Showing papers on "Relaxation (NMR) published in 2003"
TL;DR: Double-decker phthalocyanine complexes with Tb3+ or Dy3+ showed slow magnetization relaxation as a single-molecular property and a significant temperature rise results from a mechanism in the relaxation process different from that in the transition-metal-cluster SMMs.
Abstract: Double-decker phthalocyanine complexes with Tb3+ or Dy3+ showed slow magnetization relaxation as a single-molecular property. The temperature ranges in which the behavior was observed were far higher than that of the transition-metal-cluster single-molecule magnets (SMMs). The significant temperature rise results from a mechanism in the relaxation process different from that in the transition-metal-cluster SMMs. The effective energy barrier for reversal of the magnetic moment is determined by the ligand field around a lanthanide ion, which gives the lowest degenerate substate a large |Jz| value and large energy separations from the rest of the substates in the ground-state multiplets.
2,124 citations
TL;DR: In this article, a review of the relaxational properties of random-site electric dipoles in dielectrics is presented, including the role of pressure and applied dc biasing electric fields in understanding the physics of these materials including the R-to-FE crossover.
Abstract: Random lattice disorder produced by chemical substitution in ABO3 perovskites can lead to the formation of dipolar impurities and defects that have a profound influence on the static and dynamic properties of these materials that are the prototypical soft ferroelectric (FE) mode systems. In these highly polarizable host lattices, dipolar entities form polar nanodomains whose size is determined by the dipolar correlation length, rc, of the host and that exhibit dielectric relaxation in an applied ac field. In the very dilute limit (< 0.1at.%) each domain behaves as a non-interacting dipolar entity with a single relaxation time. At higher concentrations of disorder, however, the domains can interact leading to more complex relaxational behaviour. Among the manifestations of such behaviour is the formation of a glass-like relaxor (R) state, or even an ordered FE state for a sufficiently high concentration of overlapping domains. After a brief discussion of the physics of random-site electric dipoles in dielectrics, this review begins with the simplest cases, namely the relaxational properties of substitutional impurities (e.g., Mn, Fe and Ca) in the quantum paraelectrics KTaO3 and SrTiO3. This is followed by discussions of the relaxational properties of Li-and Nb-doped KTaO3 and of the strong relaxors in the PbMg1/3Nb2/3O3 and La-substituted PbZr1−xTixO3 families. Some emphasis will be on the roles of pressure and applied dc biasing electric fields in understanding the physics of these materials including the R-to-FE crossover.
681 citations
TL;DR: In this article, DFT simulations are combined with quantum dynamics calculations of electronic relaxation to investigate the interfacial electron transfer in catechol/TiO2-anatase nanostructures under vacuum conditions.
Abstract: Ab initio DFT molecular dynamics simulations are combined with quantum dynamics calculations of electronic relaxation to investigate the interfacial electron transfer in catechol/TiO2-anatase nanostructures under vacuum conditions. It is found that the primary process in the interfacial electron-transfer dynamics involves an ultrafast (τ1 ≃ 6 fs) electron-injection event that localizes the charge in the Ti4+ surface ions next to the catechol adsorbate. The primary event is followed by charge delocalization (i.e., carrier diffusion) through the TiO2-anatase crystal, an anisotropic diffusional process that can be up to an order of magnitude slower along the [−101] direction than carrier relaxation along the [010] and [101] directions in the anatase crystal. It is shown that both the mechanism of electron injection and the time scales for interfacial electron transfer are quite sensitive to the symmetry of the electronic state initially populated in the adsorbate molecule. The results are particularly releva...
369 citations
TL;DR: The relaxation time, T1, of the spin of a single electron confined in a semiconductor quantum dot (a proposed quantum bit) is measured and a lower bound on T1 is found of 50 micros at 7.5 T, only limited by the signal-to-noise ratio.
Abstract: We have measured the relaxation time, ${T}_{1}$, of the spin of a single electron confined in a semiconductor quantum dot (a proposed quantum bit). In a magnetic field, applied parallel to the two-dimensional electron gas in which the quantum dot is defined, Zeeman splitting of the orbital states is directly observed by measurements of electron transport through the dot. By applying short voltage pulses, we can populate the excited spin state with one electron and monitor relaxation of the spin. We find a lower bound on ${T}_{1}$ of $50\text{ }\ensuremath{\mu}\mathrm{s}$ at 7.5 T, only limited by our signal-to-noise ratio. A continuous measurement of the charge on the dot has no observable effect on the spin relaxation.
316 citations
TL;DR: Both techniques measure variable fluorescence, but there are a number of important differences in the methods used to calculate photosynthetic rates, which necessitates the use of a different terminology in order to avoid confusion until the underlying physiological differences are resolved.
Abstract: In this review, we briefly describe the two main techniques used to measure variable fluorescence in the aquatic environment, and show how the parameters derived from this technique can be used to estimate the rate of photosynthesis. The methods estimate the photochemical efficiency of photosystem II from ratios of fluorescence levels. Flashes of light that are transiently saturating for photochemistry (i.e. they are sufficiently bright to close all PSII reaction centres) are used to obtain the maximum fluorescence level. The type of saturating flash differs between methods. In one approach, single turnover (ST) flashes are applied. This allows only one charge separation during the flash and reduces only the primary acceptor of PS II, raising fluorescence to a level Fm(ST) . In a second approach the flashes are multiple turnover (MT), which allow repeated charge separation processes until all electron acceptors of PS II are reduced. A relaxation of quenching is induced by the longer flash, and this raises...
312 citations
TL;DR: In this paper, the authors extend the coupling model to also address the dynamics in these earlier time regimes, and the crux of the extended coupling model is the quantitatively determinable independent relaxation time, from which the characteristics of the dynamics can be deduced.
Abstract: In the past the coupling model (CM) was focused on the dynamics at long times, when all relaxing units of an interacting system participate in the terminal, cooperative Kohlrausch relaxation. No attention was paid to the dynamics at short times when all the relaxing units are caged, nor to intermediate times when an increasing number of them are no longer caged. We now extend the CM to also address the dynamics in these earlier time regimes. The crux of the extended CM is the quantitatively determinable independent relaxation time, from which the characteristics of the dynamics in the short-time and intermediate-time regimes can be deduced. This description of the evolution of the dynamics by the extended CM is supported by broadband dielectric relaxation spectra of two archetypal systems, the glassy/molten ionic conductors and supercooled liquids. In supercooled liquids, the 'universal' Johari–Goldstein β-relaxation provides evidence for the physical reality of the independent relaxation of the extended CM.
306 citations
TL;DR: In this paper, an epoxy resin matrix with randomly dispersed iron micro-particles in various amounts were prepared and their dielectric spectra were measured in the frequency range 5 Hz −13 MHz and temperature interval from ambient to 140 °C.
Abstract: Polymer composites of an epoxy resin matrix with randomly dispersed Iron micro-particles in various amounts were prepared and their dielectric spectra were measured in the frequency range 5 Hz–13 MHz and temperature interval from ambient to 140 °C. Obtained data were analysed by means of electric modulus formalism. Interfacial or Maxwell-Wagner-Sillars relaxation process was revealed in the frequency range and temperature interval of the measurements, which was found to follow the Cole-Davidson approach for the distribution of relaxation times. The examined systems exhibit strong dispersion with frequency. At low frequencies ac conductivity tends to be constant, while at higher becomes frequency dependent varying as a power of frequency. Conductivity increases with temperature in the low frequency regime, remaining almost unaffected at higher frequencies.
273 citations
TL;DR: The results reveal the spontaneous appearance of static internal magnetic fields below the superconducting transition temperature, providing unambiguous evidence for the breaking of time-reversal symmetry in the superconductor state.
Abstract: We report on muon-spin relaxation measurements of the 4f(2)-based heavy-fermion superconductor filled-skutterudite Pr(Os4Sb12. The results reveal the spontaneous appearance of static internal magnetic fields below the superconducting transition temperature, providing unambiguous evidence for the breaking of time-reversal symmetry in the superconducting state. A discussion is made on which of the spin or orbital component of Cooper pairs carries a nonzero momentum.
256 citations
TL;DR: In this article, computer modeling techniques have been used to examine the mechanistic features of oxygen ion transport in the La8Sr2Si6O26 and La9.33Si6 O26 apatiteoxides at the atomic level.
Abstract: Computer modelling techniques have been used to examine the mechanistic features of oxygen ion transport in the La8Sr2Si6O26 and La9.33Si6O26 apatite-oxides at the atomic level. The potential model reproduces the observed complex structures of both phases, which are comprised of [SiO4] tetrahedral units and La/O channels. Defect simulations have examined the lowest energy interstitial and vacancy sites. The results suggest that oxygen ion migration in La8Sr2Si6O26 is via a vacancy mechanism with a direct linear path between O5 sites. Interstitial oxygen migration is predicted for La9.33Si6O26via a non-linear (sinusoidal-like) pathway through the La3/O5 channel. The simulations demonstrate the importance of local relaxation of [SiO4] tetrahedra to assist in the facile conduction of oxygen interstitial ions. In general, the modelling study confirms that the high ionic conductivity in silicate-based apatites (with oxygen excess or cation vacancies) is mediated by oxygen interstitial migration.
253 citations
TL;DR: It is proposed that the unusual ultraslow dynamics are due to the relaxation of internal stresses, built into the sample at the jamming transition, and simple scaling arguments that support this hypothesis are presented.
Abstract: We use conventional and multispeckle dynamic light scattering to investigate the dynamics of a wide variety of jammed soft materials, including colloidal gels, concentrated emulsions, and concentrated surfactant phases. For all systems, the dynamic structure factor f(q,t) exhibits a two-step decay. The initial decay is due to the thermally activated diffusive motion of the scatterers, as indicated by the q−2 dependence of the characteristic relaxation time, where q is the scattering vector. However, due to the constrained motion of the scatterers in jammed systems, the dynamics are arrested and the initial decay terminates in a plateau. Surprisingly, we find that a final, ultraslow decay leads to the complete relaxation of f(q,t), indicative of rearrangements on length scales as large as several microns or tens of microns. Remarkably, for all systems the same very peculiar form is found for the final relaxation of the dynamic structure factor: f(q,t) ∼ exp[−(t/τs)p], with p ≈ 1.5 and τs ∼ q−1, thus suggesting the generality of this behavior. Additionally, for all samples the final relaxation slows down with age, although the aging behavior is found to be sample dependent. We propose that the unusual ultraslow dynamics are due to the relaxation of internal stresses, built into the sample at the jamming transition, and present simple scaling arguments that support this hypothesis.
253 citations
TL;DR: In this article, a microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory.
Abstract: A microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory. Thermal fluctuations are included via a random force which destroys the idealized glass transition and restores ergodicity through activated barrier hopping. The approach is predictive, containing no adjustable parameters or postulated underlying dynamic or thermodynamic divergences. Detailed application to hard-sphere colloidal suspensions reveals good agreement with experiment for the location of the kinetic glass transition volume fraction, the dynamic incoherent scattering relaxation time, apparent localization length, and length scale of maximum nongaussian behavior. Multiple connections are predicted between thermodynamics, short-time dynamics in the nearly localized state, and long-time relaxation by entropic barrier crossing. A critical comparison of the fluid volume fraction dependence of the hopping time with fit formulas which contain ideal divergences has been performed. Application of the derivative Stickel analysis suggests that the fit functions do not provide an accurate description over a wide range of volume fractions. Generalization to treat the kinetic vitrification of more complex colloidal and nanoparticle suspensions, and thermal glass-forming liquids, is possible.
TL;DR: Ultracold sodium molecules were produced from an atomic Bose-Einstein condensate by ramping an applied magnetic field across a Feshbach resonance to selectively remove the remaining atoms, preventing fast collisional relaxation of the molecules.
Abstract: Ultracold sodium molecules were produced from an atomic Bose-Einstein condensate by ramping an applied magnetic field across a Feshbach resonance. More than ${10}^{5}$ molecules were generated with a conversion efficiency of $\ensuremath{\sim}4%$. Using laser light resonant with an atomic transition, the remaining atoms could be selectively removed, preventing fast collisional relaxation of the molecules. Time-of-flight analysis of the pure molecular sample yielded an instantaneous phase-space density greater than 20.
TL;DR: This review focuses on the use of solid-state NMR techniques for the characterization of pharmaceutical solids (drug substance and dosage form) through methods for studying structure and conformation, analyzing molecular motions, and measuring internuclear distances.
TL;DR: In this article, the absorption and emission properties of the neutral oxygen vacancy in ZnO were investigated using temperature-dependent photoluminescence (PL) experiments, and the Mollwo-Ivey relation for the position of the F-centre absorption as a function of the anion-cation distance was applied to find that the oxygen vacancies fit perfectly in the line given by MgO, CaO, SrO and BaO.
Abstract: We present our investigations on the absorption and emission properties of the neutral oxygen vacancy in ZnO. Temperature-dependent photoluminescence (PL) experiments allow to determine the zero-phonon-energy of the emission and its phonon-coupling parameters. The absorption to the singlet excited state is observed in PL-excitation experiments at energies above 3.1 eV. Relaxation drives the system from the singlet, diamagnetic, excited state to the emissive, paramagnetic triplet state. Applying the Mollwo–Ivey relation for the energetical position of the F-centre absorption as a function of the anion–cation distance, we find that the oxygen vacancies in ZnO fit perfectly in the line given by MgO, CaO, SrO and BaO.
01 Mar 2003
TL;DR: In this paper, a microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory.
Abstract: A microscopic kinetic description of single-particle transient localization and activated transport in glassy fluids is developed which combines elements of idealized mode-coupling theory, density functional theory, and activated rate theory. Thermal fluctuations are included via a random force which destroys the idealized glass transition and restores ergodicity through activated barrier hopping. The approach is predictive, containing no adjustable parameters or postulated underlying dynamic or thermodynamic divergences. Detailed application to hard-sphere colloidal suspensions reveals good agreement with experiment for the location of the kinetic glass transition volume fraction, the dynamic incoherent scattering relaxation time, apparent localization length, and length scale of maximum nongaussian behavior. Multiple connections are predicted between thermodynamics, short-time dynamics in the nearly localized state, and long-time relaxation by entropic barrier crossing. A critical comparison of the fluid volume fraction dependence of the hopping time with fit formulas which contain ideal divergences has been performed. Application of the derivative Stickel analysis suggests that the fit functions do not provide an accurate description over a wide range of volume fractions. Generalization to treat the kinetic vitrification of more complex colloidal and nanoparticle suspensions, and thermal glass-forming liquids, is possible.
TL;DR: A theory of the electron-hole interaction in the photoexcited states is developed, and the one-dimensional character and tubular structure introduces a novel relaxation pathway for carriers photo Excited above the fundamental band edge.
Abstract: The electronic band gaps measured in fluorescence spectroscopy on individual single wall carbon nanotubes isolated within micelles show significant deviations from the predictions of one electron band theory. We resolve this problem by developing a theory of the electron-hole interaction in the photoexcited states. The one-dimensional character and tubular structure introduce a novel relaxation pathway for carriers photoexcited above the fundamental band edge. Analytic expression for the energies and line shapes of higher subband excitons are derived, and a comparison with experiment is used to extract the value of the screened electron-hole interaction.
TL;DR: Different designs and applications of targeted MR CA directed to specific molecular entities and the feasibility of these approaches for in vivo MRI are reviewed.
Abstract: Magnetic resonance imaging (MRI) produces high-resolution three-dimensional maps delineating morphological features of the specimen. Differential contrast in soft tissues depends on endogenous differences in water content, relaxation times, and/or diffusion characteristics of the tissue of interest. The specificity of MRI can be further increased by exogenous contrast agents (CA) such as gadolinium chelates, which have been successfully used for imaging of hemodynamic parameters including blood perfusion and vascular permeability. Development of targeted MR CA directed to specific molecular entities could dramatically expand the range of MR applications by combining the noninvasiveness and high spatial resolution of MRI with specific localization of molecular targets. However, due to the intrinsically low sensitivity of MRI (in comparison with nuclear imaging), high local concentrations of the CA at the target site are required to generate detectable MR contrast. To meet these requirements, the MR targeted CA should recognize targeted cells with high affinity and specificity. They should also be characterized by high relaxivity, which for a wide variety of CA depends on the number of contrast-generating groups per single molecule of the agent. We will review different designs and applications of targeted MR CA and will discuss feasibility of these approaches for in vivo MRI.
TL;DR: In this article, the dielectric relaxation of several molecular organic supercooled liquids, αβ-tris-naphthylbenzene (C36H24 and C36H10D14), squalane, and decahydroisoquinoline, was studied in the frequency range 10−2-107'Hz, equivalent to temperatures between Tg and approximately 1.2Tg.
Abstract: We have measured the dielectric relaxation of several molecular organic supercooled liquids, ααβ-tris-naphthylbenzene (C36H24 and C36H10D14), squalane, and decahydroisoquinoline. The dynamics is studied in the frequency range 10−2–107 Hz, equivalent to temperatures between Tg and approximately 1.2×Tg. For the very low dielectric loss materials, a resolution of tan δ≈3×10−5 is required in order to observe the details of the relaxation behavior. Characteristic quantities like fragility, relaxation time dispersion, time–temperature superposition, and the slow Johari–Goldstein type β relaxation are among the properties discussed.
TL;DR: It is shown that the Arrhenius temperature dependence of the beta relaxation time does not persist for temperatures above T(g), consistent with inferences drawn from dielectric relaxation measurements at ambient pressure.
Abstract: Dielectric spectra of the polyalcohols sorbitol and xylitol were measured under isobaric pressures up to 1.8 GPa. At elevated pressure, the separation between the alpha and beta relaxation peaks is larger than at ambient pressure, enabling the beta relaxation times to be unambiguously determined. Taking advantage of this, we show that the Arrhenius temperature dependence of the beta relaxation time does not persist for temperatures above T(g). This result, consistent with inferences drawn from dielectric relaxation measurements at ambient pressure, is obtained directly, without the usual problematic deconvolution the beta and alpha processes.
TL;DR: In this paper, the incompressible limit for an inclined one-dimensional jet was shown to not exist, but the non-hydrodynamic relaxation times were not fixed, but scaled by the Mach number in the same way as the hydrodynamic relaxations.
TL;DR: In this paper, a coarse-grained Langevin model of the polymer dynamics and a numerical solution of the flow generated by the motion of polymer segments are used to predict the dynamics of dissolved long-chain macromolecules in highly confined environments.
Abstract: The dynamics of dissolved long-chain macromolecules are different in highly confined environments than in bulk solution. A computational method is presented here for detailed prediction of these dynamics, and applied to the behavior of ∼1–100 μm DNA in micron-scale channels. The method is comprised of a self-consistent coarse-grained Langevin description of the polymer dynamics and a numerical solution of the flow generated by the motion of polymer segments. Diffusivity and longest relaxation time show a broad crossover from free-solution to confined behavior centered about the point H≈10Sb, where H is the channel width and Sb is the free-solution chain radius of gyration. In large channels, the diffusivity is similar to that of a sphere diffusing along the centerline of a pore. For highly confined chains (H/Sb≪1), Rouse-type molecular weight scaling is observed for both translational diffusivity and longest relaxation time. In the highly confined region, the scaling of equilibrium length and relaxation t...
TL;DR: In this paper, a diatomic solute was used as a probe to study the solvent properties of 1-ethyl-3-methylimidazolium chloride and 1-methyl-3methyloride hexafluorophosphate, and it was found that solvent fluctuations are chacterized by at least two distinct dynamics occurring on vastly different time scales.
Abstract: Solvation in 1-ethyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium hexafluorophosphate is studied via molecular dynamics simulations by employing a diatomic solute as a probe. It is found that solvent fluctuations are chacterized by at least two distinct dynamics occurring on vastly different time scales—rapid subpicosecond dynamics arising mainly from anion translations and slow relaxation ascribed to anion and cation diffusions. Fast subpicosecond dynamics are responsible for more than 50% of the entire relaxation of solvent fluctuations in the temperature range 350 K⩽T⩽500 K. It is also found that solvent spectral shifts and reorganization free energies in these liquids are comparable to those in ambient water.
TL;DR: In this paper, measurements on 1.3/spl mu/m quantum-dot lasers are presented that reveal a number of interesting effects, such as a second lasing line appearing at high bias, corresponding to the excited state transition.
Abstract: Measurements on 1.3-/spl mu/m quantum-dot lasers are presented that reveal a number of interesting effects. 1) At high bias, a second lasing line appears, corresponding to the excited state transition. 2) The linewidth enhancement factor increases dramatically above threshold. 3) The modulation performance is degraded when the second lasing line appears. A comprehensive numerical model is developed to explain this behavior. We attribute it to incomplete gain clamping above threshold. This is caused by a combination of the finite intraband relaxation time and the limited density of states.
TL;DR: Albeit possessing only a few conformational degrees of freedom compared with a protein, the peptide behaves highly nontrivially and provides insights into the complexity of fast protein folding.
Abstract: Ultrafast IR spectroscopy is used to monitor the nonequilibrium backbone dynamics of a cyclic peptide in the amide I vibrational range with picosecond time resolution. A conformational change is induced by means of a photoswitch integrated into the peptide backbone. Although the main conformational change of the backbone is completed after only 20 ps, the subsequent equilibration in the new region of conformational space continues for times >16 ns. Relaxation and equilibration processes of the peptide backbone occur on a discrete hierarchy of time scales. Albeit possessing only a few conformational degrees of freedom compared with a protein, the peptide behaves highly nontrivially and provides insights into the complexity of fast protein folding.
01 Jan 2003
TL;DR: In this paper, a detailed overview of NMR of molecules in uniaxial anisotropic environments can be found, including a discussion of the role of spin relaxation in orientally ordered molecules.
Abstract: I Basics.- 1 Basics of NMR of molecules in uniaxial anisotropic environments.- 2 Density matrix methods in NMR.- 3 Coherent averaging and correlation of anisotropic spin interactions in oriented molecules.- 4 Multiple Quantum NMR Spectroscopy in Orientationally Ordered Fluids.- 5 Spectral Analysis of Orientationally Ordered Molecules.- II NMR of solute atoms and molecules.- 6 NMR of Noble Gases Dissolved in Liquid Crystals.- 7 NMR of partially ordered solutes with emphasis on structure determination.- 8 Observation and interpretation of residual dipolar couplings in biomolecules.- 9 The search for high-resolution NMR methods for membrane peptide structure.- III Theory, models, and simulations.- 10 Solutes as probes of simplified models of orientational order.- 11 Molecular Models of Orientational Order.- 12 Molecular theory of orientational order.- 13 Very Flexible Solutes: Alkyl Chains and Derivatives.- 14 NMR Studies of Solutes in Liquid Crystals: Small Flexible Molecules.- 15 Simulations of Orientational Order of Solutes in Liquid Crystals.- IV Dynamic aspects and relaxation.- 16 Spin relaxation in orientationally ordered molecules.- 17 Low-frequency NMR relaxometry of spatially constrained liquid crystals.- 18 NMR on macroscopically oriented lyotropic systems.- 19 Dynamic NMR in liquid crystals and liquid crystalline solutions.
TL;DR: The aging behavior of colloidal suspensions of laponite, a model synthetic clay, is investigated using light scattering techniques and the correlation of the scattered light intensity as a function of the age of the sample t(w) for various concentrations is measured.
Abstract: The aging behavior of colloidal suspensions of laponite, a model synthetic clay, is investigated using light scattering techniques. In order to measure the complete dynamic structure factor as a function of time and of wave vector, we have developed an original optical setup using a multispeckle technique for simple light scattering. We have thus measured the correlation of the scattered light intensity as a function of the age of the sample t(w) for various concentrations. For sufficiently concentrated samples, we observe a two-stage relaxation process. The fast relaxation is diffusive, stationary, and reminiscent of the liquidlike behavior observed in less concentrated samples. The slow relaxation behavior, however, is more complex. It exhibits two successive regimes as the sample ages. In the first regime, the decay time tau(a) increases exponentially with t(w) as long as tau(a)
TL;DR: Stable, reversible, and highly efficient magnetization switching is triggered by transverse field pulses as short as 140 ps with energies down to 15 pJ and the existence of a relaxation dominated regime is established allowing switching by pulse amplitudes below the quasistatic switching threshold.
Abstract: We evidence multiple coherent precessional magnetization reversal in microscopic spin valves. Stable, reversible, and highly efficient magnetization switching is triggered by transverse field pulses as short as 140 ps with energies down to 15 pJ. At high fields a phase coherent reversal is found revealing periodic transitions from switching to nonswitching under variation of pulse parameters. At the low field limit the existence of a relaxation dominated regime is established allowing switching by pulse amplitudes below the quasistatic switching threshold.
TL;DR: Quasielastic neutron scattering experiments reveal that also the diffusive character of the relevant molecular motions seems to disappear at this length scale, giving further strong support that the glass transition has to be characterised by an inherent length scale of therelevant molecular motions.
Abstract: The glassy dynamics of poly(propylene glycol) (PPG) and poly(dimethyl siloxane) (PDMS) confined to a nanoporous host system revealed by dielectric spectroscopy, temperature-modulated DSC and neutron scattering is compared For both systems the relaxation rates estimated from dielectric spectroscopy and temperature-modulated DSC agree quantitatively indicating that both experiments sense the glass transition For PPG the segmental dynamics is determined by a counterbalance of adsorption and confinement effect The former results form an interaction of the confined macromolecules with the internal surfaces A confinement effect originates from an inherent length scale on which the underlying molecular motions take place The increment of the specific-heat capacity $\Delta c_{\mathrm p}$
at the glass transition vanishes at a finite length scale of 18 nm Both results support the conception that a characteristic length scale is relevant for glassy dynamics For PDMS only a confinement effect is observed which is much stronger than that for PPG Down to a pore size of 75 nm, the temperature dependence of the relaxation times follows the Vogel-Fulcher-Tammann dependence At a pore size of 5 nm this changes to an Arrhenius-like behaviour with a low activation energy At the same pore size $\Delta c_{\mathrm p}$
vanishes for PDMS Quasielastic neutron scattering experiments reveal that also the diffusive character of the relevant molecular motions --found to be characteristic above the glass transition-- seems to disappear at this length scale These results gives further strong support that the glass transition has to be characterised by an inherent length scale of the relevant molecular motions
TL;DR: Steady SSFP imaging during the transient phase can provide various contrasts depending on the flip angle and the number of excitation pulses applied before the acquisition of the central k‐space line, and hyperpolarized nuclei can be optimized according to their T1 and T2 relaxation times.
Abstract: The signal intensity of balanced steady-state free precession (SSFP) imaging is a function of the proton density, T(1), T(2), flip angle (alpha), and repetition time (TR). The steady-state signal intensity that is established after about 5*T(1)/TR can be described analytically. The transient phase or the approach of the echo amplitudes to the steady state is an exponential decay from the initial amplitude after the first excitation pulse to the steady-state signal. An analytical expression of the decay rate of this transient phase is presented that is based on a simple analysis derived from the Bloch equations. The decay rate is a weighted average of the T(1) and T(2) relaxation times, where the weighting is determined by the flip angle of the excitation pulses. Thus, balanced SSFP imaging during the transient phase can provide various contrasts depending on the flip angle and the number of excitation pulses applied before the acquisition of the central k-space line. In addition, transient imaging of hyperpolarized nuclei, such as (3)He, (129)Xe, or (13)C, can be optimized according to their T(1) and T(2) relaxation times.
TL;DR: An electron spin resonance (ESR) study on single crystals of the heavy fermion metal YbRh2Si2 which shows pronounced non-Fermi liquid behavior related to a close antiferromagnetic quantum critical point is reported.
Abstract: Sinuclear magneticresonance (NMR) Knight shift [3]] and dynamic (muonspin relaxation [4]). Two competing theoretical scenarioshave been advanced to describe the heavy electron QCP: aspin density wave scenario [5,6] and a localized momentscenario [7]. In the former scenario magnetism developsby the spin polarization of the Fermi surface and NFLbehavior results from the scattering of the quasiparticlesby quantum critical spin fluctuations. The localized mo-ment scenario assumes that heavy electrons are boundstates between the local moments and conduction elec-trons which disintegrate at the QCP. In YbRh