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Understanding the underlying physics of natural gas hydrate dissociation is necessary for efficient CH4 extraction and in the exploration of potential additives in the chemical injection method. Silica being "sand" is already present inside the reservoir, making the silica nanoparticle a potential green additive. Here, molecular dynamics (MD) simulations have been performed to investigate the dissociation of the CH4 hydrate in the presence and absence of ∼1, ∼2, and ∼3 nm diameter hydrophilic silica nanoparticles at 100 bar and 310 K. We find that the formation of a CH4 nanobubble has a strong influence on the dissociation rate. After the initial hydrate dissociation, the rate of dissociation slows down till the formation of a CH4 nanobubble. We find the critical concentration and size limit to form the CH4 nanobubble to be ∼0.04 mole fraction of CH4 and ∼40 to 50 CH4 molecules, respectively. The solubility of CH4 and the chemical potential of H2O and CH4 are determined via Gibbs ensemble Monte Carlo simulations. The liquid phase chemical potential of both H2O and CH4 in the presence and absence of the nanoparticle is nearly the same, indicating that the effect of this additive will not be significant. While the formation of the hydration shell around the nanoparticle via hydrogen bonding confirms the strength of interactions between the water molecules and the nanoparticle in our MD simulations, the contact of the nanoparticle with the interface is infrequent, leading to no explicit effect of the nanoparticle on the dynamics of methane hydrate dissociation. [ABSTRACT FROM AUTHOR]

Thermodynamic hydrate promoters and kinetic hydrate promoters can be used to reduce the P–T conditions for clathrate hydrate synthesis to decrease the nucleation induction time while increasing growth rates. Two commonly used promoters for hydrate research are tetrahydrofuran (THF) and sodium dodecyl sulfate (SDS), which can increase the overall hydrate promotion when used in tandem as compared to individually. There are several molecular theories regarding how SDS promotes hydrate growth. This study explores the micellular theory, for which hydrate formation depends on surfactant aggregates (micelles) at a critical micelle concentration (CMC) to increase the interfacial surface area. The micellular theory is the most investigated and criticized surfactant hydrate promotion theory. To address questions related to micellar behavior, this study investigates the intermolecular behavior between SDS and THF for the identification of micelles at hydrate-forming conditions. The systems explored contained THF at 3 and 5 wt. % with varying concentrations of SDS below and above the CMC. Several methods including a qualitative visual method, conductivity, interfacial tensiometry, 13C Liquid-state Nuclear Magnetic Resonance (NMR) spectroscopy, and 1H diffusion NMR spectroscopy were evaluated at temperatures below the Krafft point of SDS and above 0 °C. The presence of THF at low concentrations decreased the critical temperature for the formation of SDS micelles, where SDS is solubilized in THF/water solution at hydrate-forming temperatures without precipitation. The CMC of SDS was decreased significantly even at hydrate-forming conditions. Mixed surfactant–cosolvent micellular behavior of SDS in the presence of low concentrations of THF was confirmed at hydrate-forming conditions above 0 °C. [ABSTRACT FROM AUTHOR]

This study aimed to determine whether caffeine gum influenced perceptual-cognitive and physical performance during the extra-time period of simulated soccer match-play. Semiprofessional male soccer players (n = 12, age: 22 ± 3 years, stature: 1.78 ± 0.06 m, mass: 75 ± 9 kg) performed 120-min soccer-specific exercise on two occasions. In a triple-blind, randomized, crossover design, players chewed caffeinated (200 mg; caffeine) or control (0 mg; placebo) gum for 5 min following 90 min of soccer-specific exercise. Perceptual-cognitive skills (i.e., passing accuracy, reaction time, composure, and adaptability) were assessed using a soccer-specific virtual reality simulator, collected pre- and posttrial. Neuromuscular performance (reactive-strength index, vertical jump height, absolute and relative peak power output, and negative vertical displacement) and sprint performance (15 and 30 m) were measured at pretrial, half-time, 90 min, and posttrial. Caffeine gum attenuated declines in reaction time (pre: 90.8 ± 0.8 AU to post: 90.7 ± 0.8 AU) by a further 4.2% than placebo (pre: 92.1 ± 0.8 AU to post: 88.2 ± 0.8 AU; p <.01). Caffeine gum reduced composure by 4.7% (pre: 69.1 ± 0.8 AU to post: 65.9 ± 0.8 AU) versus placebo (pre: 68.8 ± 0.8 AU to post: 68.3 ± 0.8 AU; p <.01). Caffeine gum did not influence any other variables (p >.05). Where caffeine gum is consumed by players prior to extra-time, reaction time increases but composure may be compromised, and neuromuscular and sprint performance remain unchanged. Future work should assess caffeine gum mixes with substances like L-theanine that promote a relaxed state under stressful conditions. [ABSTRACT FROM AUTHOR]

This study investigated the test–retest reliability of running economy (RE) and metabolic and cardiorespiratory parameters related to endurance running performance using a multistage incremental treadmill test. On two occasions separated by 21–28 days, 12 male middle- and long-distance runners ran at 10, 11, 12, 13, and 14 km/hr for 8 min each stage, immediately followed by a ramp test to volitional exhaustion. Carbohydrate (10% maltodextrin solution) was consumed before and during the test to provide ∼1 g/min of exercise. RE, minute ventilation ( V ˙ E), oxygen consumption ( V ˙ O 2 ), carbon dioxide production ( V ˙ CO 2 ), respiratory exchange ratio (RER), heart rate (HR), ratings of perceived exertion (RPE), and blood glucose and lactate concentrations were recorded for each stage and at volitional exhaustion. Time-to-exhaustion (TTE) and peak oxygen consumption ( V ˙ O 2 peak) during the ramp test were also recorded. Absolute reliability, calculated as the coefficient of variation (CV) between repeated measures, ranged from 2.3% to 3.1% for RE, whereas relative reliability, calculated as the intraclass correlation coefficient (ICC), ranged from.42 to.79. V ˙ E , V ˙ O 2 , V ˙ O 2 peak , V ˙ CO 2 , RER, and HR had a CV of 1.1%–4.3% across all stages. TTE and RPE had a CV of 7.2% and 2.3%–10.8%, respectively, while glucose and lactate had a CV of 4.0%–17.8%. All other parameters, except for blood glucose, were demonstrated to have good-to-excellent relative reliability assessed by ICC. Measures of RE, V ˙ O 2 peak , and TTE were reliable during this two-phase multistage incremental treadmill test in a cohort of trained and highly trained male middle- and long-distance runners. [ABSTRACT FROM AUTHOR]

Despite the increased popularity of female elite road cycling, research to inform the fueling requirements of these endurance athletes is lacking. In this case study, we report for the first time the energetics of a female world-tour cyclist competing in the 2023 Tour de France Femmes, an 8-day race of the Union Cycliste Internationale. The 29-year-old athlete presented with oligomenorrhea and low T3 before the race. Total daily energy expenditure assessed with the doubly labeled water technique was 7,572 kcal/day (∼4.3 physical activity levels), among the highest reported in the literature to date for a female. Crank-based mean maximal power was consistent with female world-tour cyclists (5 min, mean 342 W, 4.8 W/kg; 20 min 289 W, 4.1 W/kg). The average daily energy intake measured with the remote food photography method (Stage Days 1–7) was 5,246 kcal and carbohydrate intake was 13.7 g/kg (range 9.7–15.9 g/kg), and 84 g/hr during stages, and an average fat intake of 15% of daily energy intake. An estimated 2,326 kcal/day energy deficit was evidenced in a 2.2 kg decrease in body mass. Notwithstanding the high carbohydrate intake, the athlete was unable to match the energy requirements of the competition. Despite signs of energy deficiency preexisting (oligomenorrhea and low T3), and other further developing during the race (weight loss), performance was in line with that of other world-tour cyclists and a best personal performance was recorded for the last stage. This case study emphasizes the need for further research to inform energy requirements for female athletes' optimal performance and health. [ABSTRACT FROM AUTHOR]

We consider the electron stimulated desorption, via dissociative electron attachment, of anionic species from thin condensed CD4 films deposited on a Pt substrate and compare experimentally observed desorption yields with density functional theory calculations of the binding energies of various anionic and neutral moieties to Pt(111). Certain species (which can be considered chemisorbed) exhibit very high binding energies and large charge transfer with the substrate. Other "physisorbed" species have much lower binding energies. Species that chemisorb have lower desorption yields than those that physisorb, especially at 1–2 monolayer coverage of the Pt substrate. The binding energy of D− to Pt is the weakest, and experimentally, the desorption yield is the highest regardless of the thickness of CD4. The calculations show that the formation and desorption of anionic species at a distance of 16 Å from the substrate, which is equivalent to the thickness of CD4 films of four monolayers, are not influenced by the short-range interactions between the substrate and the molecule and DEA products. [ABSTRACT FROM AUTHOR]

In this study, peptides designed using fragments of an antifreeze protein (AFP) from the freeze-tolerant insect Tenebrio molitor, TmAFP, were evaluated as inhibitors of clathrate hydrate formation. It was found that these peptides exhibit inhibitory effects by both direct and indirect mechanisms. The direct mechanism involves the displacement of methane molecules by hydrophobic methyl groups from threonine residues, preventing their diffusion to the hydrate surface. The indirect mechanism is characterized by the formation of cylindrical gas bubbles, the morphology of which reduces the pressure difference at the bubble interface, thereby slowing methane transport. The transfer of methane to the hydrate interface is primarily dominated by gas bubbles in the presence of antifreeze peptides. Spherical bubbles facilitate methane migration and potentially accelerate hydrate formation; conversely, the promotion of a cylindrical bubble morphology by two of the designed systems was found to mitigate this effect, leading to slower methane transport and reduced hydrate growth. These findings provide valuable guidance for the design of effective peptide-based inhibitors of natural-gas hydrate formation with potential applications in the energy and environmental sectors. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of volume traps intentionally introduced into a silicon-on-insulator (SOI) substrate by inserting a layer of polysilicon beneath buried oxide. In radio frequency applications, this type of substrate, referred to as trap-rich, is known to considerably reduce the generation of harmonics resulting from the parasitic non-linear charge dynamics introduced by the substrate handler under the buried oxide. This analysis focuses on a test vehicle in the form of an integrated coplanar waveguide on two types of substrates, namely, high-resistivity SOI substrates with and without a trap-rich layer. From a modeling point of view, a simulation methodology is implemented in order to convert the 3D simulation of the coplanar waveguide into a 2D treatment that takes into account the wave propagation effect associated with the distributed nature of the transmission line. As a first step, this modeling strategy is implemented to reproduce the effect of increasing substrate resistivity on 2nd and 3rd harmonic reductions, leading to an excellent agreement with experimental data. Building on this validation of the simulation method, we have opted to simulate the non-linear response of the transmission line on the SOI trap-rich substrate by simplifying the trap distribution model. To avoid the adoption of unverified and strongly process-dependent trap distributions across the bandgap, a midgap monovalent trap density has been introduced, either acceptor or donor density. A monovalent density of acceptor traps with a concentration of 1016 cm−3 and a carrier lifetime of 0.1 ns has been shown to reproduce the experimental data very accurately with a substantial reduction in 2nd and 3rd harmonics. A detailed analysis of the displacement current waveforms explains the beneficial role of acceptor traps compared with donor traps. [ABSTRACT FROM AUTHOR]

Carbohydrate (CHO) supplementation during endurance exercise can improve performance. However, it is unclear whether low glycemic index (GI) CHO leads to differential ergogenic and metabolic effects compared with a standard high GI CHO. This study investigated the ergogenic and metabolic effects of CHO supplementation with distinct GIs, namely, (a) trehalose (30 g/hr), (b) isomaltulose (30 g/hr), (c) maltodextrin (60 g/hr), and (d) placebo (water). In this double-blind, crossover, counterbalanced, placebo-controlled study, 13 male cyclists cycled a total of 100 min at varied exercise intensity (i.e., 10-min stages at 1.5, 2.0, and 2.5 W/kg; repeated three times plus two 5-min stages at 1.0 W/kg before and after the protocol), followed by a 20-min time trial on four separated occasions. Blood glucose and lactate (every 20 min), heart rate, and ratings of perceived exertion were collected throughout, and muscle biopsies were taken before and immediately after exercise. The results showed that trehalose improved time-trial performance compared with placebo (total work done 302 ± 39 vs. 287 ± 48 kJ; p =.01), with no other differences between sessions (all p ≥.07). Throughout the 100-min protocol, blood glucose was higher with maltodextrin compared with the other supplements at all time points (all p <.05). Heart rate, ratings of perceived exertion, muscle glycogen content, blood glucose, and lactate were not different between conditions when considering the 20-min time trial (all p >.05). Trehalose supplementation throughout endurance exercise improved cycling performance and appears to be an appropriate CHO source for exercise tasks up to 2 hr. No ergogenic superiority between the different types of CHO was established. [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR), a pivotal process in hydrogen fuel cells crucial for enhancing fuel cell performance through suitable catalysts, remains a challenging aspect of development. This study explores the catalytic potential of germanene on Al (111), taking advantage of the successful preparation of stable reconstructed germanene layers on Al (111) and the excellent catalytic performance exhibited by germanium-based nanomaterials. Through first-principles calculations, we demonstrate that the O2 molecule can be effectively activated on both freestanding and supported germanene nanosheets, featuring kinetic barriers of 0.40 and 0.04 eV, respectively. The presence of the Al substrate not only significantly enhances the stability of the reconstructed germanene but also preserves its exceptional ORR catalytic performance. These theoretical findings offer crucial insights into the substrate-mediated modulation of germanene stability and catalytic efficiency, paving the way for the design of stable and efficient ORR catalysts for future applications. [ABSTRACT FROM AUTHOR]

Methane is considered to be a cubic structure I (CS-I) clathrate hydrate former, although in a number of instances, small amounts of structure II (CS-II) clathrate hydrate have been transiently observed as well. In this work, solid-state magic angle spinning 13C NMR spectra of methane hydrate formed at low temperatures inside silica-based nanoporous materials with pores in the range of 3.8–20.0 nm (CPG-20, Vycor, and MCM-41) show methane in several different environments. In addition to methane encapsulated in the dodecahedral 512 (D) and tetrakaidecahedral 51262 (T) cages typical of the CS-I clathrate hydrate phase, methane guests in pentakaidecahedral 51263 (P) and hexakaidecahedral 51264 (H) cages are also identified, and these appear to be stabilized for extended periods of time. The ratio of methane guests among the D and T cages determined from the line intensities is significantly different from that of bulk CS-I samples and indicates that both CS-I and CS-II are present as the dominant species. This is the first observation of methane in P cages, and the possible structures in which they could be present are discussed. Broad and relatively strong methane peaks, which are also observed in the spectra, can be related to methane dissolved in an amorphous component of water adjacent to the pore walls. Nanoconfinement and interaction with the pore walls clearly have a strong influence on the hydrate formed and may reflect species present in the early stages of hydrate growth. [ABSTRACT FROM AUTHOR]

Uniquely, large-bipolarons' self-trapped holes occupy superoxygens, each comprising four oxygens circumscribed by four coppers in a CuO2 plane, formed as oxygens relax inward and coppers relax outward. Critically, concomitant oxygen-to-copper electron transfer eliminates copper spins. The d-symmetry of superoxygens' ground state molecular orbital tracks the superoxygens' predominant zero-point radial vibrations. These large bipolarons' distinctive charge transport, absorption, magnetism, local atomic vibrations, condensation into a liquid, and subsequent superconductivity are consistent with cuprate superconductors' long-established unusual properties. [ABSTRACT FROM AUTHOR]

Small molecule inhibitors (SMIs) have been gaining attention in the field of area-selective atomic layer deposition (ALD) because they can be applied in the vapor-phase. A major challenge for SMIs is that vapor-phase application leads to a disordered inhibitor layer with lower coverage as compared to self-assembled monolayers, SAMs. A lower coverage of SMIs makes achieving high selectivity for area-selective ALD more challenging. To overcome this challenge, mechanistic understanding is required for the formation of SMI layers and the resulting precursor blocking. In this study, reflection adsorption infrared spectroscopy measurements are used to investigate the performance of aniline as an SMI. Our results show that aniline undergoes catalytic surface reactions, such as hydrogenolysis, on a Ru non-growth area at substrate temperatures above 250 °C. At these temperatures, a greatly improved selectivity is observed for area-selective TaN ALD using aniline as an inhibitor. The results suggest that catalytic surface reactions of the SMI play an important role in improving precursor blocking, likely through the formation of a more carbon-rich inhibitor layer. More prominently, catalytic surface reactions can provide a new strategy for forming inhibitor layers that are otherwise very challenging or impossible to form directly through vapor-phase application. [ABSTRACT FROM AUTHOR]

We have investigated pressure-induced amorphization (PIA) of an alcohol clathrate hydrate (CH) of cubic structure type I (sI) in the presence of NH4F utilizing dilatometry and x-ray powder diffraction. PIA occurs at 0.98 GPa at 77 K, which is at a much lower pressure than for other CHs of the same structure type. The amorphized CH also shows remarkable resistance against crystallization upon decompression. While amorphized sI CHs could not be recovered previously at all, this is possible in the present case. By contrast to other CHs, the recovery of the amorphized CHs to ambient pressure does not even require a high-pressure annealing step, where recovery without any loss of amorphicity is possible at 120 K and below. Furthermore, PIA is accessible upon compression at unusually high temperatures of up to 140 K, where it reaches the highest degree of amorphicity. Molecular dynamics simulations confirm that polar alcoholic guests, as opposed to non-polar guests, induce cage deformation at lower pressure. The substitution of NH4F into the host-lattice stabilizes the collapsed state more than the crystalline state, thereby enhancing the collapse kinetics and lowering the pressure of collapse. [ABSTRACT FROM AUTHOR]

Clathrate hydrates are crystals formed by guest molecules that stabilize cages of hydrogen-bonded water molecules. Whereas thermodynamic equilibrium is well described via the van der Waals and Platteeuw approach, the increasing concerns with global warming and energy transition require extending the knowledge to non-equilibrium conditions in multiphase, sheared systems, in a multiscale framework. Potential macro-applications concern the storage of carbon dioxide in the form of clathrates, and the reduction of hydrate inhibition additives currently required in hydrocarbon production. We evidence porous mesomorphologies as key to bridging the molecular scales to macro-applications of low solubility guests. We discuss the coupling of molecular ordering with the mesoscales, including (i) the emergence of porous patterns as a combined factor from the walk over the free energy landscape and 3D competitive nucleation and growth and (ii) the role of molecular attachment rates in crystallization–diffusion models that allow predicting the timescale of pore sealing. This is a perspective study that discusses the use of discrete models (molecular dynamics) to build continuum models (phase field models, crystallization laws, and transport phenomena) to predict multiscale manifestations at a feasible computational cost. Several advances in correlated fields (ice, polymers, alloys, and nanoparticles) are discussed in the scenario of clathrate hydrates, as well as the challenges and necessary developments to push the field forward. [ABSTRACT FROM AUTHOR]

We present new results on the underlying guest–host interactions and spectral characterization of a CO2 molecule confined in the cages of the sI clathrate hydrate. Such types of porous solids raise computational challenges, as they are of practical interest as gas storage/capture materials. Accordingly, we have directed our efforts toward addressing their modeling in a proper manner, ensuring the quality of the input data and the efficiency of the computational approaches. The computational procedure for spectral simulations, within the multi-configurational time-dependent Hartree framework, involves the development of a fully coupled Hamiltonian, including an exact kinetic energy operator and a many-body representation of the potential, along with dipole moment surfaces, both obtained through neural network machine learning techniques. The resulting models were automatically trained and tested on extensive datasets generated by PW86PBE-XDM calculations, following the outcome of previous benchmark studies. Our simulations enable us to explore various aspects of the quantized dynamics upon confinement of CO2@D/T, such as constrained rotational–translational quantum motions and the averaged position/orientation of the CO2 guest in comparison to the experimental data available. Particularly notable are the distinct energy patterns observed in the computed spectra for the confined CO2 in the D and T cages, with a considerably high rotational–translational coupling in the CO2@T case. Leveraging reliable computations has proved instrumental, highlighting the sensitivity of the spectral features to the shape and strength of the potential interactions, with the explicit description of many-body contributions being significant. [ABSTRACT FROM AUTHOR]

Nitrate ( NO 3 − ) has properties that can improve muscle function, leading to improvements in metabolic cost of exercise as well as enhance force production. Gymnastics is a whole-body sport, involving events that demand a high level of strength and fatigue resistance. However, the effect of NO 3 − supplementation on both upper- and lower-body function in gymnasts is unknown. This study examined the effect of acute beetroot juice (BRJ) supplementation on isokinetic strength and endurance of the upper- and lower-body in highly trained international-level male gymnasts. In a double-blind, randomized crossover design, 10 international-level male gymnasts completed two acute supplementation periods, consuming either 2 × 70 ml NO 3 − -rich (∼12.8 mmol/L of NO 3 − ) or NO 3 − -depleted (PLA) BRJ. Maximal strength of the upper-leg and upper-arm at 60°/s, 120°/s, 180°/s, and 300°/s, and muscular endurance (50 repeated isokinetic contractions at 180°/s) were assessed. Plasma NO 3 − (BRJ: 663 ± 164 μM, PLA: 89 ± 48 μM) and nitrite ( NO 2 − ) concentrations (BRJ: 410 ± 137 nmol/L, PLA: 125 ± 36 nmol/L) were elevated following BRJ compared to PLA (both p <.001). Maximal strength of knee and elbow extensors and flexors did not differ between supplements (p >.05 for all velocities). Similarly, fatigue index of knee and elbow extension and flexion was not different between supplements (all p >.05). Acute BRJ supplementation, containing ∼12.8 mmol/L of NO 3 − , increased plasma NO 3 − and NO 2 − concentrations, but did not enhance isokinetic strength or fatigue resistance of either upper or lower extremities in international-level male gymnasts. [ABSTRACT FROM AUTHOR]

Understanding the daily energy expenditure of athletes during training is important to support recovery, adaptation, and the maintenance of performance. The aim of the current research was to assess the total daily energy expenditure (TDEE) and the acute energy expenditure (EE) of tennis training sessions during habitual training of elite tennis players. Using a cohort study design, 27 (n = 10, male; age; 22.3 ± 3.2 years and n = 17, female; age: 23.8 ± 3.5 years) elite singles tennis players were assessed for TDEE and tennis training EE. Using Actiheart activity monitors during a 2- to 5-day training period, male players were analyzed for 26 days and 33 (1.3 ± 0.5 sessions/day) tennis training sessions, and female players for 43 days and 58 (1.2 ± 0.4 sessions/day) tennis training sessions. Male TDEE (4,708 ± 583 kcal/day) was significantly higher than female (3,639 ± 305 kcal/day). Male absolute and relative tennis training EEs (10.2 ± 2.3 kcal/min and 7.9 ± 1.4 kcal·hr−1·kg−1) were significantly higher than those of females (7.6 ± 1.0 kcal/min and 6.8 ± 0.9 kcal·hr−1·kg−1). The resting metabolic rate was assessed via indirect calorimetry. The physical activity level for both groups was 2.3 AU. The TDEE of male and female players during habitual training now highlights the continual cycle of high energy demands experienced by the elite tennis player. The broad ranges of TDEE and EE reported here suggest individual assessment and nutritional planning be prioritized, with a particular focus on carbohydrate requirements. [ABSTRACT FROM AUTHOR]

In this work, the univariant two-phase coexistence line of the tetrahydrofuran (THF) hydrate is determined from 100 to 1000 bar by molecular dynamics simulations. This study is carried out by putting in contact a THF hydrate phase with a stoichiometric aqueous solution phase. Following the direct coexistence technique, the pressure is fixed, and the coexistence line is determined by analyzing if the hydrate phase grows or melts at different values of temperature. Water is described using the well-known TIP4P/Ice model. We have used two different models of THF based on the transferable parameters for phase equilibria-united atom approach (TraPPE-UA), the original (flexible) TraPPe-UA model and a rigid and planar version of it. Overall, at high pressures, small differences are observed in the results obtained by both models. However, large differences are observed in the computational efforts required by the simulations performed using both models, being the rigid and planar version much faster than the original one. The effect of the unlike dispersive interactions between the water and THF molecules is also analyzed at 250 bar using the rigid and planar THF model. In particular, we modify the Berthelot combining rule via a parameter ξO-THF that controls the unlike water–THF dispersive interactions. We analyze the effect on the dissociation temperature of the hydrate when ξO-THF is modified from 1.0 (original Berthelot combining rule) to 1.4 (modified Berthelot combining rule). We use the optimized value ξO-THF = 1.4 and the rigid THF model in a transferable way to predict the dissociation temperatures at other pressures. We find excellent agreement between computer simulation predictions and experimental data taken from the literature. [ABSTRACT FROM AUTHOR]

Clathrate hydrates are vital in energy research and environmental applications. Understanding their stability is crucial for harnessing their potential. In this work, we employ direct coexistence simulations to study finite-size effects in the determination of the three-phase equilibrium temperature (T3) for methane hydrates. Two popular water models, TIP4P/Ice and TIP4P/2005, are employed, exploring various system sizes by varying the number of molecules in the hydrate, liquid, and gas phases. The results reveal that finite-size effects play a crucial role in determining T3. The study includes nine configurations with varying system sizes, demonstrating that smaller systems, particularly those leading to stoichiometric conditions and bubble formation, may yield inaccurate T3 values. The emergence of methane bubbles within the liquid phase, observed in smaller configurations, significantly influences the behavior of the system and can lead to erroneous temperature estimations. Our findings reveal finite-size effects on the calculation of T3 by direct coexistence simulations and clarify the system size convergence for both models, shedding light on discrepancies found in the literature. The results contribute to a deeper understanding of the phase equilibrium of gas hydrates and offer valuable information for future research in this field. [ABSTRACT FROM AUTHOR]

Hydrogen clathrate hydrates are ice-like crystalline substances in which hydrogen molecules are trapped inside polyhedral cages formed by the water molecules. Small cages can host only a single H2 molecule, while each large cage can be occupied by up to four H2 molecules. Here, we present a neutron scattering study on the structure of the sII hydrogen clathrate hydrate and on the low-temperature dynamics of the hydrogen molecules trapped in its large cages, as a function of the gas content in the samples. We observe spectral features at low energy transfer (between 1 and 3 meV), and we show that they can be successfully assigned to the rattling motion of a single hydrogen molecule occupying a large water cage. These inelastic bands remarkably lose their intensity with increasing the hydrogen filling, consistently with the fact that the probability of single occupation (as opposed to multiple occupation) increases as the hydrogen content in the sample gets lower. The spectral intensity of the H2 rattling bands is studied as a function of the momentum transfer for partially emptied samples and compared with three distinct quantum models for a single H2 molecule in a large cage: (i) the exact solution of the Schrödinger equation for a well-assessed semiempirical force field, (ii) a particle trapped in a rigid sphere, and (iii) an isotropic three-dimensional harmonic oscillator. The first model provides good agreement between calculations and experimental data, while the last two only reproduce their qualitative trend. Finally, the radial wavefunctions of the three aforementioned models, as well as their potential surfaces, are presented and discussed. [ABSTRACT FROM AUTHOR]

Developing highly efficient methane (CH4) hydrate storage methods and understanding the hydrate dissociation kinetics can contribute to advancing CH4 gas storage and transport. The effects of tetrabutylammonium bromide (TBAB) (a thermodynamic promoter) addition on the kinetics of CH4 hydrate were evaluated on the microscopic scale using synchrotron x-ray computed tomography (CT) and powder x-ray diffraction. Microscopic observations showed that a 5 wt. % TBAB solution facilitated the nucleation of CH4 hydrate owing to the initial growth of TBAB semi-clathrate hydrate particles. The CH4 hydrate crystals in the CH4 + TBAB hydrate sample were sponge-like with many internal pores and exhibited slightly enhanced self-preservation compared to the pure CH4 hydrate, both in the bulk and after pulverization to a fine powder. This study demonstrates the feasibility of controlling the rate of CH4 hydrate formation and preservation by using aqueous TBAB solutions in CH4 hydrate formation. [ABSTRACT FROM AUTHOR]

The near-zero-field magnetoresistance (NZFMR) response has proven to be a useful tool for studying atomic-scale, paramagnetic defects that are relevant to the reliability of semiconductor devices. The measurement is simple to make and, in some cases, simple to interpret. In other cases, more sophisticated modeling based on the stochastic Liouville equation (SLE) is needed to access valuable information from NZFMR results. It has been shown that hyperfine and dipolar coupling interactions at atomic-scale defects affect the NZFMR line shape, but experimental parameters related to the detection method of NZFMR can also affect the nature of the response. Here, we demonstrate four distinct NZFMR detection methods in Si MOSFETs, which all access identical Si/SiO2 interface defects. In all four cases, we show that the line shape of the response is tunable based on experimental parameters alone. Using SLE-based modeling, we verify that time constants connected to physical carrier capture rates at the defect sites lead to these NZFMR line shape changes. The results demonstrate a method to extract some atomic-scale information for the purpose of defect identification. They also have broader applications to the continued development of ultra-sensitive magnetometers based on NZFMR in semiconductors. Additionally, the NZFMR effect in common Si-based devices may provide an inexpensive and accessible platform that mimics similar radical pair mechanisms that have become increasingly important in various biology fields. [ABSTRACT FROM AUTHOR]

The pervasive presence of nanoplastics (NPs) in the environment has gained increasing attention due to their accumulation in living organisms. These emerging contaminants inevitably interact with extracellular polymeric substances along respiratory or gastrointestinal tracts, and diverse organic coating on the surface of NPs, known as bio- or eco-corona, is formed. Although its impact on altering the NP properties and potential cell internalization has been extensively examined, studies on its role in NP partitioning in the cell membrane are elusive yet. In this work, molecular dynamics is used to investigate the formation of chitosan (CT) corona centered on a polyvinyl chloride (PVC) nanoparticle and the uptake of the resulting complex onto lipid membranes. Coarse-grained models compatible with the newly developed Martini 3.0 force field are implemented for the two polymers employing the atomistic properties as targets in the parameterization. The reliability of the coarse-grained polymer models is demonstrated by reproducing the structural properties of the PVC melt and of solvated CT strands, as well as by determining the conformation adopted by the latter at the NP surface. Results show that the spontaneous binding of CT chains of high and intermediate protonation degrees led to the formation of soft and hard corona that modulates the interaction of PVC core with model membranes. The structural changes of the corona adsorbed at the lipid–water interface enable a subsequent transfer of the NP to the center of the saturated lipid membranes and a complete or partial transition to a snorkel conformation depending on the hydrophilic/hydrophobic balance in the CT–PVC complex. Overall, the computational investigation of the coarse-grained model system provides implications for understanding how the eco-corona development influences the uptake and implicit toxicology of NPs. [ABSTRACT FROM AUTHOR]

The crystallization process of methane hydrates in a confined geometry resembling seabed porous silica sedimentary conditions has been studied using molecular dynamics simulations. With this objective in mind, a fully atomistic quartz silica slit pore has been designed, and the temperature stability of a methane hydrate crystalline seed in the presence of water and guest molecule methane has been analyzed. NaCl ion pairs have been added in different concentrations, simulating salinity conditions up to values higher than average oceanic conditions. The structure obtained when the hydrate crystallizes inside the pore is discussed, paying special attention to the presence of ionic doping inside the hydrate and the subsequent induced structural distortion. The shift in the hydrate stability conditions due to the increasing water salinity is discussed and compared with the case of unconfined hydrate, concluding that the influence of the confinement geometry and pore hydrophilicity produces a larger deviation in the confined hydrate phase equilibria. [ABSTRACT FROM AUTHOR]

Solar interfacial evaporation, as a novel practical freshwater production method, requires continuous research on how to improve the evaporation rates to increase water production. In this study, sets of data were obtained from molecule dynamics simulation and literature, in which the parameters included height, diameter, height–radius ratio, evaporation efficiency, and evaporation rate. Initially, the correlation between the four input parameters and the output of the evaporation rate was examined through traditional pairwise plots and Pearson correlation analysis, revealing weak correlations. Subsequently, the accuracy and generalization performance of the evaporation rate prediction models established by neural network and random forest were compared, with the latter demonstrating superior performance and reliability confirmed via random data extraction. Furthermore, the impact of different percentages (10%, 20%, and 30%) of the data on the model performance was explored, and the result indicated that the model performance is better when the test set is 20% and all the constructed model converge. Moreover, the mean absolute error and mean squared error of the evaporation rate prediction model for the three ratios were calculated to evaluate their performance. However, the relationship between the height- radius ratio and optimal evaporation rate was investigated using the enumeration method, and it was determined that the evaporation efficiency was optimal when the height–radius ratio was 6. Finally, the importance of height, diameter, height– radius ratio, and evaporation efficiency were calculated to optimize evaporator structure, increase evaporation rate, and facilitate the application of interfacial evaporation in solar desalination. [ABSTRACT FROM AUTHOR]

While SnF2 is reported as an effective additive for improving the efficiency of lead-free tin-based perovskite solar cells, the mechanism is still unclear and requires further studies. Upon incorporating SnF2 into MASnI3, SnF2 reduces the intrinsic carrier density from 1018 to 1012 cm–3 and produces a longer carrier diffusion length as confirmed by the Hall measurements. The femtosecond transient absorption spectroscopy shows that SnF2 doping enhances the hot-phonon bottleneck effect of MASnI3. The slow cooling process of hot carriers may help to reduce non-radiative recombination, increase the fluorescence lifetime, and, therefore, improve the utilization rate of carriers. Finally, lead-free low bandgap perovskite MASnI3 is utilized as a light absorbing layer in solar cells, achieving high optical current and high voltage in tin-based perovskite solar cells. The final power conversion efficiency is 10.2%, while the power conversion efficiency for the control unit is 6.69%. [ABSTRACT FROM AUTHOR]

The reactivity of heterogeneous energetic materials (HEMs) intimately depends on the underlying microstructural effects. For reactive materials, key factors include the microstructure distribution, morphology, size scale of heterogeneities, reactant mixing, and chemical kinetics of the reactants. We report the development of a mesoscale model for simulating the evolutions of the hotspot field and associated reaction processes when such materials are exposed to external excitations. The model explicitly accounts for microstructure, interdiffusion between the reactant species, advection of the species mixture, and chemical kinetics of the reaction. An Arrhenius relation is used to capture the rate of reactive heat release. The particular material analyzed is a composite of poly(vinylidene fluoride-co-trifluoroethylene) and nanoaluminum [or P(VDF-TrFE)/nAl]. The excitation leading to the initial microstructural temperature increase that kicks off the exothermic reactive processes is the dissipative heating arising from dielectric breakdown under the electric field developed through piezoelectricity and flexoelectricity of P(VDF-TrFE). As such, the model resolves both the breakdown process and the diffusion, advection, and exothermic reaction processes. The evolutions of the temperature and species distribution fields under the combined effects of breakdown and chemistry are used to predict the effects of microstructure, diffusion, and kinetics on several key metrics characterizing the reactive responses of the material. This mesoscale framework admits the quantification of uncertainties in these predicted macroscopic behavior measures due to microstructure heterogeneity fluctuations through the use of multiple, random but statistically equivalent microstructure instantiations. Although the particular hotspot inducing mechanism considered is dielectric breakdown here, the framework can be adapted to analyze reaction initiation and propagation and establish microstructure–reaction behavior relations under other types of hotspot inducing mechanisms, such as thermomechanical inelastic dissipation, frictional heating, and laser or microwave excitation. [ABSTRACT FROM AUTHOR]

Understanding the ignition and dynamic processes for the combustion of hydrate is crucial for efficient energy utilization. Through reactive force field molecular dynamics simulations, we studied the high-temperature decomposition and combustion processes of methane hydrates in a pure oxygen environment. We found that at an ignition temperature of 2800 K, hydrates decomposed from the interface to the interior, but the layer-by-layer manner was no longer strictly satisfied. At the beginning of combustion, water molecules reacted first to generate OH•, followed by methane oxidation. The combustion pathway of methane is C H 4 → CH 3 • → C H 3 O • → C H 2 O → H C • O → HCO O • → CO (C O 2 ). During the combustion process, a liquid water layer was formed between melted methane and oxygen, which hindered the reaction's progress. When there is no heat resistance, oxygen will transform into radicals such as OH• and O•, which have faster diffusion rates, allowing oxygen to conveniently cross the mass transfer barrier of the liquid water layer and participate in the combustion process. Increasing the amount of OH• may cause a surge in the reaction. On the other hand, when significant heat resistance exists, OH• is difficult to react with low-temperature hydrate components, but it can transform into O• to trigger the oxidation of methane. The H• generated has a sufficient lifetime to contact high-temperature oxygen molecules, converting oxygen into radicals that easily cross the water layer to achieve mass transfer. Therefore, finding ways to convert oxygen into various radicals is the key to solving the incomplete combustion of hydrates. Finally, the reaction pathways and microscopic reaction mechanisms of each species are proposed. [ABSTRACT FROM AUTHOR]

All-inorganic CsPbI2Br inverted perovskite solar cells (PSCs) have drawn increasing attention because of their outstanding thermal stability and compatible process with tandem cells. However, relatively low open circuit voltage (Voc) has lagged their progress far behind theoretical limits. Herein, we introduce phenylmethylammonium iodide and 4-trifluoromethyl phenylmethylammonium iodide (CFPMAI) on the surface of a CsPbI2Br perovskite film and investigate their passivation effects. It is found that CFPMAI with a –CF3 substituent significantly decreases the trap density of the perovskite film by forming interactions with the under-coordinated Pb2+ ions and effectively suppresses the non-radiative recombination in the resulting PSC. In addition, CFPMAI surface passivation facilitates the optimization of energy-level alignment at the CsPbI2Br perovskite/[6,6]-phenyl C61 butyric acid methyl ester interface, resulting in improved charge extraction from the perovskite to the charge transport layer. Consequently, the optimized inverted CsPbI2Br device exhibits a markedly improved champion efficiency of 14.43% with a Voc of 1.12 V, a Jsc of 16.31 mA/cm2, and a fill factor of 79.02%, compared to the 10.92% (Voc of 0.95 V) efficiency of the control device. This study confirms the importance of substituent groups on surface passivation molecules for effective passivation of defects and optimization of energy levels, particularly for Voc improvement. [ABSTRACT FROM AUTHOR]

This study reviews available van der Waals- and Platteeuw-based hydrate models considering multiple occupancy of cavities. Small guest molecules, such as hydrogen and nitrogen, are known to occupy lattice cavities multiple times. This phenomenon has a significant impact on hydrate stability and thermodynamic properties of the hydrate phase. The objective of this work is to provide a comprehensive overview and required correlations for the implementation of a computationally sufficient cluster model that considers up to five guest molecules per cavity. Two methodologies for cluster size estimation are evaluated by existing nitrogen hydrate models showing accurate results for phase equilibria calculations. Furthermore, a preliminary hydrogen hydrate model is introduced and compared with the results of other theoretical studies, indicating that double occupancy of small sII cavities is improbable and four-molecule clusters are predominant in large sII cavities for pressures above 300 MPa. This work lays the foundation for further exploration and optimization of hydrate-based technologies for small guest molecules, e.g., storage and transportation, emphasizing their role in the future landscape of sustainable energy solutions. [ABSTRACT FROM AUTHOR]

Before hydrates can be widely used in industry, we should better understand the problematic issues of hydrate nucleation, particularly its stochastic nature. Here, we report on measurements of the nucleation probability of mixed-gas hydrates in which the guest molecules are a mixture of methane and propane. For the pure cases, at a supersaturation near 1.0, we had previously measured an induction time for the methane hydrate of about 1 h, whereas for the propane hydrate, it was over one day. Using the same experimental setup, we examine here the nucleation probability for a mixture of 90% methane and 10% propane as the guest gas for a range of supersaturations. For the experiments, the temperature was 274 ± 0.5 K and the stirring rate was about 300 rpm. The experiments were repeated at least ten times under the same condition, exchanging the sample water every time. We define the nucleation probability at a given time as the fraction of trials that nucleated by that time and then determine the nucleation probability distribution. The resulting nucleation frequency is found to have a power-law relation to supersaturation. Then, we examine how the nucleation frequency is affected by the existence of ultrafine bubbles in the initial water. We find that the ultrafine bubbles increase the nucleation frequency but much less than that of typical changes in supersaturation. [ABSTRACT FROM AUTHOR]

To obtain high-performance THz-wave-emitting devices made of single crystals of Bi 2 Sr 2 CaCu 2 O 8 + δ (Bi2212), a high-temperature superconductor, an understanding of the device characteristics based on crystal characteristics can be a key issue because, in principle, the electrical properties of the intrinsic Josephson junctions (IJJs) constructed in Bi2212 crystals highly depend on crystal conditions, such as carrier concentration, crystal homogeneities, and crystal defects. To evaluate the tendencies of the device characteristics associated with crystal characteristics, we prepared Bi2212 crystals with different Bi/Sr ratios (x = 0.05 , 0.15, and 0.25) and δ values (annealed under N 2 or O 2 gas flow conditions). The unit cell parameter c decreased as the Bi/Sr ratio or δ increased. For the same annealing conditions under N 2 gas flow, the superconducting transition temperature as well as the size of the hysteresis loop of the current–voltage characteristics and emission characteristics were significantly suppressed for the sample with x = 0.25 compared with the corresponding values for the samples with x = 0.05 and 0.15. The experimental results clearly indicate that parameters, such as the Bi/Sr ratio and annealing conditions, are crucial factors in determining the electrical characteristics of a device. This information can be a useful guide for the preparation of crystals for IJJ THz-wave devices that can be fine-tuned according to the desired device characteristics. [ABSTRACT FROM AUTHOR]

Clathrate hydrates continue to be the focus of active research efforts due to their use in energy resources, transportation, and storage-related applications. Therefore, it is crucial to define their essential characteristics from a molecular standpoint. Understanding molecular structure in particular is crucial because it aids in understanding the mechanisms that lead to the formation or dissociation of clathrate hydrates. In the past, a wide variety of order parameters have been employed to classify and evaluate hydrate structures. An alternative approach to inventing bespoke order parameters is to apply machine learning techniques to automatically generate effective order parameters. In earlier work, we suggested a method for automatically designing novel parameters for ice and liquid water structures with Graph Neural Networks (GNNs). In this work, we use a GNN to implement our method, which can independently produce feature representations of the molecular structures. By using the TeaNet-type model in our method, it is possible to directly learn the molecular geometry and topology. This enables us to build novel parameters without prior knowledge of suitable order parameters for the structure type, discover structural differences, and classify molecular structures with high accuracy. We use this approach to classify the structures of clathrate hydrate structures: sI, sII, and sH. This innovative approach provides an appealing and highly accurate replacement for the traditional order parameters. Furthermore, our method makes clear the process of automatically designing a universal parameter for liquid water, ice, and clathrate hydrate to analyze their structures and phases. [ABSTRACT FROM AUTHOR]

The enigmatic mechanism underlying unconventional high-temperature superconductivity, especially the role of lattice dynamics, has remained a subject of debate. Theoretical insights have long been hindered due to the lack of an accurate first-principles description of the lattice dynamics of cuprates. Recently, using the r2SCAN meta-generalized gradient approximation (meta-GGA) functional, we have been able to achieve accurate phonon spectra of an insulating cuprate YBa2Cu3O6 and discover significant magnetoelastic coupling in experimentally interesting Cu–O bond stretching optical modes [Ning et al., Phys. Rev. B 107, 045126 (2023)]. We extend this work by comparing Perdew–Burke–Ernzerhof and r2SCAN performances with corrections from the on-site Hubbard U and the D4 van der Waals (vdW) methods, aiming at further understanding on both the materials science side and the density functional side. We demonstrate the importance of vdW and self-interaction corrections for accurate first-principles YBa2Cu3O6 lattice dynamics. Since r2SCAN by itself partially accounts for these effects, the good performance of r2SCAN is now more fully explained. In addition, the performances of the Tao–Mo series of meta-GGAs, which are constructed in a different way from the strongly constrained and appropriately normed (SCAN) meta-GGA and its revised version r2SCAN, are also compared and discussed. [ABSTRACT FROM AUTHOR]

The band-anticrossing (BAC) model provides the basis for the self-consistent Green's function method that we have previously developed to calculate the density of states of GaN x As 1 − x dilute nitride alloys. In this paper, we extend this Green's function method to include the complex energy states and to find the poles of the Green's function, thereby allowing one to calculate the dispersion relation, group velocity, and the carrier decay rate in disordered dilute nitride alloys. Two different models of the N states have been studied to investigate the band structure of these materials: (1) the conventional two-band BAC model, which assumes that all N states are located at the same energy, and (2) a model which includes N states distributed over a range of energies, as expected in actual dilute nitride samples. Our results for the second model show a much shorter carrier mean-free path, and lower carrier mobility for GaN x As 1 − x , with the magnitude of the calculated mobility in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

In this study, we observed natural methane (CH4) hydrate sediments, which are a type of unconventional natural gas resources, using x-ray computed tomography (CT). Because CH4 hydrates are formed by hydrogen bonding of water molecules with CH4, material decomposition becomes challenging when CH4 hydrates coexist with liquid or solid water in natural sediments. Tri-contrast (absorption, refraction, and scattering) imaging was performed via diffraction enhanced x-ray CT optics using monochromatic synchrotron x rays. The quantitative characterization of the contrast changes successfully enabled the decomposition of CH4 hydrates coexisting with frozen seawater (ice) in natural sediments obtained from the Okhotsk Sea. This study reveals complementary structural information about the microtexture and spatial relation among CH4 hydrates, ice, and pores by utilizing the distinct physical properties of x rays when passing through the materials. These results highlight the exceptional capabilities of high-resolution multicontrast x-ray tomography in materials science and geoscience applications. [ABSTRACT FROM AUTHOR]

Precise and reproducible current generation is the key to realizing quantum current standards in metrology. A promising candidate is a tunable-barrier single-charge pump, which can accurately transfer single charges one by one with an error rate below the ppm level. Although several measurements have shown such levels of accuracy, it is necessary to further pursue the possibility of high-precision operation toward reproducible generation of the pumping current in many devices. Here, we investigated silicon single-hole pumps, which may have the potential to outperform single-electron pumps because of the heavy effective mass of holes. Measurements on the temperature dependence of the current generated by the single-hole pump revealed that the tunnel barrier had high energy selectivity, which is a critical parameter for high-accuracy operation. In addition, we applied the dynamic gate-compensation technique to the single-hole pump and confirmed that it yielded a further performance improvement. Finally, we demonstrated gigahertz operation of a single-hole pump in which the estimated lower bound of the pump error rate was around 0.01 ppm. These results imply that single-hole pumps in silicon are capable of high-accuracy, high-speed, and stable single-charge pumping in metrological and quantum-device applications. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the effect of exercise intensity on the proportion and rate of carbohydrate oxidation and glucoregulatory hormone responses during recovery from exercise. Six physically active participants completed 1 hr of low-intensity (LI; 50% lactate threshold) or moderate-intensity (MI; 100% lactate threshold) exercise on separate days following a randomized counterbalanced design. During exercise and for 6 hr of recovery, samples of expired air were collected to determine oxygen consumption, respiratory exchange ratio, energy expenditure, and substrate oxidation rates. Blood samples were also collected to measure glucoregulatory hormones (catecholamines, GH) and metabolites (glucose, free fatty acids, lactate, pH, and bicarbonate). During exercise, respiratory exchange ratio, energy expenditure, and the proportion and rate of carbohydrate (CHO) oxidation were higher during MI compared with LI. However, during recovery from MI, respiratory exchange ratio and the proportion and rate of CHO oxidation were lower than preexercise levels and corresponding LI. During exercise and early recovery, catecholamines and growth hormone were higher in MI than LI, and there was a trend for higher levels of free fatty acids in the early recovery from MI compared with LI. In summary, CHO oxidation during exercise increases with exercise intensity but there is a preference for CHO sparing (and fat oxidation) during recovery from MI exercise compared with LI exercise. This exercise intensity-dependent shift in substrate oxidation during recovery is explained, in part, by the pattern of change of key glucoregulatory hormones including catecholamines and growth hormone and plasma fatty acid concentrations. [ABSTRACT FROM AUTHOR]

Natural gas hydrates, mainly existing in permafrost and on the seabed, are expected to be a new energy source with great potential. The exploitation technology of natural gas hydrates is one of the main focuses of hydrate-related studies. In this study, a large-size liquid aqueous solution wrapping a methane hydrate system was established and molecular dynamics simulations were used to investigate the phase equilibrium conditions of methane hydrate at different methane concentrations and interfacial geometries. It is found that the methane concentration of a solution significantly affects the phase equilibrium of methane hydrates. Different methane concentrations at the same temperature and pressure can lead to hydrate formation or decomposition. At the same temperature and pressure, in a system reaching equilibrium, the size of spherical hydrate clusters is coupled to the solution concentration, which is proportional to the Laplace pressure at the solid–liquid interface. Lower solution concentrations reduce the phase equilibrium temperature of methane hydrates at the same pressure; as the concentration increases, the phase equilibrium temperature gradually approaches the actual phase equilibrium temperature. In addition, the interfacial geometry of hydrates affects the thermodynamic stability of hydrates. The spherical hydrate particles have the highest stability for the same volume. Through this study, we provide a stronger foundation to understand the principles driving hydrate formation/dissociation relevant to the exploitation of methane hydrates. [ABSTRACT FROM AUTHOR]

As an optimal one-dimensional reaction coordinate, the committor function not only describes the probability of a trajectory initiated at a phase space point first reaching the product state before reaching the reactant state but also preserves the kinetics when utilized to run a reduced dynamics model. However, calculating the committor function in high-dimensional systems poses significant challenges. In this paper, within the framework of milestoning, exact expressions for committor functions at two levels of coarse graining are given, including committor functions of phase space point to point (CFPP) and milestone to milestone (CFMM). When combined with transition kernels obtained from trajectory analysis, these expressions can be utilized to accurately and efficiently compute the committor functions. Furthermore, based on the calculated committor functions, an adaptive algorithm is developed to gradually refine the transition state region. Finally, two model examples are employed to assess the accuracy of these different formulations of committor functions. [ABSTRACT FROM AUTHOR]

In this work, we determine the dissociation line of the nitrogen (N2) hydrate by computer simulation using the TIP4P/Ice model for water and the TraPPE force field for N2. We use the solubility method proposed recently by some of us to evaluate the dissociation temperature of the hydrate at different pressures, from 500 to 1500 bar. Particularly, we calculate the solubility of N2 in the aqueous solution when it is in contact with a N2-rich liquid phase and when in contact with the hydrate phase via planar interfaces as functions of temperature. Since the solubility of N2 decreases with temperature in the first case and increases with temperature in the second case, both curves intersect at a certain temperature that determines the dissociation temperature at a given pressure. We find a good agreement between the predictions obtained in this work and the experimental data taken from the literature in the range of pressures considered in this work. From our knowledge of the solubility curves of N2 in the aqueous solution, we also determine the driving force for nucleation of the hydrate, as a function of temperature, at different pressures. In particular, we use two different thermodynamic routes to evaluate the change in chemical potential for hydrate formation. Although the driving force for nucleation slightly decreases (in absolute value) when the pressure is increased, our results indicate that the effect of pressure can be considered negligible in the range of pressures studied in this work. To the best of our knowledge, this is the first time the driving force for nucleation of a hydrate that exhibits crystallographic structure sII, along its dissociation line, is studied from computer simulation. [ABSTRACT FROM AUTHOR]

The importance of nitrate and ammonium salts both in the environment and in biological processes cannot be questioned. In this work, using the TIP4P/2005 water model, aqueous solutions of nitrate and ammonium electrolytes are parametrized using scaled charges while keeping a rigid structure and nonpolarizable charge distributions. The models are optimized by systematically testing a set of properties for twelve electrolytes—eight nitrate and four ammonium salts—thus, enlarging the number of potential chemical species encompassed within the Madrid-2019 force field for ions. The capacity of the force field for predicting densities, ion–ion and ion–solvent structures, and transport properties of the solutions comprised by the trial batch of salts was tested and discussed. Both the dependence of the densities with the salt concentration and the solution structure were nicely reproduced by the models in the whole concentration range without any trace of precipitating events and with improved accuracy in comparison with recently reported models, while the agreement of the simulated transport properties with experimental data ranges from good to reasonable, depending on the ion/counterion pair. These scaled charge models might be considered as force fields embodying a reasonable compromise between exactness and general applicability and also as an important step in the development of accurate models for polyatomic ions. [ABSTRACT FROM AUTHOR]

Many experimental and theoretical studies on CH4–CO2 hydrates have been performed aiming at the extraction of CH4 as a relatively clean energy resource and concurrent sequestration of CO2. However, vague or insufficient characterization of the environmental conditions prevents us from a comprehensive understanding of even equilibrium properties of CH4–CO2 hydrates for this substitution. We propose possible reaction schemes for the substitution, paying special attention to the coexisting phases, the aqueous and/or the fluid, where CO2 is supplied from and CH4 is transferred to. We address the two schemes for the substitution operating in three-phase and two-phase coexistence. Advantages and efficiencies of extracting CH4 in the individual scheme are estimated from the chemical potentials of all the components in all the phases involved in the substitution on the basis of a statistical mechanical theory developed recently. It is found that although substitution is feasible in the three-phase coexistence, its working window in temperature–pressure space is much narrower compared to the two-phase coexistence condition. Despite that the substitution normally generates only a small amount of heat, a large endothermic substitution is suggested in the medium pressure range, caused by the vaporization of liquid CO2 due to mixing with a small amount of the released CH4. This study provides the first theoretical framework toward the practical use of hydrates replacing CH4 with CO2 and serves as a basis for quantitative planning. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations have been widely used in exploring the nucleation behavior of many systems, including gas hydrates. Gas hydrates are ice-like solids in which gas molecules are trapped in water cages. During hydrate formation, a considerable amount of heat is released, and previous work has reported that the choice of temperature control scheme may affect the behavior of hydrate formation. The origins of this effect have remained an open question. To address this question, extensive NVE simulations and thermostatted (NPT and NVT) simulations with different temperature coupling strengths have been performed and compared for systems where a water nanodroplet is immersed in a H2S liquid. Detailed analysis of the hydrate structures and their mechanisms of formation has been carried out. Slower nucleation rates in NVE simulations in comparison to NPT simulations have been observed in agreement with previous studies. Probability distributions for various temperature measures along with their spatial distributions have been examined. Interestingly, a comparison of these temperature distributions reveals a small yet noticeable difference in the widths of the distributions for water. The somewhat reduced fluctuations in the temperature for the water species in the NVE simulations appear to be responsible for reducing the hydrate nucleation rate. We further conjecture that the NVE-impeded nucleation rate may be the result of the finite size of the surroundings (here the liquid H2S portion of the system). Additionally, a local spatial temperature gradient arising from the heat released during hydrate formation could not be detected. [ABSTRACT FROM AUTHOR]

The three body fragmentation of methane dication has been studied using the technique of cold target recoil ion momentum spectroscopy. The process is initiated by impact of energetic Ar9+ ions on neutral methane and the data is subsequently collected in coincidence with Ar8+ projectile. By analysing the dissociation channels leading to (H + H+ + CH 2 + ) and (H + H 2 + + CH+) fragments, it is concluded that these fragments are formed in a sequential manner via formation of molecular intermediates CH 3 + and CH 2 + respectively. It is shown that these molecular intermediates carry a few eVs as their internal energies, part of which is released when they emit an H-atom with the open possibility that the final detected fragments may still be internally excited. This was accomplished by analysing the two-steps of the sequential process in their own native frames. For a molecular system having three-dimensional structure, our results prove to be an ideal example to highlight the importance of using native frames for correct interpretation of the obtained results. Our results indicate that the dissociation of methane dication can be a major source of production of H-atoms in addition to H+ fragments with the probability of the two being of similar order. [ABSTRACT FROM AUTHOR]

Charge diffusion from an ion track and its collection by a biased contact in a semiconductor domain is modeled and analyzed within the framework of the so-called diffusion–collection approach. We successively examine the case of charge diffusion from a point source and from a linear distribution, introducing and discussing the concept of collection velocity at the point where the collection current is evaluated. Analytical formulations of the collected charge, collection current, and collection velocity are developed. Implications for the calculation of the soft error rate in complementary metal-oxide-semiconductor circuits exposed to ionizing particles are derived. Finally, our model provides new insights into the correct definition of the charge collection velocity in collection–diffusion models. [ABSTRACT FROM AUTHOR]

Resting metabolic rate (RMR) is an important component of total daily energy expenditure; however, it is currently not understood how it varies across a typical competitive match week in professional soccer players. For the first time, we aimed to assess RMR throughout an in-season competitive week in professional soccer players. Additionally, we aimed to assess energy and carbohydrate intake across the same week. Twenty-four professional soccer players from an English Premier League club (age: 18 ± 1.6 years) completed the study. RMR was assessed each morning of a typical competitive match week (match day [MD] −3, −2, −1, +1, +2, and + 3), and dietary intake (including MD) was assessed daily via the remote food photography method and 24-hr recall. Daily training load was quantified using Global Positioning System, daily muscle soreness ratings were recorded, and body composition was assessed via dual-energy X-ray absorptiometry. There was a significant (p =.0004) increase in mean RMR of ∼261 kcal/day on MD + 1, compared with MD − 1. Additionally, volume of oxygen consumed significantly increased at MD + 1 (p =.0002) versus MD − 1. There were no significant differences in daily energy or carbohydrate intake across the competitive week (p >.05), with inadequate carbohydrate intakes on MD − 1 (∼3.9 g/kg body mass), MD (∼4.2 g/kg body mass), and MD + 1 (∼3.6 g/kg body mass) in relation to current recommendations. We report, for the first time, that RMR is significantly increased following a competitive match in professional soccer players. In addition, we confirm previous findings to reinforce that players exhibit inadequate nutrition periodization practices, which may impair physical performance and recovery. [ABSTRACT FROM AUTHOR]

1-propanol/water mixtures over the whole composition range (0 < XV ≤ 1; XV is the 1-propanol volume fraction) are shown to be structurally and dynamically heterogeneous. By combining structural (x-ray diffraction), thermodynamic (differential scanning calorimetry) and dynamical probes (dielectric spectroscopy) we construct the pertinent phase diagram. It consists of liquid 1-propanol, liquid water, hexagonal ice and different hydrates, the latter sharing the same lattice. The phase diagram can be discussed in terms of four regimes, all having in common a droplet arrangement of the minority component. When water droplets are strongly confined by 1-propanol (regime I, 0.92 < XV ≤ 1; "soft" confinement), water is unable to crystallize. It has dynamics reminiscent to the ultra-viscous water phase known as high-density liquid (HDL). When water droplets are moderately confined (regime II, 0.75 < XV ≤ 0.92) water can crystallize via homogeneous nucleation. Strikingly, the homogeneous nucleation temperature is at 205 K, well within "no-man's land." The result is in line with earlier reports that soft confinement is the key to enter into the "no-man's land". When 1-propanol is the minority component (regimes III and IV), the structure and the dynamics are dominated by the 1-propanol/water interface with the formation of hydrates. The corresponding dynamical features suggest a link between hydrate formation and the two metastable phases of ultra-viscous water, HDL and low-density liquid. [ABSTRACT FROM AUTHOR]

The Cattaneo–Vernotte model has been widely studied to take momentum relaxation into account in transport equations. Yet, the effect of reactions on the Cattaneo–Vernotte model has not been fully elucidated. At present, it is unclear how the current density associated with reactions can be expressed in the Cattaneo–Vernotte model. Herein, we derive a modified Cattaneo–Vernotte model by applying the projection operator method to the Fokker–Planck–Kramers equation with a reaction sink. The same modified Cattaneo–Vernotte model can be derived by a Grad procedure. We show that the inertial effect influences the reaction rate coefficient differently depending on whether the intrinsic reaction rate constant in the reaction sink term depends on the solute relative velocity or not. The momentum relaxation effect can be expressed by a modified Smoluchowski equation including a memory kernel using the Cattaneo–Vernotte model. When the intrinsic reaction rate constant is independent of the reactant velocity and is localized, the modified Smoluchowski equation should be generalized to include a reaction term without a memory kernel. When the intrinsic reaction rate constant depends on the relative velocity of reactants, an additional reaction term with a memory kernel is required because of competition between the current density associated with the reaction and the diffusive flux during momentum relaxation. The competition effect influences even the long-time reaction rate coefficient. [ABSTRACT FROM AUTHOR]