Reorientation Angle Research Articles

Fast right-angle spinning EPR on organic radicals: Resolution enhancement and angle determination

Fast right-angle sample spinning (RAS) with rotation frequencies up to 17 kHz at temperatures down to 205 K is applied to electron paramagnetic resonance (EPR) experiments on organic radicals. Echo-detected RAS EPR provides substantial resolution enhancements for the range of anisotropies between 10 and 100 MHz which is not accessible with either magic-angle sample spinning EPR or anisotropy-resolved EPR on the basis of slow rotation. The larger reorientation angles in experiments with fast spinning cause strong phase shifts of the echo, which manifest themselves as regions with negative intensity in the spectrum. These phase shifts and thus the lineshape in echo-detected RAS EPR depend significantly on the relative orientation of theg and hyperfine tensor. For the determination of anisotropies in poorly resolved spectra of organic radicals in disordered solids, we introduce the two-dimensional fixed-angle rotation experiment as an alternative to anisotropy-resolved EPR.

Reorientational angle distribution and diffusion coefficient for nodal and cylindrical surfaces

We present a catalogue of diffusion coefficients and reorientational angle distribution (RAD) for various periodic surfaces, such as I-WP, F-RD, S, and S1 nodal surfaces; cylindrical structures like simple, undulated, and spiral cylinders, and a three-dimensional interconnected-rod structures. The results are obtained on the basis of a simulation algorithm for a diffusion on a surface given by the general equation φ(r)=0 [Hołyst et al., Phys Rev. E 60, 302 (1999)]. I-WP, S, and S1 surfaces have a spherelike RAD, while F-RD has a cubelike RAD. The average of the second Legendre polynomial with RAD function for all nodal surfaces, except the F-RD nodal surface, decays exponentially with time for short times. The decay time is related to the Euler characteristic and the area per unit cell of a surface. This analytical formula, first proposed by B. Halle, S. Ljunggren, and S. Lidin in J. Chem. Phys. 97, 1401 (1992), is checked here on nodal surfaces, and its range of validity is determined. RAD function approaches its stationary limit exponentially with time. We determine the time to reach stationary state for all surfaces. In the case of the value of the effective diffusion coefficient the mean curvature and a connectivity between parts of surfaces have the main influence on it. The surfaces with low mean curvature at every point of the surface are characterized by high-diffusion coefficient. However if a surface has globally low mean curvature with large regions of nonzero mean curvature (negative and positive) the effective diffusion coefficient is low, as for example, in the case of undulated cylinders. Increasing the connectivity, at fixed curvatures, increases the diffusion coefficient.

Principles of centerband-only detection of exchange in solid-state nuclear magnetic resonance, and extension to four-time centerband-only detection of exchange

Theoretical principles and experimental details of the centerband-only detection of exchange (CODEX) nuclear magnetic resonance (NMR) experiment for characterizing slow segmental dynamics in solids are described. The experiment, which is performed under magic-angle spinning, employs recoupling of the chemical-shift anisotropy before and after a long mixing time during which molecular reorientations may occur. By an analysis in terms of the difference tensor of the chemical shifts before and after the mixing time, the dependence on the reorientation angle is obtained analytically for uniaxial interactions, and a relation to two-dimensional exchange NMR patterns is established; the same theory can also be applied for analyzing stimulated-echo and pure-exchange NMR data. A favorable linear dependence is derived generally for small rotations, which makes the experiment suitable for detecting small-amplitude motions. Quantification is excellent because the peaks are narrow and intense, unlike the broad powder or sideband spectra that are characteristic of all previous NMR experiments for probing slow segmental rotations. We also introduce and demonstrate a four-time CODEX experiment that yields information previously obtained only in 3D (three-dimensional) and reduced 4D (four-dimensional) exchange NMR experiments, such as the number of orientational sites accessible to the mobile groups. Chemical-shift anisotropies required in the CODEX analysis of motional amplitudes can be estimated using a closely related chemical-shift recoupling experiment. The implementation of total suppression of sidebands before detection is also explained. The experiments are demonstrated on dimethylsulfone, isotactic polypropylene, and poly(methyl methacrylate), PMMA. In isotactic poly(1-butene), the signals of the amorphous and interfacial regions have been observed selectively by using pure-exchange CODEX near the glass transition. The four-time CODEX experiment confirms that in the β-relaxation process of glassy PMMA, fewer than half of the sidegroups perform jumps between two orientations.

Shape induced in-plane magnetic anisotropy reorientation in epitaxial hexagonal close packed cobalt dots

The in-plane magnetic easy-axis reorientation was investigated for the arrays of (10⋅0) hcp Co rectangular dots 0.2 μm in width with a variable length from 3 to 5 μm perpendicular to the c axis. In the system, the magnitude of the shape anisotropy contribution is determined by a lateral aspect ratio of the dot, while the magnetocrystalline anisotropy contribution is temperature dependent. The torque curves for the dot arrays exhibited a characteristic fourfold symmetry due to the easy-axis reorientation. The reorientation angle from the initial easy axis was found to be dependent on the value of in-plane demagnetization factors as well as the temperature variable first and second magnetocrystalline anisotropy constants. The experimental results are in good agreement with the calculated effective magnetic anisotropy.

Structure and mobility in ferroelectric liquid crystalline elastomers

Time-resolved Fourier transform infrared (FTIR) spectroscopy with polarized light was employed to study the structure and mobility of a homologous series of ferroelectric liquid crystalline polymers (FLCPs) and ferroelectric liquid crystalline elastomers (FLCEs) in response to an external electric field. The chemical composition of the samples, besides the cross-linking units, is similar. For the elastomers, two different cross-linking architectures are realized: “intralayer” cross-linking leads to the formation of two-dimensional networks, whereas “interlayer” cross-linking forms three-dimensional networks. Due to its specificity, FTIR spectroscopy enables analysis of the reorientational dynamics for the different molecular moieties in detail, thus revealing information about reorientation times, angular excursion, and the phase relationship in the rearrangement of the various molecular groups. In comparison to the un-cross-linked FLCP, both elastomeric samples exhibited smaller reorientation angles and an increase of the reorientation times. In the case of the interlayer cross-linked FLCE, an elastic memory effect was observed: For the reversal from negative to positive field polarity, the reorientation times were longer than for those in the opposite direction. For the intralayer cross-linked sample, it was shown that the backbone molecules reorient slower than the other molecular units (“locomotive effect”). For the un-cross-linked FLCP and the two FLCE samples, different coupling mechanisms between the network and the mesogenic parts are derived from the measurements.

Effects of powder alignment on determination error of spin reorientation angle of cone anisotropy

The effects of powder alignment on the determination error of the spin reorientation angle (SRA) from polycrystalline magnetization curves have been examined. A theoretical calculation showed that highly aligned powder is desired to determine the SRA with a high degree of accuracy. The effect of powder alignment on the SRA-error decreases when the SRA is increased. The SRA of Nd 2Fe 14B determined from the magnetization measurements of magnetically aligned powder coincided with the value reported on single crystals, and the determination error was evaluated to be within 1°.

Photo-Induced Properties of Liquid Crystal Molecules on Alternately Assembled Charged Azobenzene Dyes and Polyelectrolyte Films Using Attenuated Total Reflection Method

ABSTRACTIn this report, we describe the photo-induced in-plane alignment of nematic liquid crystal (LC) molecules, 5CB, in a hybrid cell with alternate self-assembled films of low-molecular weight azobenzene dye and polyelectrolyte on gold electrodes using the attenuated total reflection (ATR) measurement method. The molecular self-assembly process was also investigated by the ATR method. Reflectivities due to excitations of the surface plasmon polariton (SPP) were observed in the ATR properties of the LC cell. In-plane switching of the LC molecules adjacent to the aligning layer was evaluated from the ATR curves after irradiation of linearly polarized visible light to the LC cell. The sensitivity of the ATR method gives information on the alignment, tilt angle, and extent of LC reorientation in the bulk. Thus, the importance of using the molecular self-assembly processes of individual polyion-dye pairs for fabrication of new photo-aligning layers is emphasized.

Reorientational dynamics in simple supercooled liquids

The geometry of the reorientational dynamics in the van der Waals liquid, toluene, and the hydrogen bond network, glycerol, are compared. Both systems have contributions from small angle fluctuations. In glycerol the fraction of these small angle fluctuations is much larger than in toluene, due to the stronger anisotropic interactions in the former substance. The average reorientational angle in both systems is similar and on the order of 10 ∘. In addition we analyze the stretching of the rotational correlation functions of rank one and two. In both cases we find that the second rank correlation function has a more pronounced stretching than the corresponding first rank correlation function. This effect can be understood in the framework of a recently introduced free-energy landscape model for the primary relaxation in supercooled liquids.

Internal rotation effects in the rotationally resolved S1(1Lb) ←S origin bands of 3-methylindole and 5-methylindole

The rotationally resolved ultraviolet (UV) excitation spectra of the S1(1Lb)←S0 origin bands of 3-methylindole and 5-methylindole have been measured and analyzed. As a result of an internal rotation of the methyl group, each spectrum consists of rotational lines of overlapping 0a1←0a1 and 0e←0e torsional transitions. Like indole, 3-methylindole and 5-methylindole undergo axis reorientation upon electronic excitation. The Hamiltonian used to describe all observed spectral features includes a pure rotational part, a pure torsional part, and terms describing the interaction between the internal rotation and the overall rotation. It also accounts for the axis reorientation effect. Values for the barrier heights of the methyl torsion, the angle of the methyl top axis with the inertial axes, and the rotational constants are obtained for both the S0 and the S1 state. From an analysis of the intensities of the rotational transitions, the direction of the transition moment and the axis reorientation angle are obtained. Due to quantum interference effects in the 5-methylindole spectrum the sign of these angles could be determined.

Rotated incommensurate domains of Co ultrathin films on Pt(111)

Low energy electron diffraction (LEED) and Auger electron spectroscopy were used to study the initial growth of cobalt ultrathin films on a Pt(111) surface at room and low temperatures. The films show incoherent epitaxy at room temperature. Unrotated and rotated incommensurate Co domains with two equivalent angles of rotation, +4.9° and −4.9°, with respect to the aligned substrate, are observed by LEED for 2 monolayers of Co Pt(111) after applying an annealing treatment. From a calculation of the mismatch for the corrugated surface, we confirm this reorientation angle. The evolution of the LEED satellite pattern for the deposition at 140 K is the same as for the deposition at room temperature, but a faint (2 × 2) LEED pattern was observed for higher coverages. UV photoelectron spectroscopy was used to monitor the evolution of the density of electronic states during deposition.

Molecular Orientation in Poly(4-oxybenzoate-co-1,4-phenylene isophthalate) by Slow-Magic-Angle-Spinning DECODER NMR

Slow-magic-angle-spinning DECODER NMR based on the anisotropy of chemical shift tensors is used to determine molecular-level orientation in three samples of poly(4-oxybenzoate-co-1,4-phenylene isophthalate) of comparable composition but different process histories. The two-dimensional NMR line shapes are sufficiently resolved to show quantitative differences in the degree of orientation for powder, melt-extruded monofilament, and high-speed melt-spun fiber of the wholly aromatic liquid crystal polymer produced from an approximately equimolar mixture of 4-hydroxybenzoic acid, hydroquinone, and isophthalic acid. By direct comparison of calculated and experimental NMR line shapes, the full orientation distribution functions for all repeat units were determined and found to be consistent with a combination of isotropic and anisotropic components. Multiple reorientation angles are used to confirm the proposed molecular orientation distributions. The results indicate a high degree of orientation in the melt-spun fiber, a lesser degree of orientation in the melt-extruded monofilament, and isotropic orientation in the powder sample. Legendre polynomial expansions up to order n = 14 were estimated.

Determination of spin reorientation angle of cone anisotropic material from magnetization curves of magnetically aligned powders

A method to calculate the spin reorientation angle of cone anisotropic material from parallel and perpendicular magnetization curves of an aligned particle system is suggested. In this method, the spin reorientation angle is expressed as a function of remanent magnetizations parallel and perpendicular to alignment direction and particle alignment factor. The effect of basal plane anisotropy is included in the calculation, and a slight underestimation results if it is neglected. Experiments on Nd 2(Fe 0.9Co 0.1) 14B particles showed a spin reorientation angle of 29.2° at 4.2 K. The underestimation in spin reorientation angle due to the neglect of basal plane anisotropy was about 9% for Nd 2(Fe 0.9Co 0.1) 14B at 4.2 K.

Spin waves in several Heisenberg systems:Three-sublattice with different exchange constants (Jab=Jbc≠Jca) anda superlattice with the elementary unit of four or three different layers

The quadratic Holstein-Primakoff spin-wave Hamiltonian for three-sublattice Heisenberg systems with different exchange constants (J(ab)=J(bc)not equal J(ca)) was diagonalized by a three-step procedure. The classical ground state was examined and the effects of quantum fluctuation on the ground state were discussed. The 0 K spin reorientation angles due to quantum fluctuations were found to originate from the asymmetry of the system. As an extended application of the spin-wave study of the multisublattice systems, the spin-wave spectra of a Heisenberg superlattice, which has four or three magnetic atoms or spins, in each magnetic unit cell in the x direction, were solved analytically in terms of creation and annihilation operators. It has been found that the spin-wave spectra of the present superlattice systems depend on the exchange constants J and J(1), and that the degeneracy of the spin-wave spectra remains for the superlattice of four atomic layers and is partially removed for the superlattice of three atomic layers mainly due to the asymmetry of the system. Another type of splitting of the energy level occurs which differs for those levels with different degeneracies. The mixing of the interface and the bulk modes were found for the spin-wave dispersion of the superlattices. It was predicted that even for different superlattices having the same exchange constants (either J or J'), i.e., without the oscillation of the exchange coupling, the asymmetry can lead to the oscillation of magnetic properties, such as magnetization and giant magnetoresistance.

Asynchronous Time-Resolved FT-IR Study of the Dynamical Behavior of Ferroelectric Liquid Crystal with a Tolane Ring

Transient infrared spectra of a ferroelectric liquid crystal with a tolane ring, ( S)-4-methylhexyl-4-[4-(decyloxy)phenylethynyl]-2-fluorobenzate, in the smectic C phase have been measured under various temperatures and voltages by use of an asynchronous time-resolved FT-IR method. The effects of temperature and voltage on the rate and tilt angle of the electric field-induced reorientation of the molecule have been studied. The absolute values of the observed intensity changes and their sign during the switching can be explained by the static properties of the sample. The spectra obtained under the different experimental conditions suggest that the temperature and applied voltage alter the tilt angle and angular velocity of reorientation of the liquid crystal, respectively. Dominant infrared bands show very similar time-dependent intensity changes under various conditions, indicating that the whole molecule reorients simultaneously irrespective of temperature and the applied field strength as though the molecule were a rigid rod.

Reduced gravitropism in hypocotyls of starch-deficient mutants of Arabidopsis.

Gravitropism was examined in dark- and light-grown hypocotyls of wild-type (WT), two reduced starch mutants (ACG 20 and ACG 27), and a starchless mutant (ACG 21) of Arabidopsis. In addition, the starch content of these four strains was studied with light and electron microscopy. Based on time course of curvature and orientation studies, the graviresponse in hypocotyls is proportional to the amount of starch in a genotype. Furthermore, starch mutations seem to primarily affect gravitropism rather than differential growth since both phototropic curvature and growth rates among the four genotypes are approximately equal. Our results suggest that gravity perception may require a greater plastid mass in hypocotyls compared to roots. The kinetics of gravitropic curvature also was compared following reorientation at 45 degrees, 90 degrees, and 135 degrees. As has been reported for other plant species, the optimal angle of reorientation is 135 degrees for WT Arabidopsis and the two reduced starch mutants, but the magnitude of curvature of the starchless mutant appears to be independent of the initial angle of displacement. Taken together, the results of the present study and our previous experiments with roots of the same four genotypes [Kiss et al. (1996) Physiol. Plant. 97: 237] support a plastid-based hypothesis for gravity perception in plants.

Model for the formation of large, transtensional basins in zones of tectonic escape

Research Article| March 01, 1997 Model for the formation of large, transtensional basins in zones of tectonic escape Paul Mann Paul Mann 1Institute for Geophysics, University of Texas at Austin, 8701 North Mopac Expressway, Austin, Texas 78759-8397 Search for other works by this author on: GSW Google Scholar Geology (1997) 25 (3): 211–214. https://doi.org/10.1130/0091-7613(1997)025<0211:MFTFOL>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Paul Mann; Model for the formation of large, transtensional basins in zones of tectonic escape. Geology 1997;; 25 (3): 211–214. doi: https://doi.org/10.1130/0091-7613(1997)025<0211:MFTFOL>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract “Tectonic escape” is strike-slip-dominated motion of colliding continental or arc crust in the direction of subductable oceanic crust. I describe four examples of large transtensional basins in Cenozoic zones of tectonic escape and propose that these basins formed along newly formed, transtensional faults formed between the collided and escaping parts of the plate. The reoriented direction of the escaping plate, split along the new transtensional fault zone, is determined by the presence of a “free face,” or subductable oceanic crust. Continued subduction toward the free face is driven by the force of gravity acting on dense oceanic crust (“slab pull”). The four examples presented here show that a variety of transtensional deformational styles can be generated within this specific type of divergent tectonic setting. These transtensional styles include pull-apart basins at fault stepovers, more asymmetrical, rift-like basins thought to be formed under conditions of fault-normal extensional stresses, and single or multiple short spreading ridges. Transtensional styles may be controlled more by the type and age of crust present than the angle of reorientation of the escaping plate. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Decoupling of the longitudinal modes of advanced aircraft

Billimoria, K. D., and Wie, B., Minimum Time Large Angle Reorientation of a Rigid Spacecraft, Journal of Guidance, Control, and Dynamics, Vol. 16, No. 3, 1993, pp. 446-452. Scrivner, S., and Thompson, R. C., Survey of Time-Optimal Attitude Maneuvers, Journal of Guidance, Control, and Dynamics, Vol. 17, No. 2, 1994, pp. 225-233. Pao, L. Y., Characteristics of the Time-Optimal Control of Flexible Structures with Damping, Proceedings of the 3rd IEEE Conference on Control Applications (Glasgow, Scotland, UK), 1994, Inst. of Electrical and Electronics Engineers, pp. 1299-1304.

Optimization of generalized potential in mission function control - Analytical and experimental results

The mission function control utilizes the second law of Lyapunov and employs a mission function that is a Lyapunov function, including a hypothetical potential function, generalized potential. The mission function is characterized for its ability to include any functional form of positive-definite generalized potential to complete the control objective. The functional form of the generalized potential is optimized in the sense of minimizing a performance index, and a robust optimal nonlinear and distributed control algorithm for the slew maneuver of flexible structures is presented. The employment of the optimal nonlinear generalized potential naturally achieves improvement of control performance, and it avoids the excessive excitation of the vibration of flexible structures for large attitude angle reorientation in the case of a quadratic generalized potential. The usefulness of the present optimized generalized potential for mission function control is verified both by a numerical simulation and by a hardware experiment.

Membrane curvature studied using two-dimensional NMR in fluid lipid bilayers.

The method of two-dimensional exchange spectroscopy in deuterium ${(}^{2}$H) nuclear magnetic resonance (NMR), originally developed for the study of slow, reorientational molecular motions in solids [S. Wefing and H. W. Spiess, J. Chem. Phys. 89, 1219 (1988)], has been applied to the study of multilamellar vesicle samples of phospholipid bilayer systems in their fluid (${\mathit{L}}_{\mathrm{\ensuremath{\alpha}}}$) phase. As is well known, the $^{2}\mathrm{H}$ NMR quadrupolar splitting in such fluid membranes is proportional to (3 ${\mathrm{cos}}^{2}$\ensuremath{\theta}-1), where \ensuremath{\theta} is the angle between the local bilayer surface normal and the external magnetic field. Measurements of two-dimensional exchange $^{2}\mathrm{H}$ NMR spectra using a mixing time ${\mathit{t}}_{\mathit{m}}$ were analyzed to give the reorientational angle distribution function for the local surface normals of individual lipid molecules comprising the membranes. A quantitative analysis of this correlation function taking into account the lateral diffusion of the lipid molecules demonstrated the sensitivity of the technique to the local curvature and shapes of the multilayers, which were shown to exhibit surface roughness on the mesoscopic length scale between about 10 nm and 1 \ensuremath{\mu}m. The results were consistent with an average radius of curvature between 1 and 2 \ensuremath{\mu}m, but approximately 15% of the molecules were located on relatively flat membranes having larger radii of curvature.

Magnetic anisotropy and magnetic phase transitions in a DyFe11Ti single crystal

The magnetic anisotropy of the DyFe11Ti intermetallic has been studied by measuring the angular dependence of the components of the magnetization parallel and perpendicular to the applied magnetic field. The measurements were performed on two plate-shaped samples with the surfaces parallel to the (110) and (001) planes, respectively. From the measurements in the (110) plane the thermal dependence of the spin reorientation angle has been obtained. The magnetic field dependence of M/sub /// and Mperpendicular to showed a first-order magnetization process (FOMP). A single-ion model for the crystal-electric-field interaction and a mean-field model for the exchange interaction have been used to explain theoretically the experimental results. An in-depth study of the character of the spin reorientation transition from easy cone to easy plane has been undertaken. From our study we show that for temperatures near this spin reorientation temperature, two magnetic phases (planar and conical phases) coexist in the sample, giving rise to an average angle that evolves continuously with temperature. A similar behaviour has been also observed for magnetic fields near the critical field of the FOMP, producing a continuous change of the magnetization instead of a jump at the critical field.