Relaxation Time Measurements Research Articles

Highly concentrated solvothermal synthesis of sub-10-nm BaTiO3 nanoparticles for optical applications

Single-crystalline barium titanate: BaTiO3 (BT) nanoparticles (NPs) with sub-10-nm size have been successfully obtained by a highly concentrated solvothermal synthesis using a high concentration of Ba(OH)2 and a titanium complex. To obtain sub-10-nm NPs, we focused on the gradual increase in the OH– ion concentration and the decrease in the dielectric constant of solvents, and BT NPs were produced in 1 h even at a low temperature of 200 °C. High-resolution transmission electron microscopy (HR-TEM) observation revealed that the resulting BT NPs were single-nanometer size, consisting of a single-crystalline structure. 1H-nuclear magnetic resonance (NMR) relaxation time (T2) and zeta potential measurements demonstrated that our BT NPs had high dispersibility and dispersion stability under acidic conditions. The yellowness index measurements revealed that the BT NPs dispersions exhibited colorless property. The resulting single nanometer-sized BT NPs are promising as high refractive index materials for optical applications due to being dispersed in optical resins.

Physicochemical and Morphological Study of the Saccharomyces cerevisiae Cell-Based Microcapsules with Novel Cold-Pressed Oil Blends

Vegetable oils rich in polyunsaturated fatty acids are a valuable component of the human diet. Properly composed oil blends are characterized by a 5:1 ratio of ω6/ω3 fatty acids, which is favorable from a nutritional point of view. Unfortunately, their composition makes them difficult to use in food production, as they are susceptible to oxidation and are often characterized by a strong smell. Encapsulation in yeast cells is a possible solution to these problems. This paper is a report on the use of native and autolyzed yeast in the encapsulation of oils. The fatty acid profile, encapsulation efficiency, morphology of the capsules obtained, and thermal behavior were assessed. Fourier transform infrared analysis and low-field nuclear magnetic resonance relaxation time measurements were also performed. The process of yeast autolysis changed the structure of the yeast cell membranes and improved the loading capacity. Lower encapsulation yield was recorded for capsules made from native yeast; the autolysis process significantly increased the value of this parameter. It was observed that NY-based YBMCs are characterized by a high degree of aggregation, which may adversely affect their stability. The average size of the AY capsules for each of the three oil blends was two times smaller than the NY-based capsules. The encapsulation of oils in yeast cells, especially those subjected to the autolysis process, ensured better oxidative stability, as determined by DSC, compared to fresh blends of vegetable oils. From LF NMR analysis of the relaxation times, it was shown that the encapsulation process affects both spin-lattice T1 and spin-spin T2* relaxation times. The T1 time values of the YBMCs decreased relative to the yeast empty cells, and the T2* time was significantly extended. On the basis of the obtained results, it has been proven that highly unsaturated oils can be used as an ingredient in the preparation of functional food via protection through yeast cell encapsulation.

Boundary fluctuation dynamics of a phase-separated domain in planar geometry.

Using phase-ordering kinetics and of renormalization group theories, we derive analytically the relaxation times of the long wavelength fluctuations of a phase-separated domain boundary in the vicinity of (and below) the critical temperature in the planar Ising universality class. For a conserved order parameter, the relaxation time grows like Λ^{3} at wavelength Λ and can be expressed in terms of parameters relevant at the microscopic scale: lattice spacing, bulk diffusion coefficient of the minority phase, and temperature. These results are supported by numerical simulations of 2D Ising models, enabling in addition calculating the nonuniversal numerical prefactor. We discuss the applications of these findings to the determination of the real timescale associated with elementary Monte Carlo moves from the measurement of long wavelength relaxation times on experimental systems or molecular dynamics simulations.

Pancreatic iron quantification with MR imaging: a practical guide.

Accurate determination of pancreatic iron status is crucial for preventing impairment of the exocrine and endocrine function of the pancreas and for prospectively stratifying the cardiac iron risk. The following article should be a sort of practical guide for radiologists interested in quantifying pancreatic iron overload by Magnetic Resonance Imaging (MRI). After a brief background on iron-deposition diseases, we will describe basic principles and relative advantages and disadvantages of the more widely used and clinically feasible MRI-based techniques for pancreatic iron assessment. These methods can be classified into signal intensity ratio (SIR) and relaxometry methods. We will examine different technical aspects representing the key for accurate and precise relaxation time measurement.

Indirect Measurement of Electron Energy Relaxation Time at Room Temperature in Two-Dimensional Heterostructured Semiconductors.

Hot carriers are a critical issue in modern photovoltaics and miniaturized electronics. We present a study of hot electron energy relaxation in different two-dimensional electron gas (2DEG) structures and compare the measured values with regard to the dimensionality of the semiconductor formations. Asymmetrically necked structures containing different types of AlGaAs/GaAs single quantum wells, GaAs/InGaAs layers, or bulk highly and lowly doped GaAs formations were investigated. The research was performed in the dark and under white light illumination at room temperature. Electron energy relaxation time was estimated using two models of I-V characteristics analysis applied to a structure with n-n+ junction and a model of voltage sensitivity dependence on microwave frequency. The best results were obtained using the latter model, showing that the electron energy relaxation time in a single quantum well structure (2DEG structure) is twice as long as that in the bulk semiconductor.

SORDOR pulses: expansion of the Böhlen-Bodenhausen scheme for low-power broadband magnetic resonance.

A novel type of efficient broadband pulse, called second-order phase dispersion by optimised rotation (SORDOR), has recently been introduced. In contrast to adiabatic excitation, SORDOR-90 pulses provide effective transverse 90 rotations throughout their bandwidth, with a quadratic offset dependence of the phase in the plane. Together with phase-matched SORDOR-180 pulses, this enables the Böhlen-Bodenhausen broadband refocusing approach for linearly frequency-swept pulses to be extended to any type of 90/180 pulse-delay sequence. Example pulse shapes are characterised in theory and experiment, and an example application is given with a -PROJECT experiment for measuring relaxation times with reduced distortions due to -coupling evolution.

Cover Feature: High‐Temperature Quantum Tunneling and Hydrogen Bonding Rearrangements Characterize the Solid‐Solid Phase Transitions in a Phosphonium‐Based Protic Ionic Liquid (Chem. Eur. J. 23/2022)

Tunneling driven dynamics for the PD3 group of the octyl phosphonium cation in an ionic liquid has been observed by means of solid-state NMR spectroscopy. Deuteron line-shape analysis and relaxation time measurements provide information about the structure, mobility and rearrangements of the cations in the solid, supercooled and liquid states. Hydrogen bonds of different strengths allow the change in molecular ordering upon phase transformation to be mapped. More information can be found in the Research Article by D. I. Kolokolov, R. Ludwig et al. (DOI: 10.1002/chem.202200257). The illustrations of the tunnel are used with the kind support of NOCH GmbH & Co. KG, who owns the copyright.

Comparison of MRI T1, T2, and T2* mapping with histology for assessment of intervertebral disc degeneration in an ovine model

An easy, reliable, and time-efficient standardized approach for assessing lumbar intervertebral disc (IVD) degeneration with relaxation times measurements in pre-clinical and clinical studies is lacking. This prospective study aims to determine the most appropriate method for lumbar IVD degeneration (IDD) assessment in sheep by comparing three quantitative MRI sequences (variable-flip-angle T1 mapping, and multi-echo T2 and T2* mapping), correlating them with Pfirrmann grading and histology. Strong intra- and interrater agreements were found for Nucleus pulposus (NP) regions-of-interest (ROI). T1, T2, and T2* mapping correlated with Pfirrmann grading and histological scoring (p < 0.05) except for the most ventral rectangular ROI on T2 maps. Correlations were excellent for all of the T1 ROIs and the T2* NP ROIs. Highly significant differences in T1 values were found between all Pfirrmann grades except between grades I/II and between grades III/IV. Significant differences were identified in the T2 and the T2* values between all grades except between grades I/III. T1, T2, and T2* relaxation times measurements of the NP are an accurate and time-efficient tool to assess lumbar IDD in sheep. Variable-flip-angle T1 mapping may be further considered as a valuable method to investigate IDD and to assess the efficacy of regenerative treatments in longitudinal studies.

Liver T1 relaxation time of the 'normal liver' in healthy Asians: measurement with MOLLI and B1-corrected VFA methods at 3T.

Liver T1 is a potential magnetic resonance imaging biomarker for liver diseases. This study aimed to determine the T1 relaxation time of the normal liver (PDFF<5%) in healthy Asian volunteers using modified look-locker inversion recovery (MOLLI) and B1 inhomogeneity-corrected variable flip angle (B1-corrected VFA). 60 healthy Asian volunteers without focal or diffuse liver disease underwent a liver scan at 3T magnetic resonance. Proton density fat fraction (PDFF) and liver stiffness measurements were applied for the quantification of liver fat and fibrosis. T1 mapping was performed with MOLLI and B1-corrected VFA sequences. Bland-Altman, linear regression, Student t-test, and one-way analysis of variance were used for statistical analysis. The mean T1 relaxation times of the whole liver were 901 ± 34 ms by MOLLI, and 948 ± 29 ms by B1-corrected VFA in healthy volunteers. There was a strong correlation (r = 0.86, p < 0.0001) for liver T1 between two T1 mapping methods. There were significant differences between the right and left lobes in liver T1 relaxation times using both methods (p < 0.05). Gender and Asian ethnic disparities had no impact on liver T1 relaxation times. T1 relaxation times of the normal liver (PDFF<5%) in healthy volunteers were established by MOLLI and B1-corrected VFA T1 mapping methods at 3T. It may provide suitable and robust baseline values for the assessment of liver diseases. Gender and Asian ethnic disparities do not impact liver T1 relaxation time measurements.

T1 reduction rate with Gd-EOB-DTPA determines liver function on both 1.5\xa0T and 3\xa0T MRI

Magnetic resonance T1 mapping before and after Gd-EOB-DTPA administration allows quantification of the T1 reduction rate as a non-invasive surrogate marker of liver function. A major limitation of T1 relaxation time measurement is its dependency on MRI field strengths. Since T1 reduction rate is calculated as the relative shortening of T1 relaxation time before and after contrast administration, we hypothesized that the T1 reduction rate is comparable between 1.5 and 3 T. We thus compared liver T1 relaxation times between 1.5 and 3 T in a total of 243 consecutive patients (124, 1.5 T and 119, 3 T) between 09/2018 and 07/2019. T1 reduction rates were compared between patients with no cirrhosis and patients with cirrhosis Child–Pugh A-C. There was no significant difference of T1 reduction rate between 1.5 and 3 T in any patient group (p-value 0.126–0.861). On both 1.5 T and 3 T, T1 reduction rate allowed to differentiate between patients with no cirrhosis and patients with liver cirrhosis Child A-C (p < 0.001). T1 reduction rate showed a good performance to predict liver cirrhosis Child A (AUC = 0.83, p < 0.001), Child B (AUC = 0.83, p < 0.001) and Child C (AUC = 0.92, p < 0.001). In conclusion, T1 reduction rate allows to determine liver function on Gd-EOB-DTPA MRI with comparable values on 1.5 T and 3 T.

Polymer/silica core–shell nanoparticles with temperature-dependent stability properties

This work aimed at the synthesis of hydrogel-based composite core/shell nanoparticles and their subsequent surface modification with thermoresponsive copolymers. Submicron hydrogel-based nanoparticles were obtained from the layer-by-layer coating of silica nanoparticles with two natural oppositely-charged polyelectrolytes, chitosan and sodium alginate. Further modifications with a PVAm-b-PNIPAM copolymer synthetized by RAFT polymerization was achieved by the “grafting to” approach. First, the optimum feed weight ratio (fwr) was determined by a combined approach of zeta potential and T2 relaxation time measurements. Then, diblock grafting at this optimum fwr was performed and characterized by XPS. XPS analysis confirmed the presence of copolymer at the particles’ surface with the increase of C and N atomic percentage. The quantification study was carried out by spectrofluorimetry using the fluorescently labeled PVAm-b-P(NIPAM-stat-NVC) copolymer and revealed that the grafting efficiency could reach 60 %. Finally, a study of thermosensivity properties confirmed that our smart system allowed a temperature-induced destabilization of the particles suspension at 45 °C. This work has promising prospects in the field of controlled drug delivery.

Characterization of crystalline and amorphous forms of irbesartan by multi-nuclear solid-state NMR

Irbesartan (IRB) is an antihypertensive drug which exhibits the rare phenomenon of desmotropy; its 1H- and 2H- tetrazole tautomers can be isolated as distinct crystalline forms. The crystalline forms of IRB are poorly soluble, hence the amorphous form is potentially of interest for its faster dissolution rate. The tautomeric form and the nature of hydrogen bonding in amorphous IRB are unknown. In this study, crystalline form A and amorphous form of irbesartan were studied using 13C, 15N and 1H solid-state NMR. Variable-temperature 13C SSMNR studies showed alkyl chain disorder in the crystalline form of IRB, which may explain the conflicting literature crystal structures of form A (the marketed form). 15N NMR indicates that the amorphous material contains an approximately 2:1 ratio of 1H- and 2H-tetrazole tautomers. Static 1H SSNMR and relaxation time measurements confirmed different molecular mobilities of the samples and provided molecular-level insight into the nature of the glass transition. SSNMR is shown to be a powerful technique to investigate the solid state of disordered active pharmaceutical ingredients.

Rapid Temperature-Dependent Rheological Measurements of Non-Newtonian Solutions Using a Machine-Learning Aided Microfluidic Rheometer.

Biofluids such as synovial fluid, blood plasma, and saliva contain several proteins which impart non-Newtonian properties to the biofluids. The concentration of such protein macromolecules in biofluids is regarded as an important biomarker for the diagnosis of several health conditions, including cardiovascular disorders, joint quality, and Alzheimer's. Existing technologies for the measurements of macromolecules in biofluids are limited; they require a long turnaround time, or require complex protocols, thus calling for alternative, more suitable, methodologies aimed at such measurements. According to the well-established relations for polymer solutions, the concentration of macromolecules in solutions can also be derived via measurement of rheological properties such as shear-viscosity and the longest relaxation time. We here introduce a microfluidic rheometer for rapid simultaneous measurement of shear viscosity and longest relaxation time of non-Newtonian solutions at different temperatures. At variance with previous technologies, our microfluidic rheometer provides a very short turnaround time of around 2 min or less thanks to the implementation of a machine-learning algorithm. We validated our platform on several aqueous solutions of poly(ethylene oxide). We also performed measurements on hyaluronic acid solutions in the clinical range for joint grade assessment. We observed monotonic behavior with the concentration for both rheological properties, thus speculating on their use as potential rheo-markers, i.e., rheological biomarkers, across several disease states.

Polymer Solution With Very Low Relaxation Time: A Combined Numerical-Experimental Determination Strategy

Abstract For very low relaxation time (i.e., lesser than a microsecond), viscoelastic fluid experimental determination is difficult, if not impossible. In this work, the relaxation time measurement of a weakly elastic polymer solution, too low to be measured using classical rheometry techniques, is assessed using a mixed experimental-numerical strategy. First the fluid is rheologically assessed, by measuring its shear viscosity, surface tension, and density. Then the relaxation time is determined by comparing the jetting of polymer solution from a continuous ink-jet (CIJ) device, experimentally and numerically. The numerical approach is first validated using test cases, and a viscoelastic Oldroyd-B model is used to model the experimental solution. The relaxation time is then a parameter allowing us to fit numerical simulation onto experimental results. This mixed strategy is particularly convenient for weakly elastic solution for which physical parameters cannot be measured using an experimental rheometry setup.

Elucidating the pseudocapacitive mechanism of ternary Co-Ni-B electrodes–Towards miniaturization and superior electrochemical performance for building outmatched supercapacitors

Ternary bi-metallic borides have been prepared by administrating two different solvent media utilized through co-precipitation process with particles dimension ranging from 3 to 5 nm. The X-ray photoelectron spectroscopy suggests the presence of redox states in the cobalt-nickel based bi-metallic borides that promotes excess electroactive sites. The outstanding stability of bimetallic borides has been estimated by measuring relaxation time (T2) in solvent medium. The surface area has been evaluated about 151.302 m2 g−1with associated pore diameter of 6.57 nm. Moreover, the ternary bi-metallic electrode exhibited excellent pseudocapacitance with exceptional specific capacitance (SC) of 4835 Fg−1 (606 mAh g−1) at 5 Ag−1 by upholding cycling retention of ∼94.2% over 15,000 cycles. Also, different concentrations of sodium hydroxide (NaOH) electrolyte (0.5, 1.0 & 1.5 M) are employed for comparative study to achieve optimal electrochemical performance. Simultaneously, an electrode configuration is designed with cobalt-nickel-boron (Co-Ni-B) 1:1:0.15 as positive and carbon black as negative electrodes to fabricate asymmetric device. The device illuminates a commercial light emitted diode (LED, ∼1.8 V) to justify the electrode performance and their full-scale deployment with a device efficiency ∼363 Fg−1 (358 mAh g−1) and an energy density of 114 Wh kg−1.

Measurement of muon spin relaxation time in scintillating materials

Measurement of muon spin relaxation time in scintillating materials

Измерение коэффициентов диффузии примесей внедрения в сплаве Zr – 1 масс. % Nb методом внутреннего трения

In alloys with a GPU lattice, it is possible to observe a relaxation of the Snukovsky type if there is a certain amount of substitution impurities in it. However, it is impossible to calculate the diffusion coefficients of the introduction impurities by the measured relaxation time by analogy with BCC alloys, just because of the possible interaction with substitution atoms. However, in some cases, if reliable diffusion data are available for an alloy close in composition to the studied one, the relaxation time can be calculated from the ratio τr = τr0·exp(Hm/RTm), where Hm, Tm are the parameters of the relaxation maximum of the impurity from the experiment, and τr0 can be calculated from the formula D0 = c02/(16·τr0) for the GPU lattice, taking D0 from the corresponding diffusion expert data. In this way, the diffusion coefficients of the introduction impurities in the alloy Zr – 1 wt. % Nb are calculated for several states of samples.

Determining the relaxation time from a temperature-dependent scan of the neutron spin-echo signal amplitude

Temperature-dependent scans of the neutron scattering intensity are commonly employed in high energy-resolution quasielastic measurements. Besides serving as a useful diagnostic tool for identifying the temperature range that could give rise to a measurable relaxation signal, such scans of the “elastic” (resolution-defined) intensity could be employed for determining the temperature at which the relaxation time in the system becomes equal to the resolution-defined characteristic time of the spectrometer measurement. This is a model-independent alternative to the “traditional” approach, when, at a given measurement temperature, the relaxation time in the system is obtained from fitting the full dynamic spectra with a model scattering function. Here we introduce the temperature-dependent scan of the neutron spin-echo signal amplitude. Using a well-characterized system with a complex relaxation pattern, we demonstrate that the relaxation time obtained from the approach proposed herein maps well on the previous “traditionally” measured relaxation times. Thus, despite monitoring a different variable (neutron spin-echo signal amplitude vs. neutron scattering intensity), the benefits of the model-free temperature-dependent scan approach, traditionally utilized in neutron time-of-flight and backscattering experiments, can be extended to measurements of the very slow relaxations assessable only by high-resolution neutron spin-echo.

Nuclear magnetic resonance study of the formation and dissociation process of nature gas hydrate in sandstone

In this work, the authors monitored the formation and dissociation process of methane hydrate in four different rock core samples through nuclear magnetic resonance (NMR) relaxation time (T2) and 2D imaging measurement. The result shows that the intensity of T2 spectra and magnetic resonance imaging (MRI) signals gradually decreases in the hydrate formation process, and at the same time, the T2 spectra move toward the left domain as the growth of hydrate in the pores of the sample accelerates the decay rate. The hydrate grows and dissociates preferentially in the purer sandstone samples with larger pore size and higher porosity. Significantly, for the sample with lower porosity and higher argillaceous content, the intensity of the T2 spectra also shows a trend of a great decrease in the hydrate formation process, which means that high-saturation gas hydrate can also be formed in the sample with higher argillaceous content. The changes in MRI of the sample in the process show that the formation and dissociation of methane hydrate can reshape the distribution of water in the pores.©2022 China Geology Editorial Office.

NMR relaxation time measurements of solvent effects in an organocatalysed asymmetric aldol reaction over silica SBA-15 supported proline

The behaviour of solvents in solid-supported proline organocatalysts is explored using NMR relaxation measurements coupled with reaction screening. Solvents with a lower affinity for the solid surface lead to a higher reactivity.