Polylactic Acid Technology Drumright, R. E.; Gruber, P. R.; Henton, D. E.
Advanced materials (Weinheim),
December, 2000, Letnik:
12, Številka:
23
Journal Article
Recenzirano
Polylactic acid is proving to be a viable alternative to petrochemical‐based plastics for many applications. It is produced from renewable resources and is biodegradable, decomposing to give H2O, ...CO2, and humus, the black material in soil. In addition, it has unique physical properties that make it useful in diverse applications including paper coating, fibers, films, and packaging (see Figure).
Polylactic acid (see Figure) is proving to be a viable alternative to petrochemical‐based plastics for many applications, not only because of its biodegradability (it decomposes to give H2O, CO2, and humus, the black material in soil) and its production from renewable resources, but also because of the unique physical properties that make it useful in diverse applications, including paper coating, fibers, films, and packaging.
▶ Crystallographic orientation has no effect on the stress–strain behavior of bcc micro-and nanopillars. ▶ Size dependence of bcc pillars correlates with the material specific critical temperature. ▶ ...Dependence on critical temperature shows importance of screw dislocation mobility. ▶ Contribution of screw dislocations is verified by the loading rate dependence of the yield stress and calculated activation volumes.
The size effect in body-centered cubic metals is comprehensively investigated through micro/nano-compression tests performed on focused ion beam machined tungsten (W), molybdenum (Mo) and niobium (Nb) pillars, with single slip 235 and multiple slip 001 orientations. The results demonstrate that the stress–strain response is unaffected by the number of activated slip systems, indicating that dislocation–dislocation interaction is not a dominant mechanism for the observed diameter dependent yield strength and strain hardening. Furthermore, the limited mobility of screw dislocations, which is different for each material at ambient temperature, acts as an additional strengthening mechanism leading to a material dependent size effect. Nominal values and diameter dependence of the flow stress significantly deviate from studies on face-centered cubic metals. This is demonstrated by the correlation of size dependence with the material specific critical temperature. Activation volumes were found to decrease with decreasing pillar diameter further indicating that the influence of the screw dislocations decreases with smaller pillar diameter.
The detection of the contact area formed between a human finger and a counter surface is of great interest because it is the key parameter for various interaction parameters. Adhesional friction ...forces and the thermal contact conductance critically depend on the contact area, further influencing the tactile sensation of stickiness and warmth. The contact area is also of concern regarding safety issues. Injuries caused by objects slipping out of our hands might be prevented by optimizing the contact area and the concomitant grip through appropriate surface structures and material choice. Until now the contact area is mainly studied on smooth and transparent materials. The contact area is recorded optically and rule-based image processing methods can be used for detection. These methods might be insufficient for rough surfaces where the contact area is optically unclear due to light scattering. In this paper we demonstrate the successful analysis of such optically unclear contact area images via convolutional neural networks to identify the fingerprint ridges in contact with structured surfaces. The proposed method relies on the generation of synthetic contact images that provide the pixelwise ground truth for the efficient training of a segmentation pipeline based on convolutional neural networks.
The texture, microstructure and mechanical behavior of bulk ultrafine-grained (ufg) Zr fabricated by accumulative roll bonding (ARB) is investigated by electron backscatter diffraction, transmission ...electron microscopy and mechanical testing. A reasonably homogeneous and equiaxed ufg structure, with a large fraction of high angle boundaries (HABs, ∼70%), can be obtained in Zr after only two ARB cycles. The average grain size, counting only HABs (
θ
>
15°), is 400
nm. (Sub)grain size is equal to 320
nm. The yield stress and UTS values are nearly double those from conventionally processed Zr with only a slight loss of ductility. Optimum processing conditions include large thickness reductions per pass (
ε
∼
75%), which enhance grain refinement, and a rolling temperature (
T
∼
0.3
T
m) at which a sufficient number of slip modes are activated, with an absence of significant grain growth. Grain refinement takes place by geometrical thinning and grain subdivision by the formation of geometrically necessary boundaries. The formation of equiaxed grains by geometric dynamic recrystallization is facilitated by enhanced diffusion due to adiabatic heating.
The gloss transition defect of injection-molded surfaces should be mitigated because it creates a poor impression of product quality. Conventional approaches for the suppression of the gloss ...transition defect employ a trial-and-error approach and additional equipment. The causes of the generation of a low-gloss polymer surface and the surface change during the molding process have not been systematically analyzed. This article proposes the causes of the generation of a low-gloss polymer surface and the occurrence of gloss transition according to the molding condition. The changes in the polymer surface and gloss were analyzed using gloss and topography measurements. The shrinkage of the polymer surface generates a rough topography and low glossiness. Replication to the smooth mold surface compensates for the effect of surface shrinkage and increases the surface gloss. The surface stiffness and melt pressure influence the degree of mold surface replication. The flow front speed and mold temperature are the main factors influencing the surface gloss because they affect the development rate of the melt pressure and the recovery rate of the surface stiffness. Therefore, the mold design and process condition should be optimized to enhance the uniformity of the flow front speed and mold temperature.
Plastic deformation of micron and sub-micron scale specimens is characterized by intermittent sequences of large strain bursts (dislocation avalanches) which are separated by regions of near-elastic ...loading. In the present investigation we perform a statistical characterization of strain bursts observed in stress-controlled compressive deformation of monocrystalline molybdenum micropillars. We characterize the bursts in terms of the associated elongation increments and peak deformation rates, and demonstrate that these quantities follow power-law distributions that do not depend on specimen orientation or stress rate. We also investigate the statistics of stress increments in between the bursts, which are found to be Weibull distributed and exhibit a characteristic size effect. We discuss our findings in view of observations of deformation bursts in other materials, such as face-centred cubic and hexagonal metals.
The factor structure of autistic traits Constantino, John N.; Gruber, Christian P.; Davis, Sandra ...
Journal of child psychology and psychiatry,
20/May , Letnik:
45, Številka:
4
Journal Article
Recenzirano
Background: Although DSM‐IV requires symptoms in three criterion domains for a diagnosis of autistic disorder, the extent to which those domains are phenotypically independent is an unanswered and ...important question. The identification of ‘endophenotypes’ of the autistic syndrome may be very useful for genetic and neurobiologic studies of autism, but only if they represent truly independent sub domains of the disorder.
Methods: In this study we examined the factor structure of autistic traits using data from 226 child psychiatric patients with and without pervasive developmental disorders, employing cluster analysis of data from the Autism Diagnostic Interview‐Revised (ADI‐r) and principal components factor analysis of data from the Social Responsiveness Scale (SRS, a quantitative genetic measure of autistic traits formerly known as the Social Reciprocity Scale).
Results: The results were consistent with the existence of a singular, continuously distributed underlying factor, resulting in disparate phenotypic manifestations across the three criterion domains for autistic disorder (social deficits, language deficits, and repetitive/stereotypic behaviors).
Conclusion: The analyses generally failed to support the existence of independent sub domains of dysfunction in autism spectrum conditions. Future studies of the association between genetic/neurobiologic markers and autistic symptomatology may be enhanced by approaches which consider autistic symptoms as quantitative traits, and which are informed by ongoing research on the development and phenomenology of core deficiencies in reciprocal social behavior.
Thin diamond films deposited by chemical vapour deposition (CVD) usually feature cross-sectional gradients of microstructure, residual stress and mechanical properties, which decisively influence ...their functional properties. This work introduces a novel correlative cross-sectional nano-analytics approach, which is applied to a multi-layered CVD diamond film grown using microwave plasma-enhanced CVD and consisting of a ∼8 μm thick nanocrystalline (NCD) base and a ∼14.5 μm thick polycrystalline (PCD) top diamond sublayers. Complementary cross-sectional 30 nm beam synchrotron X-ray diffraction, depth-resolved micro-cantilever and hardness testing and electron microscopy analyses reveal correlations between microstructure, residual stress and mechanical properties. The NCD sublayer exhibits a 1.5 μm thick isotropic nucleation region with the highest stresses of ∼1.3 GPa and defect-rich nanocrystallites. With increasing sublayer thickness, a 110 fibre texture evolves gradually, accompanied by an increase in crystallite size and a decrease in stress. At the NCD/PCD sublayer interface, texture, stresses and crystallite size change abruptly and the PCD sublayer exhibits the presence of Zone T competitive grain growth microstructure. NCD and PCD sublayers differ in fracture stresses of ∼14 and ∼31 GPa, respectively, as well as in elastic moduli and hardness, which are correlated with their particular microstructures. In summary, the introduced nano-analytics approach provides complex correlations between microstructure, stresses, functional properties and deposition conditions.
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When Chen et al. (Acta Mater 87:78–85, 2015) investigated the deformation behavior of oligocrystalline gold microwires with varying diameters in both uniaxial tension and torsion, contrary size ...effects were observed for the different load cases. In accompanying microstructural studies it was found that the microwires of different thicknesses reveal distinctive differences in grain size and texture, respectively. As a consequence, a significant influence of these microstructural variations on the determined size effects was assumed. However, within the frame of their work, a direct confirmation could only be presented for the effect of the grain size. In the present work, the size-dependent mechanical response of the microwires is modeled with a gradient plasticity theory. By finite element simulations of simplified grain aggregates, the influence of the texture on the size effects is investigated under both loading conditions. It is shown that the experimentally observed contrary size effects can only be reproduced when taking into account the individual textures of the microwires of different thicknesses within the modeling.
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