Variable Temperature Research Articles

Synthesis of a Station-Less Molecular Daisy Chain.

A daisy chain architecture without a preferred low energy arrangement of the mechanically linked components is presented. The molecular design combines a rigid-rod type oligophenylene ethynylene subunit with an oligoethylene glycol macrocycle that features a bipyridine coordination site. The daisy chain dimer was synthesized via kinetic trapping of the interlocked structure using a Cadiot-Chodkiewicz active metal template reaction. Comparison of the isolated interlocked dimer with its monomeric analogue indicates the presence of a variety of different geometries for the molecular daisy chain. The dynamic sliding motion in the daisy chain is studied by variable temperature UV-vis and nuclear magnetic resonance (NMR) spectroscopy experiments, which point to a highly mobile system even at low temperatures.

Dynamic Relationship Between Oil Temperature and BGCI in Bell 407 Helicopter

The primary objective of this study was to investigate the dynamic relationship between oil temperature and the Bearing Gearbox Condition Indicator (BGCI) values of the Bell 407 helicopter. The study aims to simplify the fault diagnosis process by proposing a method that utilizes only one vibration sensor and one temperature sensor per bearing. To achieve this goal, we employ robust econometric tools, such as unit root tests, cointegration tests, and Autoregressive Distributed Lag (ARDL) models, for both long-run and short-run estimates. Our findings indicate that the variable temperature tends to converge to its long-run equilibrium path in response to changes in other variables. The results of the ARDL analysis confirmed that spectral kurtosis, inner race, cage, and ball energy significantly contributed to the increase in temperature. Furthermore, we utilized the Impulse Response Function (IRF) to trace the dynamic response paths of the shocks to the system. The identification of a cointegrating relationship between oil temperature and BGCI values suggests a practical and significant connection that can potentially be used to predict hazardous changes in oil temperature using BGCI values, which is an important implication for enhancing the safety and reliability of helicopter operations. The study presents a promising direction for condition monitoring (CM) in rotating machinery, emphasizing the potential of integrating temperature data to simplify the diagnostic process while still achieving reliable results.

Heat-Triggered Dynamic Self-Healing Framework for Variable-Temperature Stable Perovskite Solar Cells.

Metal halide perovskite solar cells (PSCs) are promising as the next-generation photovoltaic technology. However, the inferior stability under various temperatures remains a significant obstacle to commercialization. Here, a heat-triggered dynamic self-healing framework (HDSF) is implemented to repair defects at grain boundaries caused by thermal variability, enhancing PSCs' temperature stability. HDSF, distributed at the grain boundaries and surface of the perovskite film, stabilizes the perovskite lattice and releases the perovskite crystal stress through the dynamic exchange reaction of sulfide bonds. The resultant PSCs achieved a power-conversion efficiency (PCE) of 26.32% (certified 25.84%) with elevated temperature stability, retaining 88.7% of the initial PCE after 1000 h at 85°C. In a variable temperature cycling test (between -40 and 80°C), the HDSF-treated device retained 87.6% of its initial PCE at -40°C and 92.6% at 80°C after 160 thermal cycles. This heat-triggered dynamic self-healing strategy could significantly enhance the reliability of PSCs in application scenarios.

Magnetotransport properties of two-dimensional tellurium at high pressure

Abstract Two-dimensional tellurium (2D-Te) exhibits strong spin-orbit coupling and chiral structure. Studying its magnetotransport properties is crucial for the development of spintronic technologies and the exploration of novel device applications. However, the magnetotransport properties of 2D-Te under variable temperatures and high pressures still merit further study. In this paper, the magnetotransport behavior of 2D-Te under low-temperature and high-pressure conditions was investigated. At room temperature, the magnetoresistance (MR) increases with increasing magnetic field, exhibiting positive MR behavior below 4.3 GPa. During decompression, MR is almost constant with decreasing pressure. MR is more sensitive to pressure at lower temperatures.

Unraveling the Nature of Vibrational Dynamics in CsPbI3 by Inelastic Neutron Scattering and Molecular Dynamics Simulations.

Cesium lead iodide, CsPbI3, is an optoelectronic material of large interest for various technological applications; however, fundamental questions surrounding the vibrational dynamics of this material, especially regarding its role in structural phase transitions, remain to be elucidated. Here, in a combined variable temperature inelastic neutron scattering (INS) and machine-learning based molecular dynamics (MD) simulation study, we show that the stable phase at room temperature, i.e., the nonperovskite δ-phase, exhibits phonon modes with weak anharmonicity with only a weak temperature dependence from 10 K all the way up to the transition to the cubic perovskite α-phase at approximately 600 K. In contrast, the α-phase features anharmonic and damped vibrational dynamics, mainly associated with overdamped tilting motions of the PbI6 octahedra. Crucially, these overdamped tilting modes, which relate to the tetragonal and orthorhombic distorted perovskite phases (β- and γ-phase, respectively) formed at lower temperatures, stay overdamped by more than 100 K above the respective phase transition. This suggests a flat energy landscape of octahedral tilting motions in α-CsPbI3 and with structural fluctuations on the picosecond time scale with tilting patterns that locally resemble the structure of the β- and γ-phases. The vibrational dynamics of α-CsPbI3 are also characterized by pronounced anharmonic motions with large thermal displacements of the Cs+ ions, but these modes remain underdamped at 600 K.

Exploiting the Dimerization Characteristic of H2PO4- to Promote Its Selective Recognition by a Tetra-Amido Macrocycle.

Creating a confined cavity that matches the size and binding site of the substrate is a prevalent strategy to achieve selective recognition of specific anions. However, this not only requires sophisticated receptor design but also leads to challenging receptor synthesis. In this contribution, by utilizing the dimerization characteristic of H2PO4-, we demonstrate that selective recognition of H2PO4- can also be achieved in DMSO by a synthetically simple tetra-amido macrocycle (1). By reaction condition optimization, the yield of the final cyclization reaction was improved. Through 1H NMR titration studies, we exhibit a sharp contrast in the binding affinity between H2PO4- and other anions, as well as the exclusive recognition of H2PO4- from competitive environments containing various anions. Through Job's plot, nonlinear fitting, single-crystal X-ray diffraction, computational study, variable temperature NMR, and DOSY NMR, the binding mechanism of 1+H2PO4- was extensively studied, including binding stoichiometry (1:2 host-guest), stability constant (β2 = 1.4 × 105 M-2), recognition sites, possible binding structure, and the corresponding hydrodynamic radius (rH). Binding studies in DCM and 50% methanol/chloroform further support the proposed binding mechanism. This study therefore explores a new approach to achieve selective recognition by taking advantage of the self-assembly characteristics of substrates.

Conformational landscapes of rigid and flexible molecules explored with variable temperature ion mobility-mass spectrometry

Understanding the effect of temperature to the structural integrity of proteins is relevant to diverse areas such as biotechnology and climate change. Variable temperature ion mobility-mass spectrometry (VT-IM-MS) can measure the effect of temperature on conformational landscapes. To delineate collision effects from structural change we report measurements using molecules with different degrees of rigidity namely: poly (L-lysine) (PLL) dendrimer, ubiquitin, β-casein and α-synuclein from 190-350 K. The CCS of PLL dendrimer varies with temperature consistent with collision theory, by contrast, the structure of each protein alters with notable restructuring at 350 K and 250 K, following predicted in vitro stability curves. At 210 K and 190 K we kinetically trap unfolding intermediates. For alpha-synuclein, the 13+ ions present two distinct conformers and VT-IM-MS measurements allow us to calculate the transition rate and activation energies of their conversion. These data exemplify the capacity of VT-IM-MS to provide insights on the thermodynamics of conformational restructuring.

Mechanistic Evaluation of Pavement Performance in Algeria Considering a High Variable Temperature: A 3D Finite Element Modeling Approach

Mechanistic Evaluation of Pavement Performance in Algeria Considering a High Variable Temperature: A 3D Finite Element Modeling Approach

Variable Temperature Plate Heat Transfer: MHD Fluid Natural Convection Flow in Porous Medium

The heat transfer from a variable temperature plate has been studied under the presence of porous medium and MHD fluid. Solutions for flat plate in porous medium are usually numeric, in this work an exact solution is found. Free convection governing equations were nondimensionalized and solved using Laplace transform. Exact solutions for the dependent non-dimensional variables were obtained. Velocity and temperature solutions that satisfy the governing equations and exponential boundary conditions were validated with a special case from the existing literature and found to be in good agreement. The temperature and velocity distributions within the porous medium were analysed for different non-dimensional numbers such as Prandtl number and Grashof number and for Newtonian and non-Newtonian fluids. It has been found that the Pr number decreases the velocity variation as a result of the increased viscosity. Higher Grashof number increases the velocity variation for the extra potential it supplies in the momentum equation. Heat generation term raises the dimensionless temperature variation in the energy equation, in its turn the dimensionless temperature increases the velocity variation.

Calcium coordination polymer containing dimethylphosphate ligands and exhibiting nucleating properties towards α and Β crystal polymorphs of isotactic polypropylene

The synthesis, structure and thermal properties of a one-dimensional coordination polymer based on calcium bis(dimethylphosphate) (CaDMP) are reported. The rod-like particles of CaDMP crystallized from water in a monoclinic space group P21/c, and contained Ca[O2P(OCH3)2]2 polymeric chains consisting of the octahedrally coordinated Ca2+ ions bridged by the tridentate dimethylphosphate ligands. The variable temperature powder X-ray diffraction measurements showed that this structure undergoes anisotropic thermal expansion upon heating, with no polymorphic transitions occurring up to 190 °C. Thermolysis of CaDMP began around 260 °C leading to the formation of calcium condensed phosphates and volatile oxophosphorus species. A detailed differential scanning calorimetry (DSC) analysis, combined with a fitting of the experimental data to the Avrami or Liu–Mo kinetic models, revealed that CaDMP accelerates isothermal and non-isothermal crystallization of isotactic polypropylene (iPP). DSC and wide-angle X-ray scattering measurements confirmed the presence of α-iPP and β-iPP crystal domains in the systems loaded with CaDMP particles. The crystallographic analysis indicated that β-iPP polymorph formed via epitaxial crystallization on the surface of CaDMP crystals. Mechanical tests proved that the CaDMP-containing composites exhibited better ductility and impact strength than neat iPP.

Decoding the CO2 adsorption of nitrogen-doped carbon under variable temperature and pressure conditions: A machine learning guideline

Decoding the CO2 adsorption of nitrogen-doped carbon under variable temperature and pressure conditions: A machine learning guideline

Novel Ag/TiO2@CaSiO3 Material Derived from Ag‐Doped Titanium Cage

AbstractThe investigation presents a newly synthesized Ag/TiO2@CaSiO3 composite derived from an orange titanium cage. Obtained through a streamlined fabrication process and calcination at variable temperatures, the material underwent distinct structural alterations. Characterization analyses indicated the emergence of a porous architecture, facilitating robust Ag+ ion adsorption. Among the variants studied, materials calcined at 150 °C demonstrated enhanced antibacterial activity against both Escherichia coli and Staphylococcus aureus. The integration of CaSiO3 into the Ag/TiO2 matrix resulted in the formation of Ag/TiO2@CaSiO3. This composite amalgamates the immediate antibacterial efficacy of Ag+ ions with the enduring antibacterial functionality of Ag/TiO2, additionally augmenting antibacterial performance through reactive oxygen species generation. Owing to its remarkable antibacterial attributes, the Ag/TiO2@CaSiO3 composite is a promising candidate for addressing infection control challenges in medical settings.

Optimal Timing for Safe Bivalving of Fiberglass Casts Is Before the Exothermic Peak.

Cast saw injury is a notable source of medicolegal risk. Previous work with plaster casts demonstrated that cast saw injury was minimized by waiting 12 minutes before removal. In this study, we evaluate the safety parameters of fiberglass casting materials. Eight-ply plaster and fiberglass casts were applied to a pediatric forearm model at variable dip-water temperatures, and the mean time to reach their exothermic peak was determined. Fiberglass casts were then maintained at the manufacturer's recommended dip-water temperature and removed at intervals of 2 (before exothermic peak), 6 (approximately fiberglass's exothermic peak), or 12 (after exothermic peak) minutes. All casts were removed by a pediatric orthopaedic surgeon blinded to the cast set time. Cast/blade temperature, saw force, blade-to-skin contact, bivalve time, cast spreading force, and cut completeness were assessed individually and as short (<6-minutes) or long (≥6-minutes) set times. Fiberglass casts exothermically peaked markedly earlier (5.2 [IQR = 5-5.4] minutes) than plaster (14.8 [IQR=13.7-15.3] minutes), P < 0.0001, at maximum temperatures, which did not markedly differ. Downward force applied during fiberglass cast removal was markedly lower in the short versus long set time groups [average forces of 8.3 (IQR=6.4-10.4) versus 12.9 (IQR=11.1-14.5) Newtons, P < 0.0001, as were maximum forces: 23.2 (IQR=18.9-26.6) versus 43.8 (IQR=38.6-48.5) Newtons, P < 0.0001]. Bivalve time and maximum cast spreading force were decreased in short set times with 40.5 (IQR=39.2-44.7) versus 44.4 (IQR=40.6-47.3) seconds ( P = 0.06) and 15.5 (IQR=14-18.5) versus 21.5 (IQR=18-26.5) N ( P = 0.07), respectively. Maximum saw blade temperature was markedly lower in the short (99.6°C [IQR=98.2-105.6°C]) versus long (130.6°C [IQR=121.9-141°C]) set times ( P = 0.04). No notable differences in blade-to-skin touches or touch duration were detected. Unlike plaster, fiberglass casts cut before exothermically peaking were associated with less downward force, faster bivalve times, and decreased spread force without increased blade temperature or skin contacts. This suggests that fiberglass casts can be bivalved markedly earlier without increased risk of injury.

Numerical simulation of thermal effects on seawater intrusion management by coastal cutoff walls.

Numerical simulation of thermal effects on seawater intrusion management by coastal cutoff walls.

Quantifying airtightness-to-infiltration conversion: A long-term field study under variable temperature differences in university classrooms.

Quantifying airtightness-to-infiltration conversion: A long-term field study under variable temperature differences in university classrooms.

Experimental Investigation on Wear Behavior of Epoxy-TiO? Composite Coatings via Taguchi Technique

In this study, the weight percentages of various composites are added to epoxy resins coating material with a fixed amount of ceramic particles in order to improve the coating's mechanical and tribological qualities. Prepared were test specimens of pure epoxy resins with varying reinforcement weight percentages (4%, 6% and 8%). The configuration of a Tribometer is used to examine the material's wear characteristics by conducting various tests on a polymer matrix composite. The results obtained indicate that the mechanical and tribological properties of the newly created epoxy coating composite are greatly enhanced by the addition of TiO2 (titanium dioxide) reinforcement material. This article summarizes the parametric effects of reinforcement, temperature, and load on the wear rate of an epoxy coating with TiO2 reinforcement. For modeling and optimization, the Taguchi technique is utilized. On a Tribometer with variable load and temperature, the wear resistance of a specimen was examined. According to the data, both reinforcements in epoxy resins result in a lower wear rate than pure epoxy. Analysis of variance (ANOVA) was conducted to determine the significance of the operating parameters on the performance characteristics under consideration. Further experimentation has been conducted to validate the performance of optimal parameters. The proper set of process parameters has been selected based on the findings of this investigation. ANOVA was utilized to examine the influence of each parameter on wear rate. Finally, a confirmation test was conducted to compare the projected wear rate value to the experimental value.

5]Cumulene Bridged Tri(9-anthryl)Methyl Dimer.

Toward the synthesis and evaluation of stable radical-based 2D frameworks, a diacetylene-bridged tri(9-anthryl)methyl (TAntM) radical dimer was designed and synthesized. X-ray crystallographic analysis revealed a strong spin-spin interaction between TAntM radical units through the diacetylene linker, resulting in a closed-shell [5]cumulene structure as the stable form. Variable-temperature (VT) 1H-NMR measurements at high temperatures showed signal broadening for aromatic protons, indicating an increased population of thermally excited triplet species as a metastable form. To facilitate spin-state modulation by external stimuli, mechanical grinding in the solid state was conducted. Due to its reactivity, mechanical grinding partially induced structural changes to radical species in the solid state.

Narrow-Linewidth Emission and Weak Exciton-Phonon Coupling in 2D Layered Germanium Halide Perovskites.

The photophysical properties of low-dimensional metal-halide semiconductors and their tunability make them promising candidates for light-absorbing and emitting applications. Yet, the germanium-based halide perovskites to date lack desirable light-emitting properties, with so far only very broad, weak, and unstructured photoluminescence (PL) reported due to significant octahedral distortion. Here, the photophysical properties of the 2D layered Ruddlesden-Popper semiconductors (4F-PMA)2GeI4 and (4F-PMA)2PbI4 (4F-PMA: 4-F-phenylmethylammonium) are characterized and compared. Using a combination of single-crystal X-ray diffraction, variable temperature time-resolved PL, and density functional theory, structure-property relations are correlated. Specifically, the results indicate that (4F-PMA)2PbI4 features stronger coupling to longitudinal optical (LO) phonons, assisting emission from a broad bound-exciton state due to a soft, deformable lattice. In contrast, (4F-PMA)2GeI4, benefitting from intermolecular bonding to scaffold a rigid octahedral structure, shows weaker LO-phonon coupling, resulting in the longest PL lifetime and most narrow linewidth (≈120 meV linewidth at 2 K) reported for a Ge-halide perovskite yet, without the occurrence of any additional bound-state emission at low temperatures. These results highlight the potential of germanium halide perovskite materials for optoelectronic applications.

Twenty-four-hour Skin Temperature Rhythms in Young People With Emerging Mood Disorders: Relationships With Illness Subtypes and Clinical Stage.

While circadian disruptions are common in some sub-groups of youth with mood disorders, skin temperature rhythms in these cohorts are understudied. We examined 24-h wrist skin temperature rhythms in youth with emerging mood disorders, exploring associations with clinical stage and proposed illness subtypes. Youth (n = 306, 23.42 ± 4.91 years, 65% females) accessing mental health care and 48 healthy controls (23.44 ± 3.38 years, 60% females) were examined. Skin temperature parameters including rhythm-adjusted mean temperature, inter-daily stability (day-to-day consistency), intra-daily variability (rhythm fragmentation), and peak temperature time were derived from a wearable sensor. Based on our illness trajectory-pathophysiology model, participants were classified by mood disorder subtypes ("hyperarousal-anxious" [n = 209], "neurodevelopmental-psychosis" [n = 40], or "circadian-bipolar spectrum" [n = 43]), as well as by clinical stage (subthreshold disorders classed as 1a or 1b [n = 47, 173, respectively], and full-threshold disorders as 2+ [n = 76]). Compared to controls, youth with mood disorders had delayed, less stable, and more variable skin temperature rhythms, indicated by lower rhythm-adjusted mean skin temperature (29.94 ± 0.10 °C vs 31.04 ± 0.25 °C, p < 0.001), delayed peak timing (0533 ± 0014 vs 0332 ± 0036, p = 0.002), reduced inter-daily stability (p = 0.009), and increased intra-daily variability (p = 0.020). Peak skin temperature also occurred later relative to sleep midpoint (0.31 ± 0.14 vs -0.48 ± 0.35 radians, p = 0.037). The "circadian-bipolar spectrum" subtype exhibited lower relative amplitude (0.07 ± 0.005 vs 0.08 ± 0.002 [hyperarousal-anxious] and 0.09 ± 0.005 [neurodevelopmental-psychosis], p = 0.039), with no delay in sleep midpoint. Clinical stages were not associated with differences in skin temperature parameters. These findings highlight the potential of use of 24-h skin temperature rhythms as a non-invasive biomarker of circadian disturbances in youth with emerging mood disorders. The observed disruptions in temperature patterns and rhythmicity support the notion that disrupted circadian rhythms may mediate the onset or illness course of some subgroups of youth with emerging major mood disorders.

Changes in thermal preference, respiratory and metabolic patterns in Tropidurus torquatus: Population responses from two distinct Brazilian biomes.

Changes in thermal preference, respiratory and metabolic patterns in Tropidurus torquatus: Population responses from two distinct Brazilian biomes.