Small Tilt Angles Research Articles

A RAIRS study of the adsorption and decomposition of methylsilane on Cu(111)

The adsorption and decomposition of methylsilane gas onto Cu(111) has been investigatedby reflection–absorption infrared spectroscopy (RAIRS). The initial adsorption ofmethylsilane at 15 K results in the formation of an initially ordered physisorbedmonolayer, adsorbed with a small tilt angle from the plane of the surface. Furtherincrease in exposure results in the formation of a more dense monolayer, withmethylsilane lying nearly parallel to the surface of the crystal, before the growth of thedisordered multilayer. Adsorption at 78 K appears to result in the formation of anSiH–CH3 species for which there is some evidence of further Si–Si coupling. At 295 K, methylsilane isobserved to adsorb with the Si–C axis perpendicular to the surface. Adsorption at 395 Kresults in the decomposition of methylsilane, with both Si–H and Si–C bond scission.Adsorbing CO at 15 K on the Cu/Si surface structure thus formed indicates that COadsorbs mostly in atop positions on Si atoms, suggesting that any metal atom sites areblocked by either adsorbed C or Si atoms.

The influence of magnetic field on refractive index profile of ferronematic cell

This paper presents the study of the influence of magnetic field on the refractive index profile of homeotropically oriented 6CHBT-based ferronematic liquid crystal cell. The direction of magnetic field was chosen in a way which ensures the one-dimensional deformation of directors field. The FN cell was placed between polarizers. On a basis of Burylov-Raikher model and measurements of light transmission throughout the ferronematic layer the mean volume concentration of magnetic particles dispersed in 6CHBT and refractive index profiles induced by magnetic filed were determined. Moreover the range of magnetic field intensity was determined in which the distribution of tilt angle can be described in a scope of the Burylov-Raikher theory and the small tilt angle approximation.

３軸角度センサに関する研究

This paper describes a 3-axes angle sensor based on laser autocollimation for simultaneous measurement of small tilt angles about X, Y and Z-axes. The sensor consists of a laser diode as the light source and quadrant photodiodes (QPDs) as the optical position-sensing device. Differing from a conventional 2-axis autocollimator, the sensor uses a diffractive grating as the target mirror. It is verified that the sensitivity of the sensor in the θx (rolling) direction is determined by the pitch of the diffractive grating and the diameter of the laser beam. The sensitivities in the θy (pitching) and the θz (yawing) direction are determined by the wavelength and the beam diameter of the laser beam. It is confirmed that the resolution of θx is about 0.2 arc-seconds, and those of θy and θz are about 0.02 arc-seconds. Optical design and experimental results are presented.

RCS OF LARGE BENT WAVEGUIDE DUCTS FROM A MODAL ANALYSIS COMBINED WITH THE KIRCHHOFF APPROXIMATION

In this paper, we present a fast method to predict the monostatic Radar Cross Section (RCS) in high-frequency of a cavity, which can be modeled as a succession of bent waveguides of the same cross section and stuffed by a perfectly-conducting termination. Based on a modal analysis combined with the Kirchhoff Approximation, this method allows us to obtain closed-form expressions of the transmission matrix at each discontinuity. In addition, to improve the efficiency, a selective modal scheme is proposed, which selects only the propagating modes contributing to the scattering. Compared to the Iterated Physical Optics (IPO) method and the Multi-Level Fast Multipole Method (MLFMM, generated from the commercial software FEKO), this approach brings good results for cavities with small tilt angles of the bends, typically smaller than 2 degrees.

Electrochemical and PM-IRRAS characterization of DMPC + cholesterol bilayers prepared using Langmuir–Blodgett/Langmuir–Schaefer deposition

Differential capacitance, chronocoulometry and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) measurements were used to characterize the structure and orientation of DMPC + cholesterol (70:30 mol%) phospholipid bilayers prepared using combined Langmuir–Blodgett/Langmuir–Schaefer (LB/LS) deposition. The electrochemical measurements indicate that incorporation of cholesterol into the membrane improves the quality of the bilayer if both leaflets contain cholesterol. Phospholipid bilayers containing DMPC and cholesterol prepared using LB/LS deposition were found to have smaller tilt angles (∼27°) than bilayers prepared by vesicle spreading (∼52°), indicating that LB/LS deposition is a superior method for preparing supported phospholipid bilayers at a gold electrode surface.

Effects of Age, Walking Speed, and Body Composition on Pedometer Accuracy in Children

The objective of this study was to investigate the effects of age group, walking speed, and body composition on the accuracy of pedometer-determined step counts in children. Eighty-five participants (43 boys, 42 girls), ages 5–7 and 9–11 years, walked on a treadmill for two-minute bouts at speeds of 42, 66, and 90 m·min-1 while wearing a spring-levered (Yamax SW-200) and a piezoelectric (New Lifestyles NL-2000) pedometer. The number of steps taken during each bout was also recorded using a hand counter. Body mass index (BMI) was calculated from height and mass, and percentage of body fat (%BF) was determined using hand-to-foot bioelectrical impedance analysis. The tilt angle of the pedometer was assessed using a magnetic protractor. Both pedometers performed well at 66 and 90 m·min-1, but undercounted steps by approximately 20% at 42 m·min-1. Although age group, BMI, waist circumference, and %BF did not affect pedometer accuracy, children with large pedometer tilt angles (≥ 10°) showed significantly greater percent bias than those with small tilt angles (< 10°). We suggest that the style of waistband on the child's clothing is a more important determinant of tilt angle and thus pedometer accuracy than body composition. Our results also indicate that the NL-2000 pedometer provides similar accuracy and better precision than the SW-200 pedometer, especially in children with large tilt angles. We conclude that fastening pedometers to a firm elastic belt may improve stability and reduce undercounting in young people.

Fullerene nanowires on graphite: Epitaxial self-organizations of a fullerene bearing double long-aliphatic chains

Lamellar nanowires with small tilt angle defects, epitaxially aligned along the lattice of highly oriented pyrolytic graphite (HOPG), have been constructed by spin-coating of a solution of a fullerene derivative covalently bearing double long-alkyl chains and characterized by atomic force microscopy (AFM) under ambient atmosphere. The small tilt angle defects in domains of lamellar assemblies are rarely found in nano-organized structures on HOPG due to the high 2D crystallinity of their long aliphatic chains in the lamellae. The distance between adjacent nanowires and the 2D crystallinity can be regulated by tuning the substituent pattern of the fullerene derivatives. Here, we also describe lamellar nanowire formation of a newly isolated fullerene bis-adduct bearing long alkyl chains.

On the Orientation of a Designed Transmembrane Peptide: Toward the Right Tilt Angle?

The orientation of the transmembrane peptide WALP23 under small hydrophobic mismatch has been assessed through long-time-scale molecular dynamics simulations of hundreds of nanoseconds. Each simulation gives systematically large tilt angles (>30 degrees). In addition, the peptide visits various azimuthal rotations that mostly depend on the initial conditions and converge very slowly. In contrast, small tilt angles as well as a well-defined azimuthal rotation were suggested by recent solid-state 2H NMR studies on the same system. To optimally compare our simulations with NMR data, we concatenated the different trajectories in order to increase the sampling. The agreement with 2H NMR quadrupolar splittings is spectacularly better when these latter are back-calculated from the concatenated trajectory than from any individual simulation. From these ensembled-average quadrupolar splittings, we then applied the GALA method as described by Strandberg et al. (Biophys J. 2004, 86, 3709-3721), which basically derives the peptide orientation (tilt and azimuth) from the splittings. We find small tilt angles (6.5 degrees), whereas the real observed tilt in the concatenated trajectory presents a higher value (33.5 degrees). We thus propose that the small tilt angles estimated by the GALA method are the result of averaging effects, provided that the peptide visits many states of different azimuthal rotations. We discuss how to improve the method and suggest some other experiments to confirm this hypothesis. This work also highlights the need to run several and rather long trajectories in order to predict the peptide orientation from computer simulations.

Enhancement of Drain Current in Planar MOSFETs by Dopant Profile Engineering Using Nonmelt Laser Spike Annealing

We investigated the effect of dopant profile engineering in planar MOSFETs, in which activation annealing was done using only nonmelt laser spike annealing (LSA). Device performance was 10% and 20% better compared to that when conventional LSA and rapid thermal annealing (RTA) are used, respectively. We achieved this by reengineering the following: 1) angle implantation in the extension of an nFET; 2) germanium preamorphization implantation in the extension of a pFET; 3) halo implantation with lower energy and smaller tilt angle; 4) deep source/drain by two-step implantation, and 5) counter implantation adjusted to the halo conditions. Hot carrier degradation was also reduced to an RTA-comparable level by halo profile engineering. Thus, we show that a submillisecond LSA is a promising technique for the fabrication of ultrashallow junctions for the 45-nm technology node and beyond and that a dopant profile engineering taking into account the minimal diffusion length of LSA is required to bring out the best device performance.

Molecular Dynamics Simulation Study of Self-Assembled Monolayers of Alkanethiol Surfactants on Spherical Gold Nanoparticles

Atomistic molecular dynamics (MD) simulations of self-assembled alkanethiol monolayers are performed to investigate the ligand shell organization of homoligand surfactants on spherical gold nanoparticle surfaces as a function of temperature, nanoparticle size, and ligand tail length. At high temperature, we show that the ligands orient randomly with respect to the surface normal with a small tilt angle. As the temperature decreases, the molecules order and adopt a larger tilt angle. The effects of alkanethiol tail length and nanoparticle size on the tilt structure are also significant. At low temperature, we find the equilibrium conformation of alkanethiols obeys the crystallographic model, whereas at high temperature the continuous model is valid. The dependence of tilt angle on different parameters and comparison with self-assembled monolayers on flat surfaces are also discussed.

On the kinematics and kinetics of mechanical seals, rotors, and wobbling bodies

Mechanical seals, rotors, and wobbling bodies whirl about a point and are characterized by a kinematical constraint that prevents them from having integral motion with respect to the axis of whirl. A valid kinematical model is a prerequisite to subsequent dynamic analyses. Three previous works have suggested distinctly different kinematical models for the same problem. The analysis herein presents yet another kinematical model that preserves (actually enforces) the proper kinematical constraint. Interestingly, it is found that although no integral rotation is allowed about the axis of whirl, the wobbling body possesses a sustained nonzero angular velocity about that axis. The derivation is done for any finite nutation angle and only final results are being degenerated to small tilt angles. The outcome reaffirms the results of a previous work. For this time-invariant problem the notion of virtual velocity and virtual power emerges, and the equations of motion are derived using Lagrange’s equations to complement results obtained previously by Newton–Euler mechanics.

2D Structure of Unsaturated Fatty Acid Amide Mono- and Multilayer on Graphite: Self-Assembly and Thermal Behavior

We investigate the self-assembly of oleamide (9-octadecenamide) on graphite by atomic force microscopy (AFM). The molecules, spin-coated from a dilute solution, form a lamellar monolayer due to epitaxial adsorption on the surface. In the monolayer, a small tilt angle boundary is observed indicating a degeneracy in the molecular positioning. The molecular domains preserve their epitaxy to the substrate as the film thickness increases from monolayer to multilayer. Thermal annealing causes changes in the film morphology. Heating the multilayer up to 75 °C results in the formation of large rods, and above 90 °C, large, highly ordered, smooth islands are observed.

Smart value-added fiber-optic modules using spatially multiplexed processing

Intelligent fiber-optic value-added modules (VAMs) are proposed using what we believe to be a novel spatially multiplexed processing technique implemented with both reconfigurable and nonreconfigurable predesigned pixels per impinging beam that enables desired optical power split states needed for realizing a two state reconfigurable VAM. The preferred design uses broadband micromirrors such as ones fabricated via optical microelectromechanical systems technology. The basic VAM design uses two broadband micromirror pixels, where each pixel has its specific location and area and only one of these pixels is electrically driven to adjust its small tilt angle. The areas of the pixels are chosen to obtain the desired tap power. A proof-of-concept VAM with 100% digital repeatability is demonstrated using a Texas Instruments Digital Micromirror Device (DMD) where several micromirrors per beam are used to produce the dual-pixel effect. Example tap ratios experimentally implemented at 1550 nm include 10:90, 20:80, 66.66:33.33, 50:50, 30:70, and 25:75. DMD multipixel diffraction limits output port optical losses to 3.2 and 3.6 dB. The proposed VAM can have an impact in both digital electronic and analog RF optically implemented systems.

A fully 3-dimensional thermal model of a comet nucleus

A 3-D numerical model of comet nuclei is presented. An implicit numerical scheme was developed for the thermal evolution of a spherical nucleus composed of a mixture of ice and dust. The model was tested against analytical solutions, simplified numerical solutions, and 1-D thermal evolution codes. The 3-D code was applied to comet 67P/Churyumov-Gerasimenko; surface temperature maps and the internal thermal structure was obtained as function of depth, longitude and hour angle. The effect of the spin axis tilt on the surface temperature distribution was studied in detail. It was found that for small tilt angles, relatively low temperatures may prevail on near-pole areas, despite lateral heat conduction. A high-resolution run for a comet model of 67P/Churyumov-Gerasimenko with low tilt angle, allowing for crystallization of amorphous ice, showed that the amorphous/crystalline ice boundary varies significantly with depth as a function of cometary latitude.

Analysis of Dielectric Waveguide Termination with Tilted Facets by Analytic Continuity Method

We apply analytic continuity method to study the reflection from terminating the dielectric waveguide with a tilted facet. Our method is based on the analytical continuity principle using the exact waveguide mode solutions. This technique is suitable for analyzing waveguide with small tilt angles. Optimization of tilt angle and numerical verification of the method is demonstrated.

Decentration Error Analysis Using Optical Centering Device and Skew Ray Tracing

Any small decentering of a lens's surface can be resolved into an angular tilt of the surface about its intersection with the optical axis. The decentration error of an optical lens has a significant effect on the quality of the image it produces. This paper presents a simple method based on skew ray tracing and an optical centering device to calculate the decentration error resulting from the surface tilt of an optical lens. The results reveal that the decentration error and the radius of the spot circle traced out on the detector of the optical centering device as the sample of interest is rotated are related via a linear approximation when the decentration error is small. Furthermore, it is found that for small surface tilt angles, an approximate value of the decentration error can be obtained simply by taking the first-order differentiation of the mathematical expression for the decentration error.

Low Thermal Sensitivity Grating Devices Based on Ex-45$^{\circ}$ Tilting Structure Capable of Forward-Propagating Cladding Modes Coupling

The authors describe a detailed investigation on tilted fiber Bragg grating (TFBG) structures with tilted angles exceeding 45deg. In contrast to the backward mode coupling mechanism of Bragg gratings with normal and small tilting structures, the ex-45deg TFBGs facilitate the light coupling to the forward-propagating cladding modes. The authors have also theoretically and experimentally examined the mode coupling transition of TFBGs with small, medium, and large tilt angles. In particular, experiments are conducted to investigate the spectra and far-field distribution, as well as temperature, strain, and refractive-index sensitivities of ex-45deg devices. It has been revealed that these ex-45deg gratings exhibit ultralow thermal sensitivity. As in-fiber devices, they may be superior to conventional Bragg and long-period gratings when the low thermal cross sensitivity is required

Investigation of a ferronematic cell influenced by a magnetic filed

This paper presents the optical study of the magnetically induced change of the spatial orientation of the directors' field in a ferronematic. This paper presents the investigations of the ferronematic that base on 6CHBT nematic liquid crystal. Magnetic field induces one-dimensional distribution of the tilt angle of a directors filed. On a basis of the optical measurements the mean volume concentration of magnetic particles was determined. Moreover the range of magnetic field intensity was determined in which the distribution of tilt angle can be described in scope of the Burylov-Raikher theory and the small tilt angle approximation.

The contrast-imaging function for tilted specimens

A theoretical description of the contrast-imaging function is derived for tilted specimens that exhibit weak-phase object characteristics. We show that the tilted contrast-imaging function (TCIF) is a linear transformation, which can be approximated by the convolution operation for small tilt angles or for small specimens. This approximation is not valid for electron tomography, where specimen tilts are above 60° and specimen dimensions amount to some 10 μm. The approximation also breaks down for electron crystallography, where atomic resolution is to be achieved. Therefore, we do not make this approximation and propose a generalized algorithm for inverting the TCIF. The implications of our description are discussed in the context of electron tomography, single particle analysis, and electron crystallography, and the improved resolution is quantitatively demonstrated.

Stabilization of Grain Boundary Morphologies in Lamellar Block Copolymer/Nanoparticle Blends

Polymer-coated nanoparticle additives are shown to stabilize the formation of high-energy tilt and twist grain boundary structures in amorphous lamellar block copolymer/nanoparticle blends. The distribution of the particle additives within the grain boundary region depends on the level of perturbation of the equilibrium structure and presents analogies to previously described block copolymer/homopolymer blends. At small tilt angles (chevron grain boundary) the particle distribution is equal to the equilibrium distribution (here: center location of PS-coated gold particles within the PS domains of a PS−PEP block copolymer) whereas at larger tilt angles (omega or T-junction grain boundary structure) the particles are found to selectively swell the high elastic energy regions along the grain boundary, thereby stabilizing the formation of otherwise energetically unfavorable grain boundary structures presumably through the relaxation of chains in the grain boundary region. The direct visualization of the swelling process provides the first experimental evidence for the mechanism of stabilization of energetically unfavorable grain boundary structures by selective swelling and stress relief that was previously postulated for block copolymer/homopolymer blends and presents a model system for comparison with theoretical predictions.