Thermal and biodegradation properties of poly(lactic acid)/rice straw composites: effects of modified pulping products

Iranian Polymer Journal - In this work, rice straw (RS) as an abundant biomass was chemically thermoplasticized through alkali pulping and benzylation reactions, which destroy inter- and...     

Influence of RIE-induced damage on luminescence and electron transport properties of AlGaAs-GaAs heterostructures

Reactive ion etching induced damage was systematically studied by photoluminescence (PL), cathodoluminescence (CL) and electronic microwave absorption in GaAs/AlGaAs multiple quantum well (MQW) and two-dimensional electron gas (2DEG) heterostructures. Using QW’s of differing widths at various depths, PL and CL characterization of the individual quantum wells allowed a depth sensitive detection of RIE induced damage. Etching was done with CC1₂F₂ at constant pressure and exposure time, while the bias voltage was successively increased from 55 to 320 V. A remarkable degradation in PL-intensity was observed for the topmost 1 nm QW located 30 nm beneath the surface, even at the lowest etch bias voltage. In 2DEG heterostructure samples investigated electrically, both mobility and carrier concentration of the 2DEG were seen to be strongly reduced. After illumination however, the initial values were almost completely restored, indicating that RIE damage predominantly reduces the electron supply efficiency of the AlGaAs barrier, whereas the 2DEG channel itself is not severely degraded even at the highest etch bias voltage.     

Direct-write fabrication of functional protein matrixes using a low-cost Q-switched laser

We report the use of an inexpensive, small, and "turn-key" Q-switched 532-nm Nd:YAG laser as a source for nonlinear, direct-write protein microfabrication. In this approach, microJoule pulses (pulse widths, approximately 600 ps) are focused using high numerical aperture optics to submicrometer focal spots, creating instantaneous intensities great enough to promote multiphoton excitation of a photosensitizer and subsequent intermolecular cross-linking of protein molecules. By scanning the femtoliter focal volume through reagent solution, extended protein-based structures can be fabricated with precise, three-dimensional topographies. As with earlier studies using a femtosecond titanium:sapphire laser costing more than 100K, physically robust and chemically responsive microstructures can be fashioned rapidly with feature sizes smaller than 0.5 microm, and cross-linking can be achieved using both biologically benign sensitizers (e.g., flavins) and by using the proteins themselves to sensitize cross-linking. We demonstrate in situ fabrication to corral neurite outgrowth and show the ability to functionalize avidin structures with biotinylated reagents, an approach that enables chemical sensing to be performed in specified microenvironments. Characterization of this inexpensive, low-power source will greatly broaden access to direct-write protein microfabrication.     

Electrophoretic deposition of colloidal crystals assisted by hydrodynamic flows

Latex-based colloidal crystals have been grown by electrophoretic deposition. The deposition has been assisted by hydrodynamic von Kármán-like flows, which lead to quantitative improvements. It has been studied the influence of applied voltage, deposition time and flow rate on the number of deposited layers and on the mean domain size. The samples were studied with microscopy and precision weight measurement. It has been found that there is a critical time after which the deposition mechanism changes, and the behavior of the system before and after this critical time is considered. The mean domain size and the deposition time were reduced to non-dimensional forms which show the collapse of the data for different applied voltages and flow rates into one curve.     

Improving the dyeability of poly (lactic acid) fiber using octa (aminophenyl) POSS nanoparticle during melt spinning

Disperse dye structure affects the dyeability of poly (lactic acid) (PLA) fiber due to the low dyeing temperature and the short dyeing time. Thus, the dye uptake value of PLA fiber is low for some disperse dyes and needs to be improved. In this study, the dyeability of PLA fiber is improved with the addition of synthesized octa (aminophenyl) polyhedral oligomeric silsesquioxane (OAP-POSS) nanoparticle during the melt spinning process. The effects of dyeing conditions including dyeing temperature and time, OAP-POSS concentration, disperse dye types, and concentrations are investigated on the dyeability properties of PLA fiber samples. The tensile, thermal, and morphological properties of the fiber samples are also characterized by tensile testing, differential scanning calorimetry, scanning electron microscopy, and transmission electron microscopy. It is concluded that the percent crystallinity and the tensile strength of pure PLA fiber decrease as the added amount of OAP-POSS increases. According to the dyeing results, OAP-POSS, which behaves as a good sorbent for the disperse dyes used in this study, greatly improves the dyeability of PLA fiber, especially for disperse dyes with low dye uptake values.     

Engineering in the Service of Law

The professional duty of the civil engineer is not limited exclusively to the scope of project design and execution; it often embraces other very different fields of activity as well. In this article, we will tackle a very specific task of the civil engineer, which is the collaboration with the Administration of Justice by means of expert opinions or testimonies that relate to specific and specialized scientific contents and subjects of the academic and professional training of the civil engineer. In Spain, incorporating civil engineers into the field of the Administration of Justice poses some questions that need to be resolved and that range from the need to authorize a regulated process that allows for the homogeneous access of professionals to the opportunity to develop additional training programs (university based or not) that train engineers in specific subjects in this field of activity; from the review and improvement of administrative matters that currently make the tasks of the engineer expert more difficult to the definition of the minimum content that the expert study should cover. In this article, we describe current Spanish legislative regulations relevant to this particular field of activity of civil engineering, and we offer some thoughts and suggestions that we feel would help improve the quality of the studies that engineers do for the judicial bodies and, consequently, the quality of service of engineers to society.     

Numerical simulation and measurement of liquid hold-up in biporous media containing discrete stagnant zones

We have studied hydrodynamic dispersion in single-phase incompressible liquid flow through a fixed bed made of spherical, permeable (porous) particles. The observed behaviour was contrasted with the corresponding fluid dynamics in a random packing of impermeable (non-porous) spheres with an interparticle void fraction of 0.37. Experimental data were obtained in the laminar flow regime by pulsed field gradient nuclear magnetic resonance and were complemented by numerical simulations employing a hierarchical transport model with a discrete (lattice Boltzmann) interparticle flow field. Finite-size effects in the simulation associated with the spatial discretization of support particles or dimension and boundaries of the bed were minimized and the simulation results are in reasonable agreement with experiment.     

以质量为核心,全面开展教学评价工作

高校扩招之后,为了促进高校建立和完善内部自我发展、自我约束机制,不断提高人才培养质量,各高校纷纷开展教学质量评价工作,此项工作的开展,在高校中产生了强烈反响,对提高教育教学质量起到了重要促进作用.教育部目前对普通高校本科教学开展了3种形式的评价工作:对本科办学历史较短、基础比较薄弱的学校进行教学合格评价;对本科办学历史较长、基础较好、水平较高的学校进行教学工作优秀评价;对介于二者之间的学校进行随机性水平评价.在评价方法上,今后还要探索吸收社会力量参与评价的新途径,继续完善教学质量的监控机制,这是政府转变观念、转变职能,进行宏观管理的重要手段.……