Thermally Generated Research Articles

Thermal generation of spin current in a quantum dot coupled to magnetic insulators

In this work, we study thermally-generated spin current in the system consisting of a quantum dot connected to two magnetic insulators. The external leads are kept at different temperatures which leads to an imbalance of magnon populations in two magnetic insulators resulting in the flow of the magnon (spin) current. We take into account many-body magnon interactions and incorporate energy-dependent density of states of the magnetic insulators. Both features can strongly affect magnon distribution in the magnetic insulators and the coupling strengths between the leads and the dot, and thus, the thermally generated spin current. All the calculations are carried out in the weak coupling regime. We show, that results obtained with a density of states being a function of energy differ significantly from the ones obtained with a density of states taken as a constant. In turn, magnon interactions in the leads proved to be important at high temperatures and large values of energy of transported spin waves.

Organic Synthesis Using Nitroxides.

Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R1R2N-O•. The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R1 and R2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R1R2N═O+) or reduced to anions (R1R2N-O-), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C-O bonds, allowing for the thermal generation of C radicals through reversible C-O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.

Site-Selective Atomic Layer Deposition at Thermally Generated Surface Oxygen Vacancies on Rutile TiO2

Site-Selective Atomic Layer Deposition at Thermally Generated Surface Oxygen Vacancies on Rutile TiO₂

Two-phase simulation of the generated entropy for the nanofluid flow inside a ribbed passage for cooling of a PV cell

• Introduce a new ribbed channel configuration with nanofluid for PV cooling. • The triangular-shaped rib demonstrates better performance. • Using the nanofluid reduces the thermal entropy generation about 65.1% • The overall irreversibility descends with nanofluid by increasing Reynolds number. Current work deals with the generated entropy of alumina–water nanofluid in a ribbed passage to cool the photovoltaic (PV) cell. The two-phase mixture approach is employed to model the nanofluid within a ribbed channel with discrete V-form and staggered rib roughness. The nanofluid is analysed at a concentration of 1%, and the outcomes are compared to pure water. This study focuses on the influences of the cross-section shape of the ribs. Four different shapes of the rib cross-section, including circular, elliptical, square, and triangular-shaped, are investigated in this paper. The results indicated that using the nanofluid rather than water considerably reduces the thermally generated entropy such that the highest reduction in this parameter is about 65.1%. Employing the ribbed channel demonstrates smaller thermal entropy by generating six intense cross-flows. The highest reduction in the thermally generated entropy rate is around 72.9% when the triangular-shaped rib is used. Besides, the positive influence of the nanofluid is about 2.3 times higher when the ribbed channel is utilised. The triangular-shaped rib demonstrates better performance and considerably contributes to the lower thermal irreversibility. The overall irreversibility descends when the nanofluid is used and by an increase of Reynolds number.

Thermal generation, manipulation and thermoelectric detection of skyrmions

Recent years have witnessed significant progresses in realizing skyrmions in chiral magnets1-4 and asymmetric magnetic multilayers5-13, as well as their electrical manipulation2,7,8,10. Equally important, thermal generation, manipulation and detection of skyrmions can be exploited for prototypical new architecture with integrated computation14 and energy harvesting15. It has yet to verify if skyrmions can be purely generated by heating16,17, and if their resultant direction of motion driven by temperature gradients follows the diffusion or, oppositely, the magnonic spin torque17-21. Here, we address these important issues in microstructured devices made of multilayers: (Ta_CoFeB_MgO)15, (Pt_CoFeB_MgO_Ta)15 and (Pt_Co_Ta)15 integrated with on-chip heaters, by using a full-field soft X-ray microscopy. The thermal generation of densely packed skyrmions is attributed to the low energy barrier at the device edge, together with the thermally induced morphological transition from stripe domains to skyrmions. The unidirectional diffusion of skyrmions from the hot region towards the cold region is experimentally observed. It can be theoretically explained by the combined contribution from repulsive forces between skyrmions, and thermal spin-orbit torques in competing with magnonic spin torques17,18,20,21 and entropic forces22. These thermally generated skyrmions can be further electrically detected by measuring the accompanied anomalous Nernst voltages23. The on-chip thermoelectric generation, manipulation and detection of skyrmions could open another exciting avenue for enabling skyrmionics, and promote interdisciplinary studies among spin caloritronics15, magnonics24 and skyrmionics3,4,12.

Mechanistic Duality in Tertiary Amine Additions to Thermally Generated Hexadehydro-Diels-Alder Benzynes.

Reported here are studies directed at understanding the mechanism of tertiary amine addition to hexadehydro-Diels-Alder (HDDA)-generated benzynes. Tertiary amines are presumed to engage benzynes by generation of a zwitterionic intermediate. Simple trialkylamines undergo intermolecular protonation by a protic nucleophile to give an aryl ammonium intermediate that is then dealkylated. Amines containing acidified β-protons undergo an intramolecular elimination to give the aniline and an alkene. Finally, amino alcohols react at either of their N- or O atoms, depending upon the extent of internal hydrogen bonding.

An Approach to Increase the Effectiveness of Electronic Devices by Reducing Thermal Generation of Current

In this paper we will do the analysis of the gate engineering impact on tri state inverter performance for the application on SOC that is system on chip with the help of different high dielectric material. The high dielectric materials used in electronic circuits for preventing tunnelling effect which will increase the thermally generated current. In order to reduce the Thermally generated current occur s in electronic circuit we can replace the sio2 with different materials having high dielectric constant. Tri State Inverter is designed by the use of microwind tool or simulator. The performance of Device is analyse for various parameter. It is measured that by the use of high dielectric constant material in Tri State Inverter the thermally generated current and dissipation of power minimised and also the performance of the circuit gets high. Among various high dielectric constant material, Lanthanum oxide La2o3 gained focus due to its property such as High Energy Band Gap, High Dielectric Constant, and can resist upto high Temperature.

Investigation of the Performance of Thermally Generated Au/Ag Nanoislands for SERS and LSPR Applications

In this work the performance of Au/Ag nanoislands was investigated for Surface Enhanced Raman Spectroscopy (SERS) and Localized Surface Plasmon Resonance (LSPR) applications. The nanoislands were generated by thermally annealing thin layers of silver and gold (having thickness in the 5-15 nm range), which were previously sputtered onto glass surfaces. Both pure (silver and gold nanoparticles – AuNP and AgNP) and composite metallic systems (silver-gold core-shell structures – Ag-Au core-shell) were evaluated based on their plasmonic and SERS sensitivity. Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) were used to measure the size, shape and distribution of the nanoparticles to correlate them with the obtained plasmonic/Raman capabilities. The technological parameters of nanoisland fabrication for optimal sensitivities are presented.

Valley caloritronics and its realization by graphene nanoribbons

We propose and theoretically investigate an idea of valley caloritronics where quantum transport of the valley degrees of freedom is thermally induced. Valley caloritronics addresses questions such as thermal generation of valley polarized current and, more importantly, pure valley current without an accompanying charge current. After establishing a general physical picture, we show that heat-induced pure valley current can be generated by virtue of wedge-shaped graphene nanoribbons in a two-probe device setup. We discover that the quantum transport properties of the valley degree of freedom can be very different when driven by a voltage bias or by a temperature bias. A very surprising result is that an alternating valley current can be thermally generated via gate control: namely the heat-induced valley current changes its flow direction in some quasiperiodic manner versus the value of a gate voltage at a fixed polarity. Our results indicate a vast potential for developing valley caloritronic devices.

Influence of thermodynamic properties of a thermo-acoustic emitter on the efficiency of thermal airborne ultrasound generation

In this work we experimentally verify the theoretical prediction of the recently published Energy Density Fluctuation Model (EDF-model) of thermo-acoustic sound generation. Particularly, we investigate experimentally the influence of thermal inertia of an electrically conductive film on the efficiency of thermal airborne ultrasound generation predicted by the EDF-model. Unlike widely used theories, the EDF-model predicts that the thermal inertia of the electrically conductive film is a frequency-dependent parameter. Its influence grows non-linearly with the increase of excitation frequency and reduces the efficiency of the ultrasound generation. Thus, this parameter is the major limiting factor for the efficient thermal airborne ultrasound generation in the MHz-range. To verify this theoretical prediction experimentally, five thermo-acoustic emitter samples consisting of Indium-Tin-Oxide (ITO) coatings of different thicknesses (from 65nm to 1.44μm) on quartz glass substrates were tested for airborne ultrasound generation in a frequency range from 10kHz to 800kHz. For the measurement of thermally generated sound pressures a laser Doppler vibrometer combined with a 12μm thin polyethylene foil was used as the sound pressure detector. All tested thermo-acoustic emitter samples showed a resonance-free frequency response in the entire tested frequency range. The thermal inertia of the heat producing film acts as a low-pass filter and reduces the generated sound pressure with the increasing excitation frequency and the ITO film thickness. The difference of generated sound pressure levels for samples with 65nm and 1.44μm thickness is in the order of about 6dB at 50kHz and of about 12dB at 500kHz. A comparison of sound pressure levels measured experimentally and those predicted by the EDF-model shows for all tested emitter samples a relative error of less than ±6%. Thus, experimental results confirm the prediction of the EDF-model and show that the model can be applied for design and optimization of thermo-acoustic airborne ultrasound emitters.

Reduction of silicon photomultipliers thermal generation in self-coincidence system applied in low level light measurements

Abstract The paper presents method for thermal generation reduction in low level light applications, especially where measured phenomena have random character. The algorithm was developed basing on cosmic ray measurements. The main parts of the system are: Silicon Photomultipliers (SiPM), front-end ASIC for amplifying and shaping signals. SiPM is a very sensitive device which can detect single photons. Comparing to a standard photomultiplier SiPM has a compact size, low operating voltage and it is immune to an electromagnetic field. Thermally generated signals are disadvantage of SiPM. This paper presents the measurement method to reduce influence of thermal generation.

Mechanically Versus Thermally Generated Quantum Turbulence of 4He Superflow

An experiment on thermally driven 4He superflow (Chagovets and Skrbek in Phys. Rev. Lett. 100:215302, 2008; J. Low Temp. Phys. 153:162, 2008) yielded very different steady state turbulence properties from a nominally identical recent realisation where the helium fountain drive was replaced by bellows. Here we argue that differences are most likely not due to fundamental reasons, but to incorrect velocity calculation in the fountain drive version. We show by a combination of direct velocity measurements and indirect analysis that the real velocity is significantly lower than predicted, and one main reason for this is unaccounted heat spent to enhance helium evaporation. The velocity correction brings the two experiments in reasonable agreement. We also suggest that the transition to a new state of superfluid turbulence claimed in Refs. (Chagovets and Skrbek in Phys. Rev. Lett. 100:215302, 2008; J. Low Temp. Phys. 153:162, 2008) may be a spurious effect of an observed nonlinearity occurring between fountain heat current and superflow velocity.

Effect of Film Thickness and Domain Spacing on Defect Densities in Directed Self-Assembly of Cylindrical Morphology Block Copolymers

Directed assembly of block copolymer thin films is recognized as a high-throughput, low-cost complement to optical lithography with the ability to overcome the 32 nm natural resolution limit of conventional lithographic techniques. For bulk block copolymer systems, desired feature sizes ranging from 5 to 100 nm can be obtained by controlling the molecular weight and composition of a block copolymer, as long as the bulk order-disorder temperature (ODT) is such that the copolymer is well-segregated at the processing conditions. However, our studies on graphoepitaxially aligned cylindrical morphology block copolymer monolayer and bilayer films demonstrate that, as domain sizes are reduced, the block copolymer becomes increasingly susceptible to an unacceptably high density of thermally generated defects, resulting in a significant reduction of the ODT. Thus, in thin films, the minimum feature spacing accessible is limited by thermal defect generation and not by the bulk ODT. Our experimental studies on monolayer films of cylindrical morphology polystyrene-b-poly(2-vinyl pyridine) with microdomain spacings approaching 20 nm reveal that defect densities and the ODT are surprisingly sensitive to variations as small as 2 nm in the microdomain spacing. Additionally, the monolayer and bilayer ODT differ by nearly 100 °C when the monolayer domain spacing is 20 nm, while the difference is only 20 °C when the monolayer domain spacing is 22 nm. We explain this behavior using a quantitative estimation of the energetic cost of defect production in terms of the domain spacing, χN, and block copolymer composition. These studies reveal unexpected consequences on the equilibrium defect densities of thin film block copolymers which must be accounted for when designing a block-copolymer-based directed-assembly process.

Dark current mechanisms in stabilized amorphous selenium based n-i detectors for x-ray imaging applications

The dark current behavior under operating bias is one of the important selection criteria for an x-ray photoconductor to be usable in a practical x-ray image detector. The authors have developed an analytical model for describing the transient and steady-state behavior of dark current in n-i-type amorphous selenium (a-Se) detectors by considering carrier injections from the metal contacts and thermally generated carriers. It has been found that the thermal generation current is almost two orders of magnitude smaller than the total steady-state dark current in n-i-type a-Se detectors. The main source of dark current is the injection of holes from the metal/n-layer interface which is described by the diffusion theory. The hole injection from the metal depends on the blocking layer (n-layer) thickness, the concentration of trap centers in the blocking layer, the characteristic carrier release time, and the effective barrier height. The fitting of the first principles model with the experimental results estimates the concentration of deep hole trap center in the n-layer, the trap depth from the valence band edge, and the effective barrier heights for the injecting carriers. The electron injection varies with the work function of the contact metal.

Thermal Generation of 3-Amino-4,5-dimethylfuran-2(5H)-one, the Postulated Precursor of Sotolone, from Amino Acid Model Systems Containing Glyoxylic and Pyruvic Acids

4,5-Dimethyl-3-hydroxy-2(5H)-furanone (sotolone), a naturally occurring flavor impact compound, can be isolated from various sources, especially fenugreek seeds. It can also be thermally produced from intermediates generated from the Maillard reaction such as pyruvic and ketoglutaric acids, glyoxal, and 2,3-butanedione. A naturally occurring precursor of sotolone, 3-amino-4,5-dimethyl-2(5H)-furanone, was thermally generated for the first time from pyruvic acid and glycine or from glyoxylic acid and alanine model systems. Isotope labeling studies have implicated 4,5-dimethylfuran-2,3-dione as an intermediate that can be converted into 3-amino-4,5-dimethyl-2(5H)-furanone through Strecker-like interaction with any amino acid. Furthermore, these studies have also indicated the presence of two pathways for the formation of 4,5-dimethylfuran-2,3-dione, one requiring pyruvic acid and a formaldehyde source and the other requiring glyoxylic acid and acetaldehyde. Self-aldol condensation of pyruvic acid followed by lactonization and further aldol reaction with formaldehyde can generate the same intermediate as the self-aldol addition product of acetaldehyde with glyoxylic acid followed by lactonization. The pyruvic acid pathway was found to be a more efficient route than the glyoxylic acid pathway. Furthermore, the pyruvic acid/glycine model system was able to generate sotolone in the presence of moisture, and in the presence of ammonia, commercial sotolone was converted back into 3-amino-4,5-dimethyl-2(5H)-furanone.

Cu2+ Ions as a Paramagnetic Probe in EPR Studies of Radicals Generated Thermally in Starch

AbstractElectron paramagnetic resonance (EPR) spectroscopy, with Cu2+ ions as a paramagnetic probe, was applied to study the process of radical generation in starch and changes occurring in its structure upon thermal treatment and oxidation. Thermally generated radicals in starch containing Cu2+ ions are localized on carbon atoms different from those in the pure starch. EPR signal parameters of the radical species (gav = 2.0047 – 2.0049; Aav = 0.9 – 1.0 mT) suggest a lower number of oxygen atoms in the vicinity of radical centres than that observed in pure starch and weakening of the interaction of the unpaired electron with the nuclear magnetic moment of the β hydrogen (for pure starch gav = 2.0059 – 2.0065; Aav = 1.2 – 1.3 mT). A mechanism of thermal generation of radicals in the native and oxidized starch containing Cu2+ ions was proposed. It consists of breaking of RCO‐Cu2+ or RCOO‐Cu2+ bonds in the native and oxidized starch, respectively, reduction of Cu2+ to Cu+ ions and formation of transient RCO• or RCOO• species, active in abstraction of hydrogen from the neighbouring C atom of the glucose unit, at which the unpaired electron became localized.

ChemInform Abstract: Thermally Generated Phenylcarbenium Ions: Acid‐Free and Self‐Quenching Friedel—Crafts Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Thermoelectric power generation using large-area Si/SiGe pn-junctions with varying Ge content

We present strategies for improving the power output of large-area pn-junctions for thermoelectric power conversion. The gradient of the pn-junction's built-in potential is used to separate thermally generated electron–hole pairs. An externally applied temperature gradient along the pn-junction induces a driving force to both electrons and holes which results in currents from the hot end to the contacts. Due to the exponential dependence of the thermal generation rate on the local temperature, the temperature distribution within the device strongly influences the device behaviour. We present simulation results describing the possible application of graded SiGe alloys in order to control the temperature distribution and thus improve the power output and efficiency of thermoelectric generators using large-area pn-junctions.

Recirculatory Pharmacokinetic Model of the Uptake, Distribution, and Bioavailability of Prochlorperazine Administered as a Thermally Generated Aerosol in a Single Breath to Dogs

A thermal aerosol generation process is capable of delivering pure drug reliably to the alveoli where it is absorbed systemically. Although deep lung absorption of drugs administered as an aerosol has been shown to be rapid, detailed characterization of their absorption and distribution has not been reported. The present study describes the pharmacokinetics of prochlorperazine from the moment of administration as either a rapid intravenous infusion or a thermally generated aerosol and determines the bioavailability of the aerosol by two independent methods. Prochlorperazine disposition was determined in four anesthetized dogs after a 5-s intravenous infusion and after thermally generated aerosol administration in one breath. Venous blood samples were collected frequently from the time of drug administration to 24 h and left ventricular blood samples were drawn more often until 10 min after drug administration. Prochlorperazine disposition after intravenous and aerosol administration was characterized by fitting a recirculatory model to left ventricular and venous drug concentration data simultaneously. Prochlorperazine aerosol administration produced plasma drug concentrations similar to those after rapid intravenous administration of the same nominal dose, with peak left ventricular concentrations achieved in less than 30 s. Plasma concentration profiles of prochlorperazine administered by both routes were well described by the recirculatory model. Bioavailability of the thermally generated aerosol was consistent and averaged more than 80% of emitted dose. Pulmonary administration of a thermally generated drug aerosol in one breath may be a viable alternative to rapid intravenous administration of drugs requiring rapid and predictable production of effective plasma concentrations.

Hydride Ion as a Two‐Electron Donor in a Nanoporous Crystalline Semiconductor 12CaO×7Al2O3.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.