Thermal Energy Dissipation Research Articles

The Effect of Chilled vs Room Temperature Irrigation on Thermal Energy Dissipation During MIS Calcaneal Osteotomy

Category: Hindfoot; Basic Sciences/Biologics; Other Introduction/Purpose: Minimally Invasive (MIS) calcaneal osteotomy has grown in popularity in recent years to address hindfoot deformity. A potential complication is thermal bone necrosis secondary to heat generation from the burr, leading to nonunion of the osteotomy. Irrigation is commonly employed to reduce this risk. The effect of irrigation on reducing this risk remains an understudied area. The purpose of this study was to evaluate the effect of cooled versus room-temperature irrigation on thermal energy dissipation on a temperature curve during calcaneal osteotomy using a Shannon burr. Methods: Ten cadaveric limbs (5 pairs) at room temperature (68 0F) were randomized to receive either cooled saline or room temperature irrigation during MIS calcaneal osteotomy. Two thermocouple probes (EL-USB-TC-LCD, Lascar Electronics) were inserted 5mm away from the plane of the osteotomy, on proximal and distal sides respectively (Fig. 1). The probes were inserted to a depth of 2cm. A 3 x 30mm Shannon burr was used to perform the osteotomy. The burr was run continuously under continuous irrigation using either room temperature (680F) and chilled (370F) irrigation, until the osteotomy was completed. All osteotomies were performed in approximately 60 seconds. Temperature was recorded at 15sec, 30sec, 45 sec and 60 sec for the two groups and used as a measure of thermal energy generation. Results: Both room temperature and chilled irrigation were effective in minimizing temperature change. On the proximal side, an overall mean increase of 2.60F (70.60F) with room temperature irrigation and a mean increase of 0.70F (68.70F) with chilled irrigation were observed at the 60 sec interval (p=0.09). On the distal side both irrigation methods were more effective in heat control (70.20F vs 67.10F; p=0.17). Conclusion: For the duration of a MIS calcaneal osteotomy, both continuous room temperature and chilled irrigation can reduce thermal energy generation. Use of chilled irrigation can be considered for osteotomies of denser bone that may take longer to perform and generate higher temperatures.

The Effect of Chilled vs Room-Temperature Irrigation on Thermal Energy Dissipation During Minimally Invasive Calcaneal Osteotomy of Cadaver Specimens.

Minimally invasive (MIS) calcaneal osteotomy has grown in popularity in recent years to address hindfoot deformity. A potential complication is thermal bone necrosis secondary to heat generation from the burr that may lead to osteotomy nonunion. Irrigation is commonly employed to reduce this risk. The effect of irrigation on reducing heat accumulation remains an understudied area. The purpose of this study was to evaluate the effect of cooled vs room-temperature irrigation on thermal energy dissipation during calcaneal osteotomy using a Shannon burr. Fourteen cadaveric limbs at room temperature (68 °F) were randomized to receive either cooled saline (7 limbs) or room-temperature (7 limbs) irrigation during MIS calcaneal osteotomy. Two thermocouple probes were inserted 5 mm away from the plane of the osteotomy, on the proximal and distal sides, respectively. A 3 × 30-mm Shannon burr was used to perform the osteotomy. The burr was run continuously with continuous irrigation using either room-temperature (68 °F) or chilled (37 °F) irrigation, until the osteotomy was completed. Temperature was recorded at 0, 15, 30, 45, and 60 seconds for the 2 groups and used as a measure of thermal energy accumulation. Both room-temperature and chilled irrigation were effective in minimizing temperature change. On the proximal side, an overall mean increase of 2.5 °F with room-temperature irrigation and a mean decrease of 1.0 °F with chilled irrigation were observed at the 60-second interval (P = .004). On the distal side, there was a mean increase of 1.3 °F with room-temperature irrigation and a mean increase of 0.5 °F with chilled irrigation (P = .05). For the duration of an MIS calcaneal osteotomy, both continuous room-temperature and chilled irrigation can minimize temperature increases and potentially reduce the risk of an osteotomy nonunion. Both room-temperature and chilled irrigation can minimize bone temperature increases during MIS calcaneal osteotomy.

The effect of tilt on turbulent thermal convection for a heated soap bubble

We use direct numerical simulation (DNS) to explore the effect of tilt on two-dimensional turbulent thermal convection on a half-soap bubble that is heated at its equator. In the DNS, the bubble is tilted by an angle δ∈[0°,90°], the Rayleigh number is varied between Ra∈[3×106,3×109], and the Prandlt number is fixed at Pr = 7. The DNS reveals two qualitatively different flow regimes: the dynamic plume regime (DPR) and the stable plume regime (SPR). In the DPR, small dynamic plumes constantly emerge from random locations on the equator and dissipate on the bubble. In the SPR, the flow is dominated by a single large and stable plume rising from the lower edge of the bubble. The scaling behavior of the Nusselt number Nu and Reynolds number Re is different in these two regimes, with Nu∝Ra0.3 for the DPR and Nu∝Ra0.24 for the SPR. Concerning Re, the scaling in the DPR lies between Re∝Ra0.48 and Re∝Ra0.53 depending on Ra and δ, while in the SPR, the scaling lies between Re∝Ra0.44 and Re∝Ra0.45 depending on δ. The turbulent thermal and kinetic energy dissipation rates (εT′ and εu′, respectively) are also very different in the DPR and SPR. The probability density functions (PDF) of the normalized log εT′ and log εu′ are close to a Gaussian PDF for small fluctuations but deviate considerably from a Gaussian at large fluctuations in the DPR. In the SPR, the PDFs of normalized log εT′ and log εu′ deviate considerably from a Gaussian PDF even for small values. The globally averaged thermal energy dissipation rate due to the mean temperature field was shown to exhibit the scaling ⟨ε⟨T⟩⟩B∝Ra−0.23 in the DPR and ⟨ε⟨T⟩⟩B∝Ra−0.28 in the SPR. The globally averaged kinetic energy dissipation rate due to the mean velocity field is shown to exhibit the scaling ⟨ε⟨u⟩⟩B∝Ra−0.47 in the DPR (the exponent reduces from 0.47 to 0.43 as δ is increased up to 30°). In the SPR, the behavior changes considerably to ⟨ε⟨u⟩⟩B∝Ra−0.27. For the turbulent dissipation rates, the results indicate the scaling ⟨εT′⟩B∝Ra−0.18 and ⟨εu′⟩B∝Ra−0.29 in the DPR. However, the dependencies of ⟨εT′⟩B and ⟨εu′⟩B on Ra cannot be described by power-laws in the SPR.

Flexible phase change composite films with improved thermal conductivity and superb thermal reliability for electronic chip thermal management

High-performance flexible composites with excellent thermal management ability are essential to dissipate the heat generated in electronic systems. Herein, micro-encapsulated phase change material (MPCM) with n-Docosane core and MF resin shell is prepared. The obtained MPCM exhibits large phase change enthalpy (192.9 J/g). Subsequently, flexible composites are prepared by incorporating the MPCM, multi-walled carbon nanotubes (MWCNT) and hexagonal boron nitride (h-BN) in styrene-ethylene-propylene-styrene (SEPS) polymer matrix. At 30 wt% MPCM, the phase change enthalpy of 60.6 J/g is achieved. 3 wt%MWCNT/10 wt%h-BN/30 wt%MPCM composites show improved thermal conductivity of 0.44 W m−1 K−1, which is 95.5 % higher than pure SEPS. The composites are applied in chip for thermal energy dissipation, the temperature of chip’s lower surface is only 62.6 °C, which is 22.84 % lower than pure SEPS. Overall, the MWCNT/h-BN/MPCM composites with superior thermal properties and mechanical characteristics are promising in the field of electronic equipment thermal dissipation.

Effect of Nanoscale Confinement on Ultrafast Dynamics of Singlet Fission in TIPS-Pentacene.

Singlet fission (SF) is a phenomenon for the generation of a pair of triplet excitons from anexcited molecule in singlet electronic state interacting with another adjacent molecule in its ground electronic state. By increasing the effective number of charge carriers and reducing thermal dissipation of excess energy, SF is promised to enhance light-harvesting efficiency for photovoltaic applications. While SF has been extensively studied in thin films and crystals, the same has not been explored much within a confined medium. Here, we report the ultrafast SF dynamics of triisopropylsilylethynyl pentacene (TIPS-Pn) in micellar nanocavity of varying sizes (prepared from TX-100, CTAB, and SDS surfactants). The nanoparticles with a smaller size contain weakly coupled chromophores which are shown to be more efficient for SF followed by triplet generation as compared to the nanoparticles of larger size which contain strongly coupled chromophores which are less efficient due to the presence of singlet exciton traps. Through these studies, we delineate how a subtle interplay between short-range and long-range interaction among chromophores confined within nanoparticles, fine-tuned by the curvature of the micellar interface but irrespective of the nature of the micelle (cationic or anionic or neutral), play a crucial role in SF through and generation of triplets.

Using TRIM-SRIM code simulations to determine defect density produced in HOPG irradiated with high energy heavy ions.

This work is part of the NUMEN Project (NUclear Matrix Elements for Neutrinoless double beta decay), which, among other goals, aims to measure cross-section of double charge exchange reactions (DCE). In the experiments to be carried out at the Laboratori Nazionali del Sud, in Catania, Italy, a target deposited on a carefully chosen backing (substrate) will be irradiated with a high energy ion beam and, importantly, neither the target nor the substrate will be allowed to overheat as this would affect their structures and its properties, which are special for the experiment. Within this context, highly oriented pyrolytic graphite (HOPG) was chosen as a substrate for the deposition of target elements that will be irradiated by ions such as 12C, 18O and 20Ne, with energies ranging from 15 MeV/u to 60 MeV/u. HOPG is considered a semimetal structured in layers, being composed of a stack of graphene sheets with a small and very subtle disorientation (less than 1°), which makes it to approach to a single crystal. With its specific flat hexagonal molecular structure, consisting only of carbon atoms, HOPG has good thermal conductivity in these sheets, making it an excellent candidate as a heat sink. However, for the HOPG to act with thermal energy dissipation functionality during the experiments proposed by the NUMEN project, it is necessary to verify whether possible changes caused by exposure to the radiation beam have a direct or indirect influence on its mechanical and thermal properties. Regarding the thermal conductivity, vacancies produced during irradiation is one of the factors that considerably decrease such property. As the production of vacancies during irradiation is one of the factors that considerably decrease thermal conductivity, in this work it was used the SRIM/TRIM code simulations to investigate the mechanisms of vacancy production in the target plus HOPG backing system. In the simulations, it was considered different types and doses of incident ion beams as well as different target thickness. From the results it was possible to estimated how long a target-HOPG system can be irradiated before the HOPG high heat conductivity property is lost.

Habitat-adapted heterologous symbiont Salinispora arenicola promotes growth and alleviates salt stress in tomato crop plants.

To ensure food security given the current scenario of climate change and the accompanying ecological repercussions, it is essential to search for new technologies and tools for agricultural production. Microorganism-based biostimulants are recognized as sustainable alternatives to traditional agrochemicals to enhance and protect agricultural production. Marine actinobacteria are a well-known source of novel compounds for biotechnological uses. In addition, former studies have suggested that coral symbiont actinobacteria may support co-symbiotic photosynthetic growth and tolerance and increase the probability of corals surviving abiotic stress. We have previously shown that this activity may also hold in terrestrial plants, at least for the actinobacteria Salinispora arenicola during induced heterologous symbiosis with a wild Solanaceae plant Nicotiana attenuata under in vitro conditions. Here, we further explore the heterologous symbiotic association, germination, growth promotion, and stress relieving activity of S. arenicola in tomato plants under agricultural conditions and dig into the possible associated mechanisms. Tomato plants were grown under normal and saline conditions, and germination, bacteria-root system interactions, plant growth, photosynthetic performance, and the expression of salt stress response genes were analyzed. We found an endophytic interaction between S. arenicola and tomato plants, which promotes germination and shoot and root growth under saline or non-saline conditions. Accordingly, photosynthetic and respective photoprotective performance was enhanced in line with the induced increase in photosynthetic pigments. This was further supported by the overexpression of thermal energy dissipation, which fine-tunes energy use efficiency and may prevent the formation of reactive oxygen species in the chloroplast. Furthermore, gene expression analyses suggested that a selective transport channel gene, SlHKT1,2, induced by S. arenicola may assist in relieving salt stress in tomato plants. The fine regulation of photosynthetic and photoprotective responses, as well as the inhibition of the formation of ROS molecules, seems to be related to the induced down-regulation of other salt stress response genes, such as SlDR1A-related genes or SlAOX1b. Our results demonstrate that the marine microbial symbiont S. arenicola establishes heterologous symbiosis in crop plants, promotes growth, and confers saline stress tolerance. Thus, these results open opportunities to further explore the vast array of marine microbes to enhance crop tolerance and food production under the current climate change scenario.

24-epibrassinolide improved chilled tomato photosyntheticperformance by stabilizing electron transport chain and function of photosystem II

To explore the protective mechanisms of brassinosteroids in the chill-induced photoinhibition in tomato (Solanum lycopersicum), we studied the effect of foliar sprayed 24-epibrassinolide (EBR, 0.1µM) on the gas exchange, chlorophyll fluorescence characteristics, and chlorophyll a fluorescence transient in tomato seedlings under chilling stress (a temperature of 8 ℃ and an irradiance of 200 µmol m-2 s-1) for 4 d. Results showed that chilling significantly inhibited CO2 assimilation and induced photoinhibition of photosystem II (PS II). However, photosystem I (PS I) was relatively tolerant to chilling stress, which was due to the downregulation of PS II activity and increase of cyclic electron transport around PS I (CEF). Chilling led to the inactivation of PS II reaction centers (RCs) and blocked the electron transport at the PS II acceptor side, but did not affect the oxygen-evolving complex (OEC) on the donor side of PS II. Exogenous EBR could alleviate chill-induced PS II photoinhibition mainly by the increase of CO2 assimilation and thermal dissipation of excitation energy in the PS II antennae, while the protective effect of CEF was relatively smaller. This study demonstrated that EBR maintained the stability of the electron transport chain and the function of PS II in chilled tomatoes. EBR promoted the absorption (ABS/CS), trapping (TRo/CS), and electron transport (ETo/CS) per leaf area in tomatoes under chilling stress, which was due to increasing the density of active reaction centers (RC/CS), rather than the activity of active RCs.

Nonlinear sound absorption of Helmholtz resonators with serrated necks under high-amplitude sound wave excitation

This paper focuses on the design and sound absorption analysis of Helmholtz resonators with serrated necks inspired by the leading edges of owl wings. Numerical models for predicting the sound absorption and the flow field of the resonators are established by a finite element method based on nonlinear acoustic wave equations. The thermal conduction and vortex energy dissipation of resonators with straight and serrated necks are evaluated. The effects of the geometrical parameters including the neck diameter, the serration height, and the serration pitch on the sound absorption behaviors of the resonator are discussed. It is found that for a lower-intensity acoustic excitation, the serration leads to periodic oscillations of the fluid in the resonator neck, and increases the acoustic resistance of the resonator. For a high-intensity sound excitation, the distributions of the velocity and vorticity in the resonator neck show that the serrated structure can produce more vorticities, which is beneficial for acoustic energy dissipation. The resistance of the resonators grows significantly and the reactance decreases slightly with an increase in intensity of the sound excitation. Sound absorption coefficients of resonators fabricated by three-dimensional (3D) printing are tested in an impedance tube for a large range of sound pressure excitations. The computed results of the sound absorption coefficients are in good agreement with the experimental data, and the superior sound absorption performance of the resonator with a serrated neck is confirmed.

A novel modified expanded graphite/epoxy 3D composite with ultrahigh thermal conductivity

Polymer-based composites with efficient thermal energy dissipation performance can be prospectively applied in electronics and military industry. However, significantly improving the thermal conductivity (TC) of polymer-based composites is still challenging. Herein, 3D sulfanilamide-modified expanded graphite/epoxy (EG-SA/EP) composites with interconnected filler network were successfully prepared by a pre-filling and hot-pressing method. Benefiting from the interconnected network, the composite with 70 wt% EG-SA demonstrated ultrahigh bulk TC of 98 W/m·K (which exceeds some commercially-used metals) and up to 44,445% TC enhancement efficiency. Meanwhile, the EG-SA/EP composites exhibited excellent electromagnetic interference shielding performance of 85 dB (which is sufficient to block 99.9999997% of incident radiation), high electric conductivity of 7153 S/m and excellent thermal infrared response capability (the time to raise surface temperature from 19 to 82 °C is only 3 s). As for the mechanism of heat transfer, the 3D structure of EG-SA maintained through epoxy pre-filling in EG-SA is the main reason for the significantly improved TC. This is because the new method enables EG-SA to build a unique dense interconnected network in composites in the subsequent hot-pressing process, but the traditional direct mixing method easily destroys the inherent micro-3D structure of EG. The above excellent performances endow the EG-SA/EP composites with huge potential application value.

Upregulation of the mitochondrial alternative oxidase pathway improves PSII function and photosynthetic electron transport in tomato seedlings under chilling stress

The aim of this study was to explore how the mitochondrial alternative oxidase (AOX) pathway alleviates photoinhibition in chilled tomato (Solanum lycopersicum) seedlings. Chilling induced photoinhibition in tomato seedlings despite the increases in thermal energy dissipation and cyclic electron flow around PSI (CEF-PSI). Chilling inhibited the function of PSII and blocked electron transport at the PSII acceptor side, however, it did not affect the oxygen-evolving complex on the donor side of PSII. Upregulation of the AOX pathway protects against photoinhibition by improving PSII function and photosynthetic electron transport in tomato seedlings under chilling stress. The AOX pathway maintained the open state of PSII and the stability of the entire photosynthetic electron transport chain. Moreover, the protective role of the AOX pathway on PSII was more important than that on PSI. However, inhibition of the AOX pathway could be compensated by increasing CEF-PSI activity under chilling stress.

Combining one and two photon polymerization for accelerated high performance (3 + 1)D photonic integration

Abstract Dense and efficient circuits with component sizes approaching the physical limit is the hallmark of high performance integration. Ultimately, these features and their pursuit enabled the multi-decade lasting exponential increase of components on integrated electronic chips according to Moore’s law, which culminated with the high performance electronics we know today. However, current fabrication technology is mostly constrained to 2D lithography, and thermal energy dissipation induced by switching electronic signal lines presents a fundamental challenge for truly 3D electronic integration. Photonics reduces this problem, and 3D photonic integration is therefore a highly sought after technology that strongly gains in relevance due to the need for scalable application-specific integrated circuits for neural networks. Direct laser writing of a photoresin is a promising high-resolution and complementary metal-oxide-semiconductor (CMOS) compatible tool for 3D photonic integration. Here, we combine one and two-photon polymerization (TPP) for waveguide integration for the first time, dramatically accelerating the fabrication process and increasing optical confinement. 3D additive printing is based on femtosecond TPP, while blanket irradiation with a UV lamp induces one-photon polymerization (OPP) throughout the entire 3D chip. We locally and dynamically adjust writing conditions to implement (3 + 1)D flash-TPP: waveguide cores are printed with a small distance between neighboring writing voxels to ensure smooth interfaces, mechanical support structures are printed at maximal distance between the voxels to speed up the process. Finally, the entire chip’s passive volume not part of waveguide cores or mechanical support is polymerized in a single instance by UV blanket irradiation. This decouples fabrication time from the passive volume’s size. We succeed in printing vertical single-mode waveguides of 6 mm length that reach numerical apertures up to NA = 0.16. Noteworthy, we achieve exceptionally low −0.26 dB injection losses and very low propagation losses of −1.36 dB/mm at λ 0 = 660 nm, which is within one order of magnitude of standard integrated silicon photonics. Finally, the optical performance of our waveguides does not deteriorate for at least ∼3000 h after printing, and remains stable during ∼600 h of continuous operation with 0.25 mW injected light.

High-light-inducible proteins HliA and HliB: pigment binding and protein-protein interactions.

High-light-inducible proteins (Hlips) are single-helix transmembrane proteins that are essential for the survival of cyanobacteria under stress conditions. The model cyanobacterium Synechocystis sp. PCC 6803 contains four Hlip isoforms (HliA-D) that associate with Photosystem II (PSII) during its assembly. HliC and HliD are known to form pigmented (hetero)dimers that associate with the newly synthesized PSII reaction center protein D1 in a configuration that allows thermal dissipation of excitation energy. Thus, it is expected that they photoprotect the early steps of PSII biogenesis. HliA and HliB, on the other hand, bind the PSII inner antenna protein CP47, but the mode of interaction and pigment binding have not been resolved. Here, we isolated His-tagged HliA and HliB from Synechocystis and show that these two very similar Hlips do not interact with each other as anticipated, rather they form HliAC and HliBC heterodimers. Both dimers bind Chl and β-carotene in a quenching conformation and associate with the CP47 assembly module as well as later PSII assembly intermediates containing CP47. In the absence of HliC, the cellular levels of HliA and HliB were reduced, and both bound atypically to HliD. We postulate a model in which HliAC-, HliBC-, and HliDC-dimers are the functional Hlip units in Synechocystis. The smallest Hlip, HliC, acts as a 'generalist' that prevents unspecific dimerization of PSII assembly intermediates, while the N-termini of 'specialists' (HliA, B or D) dictate interactions with proteins other than Hlips.

Study of the Optical and Thermoplasmonics Properties of Gold Nanoparticle Embedded in Al2O3 Matrix.

In this paper, the optical and thermoplasmonics properties of nanocomposites consisting of spherical gold nanoparticles (AuNPs) integrated in {Al}_{2}{O}_{3} matrix are determined using the Finite Element Method (FEM). Firstly, the refractive index (n), extinction coefficient (kappa ), absorption coefficient {(mu }_{a}), and optical conductivity (sigma ) are calculated from the effective complex permittivity obtained by solving the Laplace’s equation for different size and concentration of nanoparticles. The surface plasmon resonance (SPR) properties of AuNPs are optimized from the peak presented in the absorption coefficient spectrum. The results show that the optical parameters n, kappa , {mu }_{a}, and sigma undergo a strong variation around the wavelength {lambda }_{max} corresponding to the SPR phenomenon. The value of {lambda }_{max} increases from 560 to 600 nm when the radius of the particles varies between r=5 and r=30 nm. The effect of the AuNP concentration on the band gap energy {E}_{g}(eV) of Au-{Al}_{2}{O}_{3} nanocomposites is also studied, a shift from Eg=5.34 to Eg=5.49 eV is observed when the concentration of the AuNPs increases from 0 to 0.82mathrm{%}. The electric field enhancement induced by the AuNPs at plasmonic resonance is also determined depending to the particle size; the results show that the enhancement factor increases from g=4.71 to g=6.95 when the radius of the AuNPs increases from r=5 to 30 nm. The thermal dissipation of the plasmonic energy of spherical of our system dispersed in the {Al}_{2}{O}_{3} matrix is determined considering the Joule effect which occurs by the oscillation of the charges at the plasmonic resonance. The generated thermal power by particles is calculated for different sizes, which allows to calculate the thermal power per gram of particles depending on the intensity of the incident electric field. The results show that the plasmonic thermal power is almost identical for small particles when the radius is less than r=15 nm and increases considerably when the size increases from r=15 to 30 nm. For a fixed size and incident field amplitude, we calculated the temperature change in the nanocomposites Au-{Al}_{2}{O}_{3} depending of time for different particle concentrations; the temperature variation curves obtained are linear as a function of time.

A Novel Design of Rack Mount Server Thermal Simulator: Design, Assembly, and Experimental Verification

Abstract The practice of commissioning data centers (DCs) is necessary to confirm the compliance of the cooling system to the information technology equipment (ITE) load (design capacity). In a typical DC, there are different types of ITE, each having its physical characteristics. Considering these geometrical and internal differences among ITE, it is infeasible to use the actual ITE as a self-simulator. Hence, a separate device called load bank is employed for that purpose. Load banks create a dummy thermal load to analyze, test, and stress the cooling infrastructure. Available commercial load banks do not accurately replicate a server's airflow patterns and transient heat signatures which are governed by thermal inertia, energy dissipation, flow resistance, and fan system behavior. In this study, a novel prototype of the server called server simulator was designed and built with different components to be used as a server mockup. The server simulator accurately captured air resistance, heat dissipation, and the functionality of actual server behavior. Experimental data showed up to 93% improvement in ITE passive and active flow curves using the designed server simulator compared to the commercial load bank. Furthermore, the experimental results demonstrated a below 5% discrepancy on the critical back pressure and free delivery point between the actual ITE and the designed server simulator. In addition, experimental data indicated that the developed server simulator improved the actual ITE thermal mass by 27% compared to the commercial load bank.

Peristaltic transportation of Carreau–Yasuda magneto nanofluid embedded in a porous medium with heat and mass transfer

Magnetohydrodynamic rheological pumping systems based on biological sources are finding new applications in modern energy systems. These systems combine the electrically conductive properties of flowing fluids with rheological behavior, biological geometry, and propulsion mechanisms. Further improvement of transport characteristics can be achieved with the use of nanofluids. In this study, all these aspects are combined to analyze the heat and mass transfer in mixed convective peristaltic conveyance of Carreau-Yasuda (CY) magneto nanofluid with mixture of ethylene glycol and graphene nano-powder. The Carreau-Yasuda model is utilized for nanofluid rheology and the Buongiorno's model for nanoscale effects. The deemed flow situation is modelled via temperature dependent heat generation/absorption, variable thermal conductivity, porous medium, activation energy, mixed convection, Brownian diffusion, magnetic field, thermophoresis diffusion, Ohmic heating and viscous dissipation assumptions. Fluid saturated porous medium is simulated by employing a modified Darcy's law. Zero mass flux and no-slip boundary conditions are taken for concentration, heat and velocity fields. Using the lubrication assumption, the governing system of equations for the fluid transfer problem is abridged and resolved employing built-in command NDSolve in Mathematica. Effects of different pertinent parameters are shown via graphs.

Elastic strain engineered nanomechanical GaN resonators with thermoelastic dissipation dilution up to 600 K

Conventionally, mechanical resonators exhibit evident degradation in quality factor and large frequency fluctuation at elevated temperatures above room temperature. Here, we show that the quality factor of up to 105 of a highly stressed GaN on Si nanomechanical resonators experiences little change as temperature increasing to 600 K and the temperature coefficient of the resonance frequency (TCF) is as low as several ppm/K, several times lower than those of the conventional GaN mechanical resonators. The high quality factor and low TCF at high temperatures are attributed to the high stress and the geometrical nonlinearity of dynamical strain in the GaN resonator, where the dissipation caused by the change of the material properties with the increasing temperature is compensated by the increased stiffness. This observation violates the universality of thermal energy dissipation in mechanical resonators. The results provide a universal strategy for engineering nanomechanical resonators with ultrahigh sensitivity and ultralow noise.

Atomistic insight into the formation dynamics of charged point defects: A classical molecular dynamics study ofF+-centers in NaCl

This paper provides an atomistic exploration of the lattice dissipation mechanisms accompanying the formation of charged point defects through a femtosecond resolved study of ${\mathrm{F}}^{+}$-center creation in NaCl. Our findings, following from a classical molecular dynamics based investigation of this model system, point to general range of properties that should be present in similar systems. Immediately after the creation of such a charged defect center, its excess energy is imparted amongst the highest energy optical modes with no clear preference based on their degree of localization. This energy is then dissipated through equilibration amongst a bath of lower energy phonon modes. The temporal behavior primarily follows exponential decay trends at all the temperatures and energies explored, with a small degree of competition between phonon population and depopulation amongst lower energy bath modes. Moreover, the dissipation timescale is found to be approximately the same amongst all phonon energies. A temperature-dependent analysis shows the expected decrease in phonon lifetimes with increasing temperature. This is accompanied by similarly more rapid dissipation of thermal energy around the defect center at lower temperatures when the phonon mean free path is increased. An intuitive phenomenological model based on Langevin dynamics is also provided to interpret the atomistically derived phonon decay characteristics in the temporal domain. More broadly, these results are expected to aid the design and experimental investigation of strongly correlated materials where charged defect centers can play an important role in technological applications.

In-situ thermal analysis of intermetallic and thermite projectiles in high velocity impact experiments

Particle fragmentation influences thermochemical energy conversion processes in different ways and is of significance in energy generation technologies. Different reactive material formulations trigger varied thermal response in extreme environments such as high velocity impact. This study investigated optical thermal response of powder gun launched intermetallic (Al:Zr) and thermite (Al:MoO3) projectiles using pyrometry and thermography. Projectiles were launched at 1250 m/s into an air-filled chamber and impacted a steel witness plate to create a dust explosion. The pyrometer was configured to measure temperatures directly at the point of impact, while the thermographic system measured temperatures throughout the explosion chamber. Results show that impact temperatures ranged between 3500 and 4000 K, but that the dynamics of energy conversion were different for the intermetallic and thermite projectiles. The intermetallic exhibited secondary reactions due to fragmented debris impacting the walls of the chamber. The thermite exhibited greater gas generation, propelling the debris field, and producing a more stochastic response with faster spreading and dissipation of thermal energy. Unique features such as microexplosions within fragmented particles were also analyzed. While both reactive materials produce similar temperatures, their mechanisms of energy conversion and release are different, indicating the potential of these materials for different ballistic applications.

Calcium Affects Growth and Physiological Indices of Panax quinquefolium L.

Calcium (Ca) is necessary for plant growth and stress resistance, which are essential for the successful cultivation of Panax quinquefolium L. (American ginseng). However, information about the physiology of Ca nutrition in this species is limited. Therefore, the objective of this study was to determine the effect of Ca on the growth and physiological performance of American ginseng. Two-year-old American ginseng plants were supplemented with the following Ca concentrations [Ca2+] in a hydroponic system: 0, 160.17, 320.34, 640.68, and 961.02 mg⋅L−1. Measurements included growth biomass accumulation, chlorophyll (Chl) content and fluorescence, photosynthetic parameters, antioxidant enzyme activity, root activity, and malondialdehyde content. Biomass, stem height, leaf area, maximum photochemical efficiency, and superoxide dismutase activity peaked at [Ca2+] of 640.68 mg⋅L−1. Actual photochemical efficiency, minimum saturating irradiance, photosynthetic rate, catalase and peroxidase activities, and root activity reached their maximum at [Ca2+] of 320.34 mg⋅L−1. Stem diameter and regulated thermal energy dissipation increased with [Ca2+]. The sum of nonregulated heat dissipation and fluorescence emission and malondialdehyde content decreased to a minimum at [Ca2+] of 320.34 mg⋅L−1. The Chl content reached a maximum at [Ca2+] of 160.17 mg⋅L−1, but the Chl a/b ratio increased with [Ca2+]; the actual photochemical efficiency and photosynthetic rate reached their maximum level at Chl a/b ratios of 2.04 and [Ca2+] of 320.34 mg⋅L−1. Therefore, the optimal [Ca2+] for American ginseng growth was 320.34 mg⋅L−1. Furthermore, an appropriate increase [Ca2+] in the growth medium may improve biomass accumulation, light energy utilization efficiency, and stress resistance in American ginseng.