Negative Thermal Effect Research Articles

Development of surface‐treated poly(lactic acid)/zinc oxide biocomposites for 3D printing in bone tissue engineering

AbstractThe increase in bone fractures has been driving the development of materials for bone repair with better mechanical and biological properties. This work reports the development of poly (lactic acid) (PLA)‐zinc oxide (ZnO) biocomposites for 3D printing of scaffolds to be applied in bone tissue engineering. The ZnO surface was functionalized with maleic anhydride (ZnOMA) by applying radio frequency plasma treatment as an alternative to control the catalytic effects of ZnO on the degradation of the PLA during the molten state processing. PLA and ZnOMA powders were processed using a heated internal mixer and the resulted biocomposites were used to manufacture scaffolds by 3D printing. The scaffolds were characterized by their rheological, thermal, microstructural, mechanical, and biological properties. Compositions containing ZnOMA presented higher viscosities, evidencing the control of degradation by surface functionalization, and achieved an elastic modulus near 1 GPa, suitable for bone applications, unlike the untreated samples. In relation to cell functions, PLA‐ZnOMA scaffolds exhibited cell viabilities at 160%, compared to 50% for untreated samples and stimulated mesenchymal stem cells toward osteoblast. Therefore, ZnO's negative thermal degradation effect on PLA was successfully overcome using plasma functionalization, enabling the 3D printing of bioactive scaffolds with great potential for application in tissue engineering.

Lithium oxides LiRO2 (R = rare earth elements) with negative thermal expansion behavior and inverse barocaloric effect

Negative thermal expansion (NTE) defies the conventional wisdom of lattice dynamics and offers a novel way to control the expansion coefficient and address some challenges in modern science and technology. From an application standpoint, materials exhibiting NTE across a broad temperature range, including room temperature, are highly sought after. In this work, we propose the multi-doping strategy and prepared a series of rare-earth-based lithium oxides featuring negative thermal expansion, with the objective of adjusting their temperature range. The phase transition temperatures of these materials range from 202 K to 467 K, demonstrating a linear correlation with the average ionic radius of the rare-earth elements. By capitalizing on the synergistic effects of four rare-earth elements, we expand the full width at half maximum of the thermal expansion peak in Li(ErYHoDy)0.25O2 from 1.6 K to 14.5 K, a notable improvement of nearly tenfold is achieved. Additionally, we investigate the low-temperature magnetocaloric effects and inverse barocaloric effects within these rare-earth-based lithium oxides. Temperature- and pressure-dependent Raman scattering measurements indicate that the phase transitions and the barocaloric effects are associated with the stretching mode of the Li–O bond and the vibrational mode of the YO6 octahedron.

Electron-phonon coupling dictates electron mean free paths and negative thermal diffusion in metals

The spatiotemporal dynamics of the fundamental energy carriers in metals underpin the efficiency of a wide array of technologies. Although much progress in our understanding of the temporal response of electronic relaxation processes following an external field perturbation has been achieved, the spatial relaxation dynamics of electrons after excitation remains unclear. Here, we employ a scanning ultrafast microscopy with high spatial resolution to directly measure the mean free paths of electrons in different metals. We show that the strength of electron-phonon coupling not only dictates the mean free paths, but also controls a peculiar spatial shrinking of the electronic temperature profile immediately after the electrons have thermalized with the ‘colder’ lattice. More specifically, from our experimental tracking of the spatial relaxation profiles, a clear observation of an effective negative thermal diffusion is apparent for metals with weaker electron-phonon coupling, while for metals with stronger electron-phonon coupling, the negative thermal diffusion effect is not observable. Our spatiotemporal modeling based on the two-temperature approach provides evidence that although negative diffusion occurs universally for materials with two different species that have varying diffusivities and are thermodynamically coupled, effective negative diffusion is masked for cases with stronger coupling between the species.

Continuous-wave and Fe2+:ZnSe passively Q-switched mid-infrared lasers based on 2at.% Er3+:CaF2 crystal

A compact high-power 2.8-µm laser with a 2 at.%-doped Er3+:CaF2 crystal was demonstrated, which delivered a maximum output power of 2.848 W with a slope efficiency of 26.3 %. To the best of our knowledge, this is the highest output power among all the reported LD end-pumped Er3+-doped fluoride crystal lasers. Experimentally, the negative thermal lens effect was characterized and the thermal lens optical diopters for two axes were obtained as Mx = -0.21 m−1/W and My = -0.33 m−1/W. In addition, the visible fluorescence spectra of Er3+:CaF2 crystal with and without laser operation were measured and analyzed. With Fe2+:ZnSe as saturable absorber, a passively Q-switched 2.759-µm Er3+:CaF2 laser with an average output power of 75 mW, a peak power of 2.39 W, a single pulse energy of 1.81 µJ, and a pulse width of 755.3 ns was obtained at a repetition rate of 41.55 kHz.

All-solid-state CW Pr3+:YLF green laser at 522 nm end-pumped by a high-power fiber-coupled 444 nm blue LD module

Continuous wave (CW) green lasers have a lot of important applications in many fields, including holography, interferometry, atom cooling and trapping, and quantum optics, and they are usually achieved by frequency-doubling 1 µm lasers based on the Nd3+ gain media. In this paper, we present an all-solid-state CW green laser with an output wavelength of 522 nm, which was directly attained by employing a Pr3+:YLF crystal pumped with a high-power fiber-coupled blue laser diode (LD) module as the gain medium. Due to the negative thermal lens effect of the Pr3+:YLF crystal, the designed laser resonator had to be lengthened with the increase in the incident pump power. As a result, when a 0.5% doped Pr3+:YLF crystal was employed as the gain medium and the incident pump power was 12 W, the length of the resonator was optimized to 311.3 mm and the maximum output power of 522 nm green laser was up to 886 mW. The obtained conversion efficiency and beam quality M2 were 11.25% and 1.15, respectively. The long-term power stability within 4.5 h was better than ±1.5% at an output power of 700 mW. The obtained watt-level green laser can also be used to generate high power CW deep UV laser for laser processing of silicon and organic materials, inspection, etc.

ANALYSIS OF POWER AND ENERGY PARAMETERS OF THE CONVEYOR INFRARED DRYER OF OIL-CONTAINING RAW MATERIALS

Infrared drying of bulk agricultural products is becoming increasingly widespread in processing and food industries due to energy efficiency, compactness of technological equipment, and ease of operation. The purpose of the presented research is to determine the influence of the technological parameters of the process of infrared drying of the moving layer of oil-containing raw materials. An experimental model of a vibro-conveyor dryer and a set of measuring equipment were developed to solve the problems. The scientific novelty of the work is the confirmation that in the conditions of a vibro-liquefied layer of products, unique conditions are created for the constant renewal of heat exchange surfaces and, accordingly, the leveling of the negative thermal radiation effect on the products, the possibility of advancing the product layer along the working zone, reducing the forces of internal friction in the technological mass, which leads to a decrease in energy consumption on the process Laws have been established regarding the effect of the number of thermoradiation blocks, the load on the flexible belt of the wave conveyor, the speed of product advancement on the belt on the dynamics of infrared drying of soybeans and rapeseed. The practical value of the work was the substantiation of the operating modes of thermoradiation drying with the help of a vibrating wave conveyor installation based on the energy saving of the technological impact, high intensification of the process and minimization of the negative effect on the properties of the processed products.

Detection and Prediction of the Early Thermal Runaway and Control of the Li-Ion Battery by the Embedded Temperature Sensor Array.

Sorts of Li-ion batteries (LIB) have been becoming important energy supply and storage devices. As a long-standing obstacle, safety issues are limiting the large-scale adoption of high-energy-density batteries. Strategies covering materials, cell, and package processing have been paid much attention to. Here, we report a flexible sensor array with fast and reversible temperature switching that can be incorporated inside batteries to prevent thermal runaway. This flexible sensor array consists of PTCR ceramic sensors combined with printed PI sheets for electrodes and circuits. Compared to room temperature, the resistance of the sensors soars nonlinearly by more than three orders of magnitude at around 67 °C with a 1 °C/s rate. This temperature aligns with the decomposition temperature of SEI. Subsequently, the resistance returns to normal at room temperature, demonstrating a negative thermal hysteresis effect. This characteristic proves advantageous for the battery, as it enables a lower-temperature restart after an initial warming phase. The batteries with an embedded sensor array could resume their normal function without performance compromise or detrimental thermal runaway.

THERMOPHYSICAL PROPERTIES OF SOILS OF THE VOLGOGRAD REGION

The study of soil thermophysics is a complex process. It is connected with the weather conditions, the time of year, the cloud cover of the atmosphere. In addition, studies were carried out in a system of bands and the state of the surface layer was influenced by such processes as the number of LP, rock composition. On the interstitial cell – the presence or absence of vegetation, the phases of its development. Therefore, qualitative interpretations of soil temperature indicators will be subjective.
 Goal. Based on empirical data, using mathematical modeling based on soil temperature data, calculate the thermophysical characteristics of chestnut soils of the Volgograd region.
 Novelty. For the first time, the characteristics of their thermophysical properties have been calculated for chestnut complex soils.
 Methods. The soil temperature at a depth of 0–20 and 20–40 cm in the zone of influence of forest strips for a longterm period is considered. The studies were carried out on chestnut and light chestnut soils of the Volgograd region in the system of forest strips (LP). The soil temperature was determined in fields without plants and under crops.
 Results. The thermal conductivity and thermal conductivity of chestnut soils were determined. A method of thermal reclamation is considered, which, in the absence of evaporation from the soil surface, causes a negative thermal effect (-∆T). When the soil is open in the interband cell (due to increased heat capacity), it warms up more in forested fields than without forest strips (LP).
 Conclusion. Mathematical modeling was used in the calculations of the thermophysical characteristics of soils. Linear, for soil without plants, and exponential (under agricultural crops) dependences are obtained. Mathematical analysis of empirical data on soil temperature showed no differences in the thermophysics of soils with and without vegetation.

Performance estimation of dehydriding process in metal hydride hydrogen storage tank with coiled-tube heat exchanger

Various thermal management methods are widely adopted in the metal hydride (MH) system to release the thermal effect and obtain acceptable hydrogen storage performance. In this work, an axisymmetric numerical model for a simple MH system without a heat exchanger (HE) has been established and validated to study the system performance during dehydriding. Then the coiled-tube heat exchanger (CTHE) and the phase change material heat exchanger (PCMHE) are used in the hydrogen storage system to improve heat transfer and release negative thermal effect, respectively. The performance of the MH-CTHE system and the MH-PCMHE has been estimated in the dehydriding process. CTHE shows more obvious impact than that of PCMHE. Effects of three common operation parameters on the hydrogen storage capacity of the MH-CTHE system have been investigated. The research results show that the influences of the heating water temperature and the outlet pressure on the system performance are more prominent than that of the heat transfer coefficient. In addition, the relationship between the average dehydriding rate of the MH-CTHE system and the two main operation parameters has been fitted as a simple equation, which can be used to predict and control the dehydriding rate based on given operation conditions.

Building wall corner structures, its microclimate and seismic resistance

Widespread low-rise residential buildings with a seismically resistant concrete frame and brick infill walls have lower microclimate levels in cold seasons due to low temperatures on the inner wall corner surfaces.These temperatures are lower if there is a corner column. For Bishkek, this temperature is 4.6 °C lower than that for permissible microclimate, even when the external wall has the required 70 mm of mineral wool slab insulation. It is caused by the negative effect of the wall corner thermal bridge. This effect is determined by ArchiCAD 20 software packages by visualizing the temperature distribution in the cross-section of the corner, which needs an additional thermal insulation layer of 40 mm. Using the LiraSAPR 2013 software package, the authors reduced the square cross-section dimensions of the column by 40 mm to allow for that additional thermal insulation layer. The optimal width of this layer is determined for different options for the meeting angle of two external walls from 70° to 180°. For a typical 90° angle, an acceptable width is 860 mm. With this insulation, it is possible to achieve the required temperature at the corner. The authors eliminated the negative thermal effect of the corner by rounding it with cement-sand plaster. Using the isotherms, it was determined that the rounding radius of 300 mm allowed for equal temperatures on the corner and inner surface of the external walls. The achieved results show that the microclimate formed as in a room without external wall corners.

Experimental Studies on Thermal Effect of H2O on the Combustion of Pulverized Coal Char

ABSTRACT The differences in the gas thermophysical properties (including heat capacity, thermal conductivity and diffusivity) between char combustion in wet and dry environments have remarkable influences on the combustion process. We conducted a detailed experimental study on the thermal effects of H2O on the coal char combustion at 1773 K in a high-temperature drop tube furnace (HTDTF). An appropriate portion of Ar was introduced into the bulk gas (O2/H2O/N2) during combustion to eliminate the opposed thermal effect of H2O. Results indicate that the H2O thermal effect initially increased with higher H2O concentrations from 0 to 10 vol.%, but it declined with a further increase in H2O concentrations in the bulk gas. Meanwhile, its effect was dominant in the preliminary and middle stages of char burning at low H2O concentrations. The increased H2O concentration and residence time promoted the gasification reaction and the water-gas shift reaction so as to weaken the negative thermal effect of H2O and improve the carbon conversion. In the 15%O2/5%H2O/80%N2 environment, the relative contribution of thermal effects to carbon conversion ratios ranked up to −36% at the residence time of 0.3 s, but it decreased to −0.3% at 21%O2/30%H2O/49%N2 atmosphere and the residence time of 0.4 s.

Magnetically Tunable Near-Field Radiative Heat Transfer in Hyperbolic Metamaterials

Active control of radiative heat transfer still remains open due to its exciting application potential. In view of this, we present a theoretical demonstration of dynamically tunable near-field radiative heat transfer (NFRHT) between two multilayer hyperbolic metamaterials (consisting of alternating layers of a magneto-optical (MO) material and a dielectric) using an external magnetic field. We show that magnetization-induced hyperbolic modes play a significant role in radiative heat transfer and allow a highly tunable heat flux. Moreover, the hybridization of intrinsic and magnetization-induced hyperbolic modes significantly enhances the radiative heat transfer. In particular, we find that polarization conversion due to nonzero off-diagonal elements enables the spectral heat transfer coefficient for the TE polarization to be as large as that for the TM polarization, which is vastly different from the case of two closely spaced bulk MO plates. In addition, to quantitatively characterize the thermal modulation, we show a negative thermal magnetoresistance effect in this system, which approaches $\ensuremath{-}59.6\mathrm{%}$ when the magnetic field intensity reaches 10 T. Our findings may be beneficial for active noncontact thermal management at the nanoscale, and facilitate a deeper understanding of the mechanisms of MO hyperbolic metamaterials in terms of NFRHT.

The use of hydronic asphalt pavements as an alternative method of eliminating hot spots of underground power cables

It is well-known that a Hydronic Asphalt Pavement (HAP) system represents an alternative method to collect heat from the Sun. In case of installation above underground power cables whose trench is completely filled with high thermal conductivity bedding, the HAP system could also collect a portion of heat generated in the cables. By collecting heat from the Sun and cables, the HAP would behave as a cooler for the cables. The application of this method to a hot spot of underground power cables is regarded as a novelty. This paper considers the use of the proposed method for eliminating the negative thermal effect of an actual hot spot on the ampacity of a 110 kV cable line, which is installed in parallel with the group of four 35 kV cables and which crosses an underground heating pipeline. The mutual thermal effects between the underground installations are simulated using FEM-based models for specified environmental conditions. In addition, an appropriate experimental background, one reference FEM-based model and two required base cases are provided. Finally, it is found that the hot spot effect can be completely eliminated and that the ampacities of the 110 kV and 35 kV cables can be increased significantly.

Seasonal thermal adaptability of shopping arcades in hot and dry climates. The case of Nicosia’s historic centre

‘Traditional’ semi-open retail environments have recently received increasing scientific attention due to their ‘rediscovery’ as passive and low-energy architectural elements, which could promote sustainability in the urban realm. This is of particular importance when considering that fully-closed contemporary shopping centres constitute high-energy consuming spaces during the cooling period, in hot climates. The present study deals with the thermal behaviour of shopping arcades, a ‘traditional’ bioclimatic urban feature, in the hot and dry climate of Cyprus, by means of on-site air temperature recordings. The aim of this research is the bi-seasonal thermal performance assessment of this semi-open space, so as to inform energy retrofitting practices and promote bioclimatism in contemporary designs. The research shows that arcades were designed mainly to address the hot climatic conditions of the island. The sample tested achieved a significant daytime cool island up to 4.4K, during the cooling period. The best performance was achieved in arcades which presented minimum openings to envelope areas. In contrast, a daytime air temperature reduction which reached 2.1K, was observed in arcades during the heating period, indicating a negative thermal effect. Overall, the positive thermal contribution of arcades during the cooling period proved stronger than the negative thermal effect during the heating period.

Calculus Removal and Root Surface Roughness When Using the Er:YAG or Er,Cr:YSGG Laser Compared with Conventional Instrumentation Method: A Literature Review.

Objective: The purpose of this literature review was to evaluate the effectiveness of using Er:YAG (erbium-doped yttrium/aluminum/garnet) laser or Er,Cr:YSGG (erbium, chromium-doped yttrium/scandium/gallium/garnet) laser on calculus removal and their effect on the topography and roughness of root surface in comparison with the conventional instruments in the nonsurgical periodontal therapy. Background data: One of the most challenging problems in treatment of periodontal disease is the elimination of plaque and calculus, leaving a clean and smooth root surface to decrease plaque and calculus retention, and for good gingival reattachment. Materials and methods: PubMed and Google Scholar were searched for available literature. The electronic search was limited to articles published in the period between January 2007 and April 2017, in the English language. Results: A total of 47 publications fulfilled the inclusion criteria of this systematic review and screened according to the research questions. Calculus removal using the ultrasonic instrument showed remaining calculus compared with the hand instrument, whereas, on the contrary, erbium lasers revealed no remaining calculus or smaller amounts compared with the conventional instruments when used in appropriate settings. The results of this review showed that ultrasonic instrumentation produced effects on the root surface almost similar to that of hand instrumentation. Er:YAG laser and Er,Cr:YSGG laser clarify a little more surface roughness when compared with conventional instruments. Conclusions: The present systematic review indicates that a combination of scaling and root planing (SRP) using the erbium lasers as an adjunctive therapy at certain parameters can be appropriate to remove residual debris from the root surface and at the same time have little or no negative thermal effect on the root surface. The Er:YAG laser also seems to be the most suitable for nonsurgical periodontal therapy. Additional new good-designed studies are needed to evaluate the effectiveness of erbium lasers with SRP in nonsurgical periodontal therapy.

Potassium titanyl arsenate based cascaded optical parametric oscillator emit at 2.5 µm derived by neodymium-doped yttrium lithium fluoride laser

We reported a potassium titanyl arsenate (KTA) based cascaded optical parametric oscillator (OPO). The secondary OPO signal light at 2.5 µm was obtained with two OPO processes in one non-critical phase matching cut KTA crystal. This cascaded OPO was driven by a Q-switched neodymium-doped yttrium lithium fluoride (Nd:YLF) laser at 1047 nm. Making full use of the negative thermal lens effect and long upper level fluorescence lifetime of Nd:YLF, signal power of 605 mW at 2503 nm was achieved with a pulse repetition frequency of 15 kHz and an incident diode pump power of 9.7 W. Therefore, the cascaded OPO derived by Q-switched Nd:YLF laser could provide high peak power pulsed laser emission in mid-infrared band.

Research on the Law of Thermal Effect of Floating Nuclear Power Plants Thermal Discharge

The waste heat emissions of thermal discharge from floating nuclear power plants may have a negative thermal effect on the environment. Study on the dilution and diffusion of cooling water plays an important role in thermal pollution prevention. The cooling water discharge process can be condensed into the thermal jet in cross flow. According to the theory of computational fluid dynamics, the mathematical model of round horizontal thermal jets in cross flow is established. The 3D numerical simulation of thermal jets based on finite volume method is achieved by using the Realizable k-ε turbulence model and the Semi-implicit method for pressure linked equations, and the three-dimensional trajectory of thermal jet are obtained. The rationality of analysis method is approved by comparing calculation value with experimental value. The temperature distributions in thermal jets are studied through the numerical experiments conducted under different cross-flow velocity and different emission angle. As a result, the impacts of these conditions on thermal pollution area are found, and the theoretic bases are provided for the design of the cooling water discharge pipe.

Temporal behavior of DNA thermal stability in the presence of platinum compounds. Role of monofunctional and bifunctional adducts

Penetrating into cell nuclei, antitumor drug cisplatin sequentially forms various intermediate and final adducts destroying local DNA structure. The demonstrated disappearance of the fine structure of melting curve of long DNAs along with a strong decrease in melting enthalpy conforms to the structural impact. However, the negative thermal effect (δTm) caused by cisplatin is relatively small if neutral medium is used in melting experiments. Cisplatin's inactive analogs transplatin and diethylenetriaminechloroplatinum {Pt[(dien)Cl]Cl} also distort DNA structure but their thermal effect is even positive. We have found that the use of alkaline medium in melting experiments strengthens the negative thermal effect for cisplatin. For transplatin and Pt[(dien)Cl]Cl, the thermal effect becomes negative that makes it qualitatively consistent with structural distortions. Those changes are explained by elimination of nonspecific electrostatic stabilization of DNA under platination. Additionally, alkaline medium fixes intermediate states of DNA platination and makes them stable against heating. These results allowed us to monitor δTm under binding of platinum compounds to DNA and their further transformation. The kinetic and thermal characteristics of monofunctional and bifunctional adducts were evaluated. It has been demonstrated that monofunctional adducts of cisplatin, transplatin and Pt[(dien)Cl]Cl produce approximately the same thermal destabilization. Cisplatin intrastrand crosslinks cause a two-fold stronger thermal destabilization than its monofunctional adducts. The value of δTm for cisplatin's final adducts is ten times larger than for transplatin. This difference mainly comes from the much stronger thermal destabilizing power of cisplatin's intrastrand crosslinks, which are responsible for antitumor activity of this compound.

AlN/AlGaN/GaN/AlGaN multilayer heterostructures with quantum well channel on heat conducting substrates for power microwave transistors

AbstractMolecular beam epitaxy using ammonia as a nitrogen source is applied to obtain III‐nitride multilayer heterostructures having high structural quality and low dislocation density. To provide strong carrier confinement in two‐dimensional electron gas for collapse‐free transistor operation, GaN quantum well as thin as 5 nm was formed between AlGaN barrier layers of various Al content, keeping high sheet conductivity in 280‐350 Ohm/square range. Due to rather thick AlN “template” grown at extremely high (up to 1200 °C) substrate temperatures directly in the same growth run prior to the growth of heterostructure, technology developed on sapphire is easily transferred to alternative substrates, for example AlN/SiC or Si. In contrast to sapphire, where noticeable drop of transistor saturation current at drain voltages higher than 5‐10 V is usually observed, heat conducting substrates allow to avoid this negative thermal effect and no drop is observed at drain voltages up to 20 V and even higher. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of repeated microwave irradiation on the frequency of sex-linked recessive lethal mutations in Drosophila melanogaster

The effect of repeated microwave irradiation (2375 MHz, CW) on mutagenic changes in Drosophila melanogaster was investigated. Oregon-R males were exposed to sublethal doses of microwaves (15 W/cm 2 for 60 min, 20 W/cm 2 for 10 min, and 25 W/cm 2 for 5 min) for 5 days. The Muller-5 cross was used to detect sex-linked recessive lethal mutations. 4 lethals were found in treated groups but their frequency was not significantly different from that of the control group. No cumulative effect of repeated exposures on the mortality of the treated males was observed; on the contrary, their mortality decreased with the number of exposures. Irradiation did not affect the sex ratio of the F 1. A significant decrease in the number of F 1 offspring was noted in the group exposed to the power density of 15 W/cm 2. A negative thermal effect of microwaves on male germ cells was probably manifested by this long exposure.