Thermal Perturbation Research Articles

Optomechanical force sensor operating over wide detection range.

A detector with both broad operation range and high sensitivity is desirable in the measurement of weak periodic forces. Based on a nonlinear dynamical mechanism of locking the mechanical oscillation amplitude in optomechanical systems, we propose a force sensor that realizes the detection through the cavity field sidebands modified by an unknown external periodic force. Under the mechanical amplitude locking condition, the unknown external force happens to modify the locked oscillation amplitude linearly to its magnitude, thus achieving a linear scaling between the sideband changes read by the sensor and the magnitude of the force to be measured. This linear scaling range is found to be comparable to the applied pump drive amplitude, so the sensor can measure a wide range of force magnitude. Because the locked mechanical oscillation is rather robust against thermal perturbation, the sensor works well at room temperature. In addition to weak periodic forces, the same setup can as well detect static forces, though the detection ranges are much narrower.

An Unusually Warm Upper‐Crust in the Late Paleozoic North China Continental Arc: Implications for the Thermal Modification of the Giant Bayan Obo REE Deposit

AbstractThe genesis and timing of formation of the giant Bayan Obo deposit, the world's largest rare earth element (REE) deposit in the western part of the late Paleozoic northern North China continental arc (NCA), are highly controversial due to complex mineral assemblages and reported ages of mineralization. We conducted new zircon U‐Pb and40Ar/39Ar dating of metamorphic and igneous Neoarchean to Permian mid‐to upper‐crustal rocks exhumed along a north−south corridor across the western NCA and its retroarc foreland. The results show that the mid‐ to upper‐crust of the western part of the NCA has been strongly affected by thermal modifications during arc construction in the late Paleozoic, while the retroarc foreland remained thermally stable. Our results first reveal an unusually warm upper‐crust around Bayan Obo during the late Paleozoic with high geothermal gradients of 50.0 ± 8.3 to 88.3 ± 8.3°C/km and strong thermal modification of the upper‐crust during arc construction. This unusually warm upper‐crust and high geothermal gradients resulted in intensive thermal perturbations and recrystallization of REE‐bearing minerals in the Bayan Obo deposit, as well as formation of high‐grade REE ores and complete or partial resetting (U‐)Th‐Pb isotopic systems of REE minerals. Our identification of the unusually warm upper‐crust and high geothermal gradients in the western part of the NCA provides important constraints on genesis, timing and thermal modification of the giant Bayan Obo deposit, as well as other REE deposits with complex isotopic ages.

Ultrabroadband Imaging Based on Wafer-Scale Tellurene.

High-resolution imaging is at the heart of the revolutionary breakthroughs of intelligent technologies, and it is established as an important approach toward high-sensitivity information extraction/storage. However, due to the incompatibility between non-silicon optoelectronic materials and traditional integrated circuits as well as the lack of competent photosensitive semiconductors in the infrared region, the development of ultrabroadband imaging is severely impeded. Herein, the monolithic integration of wafer-scale tellurene photoelectric functional units by exploiting room-temperature pulsed-laser deposition is realized. Taking advantage of the surface plasmon polaritons of tellurene, which results in the thermal perturbation promoted exciton separation, in situ formation of out-of-plane homojunction and negative expansion promoted carrier transport, as well as the band bending promoted electron-hole pair separation enabled by the unique interconnected nanostrip morphology, the tellurene photodetectors demonstrate wide-spectrum photoresponse from 370.6 to 2240nm and unprecedented photosensitivity with the optimized responsivity, external quantum efficiency and detectivity of 2.7×107 AW-1 , 8.2×109 % and 4.5 × 1015 Jones. An ultrabroadband imager is demonstrated and high-resolution photoelectric imaging is realized. The proof-of-concept wafer-scale tellurene-based ultrabroadband photoelectric imaging system depicts a fascinating paradigm for the development of an advanced 2D imaging platform toward next-generation intelligent equipment.

Transient and periodic steady-state characteristics of the local heat transfer measurement by thermal perturbation with Gaussian power density distribution

The local heat transfer coefficient measurement with temperature oscillation induced by periodic thermal perturbation – usually via a Gaussian laser beam, was investigated for the impact of the spikiness (i.e., the standard deviation) elaborated in comparison with the analytical model for dimensional analysis. The statistically more robust technique that relies on the linearity of the spatial phase distribution of the test point array was favored when the target Biot number approaches unity in terms of its order of magnitude. The preferred upper limit for thermographic scanning was discussed as the simplification of later data processing is concerned. Nonetheless, the time elapsed for an acceptable periodic steady state, which in principle leans to the higher end of the target Biot number spectrum in a log scale, indicates the benefit from the time series of pointwise temperature measurement – as in the conventional single-blow testing, where the effect of spikiness, as well as that of the location of individual test point, holds. Note that the vicinity as the target Biot number approaches unity was again observed with higher preference.

A compact LWIR borescope sensor for 2D engine component surface temperature measurement

A compact long-wavelength infrared (LWIR) borescope imaging sensor operating in the wavelength range of 8–14 μm is designed and developed for non-contact two-dimensional (2D) surface temperature measurements in gas-turbine engines. The LWIR detection minimizes optical interferences from hot combustion gases and soot (emission within UV–mid IR region). Using simulations, the system is optimized for improving the signal collection efficiency and minimize image aberrations. The LWIR borescope probe is shielded by the custom-build compact water-cooled probe housing (outer diamter (OD) 19 mm, inner diameter (ID) 10 mm), which can sustain flame temperature up to 2400 K at a pressure of 50 bar. It facilitates long-term optical diagnostics inside the actual high-pressure combustion facilities where extreme thermal acoustic perturbation and intense heat fluxes are encountered. The design, construction, and characterization of the LWIR borescope sensor are discussed in detail. We present the 2D surface temperature measurements of a V-gutter bluff-body with simple nitrogen gas cooling in a laboratory testbed. The results indicate the sensor’s ability to accurately measure surface temperature with low background noise and to track transient cooling effect. The water-cooled probe housing was tested to verify the effectiveness of fast heat dissipation in high-temperature combustion environment to avoid unwanted thermal signals from the LWIR probe window. The developed LWIR sensor suite has promising applications in surface temperature measurements of engine components. The findings of this study may aid propulsion system engineers and researchers in designing thermal management systems and optimizing operation.

Magmatism and thermal effect of the Late Paleoproterozoic layered complex in the Jining terrane, North China Craton: Evidence from magmatic cooling duration and crust-mantle interaction

The Paleoproterozoic Khondalite Belt from the northwestern North China Craton (NCC) is characterized by a wide distribution of high-temperature/ultrahigh-temperature (UHT) metamorphism and extensive magmatic events in its eastern segment, the Jining terrane. Although it has been proven that UHT metamorphism is related to large-scale thermal perturbation at the crustal level, the ultimate heat source has been kept unclear and the reliable interrelationship between the formation of UHT metamorphism and mantle-derived magmatism has not been established yet. We report data of two-layered complexes emplaced in duration over 100 Ma, as the candidates of the heat source of the UHT metamorphism. The samples include 1929 ± 23 Ma Sanchakou amphibole-gabbro (ZK0-3) and 1824 ± 2 Ma Hulu norite-gabbro(HL1517). Based on the published geochronological data of basic intrusive rocks in the Jining terrane, it is found that the Late Paleoproterozoic magmatism appears as two stages of ∼1.95 Ga (M1) and ∼1.85 Ga (M2). We calculated that the duration of M1-magmatism can reach ∼71 Myr through Monte Carlo simulation. The sample ZK0-3 is formed in M1-magmatism, coupled with the peak period of metamorphism and the slow cooling process of UHT pelitic granulite/gneiss. We used the “Magma Chamber Simulator (MCS_PhaseEQ_2019AC)” to simulate the genesis of these basic intrusive rocks. It is found that they have experienced the magmatic process of assimilationand fractional crystallizationunder energy constraints(EC-AFC). The augite, pargasite, and zircon record the crystallization temperatures during the slow cooling process of magma. Therefore, mantle-derived magmatism might have supplied heat to generate the UHT metamorphism in the Jining terrane.

Divergent Urban Signatures in Rainfall Anomalies Explained by Pre‐Storm Environment Contrast

AbstractDiverse urban‐induced rainfall anomalies across different cities highlight the need for additional insights into land‐atmosphere interactions over complex urban environments. Based on empirical analyses of 144 warm‐season storms and high‐resolution numerical simulations over Nanjing, China, we show divergent patterns of urban‐induced rainfall anomalies for storms with contrasting synoptic conditions, despite of rainfall enhancement over downtown from a climatological perspective. We propose two simple gage‐based metrics to characterize both the thermal and turbulent conditions in pre‐storm environment, and classify storms into different groups. Our results show that elevated rainfall magnitudes and heavy rainfall frequency are equally expected in either downtown or suburb regions (upwind or downwind). This is mainly dictated by the relative dominance of urban‐induced thermal perturbations and mechanical turbulence (i.e., related to surface roughness) under different synoptic conditions. We develop four paradigms of urban rainfall modification, and thus provide a predictive understanding of rainfall anomalies in urban environments.

Electrical resistivity structure across the Late Cenozoic Abaga-Dalinor volcanic field, eastern China, from 3-D magnetotelluric imaging and its tectonic implications

The Abaga-Dalinor volcanic field (ADVF) in Inner Mongolia, China, located to the west of the North-South Gravity Lineament (NSGL), is the largest and less known area of Late Cenozoic intraplate volcanism in Northeast China. Knowledge of the subsurface structure beneath the ADVF will improve our understanding of its evolution process and formation mechanisms. New broadband magnetotelluric (MT) data were collected along a profile of about 300 km that crosses the major basaltic areas exposed at the surface in the ADVF and a series of east-north-east (ENE) trending faults. The electrical resistivity structure of the crust and uppermost mantle across the ADVF was generated by 3-D inversion of full impedance tensor and tipper data. This model reveals a thick high-resistivity layer (>1000 Ωm) in the upper crust that may represent the Precambrian basement and Late Paleozoic-Mesozoic granitic plutons. In contrast, high conductivity anomalies dominate the middle-lower crust. The northward-dipping high-conductivity feature at depths of 20–40 km below sea level under the Chagan Obo fault is suggested to be the involvement of the Early Paleozoic subducted oceanic crust. A remarkably high-conductivity zone (1–20 Ωm) exists in the middle-lower crust beneath the Abaga and Dalinor volcanic areas. It is explained to be a saline fluid zone of ∼0.45%–0.48% that exsolved from the partial melts as magma ascent rapidly. The impermeable upper crust traps these fluids in the middle-lower crust. A moderately high-conductivity anomaly in the uppermost mantle below near the Solonker Suture Zone (SSZ) is attributed to a minimum partial melt of ∼3–4% associated with the localized asthenospheric upwelling, which feeds the Abaga and Dalinor volcanos as a common magma source. Integrating our resistivity model with previous geophysical and geochemical studies, we suggest that intraplate volcanism in the ADVF is mainly controlled by the pre-existing tectonic weak zones. The lithosphere within the SSZ is susceptible to thermal perturbation from the upwelling mantle, providing the preconditions for melt generation. A set of ENE trending faults and an inferred NW-SE trending fault jointly dominated the vertical transport of magma and lateral extension along the faults, which may have influenced the spatial distribution of basalts and volcanic cones at the surface in the ADVF. In addition, we tend to suggest that Late Cenozoic intraplate volcanism in the ADVF could be the result of decompressing melting within the localized small-scale asthenospheric upwelling induced by the edge-driven convection near the NSGL, which is indirectly related to the westward subduction and retreat of the (Paleo-)Pacific plate during the Late Mesozoic to Cenozoic.

Thermal dependence of soft mode frequency, dielectric constant, and tangent loss in lead hydrogen phosphate (LHP) crystal

Ferroelectric materials have promising uses in modulators, infrared detectors, data storage devices, and other circuits. The ferroelectric properties in LHP crystallites are investigated theoretically in the study that followed, with some modifications, including the incorporation of fourth and third-orderphonon anharmonic connections, indirect connections, four-body connections, and electric field terms. We will take into account the PLCM model Hamiltonian. Calculations of soft mode frequency, loss tangent, and dielectric constant for said LHP crystal have been computed by using Green's function methodology. The analysis has been done mathematically by putting numerous model values into theoretical expressions that have been established, as well as thermal perturbations of soft mode frequency, Tangent loss (dielectric loss) and dielectric constant have been established. The findings of this study for the LHP crystal are quite well consistent with Negran et al studies of experimental data.

Research Progress on Dynamics of Skyrmions Under the Effect of Pinning

Magnetic skyrmions offer the potential as an information carrier for the next-generation storage and computing devices such as racetrack memory devices, logic gates, and even neurocomputing owing to the topology-protected structure, nano-scale size and relatively low driving current compared to traditional devices. The discovery of magnetic skyrmions at room temperature also lays the foundation for realizing room-temperature magnetic skyrmion spintronic devices. Defects and impurities are unavoidable in real materials. These pinning centers significantly affect the dynamics of the skyrmion, including the critical driving current, and the Hall angle, etc. The study on room-temperature magnetic skyrmions in thin films has shown that the effect of pinning can be dominant at room temperature. Hence, the study of pinning effects and the skyrmion-pinning interaction is significant to the motion of magnetic skyrmions at room temperature and the realization of room-temperature magnetic skyrmion spin devices Magnetic skyrmion motion can be strongly modified under the effect of pinning (defects and purities). Moreover, these effects can inspire us to utilize artificial pinning centers to manipulate the dynamics of skyrmions. In this article, we introduce the models for skyrmion motion and pinning effect at room temperature and gives an overview of the methods for creating different types of pinning and their impact on the skyrmions. When pinning is induced by replacing or adding atoms, setting vacancies, changing the material thickness or curvature, or changing magnetic parameters, the skyrmions hall angle will vary. Moreover, the magnetic skyrmions can be fixed in a particular region, move along a specific orbit and overcome thermal perturbations at room temperature under the effect of pinning, which helps to realize magnetic skyrmion spin devices at room temperature.

Contrasting the thermal performance of cultured coral endosymbiont photo-physiology

Cnidarian-microalgae (Family: Symbiodiniaceae) endosymbiotic relationships are central to the success of reef building corals, particularly shaping stress tolerance and capacity to adapt to ever-changing environmental conditions. Studies have particularly examined Symbiodiniaceae susceptibility (and adaptation) to thermal stress to aid reef management as reef temperatures continue to rise. Thermal Performance Curves (TPCs) have previously been well studied to resolve how changing temperatures influence organism competitive fitness but have only recently been applied to corals and never before to Symbiodiniaceae. We therefore developed and applied rapid assay TPCs to 7 Symbiodiniaceae isolates (spanning 5 genera) from different reef origins. Isolates were exposed to temperature gradients, ramping up (26-35 °C) and down (26-17 °C) by 1 °C every 3 days. Photophysiological performance (maximum and effective photochemical efficiency, Fv/Fm and Fq´/Fm´) measured at each temperature was used to fit TPC algorithms describing temperature for optimal performance (Topt), critical thermal minimum or maximum (Ctmin or Ctmax), and thermal performance breadth (Tbr). TPC characteristics varied across the isolates revealing diverse performance ranges. Fv/Fm-derived Topt across all 7 isolates was 25.84 °C, with isolate WT3.2 (Symbiodinium spp.) returning the highest overall Topt (26.89 °C) and Ctmax (36.63 °C) values. In contrast, isolate RT141 (Breviolum psygmophilum) had the greatest Tbr (16.15 °C). As such, Fv/Fm-derived TPCs revealed thermal “generalism” of the temperate originating RT141 in comparison to more thermal “specialism” of WT3.2 originating from a hot tropical mangrove lagoon. Thermal characteristics were more varied across isolates when fitting TPCs to the effective photochemical efficiencies (Fq´/Fm´). We discuss how TPC-based characteristics are ultimately operationally defined in terms of thermal perturbation, choice of TPC algorithm and physiological descriptor, and in turn how more standardised approaches could aid future efforts attempting to resolve differences in thermal adaptation in coral endosymbionts.

Atomic structure of intermetallic compound Nb5Si3 by new cluster transformation analysis method

The structure of Nb5Si3 at the atomic level is fundamental for identifying its complicated structure in atomic simulations and for further understanding the phase selection behaviors during the solidification of Nb-Si alloys. In this study, the structure of Nb5Si3 was investigated using deep-learning molecular dynamic simulations. The ideal βNb5Si3 is characterized by Nb-centered Voronoi polyhedrons (VPs) <0,0,12,3>, <0,0,12,2>, and Si-centered VPs <0,2,8,2>, <0,2,8,0>. Most initial VPs are distorted at high temperatures due to intense thermal perturbation. A new cluster transformation analysis (CTA) method was proposed to evaluate the stability of ideal VPs against perturbation and predict the possible transformations of the initial VPs in atomic simulations. Most transformations of the initial VPs in βNb5Si3 originate from distortions at the edges of the Nb-centered VPs and the faces/vertices of the Si-centered VPs. The distorted VPs in βNb5Si3 at high temperatures are dominated by <0,1,10,4>, <0,1,10,5>, <0,2,8,1> and <1,2,5,3> VPs, which are predicted as the primary transformations by the CTA.

Phase diagram of superconducting vortex ratchet motion in a superlattice with noncentrosymmetry

Ratchet motion of superconducting vortices, which is a directional flow of vortices in superconductors, is highly useful for exploring quantum phenomena and developing superconducting devices, such as superconducting diode and microwave antenna. However, because of the challenges in the quantitative characterization of the dynamic motion of vortices, a phase diagram of the vortex ratchet motion is still missing, especially in the superconductors with low dimensional structures. Here we establish a quantitative phase diagram of the vortex ratchet motion in a highly anisotropic superlattice superconductor, (SnS)1.17NbS2, using nonreciprocal magnetotransport. The (SnS)1.17NbS2, which possesses a layered atomic structure and noncentrosymmetry, exhibits nonreciprocal magnetotransport in a magnetic field perpendicular and parallel to the plane, which is considered a manifest of ratchet motion of superconducting vortices. We demonstrated that the ratchet motion is responsive to current excitation, magnetic field and thermal perturbation. Furthermore, we extrapolated a giant nonreciprocal coefficient ({\gamma}), which quantitatively describes the magnitude of the vortex ratchet motion, and eventually established phase diagrams of the ratchet motion of the vortices with a quantitative description. Last, we propose that the ratchet motion originates from the coexistence of pancake vortices (PVs) and Josephson vortices (JVs). The phase diagrams are desirable for controlling the vortex motion in superlattice superconductors and developing next-generation energy-efficient superconducting devices.

Chiral spin symmetry and the QCD phase diagram

Lattice QCD simulations with chirally symmetric quarks have recently established approximate SU(2)_{CS} and SU(2N_F) symmetries of the quantum effective action in a temperature range above the chiral crossover T_textrm{ch}, in which color-electric interactions between quarks dominate the dynamics. We show that such an intermediate temperature range between the chirally broken and plasma regimes is fully consistent with published screening mass spectra, which demonstrate the breakdown of thermal perturbation theory at the crossover between the partonic and the chiral spin symmetric regime at T_ssim (2-3)T_textrm{ch}. From the known behavior of screening masses with baryon chemical potential, we deduce qualitatively how this chiral spin symmetric band extends into the QCD phase diagram. In the cold and dense region, we propose parity doubled baryons as possible candidates for chiral spin symmetric matter. This represents a special case of quarkyonic matter with confinement and restored chiral symmetry, and can smoothly transform to quark matter at sufficiently high densities. Finally, we discuss the potential of dilepton spectra to identify such matter forms.

Surface‐To‐Ocean Exchange by the Sinking of Impact Generated Melt Chambers on Europa

AbstractImpacts into icy bodies often generate near‐surface melt chambers and thermal perturbations that soften the ice. We explore the post‐impact evolution of non‐penetrating impacts into Europa's ice shell. Simulations of viscous ice deformation show that dense impact melts founder before refreezing. If the transient cavity depth exceeds half the ice shell thickness, over 40% of the impact melt drains into the underlying ocean. Drainage of impact melts from the near‐surface to the ocean occurs on timescales of 103–104 years. The drainage of melts to the ocean occurs for all plausible ice shell thicknesses and ice viscosities, suggesting that melt foundering is a natural consequence of impacts on icy worlds. Post‐impact viscous deformation is an important process on icy worlds that affects cryovolcanism, likely modifies crater morphology, creates porous columns through the ice for surface‐to‐ocean exchange, and may supply the oxidants required for habitability to subsurface oceans.

Stochastic Switching in a Magnetic-Tunnel-Junction Neuron and a Bias-Dependent Néel-Arrhenius Model

Back hopping or telegraphic switching describes stochastic bistate oscillation in magnetic tunnel junctions (MTJ) at high bias, which significantly increases the write error rate of memory storage. Nevertheless, this unfavorable stochastic switching could be utilized to construct extremely compact spiking neuron circuits, where both the spike frequency and duty cycle are proportional to the applied bias voltage. This MTJ neuron is the fundamental building block of future all-spin neural networks. This paper analyzes the mechanism of stochastic switching in the MTJ neuron in detail. The self-heating effect at high bias is identified to induce thermal perturbation through a reduced energy barrier of a weakened perpendicular magnetic anisotropy. The high spike frequency is measured up to 10 MHz, which is mainly limited by the transition time between states and the multistate switching when approaching the Curie temperature of the ferromagnetic phase. Finally, to quantitatively describe the stochastic switching phenomenon, we establish a bias-dependent N\'eel-Arrhenius compact model, which calibrates well with experimental data. Based on this model, the potential and design guideline for realizing MTJ neurons with a spike frequency toward the gigahertz range are also discussed.

Optical-resolution functional gastrointestinal photoacoustic endoscopy based on optical heterodyne detection of ultrasound

Photoacoustic endoscopy shows promise in the detection of gastrointestinal cancer, inflammation, and other lesions. High-resolution endoscopic imaging of the hemodynamic response necessitates a small-sized, high-sensitivity ultrasound sensor. Here, we utilize a laser ultrasound sensor to develop a miniaturized, optical-resolution photoacoustic endoscope. The sensor can boost the acoustic response by a gain factor of ωo/Ω (the frequency ratio of the signal light and measured ultrasound) by measuring the acoustically induced optical phase change. As a result, we achieve a noise-equivalent pressure density (NEPD) below 1.5 mPa·Hz-1/2 over the measured range of 5 to 25 MHz. The heterodyne phase detection using dual-frequency laser beams of the sensor can offer resistance to thermal drift and vibrational perturbations. The endoscope is used to in vivo image a rat rectum and visualize the oxygen saturation changes during acute inflammation, which can hardly be observed with other imaging modalities.

Assessing the long-term low-temperature thermal evolution of the central Indian Bundelkhand craton with a complex apatite and zircon (U-Th)/He dataset

Modern approaches in low-temperature thermochronometry are capable of extracting long-term thermal histories from cratonic settings that may elucidate potential drivers of deep-time phases of intracontinental burial and erosion. Here, we assess the utilization of the Radiation Damage Accumulation and Annealing Model for apatite (RDAAM) and zircon (ZRDAAM) to track the long-term low-temperature thermal evolution of the Archean Bundelkhand craton and the surrounding undeformed strata of the ∼1.7–0.9 Ga Vindhyan successions in central India. We correspondingly interpret a complex basement and detrital zircon and apatite (U-Th)/He (ZHe and AHe, respectively) dataset in light of observed model limitations and known geologic context. ZHe and AHe dates from across the craton reveal a significant (&gt;300 Myr) date inversion between the two systems within grains with moderate to high effective uranium (eU) concentrations. Inverse thermal models utilizing current ZRDAAM and RDAAM parameters are not capable of reproducing observed coupled basement ZHe and AHe data for the same thermal history. However, meaningful thermal information can be extracted from AHe inverse models coupled with a forward modeling approach applied to detrital ZHe data from Vindhyan deposits, which have notably lower eU concentrations and yield significantly older ZHe dates (between ∼1,475 and 575 Ma) than basement zircon. Resulting thermal models indicate that the Bundelkhand craton experienced peak burial temperatures of ∼150°C between 850 and 475 Ma, followed by a major crustal cooling event at ∼350–310 Ma, possibly driven by late Paleozoic glaciations and/or epeirorogenic uplift. Inverse models including AHe data require a Deccan Traps related thermal perturbation between ∼66 and 65 Ma, and we suspect that this event overprinted basement zircon with moderate to high eU concentrations. Although the effects of zonation, grain morphology, and/or uncertainties in damage-annealing parameters contribute to disparities between predicted and observed AHe and ZHe dates, these factors alone cannot account for the major ZHe and AHe date inversion observed from the Bundelkhand craton. Instead, it is likely the case that current damage-dependent models for ⁴He diffusion are not adequately calibrated at the resolution necessary to predict short-lived thermal perturbations that occurred in a late phase relative to a prolonged period of extensive damage accumulation.

Oscillatory thermal response test using heating cables: A novel method for in situ thermal property analysis

In situ subsurface thermal conductivity (λ) and thermal diffusivity (α) are critical parameters to design ground-coupled heat pump systems (GCHP). λ is conventionally determined from thermal response tests (TRT), whereas α is commonly selected from literature data or with laboratory analyses. Alternatively, both thermal properties can be assessed independently with an oscillatory thermal response test (O-TRT), which consists of heating the subsurface at an oscillatory rate and monitoring the resulting thermal perturbation. Due to their flexibility and relatively small radius, heating cables can be used to carry out tests in shallow unconsolidated deposits in the scope of horizontal GCHP design. The duration of the tests is short compared to vertical ground heat exchangers (fractions of a day) since the thermal resistance between the heating cable and the soil is negligible. The objective of this work was to develop an apparatus and an analytical approach to assess λ and α from an O-TRT carried out in shallow unconsolidated deposits. Nine different O-TRTs were performed in the lab for a dry standard material and five O-TRTs were performed in situ in a natural sandy deposit. After validation via numerical modelling, results show that the analytical approach using correction factors allowed the estimation of λ and α with an accuracy of < 2%. The study demonstrates that O-TRTs are a useful method to estimate both λ and α. Further testing in other reference materials and with different apparatus configurations is needed to enhance the experimental setup and extend O-TRTs towards new applications.

Thermal Perturbations at Crystal Nucleation in Glass-Forming Liquids

Understanding the processes occurring during the nanocrystallization of glass-forming liquids is important for creating artificial nanostructures for various applications. In this article, local thermal perturbations in supercooled glass-forming liquids and polymers during the nucleation of a crystalline phase are studied. To describe the thermal response of supercooled glass-forming liquids, an integro-differential heat equation with dynamic heat capacity is used. We have found that the effect of the dynamic heat capacity is significant for fast local thermal perturbations that arise in the early stages of crystal nucleation in glass-forming liquids and polymers. It has been established that local temperature perturbations during the nucleation of crystals in silicate glasses and polymers can change the nucleation rate by 2–5 orders of magnitude. The knowledge gained can be useful for the technology of artificial microstructures and advanced materials.