Step Heating Research Articles

A Transient Resistance/Capacitance Network-Based Model for Heat Spreading in Substrate Stacks Having Multiple Anisotropic Layers

Abstract Heat spreading from local, time-dependent heat sources in electronic packages results in the propagation of temperature nonuniformities through the stack of material layers attached to the chip. Available models either predict the chip temperatures only in the steady-state or a single substrate for transient analysis, without the ability to predict the transient response in compound substrates having multiple anisotropic layers. We develop a transient resistance/capacitance network-based modeling approach capable of predicting the spatiotemporal temperature fields for this chip-on-stack geometry, accounting for in-plane heat spreading, through-plane heat conduction, and the effective convection resistance boundary conditions. The transient heat spreading resistance for an anisotropic substrate has been formulated by converting it to an effective isotropic substrate for which there is an available half-space solution. The transient heat spreading model for a step heat input to a single substrate is subsequently extended to any arbitrary transient heat input using a Fourier series and extending the half-space formulation from a step heat input to sinusoidal heat input. For obtaining the transient spreading resistance for heat inputs into multiple stacked substrates, a method has been outlined to convert the multisubstrate stack to a single substrate with effective isotropic properties by properly accounting for the in-plane and through-plane thermal conductivities, and the heat capacity. The estimates from the present model are validated with direct comparison to a finite volume numerical model for three-dimensional heat conduction. Case studies are presented to demonstrate the capabilities of the proposed network-based model and compare its estimates with the numerical conduction solution. In the presence of a step heat input, the results demonstrate that the model accurately captures the transient temperature rise across the multisubstrate stack comprising layers with different anisotropic properties. For a case where the rectangular stack is exposed to a sinusoidally varying heat input, the model is able to capture the general trends in the transient temperature fields in the plane where the heat source is applied to the multisubstrate stack. In summary, the developed resistance/capacitance network-based transient model offers a low-computational-cost method to predict the spatiotemporal temperature distribution over an arbitrary transient heat source interfacing with a multilayer stack of substrates.

Exploring Step-Heating and Lock-In Thermography NDT Using One-Sided Inspection on Low-Emissivity Composite Structures for New Rail Carbodies.

This paper aims to explore the qualification of step- and lock-in heating thermography as techniques capable of inspecting new composite rail carbodies following input and inspection requirements set by the rail manufacturing industry. Specifically, we studied (a) a monolithic CFRP sample (20 mm thickness) and (b) a CFRP-PET foam-CFRP sandwich (40 mm total thickness) component, that were manufactured with artificial defects, to replicate the side wall sections of a carbody. The samples proved to be very challenging to test using only one-sided inspection due to (1) exhibiting significant thickness compared to existing literature, (2) low surface emissivity and (3) that the foam core of the sandwich sample was a thermal insulating material. In addition, the sandwich sample was designed with defects on both skins. Both thermography techniques provided similar defect detection results, although step heating offered faster detection. In the case of the monolithic panel, defects up to 10 mm depth were detected, with minor detection of defects at 15 mm depth with a step-heating protocol between 90 s and 120 s overall acquisition, which was faster than the 140 s used with the lock-in technique. For the sandwich component only the front skin defects were detected, with both techniques using heating protocols between 70-120 s.

Role of powder handling on resulting impurities in ZnSe-doped As-S-Se composite materials

Optical composite materials made by powder processing routes can suffer from unwanted absorption loss introduced through powder handling. This can be due to impurities that are introduced during different stages of a powder processing protocol such as mixing, sieving, or grinding. The present work has evaluated the prevalence of impurities imparted to powders used to create an optical composite comprised of an As-S-Se chalcogenide base glass and ZnSe powders. The goal of this study was to identify a suitable powder handling protocol that demonstrates control of the starting particle sizes of the refractive index matched glass matrix and dopant ZnSe to acceptable levels and minimizes adverse impurities that can create loss in a glass-ceramic composite preform and envisioned fiber preforms, and fibers formed from them. Employing a heat treatment step under vacuum prior to re-melting glass powders was shown to reduce the concentration of key impurities, OH-, S-H, and Se-H, by 45.0%, 31.1% and 21.2%, respectively, as compared to re-melted material made from powders without specialized handling.

Nanofibrous Wound Healing Nanocomposite Based on Alginate Scaffold: In Vitro and In Vivo Study

The combination of nanofibers with 3D scaffolds has shown promising results as the wound healing/dressing/care biomaterials. The present study aimed to fabricate and optimized alginate hydrogel composited by Lignin-derived carbon nanofibers (CNFs). The nanofibers were obtained from electrospun Lignin nanofibers as the precursor through two steps heat treatments. The synthesized nanofibers blended with an alginate polymer solution with different concentrations (1, 5, and 10 wt.%) and cross-linked using CaCl2 through the physical cross-linking. The findings illustrated that the prepared Lignin and CNFs have acceptable diameter. The composited Alginate hydrogels possessed a porous internal-structure with interconnected architecture. The fabricated hydrogel exhibited proper porosity and swelling behavior beneficial for wound healing application. The In Vitro experiments revealed that the hydrogel were red blood cell (RBC)-compatible, cytocompatible, and induced proliferative effects on cells. The animal experiments indicated that the application of the hydrogel promoted the process of wound healing. These observations implied that the prepared hydrogel nanocomposites exhibited promising properties and can be considered as wound healing nanobiomaterials.

Faceted Antimony Particles with Interiors Reinforced with Reduced Graphene Oxide as High-Performance Anode Material for Sodium-Ion Batteries.

The attainment of "true reinforcement" in a composite and harnessing of the associated beneficial effects have been demonstrated here through the development of faceted crystalline Sb particles having the interiors reinforced with reduced graphene oxide (rGO). Such a unique and "near-ideal" micro/nanocomposite architecture has been achieved via a facile/cost-effective route by facilitating heterogeneous nucleation/growth of Sb-oxide particles on/around dispersed rGO sheets upon incorporation of the same directly into the precursor suspension, followed by the reduction of Sb-oxide to Sb, in intimate contact with the rGO, during the subsequent single heat-treatment step. As a potential anode material for Na-ion batteries, the as-developed Sb/rGO composite exhibits a reversible Na-storage capacity of ∼550 mAh/g (@ 0.2 A/g) and a fairly high first cycle Coulombic efficiency (CE) of ∼79%, with the good reversibility being attributed to the coarse particle size of Sb and encompassing of rGO sheets inside the Sb particles. Furthermore, despite the coarse particle size, the Sb/rGO-based electrode exhibits outstanding cyclic stability, with negligible capacity fade up to 150 cycles (viz., ∼97% capacity retention), and rate capability, with >86% capacity being obtained upon raising the current density from 0.1 to 2 A/g, resulting in a capacity of ∼490 mAh/g, even at 2 A/g.

CRYSTAL STRUCTURE OF AgGa2Te3I COMPOUND

A compound AgGa2Te3I belongs to the quaternary semiconductors of the general formula AІВІІІ2X3Y (AІ – Cu, Ag; ВІІІ – Ga, In; X – S, Se, Те; Y - Cl, Br, I). For the first time, its structure, which forms in tetragonal syngony, was studied by the powder method, Sp.Gr. I-4, structural type CuIn2Te3Cl, with cell parameters: a = 6,0041 (4) Å, c = 11,965 (1) Å. The compound was synthesized in evacuated quartz ampoules from simple substances and pre-synthesized AgI by step heating. Based on the melting temperatures of the components, the 1070 K maximum synthesis temperature was chosen, followed by homogenizing annealing at 770 K during 300 h and subsequent quenching in water at room temperature. As a result of the synthesis, a compact, gray alloy was obtained, which was resistant to air. The diffraction pattern of the powdered sample was taken on a DRON 4-13 diffractometer, CuKα radiation, irradiation at one point during 15 sec. WinCSD program was used to calculate the structure, which was refined by the Rietveld method. The obtained results on the structure of the compound were analyzed and its belonging to defective semiconductors was discussed.

Interface-reinforcing sintering step for highly stable operation of proton-conducting fuel cell stack

Proton conducting fuel cells (PCFCs) are promising power generation systems due to their low operating temperature by conducting proton activated with low kinetic energy. However, well-known proton conducting materials such as Y-doped BaCeO3−δ (BCY), Y-doped BaZrO3−δ (BZY), and BaCe0.8-xZrxY0.1Yb0.1O3−δ (BCZYYb) have a limitation in that the planar cell is fragile during operation attributed to the low mechanical strength. This study proposes a two-step sintering method to fabricate mechanically superior PCFC large cells based on the BCZYYb electrolyte. The two-step sintering process consists of a heat treatment step at a temperature in which the anode and electrolyte have similar shrinkage values during the sintering process and another step that can improve the bonding strength of each layer by grain growth. The vulnerable anode/electrolyte interface, which acts as a significant mechanical failure factor, is optimized through the two-step sintering process. Two-step sintered cells show high mechanical stability in lab-scale and 6 cm × 6 cm planar cells for stack systems. A two-step sintered large cell exhibits outstanding stability during 350 h at 600 °C with the stack system. Our strategy provides a method to build practical proton-conducting fuel cells.

Numerical investigations on the effect of multi-dimensional stepness in open micro pin fin heat sink using single phase liquid fluid flow

In present work, the square shaped micro pin fin configuration of microchannel heat sink has been numerically investigated under different geometrical variation. Considering effectiveness of open microchannel, the pin fin height has been varied in two different styles. Firstly, the consecutive pin fins are varied in step of two and three rows. Secondly, the step variations were opted along only the channel length (unidirectional) and along both channel length and channel width (bidirectional). Furthermore, all configurations are having equal convective area so that influence of out of plane mixing can be studied more precisely. Estimated findings clearly indicated that stepped configuration has superior thermo-hydraulic performance compared to uniform configuration due to out of plane fluid motion resulting in enhanced flow mixing. Afterwards, bidirectional step has shown augmented performance compared to unidirectional step heat sink configuration because of enhanced secondary fluid flow and distinct vortices formation behind each pin fins. Among all considered configurations, three stepped bidirectional micro pin fin heat sink has yielded best performance i.e. 28.3% higher heat transfer rate and 2% lesser average bottom wall temperature compared to uniform height pin fin configuration.

Monitoring the precipitation of the hardening phase in the new VDM® Alloy 780 by in-situ high-temperature small-angle neutron scattering, neutron diffraction and complementary microscopy techniques

The hardening phase precipitation process plays an important role in the development of new Ni-base superalloys. In the present work, we apply a powerful combination of complementary characterization techniques to characterize in-situ the γ’ precipitation in the new VDM® Alloy 780. During the whole heat treatment process, in-situ time-of-flight (TOF) neutron diffraction (ND) unambiguously identified the γ’ phase as well as its weight fraction and the misfit with the matrix while in-situ small-angle neutron scattering (SANS) provided precise precipitates’ size analysis. Atom probe tomography (APT) and scanning electron microscopy (SEM) provided detailed microstructural characterization and chemical composition of the phases necessary for a proper neutron scattering data evaluation. This contribution reveals more detailed information on the nucleation, growth, and Ostwald ripening processes starting from the early precipitation stage in bulk samples using the complementary microstructure investigation methods. The nucleation and growth kinetics of precipitates at 720 °C depend on heating rates and the size distribution obtained in the pre-heating history of the sample. A subsequent heat treatment step at 620 °C, typically used in Ni-base superalloys, does not lead to similar progressive precipitation or growth. The expected matrix-diffusion-controlled Ostwald ripening process of the γ’ precipitates was in-situ monitored by SANS on a full precipitation hardened sample at expected operating temperatures (750 °C) showing slower coarsening kinetics than other reported Ni-based superalloys.

Size determination of interior defects by reconstruction of subsurface virtual heat flux for step heating thermography

Step heating thermography is a non-destructive testing (NDT) technique that inspects interior defects by observing surface temperature rises during a long pulse heat stimulation. Due to the heat diffusion induced blurring of defect shapes, it is a challenging task to accurately determine the sizes of deep and small defects. This work focuses on estimating the size of a subsurface defect by an inversion of temperature images for the step heating thermography, to overcome the information loss during the propagation of thermal waves. We assume a space- and time-dependent virtual heat flux on the defect surface, which is reconstructed from surface temperature measurements by solving a two-dimensional inverse heat conduction problem. The local future time concept is combined with the Tikhonov's regularization to stabilize the inverse solution. A prudent choice of the regularization parameter is carried out through the L-curve. The feasibility of the proposed approach is assessed by numerical simulations and experiments. It is shown that the inversion brings an improvement in defect sizing accuracy for defects with low width-to-depth ratios and an efficient suppression of measurement noises.

Structural integrity evaluation of cyclic loading Glass Fibre Reinforced Polymer composite by acoustic emission and heat transfer

GFRP composites experience structural changes like matrix cracking, debonding, delamination, and fibre failure on static and dynamic loading. In this work, composites with varying fibre orientation interaction angle and volume fractions are prepared and exposed to cyclic load. The cyclic load (R = 0) is a constant amplitude flexural load imposed on the cantilever beam specimen with varying frequencies (2.6, 4.6, 8.6 Hz) and cycles (up to 44 × 103). The structural integrity of the specimens on loading is examined in terms of Flexural, modulus, Acoustic Emission (AE) and heat transfer changes. The drop in flexural modulus is minimum in higher Vf = 32% laminate (A1 = 7.01%, B1 = 1.86%) than the lower Vf = 25% (A2 = 19.86%, B2 = 8.6%). The observed AE peak frequency for the induced damages is in the range of 50–100, 110–230, 245–380 kHz. The drop-in fibre volume fraction has a significant role in laminate with lower fibre interaction (Type A) to offer minimum variation (5.25%) in AE activity count which is the opposite in laminates with higher fibre interaction angle (31.75%). The step heat thermography exhibits minimum temperature difference (∆T) for moderate loading frequency and in a few cases, ∆T drops well below the virgin, insisting on in situ thermography to study the dynamic changes in composites. A fibre dominant behaviour can be observed with minimum variation in AE activity in a lower fibre interaction angle. Thus, the fibre orientation angle and fibre volume fraction have a significant role in the retention of the structural integrity of composites in dynamic loading.

Heat Treatment-Induced Conductivity Enhancement in Sulfide-Based Solid Electrolytes: What is the Role of the Thio-LISICON II Phase and of Other Nanoscale Phases?

Sulfide-based solid Li+ electrolytes are one of the most promising electrolyte classes for solid-state battery applications. These solid electrolytes are typically prepared by means of high-energy ball milling, often followed by a heat treatment step for enhancing the Li+ ion conductivity. In many cases, heat treatment-induced conductivity enhancements have been attributed to the formation of a superionic thio-LISICON II phase. However, the chemical composition and structure of this phase as well as the origin of the conductivity enhancement are still under debate. Here, we have carried out a comprehensive study on the thiophosphate-based electrolyte system (1 – x) Li3PS4 + x LiI with x = 0–0.5. By combining electrochemical impedance spectroscopy, X-ray diffraction, and Raman spectroscopy as well as 7Li NMR line-shape analysis and high-resolution multidimensional 31P solid-state NMR measurements, we show that the widely used concept of a thio-LISICON II phase governing the ionic conductivity of heat-treated samples cannot explain the experimental observations. Double-quantum constant-time 31P NMR proves that P2S64– units are embedded in the amorphous phase of the ball-milled pristine samples. Upon heat treatment, the amorphous phase with the embedded P2S64– units is transformed into different nanoscale crystalline phases, a thio-LISICON II phase, a β-Li3PS4 phase, and a Li4PS4I-related phase. A structural model of the thio-LISICON II phase needs to explain the coupling pattern from two-dimensional double-quantum NMR presented here, showing two phosphorus environments with an approximate ratio of 2:1. Furthermore, our results indicate that in heat-treated samples, a highly disordered nanoscale Li4PS4I-related phase exists with an ionic conductivity even exceeding that of the thio-LISICON II phase.

Complex 40Ar ∕ 39Ar age spectra from low-grade metamorphic rocks: resolving the input of detrital and metamorphic components in a case study from the Delamerian Orogen

Abstract. In this study, we provide 40Ar / 39Ar geochronology data from a suite of variably deformed rocks from a region of low-grade metamorphism within the Cambro–Ordovician Delamerian Orogen, South Australia. Low-grade metamorphic rocks such as these can contain both detrital minerals and minerals newly grown or partly recrystallised during diagenesis and metamorphism. Hence, they typically yield complex 40Ar / 39Ar age spectra that can be difficult to interpret. Therefore, we have undertaken furnace step heating 40Ar / 39Ar geochronology to obtain age spectra with many steps to allow for application of the method of asymptotes and limits and recognition of the effects of mixing. The samples analysed range from siltstone and shale to phyllite and contain muscovite or phengite with minor microcline as determined by hyperspectral mineralogical characterisation. Whole rock 40Ar / 39Ar analyses were undertaken in most samples due to their very fine-grained nature. All samples are dominated by radiogenic 40Ar, and contain minimal evidence for atmospheric Ca- or Cl-derived argon. Chloritisation may have resulted in limited recoil, causing 39Ar argon loss in some samples, which is especially evident within the first few percent of gas released. Most of the age data, however, appear to have some geological significance. Viewed with respect to the known depositional ages of the stratigraphic units, the age spectra from this study do appear to record both detrital mineral ages and ages related to the varying influence of either cooling or deformation-induced recrystallisation. The shape of the age spectra and the degree of deformation in the phyllites suggest the younger ages may record recrystallisation of detrital minerals and/or new mica growth during deformation. Given that the younger limit of deformation recorded in the high-metamorphic-grade regions of the Delamerian Orogen is ca. 490 Ma, the ca. 470 to ca. 458 Ma ages obtained in this study suggest deformation in low-grade shear zones within the Delamerian Orogen may have persisted until ca. 20–32 million years after high-temperature ductile deformation in the high-grade regions of the orogen. We suggest that these younger ages for deformation could reflect reactivation of older structures formed both during rift basin formation and during the main peak of the Delamerian orogeny itself. The younger ca. 470 to ca. 458 Ma deformation may have been facilitated by far-field tectonic processes occurring along the eastern paleo-Pacific margin of Gondwana.

Performance of flat-plate, flexible polymeric pulsating heat pipes at different bending angles

The heat transfer performance of a flat-plate, flexible polypropylene pulsating heat pipe (PHP) is evaluated experimentally when the device is bent at different angles, and for different layouts of the evaporator and the condenser. Flexible pulsating heat pipes are a passive thermal management technology with important prospective applications in foldable portable electronics, deployable systems (such as cube satellites), soft robotics, and many others. While a number flexible PHPs have been developed in the recent past, to date, there is insufficient information about the influence of the bending angle (conformation) and of the reciprocal positions of the heat sink and source (configuration) on their thermal performance. Several polypropylene PHP prototypes (250 mm ×100 mm ×1.5 mm) with a channel width of 5 mm and different loop geometries were fabricated using selective transmission laser welding technology. Ethanol and FC-72 were used as heat transfer fluids at a filling ratio of 50%. The PHP performance was evaluated through the equivalent thermal resistance of the device, calculated from the surface temperatures of both the evaporator and the condenser during an ascending/descending stepped heat input ramp applied to the evaporator. The experimental results show that conformation arrangements have no significant effect on the thermal performance, however it may affect the PHP start-up.

Irreducible IrO2 Anode Co-Catalysts for PEM Fuel Cell Voltage Reversal Mitigation and Their Stability Under Transient Operation Conditions

The cell voltage reversal that can occur during the transient operation of a proton exchange membrane fuel cell (PEMFC) stack leads to a substantial degradation of the anode catalyst. During cell reversal, the anode potential increases (>>1 V vs. the reversible hydrogen electrode potential (RHE)), causing severe oxidation of the anode catalyst carbon support, which leads to a collapse of the anode catalyst layer and to cell failure. One strategy to mitigate the damages of H2 starvation is the addition of a co-catalyst to the anode electrode, which catalyzes the oxygen evolution reaction (OER), so that the non-damaging OER rather than the damaging carbon oxidation reaction (COR) takes place. A commonly used anode co-catalyst to favor the OER over the COR during cell reversal events is iridium oxide (IrO2).1 Recent findings show that the near-surface layer(s) of IrO2 can be completely reduced to metallic Ir upon exposure to H2, e.g., under the operating conditions of a PEMFC anode.2, 3 Such alteration of the near-surface layer(s) of IrO2 drastically affects its stability during the anode potential transients that occur during start-up/shut-down (SUSD) events, where our recent study showed that the dissolution of metallic Ir and crossover of the dissolved Irn+ species through the membrane to the cathode electrode cause iridium deposition on the Pt/C cathode catalyst.3 Such iridium-based contamination on the cathode catalyst surface deteriorates the oxygen reduction reaction (ORR) activity of Pt and results in a significant performance loss during the normal operation of the fuel cell. At the same time, SUSD transients also cause an OER activity loss of the anode co-catalyst, which was shown to be mainly due to the redeposition of Pt dissolved from the anode hydrogen oxidation reaction (HOR) catalyst onto the reduced IrO2 anode co-catalyst, blocking its OER active sites.3 Since these degradation mechanisms are caused by the chemical reduction of the typically employed IrO2 anode co-catalysts in the PEMFC anode, a reduction-resistant OER catalyst would be required.In this contribution, we introduce an unprecedented approach to synthesize IrO2 catalysts that are not reduced in the PEMFC anode environment. The preparation of such irreducible IrO2 (Irr-IrO2) catalysts is based on an industrially scalable procedure consisting of a high-temperature (650-1000 ᵒC) heat treatment step followed by a deagglomeration step and a post annealing step to prepare catalyst powders with specific surface areas of ~25 m2/g. Figure 1 shows the thermogravimetric analysis (TGA) according to our previously proposed evaluation protocol3 under 3.3 vol.% H2/Ar of an as-received commercial benchmark catalyst (IrO2/TiO2 (Umicore)), a self-made IrO2 catalyst heat-treated near the conventional temperature of 500 °C (IrO2-500 °C), and a stabilized IrO2 catalyst prepared by a procedure introduced in this contribution (Irr-IrO2). It can be seen that the temperature that corresponds to the reduction of 20% of the IrO2 phase (α = 20%) of the Irr-IrO2 catalyst is ~38 °C and ~53 °C higher than those of the IrO2-500 °C and the IrO2/TiO2 (Umicore) catalysts, respectively. Considering the fact that all of these catalysts have a specific surface area of ~25 m2/g, the observed reductive stability improvement of Irr-IrO2 catalyst is due to its intrinsic structural distinctions from the typically synthesized IrO2 and the commercial benchmark IrO2 catalysts. As will be shown, this higher stability is reflected by the observation that SUSD cycling of MEAs with the Irr-IrO2 as anode co-catalyst does not result in iridium dissolution and the associated iridium poisoning of the ORR activity of the cathode catalyst. Furthermore, while its OER activity is lower than that of conventional IrO2 catalysts, it still dramatically increases the cell reversal tolerance time of a conventional Pt/C anode. References T. R. Ralph, S. Hudson, and D. P. Wilkinson, ECS Transactions, 1 (8), 67-84 (2006).P. J. Rheinländer and J. Durst, Journal of the Electrochemical Society, 168 (2), 024511 (2021).M. Fathi Tovini, A. M. Damjanovic, H. A. El-Sayed, J. Speder, C. Eickes, J.-P. Suchsland, A. Ghielmi, and H. A. Gasteiger, Journal of The Electrochemical Society, 168 (6), 064521 (2021). Figure 1. TGA (5 K min-1) experiments under 3.3 vol.% H2/Ar with the as-received IrO2/TiO2 (Umicore), the IrO2-500 °C, and the Irr-IrO2 catalyst powder samples (following a drying/cleaning step; see Ref. 3 for further details). The y-axis represents the fraction of the IrO2 phase in the catalyst powder samples that is reduced to metallic Ir (α). The black horizontal dashed line illustrates a reaction extent of α= 20%, to compare the stability of different samples in a H2-containing atmosphere. Figure 1

A cost-effective way of sintering Ce3+:YAG based ceramic phosphors for high power/high brightness phosphor-converted solid state light sources

Transparent or translucent Ce3+:YAG single-phase ceramics and Ce3+:YAG/Al2O3 ceramic composite were prepared by simple sintering in flowing oxygen at atmospheric pressure. The sintered samples presented similar optical transmittance spectra as those sintered in vacuum except the oxygen vacancies related absorption band peaked at 320 nm. SEM morphology of the ceramic plates showed dense microstructures when sintered at about 1700 °C, and the mechanism of densification in oxygen atmosphere was analyzed. In addition, the chromaticity and luminescence spectra of the light source prototypes combining blue LD and the as-prepared ceramics were measured, the effect of the optical transmittance, Ce3+ doping concentration and the secondary phase alumina on the color coordinates and luminous efficacy were also discussed. This process obviates the need for expensive sintering equipment and extra heat treatment steps, which may pave the way for obtaining Ce3+:YAG based ceramic phosphors for practical applications through a cost-effective method.

Novel use of selectivity of resonance Raman spectroscopy to study polytypism and mixed to pure phase conversion in individual InAs NWs on laser irradiation

Conversion of Wurtzite to Zincblende phase of InAs NWs at high simulated temperature (>1300 K) is investigated using resonance Raman spectroscopy with specially designed two step heating–cooling experiment. For smaller nanowires (diameter < 700 nm), the certainty of determining the polytypism using polarized Raman spectroscopy, reduces significantly. Low signal to noise ratio for smaller diameter NWs is improved by employing the wavelength dependent unpolarized and polarized Raman spectroscopy to examine the sensitivity of resonance Raman spectroscopy as an alternate for probing polytypism. Innovative use of resonance Raman spectroscopy to probe phase purity of the III-V individual nanostructures, where, conventional methods may not be applicable is realized in this work.This work paves the way for online monitoring of the conversion of mixed phase to phase pure III-–V nanowires using laser irradiation for their fast electronic device applications. Further, this kind of surface modification study provides basis for the futuristic crystal structure engineering, which can facilitate the controlled tailoring of material properties in order to enhance their functionality.

Influence of three dimensionality effects on thermal hydraulic performance for stepped micro pin fin heat sink

Influence of three dimensionality effects on thermal hydraulic performance for stepped micro pin fin heat sink

Numerical estimation of temperature response with step heating of a multi-layer skin under the generalized boundary condition

In this article, we discussed a one-dimensional bioheat transfer mathematical model that describes the process of temperature distribution in tissue for the multi-layer skin under the step heating generalized boundary condition. The finite difference scheme is used to estimate the temperature profile along with time and distance. We discussed the stability of the numerical scheme and also validated the accuracy of the numerical code by comparing the present results with the previous reference results. To remove heat from the skin is considered by the surface temperature, heat flux, and ambient temperature to be zero with the help of the unit step like function. Then, we observed that the skin temperature in the second kind boundary condition was slowly decreasing over time as compared to the first and third kind boundary conditions. The temperature or heat flux at the skin surface is assumed to be high then there is negligible effect of the blood perfusion rate on the temperature response over a short time period and the effect of blood perfusion rate is visible when the time duration is long. Effect of blood perfusion rate, heating and after removal of heating, water diffusion, and generalized boundary condition for the analysis of the behavior of temperature response in multi-layer skin are discussed in detail and the results obtained are presented graphically.

Utilization of Bayesian Optimization and KWN Modeling for Increased Efficiency of Al-Sc Precipitation Strengthening

The Kampmann and Wagner numerical model was adapted in MATLAB to predict the precipitation and growth of Al3Sc precipitates as a function of starting concentration and heat-treatment steps. This model was then expanded to predict the strengthening in alloys using calculated average precipitate number density, radius, etc. The calibration of this model was achieved with Bayesian optimization, and the model was verified against experimentally gathered hardness data. An analysis of the outputs from this code allowed the development of optimal heat treatments, which were validated experimentally and proven to result in higher final strengths than were previously observed. Bayesian optimization was also used to predict the optimal heat-treatment temperatures in the case of limited heat-treatment times.