Temperature Dependence Research Articles

Environmentally Acceptable Lubricants for Stern Tube Application: Shear Stability and Friction Factor

Stern tube lubricants are essential in maritime operations, safeguarding ship propeller shafts from wear and corrosion while ensuring efficient propulsion. Their role in reducing friction and maintaining system integrity is critical. With growing environmental concerns, the adoption of environmentally acceptable lubricants (EALs) for stern tubes has gained importance, balancing operational performance with environmental protection. This study investigates the rheological and tribological properties of EALs formulated for ship propeller stern tube applications. The primary focus is on comparing these EALs with conventional mineral oils to assess their suitability in marine environments. EALs are increasingly favored due to their biodegradability and reduced environmental impact. Key parameters such as shear stability, friction factor, and temperature dependency were evaluated using a range of experimental methods including rotational viscometry and tribological analysis. The results indicate that the newly formulated EALs based on synthetic esters exhibit the highest viscosity index, a higher range of shear stability, and lower friction factors, compared to commercially available mineral oils, especially under varying operational conditions. These findings contribute to the ongoing efforts to promote eco-friendly lubricants in maritime industries, aligning with global environmental protection initiatives.

Temperature dependence of piezoelectric properties ofthe binary Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals prepared by continuous feeding Bridgeman method

Abstract We have confirmed that the temperature dependence of the dielectric constant and piezoelectric charge constant of length-extensional mode d31 of AC poled (ACP) Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals (SC) is 15 °C better than that of DC poled (DCP) SC. The ACP SC grown by continuous feeding Bridgman process with a better uniformity of piezoelectric properties showed d31 of -2500 pC/N at 88 oC and hold over -700) pC/N up to 105 oC compared to DCP SC (-1500 pC/N at 88 oC, and -700 pC/N at 90 oC), respectively. In addition, low frequency constant N31 of 560 Hz•m at 25 oC and 390 Hz•m at 88 oC of the ACP SC showed 25% and 37% lower than those of DCP SC. The ACP SC outperforms DCP SC not only in piezoelectric properties at room temperature but also heat resistance and this information is important for future ultrasound devices design.

Temperature Dependence of the Pre-Chromatographic ‘Lawrence’ Method for Bivalves Contaminated with Paralytic Shellfish Poisoning Toxins

AbstractSaxitoxins are potent neurotoxins originating the acute human neurological syndrome of paralytic shellfish poisoning (PSP) via bivalve vectors. The official testing method in the European Union, commonly known as the ‘Lawrence method’, involves pre-column oxidation steps. The Portuguese monitoring adopted the hydrogen peroxide oxidation screening approach for bivalves contaminated with Gymnodinium catenatum toxins, which can quantify chromatographically at once 6 out of 10 analogues commonly found in bivalves. Seasonal fluctuation in the fluorescence yield of calibration curves was observed across years in a consistent manner. It correlated with fluctuations in average monthly air temperature in Lisbon, highlighting the importance of recording the room temperature during the oxidation steps as a matter of routine practice. Incubation experiments also showed an increase in fluorescence yield with temperature, more pronounced for the 11-hydroxysulphate analogues (dcGTX2 + 3, C1 + 2, GTX2 + 3) than for the 11-H toxins (dcSTX, GTX5[B1], STX). Temperature can be exploited to increase fluorescence yield, assisting in spectral confirmation, but must not exceed 40–50 °C to avoid toxin decomposition or production of extra oxidation products.

Unraveling the origin of Kondo-like behavior in the 3d-electron heavy-fermion compound YFe2Ge2

The heavy fermion (HF) state of d -electron systems is of great current interest since it exhibits various exotic phases and phenomena that are reminiscent of the Kondo effect in f -electron HF systems. Here, we present a combined infrared spectroscopy and first-principles band structure calculation study of the 3 d -electron HF compound YFe 2 Ge 2 . The infrared response exhibits several charge-dynamical hallmarks of HF and a corresponding scaling behavior that resemble those of the f -electron HF systems. In particular, the low-temperature spectra reveal a dramatic narrowing of the Drude response along with the appearance of a hybridization gap ( Δ ∼ 50 meV) and a strongly enhanced quasiparticle effective mass. Moreover, the temperature dependence of the infrared response indicates a crossover around T ∗ ∼ 100 K from a coherent state at low temperature to a quasi-incoherent one at high temperature. Despite of these striking similarities, our band structure calculations suggest that the mechanism underlying the HF behavior in YFe 2 Ge 2 is distinct from the Kondo scenario of the f -electron HF compounds and even from that of the d -electron iron-arsenide superconductor KFe 2 As 2 . For the latter, the HF state is driven by orbital-selective correlations due to a strong Hund’s coupling. Instead, for YFe 2 Ge 2 the HF behavior originates from the band flatness near the Fermi level induced by the combined effects of kinetic frustration from a destructive interference between the direct Fe-Fe and indirect Fe-Ge-Fe hoppings, band hybridization involving Fe 3 d and Y 4 d electrons, and electron correlations. This highlights that rather different mechanisms can be at the heart of the HF state in d -electron systems.

Phase Diagrams of a Relativistic Self-Interacting Boson System

Within the Canonical Ensemble, we investigate a system of interacting relativistic bosons at finite temperatures and finite isospin densities in a mean-field approach. The mean field contains both attractive and repulsive terms. Temperature and isospin density dependences of thermodynamic quantities are obtained. It is shown that, in the case of attraction between particles in a bosonic system, a liquid-gas phase transition develops against the background of the Bose–Einstein condensate. The corresponding phase diagrams are given. We explain the reasons for why the presence of a Bose condensate significantly increases the critical temperature of the liquid-gas phase transition compared to that obtained for the same system within the framework of Boltzmann statistics. Our results may have implications for the interpretation of experimental data, in particular, how sensitive the critical point of the mixed phase is to the presence of the Bose–Einstein condensate.

Effect of doping with iron and cations deficiency in the high conductive electrolyte La0.8Sr0.2Ga0.8Mg0.2O3–δ on oxygen exchange kinetics

The oxygen isotope exchange method was used to investigate the kinetics of the interaction between gaseous oxygen and LaGaO3-based oxides in a temperature range of 650 to 850 °C, with an oxygen pressure of 10 mbar. The stable isotopes of 18O/16O were used as labelled ions. The temperature dependencies of the heterogeneous oxygen exchange rate (rH), the oxygen dissociative adsorption rate (ra), the oxygen incorporation rate (ri), and the oxygen diffusion coefficient (D) were determined. A comparative analysis of the rH and D values for La0.8Sr0.2Ga0.8Mg0.2O3–δ was carried out with a view to identifying any similarities or differences when compared with the literature data on oxides with similar compositions. The effect of FeGa′ doping and the creation of an A-sublattice deficiency on the kinetic characteristics were investigated using the (La0.8Sr0.2)0.98Ga0.7Fe0.1Mg0.2O3–δ oxide as a case example. Correlations between the rate-determining step of oxygen exchange and the modification of the oxide composition were identified.

Heavy-Atom Tunneling in Ring-Closure Reactions of Beryllium Ozonide Complexes.

Quantum mechanical tunneling (QMT) has long been recognized as crucial for understanding chemical reaction mechanisms, particularly in reactions involving light atoms like hydrogen. However, recent findings have expanded this understanding to include heavy-atom tunneling reactions. In this report, we present the observation of two heavy-atom tunneling reactions involving the spontaneous conversions from end-on bonded beryllium ozonide complexes, OBeOOO (A) and BeOBeOOO (C), to their corresponding side-on bonded ozonide isomers, OBe(η2-O3) (B) and BeOBe(η2-O3) (D), respectively, in a cryogenic neon matrix. This discovery is supported by the weak temperature dependence of the rate constants and unusually large 16O/18O kinetic isotope effects. Quantum chemistry calculations reveal extremely low barriers (<1 kcal/mol) for both ring-closure reactions. Additionally, instanton theory calculations on both reactions unveil that the tunneling processes involve the concerted motion of all four oxygen atoms.

Temperature Dependence Strategy for Achieving Enhanced Reflow-Capable MRAM with a Multi-Interface Structure

Temperature Dependence Strategy for Achieving Enhanced Reflow-Capable MRAM with a Multi-Interface Structure

Temperature dependence of optical phase transitions in a system of two-level atoms and photons interacting inside a nonlinear cavity

Temperature dependence of optical phase transitions in a system of two-level atoms and photons interacting inside a nonlinear cavity

Microscopic analysis of relaxation behavior in nonlinear optical conductivity of graphene

Abstract We produce a general formalism to study the interband dynamical optical conductivity in the nonlinear regime of graphene in the presence of a quantum bath comprising phonons and electrons. When a quantum solid of graphene is subjected to an intense electric field in the optical frequency range, the observation of a nonlinear response is facilitated by formulating a quantum master equation of the density operator associated with the Hamiltonian encapsulated in a spin-boson model of dissipative quantum statistical mechanics. Our results reveal the nonlinear steady-state regime's population inversion and decoherence. The present method enables us to investigate further the nonlinear interband optical conductivity of pristine and gapped graphene characterized by a single dimensionless parameter at finite temperatures. The effects of different bath spectra for phonons and electrons are examined in detail. {\color{red} The temperature dependence of conductivity reveals that changing temperature can enable us to make the transition from the linear to the nonlinear regime for fixed optical field parameters.} Interestingly, a fascinating switching-like behavior is observed for the low-temperature optical conductivity of the gapped graphene while we vary the energy gap as well as the frequency of the externally applied field. Although our general formulation can address a variety of nonequilibrium responses of the two-band system, it also facilitates a connection with the phenomenological modeling of nonlinear optical conductivity.

Evidence for vertical line nodes in Sr2RuO4 from nonlocal electrodynamics

By determining the superconducting lower and upper critical fields Hc1(T) and Hc2(T), respectively, in a high-purity spherical Sr2RuO4 sample via ac-susceptibility measurements, we obtain the temperature dependence of the coherence length ξ and the penetration depth λ down to 0.04Tc. Given the high sample quality, the observed T2 dependence of λ at low temperatures cannot be explained in terms of impurity effects. Instead, we argue that the weak type-II superconductor Sr2RuO4 has to be treated in the nonlocal limit. By comparing our data with existing theory in that limit, the penetration depth in Sr2RuO4 agrees with a gap structure having vertical line nodes, while horizontal line nodes cannot account for the observation. The work highlights the potential benefits of purifying other unconventional superconductors in order to access the fascinating nonlocal regime in more materials and to determine their Cooper pair wave functions. Published by the American Physical Society 2024

Unraveling Superior Elasticity and Controlled Thermal Expansion in Trigonal MBO3 (M=Al, Ga) with Isolated [BO3] Group: A Theoretical Perspective

AbstractA comprehensive theoretical investigation employing density functional theory explores the electronic structure, temperature‐dependent elasticity, thermodynamic properties, and chemical bonding of trigonal MBO3 (M=Al, Ga) with isolated [BO3] groups. The results uncover MBO3 (M=Al, Ga) as indirect semiconductors with superior mechanical stability, characterized by greater resistance to volume compression over shear deformation. Their elasticity exhibits relatively weak temperature dependence, suggesting excellent thermal stability. Thermodynamic analysis predicts that GaBO3 has a higher thermal expansion coefficient than AlBO3, approximately 2.1×10−5 K−1 and 1.8×10−5 K−1 at 300 K, respectively. Significantly, the overall thermal expansion coefficients of GaBO3 and AlBO3 are lower compared to other borate materials containing isolated [BO3] groups. Chemical bonding insights reveal that GaBO3′s larger thermal expansion is attributed to its larger atomic displacement parameters and weaker Ga−O bond strength. This research positions MBO3 (M=Al, Ga) as prime candidates for optical device applications due to their well‐characterized elasticity and controlled thermal expansion.

Multi-color emission composites of white carbon dots and dyes through inner filter effect

A series of multi-color carbon dot composites were obtained by transforming white carbon dots (WCDs) into three primary colors using the dyes' inner filter effect (IFE). WCDs were combined with three distinct dyes (methyl red, bromocresol green, and methylene blue), and three fluorescence colors (red, yellow, and blue) were obtained. The colors of the emitting light excited by the same UV light were similar to the colors of the respective dyes, and have a large Stokes shift. The presence of the IFE between WCDs and dyes was proved through a variety of methods, the analysis of the relationship between the UV of dyes and fluorescence spectra of WCDs, the excitation-emission matrix, as well as the comparison PL decay profiles of WCDs before and after dye addition. The Stern-Volmer quenching constant KSV exhibited no temperature dependence during the IFE process with increasing concentrations of dyes. The UV spectra of the mixture of WCDs and dyes were simply the sum of two individual components, which implies that there is no chemical interaction between WCDs and dyes. Since methyl red and bromocresol green are acid-base indicators, the fluorescence color of the carbon dot composite also changed continuously during the dilute NaOH solution titration process. In furtherment, distributing the binary system of “WCDs + dye” within poly (vinyl alcohol) (PVA), three colors fluorescent composite films of “WCDs / Dye / PVA” were produced successfully.

Temperature dependence of mosquitoes: Comparing mechanistic and machine learning approaches.

Mosquito vectors of pathogens (e.g., Aedes, Anopheles, and Culex spp. which transmit dengue, Zika, chikungunya, West Nile, malaria, and others) are of increasing concern for global public health. These vectors are geographically shifting under climate and other anthropogenic changes. As small-bodied ectotherms, mosquitoes are strongly affected by temperature, which causes unimodal responses in mosquito life history traits (e.g., biting rate, adult mortality rate, mosquito development rate, and probability of egg-to-adult survival) that exhibit upper and lower thermal limits and intermediate thermal optima in laboratory studies. However, it remains unknown how mosquito thermal responses measured in laboratory experiments relate to the realized thermal responses of mosquitoes in the field. To address this gap, we leverage thousands of global mosquito occurrences and geospatial satellite data at high spatial resolution to construct machine-learning based species distribution models, from which vector thermal responses are estimated. We apply methods to restrict models to the relevant mosquito activity season and to conduct ecologically plausible spatial background sampling centered around ecoregions for comparison to mosquito occurrence records. We found that thermal minima estimated from laboratory studies were highly correlated with those from the species distributions (r = 0.87). The thermal optima were less strongly correlated (r = 0.69). For most species, we did not detect thermal maxima from their observed distributions so were unable to compare to laboratory-based estimates. The results suggest that laboratory studies have the potential to be highly transportable to predicting lower thermal limits and thermal optima of mosquitoes in the field. At the same time, lab-based models likely capture physiological limits on mosquito persistence at high temperatures that are not apparent from field-based observational studies but may critically determine mosquito responses to climate warming. Our results indicate that lab-based and field-based studies are highly complementary; performing the analyses in concert can help to more comprehensively understand vector response to climate change.

Kinetic Study of OH Radical Reactions with Cyclopentenone Derivatives.

We investigated the reactions of the hydroxyl radical (OH) with cyclopentenone derivatives and cyclopentanone in a quasi-static reaction cell at 4 Torr across a 300-500 K temperature range. The OH radicals were generated using pulsed laser photolysis of hydrogen peroxide vapors, and the ketone reactants were introduced in excess. The relative concentrations of the radicals were monitored as a function of reaction time using laser-induced fluorescence. At room temperature, the reaction rate coefficients were measured to be 1.2(±0.1) × 10-11 cm3 s-1 for reaction with 2-cyclopenten-1-one (R1); 1.7(±0.2) × 10-11 cm3 s-1 for reaction with 2-methyl-2-cyclopenten-1-one (R2); and 4.4(±0. 7) × 10-12 cm3 s-1 for reaction with 3-methyl-2-cyclopenten-1-one (R3). Over the experimental temperature range, the rate coefficients can be fitted with the modified Arrhenius expressions k1(T) = 1.2 × 10-11 (T/300)0.26 exp (6.7 kJ mol-1/R {1/T - 1/300}) cm3 s-1, k2(T) = 1.7 × 10-11 (T/300)6.4 exp (27.6 kJ mol-1/R {1/T - 1/300}) cm3 s-1, k3(T) = 4.4 × 10-12 (T/300)17.8 exp (57.8 kJ mol-1/R {1/T - 1/300}) cm3 s-1. In the cases of 2-cyclopenten-1-one and 2-methyl-2-cyclopenten-1-one, the temperature dependence of the rate coefficients is similar to that calculated or measured for noncyclic conjugated ketones. We also found that the reaction with 3-methyl-2-cyclopenten-1-one was slower, with rate coefficients similar to those measured for the reaction with the saturated cyclic ketone cyclopentanone. To discuss the experimental data, we use potential energy surfaces (PES) calculated at the CCSD(T)/cc-pVTZ//M06-2X/6-311+G** level of theory. RRKM-based Master equation calculations were also performed to infer the most likely reaction products over a wide range of temperatures and pressures. We suggest that both abstraction and addition mechanisms contribute to the overall OH removal, forming radical products stabilized by resonance. We also discuss the relevance for combustion and atmospheric chemistry.

Organic compounds as temperature calibrants for fast scanning calorimetry

Organic compounds can be used as temperature calibrants in fast scanning calorimetry. Their advantages include ease of surface cleaning of the calorimetric chip and good thermal contact with the chip surface. Among several compounds tested, benzoic acid was identified as a convenient and reliable calibrant for temperatures below approximately 130 °C. However, organic calibrants often exhibit unusual heating rate dependencies of the onset temperatures of melting. This phenomenon can be semi-quantitatively explained by considering different heat flows within the sensor. Notably, the thermal resistance between the heater and thermopile, often overlooked, introduces an additional time constant that can sometimes result in a negative apparent thermal lag. In addition, the onset temperatures are influenced by factors such as sample position, thickness, surface wetting, and spreading. These factors limit the accuracy of transition temperature determinations to approximately ±1 K below 130 °C and ±5 K up to 220 °C.

Effect of cosolvents on the phase separation of polyelectrolyte complexes.

Evidence is shown that cosolvent mixtures control the coacervation of mixtures of oppositely charged polyelectrolytes. Binary and ternary solvent mixtures lead to non-monotonic solubility as a function of the average dielectric constants of the solvent mixtures. These data are rationalized by considering both electrostatic-driven phase separation and solvophobic-driven phase separation using group contribution effects on solubility parameters. These estimates are introduced into an effective Flory-Huggins interaction parameter within the framework of Voorn-Overbeek theory with variable dielectric constants and temperature dependences. Despite its simplicity, the model recovers salient experimental observations not only on their coacervate stabilities, but also on their lower critical solution temperature behaviors. These observations highlight the importance of weak van der Waals interactions in determining the phase behaviors of polyelectrolyte complexes relative to electrostatic correlations.

Freezing of short-range ordered antiferromagnetic clusters in the CrFeTi2O7system.

We report on the CrFeTi2O7(CFTO) system using a combination of x-ray diffraction, dc magnetization, ac susceptibility, specific heat and neutron diffraction measurements. CFTO is seen to crystallize in a monoclinic P21/a symmetry. It shows a glassy freezing at Tf ~ 22 K, characterized by the observation of bifurcation between ZFC and FC χ (T) curves, frequency dispersion across Tf in ac susceptibility, and follows Vogel-Fulcher and power law type critical dynamics, very slow relaxation of iso-thermal remanent magnetization with time and the absence of an anomaly in the temperature dependence of specific heat measurements. The microscopic neutron diffraction analysis of CFTO not only confirms the absence of long-range antiferromagnetic ordering but also exhibits diffuse scattering due to the presence of short-range ordered antiferromagnetically correlated spin clusters.&#xD.

Boolean Logic Gate Operation in Bacteriorhodopsin of Purple Membrane Based on a Molten Globule-like State.

Bacteriorhodopsin (bR) of purple membrane (PM) has increasing technical interests, particularly in photonic devices and bioelectronics. The present work has concerned with monitoring the temperature dependence of passive electric responses in-plane and out-of-plane of the membranes. Based on thermal properties observed orthogonally here for PM, a high-temperature intermediate of bR has been suggested to populate at around 60 °C, which may be ascribed to a molten globule-like state. This intermediate has been found to be enclosed between two reversible thermal transitions for PM. Large-scale turnover in the energy of activation, for these two thermal transitions, occurs steeply at such state at 60 °C, above which does bR reverse the sign of dielectric anisotropy (i.e. crossover) provided the operating frequency should be above the crossover frequency, at which the reversal occurs. No such crossover was found to occur below the crossover frequency, even above the crossover temperature (i.e. 60 °C). Likewise, no such crossover was found to occur below the crossover temperature, even above the crossover frequency. Relying on this reasoning, a logic gate operation may be declared implicating bR for bioelectronics and sense technological relevance. In addition, the results specify "dual frequency" as well as "dual temperature" characteristics to bacteriorhodopsin.

Structural, morphological, and magnetic characterizations of (Fe0.25Mn0.75)2O3 nanocrystals: A comprehensive stoichiometric determination

This report aims to investigate in depth FeMnO3, a material of interest due to its fascinating magnetic and multiferroic properties and its many applications in fields including lithium-ion batteries, microwave devices, and catalysis. However, understanding the precise stoichiometry of the material is crucial for a better comprehension of its physical properties. A cheap, simple, and repeatable sol-gel process was used to fabricate the FeMnO3 nanocrystals. Comprehensive multi-technique characterization of the as-fabricated FeMnO3 indicates that the main phase (94 wt%) is Fe0.5Mn1.5O3, although hematite appears as the minority phase (6 wt%). Magnetic characterization shows core-shell spin-glass like behavior, as well as paramagnetic-ferrimagnetic transitions and a Griffiths phase regime. EPR measurements revealed a strong and broad resonance line across the temperature range of 4.3 K–300 K, primarily influenced by the majority phase. The g-value decreases monotonically from 2.93 at 50 K to 2.18 at 300 K. There is a notable change in the resonance field and linewidth between 40 and 50 K, attributed to surface spin glass behavior. The EPR data below 50 K are in line with the core-shell model of (Fe0.25Mn0.75)2O3 nanoparticles. Below 50 K, the shell's spin system undergoes a transition from paramagnetic to spin-glass-like, with a critical temperature around 43 K. Above 50 K, the superparamagnetic minority phase significantly affects the temperature dependence of the resonance linewidth. These results hold particular importance as they advance our understanding of the intricate magnetic interactions present in FeMnO3. For the best possible use of this material platform in new technologies, such insights are essential.