjustable parameters to four. Such a flexible model is the two-parameter exponential temperature-dependence term, a simpler substitute to the Arrhenius equation, whose two parameters’ moisture dependencies are also described by two similar exponential terms. This model’s flexibility is demonstrated with computer simulations of chemical degradation under varying temperature and moisture conditions. Testing a large number of products stored for long times by the traditional methods to determine a reaction’s kinetic parameters and their temperature and moisture dependencies can create logistic problems. Theoretically, they can be avoided by estimating the kinetic parameters directly from several successive concentration determinations during a single dynamic storage experiment whereby the monitored temperature and moisture are allowed to vary arbitrarily. The principle is demonstrated with simulated data having no or very small errors. However, its practical implementation might not be effective if the experimental concentration measurements have a substantial scatter.