Discontinuous Research Articles

A Discrete Model for the Natural Frequencies and Mode Shapes of Constrained Vibrations of Beams with Various Boundary Conditions

The purpose of the present paper is the development of a physically discrete model for free transverse constrained vibrations of beams. The discrete model consists on an N -degree of freedom system made of masses placed at the end of solid bars connected with spiral springs. The calculations made involve two tensors, namely the mass tensor [ m ij ] and the linear rigidity tensor [ k ij ]. The results obtained by the physically discrete model show a good agreement and a quick convergence to the equivalent continuous beam for various end conditions for both the natural frequencies and the corresponding mode shapes. The model proposed in the present paper, which has been validated here using classical cases, may be easily applied to the flexural vibration of beams with various types of discontinuities, and to beams carrying concentrated masses.

DESCRIPTION OF SHOCK WAVE PROCESSES IN DENSE GAS SUSPENSIONS USING THE MOLECULAR-KINETIC COLLISIONAL MODEL

A model of reacting flow in suspensions of incompressible particles in gas with description of the chaotic motion of particles on the base of the molecu-lar-kinetic approach is presented. A class of granulated gases is distinguished, for which the equations are of the divergent form. The shock conditions and the types of strong discontinuities are determined. Domains of the existence of shock depending on restitution and roughness parameters, shock wave velocity and initial particle concentration are obtained. The model is verified by the equilibrium sound velocity to the experiments of Gelfand et al. (1986) on particle suspension expansion with high pressure chamber destroying.

Deformation Temperature Effects on Microstructure and Texture Evolution in High Strain Rate Extrusion-Machining of Mg-AZ31B

Deformation microstructure and texture in Mg-AZ31B bulk strips processed through extrusion-machining were studied as a function of deformation temperature. At warm deformation temperatures (~200°C), cold-worked type microstructures with predominant tilted basal texture were observed. With increase in temperature, grain structure sharply transformed into equiaxed type with predominant in-plane basal texture. This sharp transition was found to be consistent with change in temperature dependent dynamic recrystallization mechanism from continuous to discontinuous type.

High-Resolution Numerical Method for Supercritical Flows with Large Density Variations

is introduced with the aim of simulating jet mixing under supercritical pressure environments. The nonlinear localized artificial diffusivity provides the stability to capture different types of discontinuity, such as shock wave, contact surface, and material interface, whereas the high-order compact difference scheme resolves broadband scales in the rest of the domain. The present method is tested on several one-dimensional discontinuity-related problems under super/transcritical conditions and a comparatively more illustrative two-dimensional lowtemperature planar jet problem under a supercritical pressure condition. The localized artificial diffusivity, especially artificial thermal conductivity for temperature gradients, effectively suppresses numerical wiggles near the interfaces. The effects of the artificial thermal conductivity on numerical stability and accuracy are examined. Comparisons between the present method and a conventional low-order scheme demonstrate the superior performance of the present method for resolving a wide range of flow scales while successfully capturing large density/temperature variations at interfaces.

Visual Evaluation of Cast Dental Alloys Welds Discontinuities in the Field of Fixed Prosthodontics

It is essential for a weld to satisfy the requirements of certain standards in the field where it is applied. The aim of the study was to highlight the discontinuities which can appear in the joints achieved by laser and microplasma welding of base metal dental alloys used in fixed prosthodontics. All types of discontinuities which are visible from visual inspection were searched: inclusions, inadequate joint penetration, incomplete fusion, undercuts, overlaps, underfills. Recognizing the defects and discontinuities and their delimitation was essential in determining the weld quality. The obtained results were satisfactory for the purpose both for microplasma and laser welding. Using these methods, welds without defects, which meet minimum acceptable standards for each case, could be obtained.

Typical fatigue-initiating discontinuities in metallic aircraft structures

A fatigue lifing framework using a lead crack concept, based on years of detailed inspection and analysis of fatigue cracks in many specimens and airframe components, has been developed by the DSTO for metallic primary airframe components. This framework is an important additional tool for determining aircraft component fatigue lives in the Royal Australian Air Force fleet. Like the original Damage Tolerance concept, developed by the United States Air Force, this framework assumes that fatigue cracking begins as soon as an aircraft enters service. However, there are major and fundamental differences. Instead of assuming initial crack sizes and deriving early crack growth behaviour from back-extrapolation of growth data for long cracks, the framework uses data for real cracks growing from small discontinuities inherent to the material and the production of the component. To this end, this paper examines the types of discontinuities that initiate fatigue cracks in typical metallic airframe structures. These discontinuities and the fatigue cracks that have grown from them are taken from coupon, component and full-scale tests, and also from service aircraft, including commercial transport aircraft and high performance military aircraft.

Examination of the influence of ossification of the anterior longitudinal ligament on symptom progression and surgical outcome of ossification of the thoracic ligamentum flavum: a multicenter study

The purpose of this study was to provide the first evidence for the influence of an ossified anterior longitudinal ligament (OALL) on the clinical features and surgical outcomes in an ossified ligamentum flavum (OLF) in the thoracic region. Sixty-three patients who underwent surgery for a 1-level thoracic OLF were identified, and preoperative symptoms, severity of symptoms and myelopathy, disease duration, MR imaging and CT findings, surgical procedure, intraoperative findings, complications, and postoperative recovery were investigated in these patients. Entities of OALLs were found on sagittal CT images to be adjacent to or at the same vertebral level as the OLF were classified into 4 types: no discernible type (Type N), one-sided (Type O), discontinuous (Type D), and continuous (Type C). The duration of symptoms was especially long for Types D and C OALLs. Patients with Type D OALLs had a significantly worse percentage of recovery, as well as worse preoperative JOA scores. The authors' results showed that a Type D OALL had strong associations with preoperative severity of symptoms and surgical outcomes. These findings may allow surgeons to determine the severity of preoperative symptoms and the probable surgical outcomes from the OALL classifications. Moreover, surgery with instrumentation for Type D OALLs may produce better surgical outcomes.

Analysis of the Extracellular Polysaccharide-based Structures Produced by a Halophylic Archaeon

This paper investigates the components distribution and structure of an extracellular polysaccharide (EPS) produced by the halophilic archaeon Haloferax mediterranei in the presence or absence of the archaeon by using optical microscopy. The results show that EPS at the end of cultivation is arranged as a discontinuous biofilm and the cells are embedded in this biofilm. EPS and cells cannot be separated through centrifugation, cells remaining attached to the polysaccharide; the biofilm in the supernatant has a similar aspect as in the cultivation broth. The biofilm formed from the supernatant by drying at room temperature is very rich in salts from the cultivation broth (around 200 g/l from which 125 g/l NaCl) and consists on salt crystals which incorporate or are embedded by a film of EPS, distributed discontinuously and having some globular components. In the absence of salts (removed through dialysis), the biofilm formed in the aqueous environment is discontinuous and consists on globular polysaccharides connected by linear EPS which entraps cells remained after centrifugation.

Influence of Dispersion and Alignment of Nanotubes on the Strength and Elasticity of Carbon Nanotubes Reinforced Composites

In this paper, the effective strength and elastic properties of carbon nanotube reinforced composites are evaluated using a representative volume element with a number of carbon nanotubes embedded in the matrix. This concept is used to predict the mechanical properties of multiple, unidirectional, aligned, and also randomly dispersed carbon nanotube reinforced composites. To characterize these nanocomposites, a continuum model has been developed for large-scale analysis. The effective Young’s and shear moduli of the composites are determined using finite element analysis under the effect of elastic deformation. The role of design parameters like length and volume fraction of carbon nanotubes, tensile and shear strength as well as type of loading conditions are analyzed for multiple carbon nanotubes based composites. The discontinuous and continuous types of carbon nanotubes, with aligned and random distribution, are evaluated. The results show that the continuous and aligned carbon nanotubes produce the largest tensile modulus, compared to the discontinuous and aligned as well as discontinuous and randomly oriented carbon nanotubes along the longitudinal direction.

Implications of Farrowing Crates on Welfare Lactating Sows

The research monitored the welfare evolution of lactating sows that were housed in farrowing crates, in commercial farms, based on the skin lesions and lameness. The observations were carried out on lactating sows (Mangalitza, n: 40), during their entire lactation period and the animals were grouped in two lots: A lots, housed in farrowing crates with continuous, concrete flooring on 75% of the surface and a type of grate in the defecation area for the sows and the piglets to use (25%); B lot, housed in improved farrowing crates featuring discontinuous plastic flooring on the entire surface of the box. The skin lesions on the sow and piglets were assessed by inspection on days 7th, 15th, 24th following farrowing. The number of sows displaying skin lesions was higher in A lot (59%) compared to B lot (41%), while skin lesions in piglets was 65% for the B lot compared to 35% for A lot. The monitored indicators varied in both types of farrowing crates. Welfare of lactating sows must be assessed depending on the animals' housing system.

Wavelets for uncertainty estimates of propagating shock and detonation waves

The propagation speed of a shock or detonation wave in a shock or detonation tube is usually determined by a time-of-flight method by dividing the distance between two transducers with the propagation time of the disturbance signal. Some arbitrariness is inherent in determining the propagation time by this method. A new method based on Haar and Morlet wavelet transforms is reported. The method was applied to shock and detonation waves representing a step and a decaying spike discontinuity. The wavelet methods can be applied to the step discontinuity provided that the SNR ratio is good. The wavelet methods worked well for a decaying spike in the presence of noise.

On multiple Fourier integrals of piecewise smooth functions with discontinuities of the second kind

It is well known that the Riesz means of eigenfunction expansions of piecewise smooth functions of order s > ( n − 3 ) / 2 converge uniformly on compacts where these functions are smooth. In 2000 L. Brandolini and L. Colzani considered eigenfunction expansions of piecewise smooth functions with discontinuities of the second kind across smooth surfaces. They showed that the Riesz means of these functions of order s > ( n − 3 ) / 2 may diverge even at certain points where these functions are smooth. Here it is argued that this effect depends on the measure of the singularity area, i.e. we consider functions with singularities across more limited areas and prove that the Riesz means of their eigenfunction expansions of order s > ( n − 3 ) / 2 converge uniformly on compacts where these functions are continuous.

Controlled observation of ieflunomide and cyclophosphamide on lupus nephritis

Objective To compare the therapeutic effect, adverse effects and safety of leflunomide (LEF)and cyclophosphamide(CTX) on lupus nephritis(LN). Methods 43 patients with reactive LN were randomly divided into two groups. Based on hormone application,22 cases in LEF group were given LEF orally and 21 cases in CTX group were given CTX intravenous drip discontinuously. They were followed up for six months. The related indexes and possible concomitant adverse effects were detected. Results The total effective rate in LEF group was 81.8％ and that in CTX group was 85.7％. The tolerance in LEF group was better and 3 cases had adverse effects. 13 cases in CTX group had adverse effects. Conclusion LEF had the same efficacy as CTX in the LN therapy, but the tolerance is better and the side effects are minor than CTX. Key words: Leflunomide; Cyclophosphamide ; Lupus nephritis

Le transport ferroviaire régional de voyageurs : un processus collectif d’apprentissage

Le transport ferroviaire regional de voyageurs se presente depuis la fin des annees 1990 comme une sorte d’exception francaise. C’est en effet un secteur ou une reforme a ete conduite sereinement et a connu un reel succes, sans doute car elle a ete progressive et a pris le temps de l’experimentation. Ainsi, apres les six, puis sept regions experimentatrices, qui se sont lancees en 1997 dans ce qui est encore un processus collectif d’apprentissage, ce sont l’ensemble des regions metropolitaines (Corse et Ilede-France exceptees) qui sont entrees en janvier 2002 dans l’ere de la gestion decentralisee du transport regional de voyageurs. Aujourd’hui, nous avons le recul necessaire pour evaluer ce processus d’apprentissage, son cheminement, ses resultats et ses perspectives. Une evaluation qui est, dans un premier temps, retrospective, pour eclairer le jeu des acteurs et la nouvelle dynamique qui en a decoule, tant pour l’offre que pour la demande. Nous proposons ensuite une evaluation prospective, car le succes meme de la regionalisation invite a poursuivre le processus d’apprentissage, fut-ce en s’approchant de transformations qui relevent sans doute plus de la discontinuite que de la continuite.

Stepped discontinuity in a quantum well as a spin flipper

AbstractElectron reflection off and transmission through a stepped discontinuity in quantum well (QW), for example, due difference in spin–orbit (SO) interaction constants, effective masses, or potential step, is analyzed in a general case. Correct boundary conditions at the discontinuity are taken into account. It was found that spin flipping of the transmitted beam can be as high as 100%. A simple formula that relates the transmitted spin polarization and SO interaction constants on both sides of the discontinuity is presented and a relevant experimental set‐up is proposed to measure SO interaction constants using a homobarrier in the QW.

Band offsets, wells, and barriers at nanoscale semiconductor heterojunctions

Epitaxially-grown semiconductor heterostructures give the possibility to tailor the potential landscape for the carriers in a very controlled way. In planar lattice-matched heterostructures, the potential has indeed a very simple and easily predictable behavior: it is constant everywhere except at the interfaces where there is a step (discontinuity) which only depends on the composition of the semiconductors in contact. In this paper, we show that this universally accepted picture can be invalid in nanoscale heterostructures (e.g., quantum dots, rods, nanowires) which can be presently fabricated in a large variety of forms. Self-consistent tight-binding calculations applied to systems containing up to 75 000 atoms indeed demonstrate that the potential may have a more complex behavior in axial hetero-nanostructures: The band edges can show significant variations far from the interfaces if the nanostructures are not capped with a homogeneous shell. These results suggest new strategies to engineer the electronic properties of nanoscale objects, e.g. for sensors and photovoltaics.

The psycho-discursive origins of moral panics: Attempting a new theoretical synthesis

This paper attempts a new theoretical synthesis for studying ‘moral panics’. Its proposed model ties together Bion's psychoanalytic theory of the development of collective emotions with Foucault's discourse theory, particularly his account of the role of the moral code in the cultivation of subjectivity. This psycho-discursive model posits that moral panics are a collective emotional reaction to subjectively strenuous moral requirements and expectations produced by a particular type of discursive strain or discontinuity. Its central premise is that the Kleinian object relations that Bion saw as central to understanding collective emotions develop in relation to Foucault's notion of a socially sanctioned “moral self” – to “self” as an object of moral knowledge.

Differentiating the discontinuous

Differentiating the discontinuous

Bending moments in D-regions of reinforced concrete beams

This paper presents a study of the behaviour of D-regions in reinforced concrete frames. Within the study, 12 two-span beams were tested to failure. The type of discontinuity imposed on the test beams reflects some common layouts that take place in nodes of actual reinforced concrete frames. The beams, 6 m long, were divided into two series (a first set had six beams with no crossing column and a second set had six beams with a crossing column at the inner support). The strength and the deformation capacity in beams with geometric discontinuities were studied as well as the influence of the column presence in the development of the plastic hinges. The main results are presented and discussed: evolution of the bending moment diagrams, moment–curvature relationships, plastic rotation behaviour, stiffness of the connection between the two spans and moment redistribution. As explained in the paper, the presence of a geometric discontinuity at the inner support region leads to a sharp decreasing of the ultimate moment at this region and consequently to a great decreasing of the ultimate load of the beam. Other consequences of having discontinuity in beams are explained. A strut-and-tie model was developed and presented. This model could be useful for the design D-regions.

Indoor soccer-related eye injuries: should eye protection be mandatory?

Our objectives were to present the spectrum of eye injuries caused by indoor soccer, as seen at our institution, and to initiate discussion as to whether eye protection should become mandatory for this indoor sport. Chart review of patients presenting to our institution with eye injuries from indoor soccer. Five cases were identified from 2001-2005, all occurring during the winter or late fall. Each injury was due to contact with the soccer ball itself. Initially, all 5 patients presented with commotio retinae (1 with a prominent retinal and vitreous hemorrhage and 2 with smaller retinal hemorrhages), 2 with hyphema and traumatic mydriasis, 1 with subconjunctival hemorrhage, and 1 with upper lid edema and ecchymosis. Three resolved uneventfully with 20/20 or better vision; however, in 2 there were findings of choroidal rupture with chorioretinal scarring. One of these had 20/20 vision and a discontinuous choroidal rupture peripherally, and the other had 20/40 vision and extensive chorioretinal scarring. One patient also showed a peculiar persistent iris scar. Soccer-related eye injuries have been recognized as an important ophthalmologic problem in Europe and now increasingly so in North America. With the increasing popularity of indoor soccer in Canada, serious eye injuries have become more prevalent. On the basis of the prevalence and the nature and mechanism of the ocular trauma, we believe there may be a need to make eye protection mandatory for all forms of soccer.