Range Of Tilt Angles Research Articles

Preventive Effect of Artificial Ligamentous Stabilization on the Upper Adjacent Segment Impairment Following Posterior Lumbar Interbody Fusion

A retrospective, comparative study. To assess the effects of soft stabilization with artificial ligamentous bands placed on the upper segment adjacent to posterior lumbar interbody fusion (PLIF) for prevention of transition syndrome compared with patients who underwent PLIF without soft stabilization. Spine fusion increases mechanical stress and can cause other spinal problems adjacent to the fusion level. Soft stabilization using artificial ligamentous bands has been reported to decrease the flexion instability and this iatrogenic problems. There is no report concerning the effect of soft stabilization to transition syndrome following PLIF. In 225 patients undergoing L4/5 PLIF, 70 consecutive patients who were treated concomitantly with decompression of L3/4 with minimum 2-year follow-up were included. Thirty-five patients underwent soft stabilization of L3/4 (soft stabilization [S] group) with natural neutral concept rods, and 35 patients did not (decompression [D] group). Radiographic changes in the disc height, vertebral slip, intervertebral angle, range of motion, lumbar lordosis, and L3 tilt angle were measured. On magnetic resonance imaging (MRI), postoperative progression of the disc degeneration and spinal canal stenosis were evaluated. RESULTS.: In the S group, significant posterior intervertebral expansion on radiograph was less advanced at the final follow-up (P < 0.005). MRI images demonstrated less significant aggravation of disc degeneration (P < 0.001) and progression of adjacent stenosis (P < 0.01), at L3/4 in the S group. Adjacent intervertebral changes on MRI occurred relatively early after surgery, suggesting that changes were due to transition syndrome, but not age-related changes. These results demonstrated an effect of soft stabilization for the prevention of transition syndrome in lumbar spine fusion. Although the postoperative follow-up periods in this study were not sufficiently long to reach a definitive conclusion, intervertebral breakdown adjacent to the rigid spine fusion could be diminished by the application of soft stabilization.

Zero-field precession and hysteretic threshold currents in a spin torque nano device with tilted polarizer

Using nonlinear system theory and numerical simulations, we map out the static and dynamic phase diagrams in the zero applied field of a spin torque nano device with a tilted polarizer (TP). We find that for sufficiently large currents, even very small tilt angles (β>1°) will lead to steady free layer precession in zero field. Within a rather large range of tilt angles, 1°<β<19°, we find coexisting static states and hysteretic switching between these using only current. In a more narrow window (1°<β<5°) one of the static states turns into a limit cycle (precession). The coexistence of current-driven static and dynamic states in the zero magnetic field is unique to the TP device and leads to large hysteresis in the upper and lower threshold currents for its operation. The nano device with TP can facilitate the generation of large amplitude mode of spin torque signals without the need for cumbersome magnetic field sources and thus should be very important for future telecommunication applications based on spin transfer torque effects.

Anatomical information is needed in ultrasound imaging of muscle to avoid potentially substantial errors in measurement of muscle geometry

This study validates two-dimensional (2D) ultrasound measurements of muscle geometry of the human medial gastrocnemius (GM) and investigates effects of probe orientation on errors in these measurements. Ultrasound scans of GM muscle belly were made both on human cadavers (n = 4) and on subjects in vivo (n = 5). For half of the cadavers, ultrasound scans obtained according to commonly applied criteria of probe orientation deviated 15 degrees from the true fascicle plane. This resulted in errors of fascicle length and fascicle angle up to 14% and 23%, respectively. Fascicle-like structures were detectable over a wide range of probe tilt and rotation angles, but they did not always represent true fascicles. Errors of measurement were either linear or quadratic functions of tilt angle. Similar results were found in vivo. Therefore, we conclude that similar errors are likely to occur for in vivo measurements. For all cadavers, at the distal end of GM, the true fascicle plane was shown to be perpendicular to the distal aponeurosis. Using transverse images of GM to detect the curvature of the deep aponeurosis at the distal end of the muscle belly is a simple strategy to help identify the fascicle plane. For subsequent longitudinal imaging, probe alignment within this plane will help minimize measurement errors of fascicle length, fascicle angle, and muscle thickness. Muscle Nerve, 2009.

Thermo-nematicon: an unnatural coexistence of solitons in liquid crystals?

Spatial solitons can be excited in liquid crystal, with the required self-focusing being achieved by setting either a thermal gradient or an orientational one. Although the thermal gradient yields to ordinary wave self-focusing, it also yields to extraordinary wave defocusing, thereby killing the reorientational focusing effect. Thus, coexistence of both solitons looks unlikely. However, by analyzing the optical properties of the used mixture, it is shown that the focusing orientational contribution to the index gradient is two orders of magnitude larger than the thermal defocusing one. Then, by properly choosing the materials and geometry, it becomes possible to excite simultaneously the thermal soliton and the nematicon. This can be done in a large range of optical axis tilt angle.

Scaling law of stable single cells in density fingering of chemical fronts

Stable single fingers evolving in a thin layer of hydrodynamically unstable reactive solution are investigated in moderately wide Hele-Shaw cells. The mixing length associated with the final pattern is shown to be proportional to the width of the container. The scaling law, which is best illustrated by the overlay of temporal average front profiles, is demonstrated for two chemical compositions and boundaries of different thermal conductances. The observed single finger is found to be independent of the orientation of the reaction vessel for a wide range of tilt angles.

Reprint of “Three-dimensional elemental mapping of phosphorus by quantitative electron spectroscopic tomography (QuEST)” [J. Struct. Biol. 160 (2007) 35–48

We describe the development of quantitative electron spectroscopic tomography (QuEST), which provides 3-D distributions of elements on a nanometer scale. Specifically, it is shown that QuEST can be applied to map the distribution of phosphorus in unstained sections of embedded cells. A series of 2-D elemental maps is derived from images recorded in the energy filtering transmission electron microscope for a range of specimen tilt angles. A quantitative 3-D elemental distribution is then reconstructed from the elemental tilt series. To obtain accurate quantitative elemental distributions it is necessary to correct for plural inelastic scattering at the phosphorus L(2,3) edge, which is achieved by acquiring unfiltered and zero-loss images at each tilt angle. The data are acquired automatically using a cross correlation technique to correct for specimen drift and focus change between successive tilt angles. An algorithm based on the simultaneous iterative reconstruction technique (SIRT) is implemented to obtain quantitative information about the number of phosphorus atoms associated with each voxel in the reconstructed volume. We assess the accuracy of QuEST by determining the phosphorus content of ribosomes in a eukaryotic cell, and then apply it to estimate the density of nucleic acid in chromatin of the cell's nucleus. From our experimental data, we estimate that the sensitivity for detecting phosphorus is 20 atoms in a 2.7 nm-sized voxel.

Performance of two photovoltaic arrays in the UK

There are numerous conflicting reports into the economic and embodied energy return of photovoltaic (PV) arrays installed in the UK. Using actual performance data measured on two PV arrays installed on the Zicer building at the University of East Anglia, this paper attempts to resolve some of the issues arising from earlier predictions made using theoretical test bed performance data. A PV model using the monitored data, in combination with solar radiation and geometry data from across the UK, was used to predict the average annual electricity output from the installations over a range of tilt angles, orientations and geographical locations. Six separate capital cost scenarios are considered and the predictions of the unit cost for electricity range from £0·10 (€0·14) per kWh under the most favourable conditions to £2·68 (€3·83) per kWh. At a mean solar radiation of 1000 kWh/ m2 per year, typical of many locations in the UK, the energy yield ratio (EYR) ranges from 4·3 to 5·1 depending on whether the cells are monocrystalline or polycrystalline and the assumptions made in the scenarios. Even on a vertical west-facing face, an EYR of over 2·5 is achieved.

Polarimetric method for the determination of the optical axis tilt angle at boundaries of a liquid-crystal layer

A polarimetric method is proposed to determine the tilt angle of the local optical axis of a liquid crystal at layer boundaries. The method is based on the measurement of the azimuthal polarization angles of light waves passed through a liquid-crystal cell or reflected from it. This method requires neither the knowledge of the refractive indices of a liquid crystal nor the homogeneity of the layer. The method can be applied in the whole range of tilt angles. Experimental data on the measurement of the tilt angles in cells assembled by the scheme of a prism liquid-crystal polarizer are presented.

Modelling the Global Solar Corona: Filament Chirality Observations and Surface Simulations

The hemispheric pattern of solar filaments is considered in the context of the global magnetic field of the solar corona. In recent work Mackay and van Ballegooijen have shown how, for a pair of interacting magnetic bipoles, the observed chirality pattern could be explained by the dominant range of bipole tilt angles and helicity in each hemisphere. This study aims to test this earlier result through a direct comparison between theory and observations, using newly developed simulations of the actual surface and 3D coronal magnetic fields over a 6-month period, on a global scale. We consider two key components: (1) observations of filament chirality for the sample of 255 filaments and (2) our new simulations of the large-scale surface magnetic field. Based on a flux-transport model, these will be used as the lower boundary condition for the future 3D coronal simulations. Our technique differs significantly from those of other authors, where the coronal field is either assumed to be purely potential or has to be reset back to potential every 27 days for the photospheric field to remain accurate. In our case we ensure accuracy by the insertion of newly emerging bipolar active regions, based on observed photospheric synoptic magnetograms. The large-scale surface field is shown to remain accurate over the 6-month period, without any resetting. This new technique will enable future simulations to consider the long-term buildup and transport of helicity and shear in the coronal magnetic field over many months or years.

Three-dimensional elemental mapping of phosphorus by quantitative electron spectroscopic tomography (QuEST)

We describe the development of quantitative electron spectroscopic tomography (QuEST), which provides 3-D distributions of elements on a nanometer scale. Specifically, it is shown that QuEST can be applied to map the distribution of phosphorus in unstained sections of embedded cells. A series of 2-D elemental maps is derived from images recorded in the energy filtering transmission electron microscope for a range of specimen tilt angles. A quantitative 3-D elemental distribution is then reconstructed from the elemental tilt series. To obtain accurate quantitative elemental distributions it is necessary to correct for plural inelastic scattering at the phosphorus L2,3 edge, which is achieved by acquiring unfiltered and zero-loss images at each tilt angle. The data are acquired automatically using a cross correlation technique to correct for specimen drift and focus change between successive tilt angles. An algorithm based on the simultaneous iterative reconstruction technique (SIRT) is implemented to obtain quantitative information about the number of phosphorus atoms associated with each voxel in the reconstructed volume. We assess the accuracy of QuEST by determining the phosphorus content of ribosomes in a eukaryotic cell, and then apply it to estimate the density of nucleic acid in chromatin of the cell’s nucleus. From our experimental data, we estimate that the sensitivity for detecting phosphorus is 20 atoms in a 2.7nm-sized voxel.

Prediction of Energies of Tilt Boundaries in Al-Pb Alloy

ABSTRACTEnergies for symmetric tilt grain boundaries in pure Al and in Al with substitutional Pb defects at coincident sites along the grain boundaries were calculated using a modified embedded atom method potential and density functional theory. The agreement between the analytic potential, the first principles calculations and experiment is reasonably good for the pure system. For the Al-Pb system both the analytic potential and first principles calculations predict that Pb segregation to the interface is energetically preferred compared to the dilute solution. The application of a disclination structural unit model to calculating grain boundary energies over the entire range of tilt angles is also explained.

Orientations of Liquid Crystals in Contact with Surfaces that Present Continuous Gradients of Chemical Functionality

We report the formation of continuous spatial gradients in the density of grafted semifluorinated chains on silicon oxide surfaces by vapor-phase diffusion of semifluorinated silanes. We quantify the orientations of the nematic liquid crystal (LC) 4-cyano-4‘-pentylbiphenyl on these surfaces as a function of local surface composition obtained by using NEXAFS. These measurements demonstrate that it is possible to obtain the full range of tilt angles of a LC on these surfaces. We also use the data provided by these gradient surfaces to test hypotheses regarding the nature of the interaction between the LC and surfaces that give rise to the range of tilted orientations of the LC. We conclude that the orientations of the LC are not determined solely by the density of grafted semifluorinated chains or by the density of residual hydroxyl groups presented at these surfaces following reactions with the silanes. Instead, our results raise the possibility that the tilt angles of the semifluorinated chains on these surfaces (which are a function of the density of the grafted chains) may influence the orientation of the LC. These results, when combined, demonstrate the potential utility of gradient surfaces for screening surface chemistries that achieve desired orientations of LCs as well as for rapidly assembling experimental data sets that can be used to test propositions regarding mechanisms of anchoring LCs at surfaces.

Out-of-substrate plane orientation control of thin YBa2Cu3Ox films on NdGaO3 tilted-axes substrates

Epitaxial heterostructures YBa2Cu3Ox(YBCO)/CeO2/NdGaO3 were prepared on tilted-axes NdGaO3 substrates using laser ablation technique. Morphology, crystal structure and electrical properties of the obtained films were characterized. The seeding mechanisms are affected by the tilt angle, resulting in superior YBCO films on NdGaO3 substrates in an intermediate range of tilt angles of 6–14°. The introduction of CeO2 layer leads to change of the YBCO film orientation: at low deposition rate c-oriented films are formed, while at high deposition rates the film grows with c-axis tilted along the [110] NdGaO3 direction. Bi-epitaxial films and structures were prepared by removal of part of the CeO2 layer using ion-beam milling.

Design of sidetap fiber Bragg grating filters

A comprehensive theoretical treatment is presented for bound-mode to radiation mode coupling loss (transmission loss) and for bound-mode to bound-mode Bragg reflection (back reflection) in a sidetap fiber phase grating. The spectra of the reflection and transmission loss in a tilt angle range useful for fiber sidetap filter design is presented for the first time. Important dependencies between the designed wavelength of operation and parameters of the fiber grating, which give a clear understanding of the process of the fiber mode to radiation mode coupling and back reflection is also discussed. A practical procedure for the design of sidetap gain flattening filter is also presented.

Impact of Radar Tilt and Ground Clutter on Wind Measurements in Clear Air

Abstract From geometrical considerations, the optimum tilt angle for a meteorological radar at which the best possible vertical resolution results is derived. This optimum angle is a compromise between the effects of beam divergence and range gate spacing. For typical S-band radar parameters, this optimum tilt angle is found to be about 7°. However, wind analyses at this tilt angle were found not to be accurate in practice because of ground clutter contamination, and suboptimal angles need to be used. Most of the ground clutter was found to be sensed in the radar beam sidelobes. The data presented here imply that ground clutter is a serious contaminant at tilt angles as high as 45°. For clear-air wind profiling in the boundary layer, the impact of ground clutter contamination increased as the tilt angle was increased. Data presented from four radars [the Goodland, Kansas, Weather Surveillance Radar-1988 Doppler (WSR-88D); the University of Oklahoma’s Doppler on Wheels; NCAR’s S-band dual-polarization Doppler radar (S-Pol); and NSSL’s Cimarron] suggest that a fairly narrow range of tilt angles from 1° to 2° is generally acceptable for wind profiling of the boundary layer in clear-air conditions. Tilt angles outside this range lead to significant systematic errors, primarily from ground clutter contamination.

Assembly of Human Immunodeficiency Virus Precursor Gag Proteins

To investigate the mechanism by which human immunodeficiency virus (HIV) precursor Gag (PrGag) proteins assemble to form immature virus particles, we examined the in vitro assembly of MACANC proteins, composed of the PrGag matrix, capsid, and nucleocapsid domains. In the absence of other components, MACANC proteins assembled efficiently at physiological temperature but inefficiently at lower temperatures. However, the addition of RNA reduced the temperature sensitivity of assembly reactions. Assembly of MACANC proteins also was affected by pH because the proteins preferentially formed tubes at pH 6.0, whereas spheres were obtained at pH 8.0. Because neither tubes nor spheres were amenable to analysis of protein-protein contacts, we also examined the membrane-bound assemblies of MACANC proteins. Interestingly, MACANC proteins organized on membranes in tightly packed hexameric rings. The observed hexamer spacing of 79.7 A is consistent with the notion that more PrGag proteins assemble into virions than are needed to provide capsid proteins for mature virus cores. Our data are also consistent with a model for PrGag contacts in immature virions where capsid hexamers are tightly packed, where nucleocapsid domains align beneath capsid C-terminal domains, and where matrix domains form trimers at the nexus of three neighbor hexamers.

New Results in Modeling the Hemispheric Pattern of Solar Filaments

New results in modeling the hemispheric pattern of solar filaments through magnetic flux transport and magnetofrictional simulations are presented. The simulations consider for the first time what type of chirality forms along the polarity inversion line lying in between two magnetic bipoles as they interact. Such interactions are important for filament formation, as observations by F. Tang show that the majority of filaments form in between bipolar regions rather than within a single magnetic bipole. The simulations also include additional physics of coronal diffusion and a radial outflow velocity at the source surface, which was not included in previous studies. The results clearly demonstrate for the first time not only the origin of the dominant hemispheric pattern but also why exceptions to it may occur. The dominant hemispheric pattern may be attributed to the dominant range of bipole tilt angles and helicities in each hemisphere. Exceptions to the hemispheric pattern are found to only occur in cases of no initial helicity or for helicity of the minority type in each hemisphere when large positive bipole tilt angles (α > 20°) are used. As the simulations show a clear dependence of the hemispheric pattern and its exceptions on observational quantities, this may be used to check the validity of the results. Future programs to consider this are put forward.

Annual and semiannual variations of the location and intensity of large‐scale field‐aligned currents

The present study examines seasonal variations of large‐scale field‐aligned current (FAC) systems in terms of the dipole tilt and clock angles. Magnetic field measurements from the DMSP F7 and F12‐F15 satellites are used. This data set consists of a total of ∼185,000 auroral oval crossings, out of which ∼121,000 crossings were selected for the present analysis. Focus is placed on the latitude at the demarcation between the region 2 (R2) and region 1 (R1) currents and the intensities of these currents. It is found that the dayside FAC moves poleward and equatorward in the summer and winter hemispheres, respectively, and the nightside FAC has the opposite seasonal dependence. In the midday sector the peak‐to‐peak variation of the FAC latitude over the entire range of the dipole tilt is ∼5°, whereas it is ∼4° around midnight. In the flank sectors the average FAC latitude is higher around the solstices than around the equinoxes irrespective of hemisphere. The corresponding dependence on the dipole clock angle can actually be found for almost all local time sectors, although the peak‐to‐peak variation of the expected semiannual variation, 2° around noon and &lt;1° in other local time sectors, is smaller than that of the annual variation except for the flank sectors. A comparison with a model magnetic field strongly suggests that the dipole tilt effect on the magnetospheric configuration is the primary cause of the annual variation, whereas the semiannual variation is inferred to reflect the fact that geomagnetic activity tends to be higher around the equinoxes. The average dayside FAC intensity is larger in the summer hemisphere than in the winter hemisphere, which can be explained in terms of the seasonal variation of the ionospheric conductivity. The dayside R1 current intensity depends more strongly on the dipole tilt than the dayside R2 current intensity, and it changes by a factor of 2–3 over the entire range of the dipole tilt angle. In contrast, the annual variation of the nightside FAC intensity is more complicated, and the nightside R2 current seems to be more intense in the winter hemisphere than in the summer hemisphere. The dependence of the FAC intensity on the dipole clock angle is less significant especially for the R1 system. Nevertheless, the result suggests that the FAC tends to be more intense around the equinoxes, which is consistent with the semiannual variation of geomagnetic activity.

Tilt-Angle Stabilization of Electrostatically Actuated Micromechanical Mirrors Beyond the Pull-In Point

Recently proposed optical subsystems utilizing microelectromechanical system (MEMS) components are being developed for use in optical crossconnects, add-drop multiplexers, and spectral equalizers. Common elements to these subsystems are electrostatically actuated micromechanical mirrors that steer optical beams to implement the subsystem functions. In the past, feedback control methods were used to obtain precise mirror orientations to minimize loss through optical switch fabrics or to stabilize attenuation through spectral equalizers. However, the mirror tilt angle range is limited because of inherent instability beyond a critical tilt angle (pull-in angle), and the usual feedback schemes do not counteract this effect. This work presents a feedback control method to enable operation of electrostatic micromirrors beyond the pull-in angle, yielding advantages including greater scalability of switch arrays and increased dynamic range of optical attenuators. Both static and dynamic tilting behaviors of electrostatic micromirrors under the feedback control are studied. In addition, a practical implementation of the feedback control system by using linear voltage control law is developed. A voltage slightly larger than the pull-in voltage is first applied when the mirror is at small angle positions, and the voltage is then linearly reduced as the mirror approaches the desired position. Experimental measurements, showing that tilt angles beyond the pull-in point can be achieved, are in good agreement with theoretical analysis.

Numerical study of desirable solar-collector orientations for the coastal region of South China

The overall performance of any solar energy project depends very much on the availability of solar radiation and the orientations of solar collectors. Presented in this paper is a numerical analysis of the solar irradiation received at the coastal region of South China. This region, with latitudes from 20.5°N to 24°N, belongs to the subtropical monsoon climatic zone. The computations were based on the typical meteorological year (TMY) weather data of Macau, compiled as a result of the ASHRAE International Weather for Energy Calculations Project. The hourly data were applied to the ESP-r building simulation program with the adoption of the Perez solar model. The analyses estimated the solar irradiation received on inclined surfaces at different orientations and slopes, and for different periods of the year. It was found that a solar collector facing the south-west direction could be most desirable for a wide range of tilt angles, and for maximizing the annual yield. The trends of variations towards other directions, tilt angles, and shorter periods of the year are also explored.