Screw Rotations Research Articles

Clear Zone Formation around Screws in the Early Postoperative Stages after Posterior Lumbar Fusion Using the Cortical Bone Trajectory Technique.

Study DesignRetrospective study.PurposeTo evaluate the initial fixation using the cortical bone trajectory (CBT) technique for posterior lumbar fusion through assessment of the clear zones around the screws and the risk factors involved.Overview of LiteraturePostoperative radiolucent zones (clear zones) are an indicator of poor conventional pedicle screw fixation.MethodsBetween January 2013 and April 2014, 19 patients (8 men and 11 women) underwent posterior lumbar interbody fusion or posterior lumbar fusion using the CBT technique. A total of 109 screws were used for evaluation with measurement of the maximum insertional torque of last two screw rotations. Clear zone-positivity on plain radiographs was investigated 6 months after surgery. The relation between intraoperative insertional torque and clear zone-positivity was investigated by one-way analysis of variance. In addition, the correlation between clear zone-positivity and gender, age (<75 years old or >75 years old), or operative stabilization level (<2 or >3 vertebral levels) was evaluated using the chi-square test.ResultsClear zones were observed around six screws (5.50%) in five patients (26.3%). The mean insertional torque (4.00±2.09 inlbs) of clear zone-positive screws was lower than that of clear zone-negative screws (8.12±0.50 in-lbs), but the difference was not significant. There was a significant correlation between clear zone-positivity and operative level of stabilization.ConclusionsThe low incidence of clear zone-positive screws indicates good initial fixation using the CBT technique. Multilevel fusions may be risk factors for clear zone generation.

The Influence of Extrusion Conditions on Mechanical and Thermal Properties of Virgin and Recycled PP, HIPS, ABS and Their Ternary Blends

Abstract A recyclable plastics waste stream of electrical and electronic equipment has previously been found to contain acrylonitrile-butadiene-styrene copolymer (ABS, ∼40 wt%), high impact polystyrene (HIPS, ∼40 wt%), polypropylene (PP, ∼10 wt%) and a rest fraction consisting mainly of other styrene-based thermoplastics. In this work, one virgin and one recycled ternary blend consisting of these three components were melt-blended in an extruder to study the influence of processing conditions on the mechanical and thermal properties. The aim of the work has been to understand the inherent compatibility between ABS, HIPS and PP without added compatibilisers, in order to investigate the recycling potential of a real recyclable WEEE plastics fraction. Favourable processing conditions with respect to tensile properties of the virgin blend were found at intermediate screw rotations (40 to 80 min−1) and relatively low barrel temperatures (170 to 220°C), which can be understood from the low onset of thermo-oxidative degradation at 200°C. The recycled blend and recycled ABS, HIPS and PP showed higher stiffness and yield stress, but lower elongation at break than the corresponding virgin materials. The stiffness and yield stress of the blends were found mainly to follow the rule of mixtures of their components while the elongation at break exhibited adverse characteristics indicating incompatibility between ABS, HIPS and PP. The significant variations in the elongation at break of the blends appeared to be due to the ABS component. Differential scanning calorimetry showed an additional melt peak for the recycled blend compared to the virgin blend, otherwise the transitions were similar. The additional peak could be assigned to polyethylene in the PP component. The onset of the thermo-oxidative degradation was found to be at almost 190°C in the case of the recycled blend, which was high considering that it was close to that of the virgin blend and higher than expected from the rule of mixtures of the recycled components.

Key considerations for optimization of formulation and melt-extrusion process parameters for developing thermosensitive compound

The melt-extrusion process is currently applied in the pharmaceutical field in the manufacturing of a variety of dosage forms and formulations, including solid dispersions. Though this technology is considered efficient and continuous, there are potential challenges of which, additional thermal degradation of drug substance because heat stress and shear forces are of a primary concern. This paper attempts to understand the impact of thermal and/or mechanical components of the melt-extrusion process on the stability of a thermosensitive drug substance during scale-up. The overall degradation profile of the drug substance was correlated with the various physical changes made to the extruder as well as the process temperature. The results suggested that the degradation profile of a thermosensitive drug substance could be controlled by proper design of screw assemblies and by optimization of screw rotations per minute, process temperature, and feed rate during development and scale-up.

3110 階間調整機能付ダブルデッキエレベーター

We have developed a function that enables adjustment of the distance between two cars of a double-deck elevator to boost the traffic capacity by vertically connecting two cars. The development of this function has led to commercialization of a double-deck elevator that always lands accurately at platforms in a building that has different distances between floors. Two ball screws are installed on both sides of the cars. These ball screws support the upper and lower cars. By reversing the directions of the screws that support the upp* and lower cars, the upper and lower cars move in opposite directions while canceling their own weights through screw rotations. This paper reports the configuration and features of this elevator.

Implant abutment screw rotations and preloads for four different screw materials and surfaces

Statement of problem. Chronic implant screw loosening remains a problem in restorative practices. Some implant manufacturers have introduced abutment screws with treated surfaces in an effort to increase preload and reduce potential loosening. Purpose. This study evaluated the materials and surfaces of 4 commercially available abutment screws on preload generation. Material and methods. Twenty of each of the following abutment screws—Gold-Tite (Gt), TorqTite (Tt), gold alloy (Ga), and titanium alloy (Ta)—were divided into 2 groups. Measurements were recorded for each abutment screw on a mounted 3.75 × 18 mm external hex implant with a titanium abutment. Rotational angle measurements were conducted on the 4 abutment screws at 20 and 32 Ncm. Removal torque values were recorded and used to indirectly generate preload values. Random implant block specimens were sectioned and qualitatively evaluated with an SEM. Results. At 20 and 32 Ncm, the largest rotational angles were recorded for the Tt groups: 21.2 ± 3.1 degrees and 38.1 ± 8.7 degrees, respectively. The greatest preload values at 20 and 32 Ncm were calculated for the Gt groups: 596.8 ± 101.2 N and 1015.3 ± 191.2 N, respectively. SEM analysis of the 4 implant block specimens revealed mating thread contacts located in the middle portion of the superior surface of the abutment screw thread. The greatest number of mating thread contacts were seen in the Gt implant block specimen (14 of 20 possible thread contacts). Conclusion. The Gt and Tt abutment screws with enhanced surfaces that help reduce the coefficient of friction produced greater rotational angles and preload values than the conventional gold alloy and titanium alloy screws. (J Prosthet Dent 2001;86:24-32.)

Origin of Soft Spin Structure in Mn Formate Di-Urea

Proton NMR measurements at low temperature show that Mn moment direction in Mn formate di-urea easily changes by temperature as well as the replacement of hydrogen with deuterium atom in urea. The change in the moment direction is due to the competition of the magnetic anisotropy caused by the dipole interaction with the anisotropy caused by the surrounding ligand ions. The observed spin structure of four-fold screw rotations of antiferromagnetic layers is well understood by very small interlayer exchange interactions and magnetic anisotropies. The possibility is pointed out that the dipole interaction between the first nearest neighboring layers is the important origin of the transition to the three-dimensional long range order of this compound.

Screw rotations and glide mirrors: crystallography in Fourier space.

The traditional crystallographic symmetry elements of screw axes and glide planes are subdivided into those that are removable and those that are essential. A simple real-space criterion, depending only on Bravais class, determines which types can be present in any space group. This terminological refinement is useful in expressing the complementary relation between the real-space and Fourier-space formulations of crystal symmetry, particularly in the case of the two nonsymmorphic space groups that have no systematic extinctions (I212121 and I213). A simple analysis in Fourier space demonstrates the nonsymmorphicity of these two space groups, which finds its physical expression not in a characteristic absence of Bragg peaks, but in a characteristic presence of electronic level degeneracies.

Study of Fracture Mechanisms of FRPP by Acoustic Emission Technique. Effects of Screw Design and Number of Screw Rotations.

Effects of screw design and number of screw rotations on fracture mechanisms of fiber-reinforced polypropylene (FRPP) are studied by means of acoustic emission (AE) technique. The fiber length, the fiber orientation angle and the AE characteristics are explained in terms of the apparent shearing stresses on the various number of rotations for B and C screws with shallow groove and deep one. It is clear from specimen molded by a screw with shallow groove that the maximum load is high, the maximum cumulative AE event count and the maximum total AE energy are low on the smaller fiber orientation angle, but the load is low and the AE characteristics are high on the larger orientation angle. It is found from the AE frequency analysis that the fiber breakings dominate the damage modes of specimens molded by B screw, but the fiber debonding and the breaking appear on the specimens molded by C screw.

Fracture Mechanisms of FRPC by Acoustic Emission Technique. Effects of Screw Design and Numbers of Screw Rotations.

The fracture mechanisms of FRPC (fiber-reinforced polycarbonate) molded using various screw shapes and numbers of screw rotations are investigated by the acoustic emission technique. The fracture mechanisms of the molded FRPC are considered from the viewpoint of the apparent shearing stress at the metering zone of the screw. It is found that the apparent shearing stress affects the fiber length and the fiber orientation of the molded specimen, and the loads representing the change in the damage mechanisms which are determined by the AE gradient method. The AE frequency analysis also reveals what damage mode occurs easily at the apparent shearing stress zone.

Fracture Mechanisms of FRPC by Acoustic Emission Technique. Effects of Screw Design and Resin Feed Method.

The fracture mechanisms of FRPC (fiber reinforced polycarbonate) composites which are molded using various screw designs and resin feed methods with experimental values for the number of screw rotations are studied by the acoustic emission technique. The optimal screw design and resin feed method are found from the loads Pb and Pc at which changes in the fracture mechanisms are observed by the AE energy gradient method. The specimens which are molded using the screw of lower compression ratio and the direct resin feed show the highest values of loads Pb and Pc, and hence the experimental values for the number of screw rotations are important factors. It is found that the effect of these factors on the tensile strength and loads Pb and Pc can be explained by the shearing stress of melted resin at the metering zone of screw.

Injection Mold Method of FRPC and Evaluation of Its Tensile Impact Strength by Hopkinson Pressure Bar System. Effects of Screw Design and Number of Screw Rotations.

Injection Mold Method of FRPC and Evaluation of Its Tensile Impact Strength by Hopkinson Pressure Bar System. Effects of Screw Design and Number of Screw Rotations.

Planetenbewegungen des Flaggenraumes

In [8] the author gave a report on some properties of flag space motions, especially of the composition of screw motions or rotations in flag space. Planet motions more generally are motions which can be composed by two one-parameter-groups. These motions are investigated with respect to their orbits, their multiple ways of construction and the tubular surfaces they can determine. Some of them yield tubular screw surfaces, some others move every sphere the way that it again envellopes a sphere. These motions, which have no Euclidean counterpart, determine non-trivial, kinematically generated LIE-transformations in flag space.

Void content of a viscoelastic composite melt: Reduction during mixing

AbstractMica and polystyrene in four ratios were sheared for three different times, each at three speeds, and at two temperatures in the viscoelastic region, in a screw mixer. From precise density measurements on the resulting composites, void volume fractions were calculated and found to be proportional to mica concentration and independent of total screw rotations. Experimental void/mica ratios were represented by a kinetic model; they decreased from a single value common to all conditions to a steady‐state value proportional to the square root of the screw speed. Void formation and elimination occur simultaneously. The goodness of the fit to the data is insensitive to the details of the kinetic model. The characteristic rate constant depends only on temperature, increasing at the same rate as the reciprocal of the low‐frequency dynamic viscosity. Cavitation in regions of diverging flow of the mixer may inhibit void elimination.

ON FLOW CHARACTERISTICS OF DENSE SOLUTION IN SCREW EXTRUDERS

The authors have shown the possibility to introduce the Newtonian theory to the polymer flow in extruder.In this paper the behaviour of polymer in extruders was observed and dealt with some theoretical methods. The tranceparent acrylic barrel was deviced to observe the behaviour in extruder, (shown in Fig.1, Fig.2 in the previous report (1)). With the aim of observation of behaviour of polymer flow, small glass balls (diameter about 0.8mm) were suspended as a fluid element, and the behaviour of the polymer was observed in the case of flat screw and the open out-let as shown in Fig.3.Fig.3 shows the feature of the moving of the element in extruder, and Fig.3′ shows the relative position of the ball in screw channel, (here after the non-dashed number of figure shows the fluid element movement in extruder and dashed number of figure shows the relative position of it in screw chnnel).The number in glass ball shows the position of the observed ball in time.Then the behaviuor of a element in the cass of closing the out-let of the flat screw was observed under the conditions of screw rotations 10r.p.m. 25r.p.m. 40r.p.m. (the interval of observation is 1/2 sec in 10r.p.m. 1/3 sec in 25r.p.m. 40r.p.m.).In case of closed out-let of screw, no substantial flow causes in the channel, but the intense transeverse flow is observed (see Fig.5, 5′, Fig.6, 6′, Fig.7, 7′).In order to discuss this flow pattern by the method of velocity vector, the authors introduce the non-dimensional number, a (in z axis), c (in x axis), defined by the viscosity and pressure gradient.At first in the extreme case of closed out-let and opened out-let by using the flat screw, the velocity vector is shown in Fig.2 (a) and Fig.4 (a).Then the authors applyed this consideration to the general metering screw having three sections, that is; feed section (flat part), compressing section (transilient part), and the end section. The feature of flow in those three sections are shown in Fig.9, 9′, Fig.11, 11′, Fig.13, 13′.The velocity vector in those three sections are shown in Fig.8, Fig.10 and Fig.12.As the results it was obtained that the transverse flow becomes more violent with the increase in back pressure gradient and in general metering screw, there is the most violent transeverse flow at the front of the comperssion part. (see Fig.15 of the preceeding report (1)).