Specific Temperature Values Research Articles

Mechanical deformation destabilizing hydrate within thermodynamic equilibrium region

Natural gas hydrates are a significant potential energy source and key player in global geological climate dynamics, with our all understandings on both sides basing on hydrate stability conditions consisting of pressure (P) and temperature (T). Considering important significance of theoretical researches in two sides, whether there is another factor playing same role with P or T is worth being answered. Using molecular dynamics simulations, changes of non-clathrated water structures and gas bubbles during mechanical deformation processes of methane hydrates were investigated to characterize their destabilizing natures and the deformation is then identified as this new factor. Similar to P-T profile but at a new level of complexity, deformation also characterizes hydrates stability but in three-dimensional space form while combining with T, reflecting deeper influences of specific temperature values, hydrate purities and deformation modes on hydrates stability. Over two tensile andcompressive deformations, the mechanisms responsible for hydrate destabilization vary, with stretching favoring formation of gas bubbles and compressing damaging internal hydrogen-bond structures. Once alternating, such two to-and-fro continuing deformations can act as a piston-like accelerator as well as one-way valve for dissociation of hydrates, destabilizing them rapidly. In summary, P and T act as the prerequisite of hydrate existences, but cannot accurately account for the influence of such dynamic events as earthquakes, ocean tides, and changes of ice shelves on dissociations. This research sheds a new light on the reasonable explanation to dynamic hydrate dissociations, e.g. some abnormal disappearances of reservoirs within appropriate P-T conditions. Stronger, current bottleneck of hydrate exploitation efficiency might also be broken down; likewise, the ultra-rapid dissociation performance during the terminal procedure of hydrate-based natural gas storage/transportation technology might achieve success.

Correlation of supersonic wind tunnel measurements with a nonlinear aeroelastic theoretical/computational model of a thin plate

Supersonic wind tunnel test data is compared with a nonlinear aeroelastic computational model, considering a freestream flow with Mach nearly 2, coupled cavity, and no-shock impingement. The measurements include Limit Cycle Oscillations (LCO) for the given set of flow and structural parameters. The effect of a static pressure differential, temperature differential, and the type of LCO is also studied: periodic or chaotic. A fully coupled aero-thermal–acoustic–elastic analysis was carried out, where the strong dependency of the dynamic instability upon the in-plane boundary stiffness was discovered. Associated with aerodynamic and acoustic formulations, the nonlinearities from the structure are found to be the strongest factor determining the occurrence and character of LCO. At the same time, the cavity effect was found to be negligible for this experimental configuration. Additionally, a comparison analysis was performed on the aerodynamic model for this flow condition between the Linear Piston Theory and the Full Potential Aerodynamics. The calculation of the critical flutter boundary was also performed in terms of the static pressure differential between the cavity pressure and the panel surface pressure, presenting regions where the panel is in static deformation due to the pressure differential versus LCO response. The comparison with the analytical model showed good agreement with the measured data, achieving a similar panel displacement at three-quarters of the panel length as well as the expected behavior of periodicity or chaos for specific values of temperature and static pressure differential.

Improvement of the automatic temperature stabilisation process in the cryovacuum unit

This study concerns the issues of temperature stabilization in units used to research the properties of molecules at low and ultra-low temperatures. This research is relevant due to the need to increase the speed and accuracy of the data obtained. Using the LabView graphical programming environment tools, a control program was created for the LakeShore 325 thermocontroller which reacts when the current temperature is close to the control point temperature set by the researcher. By adding controls for the heating element power and PID controller boot times, it is possible to use them more flexibly. The method was verified for the temperature control points of 40 K, 100 K, 150 K and 200 K. A comparison of the proposed temperature stabilization program with the standard PID controller solution demonstrates the advantages of the former. The speed of reaching the control points was doubled. The digitalization of the LakeShore 325 thermocontroller makes it possible to work further on improving temperature stabilization. The resulting increase in the accuracy–time stabilization ratio makes it possible for those who conduct low-temperature experiments to improve the quality of their measurements dramatically. The introduction of a digital version of the temperature control device opens up possibilities for further automation of cryovacuum units by linking the thermal control program with other programs, for example, recording the spectra at specific temperature values.

Thermal evaluation of rubber compounds containing pecan nutshell powder for tire treads

This work presents the thermal study of rubber compositions with the addition of pecan nutshell powder, which is renewable and environmentally friendly, as a replacement for carbon black in treads for tires. Pecan nutshell is composed of cellulose, hemicellulose and lignin, and their quantity was evaluated by thermogravimetric analysis (TG) through the step-and-hold method. Thermal stability of the samples with pecan nutshell was verified by TG compared with the sample with only carbon black. The value of tan δ evaluated by dynamic mechanical analysis in the specific temperature values indicates the wet traction and rolling resistance for tires. Higher tan δ at 0 °C was observed in the samples containing pecan nutshell, which indicates better wet traction; however, the higher results observed at 60 °C indicate a worst rolling resistance. Results of oxidation induction time, by differential scanning calorimetry, show that the oxidation time increased with the addition of pecan nutshell in the compounds, indicating better antioxidant properties, justified by the presence of lignin.

Effect of Thermal Fluctuation Field on the Magnetization Switching by Spin-Transfer Torque

In this work, the effect of thermal fluctuation field on the magnetization dynamics in Co1.5Fe1.5Ge alloy free layer is reviewed in a spin-valve structure with in-plane magnetization using the stochastic Landau-Lifshitz-Gilbert-Slonczewski (s-LLGS) equation taking into account the thermally assisted switching. The ultimate goal is to systematically study the heating effect on the magnetization reversal by simulating the magnetization dynamics in different thicknesses under very low current densities of about 106–105 A/cm2 in the presence of the thermal effect by applying different temperature values between T = 50 and T = 200 K. Results showed that the magnetization has different reversal processes among the large and small temperature values due to the competition between the thermal energy Et and magnetic energy barrier Eb, which allows the magnetization to trigger switching for specific temperature values. Consequently, at a temperature increase of about 200 K, we have proved that the magnetization reversal in Co1.5Fe1.5Ge alloy free layer is possible under a low current density of J =− 3.5 × 106 A/cm2. Additionally, we carefully examined the thermal impact on the threshold current density and switching time through analyzing the magnetization behavior for each temperature value, and as a result, we succeeded to reduce the critical current density in Co1.5Fe1.5Ge/Ag/Co1.5Fe1.5Ge structure from Jc = − 5.7 × 106 A/cm2 to Jc = − 9.5 × 105 A/cm2 for a thickness of 1 nm.

Magnetic Properties Study of the Nano-Alloy Fe1+xCo1−x by Monte-Carlo Simulations

Motivated by spintronic devices and their applications, we engineer a model to investigate the magnetic properties of the magnetic nano-alloy Fe[Formula: see text]Co[Formula: see text]. Where [Formula: see text] is the fraction of iron atoms Fe substituted by the cobalt Co atoms, [Formula: see text] corresponds to 50% Fe atoms and 50% Co atoms, this compound is then called equiatomic FeCo. The purpose of this work is to apply the Monte-Carlo Simulations (MCS), under Metropolis algorithm to predict the magnetic properties of such system. In a first step, we propose a model describing this system including different exchange coupling interactions. Then, we establish and analyze the ground state phase diagrams, in different planes. For non-null temperature values, applied MCS under the Metropolis algorithm. The behavior of both the magnetizations and the susceptibilities are illustrated as a function of temperature. Also the effect of the different exchange coupling interactions is studied and discussed. The hysteresis loops are presented and analyzed for specific values of temperature, exchange coupling interactions and concentrations.

Groundwater Temperature as an Indicator of the Vulnerability of Karst Coastal Aquifers

Coastal karst aquifers show a three-dimensional vulnerability, which consists of the whole of the “intrinsic vulnerability” and the “groundwater vulnerability to seawater intrusion”. The results of a study carried out in the Salento karst coastal aquifer (southern Italy) show that temperature, as well as being a reliable tracer of groundwater flow, is also an effective indicator of vulnerability in anisotropic media. The trend of isotherms related to a cross-section of the aquifer thermal field, combined with geological, geomorphological, and hydrogeological information, allows the role of faults and dolines in the mass transport from ground surface to be inferred. Isotherm trends may also give information on the permeability distribution along faults. A specific temperature value evidence the saltwater top, thus indicating the groundwater vulnerability to salinization.

Experimental investigation on the sputtering and micro-explosion of emulsion fuel droplets during impact on a heated surface

Micro-explosion has been concerned for decades due to its potential effect on fuel atomization and combustion. In this work, the characteristics of sputtering and micro-explosion induced by water-diesel emulsion fuel droplets impact on a heated surface under different water content (from 5% to 20% with an interval of 2.5%) and surface temperature conditions was investigated by a high speed camera synchronized with backlit technique. It was found that the secondary droplets was still heated by the environment to induce sputtering. It was observed the secondary droplets induced by sputtering would trigger further sputtering. Higher water content and higher temperature are necessary to induce sputtering and micro-explosion. The variation of an emulsion fuel droplet impacts on the surface from 100 °C to 320 °C was investigated. Typical Leidenfrost phenomenon was observed when the temperature was above the range when temperature was more than 300 °C. Various types of bubbles depending on the specific temperature value will generate when the surface temperature is below the range, while no bubble generates for neat diesel droplet.

The influence of species composition on flow field's optical computerized tomography diagnosis

The species composition is one of the factors which could affect the refractive index of flow fields. So, the determination of species composition should be a key point, when optical computerized tomography (OCT) methods are applied to measure the key parameters of flow fields. In this paper, the influence of species composition on flow field's temperature diagnosis will be discussed both in theory and experiment. The final results manifest that the determination of species composition could affect not only the specific temperature values, but also the structure and distribution of the temperature. Meanwhile, it is also found that the nonlinear regular of the maximal temperature variation with the distance between the cross section and nozzle is the same in different models. Finally, the condition, which could be applied to judge whether the effect of species composition can be omitted, is proposed.

Cognitive function and short-term exposure to residential air temperature: A repeated measures study based on spatiotemporal estimates of temperature

Few studies have examined the association between ambient temperature and cognitive function, or used exposure to temperature at a given address instead of a single stationary monitor. The existing literature on the temperature-cognition relationship has mostly consisted of experimental studies that involve a small sample size and a few specific temperature values. In the current study, we examined the association between residential air temperature and Mini-Mental State Examination (MMSE) scores, a quantitative measurement of cognitive function, in a longitudinal cohort of elderly men. Residential air temperature was estimated by a novel spatiotemporal approach that incorporates satellite remote sensing, land use regression, meteorological variables and spatial smoothing in the Northeastern USA. We then applied logistic regression generalized estimating equations to examine the relationship between residential temperature (range: −5.8–25.7°C), and the risk of low MMSE scores (MMSE scores ≤25) among 594 elderly men (1085 visits in total) from the Veterans Affairs Normative Aging Study, 2000–2008. Sensitivity analysis on visits wherein subjects lived within 30km of the clinic center in Massachusetts or aged ≥70 years was also evaluated. A statistically significant, U-shaped association between residential air temperature and low MMSE score (p-value=0.036) was observed. Sensitivity analysis suggested that the estimated effect remains among individuals aged ≥70 years. In conclusion, the data suggest that risk of low MMSE scores is highest when temperature is either high or low, and lowest when ambient temperature is approximately within 10–15°C in a cohort of elderly men. Further research is needed to confirm our findings and assess generalizability to other populations.

Accurate calculation of conductive conductances in complex geometries for spacecrafts thermal models

The thermal subsystem of spacecrafts and payloads is always designed with the help of Thermal Mathematical Models. In the case of the Thermal Lumped Parameter (TLP) method, the non-linear system of equations that is created is solved to calculate the temperature distribution and the heat power that goes between nodes. The accuracy of the results depends largely on the appropriate calculation of the conductive and radiative conductances.Several established methods for the determination of conductive conductances exist but they present some limitations for complex geometries. Two new methods are proposed in this paper to calculate accurately these conductive conductances: The Extended Far Field method and the Mid-Section method. Both are based on a finite element calculation but while the Extended Far Field method uses the calculation of node mean temperatures, the Mid-Section method is based on assuming specific temperature values. They are compared with traditionally used methods showing the advantages of these two new methods.

Non-invasive measurement of the human core temperature

The direct measurement of the temperature of the human body core, while being of great significance for the evaluation of patient health, is inconvenient. This realization has motivated attempts to measure the core temperature indirectly, for the most part at locations which do not require invasion of the body. In the investigation described here, a new approach to noninvasive measurement of the core temperature is set forth. The site of the proposed measurement is on the forehead where the anatomy is relatively uniform amongst individuals and also well established to be modeled accurately. The approach described here consists of simple hardware and a logic-based and customized control algorithm. The connection between the core temperature, the sensor temperature, and the temperature of a sensor-system heater was determined by numerical simulations of the heat transfer in the tissue bed fronted by the forehead skin and backed by the frontal bone. For heat transfer through each tissue layer in the tissue bed, the bioheat equation was employed, while for a resistance element in the sensing system, the Fourier heat conduction equation was used. These were solved in the transient mode. The controller read the temperatures of the core, the sensor, and the ambient, and the algorithm instructed the sensor-system heater to obtain a specific temperature value. The iterative use of the control algorithm resulted in near-equality of the sensor and core temperatures. An optimization routine performed operations needed to find the best performing sensor system. After optimization, that system is capable of yielding core temperature results that are approximately in error by 0.2 °C. A model problem was formulated to assess the capabilities of the sensing system to follow a time-varying core temperature. It was found that for core temperatures that varied by 0.05 °C per minute, the sensor followed the core within 0.2 °C or better.

On the nonlinear vibration of heated corrugated circular plates with shallow sinusoidal corrugations

The large amplitude free vibration of corrugated circular plates with shallow sinusoidal corrugations under uniformly static temperature changes is investigated. Based on the nonlinear bending theory of thin shallow shells, the governing equations for corrugated plates are established from Hamilton's principle. These partial differential equations are reduced to corresponding ordinary ones by elimination of the time variable with Kantorovich averaging method following an assumed harmonic time mode. Then by introducing the Green's function, the resulting dynamic compatible equation and corresponding boundary conditions are converted into equivalent integral equations. Taking the central maximum amplitude of the plate as the perturbation parameter, the perturbation-variation method is used to dynamic equilibrium equation with the aid of Computer Algebra Systems, Maple, from which, the third-order approximate characteristic relation of frequency vs. amplitude for nonlinear vibration of heated corrugated plates is obtained, and the frequency–amplitude characteristic curve is plotted for some specific values of temperature and geometrical parameters. It is found that the rise in temperature will decrease the frequency and vice versa. The nonlinear effect weakens when corrugations become deeper and dense. The present method can easily be expanded for the analysis of nonlinear vibration problem for other heated thin plates and shells.

Stability analysis of shear banding flow with the BMP model

The Bautista–Manero–Puig (BMP) model, consisting of the upper-convected Maxwell constitutive equation coupled to a kinetic equation that takes into account structural changes induced by flow, predicts the basic features of shear banding flow in polymer-like micellar solutions. In this work, the Lyapunov stability analysis applied to this model is used to determine the regions of stability and instability under conditions of shear banding flow. Results indicate that the steady state is reached very slowly within the meta-stable regions and quite rapidly in the homogeneous flow regions as well as in the unstable region where the slope of the constitutive flow curve is negative. Moreover, the Lyapunov stability criterion suggests the locus of the spinodal curve and the existence of a critical point for specific values of temperature and surfactant concentration. In addition, a criterion to set the stress plateau is derived from Extended Irreversible Thermodynamic (EIT) that consists in the equality of the minima in extended Gibbs free energy of the stable flow branches. This approach relates the EIT criterion for the stress plateau to the stability analysis for shear banding flow.

Calculation of the Uncertainty in the Determination of the Equilibrium Moisture Content of Pumpkin Seed Flour

Empiric equations for the determination of the equilibrium moisture content as a function of temperature and relative humidity of air are normally obtained from experimental data by curve fitting. Once the fitting parameters of a function for a given product are determined, the value of that function for specific values of temperature and humidity of air is obtained by substituting these values into the function, which represents an indirect measurement. Generally, the results of these modelings are stated without the uncertainties inherent in the measurement. This article proposes a method for the determination of these uncertainties. For that, a computer code was developed which calculates the error propagation in first order approximation from the obtained fitting parameters and their covariances. The code was used for the determination of the uncertainties of the equilibrium moisture content of pumpkin seed flour, both for adsorption and desorption. This procedure allows a report of the measurement in agreement with the rules established by international standardization organizations.

Investigation of a Color‐Color Method to Determine Temperatures along Coronal Structures UsingTRACEData

This paper readdresses the double filter ratio temperature analysis method employed on TRACE 171, 195, and 284 A coronal images. Here we reanalyze a feature from a TRACE data set published initially in 2002 along with a new TRACE example. The revised data set was termed an jet and was observed on 1998 July 29. The new example is at the base of a large (relatively static) loop structure on the solar limb and was observed on 2005 July 26. In both cases the structures are easily shown to be present in all three EUV passbands. This work investigates two important changes to the original analysis. First, a new temperature color-color curve is employed that utilizes revised TRACE response functions; these take into account the emission from Fe VIII, which significantly affects the 195 A passband. Second, three different background subtraction techniques are used. The results subsequently show that when using this method for these examples, it is very difficult to assign specific temperature values to individual data points. Reasons for this conclusion are discussed.

The Influence of Annealing on the Microstructure and Electrical Resistivity of Jelly-Rolled Cu-Nb Composite Wires

In this paper, the annealing effects on the microstructure and electrical resistivity of jelly-rolled Cu-x% vol. Nb (x=25, 33, 50, and 63) composite wires were investigated. During annealing, noticeable changes take place in the microstructure, including recovery and recrystallization of copper and niobium, followed by spheroidization and further coalescence of niobium filaments. With increasing annealing temperature, the diffusion-controlled coalescence of niobium filaments is enhanced due to their proximity. The behavior of the electrical resistivity in the normal state of the Cu-Nb composite shows a noticeable change at a specific value of temperature in the range between 50K and 70 K. This temperature varies with the niobium volume fraction. Such a behavior is discussed in terms of the decrease of the amount of Cu-Nb interfaces promoted by coarsening and by electron scattering effects at these interfaces.

Oxidation‐derived flavor compounds as quality indicators for packaged olive oil

AbstractAroma compounds in packaged extra virgin olive oil can be present naturally or be derived through oxidative degradation under favorable conditions of temperature, light, and oxygen availability. In this study, the identity and quantity of flavor compounds were determined for extra virgin olive oil packaged in 0.5‐L glass, poly(ethylene terephthalate), and poly(vinyl chloride) bottles and stored at 15,30, and 40°C under fluorescent light or in the dark for 1 yr. A set of mathematical equations concerning the rates of the most fundamental oxidation reactions in the oil was prepared and numerically solved, and the reaction constants were estimated for specific temperature values. Mainly, the presence of fluorescent light, followed by elevated temperature, stimulated oxidative alterations in the olive oil. Separated and identified flavor compounds were recorded for all the olive oil samples. Based on their abundance and evolution in the oil samples, those most clearly describing oxidation were hexanal, nonanal, (E)‐2‐decenal, (E)‐2‐heptenal, and 2‐pentyl furan. These compounds could be used as markers of the oxidation process to monitor and describe the quality of packaged olive oil quantitatively.

The influence of annealing on the microstructure and electrical resistivity of jelly-rolled Cu-Nb composite wires

In this paper, the annealing effects on the microstructure and electrical resistivity of jelly-rolled Cu-x% vol. Nb (x=25, 33, 50, and 63) composite wires were investigated. During annealing, noticeable changes take place in the microstructure, including recovery and recrystallization of copper and niobium, followed by spheroidization and further coalescence of niobium filaments. With increasing annealing temperature, the diffusion-controlled coalescence of niobium filaments is enhanced due to their proximity. The behavior of the electrical resistivity in the normal state of the Cu-Nb composite shows a noticeable change at a specific value of temperature in the range between 50K and 70 K. This temperature varies with the niobium volume fraction. Such a behavior is discussed in terms of the decrease of the amount of Cu-Nb interfaces promoted by coarsening and by electron scattering effects at these interfaces.

The Melting Process of Ice Inside a Horizontal Cylinder: Effects of Density Anomaly

In the present investigation heat transfer during melting of ice confined within a heated, horizontal cylinder is studied experimentally and by analysis. Because of the well-known density inversion effect of water in the proximity of the melting point of ice the first-order influence of convection flow for phase change processes becomes obvious. Depending on the inner diameter of the cylinder and on the specific temperature value Tw > 0° of the cylinder wall, quite different shapes of the melting ice body, the flow pattern, and the temperature field were predicted by numerical analysis. Also provided are local and overall heat transfer coefficients, revealing a reasonable agreement between experiments and predicted data. Computations were performed for wall temperatures in the range 4°C ≤ Tw ≤ 15°C and two inner diameters of the cylinder.