Добірка наукової літератури з теми "Field-dependent resonance mixing"

AbstractStatic mixers are widely used in various industrial applications to intensify the laminar mixing of non-Newtonian fluids. Non-Newtonian fluids can be categorized into (1) time-independent, (2) time-dependent, and (3) viscoelastic fluids. Computational fluid dynamics studies on the laminar mixing of viscoelastic fluids are very limited due to the complexity in incorporating the multiple relaxation times and the associated stress tensor into the constitutive equations. This review paper provides recommendations for future research studies while summarizing the key research contributions in the field of non-Newtonian fluid mixing using static mixers. This review discusses the different experimental techniques employed such as electrical resistance tomography, magnetic resonance imaging, planar laser-induced fluorescence, and positron emission particle tracking. A comprehensive overview of the mixing fundamentals, fluid chaos, numerical characterization of fluid stretching, development of pressure drop correlations, and derivations of generalized Reynolds number is also provided in this review paper.

All of the hyperfine interactions associated with localized and delocalized electron spin in the four isotopes of the triatomic radical H2N are treated. With nuclear Zeeman energy included, the resulting magnetic-field-dependent nuclear spin states are used to calculate the energies and nuclear spin-state mixing of the nuclear levels and the corresponding hyperfine effects upon electron paramagnetic resonance (EPR) transition energies and nuclear state transition probabilities. In the absence of nuclear spin-state mixing there would be, for example, 10 EPR transitions in D2 15N and 15 in D2 14N, all ΔmI = 0 fully allowed. In the presence of mixing, there are 243 in D2 15N and 729 in D2 14N, with large differences in probability among transitions, many 0 or small. Because of numerous (at least partially allowed) transitions, spectra from isotopes of H2 N radicals are the superposition of signals at greatly different levels of saturation. In this report, EPR spectra from D2 15N models, with either N or 2D hyperfine interaction suppressed, are simulated as a function of microwave frequency and power × spin-lattice relaxation time product. A large range of microwave frequency (and, concomitantly, magnetic field strength) will be needed to evaluate the effect of the nuclear Zeeman energy. The experimental requirements for microwave power and low temperature (long spin-lattice relaxation rate) are quantified.PACS Nos.: 33.15.Pw, 33.35.+r, 33.25.+k

The Fontan procedure for univentricular heart defects creates a nonphysiologic circulation where systemic venous blood drains directly into the pulmonary arteries, leading to multiorgan dysfunction secondary to chronic low-shear nonpulsatile pulmonary blood flow and central venous hypertension. Although blood viscosity increases exponentially in this low-shear environment, the role of shear-dependent (“non-Newtonian”) blood viscosity in this pathophysiology is unclear. We studied three-dimensional (3D)-printed Fontan models in an in vitro flow loop with a Philips 3-T magnetic resonance imaging (MRI) scanner. A 4D flow phase-contrast sequence was used to acquire a time-varying 3D velocity field for each experimental condition. On the basis of blood viscosity of a cohort of patients who had undergone the Fontan procedure, it was decided to use 0.04% xanthan gum as a non-Newtonian blood analog; 45% glycerol was used as a Newtonian control fluid. MRI data were analyzed using GTFlow and MATLAB software. The primary outcome, power loss, was significantly higher with the Newtonian fluid [14.8 (13.3, 16.4) vs. 8.1 (6.4, 9.8)%, medians with 95% confidence interval, P < 0.0001]. The Newtonian fluid also demonstrated marginally higher right pulmonary artery flow, marginally lower shear stress, and a trend toward higher caval flow mixing. Outcomes were modulated by Fontan model complexity, cardiac output, and caval flow ratio. Vortexes, helical flow, and stagnant flow were more prevalent with the non-Newtonian fluid. Our data demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism. NEW & NOTEWORTHY Although blood viscosity increases exponentially in low-shear environments, the role of shear-dependent (“non-Newtonian”) blood viscosity in the pathophysiology of the low-shear Fontan circulation is unclear. We demonstrate that shear-dependent viscosity significantly alters qualitative flow patterns, power loss, pulmonary flow distribution, shear stress, and caval flow mixing in synthetic models of the Fontan circulation. Potential clinical implications include effects on exercise capacity, ventilation-perfusion matching, risk of pulmonary arteriovenous malformations, and risk of thromboembolism.

Singlet fission (SF) is a photophysical process in which one of two adjacent organic molecules absorbs a single photon, resulting in rapid formation of a correlated triplet pair (T1T1) state whose spin dynamics influence the successful generation of uncorrelated triplets (T1). Femtosecond transient visible and near-infrared absorption spectroscopy of a linear terrylene-3,4:11,12-bis(dicarboximide) dimer (TDI2), in which the two TDI molecules are directly linked at one of their imide positions, reveals ultrafast formation of the (T1T1) state. The spin dynamics of the (T1T1) state and the processes leading to uncoupled triplets (T1) were studied at room temperature for TDI2aligned in 4-cyano-4′-pentylbiphenyl (5CB), a nematic liquid crystal. Time-resolved electron paramagnetic resonance spectroscopy shows that the (T1T1) state has mixed5(T1T1) and3(T1T1) character at room temperature. This mixing is magnetic field dependent, resulting in a maximum triplet yield at ∼200 mT. The accessibility of the3(T1T1) state opens a pathway for triplet–triplet annihilation that produces a single uncorrelated T1state. The presence of the5(T1T1) state at room temperature and its relationship with the1(T1T1) and3(T1T1) states emphasize that understanding the relationship among different (T1T1) spin states is critical for ensuring high-yield T1formation from singlet fission.

Abstract Tidal interactions play an important role in many astrophysical systems, but uncertainties regarding the tides of rapidly rotating, centrifugally distorted stars and gaseous planets remain. We have developed a precise method for computing the dynamical, nondissipative tidal response of rotating planets and stars, based on summation over contributions from normal modes driven by the tidal potential. We calculate the normal modes of isentropic polytropes rotating at up to ≃90% of their critical breakup rotation rates, and tabulate fits to mode frequencies and tidal overlap coefficients that can be used to compute the frequency-dependent, nondissipative tidal response (via potential Love numbers k ℓm ). Although fundamental modes (f-modes) possess dominant tidal overlap coefficients at (nearly) all rotation rates, we find that the strong coupling of retrograde inertial modes (i-modes) to tesseral (ℓ > ∣m∣) components of the tidal potential produces resonances that may be relevant to gas giants like Jupiter and Saturn. The coupling of f-modes in rapid rotators to multiple components of both the driving tidal potential and the induced gravitational field also affect the tesseral response, leading to significant deviations from treatments of rotation that neglect centrifugal distortion and high-order corrections. For very rapid rotation rates (≳70% of breakup), mixing between prograde f-modes and i-modes significantly enhances the sectoral (ℓ = ∣m∣) tidal overlap of the latter. The tidal response of very rapidly rotating, centrifugally distorted planets or stars can also be modified by resonant sectoral f-modes that are secularly unstable via the Chandrasekhar–Friedman–Schutz mechanism.

Abstract. The importance of chaotic advection relative to turbulent diffusion is investigated in an idealized model of a 3-D swirling and overturning ocean eddy. Various measures of stirring and mixing are examined in order to determine when and where chaotic advection is relevant. Turbulent diffusion is alternatively represented by (1) an explicit, observation-based, scale-dependent diffusivity, (2) stochastic noise, added to a deterministic velocity field, or (3) explicit and implicit diffusion in a spectral numerical model of the Navier–Stokes equations. Lagrangian chaos in our model occurs only within distinct regions of the eddy, including a large chaotic “sea” that fills much of the volume near the perimeter and central axis of the eddy and much smaller “resonant” bands. The size and distribution of these regions depend on factors such as the degree of axial asymmetry of the eddy and the Ekman number. The relative importance of chaotic advection and turbulent diffusion within the chaotic regions is quantified using three measures: the Lagrangian Batchelor scale, the rate of dispersal of closely spaced fluid parcels, and the Nakamura effective diffusivity. The role of chaotic advection in the stirring of a passive tracer is generally found to be most important within the larger chaotic seas, at intermediate times, with small diffusivities, and for eddies with strong asymmetry. In contrast, in thin chaotic regions, turbulent diffusion at oceanographically relevant rates is at least as important as chaotic advection. Future work should address anisotropic and spatially varying representations of turbulent diffusion for more realistic models.

Interdot coherent excitonic dynamics in nanometric colloidal CdSe quantum dots (QD) dimers lead to interdot charge migration and energy transfer. We show by electronic quantum dynamical simulations that the interdot coherent response to ultrashort fs laser pulses can be characterized by pump-probe transient absorption spectroscopy in spite of the inevitable inherent size dispersion of colloidal QDs. The latter, leading to a broadening of the excitonic bands, induce accidental resonances that actually increase the efficiency of the interdot coupling. The optical electronic response is computed by solving the time-dependent Schrodinger equation including the interaction with the oscillating electric field of the pulses for an ensemble of dimers that differ by their size. The excitonic Hamiltonian of each dimer is parameterized by the QD size and interdot distance, using an effective mass approximation. Local and charge transfer excitons are included in the dimer basis set. By tailoring the QD size, the excitonic bands can be tuned to overlap and thus favor interdot coupling. Computed pump-probe transient absorption maps averaged over the ensemble show that the coherence of excitons in QD dimers that lead to interdot charge migration can survive size disorder and could be observed in fs pump-probe, four-wave mixing, or covariance spectroscopy.

AbstractThe Ce3Pd6Sb5-type rare earth stannides RE3Au6Sn5 (RE= La, Ce, Pr, Nd, Sm) were synthesized by arc-melting of the elements and subsequent annealing in open tantalum crucibles within sealed evacuated silica ampoules. The polycrystalline samples were studied by powder X-ray diffraction. The structures of three crystals were refined from single crystal X-ray diffractometer data: Pmmn, a= 1360.3(9), b= 455.9(2), c= 1023.6(4) pm, wR2 = 0.0275, 1069 F2 values, 48 variables for Ce3Au6Sn5, a= 1352.4(4), b= 455.1(1), c= 1023.7(3) pm, wR2 = 0.0367, 1160 F2 values, 48 variables for Nd3Au6Sn5, and a= 1339.8(2), b= 452.80(7), c= 1012.4(2) pm, wR2 = 0.1204, 1040 F2 values, 49 variables for Sm3Au5.59(2)Sn5.41(2). One of the gold sites of the samarium compound shows a significant degree of Au/Sn mixing. The RE3Au6Sn5 structures are composed of three-dimensional [Au6Sn5] polyanionic networks with the two crystallographically independent rare earth atoms in larger cages, i.e., RE1@Au10Sn6 and RE2@Au8Sn8. The [Au6Sn5] network is stabilized by Au–Sn (266–320 pm), Au–Au (284–301 pm) as well as Sn–Sn (320 pm; distances given for the cerium compound) interactions. Temperature-dependent magnetic susceptibility measurements reveal an antiferromagnetic ordering only for Sm3Au6Sn5, while the other compounds exhibit Curie–Weiss paramagnetism. 119Sn Mössbauer spectroscopy shows resonances in the typical range for intermetallic tin compounds where tin takes part in the polyanionic network [isomer shifts between 1.73(1) and 2.28(1) mm·s−1]. With the help of theoretical electric field gradient calculations using the WIEN2k code it was possible to resolve the spectroscopic contributions of all three crystallographically independent atomic tin sites in the 119Sn spectra of RE3Au6Sn5 (RE= La, Ce, Pr, Nd, Sm).

Abstract We study inserting Co layer thickness-dependent spin transport and spin-orbit torques (SOTs) in the Pt/Co/Py trilayers by spin-torque ferromagnetic resonance. The interfacial perpendicular magnetic anisotropy (IPMA) energy density (K s = 2.7 erg/cm2), which is dominated by interfacial spin-orbit coupling (ISOC) in the Pt/Co interface, total effective spin-mixing conductance (G eff,tot ↑↓=0.42×15 Ω-1 m-2) and two-magnon scattering (β TMS= 0.46 nm2) are first characterized, and the damping-like torque (ξDL= 0.103) and field-like torque (ξFL=-0.017) efficiencies are also calculated quantitatively by varying the thickness of the inserting Co layer. The significant enhancement of ξDL and ξFL in Pt/Co/Py than Pt/Py bilayer system originates from the interfacial Rashba-Edelstein effect due to the strong ISOC between Co-3d and Pt-5d orbitals at the Pt/Co interface. Additionally, we find a considerable out-of-plane spin polarization SOT, which is ascribed to the spin anomalous Hall effect and possible spin precession effect due to IPMA-induced perpendicular magnetization at the Pt/Co interface. Our results demonstrate that the ISOC of the Pt/Co interface plays a vital role in spin transport and SOTs-generation. Our finds offer an alternative approach to improve the conventional SOTs efficiencies and generate unconventional SOTs with out-of-plane spin polarization to develop low power Pt-based spintronic via tailoring the Pt/FM interface.

Abstract The magnesium-rich intermetallic compounds RE 3Ag4Mg12 (RE = Y, La–Nd, Sm–Dy, Yb) and AE 3Ag4Mg12 (AE = Ca, Sr) were synthesized from the elements in sealed tantalum ampoules through heat treatment in an induction furnace. X-ray powder diffraction studies confirm the hexagonal Gd3Ru4Al12 type structure, space group P63/mmc. Three structures were refined from single crystal X-ray diffractometer data: a = 973.47(5), c = 1037.19(5) pm, wR2 = 0.0296, 660 F 2 values, 30 variables for Gd3Ag3.82(1)Mg12.18(1), a = 985.27(9), c = 1047.34(9) pm, wR2 = 0.0367, 716 F 2 values, 29 variables for Yb3Ag3.73(1)Mg12.27(1) and a = 992.41(8), c = 1050.41(8) pm, wR2 = 0.0373, 347 F 2 values, 28 variables for Ca3Ag3.63(1)Mg12.37(1). Refinements of the occupancy parameters revealed substantial Ag/Mg mixing within the silver-magnesium substructure, a consequence of the Ag@Mg8 coordination. The alkaline earth and rare earth atoms build Kagome networks. Temperature dependent magnetic susceptibility measurements indicate diamagnetism/Pauli paramagnetism for the compounds with Ca, Sr, Y and YbII, while the others with the trivalent rare earth elements are Curie-Weiss paramagnets. Most compounds order antiferromagnetically at T N = 4.4(1) K (RE = Pr), 34.6(1) K (RE = Gd) and 23.5(1) K (RE = Tb) while Eu3Ag4Mg12 is a ferromagnet (T C = 19.1(1) K). 151Eu Mössbauer spectra confirm divalent europium (δ = −9.88(1) mm s−1). Full magnetic hyperfine field splitting (18.4(1) T) is observed at 6 K. Yb3Ag4Mg12 shows a single resonance in its 171Yb solid state NMR spectrum at 6991 ppm at 300 K indicating a strong, positive Knight shift.

Protein structure, including its dynamics, is of pervasive significance in biology. A protein’s structure determines its bindings with other molecules [1], and from that its roles in signal transduction, enzymatic activity and mechanical structure. Few cellular processes have no protein involvement. The relationship between a protein’s sequence of amino-acid residues and its three-dimensional structure, partial or otherwise, has long been of considerable interest [2]. A theory of protein folding is proposed in Section 4.10.4 (Hypotheses/Protein folding). This theory varies and extends the backbone-based theory proposed by Rose et al. [3]. This theory may prove to be the most significant offering of the thesis. Overall, this thesis investigates the variation in peptide group resonance and its implications for Resonance-Assisted Hydrogen Bonding [4, 5], RAHB, such as exists in inter-peptide group hydrogen bonding. Natural Bond Orbital [6], NBO, analysis is used for this investigation, and Section 2.1 summarizes the virtues of NBO. Chapter 3 is concerned with methods for computational investigation of protein structures, and finds that methods and basis sets most often used for these investigations are particularly unsuitable when any beta sheets are present due to poor modelling of amide resonance and hence of RAHB that features in the hydrogen-bonded chains of backbone amides of protein secondary structures such as beta sheets [7] and alpha helices [8]. Chapter 4 reports experiments quantifying the sensitivity of amide resonance to electrostatic field with component parallel or antiparallel to the amide C-N bond. This sensitivity allows electrostatic properties including permittivity of amino-acid residue sidechains to influence backbone amide resonance and hence secondary structure RAHB chains, giving a novel mechanism relating residue sequence to structure. Also, this variation in amide resonance is energetically significant even without considering a hydrogen bonding context. Variation of peptide group resonance is expected to vary the barrier height of prolyl isomerization [9]. Subsequent to quantifying this effect in isolated amides and in a RAHB chain, hypotheses are offered concerning the stability of beta sheets, amyloid fibrils [10] and polyproline helices [11]. An analogous sensitivity in nitrogenous base pairing [12] is conjectured. A hypothesis is offered concerning protein complexation and molecular chaperone [13] action. Chapter 5 is motivated by the observed increase of stabilization when cooperative hydrogen bonding chains are cyclized in non-protein contexts [6] and by the phenomena anticipated if these cycles exist in proteins as described in the chapter. The question of the optimal geometry for amide-amide hydrogen bonding is revisited with emphasis on the inequivalence of amide oxygen lone pairs. A possible avenue for the design of HB-chain polymers with improved stability is discussed. Chapter 6 studies a dependency of amino acid residue preference against beta sheet secondary structure by backbone hydration in the presence of cation, doing so by Quantum Molecular Dynamic simulation of a beta sheet with a full quantum mechanical treatment of each solvent molecule.
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2016