We compute the thermodynamic properties of the Sachdev-Ye-Kitaev (SYK) models of fermions with a conserved fermion number Q. We extend a previously proposed Schwarzian effective action to include a ...phase field, and this describes the low-temperature energy and Q fluctuations. We obtain higher-dimensional generalizations of the SYK models which display disordered metallic states without quasiparticle excitations, and we deduce their thermoelectric transport coefficients. We also examine the corresponding properties of Einstein-Maxwell-axion theories on black brane geometries which interpolate from either AdS4 or AdS5 to an AdS2×R2 or AdS2×R3 near-horizon geometry. These provide holographic descriptions of nonquasiparticle metallic states without momentum conservation. We find a precise match between low-temperature transport and thermodynamics of the SYK and holographic models. In both models, the Seebeck transport coefficient is exactly equal to the Q derivative of the entropy. For the SYK models, quantum chaos, as characterized by the butterfly velocity and the Lyapunov rate, universally determines the thermal diffusivity, but not the charge diffusivity.
An array of temperature sensors based on the thermal diffusivity (TD) of bulk silicon has been realized in a standard 40-nm CMOS process. In each TD sensor, a highly digital voltage-controlled ...oscillator-based ΣΔ ADC digitizes the temperature-dependent phase shift of an electrothermal filter (ETF). A phase calibration scheme is used to cancel the ADC's phase offset. Two types of ETF were realized, one optimized for accuracy and one optimized for resolution. Sensors based on the accuracy-optimized ETF achieved a resolution of 0.36 °C (rms) at 1 kSa/s, and inaccuracies of ±1.4 °C (3σ, uncalibrated) and ±0.75 °C (3σ, room-temperature calibrated) from -40 °C to 125 °C. Sensors based on the resolution-optimized ETFs achieved an improved resolution of 0.21 °C (rms), and inaccuracies of ±2.3 °C (3σ, uncalibrated) and ±1.05 °C (3σ, room-temperature calibrated). The sensors draw 2.8 mA from supply voltages as low as 0.9 V, and occupy only 1650 μm 2 , making them some of the smallest smart temperature sensors reported to date, and well suited for thermal monitoring applications in systems-on-chip.
The dissipative dynamics of strongly interacting systems are often characterized by the timescale set by the inverse temperature τP∼ℏ/(kBT). We show that near a class of strongly interacting quantum ...critical points that arise in the infrared limit of translationally invariant holographic theories, there is a collective excitation (a quasinormal mode of the dual black hole spacetime) whose lifetime τeq is parametrically longer than τP: τeq≫T−1. The lifetime is enhanced due to its dependence on a dangerously irrelevant coupling that breaks the particle-hole symmetry and the invariance under Lorentz boosts of the quantum critical point. The thermal diffusivity (in units of the butterfly velocity) is anomalously large near the quantum critical point and is governed by τeq rather than τP. We conjecture that there exists a long-lived, propagating collective mode with velocity vs, and in this case the relation D=vs2τeq holds exactly in the limit Tτeq≫1. While scale invariance is broken, a generalized scaling theory still holds provided that the dependence of observables on the dangerously irrelevant coupling is incorporated. Our work further underlines the connection between dangerously irrelevant deformations and slow equilibration.
Yttrium aluminium garnet doped with rare earth ions is one of the most common active media in solid state lasers. In high-power lasers, thermal management is crucial, requiring information on the ...thermal properties. In this work, the thermal diffusivity and conductivity of polycrystalline YAG ceramics doped with Yb and Er were measured by laser flash method at various temperatures ranging from room temperature to 900 °C. Transparent ceramic YAG samples were prepared by solid state reactive sintering of oxide powders under vacuum. Thermal diffusivity and conductivity showed similar trends, decreasing with increasing temperature as well as with the increase of dopant content from 0 to 20 at.%. The measured values were compared with literature data and empirical relations. Similar values were obtained both for Yb and Er doping. We thus suggest that the data of thermal diffusivity and conductivity of Yb:YAG may be used as a first approximation for Er:YAG.
•Fired brick buttons added with 5%, 10%, 20% and 30% vermiculite were prepared.•Vermiculite altered the nature and timing of phase transitions during firing.•Five weight loss steps and six ...dilatometric/contraction steps were identified.•The compressive strength first increases then drops with vermiculite content.•5% of vermiculite is an optimum ratio added for brick production.
Vermiculite is a hydrous clay mineral that occasionally occurs in raw materials for brickmaking. The presence of vermiculite affects the drying and firing processes of brick production; thus, the functions of this clay mineral should be clarified. In this study, vermiculite from 0 wt% to 30 wt% have been added to clay mixtures for brick button firing. Through effective integration of in-situ XRD, thermogravimetric and dilatometric analyses, the real-time thermal behaviours have been interpreted, and the microstructure, physical and compressive characteristics of brick buttons have been investigated. The incorporation of vermiculite has changed the temperatures of kaolinite dehydroxylation and rutile formation. Enstatite, cordierite and amorphous contents increased in fired brick buttons, while mullite, quartz and cristobalite decreased. Vermiculite retained a partial sheet-like morphology at 1150 °C firing. From 25 to 1150 °C, five weight loss steps have been defined with six shrinkage/expansion processes observed. Cracks appeared on brick button surfaces when 30 wt% of vermiculite was added. The colour of fired brick buttons changed from “light camel” to “black olive”. Drying shrinkage, firing shrinkage and bulk density increased with an increased proportion of vermiculite. The maximum compressive strength reached 150.94 MPa (a rise of 21.6% towards the control sample) when 5 wt% of vermiculite was added.
Abstract
Whether the presence of adsorbates increases or decreases thermal conductivity in metal-organic frameworks (MOFs) has been an open question. Here we report observations of thermal transport ...in the metal-organic framework HKUST-1 in the presence of various liquid adsorbates: water, methanol, and ethanol. Experimental thermoreflectance measurements were performed on single crystals and thin films, and theoretical predictions were made using molecular dynamics simulations. We find that the thermal conductivity of HKUST-1 decreases by 40 – 80% depending on the adsorbate, a result that cannot be explained by effective medium approximations. Our findings demonstrate that adsorbates introduce additional phonon scattering in HKUST-1, which particularly shortens the lifetimes of low-frequency phonon modes. As a result, the system thermal conductivity is lowered to a greater extent than the increase expected by the creation of additional heat transfer channels. Finally, we show that thermal diffusivity is even more greatly reduced than thermal conductivity by adsorption.
This paper presents a methodology and instrumentation system for the indirect measurement of the thermal diffusivity of a soil at a given depth from measuring its temperature at that depth. The ...development has been carried out considering its application to the design and sizing of very low enthalpy geothermal energy (VLEGE) systems, but it can has many other applications, for example in construction, agriculture or biology. The methodology is simple and inexpensive because it can take advantage of the prescriptive geotechnical drilling prior to the construction of a house or building, to take at the same time temperature measurements that will allow get the actual temperature and ground thermal diffusivity to the depth of interest. The methodology and developed system have been tested and used in the design of a VLEGE facility for a chalet with basement at the outskirts of Huelva (a city in the southwest of Spain). Experimental results validate the proposed approach.
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