Stable Radius Research Articles

Are there any differences in various polyaxial locking systems? A mechanical study of different locking screws in multidirectional angular stable distal radius plates

Numerous angular stable plates for the distal radius exist, and technically based comparisons of the polyaxial locking interfaces are lacking. The aim of this mechanical study was to investigate three different locking interfaces of angular stable volar plates by cantilever bending: VA-LCP Two-Column Distal Radius Plates 2.4 mm (Synthes® GmbH, Oberdorf, Switzerland), IXOS® P4 (Martin, Tuttlingen, Germany) and VariAX™ (Stryker®, Duisburg, Germany). We assessed the strength of 0°, 5°, 10° and 15° screw locking angles and tested the bending strength from 10° to 5° angles by cyclic loading until breakage. The final setup repeated the above assessments by inclusion of four locking screws. The single screw-plate interfaces of the VA-LCP showed the highest bending moment at an angle of 0° and 5°, the IXOS® P4 at an angle of 10° and 15° and the VariAX™ when changing the insertion angle from 10° into 5°. The strength of polyaxial locking interfaces and mechanism of failure proved to be different among the examined plates.

Conservative treatment of the distal radius fracture using thermoplastic splint: pilot study results

Fractures of the distal radius are common accounting for approximately one-sixth of all fractures treated in the emergency room. This study reviews a series of patients with stable distal radius fractures who have been treated with thermoplastic splint. This study was undertaken between November 2009 and May 2010 in a single orthopaedic fracture outpatient clinic. All patients had undisplaced or minimally displaced distal radius fractures. Children and open fractures were excluded. Patients had been reviewed in the outpatients with radiographs on 1, 2, 6 and 12weeks after injury. Skin condition and satisfaction were assessed on splint removal. Radiological parameters of radial inclination, radial length and palmer tilt were measured. In total, 26 patients were treated with the splint. The average age of the patients was 45.1 (range, 21-73), and male/female ratio was 12:14. On average, the splint was removed at 5.1weeks (mode=6weeks). The right- to left-side ratio was 11:15. Eleven of those fractures were on the dominant side. There was no significant difference in the radiological outcomes pre- and post-splinting. Nearly all patients had been satisfied with the splint. Two patients had minor cast complications whilst 23 patients were able to shower whilst in splint. Patients treated with thermoplastic splint showed no deterioration in their radiological outcomes. Nearly all the patients had been satisfied with the splint.

Dissolution of coated microbubbles: The effect of nanoparticles and surfactant concentration

The ability of solid particles to stabilise emulsions is a well known phenomenon which has recently been demonstrated for the stabilisation of gas bubbles. In this paper, a new theoretical model is developed which describes how an adsorbed layer of solid nanoparticles modifies the interfacial tension and diffusivity of a gas bubble in a liquid and hence its stability. In agreement with experimental observations on microbubbles coated with 15nm diameter spherical gold particles, the results of simulations with the model indicate that the particles substantially decrease the rate at which bubble dissolution occurs and enables them to maintain a stable radius once a critical particle concentration has been reached.

A mechanical model of retinal detachment

We present a model of the mechanical and fluid forces associated with exudative retinal detachments where the retinal photoreceptor cells separate, typically from the underlying retinal pigment epithelium (RPE). By computing the total fluid volume flow arising from transretinal, vascular and RPE pump currents, we determine the conditions under which the subretinal fluid pressure exceeds the maximum yield stress holding the retina and RPE together, giving rise to an irreversible, extended retinal delamination. We also investigate localized, blister-like retinal detachments by balancing mechanical tension in the retina with both the retina–RPE adhesion energy and the hydraulic pressure jump across the retina. For detachments induced by traction forces, we find a critical radius beyond which the blister is unstable to growth. Growth of a detached blister can also be driven by inflamed lesions in which the tissue has a higher choroidal hydraulic conductivity, has insufficient RPE pump activity, or has defective adhesion bonds. We determine the parameter regimes in which the blister either becomes unstable to growth, remains stable and finite-sized, or shrinks, allowing possible healing. The corresponding stable blister radius and shape are calculated. Our analysis provides a quantitative description of the physical mechanisms involved in exudative retinal detachments and can help guide the development of retinal reattachment protocols or preventative procedures.

Dynamics of gas bubble growth in oil-refrigerant mixtures under isothermal depressurization

This paper proposes a numerical model to predict the growth of gaseous refrigerant bubbles in oil-refrigerant mixtures with high contents of oil subjected to isothermal depressurization. The model considers an Elementary Cell (EC) in which a spherical bubble is surrounded by a concentric and spherical liquid layer containing a finite amount of dissolved liquid refrigerant. The pressure reduction in the EC generates a concentration gradient at the bubble interface and the refrigerant is transported to the bubble by molecular diffusion. After a sufficiently long time, the concentration gradient in the liquid layer and the bubble internal pressure reach equilibrium and the bubble stops growing, having attained its stable radius. The equations of momentum and chemical species conservation for the liquid layer, and the material balance at the bubble interface are solved via a coupled finite difference procedure to determine the bubble internal pressure, the refrigerant radial concentration distribution and the bubble growth rate. Numerical results obtained for a mixture of ISO VG10 polyolester oil and refrigerant HFC-134a showed that the bubble growth dynamics depends on model parameters such as the initial bubble and liquid layer radii, the initial refrigerant concentration in the liquid layer, the initial pressure in the liquid phase, the decompression rate and the EC temperature. Despite its simplicity, the model demonstrated to be a potential tool for predicting bubble growth and foaming that may occur as a result of cavitation in oil-lubricated bearings and refrigerant degassing from the oil sump during compressor start-up. Keywords: refrigeration compressor, oil-refrigerant mixtures, bubble growth, numerical modeling

Resolving the inner structure of QSO discs through fold-caustic-crossing events

Though the bulk of the observed optical flux from the discs of intermediate-redshift lensed quasars is formed well outside the region of strong relativistic boosting and light-bending, relativistic effects have important influence on microlensing curves. The reason is in the divergent nature of amplification factors near fold caustics increasingly sensitive to small spatial size details. Higher-order disc images produced by strong light bending around the black hole may affect the amplification curves, making a contribution of up to several percent near maximum amplification. In accordance with theoretical predictions, some of the observed high-amplification events possess fine structure. Here we consider three putative caustic crossing events, one by SBS1520+530 and two events for individual images of the Einstein's cross (QSO J2237+0305). Using relativistic disc models allows to improve the fits, but the required inclinations are high, about 70deg or larger. Such high inclinations apparently contradict the absence of any strong absorption that is likely to arise if a disc is observed edge-on through a dust torus. Still, the high inclinations are required only for the central parts of the disc, that allows the disc itself to be initially tilted by 60-90deg with respect to the black hole and aligned toward the black hole equatorial plane near the last stable orbit radius. For SBS1520+530, an alternative explanation for the observed amplification curve is a superposition of two subsequent fold caustic crossings. While relativistic disc models favour black hole masses ~10^10 solar (several times higher than the virial estimates) or small Eddington ratios, this model is consistent with the observed distribution of galaxies over peculiar velocities only if the black hole mass is about 3 10^8 solar.

Swifter than the Sun

Astrophysics![Figure][1] CREDIT: ISTOCKPHOTO.COM Stars form from the gravitational collapse of clouds of gas and dust. Before they attain a stable radius, they spin faster and faster as they contract, much like a spinning ice skater does as she folds her arms to her body. After gravitational

Optimized tool path generation for fast tool servo diamond turning of micro-structured surfaces

Fast tool servo (FTS) diamond turning is a promising machining process for fabricating ultra-precision micro-structured surfaces which have already gained wide application especially in the optics industry. However, most research focused on designing different types of FTSs for better performance, including bandwidth, stroke, stiffness, acceleration, accuracy, etc. There is a lack of systematical tool path generation (TPG) for FTS diamond turning, especially from the influence of TPG on surface quality point of view. This paper presents an optimized tool path generation for FTS diamond turning of micro-structured surfaces with either analytical description or non-uniform rational B-spline description. The tool path is optimized from three aspects to ensure high precision form and nanometric surface finish. Firstly, the tool path is optimized by a stable tool nose radius compensation method, which is different from the conventional one, to reduce the form error caused by the tool nose radius. Secondly, the ideal machined surface profiles are simulated to predict the ideal surface quality, with which the cutting conditions and tool geometry can be optimized to ensure nanometric surface finish and avoid tool interference. Thirdly, the influence of the control dynamics of the machine axes on machined surface quality, which is ignored in conventional machining, was considered. As the FTS dynamics dominate the influence, it is controlled to be a desired dynamics which was then used to modify the tool path to minimize the form error in machined surface. Experiments were carried out to prove the effect of TPG on surface quality and the effectiveness of the optimized TPG method.

Laser reshaping of costal cartilage for transplantation

Laser reshaping of cartilage is a new effective and safe technique for correction of nasal septum and ear deformities. Costal cartilage is a most suitable natural material for transplantation. The problem is to obtain stable proper shape of cartilage implants. The objective of this article is to study reshaping of porcine costal cartilage for larynx stenosis surgery using Erbium glass fiber laser. Porcine cartilage plates 3 mm in thickness were mechanically curved and irradiated (1) on one side (stretched or compressed) and (2) on both sides with different sequence. Irradiation was performed using a 1.56 µm laser with power varied from 1 to 2.5 W, exposure time from 5 to 20 seconds, spot diameter of 2.5 mm, pulse duration of 500 milliseconds, pulse repetition rate of 1.4 Hz. For each laser setting, stable curvature radius was measured during 24 hours after the experiment. Irradiated samples were analyzed by means of differential scanning calorimerty (DSC) to reveal the collagen denaturation degree. The optimum laser setting for stable reshaping of costal cartilage without visual thermal damage of cartilage matrix was established: laser power of 2.2 W, exposure time of 6 seconds. Nonlinear thermomechanical behavior of cartilage in the course of its laser reshaping is experimentally revealed. The influence of irradiation sequence on the curvature radius of cartilage implant is found for the first time. It is shown that (1) it is possible to use laser reshaping technique for making stable proper shape of costal cartilage, and (2) primary irradiation of compressed side followed with an irradiation of stretched side is more effective than reverse sequence of laser treatment. DSC analysis showed that thermal effect of irradiated specimens (2.58-3.79 J/g) was slightly lower that that for intact cartilage specimens and considerably lower than that for denaturation of collagen (65 ± 5 J/g). It is possible to use laser reshaping technique for preparation of stable cartilage implants. Nonlinear thermomechanical behavior of cartilage is experimentally revealed. The influence of irradiation sequence on curvature radius of cartilage grafts is established for the first time.

Atomistic Mechanisms and Diameter Selection during Nanorod Growth

We study in this paper the atomic mechanisms of nanorod growth and propose the mechanism of diameter selection of nanorods. A characteristic radius is demonstrated to be crucial in nanorod growth. If the critical size of the two-dimensional nucleus is assumed to be 1, the characteristic radius increases proportional to 1/5 power of the ratio of the interlayer hopping rate of adatoms across the monolayer steps to the deposition rate. When the radius of the initial island is larger than this characteristic radius, a screening effect is important for nanorod growth. The growth morphology evolves from a taper-like structure to a nanorod with a radius equal to the characteristic radius after some transient layers, depending on the screening strength. When the radius of the initial island is smaller than this characteristic radius, the nanorod morphology can be maintained during the growth, with the stable radius being limited by both the radius of the initial island and the threedimensional Ehrlich-Schwoebel barrier. Therefore, different growth modes and the diameter of nanorod can be selected by changing the characteristic radius, via controlling the growth condition. The theoretical predictions are in good agreement with experimental observations of ZnO growth.

Diffusion potentials in porous mortar in a moisture state below saturation

Diffusion potentials (membrane potentials) were measured in mortar in a moisture state below saturation for the first time. In contrast to conventional diffusion cell setups, the experimental approach was based on embedded ion selective electrodes. A numerical model with coupled Nernst–Planck equations for the most abundant species in the pore solution allowed simulating ion transport processes and the correspondingly arising diffusion potentials. It was found that Portland cement mortar with a water/cement ratio of 0.6 does not exhibit any significant permselective behaviour – even not in an unsaturated state determined by self-desiccation. Apparently, the stable radius of water-filled capillaries is still large enough to allow ionic transport through those fractions of pore solution that are unaffected by double layer effects. In addition, the relative importance of liquid junction potentials at the reference electrode/sample interface and internal diffusion or membrane potentials are discussed with respect to application of direct potentiometry to cement based materials.

Effect of Titanium, Antimony, Cerium and Carbon Nanotubes on the Morphology and Microhardness of Mg-based Icosahedral Quasicrystal Phase

F or the flrst time, petal-like and spherical Mg-based icosahedral quasicrystal phase (I-phase) were obtained by introducing Ti, Sb, Ce and C nanotubes into Mg-Zn-Y alloy under normal casting conditions. The formation mechanism and stability criterion of spherical I-phase were discussed. The morphology and microhardness of I-phase and their determinants were studied in this paper. The results show that the difierent value of microhardness of I-phase could be attributed to the difierent kinds of the fourth component and its content, and its difierent innate characters. The flnal morphology of icosahedral quasicrystalline (IQC) is decided by the size of critical stable radius Rr, the content of the fourth component and degree of undercooling.

Effects of encapsulation elasticity on the stability of an encapsulated microbubble

A model for gas transport from an encapsulated microbubble into the surrounding medium is developed and investigated incorporating the effects of encapsulation elasticity. Encapsulation elasticity stabilizes microbubbles against dissolution and explains the long shelf life of microbubble contrast agent. We consider air bubbles as well as bubbles containing perfluorocarbon gas. Analytical conditions between saturation level, surface tension and interfacial dilatational elasticity are determined for attaining non-zero equilibrium radius for these microbubbles. Numerical solution of the equation verifies the stability of the equilibrium radii. In an undersaturated medium all encapsulated bubbles dissolve. In a saturated medium, an encapsulated bubble is found to achieve a long-time stable radius when interfacial dilatational elasticity is larger than equilibrium surface tension. For bubbles with interfacial dilatational elasticity smaller than the equilibrium surface tension, stable bubble of non-zero radius can be achieved only when the saturation level is greater than a critical value. Even if they initially contain a gas other than air, bubbles that reach a stable radius finally become air bubbles. The model is applied to an octafluoropropane filled lipid-coated 2.5 μm bubble, which displayed a transient swelling due to air intake before reaching an equilibrium size. Effects of elasticity, shell permeability, initial mole fraction, initial radius and saturation level are investigated and discussed. Shell permeability and mole fraction do not affect the final equilibrium radius of the microbubble but affect the time scale and the transient dynamics. Similarly, the ratio of equilibrium radius to initial radius remains unaffected by the variation in initial radius.

Boson stars with repulsive self-interactions

The properties of compact stars made of massive bosons with a repulsive self-interaction mediated by vector mesons are studied within the mean-field approximation and general relativity. We demonstrate that there exists a scaling property for the mass-radius curve for arbitrary boson masses and interaction strengths which results in a universal mass-radius relation. The radius remains nearly constant for a wide range of compact star masses. The maximum stable mass and radius of boson stars are determined by the interaction strength and scale with the Landau mass and radius. Both the maximum mass and the corresponding radius increase linearly with the interaction strength so that they can be radically different compared to the other families of boson stars where interactions are ignored.

A NEW DIAGNOSTIC METHOD FOR ASSESSMENT OF STELLAR STRATIFICATION IN STAR CLUSTERS

We propose a new method for the characterization of stellar stratification in stellar systems. The method uses the mean-square radius (also called the Spitzer radius) of the system as a diagnostic tool. An estimate of the observable counterpart of this radius for stars of different magnitude ranges is used as the effective radius of each stellar species in a star cluster. We explore the dependence of these radii on magnitude as a possible indication of stellar stratification. This method is the first of its kind to use a dynamically stable radius, and though seemingly trivial it has never been applied before. We test the proposed method using model star clusters, which are constructed to be segregated on the basis of a Monte Carlo technique, and on Hubble Space Telescope observations of mass-segregated star clusters in order to explore the limitations of the method in relation to actual data. We conclude that the method performs efficiently in the detection of stellar stratification and its results do not depend on the data, provided that incompleteness has been accurately measured and the contamination by the field population has been thoroughly removed. Our diagnosis method is also independent of any model or theoretical prediction, in contrast to the `classical' methods used so far for the detection of mass segregation.

Strange quark matter and strangelets in the quasiparticle model

The quasiparticle model has been extended to include finite-size effects, and applied to study the properties of strange quark matter and strangelets. A chemical potential- and radius-dependent effective bag quantity is derived. In this extended version of the quasiparticle model, strange quark matter and/or strangelets still have the chance to be metastable or absolutely stable. The stable radius of a strangelet in the present model is smaller than, but comparable with that of the corresponding nucleus with the same baryon number, which might be relevant for the analysis of the strangelet propagation and detection. The influence of the model parameters on the stability of strangelets is discussed.

Zhang Hongren and the Introduction of Transient Flow Theory to China

Puzzled over a Pumping Test Zhang Hongren (Figure 1) was trained in the 1950s as a classical geologist, first in China and then in the former Soviet Union. From 1959 to 1962, he worked on mineral exploration and geological mapping in Yunnan Province, southern China. After a 3-year stint in the field, he moved to the capital city of Beijing and became a technical specialist in the Ministry of Geology. Then, in 1970, Zhang was sent to the Hydrogeological Survey of Beijing to work on water resource evaluation for the rapidly growing city. For those who are familiar with recent Chinese history, 1970 was still at the height of the ‘‘Cultural Revolution,’’ a chaotic period from 1966 to 1976 during which many intellectuals were sent to the remote countryside or factories to receive ‘‘reeducation’’ from peasants and workers. But everyone needed drinking water no matter what they did. So Zhang was assigned the responsibility to do whatever it took to solve the water supply problem quickly. With little background in hydrogeology, Zhang and his coworkers decided to conduct a pumping test in a river basin not far from Beijing. At that time, the ground water texts available in China were mostly translated from Russian, and they only discussed the theory of ground water flow to wells under steady-state conditions. Having read some of these texts, Zhang expected to observe a stable radius of influence and then use that information to establish the long-term pumping rate for the water supply well. However, it became immediately apparent that things were not adding up. Head measurements at the observation wells indicated that the cone of depression continued to expand. A small creek near the pumping well went dry not long after the start of the pumping test, causing some fish to be out of water. Zhang and his colleagues managed to complete the pumping test. But the experience planted a seed of doubt in the mind of Zhang about the validity of the prevailing theory of well hydraulics that assumed steady-state conditions.

Charge, strangeness and radius of strangelets

We investigate, at both zero and finite temperatures, the properties of strangelets versus the electric charge Z and strangeness S. The strangelet radius is not a monotonic function of either charge or strangeness, and a minimum is reached in the (Z, S) plane. However, the thermodynamically stable strangelets do not correspond to the radius minimum. The minimum radius always appears at positive strangeness, while the stable radius may appear at negative strangeness for very small baryon numbers. For large baryon numbers, the stable radius is proportional to the cubic root of baryon numbers, but inversely proportional to the square root of the confinement parameter in the present model. If bulk strange quark matter is absolutely stable, the reduced size of strangelets is about 1 fm, which may be relevant for the analysis of the strangelet production and detection.

Structure and stability of bent core liquid crystal fibers

Recently it was found that fluid smectic phases of bent core liquid crystals formed freestanding fibers of extremely high slenderness ratios. Studies of these fibers showed that their structure was composed of concentric cylindrical smectic layers. For this configuration to be stable there must be an energy term that desires bending of the smectic layers. We show that an energy term that deals with the divergence of the dipolar direction can encourage layer bending if the layer chirality value is allowed to vary. The energy term associated with holding the layer chirality is closely related to layer compressions and electrical self-interactions. For our model, we assumed a simple smectic-C geometry with constant molecular tilt and cone angle defined by the director with respect to the layer normal, but allowed a constant variation of the polar direction about the director. Applying this simplified model to a free energy which accounts for director distortions, divergence of the polar direction, biaxial layer strain, surface tension, and electrical self-interactions, we were able to show consistency between the stable fiber radius and other properties predicted in our model to results from experimental studies.

Numerical dynamo models of Uranus' and Neptune's magnetic fields

The non-axisymmetric, non-dipolar magnetic fields of Uranus and Neptune are markedly different from the axially-dipolar dominated fields of the other planets in our Solar System with active dynamos. Stanley and Bloxham [Stanley, S., Bloxham, J., 2004. Nature 428, 151–153] used numerical modeling to demonstrate that Uranus' and Neptune's unusual fields could be the result of a different convective region geometry in these planets. They found that a numerical dynamo operating in a thin shell surrounding a stably-stratified fluid interior produces magnetic field morphologies similar to those of Uranus and Neptune. This geometry for the convective region was initially proposed by Hubbard et al. [Hubbard, W.B., Podolak, M., Stevenson, D.J., 1995. In: Cruickshank, D. (Ed.), Neptune and Triton. Univ. of Arizona Press, Tucson, pp. 109–138] to explain both the magnetic field morphology as well as the low intrinsic heat flows from these planets. Here we examine the influence of varying the stable layer radius in numerical models and compare the results to thin shell models surrounding solid inner cores. We find that a limited range of stable-layer shell thicknesses exist in which Uranus/Neptune-like field morphologies result. This allows us to put constraints on the size of the convective layers in Uranus and Neptune.