Controlled Temperature Gradient Research Articles

Randomness of optical turbulence generated by Rayleigh–Bénard convection using intensity statistics

The experimental study of optical turbulence proves difficult due to challenges in generating controllable conditions in a laboratory environment. Confined water tanks that produce Rayleigh–Bénard (RB) convection are one method to generate optical turbulence using a controllable temperature gradient. It is of utmost concern to quantify the properties of the optical turbulence generated for characterization of other optical applications such as imaging, sensing, or communications. In this experimental study a Gaussian beam is propagated through a RB water tank where two intensity measurements are made at the receiver’s pupil and focal plane. The pupil and focal plane results include quantification of the intensity fluctuation distribution, scintillation distribution, and refractive index structure constant at various values of the temperature gradient. The angle of arrival fluctuations is also calculated at the focal plane to obtain a second estimate of C n 2. The pupil plane estimate for C n 2 using scintillation index and focal plane angle of arrival fluctuations is compared to preliminary predictions of C n 2 as a function of RB temperature gradient showing C n 2∼ΔT4/3. The outcomes of the study confirm that the RB process produces intensity fluctuations that follow gamma–gamma and log-normal probability density functions. Estimates of the refractive index structure constant C n 2 produce the same trends with different magnitudes when measured from the pupil and focal plane.

The local potential variation mapping including thermoelectromotive force in nanocomposite materials under non-thermal equilibrium

Thermoelectric nanocomposite materials are attracting much attention due to their high thermoelectric performance brought by effectively combining thermoelectric properties of the matrix and introduced nanostructures. However, understanding the mechanism of Seebeck coefficient enhancement brought in nanocomposite materials is difficult because there are no measurement methods of thermoelectromotive force V TE on the nanoscale. In this study, we demonstrate that the controlled temperature gradient Kelvin force microscopy (T-KFM) measurement we developed in 2021 can be applied to nanocomposite films. We observe temperature difference ΔT-induced vacuum level V vac variation, which is related to V TE, in PEDOT:PSS/Si nanowire nanocomposite films using T-KFM. The large ΔT-induced V vac variation at the tops of Si nanowires is generated, which is mainly explained by the larger Seebeck coefficient value of the Si nanowire. This application of T-KFM to the nanocomposites highlights that T-KFM will be a powerful tool for the development of nanocomposite materials with controlled thermoelectric properties on the nanoscale.

Thermal and Aerodynamic Characterization of a Creviced and Squared Piston Rapid Compression Machine: Extending the Validity of the Adiabatic Core Hypothesis, Generating Controlled Temperature Gradients

Thermal and Aerodynamic Characterization of a Creviced and Squared Piston Rapid Compression Machine: Extending the Validity of the Adiabatic Core Hypothesis, Generating Controlled Temperature Gradients

Thermally enhanced osmotic power generation from salinity difference

Recently, membrane-based power generation from salinity difference has been in the spotlight as a blue energy harvesting, but achieving a high power density and conversion efficiency still remains as a major challenge in this approach. Instead of developing new membranes, regulating the thermal condition within the membrane has been proposed as a way to enhance the power generation by several numerical studies, but this concept has rarely been explored through the systematic experimental studies due to the difficulty of imposing a controlled temperature gradient within the membrane. In this work, we experimentally and systematically study how the temperature difference can influence osmotic power generation using a commercial polycarbonate membrane and demonstrate that even when a thermal gradient is negligibly small within the nanoporous membrane, it is still possible to achieve a significant enhancement of the power generation. We propose that the effective ion concentration at the interfacial region between the reservoir and the membrane varies with the direction of the imposed temperature difference, such that the opposite direction of salinity and temperature differences can lead up to 5.3 times power enhancement as a result of the increase of the effective ion concentration ratio across the membrane. As an example of practical applications, we apply our findings to a floating type nanogenerator by incorporating a solar absorber to generate the temperature difference spontaneously under solar radiation conditions, and the results with the nanogenerator show that the power generation is indeed enhanced under both simulated and actual solar radiation conditions. We believe that our approach can be applied to any nanoporous membrane regardless of its thermal property, and therefore would provide a practical path to the power enhancement of reverse electrodialysis systems.

Stress accumulation by confined ice in a temperature gradient

When materials freeze, they often undergo damage due to ice growth. Although this damage is commonly ascribed to the volumetric expansion of water upon freezing, it is usually driven by the flow of water toward growing ice crystals that feeds their growth. The freezing of this additional water can cause a large buildup of stress. Here, we demonstrate a technique for characterizing this stress buildup with unprecedented spatial resolution. We create a stable ice-water interface in a controlled temperature gradient and measure the deformation of the confining boundary. Analysis of the deformation field reveals stresses applied to the boundary with [Formula: see text](micrometers) spatial resolution. Globally, stresses increase steadily over time as liquid water is transported to more deeply undercooled regions. Locally, stresses increase until ice growth is stalled by the confining stresses. Importantly, we find a strong localization of stresses, which significantly increases the likelihood of damage caused by the presence of ice, even in apparently benign freezing situations. Ultimately, the limiting stress that the ice exerts is proportional to the local undercooling, in accordance with the Clapeyron equation, which describes the equilibrium between a stressed solid and its melt. Our results are closely connected to the condensation pressure during liquid-liquid phase separation and the crystallization pressure for growing crystals. Thus, they are highly relevant in fields ranging from cryopreservation and frost heave to food science, rock weathering, and art conservation.

Dynamics of magnetic skyrmions driven by a temperature gradient in a chiral magnet FeGe

We experimentally demonstrate the reversible motion of skyrmions driven by the controlled thermal fluctuations in a chiral magnet FeGe. A temperature gradient applied to the chiral magnet not only induces a flow of electrons but also excites a flow of magnons. Consequently, it is found that the skyrmion shows directional thermal diffusion toward two opposite directions along the gradient of temperature. We show that the skyrmions driven by the temperature gradient move from the cold terminal to the hot terminal due to the effect of magnon current induced by the temperature gradient. An obvious transverse shift of skyrmions is observed, which indicates the thermal-induced skyrmion Hall effect. Moreover, the thermal diffusion of skyrmions from the hot terminal to the cold terminal with a Hall motion as a result of competition of the magnon current, entropic force, and the spin-transfer torques induced by the thermally excited electron flow is also observed when the temperature at the hot terminal is high enough. Our results demonstrate an efficient manipulation of skyrmion dynamics by a controllable temperature gradient, which may provide a promising way for the realization of caloritronic applications based on topological spin textures.

Orbital angular momentum sidebands in second harmonic generation of a vortex beam by a nonlinear crystal with inhomogeneous refractive index

The manipulation of the orbital angular momentum (OAM) spectrum in new wavelengths generated by frequency conversion has a wide range of applications in quantum information technology and modern communications. Here, the second harmonic generation of a vortex beam in a nonlinear crystal with an inhomogeneous refractive index is considered. It is shown that by using a segmented oven and generating a controllable temperature gradient along the thickness of the nonlinear crystal, a transverse phase mismatch can be induced in the vortex beam. Accordingly, the OAM spectrum of the vortex beam can be changed by generating new OAM components in the spectrum. Compared with the nonlinear Bragg diffraction method, the presented method has the advantage of longer interaction length and higher efficiency.

CuBi2O4 photocathode with integrated electric field for enhanced H2O2 production

Metal oxide semiconductors are promising for photosynthetic H2O2 production, provided the issue of excessive charge recombination can be adequately addressed. Inducing internal electric field is a common remedial strategy to inhibit carrier recombination but challenging to accomplish without external power input. To overcome this drawback, a novel photocathode was designed and fabricated by combing photothermoelectricity and photoelectricity by adding a NaCo2O4 film under the CuBi2O4 film to generate an internal electric field from photoinduced temperature gradients. Our results show the significantly enhanced photoelectrochemical activity for the composite photocathode with an H2O2 production concentration of 192.9 µmol/L, 2.4 times higher than CuBi2O4. Photocurrent under controlled temperature gradients and COMSOL simulation defined that the enhancement comes from the synergy of photothermoelectricity and photoelectricity. This work demonstrates a feasible strategy to inhibit carrier recombination in photoelectrode with internal thermoelectric potential, which can significantly enhance the energy conversion efficiency without extra energy consumption.

Flexible and high precision thermal metasurface

Thermal metamaterials are artificial materials used to manipulate heat flow in many applications, such as thermal protection, thermal camouflage, and precise temperature control. Most of the existing thermal metamaterials are mainly based on metal, which makes their fabrication complex and time-consuming, and limits their flexibility. Here, we show a strategy to simplify the fabrication process, improve machining accuracy, and realize flexibility in thermal metasurfaces. Our proposed thermal metasurface is fabricated by laser engraving of copper-graphene coating surface, utilizing graphene coating with high thermal conductivity instead of the traditional filling materials of low thermal conductivity. It maintains the integrity of copper substrate, giving the metasurface a good heat dispersion. Controlled temperature gradient patterns are established, and the metasurface can be bent without changing its features, except for a slight variation in its thermal gradient. Finally, its cloaking ability is demonstrated by camouflaging the same heat source in the shape of different objects. Our designed metasurface mitigates the limitations in design and fabrication of existing thermal metamaterials, and can be used in applications requiring large flexibility, thermal illusion, and large thermal gradients on small scales.

The investigation of the growth and perfection of the poly(ethylene terephthalate) crystalline region from amorphous state during annealing using a controlled temperature gradient

The investigation of the growth and perfection of the poly(ethylene terephthalate) crystalline region from amorphous state during annealing using a controlled temperature gradient

Tuning temperature gradients in subwavelength plasmonic nanocones with tilted illumination.

Inducing and controlling temperature gradients in illuminated subwavelength plasmonic structures is a challenging task. Here, we present a strategy to remotely induce and tune temperature gradients in a subwavelength metallic nanocone by adjusting the angle of incidence of linearly polarized continuous-wave illumination. We demonstrate, through rigorous three-dimensional numerical simulations, that properly tilting the incident illumination angle can increase or decrease the photoinduced temperature gradients within the nanostructure. We analyze the apex-base photoinduced temperature gradient for different illumination directions, resembling typical illumination schemes utilized in surface or tip-enhanced Raman spectroscopy.

Heating Characteristic and Thermal Optimization of Superconducting DC Induction Heater With Adjustable Air Gap Structure

The novel superconducting direct-current (DC) induction heater shows great advantages of high efficiency and heating quality compared to traditional alternating-current (AC) induction heater in aluminum extrusion. The efficiency of the superconducting DC induction heater can be up to 80–90%, which is much higher than the 40–50% efficiency of the AC induction heater. The uniform and gradient temperature distributions of the aluminum billet are the most significant parameters to evaluate the heating quality of this induction heater, which has a strong influence on the product quality of extrusion processing. In this paper, the superconducting magnet with adjustable air gap structure is designed to achieve controllable axial temperature uniformity and axial temperature gradient distribution. Each adjustable air-gap structure consists of 10 identical iron pieces whose position can be changed independently. Therefore, the uniformity and gradient temperature of the aluminum billet in the axial direction are controllable. The thermal optimization of the uniform and gradient temperature distributions for typical aluminum billets (Φ = 446 mm) is measured. A numerical finite-element method (FEM) model is built to analyze the heating behavior of the aluminum billet. The simulation and experimental results match well. The result of uniform and gradient axial temperatures are ±3 °C and the controllable range from 10 °C/m to 40 °C/m, respectively. The result obtained from the temperature-distribution optimization is useful for industrial applications.

Impact of a controlled culture temperature gradient on mouse embryo development and morphokinetics.

Temperature control within the IVF laboratory is an important aspect of a quality control system, helping to reduce environmental stress and ensure good-quality embryo development. Temperature fluctuations are probably more common than expected and the optimal temperature for embryo culture is not known. Modern incubators offer the opportunity to examine the impact of culture temperature on preimplantation embryo development while controlling for other variables within the system. The purpose of this study was to examine the effect of a range of temperatures during extended embryo culture on resulting mouse embryo development and morphokinetic timings. Using a single time-lapse incubator with six individual chambers, frozen-thawed one-cell mouse embryos were cultured individually at temperatures adjusted by 0.5°C between chambers to cover the range of 35.0-37.5°C. Resulting blastocyst formation and embryo morphokinetic timings were recorded and compared. Changes in culture temperature had a significant impact on mouse blastocyst development and morphokinetic timings (P<0.05). Under the conditions used in this study, blastocyst development was best at 37.0°C. Mouse preimplantation embryo mitotic cell divisions were generally slower at cooler temperatures and accelerated as the temperature increased from 35.0°C to 37.5°C. Incubator culture temperature must be carefully controlled, as even slight variations of 0.5°C in the temperature used for extended embryo culture can have significant impacts on embryo development and mitotic cell divisions. These data have potential implications for application of universal morphokinetic selection algorithms and may help explain differences in mitotic errors/embryo mosaicism between laboratories.

Multi-scale surface patterning – an approach to control friction and lubricant migration in lubricated systems

Purpose The paper aims to investigate the possibilities to control friction in lubricated systems by surface patterning, making use of a multi-scale approach. Surface patterns inside the tribological contact zone tend to directly reduce friction, whereas surface patterns located in the close proximity of the contact area can improve the tribological performance by avoiding lubricant starvation and migration. Finally, optimized surface patterns were identified by preliminary laboratory tests and transferred to a journal bearing, thus testing them under more realistic conditions. Design/methodology/approach Surface patterns on a large scale (depth &gt; 10 µm) were fabricated by micro- and roller-coining, whereas surface patterns on a small scale (depth &lt; 2 µm) were produced by direct laser interference patterning. The combination of both techniques resulted in multi-scale surface patterns. Tribologically beneficial surface patterns (verified in ball-on-disk laboratory tests) were transferred onto a journal bearing’s shaft and tested on a special test-rig. To characterize the lubricant spreading behavior, a new test-rig was designed, which allowed for the study of the lubricant’s motion on patterned surfaces under the influence of a precisely controlled temperature gradient. Findings All tested patterns accounted for a pronounced friction reduction and/or an increase in oil film lifetime. The results from the preliminary laboratory tests matched well, with results from the journal bearing test-rig, both tests showing a maximum friction reduction by a factor of 3-4. Numerical investigations, as well as experiments, have shown the possibility to actively guide lubricant over patterned surfaces. Smaller periodicities, as well as greater structural depths and widths, led to a more pronounced anisotropic spreading and/or greater spreading velocities. Multi-scale surfaces demonstrated the strongest effects regarding the lubricant’s spreading behavior. Originality/value Friction, as well as lubricant migration, can be successfully controlled by using micro-coined, laser-patterned and/or multi-scale surfaces. To the best of the authors’ knowledge, the study demonstrates for the first time the unique possibility to transfer results obtained in laboratory tests to a real machine component.

Microscale Rearrangement of Ammonium Induced by Snow Metamorphism

Earth’s snowpack hosts chemical impurities that exchange with the overlying air, strongly impacting atmospheric chemistry. Being embedded in firn and glacier ice formed from surface snow, impurities provide the basis for reconstructing past atmospheric composition from ice core records. The location of these impurity compounds within the snow critically controls their reactivity and preservation. Ammonium (NH4+) determines acid-base equilibria and buffer capacity within the snow and is a fundamental ice-core proxy, especially for biogenic, forest fire, and anthropogenic emissions. However, the redistribution during snow metamorphism affecting snow chemical reactivity and potential post-depositional relocation is not understood so far. Here, we study the rearrangement of NH4+ and five other major ions (Ca2+, Cl–, F–, Na+ and SO42–) during dry snow metamorphism using a series of elution experiments. Artificial and natural snow samples were stored for up to three months at a controlled temperature gradient of 40 K/m and isothermal conditions. The different types of snow increase complexity as natural and artificial snow have a different history that impacts their physical properties and the initial distribution of impurities. Further, we test our findings using natural snow samples taken from different depths of a natural snowpack at the Weissfluhjoch (Swiss Alps) to confirm the impact of our laboratory results to the cryosphere. With progressing temperature gradient metamorphism, snow structures in natural and artificial snow converged and ions with high solubility in ice (NH4+, F- and Cl-) were incorporated into the less accessible ice interior. In contrast, ions with lower solubility (Ca2+, SO42- and Na+) became better accessible for the eluent. Our results show that the redistribution during snow metamorphism is strongly dependent on the temperature gradient, exposure time and chemical composition. This study allowed for the first time to explicitly relate the general low relocation proneness of NH4+ during post-depositional processes such as meltwater percolation to the preferred incorporation of this ion into the less accessible ice interior during snow metamorphism. Furthermore, our results imply that with ongoing aging of a snowpack, NH4+, independent of its primary location, is less available for chemical reactions at the air-ice interface.

Flexible and rapid fabrication of silver microheaters with spatial-modulated multifoci by femtosecond laser multiphoton reduction.

In this Letter, parallel writing of silver microwire (AgMW) arrays based on femtosecond laser multiphoton reduction (MPR) is realized by modulating a femtosecond laser beam into a multifoci pattern with a spatial light modulator (SLM). Arbitrarily distributed multifoci are generated with predesigned holograms loaded on a SLM for MPR. The experimental parameters for the desired fabrication of AgMWs with multifoci are systematically investigated and optimized. On this basis, different AgMW patterns are dynamically and simultaneously fabricated by loading different holograms onto a high-frequency refreshed SLM in sequence. The quantity and distribution of multifoci can be controlled dynamically by the SLM in the fabrication process, and even the intensity of individual focus is dynamically modulated by the control of the gray level of holograms. Finally, the potential application of this flexible and rapid AgMW fabrication method in microheater fabrication is demonstrated. The microheaters exhibit a controllable temperature gradient after energized.

Impact of a controlled temperature gradient from 35.0°- 37.5°C on mouse embryo development and morphokinetics

To examine the impact of different in vitro culture temperatures on mouse embryo development and morphokinetic timings. Prospective study An embryo culture incubator with 6 individual chambers and time-lapse imaging (ESCO MIRI TLTM) was set to vary the temperature between chambers by 0.5°C to give a gradient that ranged from 35.0-37.5°C. Gas concentration was consistent between chambers (6% CO2, 5% O2, 89% N2). Frozen-thawed 1-cell mouse embryos (B6C3F1xB6D2F1, EmbryotechTM) were thawed, pooled and randomly distributed between 6 culture dishes in Global culture medium + 10% SPS. One dish containing individually cultured embryos was placed into each culture chamber/temperature for simultaneous culture and assessment. Embryos were cultured over 96h, recording blastocyst formation as well as morphokinetic timings for time to 2-cell, 3-cell, 4-cell, compaction and blastocoel formation. Experiments were repeated 3-times. Data were analyzed using ANOVA and Fisher Multiple-Comparison Test and are presented as the mean ± SEM. Statistically significance was measured at p<0.05. Changes in temperature during mouse embryo culture significantly impacted blastocyst formation and morphokinetic timings. Blastocyst formation rates were highest at 37.0°C and decreased at other temperatures examined. Cell division timings became more rapid as temperature increased and significantly differed between temperature treatments for most endpoints examined.Tabled 1Mouse morphokinetic timings and blastocyst development at different culture temperaturesTemperatureCell Division Timings (hrs)% Blastocystt-2cellt-3cellt-4cellt-Compactiont-Blastocyst35.0° C8.7±0.633.6±1.0a34.9±1.1a61.2±1.6a80.5±5.1a31.2%a35.5° C9.1±0.5a34.1±0.8a35.4±0.8a61.4±0.8a81.5±1.1a52.7%b36.0° C8.6±0.431.7±0.9ab33.4±0.7a57.9±1.3b77.5±1.6a55.5%b36.5° C7.7±0.430.3±0.7bc31.1±0.6b53.1±0.8c69.3±1.2b52.7%b37.0° C7.3±0.428.6±0.4c30.5±0.7bc53.5±1.3c70.7±3.0bc65.5%c37.5° C6.8±0.4b28.0±0.c28.6±0.7c49.2±0.9d62.1±0.6c56.7%bcDifferent superscripts within a column represent statistically significant differences between tempertaures p<0.05. Open table in a new tab Different superscripts within a column represent statistically significant differences between tempertaures p<0.05. New incubator technology offers the opportunity to examine the impact of temperature on embryo development while controlling for other culture variables. Changes in incubation temperature as little as 0.5°C have a significant impact on mouse embryo development, affecting blastocyst formation and morphokinetic timings. This data has potential implications for application of morphokinetic selection algorithms between facilities, as temperature between labs must be tightly controlled.

A temperature-controlled stage for laser scanning confocal microscopy and case studies in materials science

If confocal microscopy is an ubiquitous tool in life science, its applications in chemistry and materials science are still, in comparison, very limited. Of particular interest in these domains is the use of confocal microscopy to investigate temperature-dependent phenomena such as self-assembly, diffusio- or thermophoresis, or crystal growth. Several hurdles must be solved to develop a temperature-controlled stage for laser scanning confocal microscopy, in particular regarding the influence of an elevated temperature gradient close to the microscope objective, which most people try very hard to avoid. Here we report the design of a temperature-controlled stage able to generate stable temperature gradients in both positive and negative temperature range and does not require use of liquid nitrogen. Our setup provides an excellent control of the temperature gradient, which can be coupled with a controlled displacement of the sample, making it useful in particular for a variety of solidification, chemistry, and interfacial problems. We illustrate the benefits of our setup with several case studies of interest in chemistry and materials science: the 3D real-time imaging of ice growth, the segregation of hard particles by growing crystals, the freezing behaviour of single emulsions, the self-shaping of oil droplets upon cooling, and the self-assembly of amphiphile molecules into helical structures. These results show how confocal microscopy coupled with a temperature-controlled stage that provides a controlled temperature gradient is a welcome addition to the toolkit of chemists and materials scientists.

Low-Temperature Synthesis of Boron Carbide Ceramics

This study has been the first to demonstrate the possibility of producing boron carbide ceramics from coarse (D = 25–150 μm) B4C powder (which is impossible to sinter by conventional methods) through infiltration with molten silicon and subsequent treatment within the field of the controlled temperature gradient. This produces yields a composite ceramics B4C–SiC–Si with a hardness of 26 to 35 GPa and a splitting tensile strength of 110 to 170 MPa. The influence of the velocity of movement of the temperature gradient on the structure, phase composition, and properties of the prepared composites has been studied.

Graphite to diamond transformation during sediment–peridotite interaction at 7.5 and 10.5 GPa

Diamond nucleation and growth were investigated experimentally at 7.5 and 10.5 GPa and temperatures up to 1500 °C. Samples consisted of two layers: i) H2O- and CO2-bearing model sediment and ii) graphite-bearing garnet harzburgite comprising natural minerals. Two experimental series were conducted, one under a controlled temperature gradient with the sedimentary layer usually in the cold zone and the other under isothermal conditions. In the latter case, diamond seeds were added to the sedimentary mixture. During the experiments, the sedimentary layer partially or completely melted, with the melt percolating and interacting with the adjacent harzburgite. The graphite-to-diamond transition in the peridotite was observed above 1300 °C at 7.5 GPa and 1200 °C at 10.5 GPa in the temperature-gradient experiments, and at temperatures ~100 °C lower in the isothermal experiments with diamond seeds. Newly formed diamond occurs mostly as individual grains up to 10 μm in size and is separate from graphite aggregates. In some cases, an association of diamond with magnesite was observed. Diamond nucleation occurs in hydrous and CO2-bearing silicate melt following graphite dissolution and recrystallization. In the case of the diamond–magnesite association, diamond was probably formed through carbonate reduction coupled with graphite oxidation. The composition of the melts ranged from “carbonatitic” with ~10 wt% SiO2 and >50 wt% volatiles to hydrous silicate with ~40 wt% SiO2 and <10 wt% volatiles. This variation has no strong effect on diamond nucleation or growth.