Pretreatment of yellow poplar sawdust by pressure cooking in water

The pretreatment of yellow poplar wood sawdust using liquid water at temperatures above 220°C enhances enzyme hydrolysis. This paper reviews our prior research and describes the laboratory reactor system currently in use for cooking wood sawdust at temperatures ranging from 220 to 260°C. The wood sawdust at a 6–6.6% solid/liquid slurry was treated in a 2 L, 304 SS, Parr reactor with three turbine propeller agitators and a proportional integral derivative (PID) controller, which controlled temperature within ±1°C. Heat-up times to the final temperatures of 220, 240, or 260°C were achieved in 60–70 min. Hold time at the final temperature was less than 1 min. A serpentine cooling coil, through which tap water was circulated at the completion of the run, cooled the reactor’s contents within 3 min after the maximum temperature was attained. A bottoms port, as well as ports in the reactor’s head plate, facilitated sampling of the slurry and measuring the pH, which changes from an initial value of 5 before cooking to a value of approx 3 after cooking. Enzyme hydrolysis gave 80–90% conversion of cellulose in the pretreated wood to glucose. Simultaneous saccharification and fermentation of washed, pretreated lignocellulose gave an ethanol yield that was 55% of theoretical. Untreated wood sawdust gave less than 5% hydrolysis under the same conditions.     

Intramolecular [4 + 2] cycloadditions of benzynes with conjugated enynes, arenynes, and dienes

Benzynes generated by the reaction of o-(trimethylsilyl)aryl triflates with TBAT participate in intramolecular [4 + 2] cycloadditions with conjugated enynes, arenynes, and dienes to furnish highly condensed polycyclic aromatic compounds. [reaction: see text]     

Synthesis of highly substituted indolines and indoles via intramolecular [4 + 2] cycloaddition of ynamides and conjugated enynes

Ynamides react with conjugated enynes in intramolecular [4 + 2] cycloadditions to afford substituted indolines that undergo oxidation with o-chloranil to furnish the corresponding indoles. The cycloaddition substrates are easily assembled from derivatives of 3-butynylamine by Sonogashira coupling with alkenyl halides followed by copper-catalyzed N-alkynylation with acetylenic bromides. Diynamides participate as particularly reactive 2pi components in the cycloaddition, providing access to indolines with carbon substituents at the C-7 position. Enynamides serve as 4pi components in a complementary version of the cycloaddition strategy which provides access to indoles and indolines substituted with carbon substituents at C-4. These enyne cycloadditions take place upon heating the substrates at 110-210 degrees C in toluene or 2,2,2-trifluoroethanol and in some cases can be achieved at 0 degrees C to room temperature in the presence of Lewis acids such as Me2AlCl.     

Implementation of the direct SCF and RPA methods on loosely coupled networks of workstations

The use of a cluster of workstations as an alternative supercomputer resource is demonstrated using the ab initio direct SCF and RPA code DISCO. DISCO was implemented using several different mechanisms to achieve the requisite parallelization. The various parallel software mechanisms are characterized based upon several different criteria, including portability, ease of use, and relative efficiency. The application of direct SCF and RPA techniques to study the static polarizability of paranitroaniline is described. © 1993 John Wiley & Sons, Inc.     

Towards understanding the behavior of physical systems using information theory

One of the goals of complex network analysis is to identify the most influential nodes, i.e., the nodes that dictate the dynamics of other nodes. In the case of autonomous systems or transportation networks, highly connected hubs play a preeminent role in diffusing the flow of information and viruses; in contrast, in language evolution most linguistic norms come from the peripheral nodes who have only few contacts. Clearly a topological analysis of the interactions alone is not sufficient to identify the nodes that drive the state of the network. Here we show how information theory can be used to quantify how the dynamics of individual nodes propagate through a system. We interpret the state of a node as a storage of information about the state of other nodes, which is quantified in terms of Shannon information. This information is transferred through interactions and lost due to noise, and we calculate how far it can travel through a network. We apply this concept to a model of opinion formation in a complex social network to calculate the impact of each node by measuring how long its opinion is remembered by the network. Counter-intuitively we find that the dynamics of opinions are not determined by the hubs or peripheral nodes, but rather by nodes with an intermediate connectivity.     

Accelerated weathering of polyaramid and polybenzimidazole firefighter protective clothing fabrics

Exposure to simulated ultraviolet sunlight at 50 °C and 50% relative humidity caused a significant deterioration in the mechanical performance of polyaramid and polyaramid/polybenzimidazole based outer shell fabrics used in firefighter jacket and pants. After 13 days of exposure to these conditions the tear resistance and tensile strength of both fabrics decreased by more than 40%. The polybenzimidazole containing fabric was less impacted by these conditions as it maintained approximately 20% more of its mechanical properties. These conditions also significantly degraded a water repellant coating on the fabric, which is critical to the water absorption performance of the outer shell fabrics. However, these conditions had little impact on the ultraviolet light protection of the outer shell as both fabrics still blocked 94% of ultraviolet light after 13 days of exposure. Confocal microscopy showed these conditions caused significant surface decomposition of and the switch from ductile to brittle failure of the polyaramid fibers. Cleavage of the amide linkages and the formation of oxidation species (as observed by Infrared spectroscopy) suggested these conditions caused photo-oxidation of the polyaramid fibers. There was little evidence of polybenzimidazole fiber degradation.     

嵌入式多媒体系统的优化权衡

随着嵌入式多媒体应用的不断发展,系统控制和信号处理之间的交互性不断增强。最新的嵌入式多媒体处理器已能够同时处理MCU和DSP的任务,从而将那些熟悉用MCU方式进行应用开发的C程序员带入了一个新的领域。其中对代码和数据流的智能管理会显著提高系统的性能。然而,对多媒体处理     

低功耗嵌入式实现的方方面面

在嵌入式应用中,影响功耗指标的因素很多.在进行具体设计预算时,了解这些因素将有助于设计出理想的低功耗系统.本文将考虑影响功耗的不同方面,同时,这些知识对于某个特定项目的处理器选择也有帮助.     

Prompt gamma-ray activation analysis for certification of sulfur in fuel oil SRMs

A combination of cold neutron prompt gamma-ray activation analysis (CNPGAA) and thermal neutron (TN) PGAA was used to determine sulfur in fuel oils to develop a method to provide values for certification. CNPGAA was used to measure S/H mass ratios, and TNPGAA to measure hydrogen mass fractions. Measurements were combined to determine sulfur mass fractions (with expanded uncertainties) of 2.159 ± 0.072 % for SRM 1622e, 0.7066 ± 0.0120 % for SRM 1619b, and 0.1266 ± 0.0030 % for SRM 1617b, in agreement with certified values. The results validate the method as suitable for certification of sulfur at mass fractions ≥0.1 %.

     

Certification of total arsenic in blood and urine standard reference materials by radiochemical neutron activation analysis and inductively coupled plasma-mass spectrometry

Radiochemical neutron activation analysis (RNAA) was used to measure arsenic at four levels in standard reference material (SRM) 955c Toxic Elements in Caprine Blood and at two levels in SRM 2668 Toxic Elements in Frozen Human Urine for the purpose of providing mass concentration values for certification. Samples were freeze-dried prior to analysis followed by neutron irradiation for 3 h at a fluence rate of 1 × 10¹⁴ cm^?2 s^?1. After sample dissolution in perchloric and nitric acids, arsenic was separated from the matrix either by retention on hydrated manganese dioxide (urine) or by extraction into zinc diethyldithiocarbamate in chloroform (blood). ⁷⁶As was quantified by gamma-ray spectroscopy. Differences in chemical yield and counting geometry between samples and standards were monitored by measuring the count rate of a ⁷⁷As tracer added before sample dissolution. RNAA results were combined with inductively coupled plasma-mass spectrometry values from National Institute of Standards and Technology and collaborating laboratories to provide certified values of 10.81 ± 0.54 and 213.1 ± 0.73 μg/L for SRM 2668 Levels I and II, and certified values of 21.66 ± 0.73, 52.7 ± 1.1, and 78.8 ± 4.9 μg/L for SRM 955c Levels II–IV, respectively. Because of discrepancies between values obtained by different methods for SRM 955c Level I, an information value of <5 μg/L was assigned for this material.