The Landau-Teller model for vibrational energy relaxation of gases toward equilibrium is a first-order kinetic model where the rate of relaxation is proportional to the current defect between the energy in that mode and the equilibrium amount of energy in the mode. In Direct Simulation Monte Carlo (DSMC), collisions are first resolved using a total collision cross section; then, if a collision occurs, the internal energy modes of the colliding particles are tested for relaxation. To reproduce the Landau-Teller model in gases with multiple internal modes, the relaxation of multiple internal modes in a single DSMC collision must be prohibited. This work provides analytical comparison of model-form differences between four models: (1) Landau-Teller theory, (2) the vibrational master equation for a mixture of harmonic oscillators, and DSMC when (3) allowing or (4) prohibiting multiple relaxation in a single collision. This is followed by a rigorous examination of the quantitative effect of the algorithmic choice of allowing or prohibiting multiple relaxation in DSMC. The deviation from the Landau-Teller model caused by allowing multiple relaxations in DSMC is minimal compared to the statistical noise in most cases. However, DSMC practitioners are advised to carefully consider the importance of direct coupling between internal modes, as neglecting these can lead to significant errors.

The rotational correlation time ([Formula: see text]) is a one of the fundamental parameters for characterizing biomacromolecules in solution. The [15N, 1H]-TRACT (TROSY for Rotational Correlation Times) NMR experiment is a widely utilized method for determining [Formula: see text] by measuring the differential 15N-1H transverse relaxation rates of α and β states. However, extracting accurate relaxation rates from these experiments often requires researchers to rely on ad hoc scripts or tedious workflows across multiple software packages, which can introduce systematic errors during peak integration and baseline correction. To address this bottleneck, we introduce pyTRACTnmr, an open-source, modular Python application featuring a modern graphical user interface designed specifically for streamlined analysis of [15N, 1H]-TRACT data. Built on the PySide6 framework and leveraging the nmrglue library for robust data ingestion, the software provides an interactive environment for visual baseline correction, precise integration window definition, and non-linear least-squares fitting of relaxation decays. By replacing rigid automated processing with a user-friendly, visually guided workflow, pyTRACTnmr minimizes noise amplification and ensures highly reproducible analysis, and significantly simplifies the workflow.

Dulaglutide is a glucagon-like peptide 1 receptor (GLP-1R) agonist. Dulaglutide (LY2189265) is a GLP-1(7-37) analogue fused by a linker to a modified immunoglobulin G. GLP-1R agonists like dulaglutide can be used to treat diabetes type 2 and obesity. We tested the hypothesis that dulaglutide directly increased force of contraction in the human heart via GLP-1R. To this end, we conducted contraction experiments in paced (1 Hz) isolated human right atrial muscle preparations (HAP). HAP were obtained during open-heart surgery from adult patients with severe coronary heart disease. We detected a concentration- and time-dependent positive inotropic effect of dulaglutide in HAP. Dulaglutide augmented the rate of tension development, the rate of tension relaxation and accelerated the relaxation time in HAP. Dulaglutide (100 nM) augmented the phosphorylation state of phospholamban at serine 16 and the phosphorylation state of the inhibitory subunit of troponin. The positive inotropic effect of 100 nM dulaglutide in HAP was attenuated by 100 nM exendin (9-39). In contrast, dulaglutide alone or in the presence of phosphodiesterase inhibitor rolipram up to 100 nM failed to exert a positive inotropic effect in isolated electrically paced (1 Hz) mouse left atrial preparations and did not increase the beating rate of spontaneously beating mouse right atrial preparations. Our data suggest that dulaglutide raised force of contraction in the isolated paced human atrium via GLP-1R involving cAMP-dependent protein kinase in HAP.

Ag2[B10H10] and Tl2[B10H10] belong to the family of closo-hydroborates which are considered as promising solid electrolytes for battery applications. To study the dynamical properties of these compounds at the microscopic level, we have measured the 1H, 11B, and 205Tl nuclear magnetic resonance (NMR) spectra and spin-lattice relaxation rates over the temperature range of 80-545 K. For both compounds, our measurements have revealed fast reorientational motion of the [B10H10]2- anions. The reorientational jump rates are found to reach ∼108 s-1 near 380 K for Ag2[B10H10] and near 480 K for Tl2[B10H10]. This reorientational motion is characterized by the activation energies of 352 (18) meV and 685 (40) meV, respectively. For Tl2[B10H10], our experiments have not revealed any effects of long-range translational cation mobility at the NMR frequency scale up to 500 K.

Multimodal MRI assessment of levator ani function in women: Comparison with the Modified Oxford Scale.

Controlling excited-state relaxation processes is important in a variety of photochemical and photophysical processes, including the generation of ground- and excited-state spin polarization for quantum information science applications. Here, we address how specific static distortions, based on vibrational spin-orbit active modes at C2v symmetry determined by group theory, in a series of low-symmetry ligand-to-ligand charge transfer complexes enable direct spin-orbit coupling contributions to T1 → S0 excited-state decay. These results are used to address spin-vibronic coupling contributions to T1 → S0 decay in a high-symmetry (tBu2bpy)Pt(S,S) (tBu2bpy = 4,4'-di-tert-butyl-2,2'-bipyridine and S,S = benzene-1,2-dithiolate) ligand-to-ligand charge transfer complex with effective C2v symmetry, where T1 relaxation is both spin- and orbitally forbidden due to the direct spin-orbit coupling matrix element being zero by symmetry. Low-frequency vibrations that involve a pyridine-pyridine twisting motion within the bpy ligand generate large ∂⟨S0|HSO|T1⟩/∂Qi values that will contribute significantly to T1 → S0 relaxation. The work advances ligand design strategies for the generation of tailored T1 → S0 relaxation rates, which can be utilized to optimize the generation of electron spin polarization and excited state decay processes in radical-elaborated ligand-to-ligand charge transfer complexes.

Relaxation phenomena greatly influence magnetic resonance experiments, from setting repetition rates and measurement times through to measuring internal motion of molecules. RelCalc provides a convenient and efficient means for symbolic and numerical evaluation of relaxation rates using Bloch, Wagness and Redfield (BWR) theory. Users supply interactions within a spin system arranged appropriately in the molecular frame. The effects of optional fluctuations around a symmetry axis, and then under either isotropic or anisotropic global tumbling are then computed. Relaxation rates linking pairs of Liouvillian basis operators are then returned symbolically, formatted as a sum of weighted reduced spectra density functions. Parameters are then supplied to replace symbolic quantities for values for rapid computation of numerical rates. We demonstrate the utility of the software by exploring relaxation interference (TROSY) effects and 'long-lived states' in [Formula: see text] and [Formula: see text] systems, which, for n=1,2, and 3, describe NH, NH[Formula: see text] and CH[Formula: see text] groups in proteins, and small molecules with n=4,6,8,12 and 20 arranged as platonic solids. The implementation is highly efficient with 65,536 relaxation rates required to perform complete Liouvillian simulation of [Formula: see text] methyl groups rotating about a symmetric axis in the presence of adjacent static 'external' spins being symbolically calculated in a few seconds on a single processor on a 2021 laptop. From this result, a complete set of numerical rates are then computed in under one second. RelCalc is implemented in python and is freely available.

Thrombolytic recanalization rates in acute ischemic stroke (AIS) patients remain low. Magnetic resonance susceptibility vessel sign has been correlated with reduced thrombolytic susceptibility. However, the driving mechanisms have not been clarified. High-field magnetic resonance imaging is used to study relaxation rates and compaction of embolus analogs undergoing simulated AIS with varying pressures. Microscopy and perfusion tests are used to study the effect of compaction on clot microstructure and permeability, respectively. Pressure dependent compaction alters clot microstructural characteristics and increases the R2 relaxation rate. Following compaction, the R2 in red blood cell (RBC) rich clots increases up to 224%, corresponding to a twofold increase in RBC volume fraction and polyhedrocyte formation. RBC and fibrin dominant clot permeabilities decrease by 78% and 97%, respectively, when compaction pressure increases 50 mmHg. Compacted red blood cell rich clots are the most likely to present with susceptibility vessel sign and have the lowest permeability. Our results suggest that increased clot constituent density due to compaction can lead to susceptibility vessel sign and elevated thrombolytic resistance by limiting thrombolytic perfusion. This is the first study to evaluate the clinical relevance of clot compaction during AIS using multiple imaging techniques.

Hybrid single crystals exhibit remarkable optoelectronic properties that make them highly promising for photovoltaic devices and radiation detectors. However, ion migration-induced instability represents a critical barrier to their commercial viability. By integrating large language models (LLMs) with k-Nearest Neighbor (kNN) algorithms, we develop a machine-learning model that identifies rigid organic cations as effective modulators for perovskite crystal stiffness, thereby suppressing ion migration. Guided by the analysis, we replaced the flexible alkyl chains in (HDA)BiI5 (HDA = 1,6-hexanediamine) with rigid carbon rings to synthesize a highly stable (CHDA)BiI5 single crystal (CHDA = trans-1,4-diaminocyclohexane). Density functional theory (DFT) calculations revealed that the rigid CHDA molecule exhibits ordered vibrations and stronger interactions with the inorganic framework compared to the disordered vibrations of HDA. Solid-state nuclear magnetic resonance (SSNMR) spin-lattice relaxation measurements further confirmed enhanced lattice rigidity, with the relaxation rate decreasing from 1.29 s-1 to 0.15 s-1, enhancing lattice rigidity. Consequently, the ion migration activation energy increased substantially from 0.42 to 0.61 eV. The resulting (CHDA)BiI5 X-ray detector achieved an exceptional sensitivity of 8209 μC·Gyair-1·cm-2 at 175 V/mm and a low detection limit of 4.7 nGy s-1. This study underscores the pivotal role of organic cation rigidity in optimizing the structural stability and functional performance of low-dimensional hybrid semiconductors.

In situ detection of paramagnetic ions, including ions and biological macromolecules, is critical for fundamental research and applications in biology, chemistry, and medicine. The negatively charged boron vacancy (VB-) defects in hexagonal boron nitride (hBN) have emerged as versatile, highly sensitive quantum sensors for detecting various physical quantities. To further extend the scope and make practical applications of the quantum sensing, in this work, we demonstrate in situ quantum detection of the paramagnetic Mn2+ ions and ferritin in both solution and dry states using VB- defects in hBN. The experiments show that the optically detected magnetic resonance (ODMR) contrasts of VB- defects decrease with increasing concentrations of Mn2+ and ferritin in solution states; however, the ODMR contrasts remain unchanged in the case of dry states. This phenomenon is attributed to magnetic-noise-induced depopulation and modulated solution conductivity by solution paramagnetic ions. At the same time, the spin longitudinal relaxation rates monotonically increase with concentration in both solution and dried states as a function of ions concentration due to the magnetic noise from paramagnetic ions. Moreover, VB- defects can also distinguish different ionic species based on their distinct relaxation rates, requiring no prior knowledge. Finally, the all-optical relaxation method is also adopted to efficiently detect ferritin and paramagnetic ions. Collectively, our work establishes VB- defects in hBN-based sensors as a versatile quantum sensing platform for different species of paramagnetic ions in biology and chemistry, offering dual-modal detection methods including ODMR and T1 relaxation with operational flexibility and high sensitivity.

NMR relaxation of backbone amide 15N spins enables characterization of overall and intramolecular dynamic properties of proteins, including overall rotational diffusion on nanosecond time scales; internal conformational dynamics on picosecond-nanosecond time scales, through generalized order parameters and effective correlation times; and slow inter- and intramolecular processes on microsecond-millisecond time scales, termed chemical exchange. Selection between competing models for dynamic processes, such as various versions of the model-free formalism, complicates applications of these otherwise powerful methods. Chemical exchange systematically increases the transverse relaxation rate constant R2 and is a strong confounding factor in model-free or other interpretations of 15N spin relaxation measurements. The present work presents robust approaches, using 15N spin relaxation data acquired at three or more static magnetic fields, to detect and remove chemical exchange contributions to R2; to determine the local isotropic rotational correlation time and generalized order parameter for individual 15N sites without model selection; and to recursively maximize the number of local isotropic rotational correlation times used to determine the overall rotational diffusion tensor. These approaches are applied to 15N relaxation data acquired at 500, 700, and 900 MHz for Escherichia coli ribonuclease HI, and compared to conventional analyses using the model-free formalism. These methods enable facile determination of the most important parameters describing protein dynamics: the rotational diffusion tensor, generalized order parameters, and chemical exchange constants, and broaden the scope of NMR spin relaxation methods.

Objective &#xD;The use of Feraheme (ferumoxytol) as a contrast agent in MR-guided focused ultrasound (MRgFUS) tumor ablations could enhance treatment safety and efficacy by improving vascular visualization through strong T1 and T2 shortening effects. However, Feraheme impact on MR thermometry and tissue heating is unclear. This study evaluates the feasibility of incorporating Feraheme into MRgFUS by assessing its impact on MR imaging contrast, MR thermometry, and thermal response in tissue-mimicking phantoms. &#xD;&#xD;Approach&#xD;Tissue-mimicking phantoms with 0 (baseline), 0.25, and 0.5 mM Feraheme concentrations were prepared using a validated recipe. Acoustic attenuation was measured with a commercial diagnostic ultrasound scanner. MR imaging at 1.5 T was performed to assess gradient-recalled-echo (GRE)-based thermometry signal-to-noise-ratio (SNR), relaxation rates, and relaxivities. MRgFUS system integrated with 1.5 T MRI was used to perform multiple sonications in the phantoms. Temperature elevations and focal heating areas were quantified from proton resonance frequency (PRF) shift thermometry. Experiments were repeated three times over the period of eight-weeks. Separately, temperature-dependent NMR spectroscopy was performed at 3.0 T in saline-diluted Feraheme phantoms (0, 0.25, 0.5, and 1.0 mM) to assess the influence of Feraheme concentration on PRF coefficients used in MR thermometry.&#xD;&#xD;Main results&#xD;Phantoms showed nuclear relaxation times (T1: 1178.1±77.8, T2: 103.21±2.45 ms) and attenuation coefficients (0.34-0.36 dB/cm/MHz) within expected biological tissue ranges. Relaxivities demonstrated a strong linear dependence on Feraheme concentration (r1: 17.5±0.2, r2: 209.2±2.6 s⁻¹mM⁻¹). Relative to baseline (0 mM) phantom, the SNR of GRE-based thermometry increased by 12.6% at 0.25 mM and decreased by 27.1 % at 0.5 mM. Sonications in Feraheme-containing phantoms resulted in statistically higher temperature elevations (p<0.001) although no statistically significant difference was observed between 0.25 and 0.5 mM. All NMR measurements demonstrated stable, linear PRF temperature dependence (R² = 0.996-0.999), with PRF coefficients (between -0.0074 and -0.0082 ppm/°C). The resulting thermometry bias was small and predictable (+0.67 and +1.73 per 20 °C at 3.0 T for 0.25 and 0.5 mM).&#xD;&#xD;Significance&#xD;These findings demonstrate that MR thermometry remains feasible at moderate Feraheme concentrations and support its potential use to enhance visualization of critical vasculature near targeted tissues during MRgFUS.&#xD.

Collective lipid dynamics in biomembranes.

ABSTRACTInhomogeneous magnetization transfer (ihMT) is sensitive to dipolar order associated with motion‐restricted macromolecules and can be characterized by the dipolar relaxation time T1D. In this study, we propose a spin‐lock MRI framework for T1D quantification. Specifically, we introduce a T1D‐sensitive metric, RATIOdosl, derived from the distinct relaxation rate Rdosl, defined as the difference between dual‐frequency and single‐frequency R1ρ measurements. To enable dual‐frequency spin‐lock acquisition, we developed a dedicated rotary‐echo spin‐lock sequence. Based on this framework, we further estimated T1D and the macromolecular proton fraction (MPF) within a unified acquisition. The proposed method was evaluated using numerical simulations, phantom experiments, and in vivo imaging in the healthy human brain. Simulations demonstrated high sensitivity of RATIOdosl to T1D and supported the robustness of the proposed approach under the investigated conditions. Phantom experiments showed measurable ihMT contrast and supported the feasibility of T1D estimation using RATIOdosl. In vivo experiments demonstrated simultaneous T1D and MPF mapping using only three spin‐lock‐prepared images. Across 10 healthy volunteers, mean white matter T1D values ranged from approximately 3.70 to 4.80 ms. By requiring only three contrast‐prepared images, the proposed technique provides a rapid framework for simultaneous T1D and MPF mapping and may facilitate further investigation of dipolar‐order‐sensitive microstructural imaging in vivo.

Characterization of transient elasticity in neutrophils.

We report the synthesis, structures, and magnetic properties of two Dy3+ complexes supported by a tripodal tris(aryl)alkoxide ligand (Me2NCH2-o-C6H4)3CO-. The mononuclear complex [κ3-O,N,N-(Me2NCH2-o-C6H4)3CO]DyCl2(THF) (1) adopts a distorted octahedral geometry, while its reaction with a dipotassium dicarbollide K2[7,8-Me2C2B9H9] affords a heterobimetallic coordination polymer {[K(μ-Cl)Dy(κ3-O,N,N-(Me2NCH2-o-C6H4)3CO)(μ-2,3-Me2C2B9H9)]·0.5THF}n (2·0.5THF) featuring a layered structure. Both compounds exhibit single-molecule magnet (SMM) behavior, with effective barriers of 344 K (240 cm-1) for 1 and 133 K (92.5 cm-1) for 2. Ab initio calculations indicate that 1 relaxes via the third excited Kramers doublet (KD), while 2 likely relaxes through the second KD. The relaxation pathways observed experimentally for 2 do not correspond to the computed KDs, possibly due to experimental limitations at high temperatures or fast relaxation rates undetectable by alternating current susceptibility.

The goal of this study was to develop an optimized oxygen-enhanced MRI (OE-MRI) protocol for longitudinal monitoring of tumor oxygenation during radiation therapy in a pre-clinical model and to introduce the Oxygen Response Index (ORI) as a potential early biomarker of treatment efficacy. A high-throughput mouse imaging protocol was designed for a clinical 3 T MRI system using optimized variable flip angle T1 mapping for relaxometry. Six male C3H mice bearing SCC7 tumors underwent longitudinal OE-MRI during fractionated radiation therapy (2 Gy/day for 7 days), followed by a single 60 Gy dose. Tumor oxygenation response was quantified as the change in longitudinal relaxation rate (ΔR1) between normoxic and hyperoxic breathing. ORI was defined as the product of the baseline-normalized longitudinal relaxation rate under normoxia (R1 21%/R1,0 21%) and the baseline-normalized fraction of oxygen-responsive tumor voxels (∆R1 +/∆R1,0 +), providing a composite index of oxygenation competence. During fractionated irradiation, ORI declined progressively, with the change-point analysis identifying treatment response inflection at scan 4 (day 8), one scan interval before tumor volume at scan 5 (day 10). After the 60-Gy dose, conversion of putatively hypoxic tissue to oxygen-responsive tissue was observed. Spatial analysis revealed persistent oxygen-response gradients, with tumor regions adjacent to normoxic tissue demonstrating greater responsiveness than non-adjacent tumor areas. ORI captured longitudinal changes in tumor oxygenation during both ineffective and effective treatment phases and may provide a useful complementary biomarker for monitoring treatment response.

NMR monitor of 235U enrichment in UF6.

The pathophysiology of psychosis remains unclear. Preclinical, postmortem, and imaging evidence implicates iron and neuromelanin abnormalities, but the consistency and magnitude of effects are uncertain. The authors characterized brain iron and neuromelanin alterations in psychosis through a systematic review and meta-analysis of iron-sensitive MRI and neuromelanin-sensitive MRI (NM-MRI) studies. The authors searched Embase, PubMed, and PsycINFO from inception to October 31, 2025, for case-control studies using iron-sensitive MRI or NM-MRI in patients with psychosis. They used random-effects models to calculate effect sizes (Hedges' g) and meta-regressions to examine clinical confounders. The primary outcomes included effect sizes for NM-MRI and iron-sensitive MRI measures: transverse relaxation rate (R2), effective transverse relaxation rate (R2*), and quantitative susceptibility mapping (QSM). Twenty-seven reports including 879 individuals with psychosis and 813 control subjects were analyzed. Meta-analyses were conducted across the caudate nucleus, putamen, globus pallidus, thalamus, and substantia nigra. Patients with psychosis showed significantly lower R2* across all examined regions (g values, -0.40 to -0.27), lower QSM values in the substantia nigra (g=-0.61, 95% CI=-0.84, -0.38), lower R2 in the caudate nucleus (g=-0.30, 95% CI=-0.56, -0.04), and higher NM-MRI values in the substantia nigra (g=0.39, 95% CI=0.23, 0.55). However, this effect was correlated with antipsychotic dosage (β=0.001, 95% CI=0.0003, 0.0018). Psychosis is associated with lower subcortical iron-sensitive MRI values, most prominently in the substantia nigra, alongside higher nigral NM-MRI values, which index neuromelanin-bound iron in dopamine neurons. Antipsychotic exposure may contribute to higher NM-MRI values, but confounding by indication cannot be excluded, highlighting the need for longitudinal studies. These findings suggest that while subcortical iron is lower overall in psychosis, neuromelanin-bound iron is increased within dopamine neurons. Investigating the mechanisms underlying these iron alterations may provide new treatment targets.

A new NMR protocol for estimating protein side chain rotameric preferences using 1H relaxation and J couplings.