Clinical and Radiological Evaluation of Cage Subsidence Following Oblique Lumbar Interbody Fusion

Background Cage subsidence was previously reported as one of the most common complications following oblique lumbar interbody fusion (OLIF). We aimed to assess the impacts of CS on surgical results following OLIF, and determine its radiological characteristics and related risk factors. Methods Two hundred and forty-two patients underwent OLIF at L4-5 and with a minimum 12 months follow-up were reviewed. Patients were divided into three groups according to the extent disk height (DH) decrease during the follow-up: no CS (DH decrease ≤ 2 mm), mild CS (2mm < DH decrease ≤ 4 mm) and severe CS (DH decrease > 4mm). The clinical and radiological results were compared between groups to evaluate the radiological features, clinical effects and risk factors of CS. Results CS was identified in 79 (32.6%) patients, including 48 (19.8%) with mild CS and 31 (11.8%) with severe CS. CS mainly identified within 1 month postoperatively and did not progress after 3 months postoperatively, and more noted in the caudal endplate (44, 55.7%). In terms of clinical results, patients in the mild CS group were significantly worse than those in the no CS group, and patients in the severe CS group were significantly worse than those in the mild CS group. There was no significant difference in fusion rate between no CS (92.6%, 151/163) and mild CS (83.3%, 40/48) groups. However, significant lower fusion rate was observed in severe CS group (64.5%, 20/31) compared to no CS group. CS related risk factors included osteoporosis (OR = 5.976), DH overdistraction (OR = 1.175), flat disk space (OR = 3.309) and endplate injury (OR = 6.135). Conclusion CS following OLIF was an early postoperative complication. Higher magnitudes of CS were associated with worse clinical improvements and lower intervertebral fusion. Osteoporosis and endplate injury were significant risk factor for CS. Additionally, flat disk space and DH overdistraction were also correlated with the increased probability of CS.

Dynamic invariance in near field acoustic levitation

It is possible to levitate a mass by vibrating a flat disk located under the mass. This near-field acoustic levitation is particularly useful for eliminating friction between moving objects. This paper presents an experimental and theoretical study of the dynamic behavior of a levitating mass for different magnitudes of oscillation of the flat disk. The magnitude of the vibration of the mass appears to be independent of the amplitude of the vibration of the disk over a range of two orders of magnitude. This unusual behavior is due to the simultaneous changes of the stiffness of the air film and the natural frequency of the system as the plate vibration is changed. As the plate oscillation is reduced, the distance to resonance decreases, allowing an increase of the ratio of the output to input signals in such a way that the output remains constant. This result can be useful for improving the energy efficiency of the levitation.

INVESTIGATION OF UNDERWATER MOTION PARAMETERS FOR INERT CONICAL MODELS

This paper considers high-speed underwater motion of an axisymmetric inert conical model in a supercavitation flow regime. Experimental data on the model velocity variation with distance in water are obtained. Based on these data, a computational method, which is developed to determine the model velocity, is validated. A comparison of the calculated and experimental results obtained in a hydroballistic track shows that, in the first approximation, the motion of the model in a supercavitating flow regime can be considered as the motion of a flat disk having a mass and being streamed around at the developed cavitation directed normally to the surface. Experimental contours of supercaverns are compared with those calculated using the known computational methodology. The conditions ensuring supercavitation motion of the inert conical models in water are determined. As a result, the extended range of the horizontal motion is calculated for the inert conical models moving in a supercavitation regime under water at a depth up to 200 m at given initial velocity, depth of the trajectory location, and model parameters. It is found that reducing of a cavitator radius does not always have a positive effect on the range of the inert model motion.

Ginzberg-Landau-Wilson theory for flat band, Fermi-arc and surface states of strongly correlated systems

We show that we can realize the surface state together with the bulk state of various types of topological matters in holographic context, by considering various types of Lorentz symmetry breaking. The fermion spectral functions in the presence of order show features like the gap, pseudo-gap, flat disk bands and the Fermi-arc connecting the two Dirac cones, which are familiar in Weyl and Dirac materials or Kondo lattice. Many of above features are associated with the zero modes whose presence is tied with a discrete symmetry of the interaction and these zero modes are associated with the surface states. Some of the order parameters in the bulk theory do not have an interpretation of symmetry breaking in terms of the boundary space, which opens the possibility of ‘an order without symmetry breaking’. We also pointed out that the spectrum of the symmetry broken phase mimics that of weakly interacting theory, although their critical version describe the strongly interacting system.

Determination of the stress state of a hardening disk under the influence of temperature

Как известно при нагревании твердые тела, в частности металлы, испытывают температурные деформации, связанные с эффектом линейного расширения. При этом, несмотря на то, что эти деформации малы, соответствующие им напряжения могут оказаться достаточно большими, зачастую превосходящими предел текучести материала. В связи с этим для описания напряженно-деформированных состояний тел, находящихся под действием высоких температур, необходимо учитывать неупругое поведение материалов. Определению напряжений и деформаций в упругопластических задачах посвящено множество работ, в том числе исследования [1-10]. В некоторых из них [1], [5-10] рассматривается температурное воздействие на тела различной конфигурации. В настоящей работе решается задача об определении осесимметричного поля напряжений в плоском диске при воздействии на него точечного источника тепла (например, точечная сварка). Материал диска моделируется упрочняющейся упругопластической средой. Задача решалась в рамках плоско-напряженного состояния методом малых возмущений. В аналитическом виде получены соотношения, описывающие распределение полей напряжений в упругой и пластической областях деформирования. В качестве условий сопряжения решений на упругопластической границе использовались условия неразрывности радиальной и окружной компонент тензора напряжений и радиальной компоненты вектора перемещений. As you know, when heated, solids, in particular metals, experience thermal deformations associated with the effect of linear expansion. Moreover, in spite of the fact that these strains are small, the corresponding stresses can be quite large, often exceeding the yield stress of the material. In this regard, to describe the stress-strain states of bodies exposed to high temperatures, it is necessary to take into account the inelastic behavior of materials. Determination of stresses and strains in elastoplastic problems has been the subject of many works, including studies [1-10]. Some of them [1], [5-10] consider the temperature effect on bodies of various configurations. In this work, we solve the problem of determining the axisymmetric stress field in a flat disk when exposed to a point heat source (for example, spot welding). The disc material is modeled by a hardening elastoplastic medium. The problem was solved within the plane-stressed state by the method of small perturbations. In an analytical form, relations are obtained that describe the distribution of stress fields in elastic and plastic deformation regions. The conditions of continuity of the radial and circumferential components of the stress tensor and the radial component of the displacement vector were used as conditions for conjugation of solutions on the elastoplastic boundary.

Design of custom cranial prostheses combining manufacturing and drop test finite element simulations

In this work, impact puncture tests (drop tests) have been used to both tune numerical models and correlate the performance of customised titanium cranial prostheses to the manufacturing process. In fact, experimental drop tests were carried out either on flat disk-shaped samples or on prototypes of titanium cranial prostheses (Ti-Gr5 and Ti-Gr23 were used) fabricated via two innovative sheet metal forming processes (the super plastic forming (SPF) and the single point incremental forming (SPIF)). Results from drop tests on flat disk-shaped samples were used to define the material behaviour of the two investigated alloys in the finite element (FE) model, whereas drop tests on cranial prostheses for validation purposes. Two different approaches were applied and compared for the FE simulation of the drop test: (i) assuming a constant thickness (equal to the one of the undeformed blank) or (ii) importing the thickness distribution determined by the sheet forming processes. The FE model of the drop test was used to numerically evaluate the effect of the manufacturing process parameters on the impact performance of the prostheses: SPF simulations were run changing the strain rate and the tool configuration, whereas SPIF simulations were run changing the initial thickness of the sheet and the forming strategy. The comparison between numerical and experimental data revealed that the performance in terms of impact response of the prostheses strongly depends on its thickness distribution, being strain hardening phenomena absent due to the working conditions adopted for the SPF process or to the annealing treatment conducted after the SPIF process. The manufacturing parameters/routes, able to affect the thickness distribution, can be thus effectively related to the mechanical performance of the prosthesis determined through impact puncture tests.

PROCESS MODELING OF THE FIRST MECHANICAL CROP TENDING OF CULTIVATED CROP IN LABORATORY CONDITIONS

Conducted analysis of calculation methods of estimated figures of facilities for crop tending of cultivated crop according to hilled technology showed that in the theories of determination of geometrical dimensions and shapes of working parts surfaces of inter-row cultivator now some points are left, which are not solved . Besides, obtained data from studies of many scientists can be applied to new working tool with flat discs for inter-row cultivator. Consequently, additional theoretical and empirical support of optimal constructive-operating conditions of above mentioned working tools of inter-row cultivator is demanded. For mechanized crop tending of cultivated crop according to hilled technology we offered working tool of inter-row cultivator with flat disc, set for native or foreign inter- row cultivator. Offered working tool of cultivator will allow to clip off pest in seed inter rows of cultivated plants, and also dust not cut pests on the flanks of ridges and between culms of cultivated crop on upper base of soil rigs . In the article process of formation of secondary soil rigs by working tools with flat discs during modeling the first mechanized crop tending of cultivated crops in laboratory conditions is observed. Considering agrotechnical requirements and physical mechanical properties of soil, reference profile of soil rigs is accepted, forming during mechanized crop tending, which conditionally can accept as ideal, and an original optimization criterion . After practical realization of research in soil box and statistical treatment of obtained data fit equations were got, in which independent factors of process took the form of natural and coded levels. It was found out that speed change of cultivator moving within 1,2...2,4 m/s, angled к of flat disk approach angle from 5º to 20º, increases the range of soil throwing away and width of soil dust on the flanks and upper base of the first soil rigs (kсэ → max). At the angle of  attack of flat discs within 25º...30º and cultivator conveying speed from1,2 m/s to 1,6 m/s there is growth of width of dusted layers hпр, an coefficient kсэ is maximum (kсэ = 0,98 with diameter of flat discs 0,3 m).