Small Critical Angle Research Articles

Glenohumeral joint reaction forces increase with critical shoulder angles representative of osteoarthritis-A biomechanical analysis.

Osteoarthritis (OA) of the glenohumeral joint constitutes the most frequent indication for nontraumatic shoulder joint replacement. Recently, a small critical shoulder angle (CSA) was found to be associated with a high prevalence of OA. This study aims to verify the hypothesis that a small CSA leads to higher glenohumeral joint reaction forces during activities of daily living than a normal CSA. A shoulder simulator with simulated deltoid (DLT), supraspinatus (SSP), infraspinatus/teres minor (ISP/TM), and subscapularis (SSC) musculotendinous units was constructed. The DLT wrapping on the humerus was simulated using a pulley that could be horizontally adjusted to simulate the 28° CSA found in OA or the 33° CSA found in disease-free shoulders. Over a range of motion between 6° and 82° of thoracohumeral abduction joint forces were measured using a six-axis load cell. An OA-associated CSA yielded higher net joint reaction forces than a normal CSA over the entire range of motion. The maximum difference of 26.4 N (8.5%) was found at 55° of thoracohumeral abduction. Our model thus suggests that a CSA typical for OA predisposes the glenohumeral joint to higher joint reaction forces and could plausibly play a role in joint overloading and development of OA. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1047-1052, 2016.

Wrinkling of Random and Regular Semiflexible Polymer Networks

We investigate wrinkling of two-dimensional random and triangular semiflexible polymer networks under shear. Both types of semiflexible networks exhibit wrinkling above a small critical shear angle, which scales with an exponent of the bending modulus between 1.9 and 2.0. Random networks exhibit hysteresis at the wrinkling threshold. Wrinkling lowers the total elastic energy by up to 20% and strongly affects the elastic properties of all semiflexible networks such as the crossover between bending and stretching dominated behavior. In random networks, we also find evidence for metastable wrinkled configurations. While the disordered microstructure of random networks affects the scaling behavior of wrinkle amplitudes, it has little effect on wrinkle wavelength. Therefore, wrinkles represent a robust, microstructure-independent assay of shear strain or elastic properties.

Simulation of Transmission Electron Microscope Images of Dislocations Pinned by Obstacles

From a direct observation of dislocation-obstacle interaction utilizing in situ straining experiments in transmission electron microscope (TEM), the obstacle strength factor could be evaluated from pinning angles of dislocation cusps. We simulated this process: we produced a dislocation cusp by molecular dynamics simulation of interaction between an edge dislocation and a void or a hard precipitate in copper, and calculated the TEM image by multislice method. In two-beam conditions, cusp images showed inside-outside contrast depending on the sign of the diffracting vector and other variations with the specimen geometry. The pinning angles measured on TEM images ranged up to a few tens of degrees and were between the true angles for the two partial dislocations. Characteristics and contrast mechanisms of cusp images were discussed based on those of dislocation dipoles. (doi:10.2320/matertrans.MD201312) (Received September 3, 2013; Accepted October 2, 2013; Published November 15, 2013) Various crystal lattice defects induced by neutron irradi- ation, such as precipitates, voids, dislocation lines and loops are responsible for degradation in mechanical properties: increase in yield stress, loss of ductility, and increase in ductile-brittle transition temperature. A number of researches have been devoted for defect structural evolution and mechanical property changes under neutron irradiation for nuclear materials development. Understanding the mecha- nisms involved is necessary to construct models for estimating the lifetime of components of nuclear power plant. In an elementary process of dislocation-obstacle interac- tion, a gliding dislocation is pinned by obstacles and bows out to form arcs between the neighboring pinning points, which induces cusps on the dislocation at obstacles. The apex angle of the dislocation cusp is referred to as the pinning angle o. The dislocation breaks away by bypassing or cutting through the obstacle when the pinning angle reaches a critical value oc. Stronger obstacles have smaller critical angles. The obstacle strength factor i ¼ cosðoc=2Þ and the distance between the neighboring pinning points are the key parame- ters that relate the defect microstructure to the change in macroscopic mechanical properties. There have been re- ported a few attempts to evaluate the factor from a direct observation of dislocation-obstacle interaction utilizing in situ straining experiments in transmission electron micro- scope (TEM). 1­3) The method has not been widely applied so far, due to high technical levels required for in situ experiments. Another difficulty comes from TEM images with a limited resolution both in time and space for measuring pinning angles of radiation-induced obstacles, typically less than a few nanometers in size, at a moment of the breakaway. Alternatively, molecular dynamics (MD) simulations have been applied extensively for the dislocation- obstacle interaction. 4­7) In the present study, we performed TEM image simulation of dislocation cusps to examine whether TEM images reveal the cusp structure in the scale suitable for evaluating the obstacle strength factor. For this purpose, we stopped MD simulation of interaction between an obstacle and an edge dislocation just before the breakaway. We then calculated TEM images of dislocation cusps under various conditions using the multislice method. We compared apex angles between the cusp structure and on the calculated images, which would support the experimental evaluation of the obstacle strength factor.

The Structural Design Method of Multi-Layer Parabolic Reflective Surface for X-Ray Focusing

As an ultra-short electromagnetic waves, X-ray has a strong ability to penetrate with high-energy. The method for focusing visible spectral bands is not suitable for X-ray spectrum. At present, in X-ray astronomy, the X-ray focus mode which uses grazing incidence less than critical angle has been widely used. However, the small critical angle limits its effective aperture of the X-ray collection. This paper presents a multi-layer reflective structure working with grazing incidence and the surfaces coated multilayer high reflective for X-ray. It can guarantee the large effective entrance pupil and high energy collection. The 200mm diameter X-ray focusing device is designed as an example. It is found from simulation that a good focusing result is acquired.

MgO nano-facet embedded silver-based dielectric/metal/dielectric transparent electrode

We replace Indium Tin Oxide (ITO) with an MgO nano-facet Embedded WO(3)/Ag/WO(3)(WAW) multilayer for electrodes of high efficiency OLEDs. WAW shows higher values for transmittance (93%) and conductivity (1.3×10(5) S/cm) than those of ITO. Moreover, WAW shows higher transmittance (92.5%) than that of ITO (86.4%) in the blue region (<500 nm). However, due to the large difference in refractive indices (n) of glass (n=1.55) and WO(3) (n=1.95), the incident light has a small critical angle (52°). Thus, the generated light is confined by the glass/WAW interface, resulting in low light outcoupling efficiency (~20%). This can be enhanced by using a nano-facet structured MgO (n=1.73) layer and a ZrO(2) (n=1.84) layer as a graded index layer. Using these optimized electrodes, ITO-free, OLEDs with various emission wavelengths have been produced. The luminance of OLEDs using MgO/ZrO(2)/WAW layers is enhanced by 24% compared to that of devices with ITO.

In-vitro evaluation of frictional resistance between brackets with passive-ligation designs

The lower frictional resistance produced by passive self-ligating brackets can be helpful during orthodontic sliding mechanics. The aims of this study were to evaluate the frictional resistance of brackets with passive ligation and to compare these values with corresponding controls. Two passive self-ligating brackets (Damon SL II, Sybron Dental Specialties/Ormco, Orange, Calif; SmartClip, 3M Unitek, Monrovia, Calif) and 1 novel bracket with passive elastic ligation (Synergy, Rocky Mountain Orthodontics, Denver, Colo) were used. The brackets were coupled with 3 nickel-titanium archwires (0.014-in round, 0.016 x 0.022-in, 0.019 x 0.025-in) in a simulated ideal arch introducing first-order rotations of 3 degrees and 6 degrees, second-order intrusions of 0.5 and 1.0 mm, and a third-order labial crown inclination of 3 degrees . The dimensions of the brackets were measured with scanning electron micrographs. The results of initial maximum drawing forces (IMDF) were analyzed by 2-way ANOVA and 1-way ANOVA tests. The SmartClip bracket had larger critical angles and distances for binding than the other 2 brackets. When coupled with 0.019 x 0.025-in archwires in an ideal arch alignment, SmartClip brackets had lower IMDF than the other brackets. For the first-order rotations, Synergy brackets had significantly lower IMDF than the other brackets. Damon SL II brackets with smaller critical angles had greater IMDF. For the third-order inclination, the Damon SL II brackets with less torsional play also had greater IMDF. No significant differences of IMDF were found for all the brackets tested in second-order intrusions. However, IMDF increased as the severity of the malocclusion increased. No significant bracket differences were found when binding occurred in second-order distances. In an ideal arch alignment, brackets with greater slot lumen have lower frictional resistance. First-order rotational control was influenced by slot depth, bracket width, and labial cover of the brackets with the same archwire. When a sliding mechanism was used with a third-order inclination change, the brackets with smaller third-order critical contact angles had greater frictional resistance.

Three-dimensional simulations of a platelet-shaped spheroid near a wall in shear flow

We have investigated the three-dimensional motion of an oblate spheroid-shaped particle or “platelet” close to an infinite planar wall in shear flow. The completed double layer-boundary integral equation method modified to include a flat surface boundary was used to compute the effects of the wall on the flow behavior of a platelet of aspect ratio 0.25. Platelet simulations were initiated with the platelet having its axis of symmetry normal to the surface. The platelet is observed to demonstrate three distinct regimes of flow, the dominant regime of flow being dependent on its initial height from the surface. Platelets further than 1.2 platelet radii from the surface display a “modified” Jeffery orbit with periodic rotational motion in the direction of flow (regime I). The presence of the wall retards platelet flow and more importantly introduces periodic lateral motion normal to the wall. When the platelet starts flowing at a height between 1.1 and 0.75 platelet radii from the surface (regime II), it is found to dip down and then “pole vault” off of the surface. Periodic platelet rotation and contact with the surface then ensues with no drift of the platelet away from the surface. In the third regime of flow, a platelet with an initial height of 0.7 platelet radii and below demonstrates wobble motion. The platelet neither rotates nor contacts the surface, but instead, moves laterally in a periodic manner as it translates in the direction of flow. Flow behavior typical of regime III is not observed at all spheroid aspect ratios. The range of initial heights that demonstrate regime III flow diminishes with increasing aspect ratio and regime III disappears completely above an aspect ratio of 0.41. If a platelet located at heights relevant to regime III is given an initial tilt about the y axis or x axis (where x is the flow direction), the resulting flow may either continue in regime III or shift to regime II, depending on the tilt angle. There is a small critical angle of tilt, the magnitude of which depends on the initial platelet height, above which the platelet flow behavior immediately transitions from regime III flow to that of regime II. Tilts about the x axis induce fully three-dimensional flow with rotational motion occurring about all three axes. Therefore, even small tilts about the x axis that are below the critical tilt angles can cause platelet flow to transform from regime III to II eventually at some point downstream. Thus, a platelet flowing close to the surface in linear shear has ample opportunity to contact the surface, an important event for initiating receptor-ligand binding of blood platelets to the injured vascular endothelium during the onset of hemostasis.

In situ X-ray studies of vapor phase epitaxy of PbTiO 3

As part of a program to understand and control the structure of ferroelectric thin films grown by metal organic vapor phase epitaxy (MOVPE), we have used X-ray scattering to observe the surface structure of PbTiO 3 films during and following growth. Moderately high energy (24 keV) X-rays are used to penetrate the chamber walls for in situ measurements in the high-temperature, reactive MOVPE environment. Performing measurements in situ allows us to study the growth process in real time, to control the thickness of the films to sub-unit-cell accuracy, to observe the surface structure in equilibrium with the vapor, and to preserve film stoichiometry during high-temperature study by maintaining an overpressure of PbO. While the higher X-ray energy also permits a large volume of reciprocal space to be mapped, it presents challenges for surface scattering due to the small critical angle. Examples of results will be presented from studies of surface structure dynamics, crystal growth, and ferroelectric stripe domains in thin films.

Blocking- and channeling-ERDA with heavy ions

A 2-dimensional position sensitive ionization chamber was used for structural analysis of single crystalline materials by blocking- and channeling-ERDA. Radiation damage of swift heavy ions in Ge was measured by blocking-ERDA. Clear indications of annealing effects with increasing electronic stopping power were found. A transition from blocking to channeling behavior was observed for recoils from larger depth in measurements on single crystalline Si. Capture to channeling is shown to be a general phenomenon for ions with large energy loss in additional experiments on thin Si membranes. The large solid angle of the ionization chamber is advantageous in channeling-ERDA to minimize radiation damage. The position sensitivity was used in this application to align the desired crystalline direction. The lattice strain of buried CoSi 2 layers in (100) Si was measured by channeling-ERDA. The corresponding angular shift could be separated from the steering effect due to the small critical angles of high energy heavy ions. These examples demonstrate the increased potential of ERDA when channeling or blocking conditions are used.

Impact of planar microcavity effects on light extraction-Part I: basic concepts and analytical trends

We address the long-standing issue of extracting light as efficiently as possible from a high-index material, n/spl ges/2, where as little as 2%-10% of light not suffering total internal reflection is extracted at standard plane faces due to the small critical angle /spl sim/1/n. Using a planar microcavity to redirect spontaneous emission toward the surface, constructive interferences can bring 15%-50% of the light out, enhancing brightness and efficiency. In this first of two papers, an approximate approach is used showing the importance of small cavity order m/sub c/ and of the m/sub c//n/sup 2/ ratio. We define a condition for microcavity regime as m/sub c/<2n/sup 2/. It is shown that most of light extraction is usually attained for moderate mirror reflectivities /spl sim/1-m/sub c//n/sup 2/ typically below 90%, and without strong directionality. Balance between emission directionality, radiance (brightness), and spectral narrowing is discussed. We define a brightness enhancement factor B given by Bm/sub c//spl Delta//spl Omega/=4/spl pi/ where /spl Delta//spl Omega/ is the largest internal solid angle of either the cavity mode or that deduced from the material emission linewidth. Design rules are applied to distributed dielectric mirrors yielding an optimal number of periods. The underlying physical competition between emission into guided modes, Fabry-Perot modes and the so-called "leaky modes" is analyzed.

A simple model for optimization of conical capillaries in XRF analysis

AbstractThe method of total reflection in conical glass capillaries has been used for several decades for obtaining high‐intensity x‐ray microbeams of small spot size. A general problem with this technique is the small critical angle, which is energy dependent. There is a certain loss of intensity if many reflections occur in the capillary. Assuming parallel monoenergetic x‐rays, a simple relationship has been derived for the intensity enhancement as a function of the reflectivity of the glass and the number of reflections. The relationship was used to derive conditions for optimum intensity enhancement. Also for suboptimum conditions the relationship can be used to design entrance and exit diameters and length of the capillary. The model was also applied to a wedge‐shaped slit that consists of two total reflection plates.

Recent advances in nematic and smectic A anchoring on amorphous solid surfaces [1

Abstract New anchoring properties of liquid crystals on amorphous solid surfaces are presented. In nematics (N), angular anchoring is usually described in terms of the Rapini-Papoular form, assuming constant surface order parameter. We generalize this expression, predicting a decrease of surface order for strong surface disorientation. Recent experiments on anchorings of varying strength confirm these predictions. Conjectures for the angular anchoring of smectic A on a solid amorphous surface explain the two easy layer orientations, normal to the surface or parallel, faceting inside a small critical angle. Roughness-induced surface transitions are discussed. For antagonistic nematic and smectic anchorings, we expect, below the N–SA transition, a bent nematic surface boundary layer, recently observed by smectization under an electric field. Finally, the positional anchoring strength of smectics is introduced in terms of shear induced surface melting, and confirmed by a recent observation of oscillating she...

Application of fluid dynamics principles in tilted permeable media to terrestrial hydrothermal systems

Fluid dynamics principles require that circulation of aqueous fluid will be practically ubiquitous in tectonically active parts of the Earth's crust and upper mantle. Both experiment and theory [e.g. Hart, 1971] demonstrate that flow, generally in the form of unicells (Hadley circulation), always occurs for isothermal tilts above a very small critical angle (∼ 5°), for any non‐zero permeability or Rayleigh number, and even for hot over cold geometries. Interestingly, heat transport rates in the unicellular regime are essentially conductive, so such flow, unlike more vigorous flow at higher Rayleigh number, is not properly termed “convective”. These principles have numerous geological ramifications, including: 1) Many of the hydrothermal systems developed around epizonal intrusions should be dominanty unicellular in nature, which explains their aspect ratios and the smooth and very regular δ18O variations that are produced in the rocks; 2) Large, long‐lived unicells are predicted to occur deep in the Earth's crust wherever Rayleigh numbers are finite and isotherms are substantially inclined, as in zones of batholith intrusion, regional metamorphism, and collision; 3) Unicells with lateral dimensions of several hundred kilometers are predicted to be associated with subduction zones dipping more than 6–12°, with fluid advection into the hot mantle wedge being instrumental in mantle metasomatism and in the generation of andesitic magmas.

New Configurations of Single - Crystal Scintillator Detectors in SEM

There are two reasons for designing special geometrical configurations of detectors of signal electrons in EM.1. For some traditional shapes of scintillators (discs) the quantum efficiency of single crystal YAG or YAP scintillators amounting to 5% - 7% is not fully utilized for achieving the maximum light output signal propagated in the desired. The reason is the small critical angle given by the high index of refraction of both single crystal materials. The shaping of single crystal scintillators and treating of surfaces by making use of the laws of geometrical optics lead to an increase of the value of the light output signal propagated in the desired direction.2. Different kinds of information carried by signal electrons (especially BSEs) of different types must be collected by a detector of a specific geometrical shape placed in a suitable position with regard to the specimen.Non-traditional geometrical configurations and optical modifications of detectors have been designed to solve the problem of a more efficient propagation of light towards the photocathode of PMT, considering different types of signal electrons.

Ballistic Electron Emission Microscopy

Ballistic Electron Emission Microscopy (BEEM) is a scanning-tunneling-microscopy-based technique which gives a plan view, nanometer scale image of electronic properties of a buried interface. Among the properties which can be imaged are barrier height, the edges of multiple conduction and valence bands, and carrier scattering. These properties can be correlated with strain, defects, and stoichiometry variations at the interface. A topographic image of the sample surface is aquired simultaneously with the interface image. BEEM data has been reported from six laboratories to date, including images of Au/Si, Au/GaAs, NiSi2/Si, and Au/CdTe. Several new systems, some designed for ultra-high-vacuum operation, are under construction.In the simplest implementation, electrons or holes are injected from a tunnel tip into the metal electrode of a metal-semiconductor diode (figure 1). The carriers are ballistically transported across the electrode and, if momentum, energy, and scattering criteria are satisfied, are collected in the semiconductor base. Momentum conservation requires the ballistic electron or hole beam to cross the interface within a small cone of solid angle, and hence the collected current only reflects injection into a small region of the Brillouin zone. This small critical angle cone is responsible for the high spatial resolution of BEEM. By varying the potential of the initial injected beam (i.e. tip voltage with respect to electrode), the electronic dispersion relation of the substrate can be spectroscopically probed.

On the origin of anomalous ranges of 1.65 GeV 132Xe ions in Muscovite Mica

Ranges of 1.65 GeV 132Xe ions in muscovite mica, determined using solid state nuclear track detector (SSNTD) techniques, are shown to vary strongly with angle of incidence to the basal plane. This is explained within the framework of the Chadderton-Koul-Biersack (CKB) model for latent track formation in real crystals. Not only are there clear bursts of electronic energy loss at individual molecular layers, as seen in intermittent tracks in the electron microscope, but the range variation can also be ascribed to a basic refractive effect of individual molecular layers on the particle trajectories. This, in turn. provides a strong nonlinear electronic stopping. The strong uniaxial anisotropy of muscovite mica imposes a new orbital motion, referred to as “ridging” (or “bridging” in the upper angular limit) on the swift xenon ions. which are almost completely stripped of electrons. Neither “channelling” nor “quasichannelling“. which are determined by smaller critical angles, play any part in this specific aspect of anomalous range determination, which is entirely due to the smooth angular dependence of the “ridging” orbits on refracted pathways, and on the integrated stopping power sampled. The fact that incorporation of “ridging” and “bridging” into the broader picture now produces a complete angular set of classical positively charged particle orbits, encompassing all of real space in crystals. leads naturally to the construction of a new classical range ( R ) surface, quite analogous to the familiar Fermi surface of constant energy, described by conduction electron momentum vectors ( k ) in reciprocal space.

Slightly slanting impact on an elastic cantilever column—an experimental study

Experiments concerning slightly slanting impact between a flat-ended rigid body and a flat-ended elastic cantilever column with a rectangular cross-section have been performed. The experimental results are compared with the theoretical ones. The small angle of incidence was measured by using an optical method. The impact process was studied by using a split disc for the rigid body, with the two halves bonded together and electrically insulated from each other. The disc and the column were parts of an electric circuit. Different contact states could be distinguished according to different voltage levels. Reasonably good agreement between theory and experiment was found. Thus, the impact duration has its minimum under perfectly axial impact as predicted by the theory. Also, the predicted process of alternating line and surface contact was observed. Furthermore, the existence of a small critical angle of incidence was verified. This critical angle of incidence divides the impact processes into two categories: (1) The rigid body and the column end come into surface contact before separation. (2) They separate without surface contact. Comparison of axial strains between theory and experiment shows good agreement.

Almost-axial impact on an elastic cantilever column—a theoretical study

The process of contact between an initially straight flat-ended elastic cantilever column with rectangular cross section and a flat-ended rigid impacting mass with a small angle of incidence with respect to the axis of the column is studied theoretically. The equations of motion pertaining to the column, including the effects of shear deformation and rotary inertia, take the form of coupled second-order non-linear partial differential equations. These are solved by using an explicit finite difference method. The boundary values at the impacted end of the column are obtained from Hamilton's principle for the column and from the dynamics of the impacting mass. For a given column slenderness ratio and impact velocity there exists a small critical angle of incidence. When the angle of incidence is smaller than this critical value the mass and the impacted end of the column come into surface contact before separation. Otherwise they separate without coming into surface contact. The impact duration shows a sharp decrease at this critical angle of incidence for the cases studied in this paper.

Effects of variation of attenuation with depth in the sediment on the bottom reflection coefficient

The form of sediment attenuation versus depth is varied to study its effects on the bottom reflection coefficient for sand and clay layers. 300 m thick, overlaying a basalt substrate. Constant, linear, modified exponential, and sound-speed-linked dependences of attenuation on depth are input to a plane wave reflection coefficient model and the resulting bottom loss versus grazing angle curves are compared. The form of attenuation versus depth is found to have significant effects (as much as 10 dB at 50 Hz) on bottom loss for sediments with small critical angles and moderate sound speed gradients. Mode attenuation coefficients for the same physical situations gave similar results. [Work supported by the Naval Electronic Systems Command.]

Analysis of grating-coupled emission in lead-tin telluride diode lasers

The use of the grating-coupled emission concept with lead-tin telluride double-heterojunction diode lasers is analyzed theoretically. The GCE configuration is shown to be attractive for producing small divergence-angle emission from fixed-wavelength lead-salt devices, but to be of more limited interest for use with tunable lasers because of the small critical angle characteristic of the PbTe-air interface and because of the variation of the angle of emission with wavelength. The device structure studied is one incorporating a reflecting contact in close proximity to the grating, a feature which leads to resonant enhancement or reduction of the emission, depending upon the wavelength and the device dimensions.