Thermal Oscillations Research Articles

Improved carrier mobility of pentacene organic TFTs by suppressed oxide growth at remote interface using nitrogen doping in high-k NdNbO dielectric

Pentacene organic TFTs (OTFTs) using high-k Nd 2 O 3 doped with niobium and/or nitrogen as gate dielectric have been fabricated with gate-dielectric annealing at 200 °C and 400 °C. For 400 °C, the OTFT with only niobium doping in the Nd 2 O 3 gate dielectric shows an obvious improvement in carrier mobility compared with its counterpart with pure Nd 2 O 3 as gate dielectric. Moreover, for the lower temperature of 200 °C, the OTFT with both niobium and nitrogen dopings in the Nd 2 O 3 gate dielectric achieves further improvement with a small threshold voltage of −0.79 V and a high carrier mobility of 2.24 cm 2 /V·s. AFM and XPS reveal that the nitrogen doping, like the niobium doping, can reduce the hygroscopicity of Nd 2 O 3 , leading to a smoother surface of dielectric and thus larger overlying pentacene grains for reducing the scatterings of surface roughness and grain boundary respectively. Besides, highest mobility is achieved for the NdNbON gate dielectric without the best film quality because with nitrogen doping and lower-temperature annealing, a thinner interlayer between the gate dielectric and the Si gate is formed to enhance the electrostatic coupling between them, thus suppressing the phonon scattering on channel carriers caused by the thermal oscillation of the atoms inside the gate dielectric. •For pentacene OTFTs, Nb incorporation in Nd oxide as gate dielectric can reduce its hygroscopicity, leading to a smoother dielectric surface, larger pentacene grains, fewer interface traps and resultant improved performance. •Furthermore with N inclusion in NdNbO, high-performance OTFT can be achieved by using lower-temperature oxide annealing. •Besides passivation effect of nitrogen to further reduce hygroscopicity and oxygen vacancies, results show that nitrogen helps suppress formation of the dielectric/Si-gate interlayer, thus enhancing gate screening effect on the remote phonon scattering to improve carrier mobility.

V0644 Ser: An Active Ultrashort Period Contact Binary Star

The photometric solutions of the ultrashort period close binary V0644 Ser based on our new complete BVRI light curves are derived by the Wilson–Devininney code. The results show that V0644 Ser is a W-type shallow contact binary, and the third light was found in the R and I bands. Compared with the light curves in 2011, the amplitude variation of the secondary maximum can be explained by the temperature change from hot to cold in the local region of the star surface caused by magnetic activity or convective instability. Combined with the Gaia parallax, the absolute parameters of this system are obtained: M 1 = 0.29(4) M ⊙, M 2 = 0.56(9) M ⊙, R 1 = 0.48(3) R ⊙, R 2 = 0.65(3) R ⊙, L 1 = 0.11(2) L ⊙, L 2 = 0.16(2) L ⊙. To study the period variation, we fitted the SuperWASP, CSS, ASAS-SN and ZTF survey timing data to obtain light minima times spanning 14 yr. Through O − C analysis, we find that the orbital period of this system has a long-term period decrease and periodic oscillation. The long-term period decrease can be explained by the mass transfer from more-massive component to less one and angular momentum loss via magnetic stellar wind. With the period decrease, this system is evolving from the present shallow contact phase to a relatively deeper stage predicted by the thermal relaxation oscillation theory. Periodic oscillation can be explained by the light-time effect of the cool third body. This third body may play an important role in the early formation and evolution of the binary system by removing angular momentum.

URBAN LAYOUT FOR BUILDING SOLAR OPTIMIZATION AND OUTDOOR COMFORT BALANCE: NEIGHBORHOOD STRATEGY IN MEDITERRANEAN CLIMATE

The urban configuration in the Mediterranean area, which has noticeable solar radiation and significant thermal oscillation, is one of the factors that affect the microclimate and the urban heat island phenomenon of the cities located in that zone. To contribute to the improvement of urban comfort, this work presents an experimental methodological proposal for the analysis and multicriteria optimization of performance indicators using a parametric workflow through Grasshopper. This workflow can lead to the development of a set of environmental design criteria as support tools in the design of the urban configuration. The methodology is based on the quantification of two parameters on the analysis and management of daylight in interior spaces by means of dynamic metrics and, on the other hand, on the evaluation of hygrothermal conditions and the urban heat island effect, which affect both the daytime comfort of passersby and the nighttime comfort of dwellings. This study considers the most typical variables of urban layout, both morphological and material. The case study analyzed is located in the city of Seville (Spain), which has a significant percentage of its contemporary buildings without a suitable adaptation to local climate conditions. The results obtained from the case study prove the potential of the proposed methodology to evaluate and optimize lighting and thermal performance at the neighbourhood scale. Thus, it provides urban planners with a powerful decision support tool for both urban expansion and urban renewal.

CSS J075415.6+191052 and NW Leo: Two Contact Binaries at Different Evolutionary Stages

Multi-color light curves of CSS J075415.6+191052 and NW Leo are presented and the photometric solutions suggest that CSS J075415.6+191052 is an A-subtype contact binary with low mass ratio (q = 0.178) while NW Leo has a high mass ratio (q = 0.707). For CSS J075415.6+191052, the RI light curves show weakening around the left shoulder of the secondary minimum, which indicates that there may be a dark spot on the secondary component. However, the light curves of BV bands are totally symmetric. It is unreasonable if the dark spot is caused by magnetic activity or mass transfer between the two components. Therefore, weakening of the light curves in this contact binary is caused by something else. A possible explanation is mass transferring from the primary component to the common convective envelope through the inner Lagrangian point, and this part of the mass, for some reason, weakens the RI bands of light from the secondary component. O − C analysis of NW Leo reveals a cyclic period change with a modulation period of 4.7 yr, which may be caused by the light travel time effect of a third body. The positions of CSS J075415.6+191052 and NW Leo in the P–J′orb diagram indicate that CSS J075415.6+191052 mainly abides by the angular momentum loss theory while NW Leo is dominated by the thermal relaxation oscillation theory.

Conservative mass transfer on eclipsing binary AE Phe from O-C diagram analysis

Eclipsing binary is an edge-on binary system where the components appear to be eclipsing one another. Eclipsing binaries therefore give a lot of information on the systems’ behavior, one of them from their period change. O-C diagram exhibits the deviation of the observed time of minimum from the calculated ones and its analysis will reveal the responsible mechanism, such as a hidden third component, apsidal motion, and mass transfer. AE Phe (V = 8.15 mag and spectral class G0V) is a W UMa W-type binary. Previous studies of its degree of contact have revealed AE Phe to be a shallow-contact binary. Photometric data were taken using PROMPT (Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes), CTIO on October 4th, 2013 on four filters: B, V, R, and I. The Kwee and van Woerden (1956) method was also used to determine AE Phe’s time of minimum. Analysis of the O-C diagram (taken from 1975 toward our observation) suggest that the period of AE Phe shows a long-term continuous increase. These period increase and degree of contact suggest that AE Phe is undergoing thermal relaxation oscillation (TRO) and is evolving to a broken-contact phase, with a possibility of angular momentum loss (AML) through magnetic braking.

Nonlinear Boussinesq and Rosseland approximations on 3D flow in an interruption of Ternary nanoparticles with various shapes of densities and conductivity properties

<abstract> <p>In current days, hybrid models have become more essential in a wide range of systems, including medical treatment, aerosol particle handling, laboratory instrument design, industry and naval academia, and more. The influence of linear, nonlinear, and quadratic Rosseland approximations on 3D flow behavior was explored in the presence of Fourier fluxes and Boussinesq quadratic thermal oscillations. Ternary hybrid nanoparticles of different shapes and densities were also included. Using the necessary transformation, the resulting partial differential system is transformed into a governing ordinary differential system, and the solution is then furnished with two mixed compositions (Case-Ⅰ and Case-Ⅱ). Combination one looked at aluminum oxide (Platelet), graphene (Cylindrical), and carbon nanotubes (Spherical), whereas mixture two looked at copper (Cylindrical), copper oxide (Spherical), and silver oxide (Platelet). Many changes in two mixture compositions, as well as linear, quadratic, and nonlinear thermal radiation situations of the flow, are discovered. Case-1 ternary combinations have a wider temperature distribution than Case-2 ternary mixtures. Carbon nanotubes (Spherical), graphene (Cylindrical), and aluminum oxide (Platelet) exhibit stronger conductivity than copper oxide (Spherical), copper (Cylindrical), and silver oxide (Platelet) in Case 1. (Platelet). In copper oxide (Spherical), copper (Cylindrical), and silver (Platelet) compositions, the friction factor coefficient is much higher. The combination of liquids is of great importance in various systems such as medical treatment, manufacturing, experimental instrument design, aerosol particle handling and naval academies, etc. Roseland's quadratic and linear approximation of three-dimensional flow characteristics with the existence of Boussinesq quadratic buoyancy and thermal variation. In addition, we combine tertiary solid nanoparticles with different shapes and densities. In many practical applications such as the plastics manufacturing and polymer industry, the temperature difference is remarkably large, causing the density of the working fluid to vary non-linearly with temperature. Therefore, the nonlinear Boussinesq (NBA) approximation cannot be ignored, since it greatly affects the flow and heat transport characteristics of the working fluid. Here, the flow of non-Newtonian elastomers is controlled by the tension of an elastic sheet subjected to NBA and the quadratic form of the Rosseland thermal radiation is studied.</p> </abstract>

Greybody factor and thermal fluctuations of rotating regular black hole bounded by PFDM

The formulism of this paper helps to derive an exact form of greybody factor for rotating as well as regular black hole in the vicinity of the perfect fluid dark matter. In this regard, we inspect the effective potential by converting the Klein–Gordon equation into basic Schrödinger equation. We compute the asymptotic solutions in different domains such as at Black hole event horizon and far-field horizon under the influence of dark matter. In order to enhance the feasibility of the obtained results over the entire radial domain, we smoothly join them in the middle regime. It is observed that as the rotation parameter as well as strength of perfect fluid dark matter reduces around the black hole, its attractive behavior reduces, i.e., the quality to attract the radiations around itself reduces. Hence, the fewer radiations can approach infinity and the greybody factor reduces. Also, we discuss the impact of thermal oscillations on the thermodynamics of rotating regular black hole. To do so, we evaluate corrected entropy about the equilibrium state which yields variation in other thermodynamic potentials. It is found that entropy of black hole increases corresponding to larger values of rotation parameter. Moreover, it is concluded that in the presence of quantum corrections, the large black holes become stable due to positive range of specific heat.

Formation of a surfactant adsorption layer on microroughnesses of friction surfaces

Formation of an adsorption surface layer on microneralities of friction surfaces. The model of interaction of the molecule of surface-active substance with the microasperity of friction surface has been given. It has been found that the distance of interaction and the thickness of an adsorbed layer of surface-active substances depend on value of a field of an adsorbing surface and energy of thermal oscillations of molecules of surface-active. It has been shown that the distance of interaction and the thickness of an adsorbed layer of surface-active substances decrease at magnification of temperature of working liquid.

On the Impact Parameter Dependence of the Ionization Energy Loss of Fast Negatively Charged Particles in an Oriented Crystal

When a fast charged particle passes through matter, it loses some of its energy to the excitation and ionization of atoms. This energy loss is called ionization energy loss. In rather thin layers of matter, the value of such energy loss is stochastic. It is distributed in accordance with the law, which was first received by L.D. Landau. In amorphous substances, such a distribution (or spectrum), known as the Landau distribution, has a single maximum that corresponds to the most probable value of particle energy loss. When a particle moves in crystal in a planar channeling mode, the probability of close collisions of the particle with atoms decreases (for a positive particle charge) or increases (for a negative charge), which leads to a change in the most probable energy loss compared to an amorphous target. It has recently been shown that during planar channeling of negatively charged particles in a crystal, the distribution of ionization energy loss of the particles is much wider than in the amorphous target. In this case, this distribution can be two-humped, if we neglect the incoherent scattering of charged particles on the thermal oscillations of the crystal atoms and the electronic subsystem of the crystal. This paper explains the reason for this distribution of ionization energy loss of particles. The ionization energy loss distribution of high-energy negatively charged particles which move in the planar channeling mode in a silicon crystal are studied with the use of numerical simulation. The dependence of this distribution on the impact parameter of the particles with respect to atomic planes is considered. The dependence of the most probable ionization energy loss of particles on the impact parameter is found. It is shown that, for a large group of particles, the most probable ionization energy loss during planar channeling in a crystal is lower than in an amorphous target.

Quantized (or not quantized) thermal Hall effect and oscillations in the thermal conductivity in the Kitaev spin liquid candidate α-RuCl3

1. Oscillations of the thermal conductivity in the spin-liquid state of α-RuCl3 Authors: Peter Czajka, Tong Gao, Max Hirschberger, Paula Lampen-Kelley, Arnab Banerjee, Jiaqiang Yan, David G. Mandrus, Stephen E. Nagler, and N. P. Ong Nature Physics 17, 915–919 (2021); DOI: 10.1038/s41567-021-01243-x 2. The planar thermal Hall conductivity in α-RuCl3 Authors: Peter Czajka, Tong Gao, […]

The stress–pressure lag in MRI turbulence and its implications for thermal instability in accretion discs

ABSTRACT The classical alpha-disc model assumes that the turbulent stress scales linearly with – and responds instantaneously to – the pressure. It is likely, however, that the stress possesses a non-negligible relaxation time and will lag behind the pressure on some time-scale. To measure the size of this lag we carry out unstratified 3D magnetohydrodynamic shearing box simulations with zero-net-magnetic-flux using the finite-volume code pluto. We impose thermal oscillations of varying periods via a cooling term, which in turn drives oscillations in the turbulent stress. Our simulations reveal that the stress oscillations lag behind the pressure by ∼5 orbits in cases where the oscillation period is several tens of orbits or more. We discuss the implication of our results for thermal and viscous overstability in discs around compact objects.

1D_RnDPM: A freely available 222Rn production, diffusion, and partition model to evaluate confounding factors in the radon-deficit technique

The radon-deficit technique is a powerful tool to detect and delineate sub-surface accumulations of organic contaminants. Field measurements of 222Rn in soil air, however, are affected by several confounding factors that can lead to the misinterpretation of results. Among the most influential are: vertical and lateral changes of lithology, fluctuating contaminant saturations with depth, varying water saturation ratios along the soil profile and atmospheric (and, therefore, soil) thermal oscillations. To evaluate and minimize the effect of these confounding factors on the interpretation of the results of the Rn deficit technique, a Matlab® based multi-layer model of 222Rn production-partition-diffusion in unsaturated porous media (1D_RnDPM: One-Dimensional 222Rn Diffusion and Partition Model) has been developed and is freely available as Supplementary Material in this work. A laboratory protocol has also been proposed to obtain site-specific input parameters for the model, i.e., 222Rn equilibrium concentration (as determined by the accumulation chamber method), soil bulk density and soil solid-phase density. The model predictions have been contrasted with field information obtained from successive sampling campaigns in which 222Rn in soil air was measured at a site where the vadose zone, consisting of an anthropogenic backfill underlain by a silt layer, is affected by a complex mixture of benzene, phenol, (poly) chlorobenzenes, (poly) chlorophenols and hexachlorocyclohexane isomers, among other compounds. The model has successfully predicted the vertical profile of 222Rn concentrations in soil air, including the effect of the oscillations of the water table and of ground-level temperature. The results also underline that 222Rn measurements in subsoil air are representative only of local conditions around the sampling point, an expected result given that 222Rn maximum effective diffusion length is very limited. As a consequence, the influence of a highly fluctuating water table at the site goes undetected at the sampling depths used in the field campaigns. Main findingsThe combination of a numerical model and a laboratory protocol allows to predict the activity of 222Rn along the soil profile and to assess the influence of site-specific confounding factors.

Lipid-stabilized hydrophobically modified silica-coated gold nanorods generate enhanced photoacoustic signal from cavitation with nonlinear dependence on laser fluence

In this work, we report that gold nanorods coated with hydrophobically modified mesoporous silica shells not only enhance photoacoustic (PA) signal by more than 10-fold over unmodified mesoporous silica coated gold nanorods but also the relationship between PA amplitude and input laser fluence is strongly nonlinear. Mesoporous silica shells of ∼14 nm thickness and with ∼3 nm pores were grown on gold nanorods showing near infrared absorption. The silica was rendered hydrophobic with addition of dodecyltrichlorosilane, then re-suspended in aqueous media with a lipid monolayer. Analysis of the PA signal revealed not only an enhancement of PA signal compared to mesoporous silica coated gold nanorods at lower laser fluences but also a nonlinear relationship between PA signal and laser fluence. We attribute each effect to the entrapment of air in the mesopores: the air has a larger expansion coefficient than silica that enhances conversion to acoustic energy, and the air undergoes thermal size oscillations that increase with laser fluence, leading to a nonlinear trend even at fluences as low as 5 mJ cm−2. At 21 mJ cm−2, the highest laser fluence tested, the PA enhancement was >12-fold over mesoporous silica coated gold nanorods.

Nitrogen Rejection from Methane via a "Trapdoor" K-ZSM-25 Zeolite.

Nitrogen (N2) rejection from methane (CH4) is the most challenging step in natural gas processing because of the close similarity of their physical-chemical properties. For decades, efforts to find a functioning material that can selectively discriminate N2 had little outcome. Here, we report a molecular trapdoor zeolite K-ZSM-25 that has the largest unit cell among all zeolites, with the ability to capture N2 in favor of CH4 with a selectivity as high as 34. This zeolite was found to show a temperature-regulated gas adsorption wherein gas molecules' accessibility to the internal pores of the crystal is determined by the effect of the gas-cation interaction on the thermal oscillation of the "door-keeping" cation. N2 and CH4 molecules were differentiated by different admission-trigger temperatures. A mild working temperature range of 240-300 K was determined wherein N2 gas molecules were able to access the internal pores of K-ZSM-25 while CH4 was rejected. As confirmed by experimental, molecular dynamic, and ab initio density functional theory studies, the outstanding N2/CH4 selectivity is achieved within a specific temperature range where the thermal oscillation of door-blocking K+ provides enough space only for the relatively smaller molecule (N2) to diffuse into and through the zeolite supercages. Such temperature-regulated adsorption of the K-ZSM-25 trapdoor zeolite opens up a new approach for rejecting N2 from CH4 in the gas industry without deploying energy-intensive cryogenic distillation around 100 K.

Determination of Activation Energy of Surface Diffusion Based on Thermal Oscillations of Atoms

This paper covers calculations of the activation energy of surface diffusion of ad-atoms on the substrate surface from the point of view of thermal oscillations of substrate atoms and ad-atoms. The main characteristic of oscillations of atoms and geometric mean frequency was calculated based on statistical approximation of the Debye model using the reference values of entropy and heat capacity of metals. The basic principle of the model of activation energy calculation presented in the paper is the formation of potential wells and barriers during oscillations of atoms localized in the sites of the lattice. Oscillations of atoms were considered in the framework of quasiclassical quantum approximation as the oscillations of harmonic oscillators in the potential parabolic wells. Dimensions of the negative part of values of the potential well energy were determined by the amplitude of thermal oscillations of atoms. Positive values constituted a significant part of the potential well energy values. Barriers were formed owing to interaction of positive values of the energy of parabolic wells of adjacent atoms. Therefore, in order to make the ad-atom jump, it is necessary to get out of the potential well having the negative values, and to overcome the potential barrier. The energy required for the ad-atom jump on the substrate surface was the activation energy of surface diffusion. The results obtained in this paper agree satisfactorily with the results of another method, which is based on determining the energy of ad-atom binding with the substrate atoms.

First photometric and orbital period investigations of the total-eclipse contact binary V0339 Com

We presented the first photometric and orbital period investigation for the W UMa-type binary V0339 Com. The multi-bands light curves were obtained and analyzed with the Wilson–Devinney Code. The photometric solutions suggested that V0339 Com is an A-subtype shallow contact binary with a degree of contact f=12.0%. The total eclipse of V0339 Com gives a reliable mass ratio of 0.304. The asymmetry light curves are well modeled by a cool spot on either the secondary or primary. With the empirical relation derived from a catalog of individually studied contact binaries and the photometric solutions, we determined the absolute parameters of V0339 Com. Combining the eclipse timings determined from our observations and several surveys’ data with those reported in the literature, we revealed that the orbital period of V0339 Com is undergoing a secular increase at a rate of Ṗ=5.45×10−7 d⋅yr−1. The secular period increase implies a continuous mass transfer from the less massive secondary to the more massive primary. Based on the conservative mass transfer, the observed period increase and the Roche-lobe model, we analyzed the evolutionary status of V0339 Com and found that it may be just at the stage predicted by the thermal relaxation oscillation theory, and be involving from the current contact state to the broken-contact one.

Rechargeable self-assembled droplet microswimmers driven by surface phase transitions

The design of artificial microswimmers is often inspired by the strategies of natural microorganisms. Many of these creatures exploit the fact that elasticity breaks the time-reversal symmetry of motion at low Reynolds numbers, but this principle has been notably absent from model systems of active, self-propelled microswimmers. Here we introduce a class of microswimmers that spontaneously self-assembles and swims without using external forces, driven instead by surface phase transitions induced by temperature variations. The swimmers are made from alkane droplets dispersed in an aqueous surfactant solution, which start to self-propel on cooling, pushed by rapidly growing thin elastic tails. When heated, the same droplets recharge by retracting their tails, swimming for up to tens of minutes in each cycle. Thermal oscillations of approximately 5 °C induce the swimmers to harness heat from the environment and recharge multiple times. We develop a detailed elasto-hydrodynamic model of these processes and highlight the molecular mechanisms involved. The system offers a convenient platform for examining symmetry breaking in the motion of swimmers exploiting flagellar elasticity. The mild conditions and biocompatible media render these microswimmers potential probes for studying biological propulsion and interactions between artificial and biological swimmers. A class of synthetic microswimmers self-assembled from alkane oil drops in a surfactant solution offers a rechargeable platform for studying how microorganisms exploit flagellar elasticity to move around.

A Critical Review of Ground Based Observations of Earthquake Precursors

We aim at giving a short review of the seismo-associated phenomena detected on ground that in recent years have been investigated as possible earthquake precursors. The paper comes together with a companion article–published on this same volume by Picozza et al., 2021–devoted to summarize the space-based observation of earthquake–precursors by satellites missions. In the present work, we give an overview of the observations carried out on ground in order to identify earthquake precursors by distinguishing them from the large background constituted by both natural non-seismic and artificial sources. We start discussing the measurements of mechanical parameters and variations of geochemical fluids detected before earthquakes; then we review thermal and atmospheric oscillations; finally, observations of electromagnetic and ionospheric parameters possibly related to the occurrence of impeding earthquakes are discussed. In order to introduce a so large field of research, we focus only on some main case studies and statistical analyses together with the main hypotheses and models proposed in literature in order to explain the observed phenomenology.

Inhomogeneous behavior of supercritical hydrocarbon fuel flow in a regenerative cooling channel for a scramjet engine

Supercritical hydrocarbon fuel is employed to simultaneously cool associated combustors and to recover heat. Aiming to improve the thermal performance of the regenerative cooling channels in an advanced aircraft, the flow behavior, vortex structures, and transport characteristics of supercritical n-decane are investigated using an LES model. The flow patterns are identified by several common buoyancy criteria, and oscillation effects are observed in strongly mixed flows. Using temperature and density gradient fields, distinct inhomogeneity shows that the thermal oscillations aggravate the further occurrence of uneven performance. Furthermore, the positive helicity gradually increases with the accumulation of buoyancy force. The notably strong vorticity mainly concentrates near the heated wall, while a narrow section appears in the turbulent region, which indicates that the variable vorticity behavior contributes to the transport properties.

LO And: an A-subtype contact binary with a very cool third component

Despite the intensive investigations since the discovery of LO And approximately 60 yr ago, its evolutionary status and subtype are still a matter of controversy. By simultaneously modeling the radial-velocity curves and new light curves with the Wilson-Devinney code, we present new geometric, photometric and absolute parameters for this system. The simultaneous solution suggests that LO And is an A-subtype contact binary with a contact degree of 32.4%. The absolute parameters are modified to become M 1 = 1.409 M ⊙, M 2 = 0.449 M ⊙, R 1 = 1.36 R ⊙ and R 2 = 0.83 R ⊙. From our observations and data from surveys, we determined 334 eclipse timings. The O – C diagram, constructed from the new eclipse timings and those reported in the literature, reveals a secular increase and a cyclic variation in its orbital period. The former is caused by conservative mass transfer from the secondary component with less mass to the primary one with more mass. The latter may be explained by either the cyclic magnetic activity on the two components or the light-time effect due to a third body. With the absolute physical parameters, we investigated its evolutionary status, and find that LO And is an unevolved contact binary undergoing thermal relaxation oscillation, which will eventually coalesce into a single star with rapid rotation.