Relaxation Components Research Articles

Polymer Chain Mobility in Polyelectrolyte Multilayers1, "Высокомолекулярные соединения. Серия С"

Abstract-Free-standing polyelectrolyte multilayer membranes have been formed by the layer-by-layer technique using a dip-coating apparatus. The polymer-chain mobility has been studied by 1H relaxation in the rotating frame T1rho NMR with 13C chemical shift resolution. For each of the individual polymers a single relaxation component has been observed for all resolved signals. In the multilayer a significantly different relaxation time T1rho has been observed with a minor second component. The interaction between the oppositely charged polyelectrolytes influences the molecular mobility.

Test-retest reliability and concurrent validity of in vivo myelin content indices: Myelin water fraction and calibrated T1 w/T2 w image ratio.

In an age-heterogeneous sample of healthy adults, we examined test-retest reliability (with and without participant repositioning) of two popular MRI methods of estimating myelin content: modeling the short spin-spin (T2 ) relaxation component of multi-echo imaging data and computing the ratio of T1 -weighted and T2 -weighted images (T1 w/T2 w). Taking the myelin water fraction (MWF) index of myelin content derived from the multi-component T2 relaxation data as a standard, we evaluate the concurrent and differential validity of T1 w/T2 w ratio images. The results revealed high reliability of MWF and T1 w/T2 w ratio. However, we found significant correlations of low to moderate magnitude between MWF and the T1 w/T2 w ratio in only two of six examined regions of the cerebral white matter. Notably, significant correlations of the same or greater magnitude were observed for T1 w/T2 w ratio and the intermediate T2 relaxation time constant, which is believed to reflect differences in the mobility of water between the intracellular and extracellular compartments. We conclude that although both methods are highly reliable and thus well-suited for longitudinal studies, T1 w/T2 w ratio has low criterion validity and may be not an optimal index of subcortical myelin content. Hum Brain Mapp 38:1780-1790, 2017. © 2017 Wiley Periodicals, Inc.

Crystallization of a high-strength lithium disilicate glass-ceramic: An XRD and solid-state NMR investigation

The phase evolution of a high flexural strength lithium disilicate (Li2Si2O5: LS2) glass-ceramic in a complex SiO2–Li2O–Al2O3–MgO–P2O5–ZrO2 glass system has been investigated as a function of temperature using in situ and ex situ X-ray diffraction (XRD) and 31P and 29Si solid-state nuclear magnetic resonance (SSNMR) spectroscopy. In the base glass, lithium metasilicate (Li2SiO3: LS) crystallizes (at 525°C) before LS2 (at 675°C). 29Si NMR shows that LS is not only formed from the Q(2)glass species, but also by disproportionation of the Q(3)glass units. The XRD data demonstrate the formation of a minor phase of MgAl2Si4O12 from the reaction of SiO2 with minor components of Al2O3 and MgO. Diffraction peaks of Li3PO4 are firstly detected at 675°C, and they become evident at 750°C and above. The evolution of phosphorus species in the glass as a function of temperature has been revealed by 31P NMR spectroscopy. Two 29Si T1 relaxation components were observed in samples across all temperatures, suggesting the presence of glass-in-glass phase separation in the base glass. A plot of 29Si T1 relaxation measurements shows discontinuity at 750°C, indicating microstructural changes. A detailed crystallization mechanism of high-strength LS2 glass–ceramics is proposed.

An improved pulse sequence and inversion algorithm of [formula omitted] spectrum

The nuclear magnetic resonance transversal relaxation time is widely applied in geological prospecting, both in laboratory and downhole environments. However, current methods used for data acquisition and inversion should be reformed to characterize geological samples with complicated relaxation components and pore size distributions, such as samples of tight oil, gas shale, and carbonate. We present an improved pulse sequence to collect transversal relaxation signals based on the CPMG (Carr, Purcell, Meiboom, and Gill) pulse sequence. The echo spacing is not constant but varies in different windows, depending on prior knowledge or customer requirements. We use the entropy based truncated singular value decomposition (TSVD) to compress the ill-posed matrix and discard small singular values which cause the inversion instability. A hybrid algorithm combining the iterative TSVD and a simultaneous iterative reconstruction technique is implemented to reach the global convergence and stability of the inversion. Numerical simulations indicate that the improved pulse sequence leads to the same result as CPMG, but with lower echo numbers and computational time. The proposed method is a promising technique for geophysical prospecting and other related fields in future.

In Situ NMR Measurements of Vapor Deposited Ice

In situ NMR spin–lattice relaxation measurements were performed on several vapor deposited ices. The measurements, which span more than 6 orders of magnitude in relaxation times, show a complex spin–lattice relaxation pattern that is strongly dependent on the growth conditions of the sample. The relaxation patterns change from multitime scale relaxation for samples grown at temperatures below the amorphous–crystalline transition temperature to single exponential recovery for samples grown above the transition temperature. The slow-relaxation contribution seen in cold-grown samples exhibits a temperature dependence, and becomes even slower after the sample is annealed at 200 K. The fast-relaxation contribution seen in these samples, does not seem to change or disappear even when heating to temperatures where the sample is evaporated. The possibility that the fast relaxation component is linked to the microporous structures in amorphous ice samples is further examined using an environmental electron scanning microscope. The images reveal complex mesoscale microporous structures which maintain their morphology up to their desorption temperatures. These findings, support the possibility that water molecules at pore surfaces might be responsible for the fast-relaxation contribution. Furthermore, the results of this study indicate that the pore-collapse dynamics observed in the past in amorphous ices using other experimental techniques, might be effectively inhibited in samples which are grown by relatively fast vapor deposition.

Color of postponed magnetic noise inK0.4[Cr(CN)6][Mn(R/S)−pn](R/S)−pnH0.6molecular ferrimagnet

Exotic conditions for the existence and evolution of nonlinear spin ensembles (domain walls, spin solitons, skyrmions) in molecular-based magnets are incarnated in the macroscopic response of magnetization corresponding to collective stochastic behavior. The molecular ferrimagnet ${\mathrm{K}}_{0.4}[\mathrm{Cr}{(\mathrm{CN})}_{6}][\mathrm{Mn}(\mathrm{R}/\mathrm{S})\ensuremath{-}\mathrm{pn}](\mathrm{R}/\mathrm{S})\ensuremath{-}\mathrm{pn}{\mathrm{H}}_{0.6}$ manifests three types of magnetic relaxation: (a) continuous decay of magnetic moment, (b) stepwise relaxation by stochastic magnetization jumps, and (c) a single jump of magnetization in threshold magnetic field. Continuous relaxation at 20--50 K is provided by domain wall movement described in the frames of a strong pinning model, while a low-temperature continuous component of relaxation does not follow this model. Stepwise stochastic relaxation was observed below 8 K in both a sweeping reverse magnetic field and a stationary reverse magnetic field. Statistical treatment of the postponed magnetization jumps revealed a multimodal amplitude distribution of stochastic magnetization jumps corresponding to magnetic moment transitions between few clear distinguishable levels. Spectral density of magnetization jumps in a stationary magnetic field corresponds to white noise, while spectral density in a sweeping magnetic field manifests pink noise $\ensuremath{\sim}1/f$ provided by self-organized criticality. Postponed emission of magnetic noise in the ${10}^{\ensuremath{-}6}\ensuremath{-}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{Hz}$ frequency range was observed in stationary conditions in contrast to Barkhausen noise.

Synthesis and 7Li Ion Dynamics in Polyarylene‐Ethersulfone‐Phenylene‐Oxide‐Based Polymer Electrolytes

A new block‐co‐polymer based on poly(arylene ether sulfone) and nitrile‐functionalized poly(phenylene oxide) is prepared via polycondensation. Upon swelling with Li triflate dispersed in succinonitrile, a polymer electrolyte suitable for application in secondary Li ion batteries is obtained, which at temperatures above 313 K exhibits conductivities of 10−4–10−3 S cm−1. The presence of distinct coordination modes of the Li ions (not discernible from inspection of 7Li chemical shifts) is revealed based on a dynamic contrast identified from a distribution of transverse relaxation times. Three relaxation components reflecting polymer‐bound, partially and fully solvated Li ion species are identified on the basis of Carr–Purcell–Meiboom–Gill NMR data after inverse Laplace transformation and multiexponential relaxation analysis toolkit analysis thus highlighting the versatility of the applied methods. image

Weak solutions of the Landau–Lifshitz–Bloch equation

The Landau–Lifshitz–Bloch (LLB) equation is a formulation of dynamic micromagnetics valid at all temperatures, treating both the transverse and longitudinal relaxation components important for high-temperature applications. We study LLB equation in case the temperature raised higher than the Curie temperature. The existence of weak solution is showed and its regularity properties are also discussed. In this way, we lay foundations for the rigorous theory of LLB equation that is currently not available.

Adult age differences in subcortical myelin content are consistent with protracted myelination and unrelated to diffusion tensor imaging indices

Post mortem studies suggest protracted myelination of subcortical white matter into the middle age followed by gradual decline in the late adulthood. To date, however, establishing the proposed inverted-U pattern of age-myelin association proved difficult, as the most common method of investigating white matter, diffusion tensor imaging (DTI), usually reveals only linear associations between DTI indices and age among healthy adults. Here we use a novel method of estimating Myelin Water Fraction (MWF) based on modeling the short spin-spin (T2) relaxation component from multi-echo T2 relaxation imaging data and assess subcortical myelin content within six white matter tracts in a sample of healthy adults (N=61, age 18–84 years). Myelin content evidenced a quadratic relationship with age, in accord with the pattern observed postmortem studies. In contrast, DTI-derived indices that are frequently cited as proxies for myelination, fractional anisotropy (FA) and radial diffusivity (RD), exhibited linear or null relationships with age. Furthermore, the magnitude of age differences in MWF varied across the white matter tracts. Myelin content estimated by MWF was unrelated to FA and correlated with RD only in the splenium. These findings are consistent with the notion that myelination continues throughout the young adulthood into the middle age. The results demonstrate that single-tensor DTI cannot serve as a source of specific proxies for myelination of white matter tracts.

Fundamental View of Electronic Structures of β-NaYF4, β-NaGdF4, and β-NaLuF4

We discussed the electronic structures of β-NaLnF4 (Ln = Y, Gd, and Lu). We found the band gap keeps nearly constant (8–9 eV). However, the difference of the experimentally observed band gap arises from the different positions of 4f orbital levels relative to the valence band maximum. The 4f empty state of Gd falls into the band gap, led to a decreased band gap for β-NaGdF4, and is spin-polarized. In contrast, both filled and empty 4f levels of Lu widely separated below and above the valence and conduction band edges, respectively, which means they do not influence the optical transitions in the band gap of the host lattice. By projecting the components of self-energy and wave function relaxation in 4f orbitals, we indicated a hidden level of Gd and Lu ions in the β-lattices, giving three Gd/Lu ions in the lattice split into two different types of electronic levels. This analysis helped us understand the essential mechanism and modified the energy migration mediated upconversion (EMU) model. Different 4f ...

A novel approach to neutron scattering instrumentation for probing multiscale dynamics in soft and biological matter

We present a concept and ray-tracing simulation of a mechanical device that will enable inelastic neutron scattering measurements where the data at energy transfers from a few μeV to several hundred meV can be collected in a single, gapless spectrum. Besides covering 5 orders of magnitude on the energy (time) scale, the device provides data over 2 orders of magnitude on the scattering momentum (length) scale in a single measurement. Such capabilities are geared primarily toward soft and biological matter, where the broad dynamical features of relaxation origin largely overlap with vibration features, thus necessitating gapless spectral coverage over several orders of magnitude in time and space. Furthermore, neutron scattering experiments with such a device are performed with a fixed neutron final energy, which enables measurements, with neutron energy loss in the sample, at arbitrarily low temperatures over the same broad spectral range. This capability is also invaluable in biological and soft matter research, as the variable temperature dependence of different relaxation components allows their separation in the scattering spectra as a function of temperature.

A relaxation times coupling method to construct acoustic relaxation calibration for two-frequency measuring gas compositions

In our previous work (Hu et al., 2014), a method has been proposed to detect gas compositions by locating the acoustic spectral peaks, which can be detected only by two-frequency acoustic measurements in practice. However, as a ‘Detection Calibration’, the effective relaxation area (ERA) constructed by existing theoretical model cannot match the two-frequency measurements when there are more than one strong relaxational components in gas mixtures. This paper proposes a method to construct the ERA by coupling the decoupled single relaxation times together to a whole relaxation time. For gas mixtures with only one single relaxation process, the predicted ERA results match with the experimental data better than those predicted by the existing model. Moreover, for gas mixtures in which more than one relaxation process are significant, the ERA results predicted by the proposed method also match with the detection results of two-frequency measurements better than the existing model. This relaxation time coupling based ERA constructing method is validated by the application in low-quality natural gas detection.

Nanophotoactivity of Porphyrin Functionalized Polycrystalline ZnO Films.

Kelvin probe force microscopy in darkness and under illumination is reported to provide nanoscale-resolved surface photovoltage maps of hybrid materials. In particular, nanoscale charge injection and charge recombination mechanisms occurring in ZnO polycrystalline surfaces functionalized with Protoporphyrin IX (H2PPIX) are analyzed. Local surface potential and surface photovoltage maps not only reveal that upon molecular adsorption the bare ZnO work function increases, but also they allow study of its local dependence. Nanometer-sized regions not correlated with apparent topographic features were identified, presenting values significantly different from the average work function. Depending on the region, the response to the light excitation is different, distinguishing two relaxation processes, one faster than the other. This behavior can be explained in terms of electrons trapped closed to the molecule-semiconductor interface or electrons pushed into the ZnO bulk, respectively. Moreover, the origin of these differences is correlated with the H2PPIX-ZnO bonding and molecules configuration and aggregation. The chenodeoxycholic acid (CDCA) coadsorption leads to a more homogeneous surface potential distribution, confirming the antiaggregate effect of this additive, while the surface photovoltage is mostly dominated by the slow relaxation component. This work reveals the complexity of real device architectures with ill-defined surfaces even in a relatively simple system with only one type of dye molecule and hightlights the importance of nanoscale characterization with appropriate tools.

Effects of malondialdehyde-induced protein modification on water functionality and physicochemical state of fish myofibrillar protein gel

Effects of malondialdehyde (MDA)-induced modification on water distribution in fish myofibrillar proteins (MP) gels were investigated using nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). The oxidative modifications of MP gels were evaluated by surface hydrophobicity, gel strength, water holding capacity (WHC), scanning electron microscopy (SEM) and SDS-PAGE. Influence of heating procedure on water distribution and functional properties of modified MP gels was also investigated. Results from NMR and MRI indicated that the water functionality was strongly affected by the modification level, which corresponded to the changes of water holding capacity of MP upon MDA modification. Compared with unmodified MP gels, the T2 relaxation times of modified sample increased significantly, indicating an alteration of water-protein interaction upon MDA-induced modification. The fraction of P23 declined from 7.66% to 0.15% as the MDA addition increased from 0 to 50mM. Moreover, the relaxation components T2b disappeared with the addition of MDA mainly due to enhanced protein flexibility and surface hydrophobicity. Besides, the P23 (free water) of heated MP samples increased by 5.41 times compared with that of unheated MP samples.

Ultrafast dynamics of quasiparticles and coherent acoustic phonons in slightly underdoped (BaK)Fe2As2

We have utilized ultrafast optical spectroscopy to study carrier dynamics in slightly underdoped (BaK)Fe2As2 crystals without magnetic transition. The photoelastic signals due to coherent acoustic phonons have been quantitatively investigated. According to our temperature-dependent results, we found that the relaxation component of superconducting quasiparticles persisted from the superconducting state up to at least 70 K in the normal state. Our findings suggest that the pseudogaplike feature in the normal state is possibly the precursor of superconductivity. We also highlight that the pseudogap feature of K-doped BaFe2As2 is different from that of other iron-based superconductors, including Co-doped or P-doped BaFe2As2.

Reading Chaucer’s Monk’s Tale

The disjointed repetitiveness of the Monk’s brief tragedies has irritated and bored many readers. The tragedies, however, become much more appealing if one reads them like a monk. Boredom, as an ascetic challenge and as a component of meditative relaxation, is an integral feature of the long monastic tradition that Chaucer inherits. Chaucer’s “An ABC” and Deguileville’s Pelerinage de la vie humaine exemplify the monastic poetics informing the Monk’s Tale. Monastic literature encourages readers to assimilate themselves to the texts they read, and the repetitiveness of the Monk’s Tale performs such assimilation, which monks imagined as rumination: the reader is like a cow chewing the cud. Nabugodonosor, who eats grass like a ruminator, is the Monk’s only protagonist to escape destruction. His son Balthasar fails to learn from him. The Nabugodonosor-Balthasar sequence both models ruminative reading and dramatizes the misreading that has dogged the Monk’s Tale.

Origin of Photocarrier Losses in Iron Pyrite (FeS2) Nanocubes.

Iron pyrite has received significant attention due to its high optical absorption. However, the loss of open circuit voltage (Voc) prevents its further application in photovoltaics. Herein, we have studied the photophysics of pyrite by ultrafast laser spectroscopy to understand fundamental limitation of low Voc by quantifying photocarrier losses in high quality, stoichiometric, and phase pure {100} faceted pyrite nanocubes. We found that fast carrier localization of photoexcited carriers to indirect band edge and shallow trap states is responsible for major carrier loss. Slow relaxation component reflects high density of defects within the band gap which is consistent with the observed Mott-variable range hopping (VRH) conduction from transport measurements. Magnetic measurements strikingly show the magnetic ordering associated with phase inhomogeneity, such as FeS2-δ (0 ≤ δ ≤ 1). This implies that improvement of iron pyrite solar cell performance lies in mitigating the intrinsic defects (such as sulfur vacancies) by blocking the fast carrier localization process. Photocarrier generation and relaxation model is presented by comprehensive analysis. Our results provide insight into possible defects that induce midgap states and facilitate rapid carrier relaxation before collection.

Passing the time when in pain: Investigating the role of musical valence.

The effective management of pain outside of clinical settings represents a significant challenge to health services. Music listening has been successfully used as a method of pain management, with the greatest benefits to listeners evident if the music is familiar, preferred and has emotional resonance. This study examined the role of self-selected emotion-inducing music used for pain management (pain tolerance, intensity, perceived control, distraction and anxiety reduction) during the cold pressor test. In a repeated-measures design, four cold pressor tests were used to induce short-term, acute pain, whilst 41 participants listened either to happy, sad, relaxing or no music. Findings indicated that music enhanced pain tolerance over no music, and happy and relaxing music increased pain tolerance and altered time perception to a greater extent than sad music. Happy and relaxing music facilitated distraction from pain and enhanced perceived pain control. Relaxing music additionally had anxiolytic properties and reduced pain intensity. Results suggest that music’s inclusion in pain management is justified and that music with happy and relaxing components can be used to facilitate coping with pain in a non-clinical context.

Patients' experiences of a behavioural intervention for migraine headache: a qualitative study.

BackgroundMigraine headache has a high prevalence and a severe impact on personal, social and work life, forming a significant burden on patients, service providers and society. There is some evidence of the effectiveness of behavioural interventions to supplement drug therapy but a recognised need to identify an effective minimal contact approach to enhance access and provide a model for use in publicly funded health systems. This study uses in-depth interviews to examine patients’ experience and responses to a behavioural intervention with relaxation and CBT components delivered in three individual therapist sessions with follow-up.MethodsQualitative study of 20 adults aged 18–75 years in London, UK, with clinically diagnosed migraine and at least four headache days per month. Semi-structured and tape recorded interviews were held post intervention based on a topic guide. Transcripts were coded and charted for all participants and analysed thematically.ResultsThe majority of participants cited the impacts of migraine and a desire for additional non-drug treatment as their main reasons for taking part and almost all completed the course. They valued contact with the therapist and almost all reported benefiting from the therapy. Post intervention they used those techniques they found most beneficial and implemented them flexibly in their daily life to reduce stress and risks of migraine or to respond to migraine. Relaxation training (deep breathing) was easily adopted and often used post intervention. The CBT components were mainly viewed positively but regarded as more challenging to learn and implement.ConclusionsPatients’ selectively identified and employed the techniques learned as ‘tools’ to assist in preventing and managing their migraines, with reported benefits supporting the development of minimal contact behavioural therapy to increase accessibility for adults with migraine headache and the conduct of a definitive trial.

Structural relaxation of acridine orange dimer in bulk water and inside a single live lung cell.

Structural relaxation of the acridine orange (AO) dimer in bulk water and inside a single live lung cell is studied using time resolved confocal microscopy and molecular dynamics (MD) simulations. The emission maxima (λem (max)∼ 630 nm) of AO in a lung cancer cell (A549) and a non-cancer lung fibroblast cell (WI38) suggest that AO exists as a dimer inside the cell. Time-dependent red shift in emission maximum indicates dynamic relaxation of the AO dimer (in the excited state) with a time constant of 500-600 ps, both in bulk water and inside the cell. We have calculated the equilibrium relaxation dynamics of the AO dimer in the ground state using MD simulations and found a slow component of time scale ∼ 350 ps. The intra- and inter-molecular components of the total relaxation dynamics of the AO dimer reveal the presence of a slow component of the order of a few hundred picoseconds. Upon restricting intra-molecular dye dynamics by harmonic constraint between AO monomers, the slow component vanishes. Combining the experimental observations and MD simulation results, we ascribe the slow component of the dynamic relaxation of the AO dimer to the structural relaxation, namely, fluctuations in the distance between the two monomers and associated fluctuation in the number of water molecules.