Transient Relaxation Research Articles

Full-f gyrokinetic simulations of hydrogen isotope mixing in tokamak plasmas

Hydrogen isotope mixing phenomena in tokamak plasmas are analyzed using global full-f gyrokinetic simulations. Model plasma parameters are chosen based on hydrogen isotope pellet experiments on JET, in which fast hydrogen isotope mixing in the timescale of the energy confinement time τE occurred after injecting deuterium (D) pellets into hydrogen (H) plasmas. Two numerical experiments are conducted using plasma profiles before and after the pellet injection. In both cases, turbulent fluctuations in the plasma core are characterized by ion temperature gradient driven turbulence. In the former case, the density profile of bulk H ions is kept in a quasi-steady state, and the particle confinement time of bulk H ions τH is an order of magnitude longer than τE. In the latter case, the density profiles of bulk H ions and pellet D ions show transient relaxation in the timescale of τE, and both τH and the timescale of particle pinch τD become comparable to τE, indicating the fast hydrogen isotope mixing. In the toroidal angular momentum balance, it is found that the enhanced ion particle transport leading to the fast hydrogen isotope mixing is driven by the toroidal field stress.

Empirical evidence for multi-decadal transients affecting geodetic velocity fields and derived seismicity forecasts in Italy

This study critically examines the use of geodetic strain rates for forecasting long-term earthquake rates in a slow-deforming region such as Italy, challenging the prevailing assumption of their temporal stationarity in interseismic stages for seismic hazard analyses. Typically, earthquake-rate models derived from geodesy assume stationary interseismic loading rates, with stress rates in the upper crust proportional to geodetic strain rates, leading to earthquake rates directly proportional to these strain rate tensors. However, our analysis unveils a pronounced correlation between the epicenters of earthquakes that occurred in the past 60–120 years and areas forecasted for higher future earthquake rates based on geodetic strain rates. This correlation appears weak and scattered in analyses of even older earthquakes. To corroborate our findings, we select the 2009 L’Aquila earthquake (mw = 6.3) to prove that its apparently marginal viscoelastic relaxation significantly alters the time series of adjacent benchmarks for the following ~ 30–60 years, explaining the high correlation between recent earthquakes and strain rate peaks. Our findings require a methodological shift in interpreting geodetic data for earthquake forecasting, emphasizing the two-component (plate-tectonics-driven stationary long-term deformation, and decadal transient viscoelastic relaxation after an earthquake) nature of crustal stress accumulation recorded in geodetic data. We underscore the potential of geodesy-derived forecasts to provide deeper insights into seismic hazards, stressing the importance of acknowledging the long-term temporal variability inherent in geodetic measurements.

Regurgitation, eructation, and supragastric belch: retrograde esophageal motility, disorders, and treatment.

This review describes pathologic conditions of retrograde flow into the esophagus along with recent therapeutic advances and treatment options. The esophagus facilitates anterograde and retrograde movement of contents, the latter of which is mediated by transient lower esophageal sphincter relaxations (TLESRs). Gastroesophageal reflux disease (GERD) often includes esophageal-specific symptoms such as heartburn or regurgitation. Volume regurgitation responds less frequently to acid suppression with proton pump inhibitors (PPIs) than heartburn, given its relationship with incompetence of the esophagogastric junction (EGJ) and increased frequency of TLESRs. Therefore, although the refluxate pH can be altered with PPIs, the frequency of reflux episodes is generally not reduced and surgical and endoscopic treatments may be favored. Other instances of abnormal retrograde esophageal flow respond better to medical therapy, or lifestyle interventions. Compared to gastric belching because of increased stomach distension, supragastric belching is caused by intake of air from pharynx into the esophagus followed by rapid expulsion of air. These conditions can be distinguished on esophageal tests such as high-resolution manometry and are likely to respond to behavioral modifications. Retrograde flow into the esophagus can be a normal occurrence, but diagnostic testing to distinguish causes can guide appropriate intervention.

Gastroesophageal Reflux Disease: New Insights and Treatment Approaches.

Gastroesophageal reflux disease (GERD) remains a significant global health concern, with increasing prevalence and a substantial impact on quality of life. This narrative review explores recent advances in our understanding of GERD pathophysiology, diagnosis, and management. The complex interplay of factors contributing to GERD, including lower esophageal sphincter dysfunction, transient sphincter relaxations, and esophageal motility disorders, is discussed. Emerging diagnostic techniques, such as high-resolution manometry and impedance-pH monitoring, have enhanced our ability to accurately identify and characterize GERD. The review highlights the evolving landscape of GERD treatment, from conventional approaches like lifestyle modifications and proton pump inhibitors to novel strategies including potassium-competitive acid blockers, endoscopic therapies, and minimally invasive surgical techniques. The potential role of the microbiome in GERD pathogenesis and as a therapeutic target is examined. The concept of personalized medicine in GERD management is explored, considering genetic factors, biomarkers, and individual patient profiles. Complications of GERD, including erosive esophagitis, Barrett's esophagus, and esophageal adenocarcinoma, are reviewed, emphasizing the importance of early detection and appropriate management. The economic burden and impact on the quality of due to GERD are also addressed. This comprehensive review underscores the multifaceted nature of GERD and the need for a personalized, multidisciplinary approach to its management. It highlights ongoing research efforts and emerging therapies that promise to improve outcomes for GERD patients, while also identifying areas requiring further investigation to optimize diagnosis and treatment strategies.

Accelerated Decay due to Operator Spreading in Bulk-Dissipated Quantum Systems.

Markovian open many-body quantum systems display complicated relaxation dynamics. The spectral gap of the Liouvillian characterizes the asymptotic decay rate towards the stationary state, but it has recently been pointed out that the spectral gap does not necessarily determine the overall relaxation time. Our understanding on the relaxation process before the asymptotically long-time regime is still limited. We here present a collective relaxation dynamics of autocorrelation functions in the stationary state. As a key quantity in the analysis, we introduce the instantaneous decay rate, which characterizes the transient relaxation and converges to the conventional asymptotic decay rate in the long-time limit. Our theory predicts that a bulk-dissipated system generically shows an accelerated decay before the asymptotic regime due to the scrambling of quantum information associated with the operator spreading.

Transient Creep in Olivine at Shallow Mantle Pressures: Implications for Time‐Dependent Rheology in Post‐Seismic Deformation

AbstractTransient creep in olivine aggregates has been studied by stress‐relaxation experiments at pressures of 1.7–3.6 GPa and at temperatures of ≤1020 K in a DIA apparatus. Time‐dependent deformation of olivine at small strains (<0.07) was monitored with an ∼1 s of time resolution using a combination of a high‐flux synchrotron X‐ray and a cadmium telluride imaging detector. The observed deformation was found to follow the Burgers creep function with the transient relaxation time ranging from 50 (±20) to 1,880 (±750) s. We show that the Burgers creep for olivine cannot account for the low viscosities in early post‐seismic deformation reported by geodetic observations (<7 × 1017 Pa·s). In contrast, the time‐dependent increase in viscosity observed in late post‐seismic deformation (1018−1020 Pa·s) is explained by the Burgers rheology, suggesting that the combination of the Burgers model and another model is needed for the interpretation of post‐seismic deformation.

The Impact of Chronic Cannabis Use on Esophageal Motility in Patients Referred for Esophageal Manometry.

Tetrahydrocannabinol, the main psychoactive compound in cannabis, binds with high affinity to the cannabinoid 1 receptor. Small randomized controlled studies using conventional manometry have shown that the cannabinoid 1 receptor can modulate esophageal function, namely transient lower esophageal sphincter relaxation frequency and lower esophageal sphincter tone. The effect of cannabinoids on esophageal motility in patients referred for esophageal manometry has not been fully elucidated using high-resolution esophageal manometry (HREM). We aimed to characterize the clinical effect of chronic cannabis use on esophageal motility utilizing HREM. Patients who underwent HREM from 2009 to 2019 were identified at 4 academic medical centers. The study group consisted of patients with a noted history of chronic cannabis use, a diagnosis of cannabis-related disorder, or a positive urine toxicology screen. Age and gender-matched patients with no history of cannabis use were selected to form the control group. Data on HREM metrics based on the Chicago classification V3, and the prevalence of esophageal motility disorders were compared. Confounding effects of BMI and medications on esophageal motility were adjusted for. Chronic cannabis use was found to be an independent negative predictor of weak swallows (β=-8.02, P =0.0109), but not a predictor of failed swallows ( P =0.6890). The prevalence of ineffective esophageal motility was significantly lower in chronic cannabis users compared with nonusers (OR=0.44, 95% CI 0.19-0.93, P =0.0384). There was no significant difference in the prevalence of other esophageal motility disorders between the 2 cohorts. In patients with dysphagia as their primary indication for HREM, chronic cannabis use was found to be independently associated with increased median integrated relaxation pressure (β=6.638, P =0.0153) and increased mean lower esophageal sphincter resting pressure (β=10.38, P =0.0084). Chronic cannabis use is associated with decreased weak swallows and reduced prevalence of ineffective esophageal motility in patients referred for esophageal manometry. In patients referred for dysphagia, chronic cannabis use is associated with increased integrated relaxation pressure and lower esophageal sphincter resting pressure, though not to levels above the normal range.

Anomalous Transport of Small Polarons Arises from Transient Lattice Relaxation or Immovable Boundaries.

Elucidating transport mechanisms is crucial for advancing material design, yet state-of-the-art theory is restricted to exact simulations of small lattices with severe finite-size effects or approximate ones that assume the nature of transport. We leverage algorithmic advances to tame finite-size effects and exactly simulate small polaron formation and transport in the Holstein model. We further analyze the applicability of the ubiquitously used equilibrium-based Green-Kubo relations and nonequilibrium methods to predict charge mobility. We find that these methods can converge to different values and track this disparity to finite-size dependence and the sensitivity of Green-Kubo relations to the system's topology. Contrary to standard perturbative calculations, our results demonstrate that small polarons exhibit anomalous transport that manifests transiently due to nonequilibrium lattice relaxation or permanently as a signature of immovable boundaries. These findings can offer new interpretations of transport experiments on polymers and transition metal oxides.

Screw dislocation dynamics in confinement-induced layering of Yukawa liquids after quenching

Screw dislocation filaments (SDFs) with undefined phases and winded around by helical isophase fronts are fundamental topological defects, which can be used for characterizing the disorder of layered solids and unstable traveling waves. Here, we numerically demonstrate the observation of fluctuating SDFs in the transient relaxation of confinement-induced layering of Yukawa liquids after quenching. We classify the generic dynamical behaviors of screw dislocations (SDs) and unravel their topological origins, which are elusive fundamental issues for general layered systems. It is found that the spatiotemporal growth and decay of layer undulation instability causing sequential rupture and reconnection of a stack of layers are the keys for the formation of SD loops or strings of connected SDFs with alternating helicities, and their spatiotemporal fluctuations. The breaking and reconnection of two approaching SDFs with opposite or the same helicities can form two new separated SDFs. This causes an SD loop to be shed from or merged with another SD loop. The total number of SDs decreases and levels off with increasing time from quenching. Published by the American Physical Society 2024

Esophageal motor abnormalities in gastroesophageal reflux disorders.

Gastroesophageal reflux disease (GERD), a prevalent condition with multifactorial pathogenesis, involves esophageal motor dysmotility as a key contributing factor to its development. When suspected GERD patients have an inadequate response to proton-pump inhibitor (PPI) therapy and normal upper endoscopy results, high-resolution manometry (HRM) is utilized to rule out alternative diagnosis such as achalasia spectrum disorders, rumination, or supragastric belching. At present, HRM continues to provide supportive evidence for diagnosing GERD and determining the appropriate treatment. This review focuses on the existing understanding of the connection between esophageal motor findings and the pathogenesis of GERD, along with the significance of esophageal HRM in managing GERD patients. The International GERD Consensus Working Group introduced a three-step method, assessing the esophagogastric junction (EGJ), esophageal body motility, and contraction reserve with multiple rapid swallow (MRS) maneuvers. Crucial HRM abnormalities in GERD include frequent transient lower esophageal sphincter relaxations, disrupted EGJ, and esophageal body hypomotility. Emerging HRM metrics like EGJ-contractile integral and innovative provocative maneuver like straight leg raise have the potential to enhance our understanding of factors contributing to GERD, thereby increasing the value of HRM performed in patients who experience symptoms suspected of GERD.

Esofagitis, esofagitis por reflujo y enfermedad por reflujo gastroesofágico

Esophagitis is defined as the presence of inflammatory disease in different layers of the esophagus. It is a common disease that has a wide variety of causes, with reflux esophagitis being the most frequent. Gastroesophageal reflux disease (GERD) is defined as the onset of symptoms or lesions secondary to sustained pathological reflux. The main triggering mechanism is transient relaxation of the lower esophageal sphincter. Clinically, it can give rise to typical manifestations (pyrosis and regurgitation) as well as extraesophageal manifestations. It is a chronic disease with a generally benign course, although it can lead to complications such as esophagitis or Barrett's esophagus and risk of progression to esophageal adenocarcinoma. In clinical practice, GERD is diagnosed empirically and treated based on the symptoms recorded by the clinician, although performing an upper gastrointestinal endoscopy and other additional tests are sometimes required for diagnosis and to rule out complications. Treatment is based on a combination of hygienic-dietary measures and medical treatment based on proton pump inhibitors. On some occasions, resorting to surgical treatment may be required.

Three-dimensional reconstruction and optimization of porous fuel electrode in reversible solid oxide cells based on the Lattice Boltzmann method

A reversible solid oxide cell can work as a fuel cell (FC) or an electrolyzer cell (EC) with superior efficiency in a single device, which has the potential to become the core of energy conversion and storage. Since the redox reaction occurs at the three phase boundary in the porous electrode, the microstructure of which has a significant effect on the dynamic performance of the cell. Current research on porous electrodes mainly focuses on parametric and steady-state analysis but lacks studies on dynamic performance. In this study, we investigate the mass transfer process and dynamic performance of rSOC fuel electrodes by 3D reconstruction and artificial generation combined with a two-dimensional lattice Boltzmann method. The results show that the effective diffusion coefficients and cell performance of the XCT cross-sectional and random sphere method are much higher than those of the Gaussian filter and fiber rod structure. The change in H2 concentration is larger for switching from FC to EC compared to switching from EC to FC, but the transient steady-state difference and relaxation time of the voltage is smaller. These results can be used as a reference for the design and optimization of the porous electrodes in reversible solid oxide cells.

Improving the Resolution of MPM Recovered Relaxometry Parameters with Proper Time Domain Sampling

The matrix pencil method (MPM) is a powerful tool for processing transient nuclear magnetic resonance (NMR) relaxation signals with promising applications to increasingly complex problems. In the absence of signal noise, the eigenvalues recovered from an MPM treatment of transient relaxometry data reduce to relaxation coefficients that can be used to calculate relaxation time constants for known sampling time ∆t. The MPM eigenvalue and relaxation coefficient equality as well as the resolution of similar eigenvalues and thus relaxation coefficients degrade in the presence of signal noise. The relaxation coefficient ∆t dependence suggests one way to improve MPM resolution by choosing ∆t values such that the differences between all the relaxation coefficient values are maximized. This work develops mathematical machinery to estimate the best ∆t value for sampling damped, transient relaxation signals such that MPM data analysis recovers a maximum number of time constants and amplitudes given inherent signal noise. Analytical and numerical reduced dimension MPM is explained and used to compare computer-generated data with and without added noise as well as treat real measured signals. Finally, the understanding gleaned from this effort is used to predict the best data sampling time to use for non-discrete, distributions of relaxation variables.

Ultrafast Laser Pulse Induced Transient Ferrimagnetic State and Spin Relaxation Dynamics in Two-Dimensional Antiferromagnets.

We employ real-time time-dependent density functional theory (rt-TDDFT) and ab initio nonadiabatic molecular dynamics (NAMD) to systematically investigate the ultrafast laser pulses induced spin transfer and relaxation dynamics of two-dimensional (2D) antiferromagnetic-ferromagnetic (AFM/FM) MnPS3/MnSe2 van der Waals heterostructures. We demonstrate that laser pulses can induce a ferrimagnetic (FiM) state in the AFM MnPS3 layer within tens of femtoseconds and maintain it for subpicosecond time scale before reverting to the AFM state. We identify the mechanism in which the asymmetric optical intersite spin transfer (OISTR) effect occurring within the sublattices of the AFM and FM layers drives the interlayer spin-selective charge transfer, leading to the transition from AFM to FiM state. Furthermore, the unequal electron-phonon coupling of spin-up and spin-down channels of AFM spin sublattice causes an inequivalent spin relaxation, in turn extending the time scale of the FiM state. These findings are essential for designing novel optical-driven ultrafast 2D magnetic switches.

Ultrafast Plasmonic Hot Hole Transfer and Plasmon Dynamics in a Dual Plasmonic Au@p‐Cu2−xSe Heterostructure

AbstractMetal‐semiconductor heterostructures have significant potential in harvesting plasmon induced hot charge carriers for photocatalytic and photovoltaic devices. Despite numerous studies, the field of hot hole transfer in heterostructures remains unexplored. In this work, the plasmon dynamics of a dual plasmonic core–shell Au@p‐Cu2−xSe heterostructure are investigated with the aid of femtosecond broadband pump probe spectroscopy. Ultrafast studies reveal that hot holes generated within the d and sp band after 400 and 800 nm excitations are injected from Au to copper selenide. Hot hole transfer substantially reduces the transient signal intensity and electron phonon relaxation time for Au plasmon. Increment in the transient signal intensity and slower kinetics for the semiconducting plasmon of Au@Cu2−xSe validate the hot hole transfer in the valence band of copper selenide. Fluence dependent studies reveal that d band hot holes extraction is more efficient than that of sp band hot holes.

Gastro‑oesophageal reflux disease in liver cirrhosis: Possible pathogenesis and clinical intervention (Review).

Oesophageal variceal bleeding is a common complication of decompensated liver cirrhosis (LC). Some studies have reported that reflux oesophagitis (RE) is a risk factor for upper gastrointestinal bleeding, and greatly impacts the quality of life. However, the frequency and mechanism of gastro-oesophageal reflux disease (GERD) in LC remain unclear. The present review explored the possible pathogenesis, and analysed the advantages and disadvantages of the interventional measures and the need for implementation of these measures. By combining the comprehensive terms associated with LC, GERD and RE, EMBASE, Medline/PubMed and the Cochrane Library were systematically searched. The underlying pathological mechanism of GERD in LC was summarized: Transient relaxation of the lower oesophageal sphincter, delayed gastric emptying, increased intra-abdominal pressure, increased intragastric pressure and excessive nitric oxide production destroyed the 'anti-reflux barrier', causing gastric content reflux. Proton pump inhibitors (PPIs) have been widely used empirically to lower the risk of oesophageal venous rupture and bleeding. However, long-term use of acid inhibitors in patients with LC may induce complications, such as spontaneous bacterial peritonitis. The metabolic half-life of PPIs is prolonged in patients with severe liver function impairment. Therefore, the indications for using acid inhibitors lack clarity. However, after endoscopic oesophageal variceal eradication, additional benefits may be gained from the long-term use of PPIs in small doses.

Combined Use of Ultrasonic and Electromagnetic Fields for the Study of Bonding Mechanisms between Dexamethasone Disodium Phosphate Molecules

We have investigated the ultrasonically induced birefringence traces of aqueous solutions of dexamethasone disodium phosphate, a derivative of hydrocortisone (cortisol). The stationary birefringence and the transient built-up and decay relaxation processes were studied as a function of solution concentration, ultrasound frequency and intensity, as well as a function of temperature. The results were analyzed in view of structural peculiarities of the system in an effort to gain further insights into the molecular relaxation dynamics and the proposed self-association process occurring in the system. The detected ultrasonically induced birefringence relaxation is motivated by the rotational diffusion of dexamethasone disodium phosphate aggregates due to self-association depending on the solution concentration. The observed relaxation mechanism is directly linked to the hydrodynamic size of the acoustic field-induced self-assembly. The systematic analysis of the transient birefringence signals caused by the applied ultrasonic field allowed us to evaluate the interplay between permanent and induced dipoles with changing concentration, temperature, and ultrasound properties. The birefringence traces are adequately fitted with a stretched exponential law indicating the polydispersive nature of the self-aggregated molecular structures. The obtained results are described in the light of recent studies performed on this system.

Re-examination and comparison of activation volume, strain rate sensitivity, and dislocation density for coarse grain and CGP-processed UFG materials

The frequently used metallurgical parameters such as activation volume, internal stress, strain rate sensitivity, and dislocation density are identified in ultrafine-grained (UFG) materials through erudite analytical relations. It is difficult to analyze such parameters optically since the material consists of highly distorted and inhomogeneous microstructure due to the large strain imposed during the constrained groove pressing (CGP) process. Hence, transient tests like stress relaxation tests are advantageous over the optical to use. Apart from the identification of parameters in low-carbon steel materials using uniaxial loading and stress relaxation tests, the relationship between the parameters is nobly investigated in as-received and UFG structure samples produced through the CGP process. In the relationship, the exponential-power law constitutive to describe the accurate stress–strain curves, identification of mobile and forest dislocation density during strain hardening, and exponential variation between grain size and activation volume are proposed. The replenishment or exhaustion of mobile and forest dislocation density significantly affects the metallurgical parameters during uniaxial tensile loading followed by stress relaxation testing. In this experimental and analytical work, the CGP process produces a UFG material that has lower activation volume and higher stress drop, mobile dislocation density, forest dislocations density, strain rate sensitivity, and internal stress.

Optimizing the treatment of patients with gastroesophageal reflux disease: focus on nutritional risk factors and nutritional approaches

Gastroesophageal reflux disease (GERD) is a common upper gastrointestinal disease characterized by occurrence of typical symptoms associated with an increase in esophageal acid exposure. The transient lower esophageal sphincter relaxations (TLESRs) and hypotension is the key pathophysiological mechanisms of the development of reflux disease. For a long time, it was assumed that certain nutritional and lifestyle factors affect the mechanisms of the onset and progress of GERD. However, the accumulated scientific findings show contradicting results regarding contribution of these factors to the development of reflux disease. The treatment of GERD requires lifestyle modifications, diet therapy, pharmacotherapy, and, if necessary, surgery. Proton pump inhibitors (PPIs) form the basis of pharmacotherapy. Lifestyle modifications, including dietary therapy, is also part of the treatment plan for patients with reflux symptoms, however no clear guidelines in this regard are determined due to the lack of good evidence base. Yet, while the problems associated with the long-term use of PPIs are explored, patients and physicians are increasingly interested in the role of diet in the treatment of GERD. The article provides an overview of the dietary aspects in GERD with a focus on nutritional components and their impact on the pathophysiology and treatment of this disease. Although sequential food-group elimination in GERD is common in clinical practice, literature data demonstrate a broader approach, including reduction of sugar intake, increase of dietary fibres in the diet, and changes in patterns of eating habits as a general principle.

Gastroesophageal reflux disease in children: What's new right now?

Gastroesophageal reflux (GER) in children is very common and refers to the involuntary passage of gastric contents into the esophagus. This is often physiological and managed conservatively. In contrast, GER disease (GERD) is a less common pathologic process causing troublesome symptoms, which may need medical management. Apart from abnormal transient relaxations of the lower esophageal sphincter, other factors that play a role in the pathogenesis of GERD include defects in esophageal mucosal defense, impaired esophageal and gastric motility and clearance, as well as anatomical defects of the lower esophageal reflux barrier such as hiatal hernia. The clinical manifestations of GERD in young children are varied and nonspecific prompting the necessity for careful diagnostic evaluation. Management should be targeted to the underlying aetiopathogenesis and to limit complications of GERD. The following review focuses on up-to-date information regarding of the pathogenesis, diagnostic evaluation and management of GERD in children.