Temperature Jump Research Articles

Temperature-jump solution X-ray scattering reveals distinct motions in a dynamic enzyme.

Correlated motions of proteins are critical to function, but these features are difficult to resolve using traditional structure determination techniques. Time-resolved X-ray methods hold promise for addressing this challenge but have relied on the exploitation of exotic protein photoactivity, and are therefore not generalizable. Temperature-jumps (T-jumps), through thermal excitation of the solvent, have been utilized to study protein dynamics using spectroscopic techniques, but their implementation in X-ray scattering experiments has been limited. Here, we perform T-jump small- and wide-angle X-ray scattering (SAXS/WAXS) measurements on a dynamic enzyme, cyclophilin A (CypA), demonstrating that these experiments are able to capture functional intramolecular protein dynamics on the microsecond timescale. We show that CypA displays rich dynamics following a T-jump, and use the resulting time-resolved signal to assess the kinetics of conformational changes. Two relaxation processes are resolved, a fast process is related to surface loop motions and slower process is related to motions in the core of the protein that are critical for catalytic turnover.

A continuum framework for modeling liquid-vapor interfaces out of local thermal equilibrium

Continuum numerical methods modeling liquid-vapor phase change processes typically assume local thermal equilibrium at the liquid-vapor interface – continuity of temperature at phase interfaces, and a relation between interfacial saturation pressure and temperature based on phase co-existence curves. Several standard macroscopic problems have been solved accurately by adhering to this assumption. However, in micro-scale and certain non-standard macro-scale applications, significant jumps in temperature are observed at liquid-vapor interfaces during phase change, and vapor pressure can be far from equilibrium values. In this paper, we present a locally discontinuous arbitrary Lagrangian Eulerian finite element formulation with temperature discontinuities at interfaces. A penalty-based approach is used to weakly enforce the temperature jump condition. Furthermore, we use kinetic-theory-based Schrage relationship to evaluate the rate of phase change. We apply our methodology to solve the problem of flowing vapor in a planar heat pipe. The flow rates predicted by our continuum simulations are in excellent agreement with recently published molecular dynamics simulation results of the same problem. Interestingly, accounting for temperature discontinuities leads to only a slight improvement in the prediction of mass fluxes as compared to the case when temperature continuity is assumed. This is in contrast to the large improvement in the prediction of temperature profiles and is a consequence of a weak dependence of the evaporation/condensation rates on the vapor temperature.

Rapid Laser-Induced Temperature Jump Decomposition of the Nerve Agent Simulant Diisopropyl Methylphosphonate under Atmospheric Conditions

We present work detailing the destruction of the nerve agent simulant diisopropyl methylphosphonate (DIMP) via rapid laser heating under atmospheric conditions. Following Nd:YAG laser ablation of l...

Understanding Near Infrared Laser Driven Continuum White Light Emission by Graphene and Its Mixture with an Oxide Phosphor

AbstractRecent observations suggest that continuum white light generation driven by a near infrared (NIR) laser is not limited to rare earth (RE) doped phosphors, but is rather a general photophysical process of light–matter interaction as long as the NIR laser energy is efficiently absorbed. Since the proposed explanations seem to be material‐dependent, a comparative investigation on the white light generation in graphene, and its mixture with a typical RE‐doped oxide phosphor is reported here for a general understanding of this process. In contrast to the steady increase of white light intensity in graphene, the white light generated from the oxide phosphor and their mixtures with graphene exhibits a stepwise growth of intensity with laser power. By using the temperature‐dependent upconversion luminescence as ratiometric temperature sensing, it is observed that this emission is closely correlated with the jumps in temperature with the rise of excitation power. Since the black body temperatures are much higher than the temperatures derived by the ratiometric method, it is suggested that this process can be understood by a general thermally assisted direct photon‐to‐photon conversion process, rather than by pure thermal radiation. The results of this work may have important implication for the understanding and design of efficient continuum white light sources.

Effect of hypersonic flow chemical composition on the oxidation behavior of a super-strong UHTC

A super-strong ZrB2 ceramic containing WC and SiC was tested in a supersonic arc-jet wind tunnel by exposure to flows with two chemical compositions, simulated air or pure nitrogen, at temperatures of 2650 and 2800 K. Temperature jumps of 500–600 K were observed in both environments at constant flow conditions. SEM analyses revealed that oxygen in the high-enthalpy flow retards the material consumption owing to the formation of partially protective glass. Then, it appears that even 5 vol% of W-compounds is sufficient to modify the subscale oxide configuration and form a cell-like multi-layered architecture typical of tungsten, rather than that typical of ZrB2.

Interfacial Study of Nickel-Modified Pt(111) Surfaces in Phosphate-Containing Solutions: Effect on the Hydrogen Evolution Reaction.

The surface modification of electrodes attracts great interest in electrocatalysis. It has often been observed that deposition of foreign adatoms on the surface of an electrode can originate a significant enhancement in the catalytic activity. For example, it has been reported that nickel deposits on Pt surfaces improve the rate of the hydrogen evolution reaction (HER, Nature Energy 2017, 2, 17031). During the deposition process of such metal adlayers, the pH and the nature of the ions in the electrolyte play an important role. Phosphate species are typically used to prepare buffer solutions in a wide range of pH. Therefore, electrolytes containing phosphate species are used in a large number of applications. However, the effect of phosphate on platinum surface modification with nickel deposits has not been studied yet. In this work, new data about the interaction of phosphate with nickel adatoms deposited on Pt(111) at pH 5 is investigated using cyclic voltammetry and infrared spectroscopy. The results show that, when nickel is in solution, the phosphate ions are adsorbed at lower potentials than in the absence of nickel. In addition, Laser-Induced Temperature Jump Technique demonstrates that nickel facilitates the adsorption of phosphate because of a shift of the potential of zero charge (pzc) toward negative potentials. This increases the magnitude of the positive electric field on the electrode surface, at a given potential E>pzc, facilitating the adsorption of anions. CO displacement technique has been also employed to obtain additional information about co-adsorbed phosphate on nickel adlayers. Finally, the HER has been studied at pH 5 in the presence of nickel, with and without phosphate in the bulk solution.

Determination of momentum accommodation coefficients and velocity distribution function for Noble gas-polymeric surface interactions using molecular dynamics simulation

Due to the momentum and energy exchange between the gas and solid surface molecules, by means of the accommodation coefficients in the Cercignani-Lampis-Lord (CLL) model, the velocity components used in the Direct Simulation Monte Carlo (DSMC) method can be studied more accurately. The coefficients can also be used in calculation of slip velocity, temperature jumping, drag force and shear stress. In the light of rising needs for polymers in industrial applications, the scattering behavior of noble gas molecules in their collision with a surface made of diglycidyl ether bisphenol A (DGEBA) epoxy resin, cured by tetrahydrophthalic anhydride (THPA) agent and reinforced by multi-layer graphite, was simulated and investigated by Molecular Dynamics (MD). The momentum and energy accommodation coefficients for gas–surface interactions were also calculated by MD simulation. The results indicated that temperature increase, change in the gas species, reduction in surface roughness, and increase in the Knudsen number (Kn) and the wall velocity could cause the accommodation coefficients to be less than one. Based on the scattering kernel of CLL boundary condition, a suitable distribution function for calculating the velocity components of noble gas molecules (e.g., argon molecules) after interaction with polymeric surface was proposed.

Investigating the M(hkl)| ionic liquid interface by using laser induced temperature jump technique

The interface between several Room Temperature Ionic Liquids (RTILs) in contact with both Au(hkl) basal planes and Pt(111) was studied by using cyclic voltammetry and Laser Induced Temperature Jump Technique (LITJT). Three RTILs, based on the imidazolium cation and the [Tf2N] anion were investigated: [Emmim][Tf2N], [Emim][Tf2N] and [Bmmim][Tf2N]. These three RTILs were selected with the aim to analyse how the balance between the different ion-ion interactions influences the interfacial properties of the M(hkl)|RTIL interface. It was found that the voltammetric response of the Au(hkl)|[Emmim][Tf2N] was highly sensitive to the geometry of the active surface sites, displaying sharp spikes superimposed to a capacitive voltammetric current. Conversely, these sharp spikes disappeared when [Bmmim][Tf2N] replaced [Emmim][Tf2N], although the capacitive voltammetric current profile was essentially maintained. This result is most likely related to the increase of the van der Waals interactions in the [Bmmim][Tf2N]. When [Emim][Tf2N] was analysed, the increase of the hydrogen bond interactions due to the hydrogenation of C2 (second carbon at the imidazolium ring) resulted also in the disappearance of the voltammetric spikes. The laser measurements showed that the highest values of the potential of maximum entropy (pme) in RTIL media correspond to the atomically closest packet surface structures, following the order: Au(111)>Au(100)>Au(110), in agreement with work function values. The measurement with Pt(111) revealed that the voltammetric profiles for this surface are featureless in all cases. However, the laser experiments showed that solvent restructuration, as a function of both value and direction of the applied potential, is dependent on the type of cation.Finally, the interface Au(hkl)|Choline chloride:urea Deep Eutectic Solvent (DES) was also investigated by using cyclic voltammetry and LITJT. The voltammetric response of DES was also sensitive to the orientation of the Au single crystal, and the cyclic voltammograms displayed distinct sharp and characteristic features. Nevertheless, the laser response could not provide a value of the pme for the Au(hkl)|DES interface, likely due to the complex chemical structure of the DES which, in addition, strongly adsorbs on Au(hkl).

Ultrafast folding kinetics of WW domains reveal how the amino acid sequence determines the speed limit to protein folding

Protein (un)folding rates depend on the free-energy barrier separating the native and unfolded states and a prefactor term, which sets the timescale for crossing such barrier or folding speed limit. Because extricating these two factors is usually unfeasible, it has been common to assume a constant prefactor and assign all rate variability to the barrier. However, theory and simulations postulate a protein-specific prefactor that contains key mechanistic information. Here, we exploit the special properties of fast-folding proteins to experimentally resolve the folding rate prefactor and investigate how much it varies among structural homologs. We measure the ultrafast (un)folding kinetics of five natural WW domains using nanosecond laser-induced temperature jumps. All five WW domains fold in microseconds, but with a 10-fold difference between fastest and slowest. Interestingly, they all produce biphasic kinetics in which the slower phase corresponds to reequilibration over the small barrier (<3 RT) and the faster phase to the downhill relaxation of the minor population residing at the barrier top [transition state ensemble (TSE)]. The fast rate recapitulates the 10-fold range, demonstrating that the folding speed limit of even the simplest all-β fold strongly depends on the amino acid sequence. Given this fold's simplicity, the most plausible source for such prefactor differences is the presence of nonnative interactions that stabilize the TSE but need to break up before folding resumes. Our results confirm long-standing theoretical predictions and bring into focus the rate prefactor as an essential element for understanding the mechanisms of folding.

An electro-explosively actuated mini-flyer launcher

It’s crucial to develop shock loading techniques in laboratory to create pressure and temperature jumps for a wide variety of studies in material science. In this paper we have developed an electro-explosively actuated mini-flyer launcher capable of ejecting a plastic mini-flyer, typically 0.6 mm in diameter, up to several km/s. When prepared with microelectromechanical system (MEMS) scale methods, it can be mass-produced and takes only four steps, lowering manufacturing cost. Particularly, it was designed and integrated with a high-power high-voltage switch together, omitting expensive vacuum switches as well as interconnections between components. Four auxiliary exploding foils were first exploded at a certain trigger voltage to determine the optimal size, and polyvinylidene fluoride (PVDF) film was used to measure shock pressure of electro-explosion to estimate whether it’s enough to destroy the dielectric layer between top and bottom electrodes. Electrical characterizations were then carried out to obtain some important parameters, such as delay time, jitter time, risetime and peak current flowing through main exploding foil, at a series of firing voltages ranging from 600 V to 1400 V, and the results revealed that peak current increases with the rise of firing voltage dramatically, high-current pulse can be obtained at lower firing voltage, and delay time and risetime are almost constant. Finally, Photon Doppler Velocimetry (PDV) and high-speed camera were utilized to record the acceleration histories of flyers at different firing voltages, and the results showed that the flyer velocity can be controlled by the adjustment of firing energy. All the efforts demonstrated that the mini-flyer launcher is feasible and attractive.

MHD Williamson Fluid Flow Over a Permeable Moving Wedge with Heat Source, Temperature and Concentration Jump

MHD Williamson Fluid Flow Over a Permeable Moving Wedge with Heat Source, Temperature and Concentration Jump

Atmospheric Processes and Climatological Characteristics of the 79N Glacier (Northeast Greenland)

AbstractThe Nioghalvfjerdsfjorden glacier (the 79 fjord, henceforth referred to as 79N) has been thinning and accelerating since the early 2000s, as a result of calving episodes at the front of the glacier. As 8% of the Greenland Ice Sheet area drains into 79N, changes in the stability of 79N could propagate into the interior of Greenland. Despite this concern, relatively little is known about the atmospheric conditions over 79N. We present the surface atmospheric processes and climatology of the 79N region from analyses of data from four automatic weather stations (AWS) and reanalysis data from ERA-Interim. Over the floating section of the glacier, the annual average air temperature is −16.7°C, decreasing to −28.5°C during winter. Winds over the glacier are predominantly westerly and are of katabatic origin. Over the last 39 years the near-surface air temperature has increased at a rate of +0.08°C yr−1. In addition, we find that large, rapid (48 h) temperature increases (&gt;10°C) occur during the five-month dark period (November–March). Eight (±4) warm-air events occur annually from 1979 to 2017. We use the Weather Research and Forecasting (WRF) Model to simulate a particular warm-air event with above-freezing air temperatures between 30 November and 2 December 2014. The warm event was caused by warm-air advection from the southeast and a subsequent increase in the longwave radiation toward the surface due to low-level cloud formation. The frequent nature of the temperature jumps and the magnitude of the temperature increases are likely to have an impact on the surface mass balance of the glacier by bringing the skin temperatures to the melting point.

Thermodynamic analysis of a long-range interacting spin system

A long-range interacting Fermi chain placed in the uniform and the staggered magnetic field is studied via the micro-canonical approach. The relation between the entropy and the energy of the system is obtained by counting the number of microscopic states. We find that this system is non-ergodic and can exhibit first-order phase transition, second-order phase transition, or both. The microcanonical ensemble predicts negative specific heat regions and temperature jumps. Moreover, the global phase diagram of the system is constructed.

Kinetic simulation of the non-equilibrium effects at the liquid-vapor interface

Phase change phenomena at microscale is important for novel cooling microsystems with intensive evaporation, so the development of reliable models and simulations are challenging. The vapor behaviors near its condensed phase are simulated using the non-linear S-model kinetic equation. The pressure and temperature jumps obtained numerically are in good agreement with the analytical expressions derived from the appropriate Onsager-Casimir reciprocity relations. The results of the evaporation flux are close to those given by the Hertz-Knudsen-Schrage formula, only when the values of the pressure and temperature at the upper boundary of the Knudsen layer are used. Comparison with recently measured temperature jumps are provided and disagreement with some experiments are discussed.

The spectacular cluster chain Abell 781 as observed with LOFAR, GMRT, and XMM-Newton

Context. A number of merging galaxy clusters show the presence of large-scale radio emission associated with the intra-cluster medium (ICM). These synchrotron sources are generally classified as radio haloes and radio relics. Aims. Whilst it is commonly accepted that mergers play a crucial role in the formation of radio haloes and relics, not all the merging clusters show the presence of giant diffuse radio sources and this provides important information concerning current models. The Abell 781 complex is a spectacular system composed of an apparent chain of clusters on the sky. Its main component is undergoing a merger and hosts peripheral emission that is classified as a candidate radio relic and a disputed radio halo. Methods. We used new LOw Frequency ARay (LOFAR) observations at 143 MHz and archival Giant Metrewave Radio Telescope (GMRT) observations at 325 and 610 MHz to study radio emission from non-thermal components in the ICM of Abell 781. Complementary information came from XMM-Newton data, which allowed us to investigate the connection with the thermal emission and its complex morphology. Results. The origin of the peripheral emission is still uncertain. We speculate that it is related to the interaction between a head tail radio galaxy and shock. However, the current data allow us only to set an upper limit of ℳ &lt; 1.4 on the Mach number of this putative shock. Instead, we successfully characterise the surface brightness and temperature jumps of a shock and two cold fronts in the main cluster component of Abell 781. Their positions suggest that the merger is involving three substructures. We do not find any evidence for a radio halo either at the centre of this system or in the other clusters of the chain. We place an upper limit to the diffuse radio emission in the main cluster of Abell 781 that is a factor of 2 below the current radio power-mass relation for giant radio haloes.

Phase-Separation Kinetics in Protein-Salt Mixtures with Compositionally Tuned Interactions.

Liquid-liquid phase separation (LLPS) in protein systems is relevant for many phenomena, from protein condensation diseases to subcellular organization to possible pathways toward protein crystallization. Understanding and controlling LLPS in proteins is therefore highly relevant for various areas of (biological) soft matter research. Solutions of the protein bovine serum albumin (BSA) have been shown to have a lower critical solution temperature-LLPS (LCST-LLPS) induceable by multivalent salts. Importantly, the nature of the multivalent cation used influences the LCST-LLPS in such systems. Here, we present a systematic ultrasmall-angle X-ray scattering investigation of the kinetics of LCST-LLPS of BSA in the presence of different mixtures of HoCl3 and LaCl3, resulting in different effective interprotein attraction strengths. We monitor the characteristic length scales ξ( t, Tfin) after inducing LLPS by subjecting the respective systems to temperature jumps in their liquid-liquid coexistence regions. With increasing interprotein attraction and increasing Tfin, we observe an increasing deviation from the growth law of ξ ∼ t1/3 and an increased trend toward arrest. We thus establish a multidimensional method to tune phase transitions in our systems. Our findings help shed light on general questions regarding LLPS and the tunability of its kinetics in both proteins and colloidal systems.

Simulated XUV photoelectron spectra of THz-pumped liquid water.

Highly intense, sub-picosecond terahertz (THz) pulses can be used to induce ultrafast temperature jumps (T-jumps) in liquid water. A supercritical state of gas-like water with liquid density is established, and the accompanying structural changes are expected to give rise to time-dependent chemical shifts. We investigate the possibility of using extreme ultraviolet photoelectron spectroscopy as a probe for ultrafast dynamics induced by sub-picosecond THz pulses of varying intensities and frequencies. To this end, we use ab initio methods to calculate photoionization cross sections and photoelectron energies of (H2O)20 clusters embedded in an aqueous environment represented by point charges. The cluster geometries are sampled from ab initio molecular dynamics simulations modeling the THz-water interactions. We find that the peaks in the valence photoelectron spectrum are shifted by up to 0.4 eV after the pump pulse and that they are broadened with respect to unheated water. The shifts can be connected to structural changes caused by the heating, but due to saturation effects they are not sensitive enough to serve as a thermometer for T-jumped water.

Generalized single-parameter aging tests and their application to glycerol.

Physical aging of glycerol following temperature jumps is studied by dielectric spectroscopy at temperatures just below the glass transition temperature. The data are analyzed using two single-parameter aging tests developed by Hecksher et al. [J. Chem. Phys. 142, 241103 (2015)]. We generalize these tests to include jumps ending at different temperatures. Moreover, four times larger jumps than previously are studied. The single-parameter aging tests are here for the first time applied to a hydrogen-bonded liquid. We conclude that glycerol obeys single-parameter aging to a good approximation.

Discontinuous Fronts as Exact Solutions to Precipitating Quasi-geostrophic Equations

Atmospheric fronts include cold fronts, warm fronts, and stationary fronts, and they can be idealized as boundaries between two air masses with different temperatures and other properties. Simple exact solutions have previously been presented through the Margules relations, but they are lacking in two aspects: they do not propagate and they do not involve water vapor, clouds, or precipitation. Here, these two aspects are included by considering the recently derived precipitating quasi-geostrophic (PQG) equations. The PQG equations are shown to have exact solutions that are discontinuous fronts with jumps in temperature, winds, and total water. A phase change of water occurs at the location of the front, and the front propagates at a speed that is related to the rainfall velocity, jump magnitudes, and front geometry. Exact formulas for the front's properties are presented, including the classical Margules relations and many additional relations involving moisture. Estimates of physical parameters are used as an initial assessment of the realism of the model fronts. Through consideration of alternative representations of atmospheric dynamics, it is suggested that the phase change of water and the fall velocity of rain are key aspects of the PQG equations that allow propagating, discontinuous fronts.

Numerical simulation on explosion overpressure features of methane-air premixed gas at different concentrations in utility tunnels

According to the structural features of utility tunnels, the origin and development process of combustion and explosion of premixed natural gas with the volume fraction of 5%, 7%, 9%, 11%, 13% and 15% was simulated by fluid dynamics software ANSYS-Fluent. The results showed that the evolution rules of the overpressure and overtemperature produced by the flame front were basically the same within the critical concentration range of methane explosion. Local pressure and temperature jumps in right of bottom edges were formed appearing at the maximum overpressure, which was affected by the combustion front and pressure waves together with reflected wave pressure. The combustion process in utility tunnels can be divided into four stages: rapid growth of combustion, steady development of combustion, combustion jump, and pressure and temperature oscillating retrenchment after burning. The simulated maximum overpressure is around 1.7 MPa and it is obtained under the conditions when the premixed gas concentration is 9% and 7%.