Small Temperature Variations Research Articles

Chromatographic Application on a Calixarene Stationary Phase: A Novel HPLC Determination of Flumethasone Pivalate and Salicylic Acid in Their Binary Mixture and Ointment Dosage Form after Two Steps Extraction

Present study reported for the first time about a new, simple, fast, robust and accurate, routine HPLC method for simultaneous quantification of Flumethasone Pivalate and salicylic acid in bulk powder and in an ointment dosage form. Chromatographic analysis was carried out on Calixarene stationary phase after two steps extraction. Water was used in first step for extraction of salicylic acid because the excipients in the ointment interfere with salicylic acid determination upon extraction with organic solvent. After that the residue was extracted with organic solvent for Flumethasone Pivalate. Acetonitrile and H2O in the ratio of 70:30 at flow rate of 1 mLmin-1 and 40 °C were applied as isocratic binary mobile phase. Detection was done at 240 nm. Limits of detection and quantitation for both analytes were 0.125 and 0.250 µg mL-1, respectively. The recovery values of this method were 98.99 ± 0.66% and 97.50 ± 1.33% for salicylic acid and Flumethasone Pivalate, respectively. The effect of small variations in temperature, flow rate, detection wavelength, acetonitrile percentage in mobile phase and injection volume was studied to determine the robustness of the method. The proposed method was found to be robust.

Study on the lifetime characteristics of power modules under power cycling conditions

This study presents a study on non-linear accumulative modelling for power module lifetime estimation in non-accelerated operation. The model focuses on solder fatigue based on monitoring the internal thermal resistance of the module. Initially, the relatively small junction temperature variation (ΔT j) cycles contribute little to the lifetime consumption, but with an initial damage the effect becomes noticeable. The original Coffin–Manson accumulation approach is extended for complex mission profiles. The proposed non-linear accumulation model has three aspects: a Coffin–Manson relationship is first established; the thermal resistance degradation is then used to quantify damage accumulation; the effects of the average junction temperature (T jmean) and ΔT j on the rate of degradation are finally included through the parameters of the non-linear accumulation model which also depends on the effect of the present condition of the module. Experiments demonstrate the phenomena and verify the proposed model.

Thermal energy harvesting by piezoelectric PVDF polymer coupled with shape memory alloy

A novel flexible composite thermal energy harvester is presented, which couples pyroelectric and piezoelectric effects of polyvinylidene fluoride (PVDF) with shape memory effect of TiNiCu alloy. The harvester combines superior flexibility of PVDF with large temperature-induced strain of the shape memory alloy to harvest small and quasi-static temperature variations. The post-stamp size harvester (27.5mm3) achieved an energy density of 0.41mJ/cm3 per event of temperature variation of 20°C. When reaching 70°C the harvester, consisting of a stack of four PVDF, powered a wireless node instantaneously without any storage unit. The use of PVDF quadruples the energy output, compared to previously reported PZT-based composites.

Ultrasonic thermometry simulation in a random fluctuating medium: Evidence of the acoustic signature of a one-percent temperature difference

We study the development potential of ultrasonic thermometry in a liquid fluctuating sodium environment similar to that present in a Sodium-cooled Fast Reactor, and thus investigate if and how ultrasonic thermometry could be used to monitor the sodium flow at the outlet of the reactor core. In particular we study if small temperature variations in the sodium flow of e.g. about 1% of the sodium temperature, i.e., about 5°C, can have a reliably-measurable acoustic signature. Since to our knowledge no experimental setups are available for such a study, and considering the practical difficulties of experimentation in sodium, we resort to a numerical technique for full wave propagation called the spectral-element method, which is a highly accurate finite-element method owing to the high-degree basis functions it uses. We obtain clear time-of-flight variations in the case of a small temperature difference of one percent in the case of a static temperature gradient as well as in the presence of a random fluctuation of the temperature field in the turbulent flow. The numerical simulations underline the potential of ultrasonic thermometry in such a context.

Investigation of bimaterial cantilever beam for heat sensing in liquid

This paper presents the theoretical and experimental temperature profiles along a microcantilever beam operated in liquid and employed in this research as a temperature sensor. The main application of this cantilever beam is for sensing temperature variations of mammalian cells. The cantilever beam was microprocessed as a composite structure fabricated from thin layers of silicon nitride and gold. In order to achieve high sensitivity the cantilever beam was conceived with the length at microscale and the thickness at nanoscale dimensions. Very small temperature variations generated the deflection of the cantilever beam free end due to different values of the thermal expansion coefficients of silicon nitride and gold. The paper is focused on the temperature calibration of the cantilever beam temperature sensor when it is operated in liquid. In the paper a microwire heater was used as a localized heat source to generate the heat required for calibration purposes. The cantilever beam was immersed in the liquid and the heater temperature was varied from 27.5°C to 71.8°C. In analogy with the situation when temperature variations are sensed at certain distance from a cell in suspension the heater was located at 15μm distance from the cantilever beam. The experimental deflection values were compared with the theoretical deflection values and the heat transfer coefficient h of the system was calculated. At low temperatures the heat transfer coefficient value was 381W/m2K and at higher temperatures 642W/m2K. The experimental measurements illustrate that the cantilever beam deflection has the largest values when the heater was located near the midpoint of the cantilever beam. A systematic investigation of the cantilever beam deflection in liquid as a function of the applied heat is important for chemical and biological applications.

High solar cycle spectral variations inconsistent with stratospheric ozone observations

Some of the natural variability in climate is understood to come from changes in the Sun. A key route whereby the Sun may influence surface climate is initiated in the tropical stratosphere by the absorption of solar ultraviolet (UV) radiation by ozone, leading to a modification of the temperature and wind structures and consequently to the surface through changes in wave propagation and circulation. While changes in total, spectrally-integrated, solar irradiance lead to small variations in global mean surface temperature, the `top-down' UV effect preferentially influences on regional scales at mid-to-high latitudes with, in particular, a solar signal noted in the North Atlantic Oscillation (NAO). The amplitude of the UV variability is fundamental in determining the magnitude of the climate response but understanding of the UV variations has been challenged recently by measurements from the SOlar Radiation and Climate Experiment (SORCE) satellite, which show UV solar cycle changes up to 10 times larger than previously thought. Indeed, climate models using these larger UV variations show a much greater response, similar to NAO observations. Here we present estimates of the ozone solar cycle response using a chemistry-climate model (CCM) in which the effects of transport are constrained by observations. Thus the photolytic response to different spectral solar irradiance (SSI) datasets can be isolated. Comparison of the results with the solar signal in ozone extracted from observational datasets yields significantly discriminable responses. According to our evaluation the SORCE UV dataset is not consistent with the observed ozone response whereas the smaller variations suggested by earlier satellite datasets, and by UV data from empirical solar models, are in closer agreement with the measured stratospheric variations. Determining the most appropriate SSI variability to apply in models...

Effect of Evaporation Temperature on the Performance of Organic Rankine Cycle in Near-Critical Condition

Considering the large variations of working fluid's properties in near-critical region, this paper presents a thermodynamic analysis of the performance of organic Rankine cycle in near-critical condition (NORC) subjected to the influence of evaporation temperature. Three typical organic fluids are selected as working fluids. They are dry R236fa, isentropic R142b, and wet R152a, which are suited for heat source temperature from 395 to 445 K. An iteration calculation method is proposed to calculate the performance parameters of organic Rankine cycle (ORC). The variations of superheat degree, specific absorbed heat, expander inlet pressure, thermal efficiency, and specific net power of these fluids with evaporation temperature are analyzed. It is found that the working fluids in NORC should be superheated because of the large slope variation of the saturated vapor curve in near-critical region. However, the use of dry R236fa or isentropic R142b in NORC can be accepted because of the small superheat degree. The results also indicate that a small variation of evaporation temperature requires a large variation of expander inlet pressure, which may make the system more stable. In addition, due to the large decrease of latent heat in near-critical region, the variation of specific absorbed heat with evaporation temperature is small for NORC. Both specific net power and thermal efficiency for the fluids in NORC increase slightly with the rise of the evaporation temperature, especially for R236fa and R142b. Among the three types of fluids, dry R236fa and isentropic R142b are better suited for NORC. The results are useful for the design and optimization of ORC system in near-critical condition.

Variations on thermal transport modelling of subsurface temperatures using high resolution data

Although streambed dynamics are known to be complex and three-dimensional, flux within the subsurface is often estimated with simplified models for convenience, despite the errors this incurs. While three-dimensional (3D) models have the advantage of being able to capture complex flow paths within the subsurface, they are also more data intensive, requiring a detailed knowledge of both thermal and hydraulic streambed properties. Temperature data are relatively easy to acquire at a high resolution within a natural stream environment; however, it is typically more difficult to capture hydraulic head measurements at this same resolution, making it difficult to apply appropriate boundary conditions to 3D models in order to estimate streambed fluxes from heat tracer techniques alone. In this study, we examine the consequences of the lack of detailed head data for parameterizing boundary conditions. We tested the abilities of three 3D heat and water transport models with increasingly complex boundary conditions to match observed thermal patterns and predict streambed fluxes. All three models showed similar spatial patterns of high and low fluxes. The amplitude of predicted daily temperature variation at a depth of 0.25 m and 0.5 m below the streambed was generally within 0.1 °C (i.e. within sensor error) of observed, while all three models typically underestimated daily temperature variation in advective areas at a depth of 0.1 m. The results of this study suggest that 3D heat transport models of streambeds may be more limited by the low sensitivity of hydraulic conductivity to small temperature variations than by the lack of detailed hydraulic head data for parameterizing boundary conditions.

Development of Polycaprolactone/Poly(Vinyl Alcohol)/Clay Microparticles by Spray Drying

In this study, nanostructured microparticles was developed with polycaprolactone (PCL), poly(vinyl alcohol) (PVAL) and nanoparticles of the commercial sodium clay NT-25® by using the spray drying technique. The systems obtained were characterized by Nuclear Magnetic Resonance (NMR), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Dynamic Laser Light Scattering (DLS) and Differential Scanning Calorimetry (DSC). The NMR 13C and FTIR techniques showed that both polymers were present in the microparticles and the DSC analysis revealed a small variation in the glass transition temperature of the PCL. The XRD and SEM analyses showed that the microparticles produced were amorphous and had a concave morphology. The NT-25 nanoload reduced the microparticles’ size due to the multiple interactions formed in the hybrid nanocomposite material. Therefore, it was possible to develop microparticles by using biodegradable and biocompatible polymers, with different polarities, allowing the incorporation of hydrophilic and hydrophobic materials and enabling the inclusion of otherwise incompatible materials in the same system.

Experimental Study on Hygrothermal Deformation of External Thermal Insulation Cladding Systems with Glazed Hollow Bead

This research analyzes the thermal and strain behavior of external thermal insulation cladding systems (ETICS) with Glazed Hollow Beads (GHB) thermal insulation mortar under hygrothermal cycles weather test in order to measure its durability under extreme weather (i.e., sunlight and rain). Thermometers and strain gauges are placed into different wall layers to gather thermal and strain data and another instrument measures the crack dimensions after every 4 cycles. The results showed that the finishing coat shrank at early stage (elastic deformation) and then the finishing coat tends to expand and become damaged at later stage (plastic deformation). The deformation of insulation layer is similar to that of the finishing coat but its variation amplitude is smaller. Deformation of substrate expanded with heat and contracted with cold due to the small temperature variation. The length and width of cracks on the finishing coat grew as the experiment progressed but with a decreasing growth rate and the cracks stopped growing around 70 cycles.

Temperature-induced variation in gene expression burst size in metazoan cells.

BackgroundGene expression is an inherently stochastic process, owing to its dynamic molecular nature. Protein amount distributions, which can be acquired by cytometry using a reporter gene, can inform about the mechanisms of the underlying microscopic molecular system.ResultsBy using different clones of chicken erythroid progenitor cells harboring different integration sites of a CMV-driven mCherry protein, we investigated the dynamical behavior of such distributions. We show that, on short term, clone distributions can be quickly regenerated from small population samples with a high accuracy. On longer term, on the contrary, we show variations manifested by correlated fluctuation in the Mean Fluorescence Intensity. In search for a possible cause of this correlation, we demonstrate that in response to small temperature variations cells are able to adjust their gene expression rate: a modest (2 °C) increase in external temperature induces a significant down regulation of mean expression values, with a reverse effect observed when the temperature is decreased. Using a two-state model of gene expression we further demonstrate that temperature acts by modifying the size of transcription bursts, while the burst frequency of the investigated promoter is less systematically affected.ConclusionsFor the first time, we report that transcription burst size is a key parameter for gene expression that metazoan cells from homeotherm animals can modify in response to an external thermal stimulus.Electronic supplementary materialThe online version of this article (doi:10.1186/s12867-015-0048-2) contains supplementary material, which is available to authorized users.

Thermophysical Properties of Silicon Dioxide (SiO2) in Ethylene Glycol/Water Mixture for Proton Exchange Membrane Fuel Cell Cooling Application

Polymer Electrolyte Membrane Fuel Cells (PEMFC) operation is sensitive to micro electrochemical changes and can only tolerate a small temperature variation for optimal power generation. An effective cooling system is needed to comply with this condition. Nanofluids are perceived as a potential coolant for thermal management in PEMFC application that allows for more compact design. The dispersion of nanofluid in water-ethylene glycol base fluid enhances the thermal conductivity for improved heat transfer. The thermal conductivity, viscosity and electrical conductivity of different Silicon Dioxide (SiO2) concentrations diluted in Ethylene Glycol/Water (EG/W) mixtures of 40EG, 50EG and 60EG are reported. However, the electrical conductivity would contribute to electrical leakage and is a limiting factor for fuel cell operation. Highest value of thermal conductivity recorded is the dispersion of nanofluid in 40EG whereas the viscosity of SiO2 is the highest in 60EG dilution. Electrical conductivity is recorded the highest in EG/W 40:60% with 0.5% of SiO2. However, the electrical conductivity would contribute to electrical leakage and is a limiting factor for fuel cell operation.

Equivalent norms in from thermodynamical laws

In 1978, Landsberg proposed an elegant way of obtaining the inequality between arithmetic and geometric mean by using the first and second laws of thermodynamics. This result opened a debate on the logic legitimacy of this procedure to obtain some mathematical truths. Although this discussion can not be considered completed, the Landsberg approach has shown a great richness in obtaining many algebraic inequalities. In the present article we apply the Landsberg method to some properties of normed spaces trough a vector space of temperatures. In this way, the result that establishes the equivalence between all p-norms in the space and the minimal constant that guaranties this fact are readily found. Geometrical surfaces stemming from energy conservation are a consequence of this interpretation. In this manner, an application for thermal equilibrium of n reservoirs is suggested as an example of the contribution that the theory of norms may offer to physical problems when almost ideal heat baths are systems with a heat capacity of the form with . For this class of reservoirs the problem of obtaining the final temperature of two thermal baths with infinite or nearly infinite heat capacities in thermal contact is unambiguously solved. This might be the case in some systems which produce an incredibly large heat exchange due to small variations of temperature.

Spatially tunable emissions of dye-doped liquid crystal lasers between the cholesteric and smectic phases

Spatially tunable lasing emissions from dye-doped heavy chiral concentration liquid crystals (DD-HCCLCs) were investigated in this work. After thermal control of HCCLCs to below the phase transition temperature, the central wavelength of the photonic bandgap (PBG) was sensitively related to the working temperature, which could be tuned widely with the relatively small temperature variation owing to the phase transition from the cholesteric (Ch) to the smectic (Sm) phase. By means of Keating’s theory, the change in helical pitch, obtained from the transmission spectrum, versus temperature can be well fitted to derive the phase transition temperature of the smectic A phase. As the pump beam was focused on different locations of the DD-HCCLC cell with a one-dimensional temperature gradient, we demonstrated spatially tunable lasing peaks over one hundred nanometers from 556 nm to 671 nm. The experimental result regarding the spatially tunable lasing property shows that the DD-HCCLC laser could be a promising light source in display technology.

Equilibrating Effect of Maxwell-Type Boundary Condition in Highly Rarefied Gas

We study the equilibrating effects of the boundary and intermolecular collision in the kinetic theory for rarefied gases. We consider the Maxwell-type boundary condition, which has weaker equilibrating effect than the commonly studied diffuse reflection boundary condition. The gas region is the spherical domain in $\mathbb{R}^d$, $d=1,2$. First, without the equilibrating effect of collision, we obtain the algebraic convergence rates to the steady state of free molecular flow with variable boundary temperature. The convergence behavior has intricate dependence on the accommodation coefficient of the Maxwell-type boundary condition. Then we couple the boundary effect with the intermolecular collision and study their interaction. We are able to construct the steady state solutions of the full Boltzmann equation for large Knudsen numbers and small boundary temperature variation. We also establish the nonlinear stability with exponential rate of the stationary Boltzmann solutions. Our analysis is based on the explicit formulations of the boundary condition for symmetric domains.

Capillary electrophoresis analysis of different variants of the amyloidogenic protein β2 -microglobulin as a simple tool for misfolding and stability studies.

Free solution capillary electrophoresis with UV detection is here used to retrieve information on the conformational changes of wild-type β2 -microglobulin and a series of naturally and artificially created variants known to have different stability and amyloidogenic potential. Under nondenaturing conditions, the resolution of at least two folding conformers at equilibrium is obtained and a third species is detected for the less stable isoforms. Partial denaturation by using chaotropic agents such as acetonitrile or trifluoroethanol reveals that the separated peaks are at equilibrium, as the presence of less structured species is either enhanced or induced at the expenses of the native form. Reproducible CE data allow to obtain an interesting semiquantitative correlation between the peak areas observed and the protein stability. Thermal unfolding over the range 25-42°C is induced inside the capillary for the two pathogenic proteins (wtβ2 -microglobulin and D76N variant): the large differences observed upon small temperature variation draw attention on the robustness of analytical methods when dealing with proteins prone to misfolding and aggregation.

Measurements of very small temperature variations with LWIR QWIP infrared camera

Infrared thermography, thanks to its non-contact character, can be advantageously exploited to get information in lots of temperature-dependent applications. Indeed, a vast variety of infrared imaging devices is today available, allowing measurements also in complex configurations such as in presence of fast phenomena, or moving objects. Of course, the measurement accuracy depends strongly on the magnitude of temperature differences both in space and in time; some limitations may arise when attempting to measure temperature variations which are very small and at the edge of the instrument resolution. In this regard, a difficult task is to perceive the temperature variations which are related to thermo-elastic effects, e.g., developing under relatively low loads. The purpose of this work is to deepen inside the parameters that mostly affect such critical measurements and to search for a simple and reliable solution. Measurements are performed with the LWIR QWIP SC6000 camera and the obtained data are compared with those supplied by either an InSb MWIR camera, or an un-cooled camera. Particular attention is deserved to the electronic output of the infrared imaging device and to post-processing signal procedures. It is found that, through the use of a reference area, is possible to account and avoid most of the existing noise.

Numerical simulations of the influence of solar zenith angle on properties of the M1 layer of the Mars ionosphere

AbstractThe M1 layer of the Mars ionosphere is one of its most significant features, second only to the M2 layer. Observations have shown how the physical properties of this layer depend on solar zenith angle (SZA) and solar irradiance, but these trends have not yet been explored in detail by numerical simulations. Hence, the full implications of the observational findings for the M1 layer's behavior have not been established. Here we use the Boston University Mars Ionosphere Model to simulate the M1 layer over a period of 6 months. In order to adequately reproduce the SZA dependence of the observed M2 peak density, an ad hoc isothermal electron temperature profile was required. This representation was motivated by detailed energy balance calculations that predict relatively small variations in electron temperature at the M2 peak. We find several model results consistent with observations: the simulated M1 peak density is effectively proportional to Ch(SZA)−0.5, where Ch is the Chapman function; the ratio of M1 to M2 peak electron densities is independent of SZA; the simulated M1 peak altitude decreases with increasing solar irradiance; and the simulated difference in altitude between the M1 and M2 layers increases with SZA at the observed rate. Due to limitations in the assumed neutral atmosphere, the simulated increase in M1 peak altitude with increasing solar zenith angle is significantly greater than observed. In both simulations and observations, limitations in representing the width of the M1 layer prevent meaningful comparisons and connections to the neutral scale height.

High-precision flow temperature imaging using ZnO thermographic phosphor tracer particles.

Zinc oxide (ZnO) particles are characterised as a tracer for temperature measurements in turbulent flows, in the context of the thermographic particle image velocimetry technique. Flow measurements are used to compare the temperature precision of ZnO to that obtained using a well-characterised thermographic phosphor, BAM:Eu(2+), under the same conditions. For this two-colour, ratio-based technique the strongly temperature-dependent redshift of the luminescence emission of ZnO offers improved temperature sensitivity, and so at room temperature a threefold increase in the temperature precision is achieved. A dependence of the intensity ratio on the laser fluence is identified, and additional measurements with different laser pulse durations are used to independently show that there is also a dependence on the laser excitation irradiance, irrespective of fluence. A simple method to correct for these effects is demonstrated and sources of error are analysed in detail. Temperature images in a Re = 2000 jet of air heated to 363 K with a precision of 4 K (1.1%) are presented. The sensitivity of ZnO increases across the tested temperature range 300-500 K, so that at 500 K, using a seeding density of 2 x 10(11) particles/m(3), a precision of 3 K (0.6%) is feasible. This new phosphor extends the capabilities of this versatile technique toward the study of flows with small temperature variations.

Thermal imaging of Uranus: Upper-tropospheric temperatures one season after Voyager

We report on 18–25μm thermal imaging of Uranus that took place between 2003 and 2011, a time span roughly one season after the thermal maps made by the Voyager-2 IRIS experiment in 1986. We re-derived meridional variations of temperature and para-H2 fraction from the Voyager experiment and compared these with the thermal images, which are sensitive to temperatures in the upper troposphere of Uranus around the 70–400mbar atmospheric pressure range. The thermal images display a maximum of 3K of equivalent temperature changes across the disk, and they are consistent with the temperature distribution measured by the Voyager IRIS experiment. This implies that there has been no detectable change of the meridional distribution of upper-tropospheric/lower-stratospheric temperatures over a season. This is inconsistent with seasonally dependent radiative–convective-dynamical models and full global climate models that predict some variability with season if the effective temperature is meridionally constant. We posit that the effective temperature of Uranus could be meridionally variable, with the additional possibility that even the small temperature variations predicted by the GCMs are overestimated.