Superlocal chemical reaction equilibrium in low temperature plasma

Low temperature plasmas (LTP) are a unique class of open-driven systems in which chemical reactions are unpredictable using established concepts. The terminal state of chemical reactions in LTP, termed the superlocal equilibrium state, is hypothesized to be defined by a proposed set of state variables. Using a LTP reactor wherein the state variables have been measured, it is shown that CO₂ spontaneously splits and the effluent speciation is independent of the influent speciation if the state variables are held constant and the residence time is long. CO₂ conversion at long residence times, which is expected to be nominally zero from equilibrium thermodynamics, can be as high as 70% in the LTP. The employed low pressure plasma reactor (P = 10 mbar) had a similar volume, productivity, and energy efficiency compared to an atmospheric pressure dielectric barrier discharge reactor, thanks to reaction rates that were three orders of magnitude faster.     

Windows 7为测试测量带来了什么

相对于在Windows中单纯地添加全新特性与功能,微软最新推出的Windows7系统则改进了之前Windows Vista系统中的众多特性：例如优化了系统安全性、大幅提升系统的响应与运行性能等,并且借助对软硬件兼容性的进一步改进,从而使它成为工程师实现测试测量应用的强大工具。     

Influence of polyethyleneimine graftings of multi-walled carbon nanotubes on their accumulation and elimination by and toxicity to Daphnia magna

Modifications of carbon nanotubes (CNTs) for different applications may change their physicochemical properties such as surface charge. Assessments of the extent to which such modifications influence CNT ecotoxicity, accumulation, and elimination behaviors are needed to understand potential environmental risks these variously modified nanoparticles may pose. We have modified carbon-14 labeled multi-walled carbon nanotubes (MWNTs) with polyethyleneimine (PEI) surface coatings to increase their aqueous stability and to give them positive, negative, or neutral surface charges. Uptake and elimination behaviors of Daphnia magna exposed to PEI-coated and acid-modified MWNTs at concentrations of approximately 25 and 250 μg/L were quantified. PEI surface coatings did not appear to substantially impact nanotube accumulation or elimination rates. Although the PEI-modified nanotubes exhibited enhanced stability in aqueous solutions, they appeared to aggregate in the guts of D. magna in a manner similar to acid-treated nanotubes. The MWNTs were almost entirely eliminated by Daphnia fed algae during a 48 h elimination experiment, whereas elimination without feeding was typically minimal. Finally, PEI coatings increased MWNT toxicities, though this trend corresponded to the size of the PEI coatings, not their surface charges.     

A recyclable supramolecular membrane for size-selective separation of nanoparticles

Most practical materials are held together by covalent bonds, which are irreversible. Materials based on noncovalent interactions can undergo reversible self-assembly, which offers advantages in terms of fabrication, processing and recyclability, but the majority of noncovalent systems are too fragile to be competitive with covalent materials for practical applications, despite significant attempts to develop robust noncovalent arrays. Here, we report nanostructured supramolecular membranes prepared from fibrous assemblies in water. The membranes are robust due to strong hydrophobic interactions, allowing their application in the size-selective separation of both metal and semiconductor nanoparticles. A thin (12 μm) membrane is used for filtration (～5 nm cutoff), and a thicker (45 μm) membrane allows for size-selective chromatography in the sub-5 nm domain. Unlike conventional membranes, our supramolecular membranes can be disassembled using organic solvent, cleaned, reassembled and reused multiple times.     

Toward Macroscale,Isotropic Carbons with Graphene‐Sheet‐Like Electrical and Mechanical Properties

Realization of macroscale three‐dimensional isotropic carbons that retain the exceptional electrical and mechanical properties of graphene sheets remains a challenge. Here, a method for fabricating graphene‐derived carbons (GDCs) with isotropic properties approaching those of individual graphene sheets is reported. This synthesis scheme relies on direct cross‐linking of graphene sheets via the functional groups in graphene oxide to maximize electronic transport and mechanical reinforcement between sheets and the partial restacking of the sheets to increase the material density to about 1 g cm^‐3. These GDCs exhibit properties 3–6 orders of magnitude higher than previously reported 3D graphene assemblies.     

The ACODEA framework: Developing segmentation and classification schemes for fully automatic analysis of online discussions

Research related to online discussions frequently faces the problem of analyzing huge corpora. Natural Language Processing (NLP) technologies may allow automating this analysis. However, the state-of-the-art in machine learning and text mining approaches yields models that do not transfer well between corpora related to different topics. Also, segmenting is a necessary step, but frequently, trained models are very sensitive to the particulars of the segmentation that was used when the model was trained. Therefore, in prior published research on text classification in a CSCL context, the data was segmented by hand. We discuss work towards overcoming these challenges. We present a framework for developing coding schemes optimized for automatic segmentation and context-independent coding that builds on this segmentation. The key idea is to extract the semantic and syntactic features of each single word by using the techniques of part-of-speech tagging and named-entity recognition before the raw data can be segmented and classified. Our results show that the coding on the micro-argumentation dimension can be fully automated. Finally, we discuss how fully automated analysis can enable context-sensitive support for collaborative learning.     

Investigation of mixing mechanisms and energy balance in reactive extrusion using three-dimensional numerical simulation method

The polymerization of ε-caprolactone in fully-filled conveying elements of co-rotating twin-screw extruders was analyzed with three-dimensional numerical simulation method. The effects of screw rotational speed, geometry of screw element, and initial conversion at the channel inlet on polymerization progression were studied. The simulation results show that polymerization is accelerated with increasing screw pitch, due to the increase in mixing intensity. With increasing screw rotational speed, the reaction could either slow down or speed up, depending on the viscosity of the reaction system. It is found that the advancement of polymerization depends on the competition among heat from reaction, viscous dissipation and heat loss through the wall surfaces.     

Screening Level Risk Assessment of Heavy Metal Contamination in Cleveland Area Commons

Commons are public lands that are often used for recreational activities and are generally assumed to be free of soil contamination. However, in old industrial cities, urban commons may have accumulated heavy metal burdens from airborne contamination. This paper examines the heavy metal burdens and risk analysis results for 50 commons in the greater Cleveland, Ohio area. The U.S. Environmental Protection Agency Method 3050B and 1N HCl soil extraction results are presented for Cd, Cr, Cu, Ni, Pb, and Zn mass burdens, and are interpreted relative to Ohio residential soil guidance and “typical” values from the remediation guidance of 30 states. Results demonstrate that most of these soils have heavy metal burdens that are well above naturally occurring levels, and several (at least 8 of the 50 sites tested) have heavy metal burdens that exceed Ohio’s residential soil contamination guidance. Lead and cadmium were found to be the most significant contributors to site hazard index values.