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Polylactic acid (PLA) is a bio-based biodegradable polymer and is considered to be an environmentally friendly alternative to petroleum-based polymers for various applications. Neat PLA requires an extended period at elevated temperatures to attain its maximum crystallinity, which can be mitigated by the addition of nucleating agents. Orotic acid is a natural heterocyclic nucleating agent in PLA. The effect of orotic acid on the crystallization behavior of a commercial, high-purity PLA was studied in detail. A differential scanning calorimetry (DSC) technique was utilized for this purpose. A new protocol for the quantitative characterization of crystallization kinetics from DSC data was developed. It was found that the total crystallinity increased from 26% to 63% at 80 °C with 1% content of orotic acid. Meanwhile, the crystallization rate of PLA-OA blends increased by ~10 times as compared to neat PLA. The addition of orotic acid also reduced the incubation time by >17% under quiescent conditions. Injection molding experiments showed that highly crystallized (>50%) PLA samples could be fabricated with a 1% addition of orotic acid. The required mold temperature was reduced from the 120 °C recommended by the supplier to 80 °C. [ABSTRACT FROM AUTHOR]

Poly(glycerol-sebacate) (PGS) is a biodegradable elastomer that is of interest in biomedical applications. While a porous format is common for tissue engineering, PGS degradation has been primarily studied in its nonporous format. This work investigates porous PGS degradation at three cure temperatures, resulting in materials with different mechanical and chemical properties that further influence degradation. Specimens exhibit varied structural degradation, ranging from limited loss of structure to complete loss. The thermal behaviors and mechanical properties also change during degradation, depending upon cure temperature. These observations can inform the choice of polymer processing methods for porous PGS applications. [ABSTRACT FROM AUTHOR]

Objectives: Because gestational trophoblastic disease is rare, little evidence is available from randomized controlled trials on optimal treatment and follow-up. Treatment protocols vary within Europe, and even between different centers within countries. One of the goals of the European Organization for Treatment of Trophoblastic Diseases (EOTTD) is to harmonize treatment in Europe. To provide a basis for international standardization of definitions, treatment and follow-up protocols in gestational trophoblastic disease, we evaluated differences and similarities between protocols in EOTTD countries. Methods: Members from each EOTTD country were asked to complete an online structured questionnaire comprising multiple-choice and multiple-answer questions. The following themes were discussed: incidence of gestational trophoblastic disease and gestational trophoblastic neoplasia, definitions, guidelines, classification system, treatment, recurrence, and follow-up. Results: Forty-four respondents from 17 countries participated in this study. Guidelines were present in 80% of the countries and the FIGO (Fédération Internationale de Gynécologie et d'Obstétrique) staging and risk classification was often used to estimate risks. Agreement about when to start chemotherapy for post-molar gestational trophoblastic neoplasia was present among 66% of the respondents. Preferred first-line treatments in low- and high-risk gestational trophoblastic neoplasia were methotrexate (81%) and EMA-CO (etoposide, methotrexate, actinomycin D, cyclophosphamide, vincristine) (93%), respectively. The definition of human chorionic gonadotropin normalization after hydatidiform mole evacuation was two consecutive normal values for nine countries. The FIGO definition of post-molar gestational trophoblastic neoplasia based on human chorionic gonadotropin plateau or rise was agreed on by 69% of respondents, and only 69% and 74% defined low-risk and high-risk disease, respectively, using FIGO criteria. There were major differences in definitions of recurrence, chemotherapy resistance and follow-up protocols among countries, despite EOTTD consensus statements. Conclusions: This questionnaire provides a good overview of current clinical practices in different countries. Based on the survey results, it is clear that there are several gestationaltrophoblastic disease-related topics that need urgent attention within the EOTTD community to create more uniformity and to aid the development of uniform guidelines in Europe. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive, side-by-side analysis of chemical, thermal, mechanical, and morphological changes in four polymers used in tissue engineering: poly(glycerol-sebacate) (PGS), poly(lactic acid) (PLA)/poly(ε-caprolactone) (PCL) blend, poly(lactic- co-glycolic acid) (PLGA), and Texin 950, a segmented polyurethane resin (PUR). Polymer foams were created using a salt-leaching technique and then analyzed over a 16-week period. Biodegradation was analyzed by examining the morphology, thermal properties, molecular weight, chemical, and mechanical properties using scanning electron microscopy, differential scanning calorimetry, gel permeation chromatography, attenuated total reflectance-Fourier transform infrared spectroscopy, thermogravimetric analysis, and compression testing. PGS underwent the most rapid degradation and was hallmarked by a decrease in compressive modulus. PLA/PCL blend and PLGA both had rapid initial decreases in compressive modulus, coupled with large decreases in molecular weight. Surface cracks were observed in the PUR samples, accompanied by a slight decrease in compressive modulus. However, as expected, the molecular weight did not decrease. These results confirm that PUR does not undergo significant degradation but may not be suitable for long-term implants. The biodegradation rates of porous PGS, PLA/PCL blend, and PLGA found in this study can guide their use in tissue engineering and other biomedical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

The article presents a study involving the characterization of poly(glycerol-sebacate) (PGS) in curing temperatures and durations. PGS is used for creating man-made microenvironments for tissue engineering and therapeutic applications. Its samples are acquired through curing the pre-polymer in a vacuum oven at 20 kilopascals. The results showed that PGS is an elastomer that is fully amorphous over 35 degrees Celsius.

The article presents a study that investigates the effects of dynamic melt manipulation on the molecular orientation and tensile strength of polystyrene. The study made used of a vibration-assisted injection molding machine to assist in the specific melt manipulation process. The results revealed that the product response and its mechanical properties are observable and that specimens with an equal distribution of molecular orientation displayed higher tensile strength over the other samples. Moreover, it was found out that smaller specimens used in the test that was machined along the gage length exhibited an increase in tensile strength in the area of higher melt manipulation.

The article presents a study of the phenomena of melt manipulation during injection molding via in situ birefringence observation. The study involves the vibration-assisted injection molding in which oscillatory energy is imparted to the polymer melt by vibrating the injection screw during injection and packing stages. It is found that orientation develops during post-vibration and not during vibration as previously thought. Resulting effects on process parameters are also discussed.

With society focusing more and more on environmental issues, the recycling of materials of all types has become an important concern. As a result of previous processing and usage, the properties of recycled materials are often significantly inferior when compared to their unrecycled counterparts. Recycled polymeric materials, for example, have lowered molecular weights caused by previous thermal and/or shear histories. Thus, the scope of application for recycled materials has traditionally been very limited. With the aid of a new processing concept known as vibration-assisted injection molding (VAIM), the mechanical properties of products containing recycled polymeric materials could be dramatically improved. The current paper presents the results of an initial experimental investigation into the application of VAIM for recycled polystyrene (Recycled-PS) products. A number of recycled/new material blends were studied, and in all cases significant product mechanical property enhancements were realized through the use of VAIM. It was concluded that VAIM molded products containing as much as 50% low-grade recycled material could be made stronger than products made using traditional molding with 100% new polymer. Detailed results are presented in the paper, along with some insight into the likely fundamental mechanism underlying the utility of the VAIM technique. [ABSTRACT FROM AUTHOR]

Background: Hip length discrepancy (HLD) is common after total hip arthroplasty (THA); however, the effect of spinal fusion on perceived leg length discrepancy (LLD) symptoms after THA has not been examined. This study tested the hypothesis that LLD symptoms are increased in patients who underwent lumbar spinal fusion and THA, compared with patients with THA only.Methods: This retrospective cohort study included 67 patients who underwent lumbar spinal fusion and THA, along with 78 matched control patients who underwent THA only. Hip and spine measurements were taken on postoperative, standing anterior-posterior pelvic, lateral lumbar, and anterior-posterior lumbar spinal radiographs. Perceived LLD symptoms were assessed via telephone survey.Results: Between the spinal fusion and control groups, there was no significant difference in HLD (M = 7.10 mm, SE = 0.70 and M = 5.60 mm, SE = 0.49) (P = .403). The spinal fusion patients reported more frequently noticing a difference in the length of their legs than the control group (P = .046) and reported limping "all the time" compared with the control group (P = .001). Among all patients with an HLD ≤10 mm, those in the spinal fusion group reported limping at a higher frequency than patients in the control group (P = .008). Patients in the spinal fusion group were also more likely to report worsened back pain after THA (P = .011) than the control group.Conclusion: Frequencies of a perceived LLD, limping, and worsened back pain after THA were increased in patients with THA and a spinal fusion compared with patients who had THA only, even in a population with HLD traditionally considered to be subclinical. The results indicate that in patients with prior spinal fusion, precautions should be taken to avoid even minor LLD in the setting of THA. [ABSTRACT FROM AUTHOR]

Presents a numerical and experimental investigation of neural network-based intelligent control of molding processes. Application of intelligent manufacturing concepts to injection molding processes; Control of flow progression during injection molding processes; Performance of the control unit during actual injection molding processes.

A numerical investigation into the area of resin impregnation during the manufacturing of composite materials is undertaken using a macroscopic flow through porous media ap proach. This study is specifically directed at modeling the resin transfer molding and resin film stacking advanced composite manufacturing processes. Quasi-steady state isothermal flow is assumed and a two-dimensional Darcy Law based stream function formulation is utilized. The resultant single governing equation for each quasi-steady timestep is solved along with proper boundary conditions using the method of boundary-fitted coordinate systems encompassing numerical grid generation. The resultant code is validated by a comparison with previously published results for flow into a rectangular mold with a point source and a line sink. Streamlines, pressure distributions, velocity profiles, and temporal liquid free surface positions are then presented for the flow into a mold of general irregular geometry encasing both isotropic and anisotropic fibrous preforms. [ABSTRACT FROM PUBLISHER]

The present investigation focused on the controllability and reliability of AC and DC electrorheological (ER) materials based adaptive beams. The mechanical and rheological reliability of such adaptive structures was studied over an extended time period. Modal vibration frequencies exhibited relatively stable behavior over time, while modal loss factors were observed to vary significantly. Significant structural stiffening in response to electric field was observed with the DC ER material, while damping dominated the changes observed with the AC ER material. Oscillatory shear experiments with the two materials provided insight into the cause of the observed differences between AC and DC material based structural response. At small strains both ER materials behaved in a nonlinear viscoelastic fashion. The relative contributions of nonlinear loss and storage moduli were found to cause the observed differences in the performance of these adaptive structures. The structural time response upon the application or removal of electric field was also studied. Both AC and DC structures responded rapidly to the application of electric field. For the case of electric field removal, however, it was found that the field strength and application time. ER material type. and structural excitation amplitude all influenced response time. [ABSTRACT FROM PUBLISHER]

Modeling the dynamic behavior of the controllable structure itself is essential to the physical realization of electrorheological (ER) material based adaptive structures. Previous non-conclusive studies evaluated two well-known vibration theories, namely the Ross, Kerwin, and Ungar (RKU), and Mead and Markus models, in their relevance to ER based constrained layer structures. The present study consists of an in-depth theoretical and experimental investigation verifying the utility of these models in predicting the dynamic behavior of ER based structures. We restrict ourselves to a comparison between the structure's natural frequencies since the shear storage modulus dominates the material's rheological behavior. The material's loss modulus contribution to the structure's overall controllability is assumed to be negligible. The RKU and Mead and Markus theories adequately model the behavior of ER based adaptive beam structures. The model's accuracy depends upon uninhibited strain in the sandwiched layer, uniform thickness of the sandwich layer, and accurate determination of the material's rheological properties. [ABSTRACT FROM PUBLISHER]

The semi-active vibration control capabilities of Electrorheological (ER) material based adaptive beams were investigated in this study. The adaptive nature of such ER beams was achieved by controlling the pre-yield rheology of the ER material in response to varying applied electric field levels. The cross-sectional configuration of the beams considered was based on sandwiching the ER material between elastic face plates. A dynamic model of the beam structure based on thin plate theory was developed. The resulting dynamic model was able to predict the structural vibration characteristics of the ER adaptive beam. The information determined included natural frequencies, loss factors, and transverse vibration responses at any location on the beam surface. These vibration characteristics were determined as functions of excitation frequency and applied electric field level. Also the beam model was developed for generalized boundary conditions. The boundary conditions considered in this study were: clamped-clamped, clamped-free, clamped-simply supported and simply supported. Variations in the natural frequencies, loss factors, and transverse vibration response of the adaptive structure were analyzed for the listed boundary conditions. Additionally, effects of variations of the damping layer thickness of the adaptive beam on the structural loss factor was studied. Results were compared for the boundary conditions studied, and considerable variations in beam vibration responses were observed. As a result, the semi-active control capabilities of ER material based adaptive beams were theoretically illustrated. [ABSTRACT FROM PUBLISHER]

In this investigation a theoretical model for adaptive beam structures with various boundary conditions was developed, and its potential applicability to electrorheological (ER) material based adaptive beams was introduced. The cross-sectional configuration of the beam selected was based on sandwiching a damping material between elastic face plates. The transverse continuous vibration model developed is based on thin plate theory. In the model shear and rotary inertia effects are neglected, and it is assumed that no slipping between the elastic layers and the damping layer occurs. All layers are considered to have the same transverse displacement. The resulting analytical model is able to predict the structural vibration response at any location on the beam surface, and is applicable to generalized sets of boundary conditions. In this study, different boundary and external excitation conditions were considered. The transverse vibration response was studied for different boundary conditions. Variations in the mode shapes, natural frequencies, and loss factors, as functions of mode number and excitation frequency, were analyzed. ER material based adaptive beam semi-active vibration control capabilities were analyzed from the observed model results. [ABSTRACT FROM PUBLISHER]

The use of electrorheological (ER) materials in adaptive structures has received much attention recently. ER adaptive structures are based on controlling the pre-yield rheology of the ER material, which is achieved by applying different electrical fields to the ER material. In this study the dynamic behavior of an ER material based adaptive beam was modeled. Previous modeling efforts were extended towards a more detailed analysis of modal results. The adaptive beams focused on were composed of three layers: an ER material controllable damping layer and surrounding upper and lower elastic plates. A structural model of the assembly in a transverse continuous vibration mode subjected to simply supported boundary conditions was developed and analyzed. It was assumed that each structure was subjected to sinusoidal actuation applied at one or two locations. The model was tested under the conditions of varying forcing frequency from 0-300 Hz, and applied electrical field from 0-3.5 kV/mm. Time domain displacement response, natural frequencies, and loss factors of the structures at varying electric fields and varying damping layer thicknesses were obtained. The analytical results of the adaptive beam were compared with experimental results under the same physical conditions. Qualitative agreement between theory and experimentation resulted. In addition an effort was made to reduce the vibration of the structure by selecting the optimum electrical field which yields minimized vibration for each excitation frequency. [ABSTRACT FROM PUBLISHER]

This article provides a summary of the current state of electrorheological (ER) material applications research and development. The use of ER materials in a variety of intelligent material systems is covered. A description of basic material configurations used in controllable system components, as well as a discussion of controllable devices such as antivibration mounts, clutches, and dampers, is presented. More recent developments in the area of ER material adaptive structures are then reviewed. Concepts underlying such structures are presented, and models that have been developed to simulate the response of such structures are summarized. Throughout the ar ticle, an attempt is made to identify current and future key areas of research and development in ER material applications technology. [ABSTRACT FROM PUBLISHER]

This paper provides a summary of the current state of electrorheological (ER) material research and development. In particular, a description of the electrorheological effect, a defini tion of observed behavior, a critique of the proposed mechanisms for the ER phenomenon, correlations among the properties exhib ited by ER materials, an overview of the various test methodolo gies for characterizing ER materials, and a discussion of the re quirements imposed by specific applications is presented. Inherent throughout this paper are references to the properties exhibited by currently available, state-of-the-art ER materials. In order to facili tate the design of devices and to evaluate the effectiveness of a par ticular ER material in a specific application, it is necessary that experimental data reported for each material be consistent in terminology and test methodology. A recommendation as to the minimum amount of mechanical/electrical property information needed to adequately evaluate an ER material is provided. [ABSTRACT FROM PUBLISHER]

The article features the use of plants in elementary education. The principles that should control any handling of plants in elementary instruction may be stated as follows: there should be no organization of a science of botany, with a logical beginning and development. Such presentation of a science belongs to more advanced instruction; a wise selection from the vast amount of material is best made by the experienced teacher, but a general principle of selection should be that the material must be related to the experience of the pupils; if the plain facts of science are to be the occasion for flights of fancy, there is nothing left to enable the pupil later to distinguish between what is sane and what is wild.

• Economics is based on science of 260 years ago, after which science progressed and economics has not. • 7 questions are posed of science to help insights into economic analysis of ecosystems. • A revealing answer is proposed as to why energy from fuel is classed as negative enthalpy in chemistry. • Energy concept is confusing and can be replaced by accounting in electromagnetic force. • "Energy contained in fuel" is better understood as emf released in breaking the oxygen molecule bond. Seven questions that fall in the gap between economics and the science of physics and chemistry are posed in a search for eventual improved insight into the processes providing ecosystem services. Economics and science are like two different cultures that both began in an era of awe at Newtonian physics. Economics has continued with models based on that while science has made giant steps into new levels of discovery. The paths of scientific revolution have been bumpy and ad hoc, pragmatically resolving technical questions in ways that "work", sometimes oblivious of the need for elegance that would explain the macroscopic view of ecosystems. Economic analysis of ecosystem services needs to reverse engineer some scientific discoveries, especially the concept behind the term "energy", and rebuild in logical blocks that embrace a wider boundary with a clearer focus of workings in space and time. [ABSTRACT FROM AUTHOR]