Small Temperature Variations Research Articles

The role of polypropylene matrix in cyclic bending coupled thermal effects

Infrared thermography is used to visualize temperature variations which are linked to thermoelastic effects developing over the surface of a cantilever beam undergoing deflection under cyclic bending tests. Several specimens are fabricated of thermoplastic composite materials, which involve change of matrix and/or reinforcement. More specifically, the matrix is either a pure polypropylene, or a polypropylene modified with the addition of a certain percentage of compatibilizing agent (grafted); the reinforcement being made of woven glass, or jute, fibers. Cyclic bending tests are carried out with the aid of an electromechanical actuator. One surface of the specimen is continuously viewed by an infrared imaging device during deflection. The suitability of infrared thermography to distinguish the small surface temperature variations, depending on both matrix and reinforcement type, has been previously demonstrated. In this work, the matrix is separately analyzed to add information about its role when coupled with either glass, or jute, and in the presence of a certain percentage of a grafting agent. POLYM. ENG. SCI., 57:680–684, 2017. © 2017 Society of Plastics Engineers

Variation patterns of fine root biomass, production and turnover in Chinese forests

China’s forests cover 208.3 million ha and span a wide range of climates and a large variety of forest types, including tropical, temperate, and boreal forests. However, the variation patterns of fine root (<2 mm in diameter) biomass, production, and turnover from the south to the north are unclear. This study summarizes fine root biomass (FRB), production (FRP) and turnover rate (FRT) in China’s forests as reported by 140 case studies published from 1983 to 2014. The results showed that the mean values of FRB, FRP and FRT in China’s forests were 278 g m−2, 366 g m−2 a−1, and 1.19 a−1, respectively. Compared with other studies at the regional or global scales, FRB in China’s forests was lower, FRP was similar to estimates at the global scale, but FRT was much higher. FRB, FRP, and FRT in China’s forests increased with increasing mean annual precipitation (MAP), indicating that fine root variables were likely related to MAP, rather than mean annual temperature or latitude. This is possibly due to the small variation in temperature but greater variation in precipitation during the growing season. These findings suggest that spatiotemporal variation in precipitation has a more profound impact on fine root dynamics in China’s forests, and this will impact carbon and nutrient cycles driven by root turnover in the future.

MWR: Microwave Radiometer for the Juno Mission to Jupiter

The Juno Microwave Radiometer (MWR) is a six-frequency scientific instrument designed and built to investigate the deep atmosphere of Jupiter. It is one of a suite of instruments on NASA’s New Frontiers Mission Juno launched to Jupiter on August 5, 2011. The focus of this paper is the description of the scientific objectives of the MWR investigation along with the experimental design, observational approach, and calibration that will achieve these objectives, based on the Juno mission plan up to Jupiter orbit insertion on July 4, 2016. With frequencies distributed approximately by octave from 600 MHz to 22 GHz, the MWR will sample the atmospheric thermal radiation from depths extending from the ammonia cloud region at around 1 bar to pressure levels as deep as 1000 bars. The primary scientific objectives of the MWR investigation are to determine the presently unknown dynamical properties of Jupiter’s subcloud atmosphere and to determine the global abundance of oxygen and nitrogen, present in the atmosphere as water and ammonia deep below their respective cloud decks. The MWR experiment is designed to measure both the thermal radiation from Jupiter and its emission-angle dependence at each frequency relative to the atmospheric local normal with high accuracy. The antennas at the four highest frequencies (21.9, 10.0, 5.2, and 2.6 GHz) have ∼12° beamwidths and will achieve a spatial resolution approaching 600 km near perijove. The antennas at the lowest frequencies (0.6 and 1.25 GHz) are constrained by physical size limitations and have 20° beamwidths, enabling a spatial resolution of as high as 1000 km to be obtained. The MWR will obtain Jupiter’s brightness temperature and its emission-angle dependence at each point along the subspacecraft track, over angles up to 60° from the normal over most latitudes, during at least six perijove passes after orbit insertion. The emission-angle dependence will be obtained for all frequencies to an accuracy of better than one part in 10^3, sufficient to detect small variations in atmospheric temperature and absorber concentration profiles that distinguish dynamical and compositional properties of the deep Jovian atmosphere.

Reanalysis of the Much Referenced Ethanol‐trichloromethane Mixture Vapor Pressure Data: A Discussion of the Principal Association Species Present

AbstractThe Scatchard (S) and Raymond (R) 1938 data on the vapor pressure above ethanol (1)‐trichloromethane (2) mixtures at the temperatures of 35, 45 and 55° C are still being used today in discussions of the thermodynamic properties and association species present in 1‐2 mixtures. Here a detailed reanalysis of the originally published SR data has been carried out using the model free Redlich‐Kister excess chemical potential approach as applied by Barker. These results show how small temperature variations drastically affect mixture vapor pressure measurements. A number of weaknesses in SR's original analysis of their data and significant discrepancies between R's thesis results and those in the published SR paper have been uncovered. These discrepancies would impact the conclusions of anyone using SR's results. From the present reanalysis more accurate temperatures dependent Gibbs excess energies, excess entropies, excess enthalpies and activity coefficients have been calculated that could not been obtained from SR data analysis scheme. Based on available experimental and theoretical studies of the 1‐2 system it is argued that the major association species should be the cyclic 111 trimer and that the dimer 22 should be considered. This is counter to a current model for this system.

Splicing-related genes are alternatively spliced upon changes in ambient temperatures in plants

Plants adjust their development and architecture to small variations in ambient temperature. In a time in which temperatures are rising world-wide, the mechanism by which plants are able to sense temperature fluctuations and adapt to it, is becoming of special interest. By performing RNA-sequencing on two Arabidopsis accession and one Brassica species exposed to temperature alterations, we showed that alternative splicing is an important mechanism in ambient temperature sensing and adaptation. We found that amongst the differentially alternatively spliced genes, splicing related genes are enriched, suggesting that the splicing machinery itself is targeted for alternative splicing when temperature changes. Moreover, we showed that many different components of the splicing machinery are targeted for ambient temperature regulated alternative splicing. Mutant analysis of a splicing related gene that was differentially spliced in two of the genotypes showed an altered flowering time response to different temperatures. We propose a two-step mechanism where temperature directly influences alternative splicing of the splicing machinery genes, followed by a second step where the altered splicing machinery affects splicing of downstream genes involved in the adaptation to altered temperatures.

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.

Effect of increased fuel volatility on CDC operation in a light-duty CIDI engine

Alternative diesel fuels derived from biomass can vary significantly in volatility compared to their petroleum-derived counterparts, and their appropriate utilization is contingent on their compatibility with existing engine infrastructure. To investigate this compatibility, experiments were carried out to study the effect of fuel volatility on conventional diesel combustion (CDC) performance under a wide range of in-cylinder thermodynamic conditions at start of injection (SOI). Fuels of matched reactivity (i.e., cetane number (CN)) and varying volatility were produced by blending binary mixtures of 2,6,10-trimethyldodecane (farnesane) and 2,2,4,4,6,8,8-heptamethylnonane, octane number primary reference fuels (PRF), and cetane number secondary reference fuels (SRF). Nine fuel blends were tested in total, consisting of 3 volatility characteristics at 3 reactivity levels. Five engine operating conditions were utilized, ranging from 14.7–29kg/m3 and 980–1120K in-cylinder density and temperature at SOI. Testing was performed in a single-cylinder GM 1.9L diesel engine. Only small differences in ignition delay (ID), in-cylinder pressure, and heat release rate (HRR) were observed between fuels of matched CN, regardless of their volatility. An analysis of the spray breakup and mixture formation process indicated that there were only small variations in ambient air entrainment and jet temperature between fuel blends, in agreement with the observed combustion behavior.

On the underestimated impact of the gelation temperature on macro- and mesoporosity in monolithic silica.

The preparation of monolithic SiO2 with bimodal porosity using a special sol-gel procedure ("Nakanishi process") generally shows a pronounced sensitivity towards several physico-chemical parameters of the initial solution (concentrations, precursors, pH, temperature, etc.). Thus, temporal and spatial variations of these parameters during the sol-gel reactions can affect the final meso- and macropore space with respect to the pore size distributions and homogeneity. In this study we thoroughly examine the sol-gel reaction in terms of the impact of temperature accuracy and homogeneity during the gelation and their effect on meso- and macropore space. The in-depth characterization of the macroporosity in monolithic SiO2 rods, prepared by utilizing a highly homogeneous and accurate temperature profile, shows that a decrease of only 1.5 °C during the reaction doubles the mean size of the macropores in the analyzed temperature ranges (22.0-28.0 °C and 33.5-36.5 °C). Rheological measurements of the gelation points and the viscosity of the starting solutions prove that a higher reaction rate is the main reason for this marked temperature-sensitivity. Furthermore, the mesoporosity is affected to a surprising extent by the applied small temperature differences during the gelation reaction. This phenomenon is shown to be mainly caused by the temperature-dependent differences in macropore and skeleton dimensions and an inhomogeneous distribution of mesopore sizes within the skeleton. In essence, our study reveals that the impact of temperature on the formation of meso- and macroscale dimensions during the sol-gel process has been underestimated so far. The impact of a poor temperature homogeneity during monolith synthesis is exemplarily demonstrated by the application of monolithic silica capillary columns in HPLC.

Ag/Ag2S Nanocrystals for High Sensitivity Near‐Infrared Luminescence Nanothermometry

Temperature sensing in biological media (cells, tissues, and living organisms) has become essential in the development of the last generation of diagnostics and therapeutic strategies. Thermometry can be used for early detection of different diseases, such as cancer, stroke, or inflammation processes, one of whose incipient symptoms is the appearance of localized temperature singularities. Luminescence nanothermometry, as a tool to accurately provide temperature sensing in biological media, requires the rational design and development of nanothermometers operating in the second biological window. In this work, this is achieved using Ag/Ag2S nanocrystals as multiparametric thermal sensing probes. Temperature sensing with remarkably high sensitivity (4% °C−1) is possible through intensity‐based measurements, as their infrared emission is strongly quenched by small temperature variations within the biological range (15–50 °C). Heating also results in a remarkable redshift of the emission band, which allows for concentration‐independent temperature sensing based on infrared ratiometric measurements, with thermal sensitivity close to 2% °C−1. These results make Ag/Ag2S nanocrystals the most sensitive among all noncomposite nanothermometers operating in the second biological window reported so far, allowing for deep‐tissue temperature measurements with low uncertainty (0.2 °C).

A simplified stationary energy-transport model with temperature-dependent conductivity

A simplified stationary energy-transport model in semiconductors is studied while the conductivity depends on both electron density and temperature. The existence and uniqueness of classical solutions to the model is proved for small variations of electron density and temperature.

Basic temperature correction of QWIP cameras in thermoelastic/plastic tests of composite materials.

The present work is concerned with the use of a quantum well infrared photodetector (QWIP) infrared camera to measure very small temperature variations, which are related to thermoelastic/plastic effects, developing on composites under relatively low loads, either periodic or due to impact. As is evident from previous work, some temperature variations are difficult to measure, being at the edge of the IR camera resolution and/or affected by the instrument noise. Conversely, they may be valuable to get either information about the material characteristics and its behavior under periodic load (thermoelastic), or to assess the overall extension of delaminations due to impact (thermo-plastic). An image post-processing procedure is herein described that, with the help of a reference signal, allows for suppression of the instrument noise and better discrimination of thermal signatures induced by the two different loads.

Compensation method for the influence of angle of view on animal temperature measurement using thermal imaging camera combined with depth image

In the study, we proposed an animal surface temperature measurement method based on Kinect sensor and infrared thermal imager to facilitate the screening of animals with febrile diseases. Due to random motion and small surface temperature variation of animals, the influence of the angle of view on temperature measurement is significant. The method proposed in the present study could compensate the temperature measurement error caused by the angle of view. Firstly, we analyzed the relationship between measured temperature and angle of view and established the mathematical model for compensating the influence of the angle of view with the correlation coefficient above 0.99. Secondly, the fusion method of depth and infrared thermal images was established for synchronous image capture with Kinect sensor and infrared thermal imager and the angle of view of each pixel was calculated. According to experimental results, without compensation treatment, the temperature image measured in the angle of view of 74° to 76° showed the difference of more than 2°C compared with that measured in the angle of view of 0°. However, after compensation treatment, the temperature difference range was only 0.03–1.2°C. This method is applicable for real-time compensation of errors caused by the angle of view during the temperature measurement process with the infrared thermal imager.

Q&A: George Smoot.

George Smoot shared the 2006 Nobel Prize in Physics for the discovery of small temperature variations in the cosmic microwave background radiation, providing support for Big Bang theory. Smoot spoke to Nature about last year's big cosmological discovery, gravitational waves.

Flow boiling in microchannels: Fundamentals and applications

The rapid advances in performance and miniaturization of electronics and high power devices resulted in huge heat flux values that need to be dissipated effectively. The average heat flux in computer chips is expected to reach 2–4.5MW/m2 with local hot spots 12–45MW/m2 while in IGBT modules, the heat flux at the chip level can reach 6.5–50MW/m2. Flow boiling in microchannels is one of the most promising cooling methods for these and similar devices due to the capability of achieving very high heat transfer rates with small variations in the surface temperature. However, several fundamental issues are still not understood and this hinders the transition from laboratory research to commercial applications. The present paper starts with a discussion of the possible applications of flow boiling in microchannels in order to highlight the challenges in the thermal management for each application. In this part, the different integrated systems using microchannels were also compared. The comparison demonstrated that miniature cooling systems with a liquid pump were found to be more efficient than miniature vapour compression refrigeration systems. The paper then presents experimental research on flow boiling in single tubes and rectangular multichannels to discuss the following fundamental issues: (1) the definition of microchannel, (2) flow patterns and heat transfer mechanisms, (3) flow instability and reversal and their effect on heat transfer rates, (4) effect of channel surface characteristics and (5) prediction of critical heat flux.Areas where more research is needed were clearly mentioned. In addition, correlations for the prediction of the flow pattern transition boundaries and heat transfer coefficients in small to mini/micro diameter tubes were developed recently by the authors and presented in this paper.

Thermal and structural analysis of ultrasonic-welded PC/ABS blend for automobile applications

PC/ABS thermoplastic blends are widely employed in manufacturing sectors, as it yields good mechanical behavior when subjected to dynamic loading conditions. While investigating the fundamental nature of PC/ABS blends, ultrasonic welding process appears to suit their joining as compared to other conventional techniques. This paper focuses on PC/ABS welding using ultrasonic and the subsequent investigation from the insight of thermal science. It is imperative for the materials to retain key properties after subjecting it to welding. Examinations to evaluate these properties through DSC reveal a lower onset temperature change and a small variation of glass transition temperature, respectively, for parts which indicate minimal changes in thermal properties in welded and non-welded specimens. Apparent activation energies determined from TG data are practically independent of heating rates, which suggests that the most important process in the degradation of these materials corresponds to ABS. Those mixtures with high PC content show a clear increase in apparent activation energies with heating rate, suggesting that the thermal degradation mechanism of these samples is composed of several complex processes, each predominant during different stages of the overall process. SEM is used to investigate the structural morphology of the welded parts.

Which parameters, other than the water content, influence the robustness of cement paste with SCC consistency?

Robustness is the capacity of cement-based mixtures to tolerate small variations in constituent elements, mixing parameters or temperature. It is an important reason slowing down the practical implementation of self-consolidating concrete (SCC). Especially the sensitivity of fresh SCC properties to a small variation in water content can be found in literature. The influence of the mixing sequence and mixing procedure on the robustness of SCC mixtures is not extensively reported.The present paper evaluates the effect of mixing time, mixing speed and the addition time of superplasticizer on the rheological properties of cement pastes with SCC consistency, which can be related to SCC mixtures. By means of rheology, the changes induced by the variations in mixing procedure are compared to the changes induced by the variations in water and superplasticizer content. The results indicate that changing the water content is the main factor influencing rheology of cement pastes with low water-to-powder ratio (w/p). However, with increased water content in the paste mix design, other factors, such as adding time of the superplasticizer and mixing speed have equal or even superior importance as changing the water content. Dependent on the mix design, it may thus be necessary to use variables other than the water content to study robustness.

Superluminescent light emitting diodes on naturally survived InGaN/GaN lateral nanowires

We demonstrate a method for nanowire formation by natural selection during wet anisotropic chemical etching in boiling phosphoric acid. Nanowires of sub-10 nm lateral dimensions and lengths of 700 nm or more are naturally formed during the wet etching due to the convergence of the nearby crystallographic hexagonal etch pits. These nanowires are site controlled when formed in augmentation with dry etching. Temperature and power dependent photoluminescence characterizations confirm excitonic transitions up to room temperature. The exciton confinement is enhanced by using two-dimensional confinement whereby enforcing greater overlap of the electron-hole wave-functions. The surviving nanowires have less defects and a small temperature variation of the output electroluminescent light. We have observed superluminescent behaviour of the light emitting diodes formed on these nanowires. There is no observable efficiency roll off for current densities up to 400 A/cm2.

Portable IR dye laser optofluidic microresonator as a temperature and chemical sensor.

A compact and portable optofluidic microresonator has been fabricated and characterized. It is based on a Fabry-Perot microcavity consisting essentially of two tailored dichroic Bragg mirrors prepared by reactive magnetron sputtering deposition. The microresonator has been filled with an ethanol solution of Nile-Blue dye. Infrared laser emission has been measured with a pump threshold as low as 0.12 MW/cm2 and an external energy conversion efficiency of 41%. The application of the device as a temperature and a chemical sensor is demonstrated. Small temperature variations as well as small amount of water concentrations in the liquid laser medium are detected as a shift of the resonant laser modes.

Modeling and analysis of paste freezing in freeze-form extrusion fabrication of thin-wall parts via a lumped method

During the Freeze-form Extrusion Fabrication (FEF) process using aqueous-based pastes, the freezing environment solidifies the water content in the paste and thus aids the part in maintaining its shape. Because of the small temperature variation in the paste and the paste’s large latent heat introduced by the water contained in the paste, the paste typically freezes slowly during the FEF process. In this study, a lumped method was used to model the solidification process of thin-wall parts fabricated in a layer-by-layer manner. A non-dimensional analytical solution for the freezing time of parts with large numbers of layers was obtained using the lumped method, and its corresponding dimensional solution was compared with numerical simulation results. Based on the analytical solution, the effects of two non-dimensional factors (i.e., non-dimensional latent heat and effective Biot number) and six dimensional factors (i.e., convection coefficient, paste material, paste solids loading, ambient temperature, filament height, and filament width) on the freezing time were investigated. Experiments using different solids loadings pastes and extrusion parameters were conducted to validate the freezing time predictions generated by the lumped method. Possible error sources during the experiments were discussed and their effects were estimated. The results show that the lumped method can be used to accurately predict the freezing time of thin-wall parts within 17.9% differences from the measured results.

Parameter design for a phase change material board installed on the inner surface of building exterior envelopes for cooling in China

Phase change materials (PCMs) can be used for building envelope thermal management and for energy conservation because of their potential to absorb and release large amounts of heat with small wall temperature variations. In this paper, the heat transfer theory of a PCM board used for building envelopes is presented, together with a mathematical model based on the moving heat-source method. It was found that the model accurately predicted the position of the solid–liquid interface in time and space, comparing with the published data. Energy and mass efficiency (EME) was proposed to evaluate the energy efficiency of PCM boards in office buildings located in various climatic regions in China for cooling. The influences on EME of parameters, including melting temperature of PCM, PCM board thickness and the heat transfer coefficient of building envelope, were analyzed. The optimal melting temperatures of PCM board, which resulted in the peak EME, in office building were 24.1°C in Shenyang, 25.0°C in Kunming, 25.3°C in Zhengzhou and 25.5°C Changsha, respectively. The EME increased with the increasing heat transfer coefficient of building envelope. For the city of Changsha with higher outdoor air temperature, none of the PCM boards modeled contributed effectively.