High Screw Research Articles

Improvement of the Mechanical Properties of Thermosetting-Binding-System-Based Composites by Means of Kneading Procedure Modification and Composite Formulation

By understanding the effects of the physical properties of individual input materials (e.g., binding system) on the physical and thermal properties of a composite material, the latter can be engineered in advance according to the desired properties and application. Often, a need to replace a specific component in a composite material arises, due to various reasons such as high raw material prices, product price reduction, environmental issues, improvement of properties, and others. In this study, we focused on the substitution of a phenolic novolac resin binding system and the reduction of compounding process temperature in combination with material throughput and screw speed variation of a phenolic-novolac-resin-based composite material, manufactured by kneading process using a co-kneader single screw extruder. Modifications were carried out in the interest of reducing production process cost and positive environmental effect due to reduction of energy consumption in the compounding process. We achieved great success in improvement of mechanical properties with all four substituted phenolic molding compounds (PMCs), while the decrease in thermal stability was the lowest for PMCs prepared at higher screw speeds and material throughput. The results indicated that higher screw speeds produce the best combination of mechanical and thermal properties of PMCs.

Optimization and dynamic simulation of electric actuator transmission based on high precision ball screw

The actuator is an important component of missiles and other aircraft to maintain the flight attitude. A method to calculate the power of the electric servo motor was proposed according to the load characteristics’ of both the servo motor and actuator. An optimization method for the transmission reduction ratio was obtained by considering the load torque equation. Dynamics simulations of the actuator were conducted under a variety of conditions. The simulation results show that the clearance and the friction between the ball screw and the fork, which consist of the transmission mechanism, induce the torque fluctuations, as a source of noise in the motor load. According to the optimization design of the Electric, the Actuator prototype has passed the test, the performance meets the design requirements.

Multivariate data analysis of full-scale sludge dewatering

A multivariate data analysis (MVDA) was conducted to identify operating parameters that affect the sludge dewatering efficiency in a Canadian pulp and paper mill. The sludge is a mixture of waste activated sludge (WAS) and three different types of primary sludge. The dewatering efficiency was defined by three target parameters: the cake solids content after dewatering, the solids capture efficiency, and the costs of dewatering aids (chemicals) used per ton of dewatered sludge solids. The results show that the most influential parameters affecting the dewatering efficiency are 1) the type and amount of primary sludge added to the sludge mix, 2) the operating parameters of the dewatering equipment and 3) the sludge solids throughput. A high proportion of fiber-rich primary sludge in the sludge mix substantially enhances dewaterability. Operating the screw press at a low torque and/or at a high screw press speed lowers the dewatering performance. The pH adjustment of the sludge prior to dewatering also significantly affects dewaterability. The effectiveness of the dewatering aids decreases notably when the pH is not within the target range. Besides the processes in the dewatering plant, the activated sludge process and the associated amount and quality of the WAS also affect the dewaterability of the sludge mix. In particular, the dewatering efficiency seems to be seasonal. The higher temperature during the summer produces less WAS, and thus increasing the proportion of primary sludge in the sludge mix and improving dewaterability. Also, WAS with high microbial activity and firm flocs, as well as a low sludge volume index enhances dewaterability.

A Novel Optimization Design Method of Form Grinding Wheel for Screw Rotor

The profile accuracy of screw rotors plays a vital role in stabilizing the meshing operation between mated rotors. Such stability can minimize the vibration and noise, as well as improve the sealing performance and wear resistance. This is the main reason why form grinding is extensively applied as a finishing process to maintain high screw rotor profile accuracy. Since the installation parameters for form grinding wheels affect both the grinding wheel profile accuracy and grinding performance, it is essential to obtain reasonable installation parameters to guarantee the high precision and good grinding performance of form grinding wheels. In this paper, a novel optimization design method for form grinding wheels for screw rotors has been proposed. For the first time, the relationship between the grinding wheel installation parameters and profile accuracy is established to evaluate the grinding performance. A parameterized program has been designed based on space engagement theory. The characteristics of the contact line and profile features of form grinding wheels under different installation parameters have been investigated. Then, the proposed method was employed to select the correct range of installation parameters. To validate the proposed method, a set of experiments, including the manufacture and measurement of several screw rotors, was carried out. The results reveal that the precision of the screw profile is significantly improved compared with the empirical method, thus showing the effectiveness of the proposed method.

147. Prospective randomized controlled trial of implant density in AIS: results of the Minimize Implants Maximize Outcomes study

BACKGROUND CONTEXT The role of implant density (anchors per level fused) has not been prospectively studied for a large cohort of AIS patients. In the Minimize Implants Maximize Outcomes (MIMO) Clinical Trial of equivalence, patients with Lenke 1A curve patterns were randomized to more versus fewer screws (high or low density) to determine if there was a difference in percent coronal Cobb angle correction within a 10% margin. PURPOSE This prospective randomized cotrolled trial was designed to determine if there was a difference in curve correction between high density and low density pedicle screw placement in single right thoracic Lenke 1A curves where maximal curve correction was the desired goal. STUDY DESIGN/SETTING Fourteen sites accrued patients in the MIMO Clinical Trial (NCT01792609). Patients with Lenke 1A curves between 45-65° were randomized to a high- (>1.8 screws per level fused, HD) vs low- ( PATIENT SAMPLE Power analysis showed that 174 patients were needed to detect a difference in % correction with a 10% margin at each time point. Follow-up was performed at 3 month (189 patients), 1 year (156 patients), and 2 years (124 patients). OUTCOME MEASURES Data was centrally collected and X-ray images measured by trained reviewers. Cobb angle was the primary outcome variable. METHODS RCT. Surgeons were given assignment to high or low density for each patient. Preop 3-month, 1-year and 2-year radiographs were obtained. Demographic and process measure data were also collected. RESULTS There was no difference in age, gender, preop curve magnitude, or race between the two groups. Mean % Cobb correction at three months was 74% in HD vs 70% in LD (p=0.065, 95% CI −0.2 to 6.8%), 69% in HD vs 66% in LD at 1 year (p=0.25, 95% CI, −1.7 to 6.7%), and 67% vs 64% at 2 years (p=0.18, CI, −1.5 to 7.8%). There was no difference in operative time, blood loss, or length of stay amongst the two groups. There was no difference in pre- or postop thoracic kyphosis between the HD and LD groups. There were six reoperations in each group (p=1.0). Age was lower for patients who completed 2-year follow-up (11.6 years vs. 12.8, p CONCLUSIONS For Lenke 1A curves between 45°-65° randomized to low- vs high implant density, this prospective, randomized, controlled study showed equivalent % coronal curve correction. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

226. The high vs limited screw density group in posterior fusions for adolescent idiopathic scoliosis: use of the Spine Tango registry to supplement the evidence from randomized control trials

BACKGROUND CONTEXT Several randomized controlled trials (RCTs) have compared patient outcomes of The high screw density group(HSD) with those of limited screw density group(LSD). Because RCTs have known limitations with regard to their external validity, the comparative effectiveness of the two therapies in everyday practice remains unknown. PURPOSE This study was designed to compare patient-reported outcomes after HSD vs LSD based on data from an international spine registry. STUDY DESIGN/SETTING A retrospective analysis of registry data was performed. PATIENT SAMPLE Inclusion criteria were adolescent idiopathic scoliosis HSD or LSD, no previous surgery, and a Core Outcome Measures Index (COMI) completed at baseline and at least 3 months' follow-up. Overall, 877 patients were identified. OUTCOME MEASURES Construct characteristics and radiographic measurements were compared preoperatively and at last follow-up. Operative time and estimated costs were also evaluated. COMI score improvement were the outcome measures. METHODS Three separate analyses were performed to compare HSD and LSD surgical outcomes: (1) mimicking an RCT setting, with admission criteria typical of those in published RCTs, a 1:1 matched analysis was carried out in 797 patients; (2) an analysis was performed on 371 patients outside the classic RCT spectrum, that is, with one or more typical RCT exclusion criteria; (3) a subgroup analysis of all patients with additional follow-up longer than 2 years (n=279). RESULTS Matching resulted in 217 pairs with an average follow-up of 20 months that had no significant residual differences for any patient characteristics. Small but statistically significant differences in outcome were found in favor of HSD, which are potentially clinically relevant. Subgroup analyses of typical patients and of patients with longer-term follow-up showed no significant differences in outcome between the treatments. CONCLUSIONS The results of this observational study were in accordance with those of the published RCTs. Excellent curve correction, stability, and balance can be achieved using fewer screws than commonly used in posterior pedicle screw fusions for AIS. Operative time is reduced, and risk and cost are decreased with the use of limited screw density constructs.. Analysis of typical patients suggested that, in patients outside the spectrum of clinical trials, both surgical interventions appeared to work to a similar extent to that shown for the cohort in the matched study. Also, in the longer-term perspective, both therapies resulted in comparable benefits to the patients. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs. Several randomized controlled trials (RCTs) have compared patient outcomes of The high screw density group(HSD) with those of limited screw density group(LSD). Because RCTs have known limitations with regard to their external validity, the comparative effectiveness of the two therapies in everyday practice remains unknown. This study was designed to compare patient-reported outcomes after HSD vs LSD based on data from an international spine registry. A retrospective analysis of registry data was performed. Inclusion criteria were adolescent idiopathic scoliosis HSD or LSD, no previous surgery, and a Core Outcome Measures Index (COMI) completed at baseline and at least 3 months' follow-up. Overall, 877 patients were identified. Construct characteristics and radiographic measurements were compared preoperatively and at last follow-up. Operative time and estimated costs were also evaluated. COMI score improvement were the outcome measures. Three separate analyses were performed to compare HSD and LSD surgical outcomes: (1) mimicking an RCT setting, with admission criteria typical of those in published RCTs, a 1:1 matched analysis was carried out in 797 patients; (2) an analysis was performed on 371 patients outside the classic RCT spectrum, that is, with one or more typical RCT exclusion criteria; (3) a subgroup analysis of all patients with additional follow-up longer than 2 years (n=279). Matching resulted in 217 pairs with an average follow-up of 20 months that had no significant residual differences for any patient characteristics. Small but statistically significant differences in outcome were found in favor of HSD, which are potentially clinically relevant. Subgroup analyses of typical patients and of patients with longer-term follow-up showed no significant differences in outcome between the treatments. The results of this observational study were in accordance with those of the published RCTs. Excellent curve correction, stability, and balance can be achieved using fewer screws than commonly used in posterior pedicle screw fusions for AIS. Operative time is reduced, and risk and cost are decreased with the use of limited screw density constructs.. Analysis of typical patients suggested that, in patients outside the spectrum of clinical trials, both surgical interventions appeared to work to a similar extent to that shown for the cohort in the matched study. Also, in the longer-term perspective, both therapies resulted in comparable benefits to the patients.

Processing a Supertoughened Polylactide Ternary Blend with High Heat Deflection Temperature by Melt Blending with a High Screw Rotation Speed

A supertoughened ternary polylactide (PLA) blend with high heat deflection temperature was reported in this study. The ternary blend was composed of two major biocompatible and biodegradable polyme...

The Production Efficiency and Specific Energy Consumption During Processing of Corn Extrudates with Fresh Vegetables Addition

Abstract The aim of the work was to determine the influence of screw speed and variable amounts of fresh vegetable additives on selected aspects of extrusion-cooking of corn-vegetable blends. Corn grit as a basic component was supplemented with a fresh pulp of beetroot, carrot, leek and onion in amounts of 2.5-10% in the recipe. The extrusion-cooking was carried out using a single-screw extruder in the temperature range 120-145°C and extrudates were formed into directly expanded snacks. Two indicators were measured: the production efficiency (Q) and the specific mechanical energy (SME) consumption. As a result of the findings it was noted that the rotational speed of the extruder’s screw showed a greater impact on both production efficiency and SME as compared to the variable amounts of applied additives. A tendency to increased efficiency and specific mechanical energy consumption was observed along with the increase of screw speed during processing. The highest production efficiency was observed if fresh leek and onion were used as additives and the highest extrusion speed screw was applied. The largest specific energy consumption was noted during the extrusion-cooking of blends containing fresh carrot and onion addition at high screw speed.

Characterization of the Solid Physical State of API and Its Distribution in Pharmaceutical Hot Melt Extrudates Using Terahertz Raman Imaging.

In this study, a method employing THz Raman imaging to characterize the solid state of acetaminophen within a solid dispersion prepared by hot melt extrusion was reported. The peak at 89cm-1 originating from the crystalline lattice vibrations provides unambiguous discrimination between crystalline and amorphous N-acetyl-para-aminophenol (APAP; acetaminophen) contents in the hot melt extrusion (HME) extrudates. Extrudates from four different HME processes (two different temperatures and two levels of screw speeds) were analyzed and compared. The results show that both high process temperature and high screw speed favor the formation of amorphous APAP solid dispersions. Finally, the high spatial resolution (~ 1μm) Raman images of the extrudates prepared at 170°C and 200rpm show a near-complete amorphous APAP dispersion in an HPMC matrix, confirming an efficient HME process. The study demonstrates that THz Raman imaging is ideally suited for the identification of different solid physical states of the APIs in a polymer matrix, and provides direct visualization of their distribution in HME extrudates.

A finite element study on intra-operative corrective forces and evaluation of screw density in scoliosis surgeries

Scoliosis is an abnormal sideways curvature of the spine and rib cage, which may need surgical treatments. Most of the corrective maneuvers in scoliosis surgeries are based on surgeon's experience; hence, there is great interest of understanding how the correction ratio can be influenced by the magnitude of forces and moments. Therefore, the objective of this study was to develop and validate a detailed finite element model of the thoracolumbar which can be used to simulate the scoliosis surgeries based on patient-specific clinical images. The validated models of five patients were carefully developed, and the surgery procedures were simulated and the corrective forces were estimated using inverse finite element analysis during the surgery. Furthermore, parametric studies including the influences of the corrective force magnitude and screw density were evaluated. The results showed that the maximum estimated correction force and moment were 173 (±55.43) N and 10.67 (±2.02) N m, respectively, which were aligned with measured clinical observations. The sensitivity analysis on the magnitude of applied force to the screws showed that correction ratio was slightly increased in level 1 (i.e. FB = 1.3 × F) but decreased in level 2 (i.e. FB = 1.6 × F). In addition, the parametric study on increasing the number of pedicle screws showed that there was no significant difference between lower and higher screw density. However, the stress distribution was significantly greater using higher screw density during correction maneuvers. In conclusion, this study shows a direct relationship between the applied force/moment and screw density and the correction ratio up to a border line which should be defined accurately. This detailed computational modeling can be used in clinic in hope of achieving the optimum outcome of scoliosis surgery using individual patient-specific characterization.

Investigation of the Effect of Filler Concentration on the Flow Characteristics of Filled Polyethylene Melts

Abstract All polymeric slurries that have a high concentration of filler are shear thinning. Shear thinning is an important characteristic of polymers, filled and unfilled, because it enables an increase in the throughput, shear rate in a die or an injection molding system without having to use substantially more power to increase the flow rate. Newtonian fluid-based slurries show an increase in shear thinning as the concentration of “filler” increases above the percolation threshold. As particle maximum packing concentration is approached the slurries begin to approach a perfect pseudoplastic fluid. In some cases, the shear thinning characteristics of a filled polymer do not increase substantially as the filler loading is increased. This is a quite different response than in Newtonian fluid-based slurry. Therefore, it is important to understand the materials engineering interactions that control shear thinning so that process flow models can better predict the performance of filled polymer systems. Highly filled polymers can have processing issues, including high screw shaft torque, energy consumption, die pressure and melt temperature rise. Previous theoretical developments and experimental evaluations of highly filled polymer melts showed that the rheology can be effectively described with a percolation model. In this work, capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide fillers are reported using percolation theory concepts. The theoretical treatment of the rheology as a particulate percolating system with power-law behavior is used to analyze capillary rheometer data. The observed effects of resin molecular weight, filler type and size on rheology are described. Engineers that design and debottleneck polymer processes need to utilize the polymer viscosity at the minimum process shear rate to determine the smallest motor that will allow the process to run; in addition, the shear thinning characteristics of the polymer are used to indicate how much increased production may be possible with a given motor size. Thus, some examples of expected effects on melt processing are also presented.

Modeling of Solid Conveying Pressure Throughput Behavior of Single Screw Smooth Barrel Extruders under Consideration of Backpressure and High Screw Speeds

AbstractThe task of the solid conveying section is to collect the entering material and transfer it to the melt dominated sections. Therefore, its upstream interface is the hopper and its downstream interface is the section in which the first melting occurs. Beneath the hopper opening, the screw rotation collects and conveys the material forward. It is hereby assumed that the friction forces among the particles are higher than the transferring forces on the screw and barrel. For that reason commonly known models for describing the solid conveying in single screw extruders assume that the screw channel is always completely filled so that a plug flow occurs. At high screw speeds, however, these assumptions are no longer valid. To analyze and mathematically describe the solid conveying behavior at screw speeds up to 2000 rpm, simulations based on the Discrete Element Method have been executed in previous investigations. Based on this, a model for describing the solid conveying behavior was developed which enables a variation of general screw and hopper geometry parameters but neglects the backpressure that inhibits the solid movement. For that reason, further investigations based on the Discrete Element Method are presented in this paper, which enable a consideration of the backpressure and pressure build-up in the feeding zone. Astonishingly, at high screw speeds a low filling degree in the screw channel was observed which did not fulfill the expectations of an always fully filled channel due to a backpressure forced particle backlog. Based on the investigations, a mathematical model has been developed which now fully comprehends the effects occurring in the solid conveying section. The conducted simulations were subsequently validated by experimental investigations. Therefore, a test bench was designed which enables solid conveying analysis with adjustable backpressures. The results indicate a good agreement with the formulated model which now enables the calculation of solid conveying zones with consideration of the pressure build-up and filling degrees.

A Study of Concentrated Suspensions in Polyethylene Melts and the Impact on Viscosity and Polymer Processing Operations

AbstractFilled polymer compounds can present processing challenges, including poor dispersive mixing, high screw shaft torque and energy consumption, flow instabilities, and significant increases in melt pressures and temperatures. Previous theoretical development and experimental evaluations of polymer melts filled with particulate solids showed that the viscosity can be described with a model based on percolation theory concepts. This paper describes a batch mixer characterization method developed to measure the effects of filler concentration and operating conditions on the melt viscosity and process response. Experimental results are compared with capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide. The theoretical treatment of the viscosity as a particulate percolating system with power-law behavior was used to analyze and compare rheometer and batch mixer data. The effects of resin molecular weight, filler type and size on viscosity and melt processing were examined and there was good agreement between rheometer and mixer viscosity trends, and percolation model predictions. The laboratory experiments and model estimates provide quantitative information that can be used to develop and troubleshoot extrusion compounding, single screw extrusion and low-shear forming processes.

Implant Density at the Apex Is More Important Than Overall Implant Density for 3D Correction in Thoracic Adolescent Idiopathic Scoliosis Using Rod Derotation and En Bloc Vertebral Derotation Technique.

Biomechanical analysis of 3D correction and bone-screw forces through numerical simulations of scoliosis instrumentation with different pedicle screw patterns. To analyze the effect of different screw densities and distributions on 3D correction and bone-screw forces in adolescent idiopathic scoliosis (AIS) instrumentation. Instrumentation constructs with various numbers of pedicle screws and patterns have been proposed for thoracic AIS instrumentation. However, systematic biomechanical studies have not yet been completed on the appropriate screw patterns for optimal 3D correction. Patient-specific biomechanical models of the spine were created for 10 AIS cases (Lenke 1). For each case, surgical instrumentation patterns were computationally simulated using respectively a reference screw pattern (two screws per level fused) and six alternative screw patterns with fewer screws. Simulated surgical maneuvers and model definition were unchanged between simulations except the number and distribution of screws. 3D correction and bone-screw forces were compared. A total of 140 posterior instrumentations were computationally simulated. Mean corrections in the coronal and sagittal planes with alternative screw patterns were within 4° to the reference pattern. Increasing screw density in the apical region from one to two screws per level improved percent apical vertebral rotation (AVR) correction (r = 0.887, P < 0.05). Average bone-screw force associated with the reference screw pattern was 243N ± 54N and those with the alternative screw patterns were 11% to 48% lower. Compared with the reference maximal screw density pattern, alternative screw patterns allowed similar corrections in the coronal and sagittal planes. AVR correction was strongly correlated with screw density in the apical region; AVR correction varied significantly with screw patterns of the same overall screw density when an en bloc vertebral derotation technique was simulated. High screw density tended to overconstrain the instrumented spine and resulted in higher forces at the bone-screw interface. N/A.

The effect of extrusion reprocessing cycles on the structure and properties of nano-silica reinforced polypropylene/ethylene-propylene-rubber composites

In this study, the effect of repeated extrusion processing cycles on the structure and properties of polypropylene/ethylene-propylene-rubber/nano-silica composites was investigated. The recycling process was simulated by performing three extrusion runs, using a high shear twin screw extruder by varying the speed screw rotation (300, 800, and 1200 r/min), in order to get better understanding of the multi recycling effects. For comparative purposes, neat polypropylene/ethylene-propylene-rubber was also reprocessed under the same conditions as a reference material. From the morphological analyses performed by scanning electron microscopy, multiple extrusions were found to be not only helpful for decreasing the ethylene-propylene-rubber phase size, but also useful for ensuring a more homogenous dispersion of silica nanoparticles within the matrix. The physico-chemical properties analyses illustrate that the repeated cycles of extrusion processing provoke a decrease of the molar masses and an increase in the melt flow index. It was marked that, when going from the 1st to the 2nd extrusion cycle, and by increasing the rotation speed from 300 to 800 r/min at the same cycle, the mechanical properties were greatly enhanced. A substantial improvement of these properties was achieved after incorporating the silica nanoparticles and the maleic anhydride grafted polyethylene copolymer.

Investigation of the process of smoothing with ultrasound

We studied and simulated the ultrasonic smoothing process. We carried out the analysis of the contact interaction of a tool with a part in the process of ultrasonic smoothing with a preceding gap. The analysis provides an opportunity to calculate a change in a size of a part during the treatment depending on modes. We derived the dependences of a contact area at the ultrasonic smoothness with a preceding gap. We performed the experimental study of an influence of parameters of the process of ultrasonic smoothing on parameters of a quality of a surface layer of a part. We established that in order to ensure the required roughness and accuracy, the depth of introduction should not exceed 7 μm, especially when treated parts are made of materials with a low modulus of elasticity. We developed an installation for experiments based on the high precision automatic screw machine 16B05АF10. All additional devices and tools were attached to the tool holder of a given machine. We developed a technique to measure the time of contact between a tool and an article under ultrasonic smoothing with a preceding gap. We established that deformation of micro roughnesses occurs due to a pressure of projections of micro roughnesses to cavities since we excluded shift deformation by using a solid lubricant. The fact that there was no texture on the microsection of the treated surface, although we could observe hardening of a surface, indicates that there is no shift deformation. Based on this conclusion, it is possible to disregard a non-contact wave of deformation. We obtained analytical dependences of contact area under ultrasonic smoothness with a preceding gap on treatment parameters, namely, the treatment speed, the feed rate, the radius of an operation surface of a tool. The results of mathematical modeling and experimental data are quite close. We defined the region of optimal feed, which makes it possible to obtain surfaces with minimal roughness or microrelief.

EVALUATION OF CERVICAL ALIGNMENT AND ITS RELATIONSHIP WITH THORACIC KYPHOSIS AND SPINOPELVIC PARAMETERS AFTER SCOLIOSIS CORRECTION SURGERY

ABSTRACT Objectives: To evaluate the cervical alignment after the correction of idiopathic scoliosis using high screw density and direct vertebral derotation (DVD) and to correlate it with thoracic kyphosis, spinopelvic parameters, and quality of life. Methods: Retrospective cohort study. We assessed the medical records and radiographs of patients submitted to idiopathic scoliosis surgery using high density of pedicular screws (80%) and DVD with at least 6 months of follow-up. All the radiographic parameters were evaluated in the preoperative period and in the last postoperative visit. Results: A total of 43 patients were evaluated, of which 35 (81%) were female. The mean age was 15 years (11 to 30 years) with a mean follow-up of one year and four months. Regarding Lenke’s classification, 14 were of group 1, five of group 2, 10 of group 3, eight of group 4, four of group 5 and two of group 6. Only four patients had sagittal modifier (+) and two sagittal modifier (-).There was no significant difference between pre and postoperative thoracic kyphosis. When we evaluated the groups with +, N and - thoracic modifiers, we observed hypokyphotic and normokyphotic patients (- and N) had an increase in kyphosis, whereas hyperkyphotic patients (+)had a decrease. There was no statistical difference in relation to the radiographic parameters of the cervical spine in the pre and postoperative periods. There was a significant improvement in most of the parameters of the quality of life questionnaires, but no correlation with the cervical radiographic parameters. Conclusion: Correction of idiopathic scoliosis using a high density of pedicular screws and a direct vertebral derotation technique failed to improve thoracic kyphosis or change the cervical sagittal alignment, despite promoting a significant improvement in the parameters of quality of life questionnaires.

Influence of the extrusion parameters on the physical properties of chickpea and barley extrudates.

In this research, the effects of extrusion processing [exit-die temperature (120-150°C), moisture content (20-24% wet basis), and screw speed (260-340 rpm)] on the specific mechanical energy and physical properties (expansion ratio, bulk density, and hardness) of desi chickpea and hullless barley extrudates were estimated using response surface methodology. Exit-die temperature and feed moisture content, as well as the interaction between them were the factors that affected the product responses the most. Significant correlation was found between the hardness and bulk density (positive), hardness and expansion ratio (negative), and bulk density and expansion ratio (negative) for both chickpea and barley extrudates. Desirable characteristics (high expansion, low bulk density, and hardness) for chickpea were obtained at high exit-die temperature, relatively high moisture, and high screw speed. As for the barley extrudates, high exit-die temperature, low moisture, and moderate to high screw speed were identified as optimal.

Biomechanical analysis of pedicle screw density in spinal instrumentation for scoliosis treatment: first results.

Clinical studies reveal remarkable variation in screw patterns, or screw density in spinal instrumentation. Screw density may have a great impact on blood loss, operative time, radiation, risk of screw malposition, and cost. Thus, there is a need to understanding of the biomechanical effects of screw density so as to minimize the number of pedicle screws while ensuring safe and effective instrumentation. The objective of this study was to compare the deformity correction effects and bone-screw loadings of different pedicle screw densities in spinal instrumentation for scoliosis treatment. Spinal instrumentation simulations were performed on three scoliosis patients using 3 screw density patterns (low, preferred, and high screw density) proposed by two experienced surgeons and basic correction techniques: concave rod attachment, rod derotation, apical vertebral derotation, and convex side rod attachment. Simulation results showed that all tested screw densities generated quite similar correction, with differences between the achieved corrections all below 3°. The average bone-screw forces were 244±67N, 214±66 N, and 210±71 N, respectively for low, preferred, and high densities. It remains a complex challenge balancing the benefit of load sharing between more implants with the overconstraints and limited degrees of freedom introduced by the increased number of implants. Studies on additional screw densities and patterns proposed by more surgeons for a variety of cases, and using more diverse correction techniques are necessary to draw stronger conclusions and to recommend the optimal screw density.

Characterizing the flow of slurries using percolation theory‐based functions

All polymer slurries that have a high concentration of filler are shear thinning. A new function was found that linearly correlates the power law constant, n, to the concentration of the filler. The behavior of this function suggests that the Newtonian to power‐law behavior may be dominated by percolation processes and the area of the filler. A theory is presented that predicts the power law constant, n, as a function of filler cluster formation and the decrease of dissipation due to no velocity gradient in the clusters. This percolation based rheological analysis is then extended to polystyrene melts and highly filled polyethylene resin. Highly filled polymer compounds can present processing challenges, including high screw shaft torque, energy consumption, pressure and melt temperature. A percolation based evaluation of the effects of filler concentration on melt processing is presented using experiments with a batch mixer. It is demonstrated that measurements can be correlated to the theoretical treatment of the rheology as a particulate percolating system. The implications of the increase in viscosity with filler concentration on polymer processing are discussed from a practical engineering perspective. POLYM. ENG. SCI., 57:403–416, 2017. © 2016 Society of Plastics Engineers