The dynamic structure of liquid water can be disrupted by the presence of non‐polar organic molecules, in a process known as hydrophobic solvation. Maria Giménez‐López, Francisco Rivadulla et al. ...demonstrate in their Communication on page 7540 that the particular orientation of hydrocarbon chains in tetraalkylammonium and phosphonium salts induces a peculiar structure of water molecules different from the bulk, changing its physicochemical properties.
The thermal diffusivity in the ab plane of underdoped YBCO crystals is measured by means of a local optical technique in the temperature range of 25–300 K. The phase delay between a point heat source ...and a set of detection points around it allows for high-resolution measurement of the thermal diffusivity and its in-plane anisotropy. Although the magnitude of the diffusivity may suggest that it originates from phonons, its anisotropy is comparable with reported values of the electrical resistivity anisotropy. Furthermore, the anisotropy drops sharply below the charge order transition, again similar to the electrical resistivity anisotropy. Both of these observations suggest that the thermal diffusivity has pronounced electronic as well as phononic character. At the same time, the small electrical and thermal conductivities at high temperatures imply that neither well-defined electron nor phonon quasiparticles are present in this material. We interpret our results through a strongly interacting incoherent electron–phonon “soup” picture characterized by a diffusion constant
D
~
v
B
2
τ
, where vB
is the soup velocity, and scattering of both electrons and phonons saturates a quantum thermal relaxation time τ ∼ ħ/kBT.
•Laminar burning velocity was studied in a wide range of experimental conditions.•The empirical correlation between LBV and effective parameters was studied.•Empirical equations with good predictive ...ability was proposed.•The variation of flame temperature and diffusivity with hydrogen ratio were studied.•Reactions R(3) and R(4) generate key radicals to accelerates the reaction.
Carbon-free hydrogen and ammonia have their own drawbacks when used alone. The composite fuel system formed by the combination of hydrogen and ammonia can not only solve the current energy demand and environmental pollution problems, but also effectively overcome the shortcomings of pure fuel application. Laminar flames are the basis for the study of other flame forms. In this paper, the laminar combustion characteristics of hydrogen/ammonia/air mixture were studied in a constant volume combustor. The initial pressures range from 0.5 to 1.5 atm, the equivalence ratios range 0.5 to 1.5, and the hydrogen ratios range from 0 to 1.0. The laminar burning velocity increases monotonously with the increase of hydrogen ratio, while presents an inverted U-shaped relationship with the equivalence ratio. Compared with the hydrogen ratio and the equivalence ratio, the initial pressure has the weakest effect on the laminar burning velocity of hydrogen/ammonia/air mixture. The laminar burning velocity gradually decreases with the initial pressure. This paper also gives an empirical exponential fitting equation for the laminar burning velocity of hydrogen/ammonia/air mixtures, which can well predict the laminar burning velocity of the mixed gas under various equivalence ratios (0.8–1.2) and various hydrogen ratios (0–1.0) at atmospheric pressure. The influence of fuel composition on the laminar burning velocity should be the result of the combined effect of thermal diffusivity and mass diffusivity. The important fuel consumption pathways R3 and R4 generate more key radicals with increasing hydrogen ratio, thereby promoting the combustion process.
A highly efficient phenylphosphonate-based flame-retardant epoxy resin (FREP) was firstly prepared from phenylphosphonic dichloride (PPDCl) and allylamine (AA). Functionalized graphite nanoplatelets ...(fGNPs) fillers were then performed to fabricate the fGNPs/FREP nanocomposites via mixing followed by casting method. The thermally conductive coefficient (λ), thermal diffusivity (α), flame retardancy, electrical conductivities and thermal stabilities of the fGNPs/FREP nanocomposites were all enhanced with the increasing addition of fGNPs fillers. The λ and α value of the fGNPs/FREP nanocomposite with 30 wt% fGNPs fillers was increased to 1.487 W/mK and 0.990 mm2/s, about 7 times and 6 times for that of pure FREP matrix (0.234 W/mK and 0.170 mm2/s), respectively. And the corresponding electrical conductivity was also increased to 5.0 × 10−4 S/cm, far better than that of pure FREP matrix (1.0 × 10−12 S/cm). In comparison with that of pure FREP, the THR and TSP value of the fGNPs/FREP nanocomposite with 15 wt% fGNPs fillers was decreased by 37% and 32%, respectively, char yield was increased by 13%, and LOI value was increased from 31% to 37%. However, the peak of heat release rate of the fGNPs/FREP nanocomposite became worse due to its high thermal conductivity. Nanoindentation revealed that there was negligible influence of fGNPs fillers on the hardness values and Young's modulus of the fGNPs/FREP nanocomposites.
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•Molybdenum (Mo) thin films were grown on AlN by pulsed laser deposition for heat sink applications.•Smooth and crystalline Mo films were obtained at 600 ˚C and 10 mTorr of Argon ...gas.•Thermal diffusivity was measured by photo-thermal surface displacement using an IR laser.•Under optimal deposition conditions, a thermal diffusivity very close to that of bulk Mo was obtained.•The Mo-AlN system was found to be stable up to an operating temperature of 200 °C.
Thin films of molybdenum (Mo) were grown on aluminium nitride (AlN) substrates by pulsed laser deposition for heat sink applications. The effect of experimental growth parameters on the films’ structural properties were investigated by Scanning Electron Microscopy, X-Ray Diffraction and Atomic Force Microscopy. Thermal characterization was achieved by measuring the in-plane thermal diffusivity of the grown layers by means of a photothermal beam deflection technique using an IR heating laser. Within the experimental parameters studied in this work, a substrate temperature of 600 ˚C and an ambient argon gas pressure of 10 mTorr were identified as the optimal growth conditions for the synthesis of smooth and well-crystallized Mo layers. Concurrently, the thermal diffusivity of the films is significantly affected by film growth parameters. Under the optimal growth conditions, a thermal diffusivity value as high as 5.42x10-5 m2/s was measured, a value that is very close to that of bulk Mo, and which would be a result of the synthesis of polycrystalline Mo films whose grains’ size is greater than the heat carriers mean free path, namely the free electrons. The temperature dependence of the thermal diffusivity was also investigated, and the films were found to be stable up to an operating temperature of 200 °C. Beyond this temperature, photothermal beam deflection imaging shows the onset of film delamination from the underlying substrate.
This article describes a hybrid temperature sensor in which an accurate, but energy-inefficient, thermal diffusivity (TD) sensor is used to calibrate an inaccurate, but efficient, resistor-based ...sensor. The latter is based on silicided polysilicon resistors embedded in a Wien-bridge (WB) filter, while the former is based on an electrothermal filter (ETF) made from a p-diffusion/metal thermopile and an n-diffusion heater. The use of an on-chip sensor for calibration obviates the need for an external temperature reference and a temperature-stabilized environment, thus reducing the cost. To mitigate the area overhead of the TD sensor, it reuses the WB filter's readout circuitry. Realized in a 180-nm CMOS technology, the hybrid sensor occupies 0.2 mm 2 . After calibration at room temperature (~25 °C) and at an elevated temperature (~85 °C), it achieves an inaccuracy of 0.25 °C (3<inline-formula> <tex-math notation="LaTeX">\sigma </tex-math></inline-formula>) from −55 °C to 125 °C. The WB sensor dissipates 66 <inline-formula> <tex-math notation="LaTeX">\mu \text{W} </tex-math></inline-formula> from a 1.8-V supply and achieves a resolution of 450 <inline-formula> <tex-math notation="LaTeX">\mu \text{K}_{\mathrm {rms}} </tex-math></inline-formula> in a 10-ms conversion time, which corresponds to a resolution figure-of-merit (FoM) of 0.13 pJ<inline-formula> <tex-math notation="LaTeX">\cdot \text{K}^{2} </tex-math></inline-formula>. The sensor also achieves a sub-10-mHz 1/<inline-formula> <tex-math notation="LaTeX">f </tex-math></inline-formula> noise corner, which is comparable to that of bipolar junction transistor (BJT)-based temperature sensors.
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•Silver nanoparticles (AgNPs) nanowires (AgNWs) were synthesized.•AgNPs and AgNWs were dispersed into a liquid acrylic resin to form nanocomposites.•The thermal diffusivity and curing ...time of the nanocomposites were determined.•Scaffolds of the nanocomposites were 3D printed.•Physicochemical and mechanical characterization of the nanocomposites were done.
The aim of this work was to design and build novel scaffolds of different composition for application of 3D printing in organic tissues and to determine the thermal properties of these nanocomposites; therefore, novel silver/acrylic composites based on silver nanoparticles (AgNPs) of 15.7 nm average in diameter synthesized by a green method, and silver nanowires (AgNWs) of 50 nm in diameter and 1.5 µm in length synthesized by the polyol method were successfully prepared. Thermal lens spectroscopy (TLS) in a mismatched configuration was used to determine the liquid sample’s thermal diffusivity (D), and photoacoustic spectroscopy (PA) in an open cell (OPC) configuration was used to determine the nanocomposite’s characteristic curing time (τ). Values of D for the AgNPs range from 14.8 x 10-8 to 47.4 x 10-8 m2/s (4.5 to 18.5 x 10-5 wt%) with curing times (τ) of 26.7 to 57.7 s. On the other hand, the values of D for the AgNWs composites were between 6.6 x 10-8 and 36.6 x 10-8 m2/s (4.1 to 16.5 x 10-5 wt%) with curing times (τ) of 482.9 s to 1650.9 s (4.1 to 12.8 x 10-5 wt%). Scaffolds were 3D printed with a lithographic printer prototype whose experimental variables were optimized using an experimental design (DOE). Characterization techniques as transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), and UV–vis spectroscopy were used to determine AgNPs, AgNWs and resin’s morphology, physical and chemical aspects. Shore hardness D tester was used to analyze the scaffolds mechanical behavior with a linear increase for the AgNPs composites and non-linear trend for the AgNWs composites. From the results, an improvement and optimization of the thermal diffusivity, mechanical properties and curing time of the new nanocomposites was obtained with the increase in concentration.
•A heated bed of sand fluidised by N2 was used to measure thermal diffusivity.•The mid-temperature in a wooden cube was monitored after entering the bed.•Thermal conductivity increased from dried ...wood at 200 oC to char at 600 oC.•Pyrolysis times depended on the wood’s size, shape, type, temperature, etc.
Small cubes (sides ≤ 7 mm) of four different woods, with thermocouples inside them to constantly measure the temperature at their centre, have been pyrolysed in electrically heated beds of sand, fluidised by nitrogen. These determinations of a particle’s central temperature have provided values of the effective thermal diffusivity of each wood, as well as of the resulting solid, at 5 different stages, whilst it changed from dried wood at room temperature to the char left after being pyrolysed at progressively higher temperatures up to 600 °C. In addition, these woods underwent endothermic decomposition, particularly whilst being heated from ∼250 to 340 °C and from 380 to 460 °C. However, at ∼480 to 540 °C, all four woods thermally decomposed exothermally and actually raised the temperature at the cube’s centre above that of the fluidised bed. In addition, the times for complete pyrolysis were measured and their dependence on particle size was investigated.
In this Letter, we uncover a universal relaxation mechanism of pinned density waves, combining gauge-gravity duality and effective field theory techniques. Upon breaking translations spontaneously, ...new gapless collective modes emerge, the Nambu-Goldstone bosons of broken translations. When translations are also weakly broken (e.g., by disorder or lattice effects), these phonons are pinned with a mass m and damped at a rate Ω, which we explicitly compute. This contribution to Ω is distinct from that of topological defects. We show that Ω≃Gm^{2}Ξ, where G is the shear modulus and Ξ is related to a diffusivity of the purely spontaneous state. This result follows from the smallness of the bulk and shear moduli, as would be the case in a phase with fluctuating translational order. At low temperatures, the collective modes relax quickly into the heat current, so that late time transport is dominated by the thermal diffusivity. In this regime, the resistivity in our model is linear in temperature and the ac conductivity displays a significant rearranging of the degrees of freedom, as spectral weight is shifted from an off-axis, pinning peak to a Drude-like peak. These results could shed light on transport properties in cuprate high T_{c} superconductors, where quantum critical behavior and translational order occur over large parts of the phase diagram and transport shows qualitatively similar features.
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