Thermally-induced Stresses Research Articles

Immune protective, stress indicators, antioxidant, histopathological status, and heat shock protein gene expression impacts of dietary Bacillus spp. against heat shock in Nile tilapia, Oreochromis niloticus

This research evaluated the efficacy of mixed Bacillus strains probiotic supplements in mitigating acute thermal-induced stress in Nile tilapia (Oreochromis niloticus). Three experimental fish groups involved 135 Nile tilapia (49 ± 2 g); one control (no added probiotics), 0.5, and 1% of selected Bacillus strains (B. subtilis, B. licheniformis, and B. pumilus) for 58 days. After the feeding period, growth parameters, immunological parameters, stress biochemical markers, and antioxidant parameters in addition to genes related to stress and histopathological changes in fish, were assessed; subsequently subjected to heat shock at 36 ± 0.5 ◦C for 2 h. Before the heat challenge, our results exhibited a marked increase in the growth efficacy (P < 0.05), lower marked serum levels of triglycerides and cholesterol, and tissue malondialdehyde (MDA) levels along with significantly increased superoxide dismutase (SOD) and catalase (CAT) enzymes activity in fish-fed Bacillus probiotic at 0.5% concerning the control group (P < 0.05). There were no significant changes in the serum levels of glucose, cortisol, lactate, phagocytic activity, respiratory burst (ROS), total immunoglobulin Ig, alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), total protein, albumin, globulin, uric acid, urea, creatinine, as well as HSP70, GST, and GPx mRNA expression in most of the probiotic groups compared to the control group (P > 0.05). When Nile tilapia was exposed to heat stress, supplementation with Bacillus probiotic in the diet significantly decreased most of the indices related to serum biochemical (ALT (P < 0.01; P < 0.001), AST (P < 0.01), LDH (P < 0.01), urea (P < 0.05), and creatinine (P < 0.01)), triglycerides (P < 0.001; (P < 0.01)), cholesterol (P < 0.01; (P < 0.05)), glucose (P < 0.001), and cortisol (P < 0.01; (P < 0.05)), with tissue oxidative stress MDA levels (P < 0.05), and HSP70 mRNA expression (P < 0.01; P < 0.001), aligned with the stressed control group. In addition, a notable upsurge in the total protein, albumin, globulin, phagocytic and ROS activities, and total Ig, as well as the enzymatic antioxidant ability (SOD, CAT) (P < 0.01), with GST and GPx mRNA expression (P < 0.05; P < 0.01), were shown in fish-fed Bacillus spp. post-exposure compared with the stressed control group. Besides, no histopathological alterations were revealed in the spleen and brain of fish pre- and post-heat exposure. According to our findings, diet supplementation of Bacillus species has the potential to combat the suppressive effects of heat shock in Nile tilapia.

Gradient ceramic structures via multi-material direct ink writing

Dense boron carbide-silicon carbide specimens with composition tailored at the mesoscale were produced by direct ink write additive manufacturing in three configurations: I, 2 % and II, 10 % compositional layer-to-layer steps, and III, homogeneous composition throughout. Flexural strength, indicative of tensile failure, is the highest for the Type-II design (366 MPa) due to its compressive residual stress state in the surface layers. Analysis of thermally-induced residual stresses predicts the ranking of the flexural strengths obtained for Type-II (highest), Type-I (intermediate), and Type-III (lowest) specimens. Compressive strength is load-orientation independent, highly strain-rate dependent, and reduced for specimens with thermal residual stress. Mechanical tests were performed in cube and dumbbell geometries. Dumbbell geometry compression specimens have a compressive strength that is 68 % (quasistatic) and 86 % (dynamic) higher than that of cube geometry and show a greater strain rate dependence. The rate dependency is attributed to the competition between crack propagation and loading velocities. Type-I dumbbells show the highest mean compressive strength of 3.96 GPa (quasi-static) and 5.11 GPa (dynamic). The failure mode evolves from mixed intergranular/transgranular at low strain rates to transgranular at high strain rates. High-speed video analysis indicates that dumbbell geometry specimens fail in compression due to microcrack growth and coalescence, while cubes fail due to the axial macrocracks that develop at the specimen/load platen interface and propagate into the specimen parallel to the loading direction (end splitting). This work demonstrates the impact of compositional variation, tailored by additive manufacturing, on the mechanical performance of ceramic composites.

Performance of reinforced concrete slabs subjected to simultaneous fire and blast loads

Reinforced concrete (RC) slabs might experience severe damage from multiple hazards such as fire, explosion, and impact during their service life. RC slabs under independent or sequential hazard such as fire or blast loading have been intensively investigated. In reality, fire and explosion often occur simultaneously instead of occurring one after the other as assumed in some previous studies. Simultaneous actions of thermal loading and blast loading on structures are likely to generate different responses or even different response modes and failure mechanisms of structures as compared to independent or sequential actions of the two loads on structures. However, very limited study has been conducted to investigate the performance of RC slabs under simultaneous fire and blast loads. This study investigates the dynamic performance of RC slabs subjected to concurrent fire and blast loads, considering the simultaneous actions of thermal-induced stress, deformation, material deterioration and blast loading. The numerical model is first calibrated with the test results of RC slab under fire or blast loading. With the calibrated numerical model, the effect of thermal stress induced by fire loading on the blast performance is investigated. The influences of fire duration before the occurrence of explosion, as well as the blast loading scenarios and RC slab parameters on the structural responses are investigated. The dynamic responses induced by blast loading after the fire action as usually assumed in the literature are also calculated and compared with those obtained from simultaneous fire and blast loads. Their implications on representing the effects of coupled concurrent fire and blast loads on structural performances are discussed.

Thermal stress estimation of a constrained metallic plate using symmetric and antisymmetric Lamb wave group velocities

This paper presents a technique for estimating thermal-induced stress in constrained metallic plates using the group velocity of Lamb waves, the accuracy of which is crucial for assessing the structural integrity and serviceability of metallic structures. However, without the ability to gauge the current stress levels, obtaining such measurements is technically challenging. To overcome this, we propose a thermal stress estimation technique that uses changes in the group velocities of the fundamental symmetric (S0) and antisymmetric (A0) Lamb wave modes caused by thermal and stress variations. First, this study introduces a theoretical-based zero-crossing algorithm to measure the group velocities of S0 and A0 Lamb wave modes. Next, leveraging the acoustoelastic coefficients corresponding to the S0 and A0 modes, which are determined before the plate’s installation, this study generates the lines depicting the changes in group velocity induced by temperature variations (CT) for both the S0 and A0 modes. These CT lines are derived from the lines illustrating changes in group velocity due to thermal stress variations (CTS), which are obtained after plate installation. Ultimately, the generated CT lines can be used to estimate thermal stress throughout the entirety of the plate’s operational life span by isolating the distinct stress variation effects from the CTS lines. The numerical validation results show favorable accuracy in thermal stress estimation in a constrained plate subjected to temperature variation using both S0 and A0 Lamb wave modes, with average errors of 0.63 % and 0.91 %, respectively.

Mechanism of Electropulsing Treatment Technology for Flow Stress of Metal Material: A Review

Residual stress is caused by non–uniform deformation caused by non–uniform force, heat and composition, which is of great significance in engineering applications. It is assumed that the residual stress is always the upper limit of the elastic limit, so the reduction of the flow stress will reduce the residual elastic stress. It is particularly important to control the flow stress in metal materials. Compared with traditional methods, the use of electropulsing treatment (EPT) technology stands out due to its energy–efficient, highly effective, straightforward and pollution–free characteristics. However, there are different opinions about the mechanism of reducing flow stress through EPT due to the conflation of the effects from pulsed currents. Herein, a clear correlation is identified between induced stress levels and the application of pulsed electrical current. It was found that the decrease in flow stress is positively correlated with the current density and the duration of electrical contact and current action time. We first systematically and comprehensively summarize the influence mechanisms of EPT on dislocations, phase, textures and recrystallization. An analysis of Joule heating, electron wind effect, and thermal–induced stress within metal frameworks under the influence of pulsed currents was conducted. And the distribution of electric, thermal and stress fields under EPT are discussed in detail based on a finite element simulation (FES). Finally, some new insights into the issues and challenges of flow stress drops caused by EPT are proposed, which is critically important for advancing related mechanism research and the revision of theories and models.

Thermal cracking: Clarifying the effects of phases, voids and grains through characterisation and crystal plasticity modelling

Thermally-induced cracking typically occurs during the cooling stage of various manufacturing processes, and is commonly seen in multiphase or the joints of dissimilar materials due to mismatch in their thermo-mechanical properties, such as thermal expansion, elastic-plastic deformation and, in some cases, phase transformation. However, the underlying cracking mechanism associated with local microstructure is still elusive. To improve the mechanistic understanding of thermal cracking, this work uses the diffusion-bonded 9Cr-1Mo steel as an example to study the key microstructural variables, such as interfacial phases, voids, grain boundary migration and crystallographic orientations. Meanwhile, a temperature-dependent crystal plasticity model coupled with a cohesive zone model is developed to provide more insights into the thermal-induced stress distribution at the grain scale. It is found that the stress at the void-free boundary of martensite and ferrite is dominated by shear, and its magnitude is insufficient to nucleate cracks. Whereas voids at phase boundaries can induce significant tensile stress, resulting in cracking at the phase boundaries as well as diffusion-bonded interfaces. Also, the occurrence of interfacial grain boundary migration plays an important role in local stress distribution. These microstructure features and their evolution are experimentally observed and used to verify the developed crystal plasticity models. These findings enhance the understanding of the influence of microstructure features on thermal cracking and provide a guide to designing and fabricating the microstructure with improved thermal crack resistance in various manufacturing processes.

Laser-Assisted Bonding Approach for Photonic Integration Processes

Current development trends concerning miniaturizing of electronics and photonics systems are aiming at assembly and 3D co-integration of a broad range of technologies including MEMS, microfluidics, wafer level optics, and silicon photonics. To this end, on-chip integration using siliconphotonics platform offers a wide range of possibilities addressing passive optics functionality, active optoelectronic devices, and compatibility with CMOS fabrication. On the other hand, the hybrid technology enabling volume manufacturing of such system-on-chip components it is still in an early development stage. In this work, the original LAB setup with a coaxial bottom irradiation architecture was developed. The setup allows a rapid and energy-effective process with the ability to produce successful electrical bonds with negligible thermalinduced stress and warpage to bonded surfaces. The proposed machine-vision based temperature sensor is validated for photonic integration assembly processes.

A simplified model for energy pile-supported embankment

Energy piles can be used for road de-icing in winter or cooling in summer in the pile-supported embankment. This paper presents a simplified model for energy pile-reinforced foundation beneath the embankment to investigate thermal effects of piles on the performance of the system. By considering thermo-mechanical stress–strain of the pile and foundation soil, thermally-induced pile-soil interaction, and applying stress continuity and settlement continuity at the bottom of the embankment fill and the surface of the underlying soil, the settlements of the piles, the surrounding soil, the embankment fill, and the underlying soil are compatible. This proposed method is validated by comparison with numerical analysis. An increase in temperature will mobilize more friction at both the upper and lower sides of the pile, and will decrease the foundation settlement but increase the load-sharing ratio of the piles. The stiffer surrounding soil provides greater constraint to limit the deformation of the energy pile, causing larger thermal-induced stress of the pile.

Hyperelastic constitutive relations for soft elastomers with thermally-induced residual stress

Residual stress widely exists in soft materials. Besides growth, inhomogeneous thermal expansion is also a primary cause of residual stress. However, establishing a proper hyperelastic constitutive relation is a great challenge since the existing theories cannot capture the change of underlying mechanical responses triggered by temperature variations. In this paper, a general hyperelastic constitutive relation for soft elastomers with thermally-induced residual stress is developed. We first reveal the initial temperature dependence of conventional thermoelastic models. This property attributes the alteration of the underlying thermoelastic response to free thermal expansions. Then, a compatibility-broken curvature compensation (CBCC) framework is established based on finite thermoelasticity. It generates a free thermal expansion to eliminate the Riemannian curvatures of the virtual stress-free configuration derived from the isothermal stress release. Such a mechanism indicates the non-local effect of the residual stress, which fundamentally modifies the traditional view that invariant formulations cover all the possible functional dependence of residual stress. Also, the obtained governing equations are similar to Einstein field equations of the general theory of relativity. This similarity may deeply imply a standard mechanism concerning the curvature compensation leading to residual stress genesis. We finally conduct comparative analyses of the spherically symmetric and axisymmetric problems between the current constitutive relation and the existing models. The influences of adopting distinct residual stresses, the performance of the non-local effect, and the availability of the new constitutive relation are investigated in detail. This framework can shed some light on the constitutive modeling of soft materials.

Low-temperature deuterium annealing for improved electrical characteristics of SONOS

Deuterium annealing is a promising process technology for CMOS fabrication. Deuterium annealing effectively passivates interface traps at the Si-SiO2 interface, allowing for improvements in the electrical characteristics and reliability of CMOS. However, conventional deuterium annealing is typically performed at high temperatures above 400 °C, which can lead to unwanted dopant deactivation, random dopant fluctuation (RDF), and thermal-induced stress in the backend-of-the-line (BEOL). In this study, we demonstrate the use of deuterium annealing at low temperatures, resulting in improvements in SONOS devices. Device characterizations based on subthreshold swing (SS), on-state current (ION), off-state current (IOFF), and gate leakage current (IG), as well as time-of-flight secondary ion mass spectrometry (ToF-SIMS) are included to clarify the effects of annealing.

A Computationally Efficient Method for the Thermo-Structural Analysis of a Turbocharger Turbine Wheel Under Engine Transient Operation

Abstract The accurate evaluation of thermally-induced stresses is of particular importance for life-cycle analysis of modern turbochargers. Conjugated heat transfer (CHT), steady-state calculations represent the state-of-the-art, whose temperature distribution is usually imported into a structural solver as a thermal load for carrying out thermo-structural analyses. In the case of transient analyses, however, issues arise. Indeed, due to the different timescales of convective and conductive heat-transfer mechanisms, unsteady CHT simulations are burdened by high computational costs. Moreover, in the specific case of turbocharged engines, the timescales of engine load transients and turbocharger response may differ by a factor of up to 105. The present study proposes an approach for carrying out transient thermo-structural analyses of the solid domain only, characterized by a physical time in the order of 101 s, without the need for unsteady fluid flow calculations, which would imply the use of a solver time-step in the order of 10−5 s. In the proposed methodology, the effects of the fluid flow in the heat-transfer process are modeled by imposing adequate boundary conditions to wet surfaces of the solid domain with minimum computational effort. Indeed, by performing two steady-state CHT calculations and one steady-state computational fluid dynamics (CFD) calculation, time-dependent boundary conditions can be derived in terms of convective heat transfer coefficient and near-wall fluid temperature. The case study used for model development is a high-performance turbocharger turbine for automotive applications, responding to engine load transients of tenths of seconds. Initially, steady-state CFD and CHT models of the turbine stage are validated against experimental data. Then, transient analyses on the turbine wheel are carried out, and their results are imported as thermal loads into an unsteady structural solver, allowing for accurate transient thermo-structural analyses at sustainable computational cost.

Thermally induced shear displacement of sand-concrete interface under different stress levels

Energy geostructures are modern technologies developed to exploit shallow geothermal energy. Their installation has recently increased rapidly throughout the world. Their use is devoted to the heating and cooling of buildings, and their operation can induce thermal cycles at the soil-structure interface in the range of 5–40 °C [1]. In addition, their activation would produce thermally-induced stress and strain in structure. Over the last few decades, several full-scale tests have been performed to study the geotechnical aspects of energy piles [2,3]. The main results show that the thermal operations may slightly influence the mechanical performance of the energy pile by increasing the additional thermal compressive stresses and changing the pile axial strain. Numerical studies [4,5] concluded that the temperature increment can lead to thermal expansion of the pile, causing its uplift and the generation of negative shear forces at the pile–soil interface near the pile head. Considering that the thermal operation of energy geostructures leads to temperature change along the piles as well as in the neighbouring soil due to the heat exchange phenomenon, many researchers have investigated the temperature effects on the behaviour of soil and soil–structure interface [6,7,8,9]. Others investigated thermally induced soil deformation using modified triaxial or oedometric apparatuses allowing temperature control [10,11,12]. These results show expansive deformation of coarse-grained soils upon heating and contractive deformation upon cooling for all relative densities. A modified geothermal direct shear box (MGSB) developed at Gustave Eiffel University [13] was used to investigate the effects of temperature cycles on soil–concrete interface. The preliminary results showed that the sand expands upon heating and contract upon cooling. An accumulated contraction and shear displacement were observed after each thermal cycle. However, these preliminary results should be carefully re-analysed since the device was not fully calibrated under various thermo-mechanical loads.&#x0D; In this study, the MGSB was utilized after its calibration [13], to investigate the thermally induced vertical and lateral displacements of sand–structure interface. It consists of two half-shear boxes with dimensions of 200 mm x 200 mm x 80 mm. A Peltier module was used to heat and cool water connected to a pipe embedded in the concrete plate, which was used to simulate the pile surface. Normal and shear stresses were applied to represent the geostatic stress of soil and pile load, respectively. Four linear variable differential transformers (LVDTs) were placed in contact with the lower and the upper boxes of the device to measure the shear displacement. One LVDT was placed at the top of the box to measure the vertical displacement of soil. To prevent heat losses, the system was insulated using an insulating foam. Two series of test were performed. The four tests of the first series were conducted on dense (D) sand and the three tests of the second series were on loose (L) sand, with relative densities of about 90% and 30%, respectively. For each density, three normal stress levels were tested: 25, 50 and 100 kPa. For each normal stress, a shear stress equal to 40% of normal stress (45% of the shear strength) was applied. Test D_50 was repeated because of technical problems that happened during the first test. After samples preparation, two phases were carried out. The first phase corresponds to the&#x0D; application of normal and shear stresses. Regarding the second phase, 20 thermal cycles were applied, varying the soil temperature between 14 °C and 32 °C.&#x0D; The mechanical results showed a good agreement compared to standard direct shear tests. The thermo-mechanical results showed that the succession of soil expansion and contraction upon heating and cooling respectively lead to an accumulated irreversible contraction and continuous shearing displacement after each thermal cycle with different magnitudes, depending on the soil density and stress level. In addition, the rate of these incremental irreversible displacements decreases when the cycle number increases. Moreover, the increase in the stress levels will lead to an increase in the accumulated lateral displacement after 20 cycles, and this increment is significant in loose sand compared to dense sand under the same mechanical conditions. Overall, the thermally induced sand-concrete interface displacements are affected by stress level and strongly depend on the sand density. The thermally induced settlement may be critical in the case of floating energy piles under high mechanical load, and greater than 45% may lead to greater in the case of loose soil would be greater than 0.3 mm. Finally, this study suggests that using a homogeneous stress design method for energy geostructures may adversely affect the design.

Field Tests on Thermal Performance of Bridge Pile Groups under Embankment Load and Cap Constraint Condition

Based on the project of National Highway No. 310 located in Sanmenxia City, China, field tests on the thermal responses of the 2 × 2 pile groups under embankment load in winter condition are carried out. The temperatures and stresses of piles along pile depth under the combined action of embankment load and temperature are measured. The thermal characteristics of the pile body, such as thermal-induced stress, cumulative deformation of the pile top, and heat exchange efficiency per unit area, are analyzed. The feasibility of a new piping method compatible with the segmented reinforcement cage is discussed. A calculation method for heat exchange in a large-diameter energy pile is proposed. The layout of the heat exchange pipe used in this study is feasible, and there is no large stress mutation in the dense and nondense areas. The maximum tensile stress in the middle of the pile body is about 0.4 MPa, which is nearly 22% of the concrete tensile strength value. The settlement of the pile top is about 0.33 mm after seven days of cooling condition, which is about 0.27‰ of the pile diameter.

Design and analysis of an optical planar waveguide using Invar as core and silicon nitride as cladding layer to control birefringence

Abstract The main problem with optical planar waveguide is thermal stress which arises when layers inside the planar waveguide get fused together with different coefficient of thermal expansion (CTE) and due to variation in thermal properties, the problem of thermally induced strain and birefringence occurs inside the waveguide glass layer. In proposed work, the mathematical analysis of thermal induced stress and the thermal strain in waveguide glass layer is calculated. ‘C’ software is used for analysis of an optical planar waveguide to calculate the thermal stress. By using material properties of Invar (64 % iron-36 % nickel alloy) and silicon nitride (Si3N4) an optical planar waveguide is designed. Here when silicon nitride (Si3N4) is used as a cladding layer and Invar (64 % iron-36 % nickel alloy) as a core layer in an optical planar waveguide, the problem of birefringence get eradicated as zero thermal stress was achieved.

Sequentially Coupled Thermal-Hydraulic-Mechanical Simulation for Geomechanical Assessments of Caprock Integrity in SAGD

Oil sand reservoirs and caprock undergo deformations triggered by pore pressure increases and thermal induced stresses during the steam-assisted-gravity-drainage (SAGD) processes. Geomechanical assessments are mandated by energy regulators to evaluate the caprock integrity and ensure the safe SAGD operations. Commercial reservoir simulation packages started to incorporate geomechanical effects when predicting flow response; however, these geomechanical modules are not able to correctly model the plastic deformations caused by thermal-hydraulic-mechanical (THM) interactions, which has a first order effect on predicting steam chamber propagation and evaluating caprock integrity.&#x0D; An integrated coupled THM modeling methodology is proposed here to improve the modeling of reservoir deformations and caprock integrity in a heterogeneous oil sand reservoir with interbedded shale barriers. The pressure and temperature front are found to propagate at different speed and that dominate the elastic and plastic deformations caused by changes of shear and mean effective stress. Therefore, four stages are divided in the SAGD process that can be interpretations of changes in stress paths including buildup of pore pressure, generation and dissipation of thermal induced stresses. The response surfaces of minimum factor of safety (FOS) are introduced and computed to provide a conservative estimate for caprock integrity during SAGD of a heterogeneous reservoir with multiple layers of caprocks in Athabasca oil sands. &#x0D;

Physiological mechanisms preventing plant wilting under heat stress: a case study on a wheat (Triticum durum Desf.) bound water-mutant

Wilting is the main symptom of plants suffering the dehydration stresses, but the mechanisms governing this phenomenon are yet to be completely understood. In this work, a holistic analysis of physiological traits potentially involved in leaf wilting was performed, comparing a wheat wild type (WT), Trinakria and its water-mutant (WM) with a “high affinity for bound water (BW)”. In addition to the tendency to wilt, significant differences between genotypes were observed for leaf temperature achieved under heat stress, leaf turgor loss with decreasing water potential, cuticular transpiration, and Q10 of leaf water uptake velocity. We hypothesize that mutant plants prevent the increase in leaf temperature thanks to the rapid and low energetic cost of water diffusion from the vessels to the outside, driven by the BW. Under strong thermal-induced dehydration stress, BW delays leaf wilting through its positive effects on cell wall elasticity and passive osmoregulation.

Identification of glutathione metabolic genes from a dimorphic fungus Talaromyces marneffei and their gene expression patterns under different environmental conditions

Talaromyces marneffei is a human fungal pathogen that causes endemic opportunistic infections, especially in Southeast Asia. The key virulence factors of T. marneffei are the ability to survive host-derived heat and oxidative stress, and the ability to convert morphology from environmental mold to fission yeast forms during infection. Glutathione metabolism plays an essential role in stress response and cellular development in multiple organisms. However, the role of the glutathione system in T. marneffei is elusive. Here, we identified the genes encoding principal enzymes associated with glutathione metabolism in T. marneffei, including glutathione biosynthetic enzymes (Gcs1 and Gcs2), glutathione peroxidase (Gpx1), glutathione reductase (Glr1), and a family of glutathione S-transferase (Gst). Sequence homology search revealed an extended family of the TmGst proteins, consisting of 20 TmGsts that could be divided into several classes. Expression analysis revealed that cells in conidia, mold, and yeast phases exhibited distinct expression profiles of glutathione-related genes. Also, TmGst genes were highly upregulated in response to hydrogen peroxide and xenobiotic exposure. Altogether, our findings suggest that T. marneffei transcriptionally regulates the glutathione genes under stress conditions in a cell-type-specific manner. This study could aid in understanding the role of glutathione in thermal-induced dimorphism and stress response.

Thermally-Induced Stresses in a Pre-Buckling State of a Circular Plate within the Fractional-Order Framework

This paper considers a transient thermoelastic problem in an isotropic homogeneous elastic thin circular plate with clamped edges subjected to thermal load within the fractional-order theory framework. The prescribed ramp-type surface temperature is on the plate's top face, while the bottom face is kept at zero. The three-dimensional heat conduction equation is solved using a Laplace transformation and the classical solution method. The Gaver–Stehfest approach was used to invert Laplace domain outcomes. The thermal moment is derived based on temperature change, and its bending stresses are obtained using the resultant moment and resultant forces per unit length. The results are illustrated by numerical calculations considering the material to be an Aluminum-like medium, and corresponding graphs are plotted.

2.85-kW cryogenic Nd:YAG slab laser operating at 946 nm

A several-kilowatt level laser at 946 nm is demonstrated in a cryogenically cooled diode-pumped Nd:YAG slab system. The oscillator realizes the record of the output power of 2.85 kW in a compact cavity with the homemade cryogenically cooled Nd:YAG crystal slab. The pulse repetition rate and pulse width of the laser are 400 Hz and 200 µs, respectively, and the center wavelength under full power is 946.2 nm with a bandwidth of about 0.5 nm. The absorption linewidth at 808 nm is a little narrowed and blue shifts at the cryogenic temperature, while the cooling temperature decreases from 300 to 77 K. The measured thermal conductivity increases from 10 to 70 W/mˑK, and the thermal expansion coefficient decreases from 7.5*10−6 to 1.5*10−6/K. These results could guide us in simulating the temperature gradient and thermal-induced stress distributions in the crystal slab.

Metrology of infrared superconducting bolometers with a backshort

We present the detailed metrology of a superconducting Transition-Edge Sensor (TES) absorber-coupled bolometer array bonded to a variable-delay backshort to form an integral field unit. The backshort is shaped as a wedge to continuously vary the electrical phase delay of the bolometer absorber reflective termination across the array. This resonant absorber termination structure is used to define a spectral response over a 4:1 bandwidth in the far-infrared, from ∼30 to 120 μm. The metrology of the backshort-bolometer array hybrid was achieved with a laser confocal microscope and a compact cryogenic system that provides a well-defined thermal (radiative and conductive) environment for the hybrid when cooled to ∼10K. The results show the backshort free-space delays do not change with cooling. The estimated backshort slope is 1.58 milli-radians and within 0.3% of the targeted value. The sources of error in the free-space delay of the hybrid and optical cryogenic metrology implementations are discussed in detail. We also present measurements of the bolometer's single-crystal silicon membrane topography. The membranes deform and deflect out-of-plane under both warm and cold conditions. Intriguingly, the optically active area of the membranes tends to flatten when cold and repeatably achieve the same mechanical state over many thermal cycles; hence, no evidence for thermally-induced mechanical instability is observed. Most of the cold deformation is sourced from thermally-induced stress in the metallic layers comprising the TES element of the bolometer pixels. These results provide important considerations for the design of ultra-low-noise TES bolometers.