Synergistic pseudo-hydroxide extraction: synergism and anion selectivity in sodium extraction using a crown ether and a series of weak lipophilic acids

The nature of the weak lipophilic acid used in synergistic combination with a model crown ether cation host was shown to have a strong effect on the strength and selectivity of sodium hydroxide separation from alkaline aqueous salt solutions. Sodium ion-pair extraction employing only cis-syn-cis-dicyclohexano-18-crown-6 (1) in nitrobenzene (NB) was correlated with the standard Gibbs energy (deltaG(p)o) of anion partitioning into NB and was notably weak and nonselective for the hydroxide ion, in accord with Hofmeister bias. The Hofmeister order can be selectively overcome for NaOH by utilization of acid-base chemistry coupled with complexation of sodium ion in the NB phase. Upon addition of a lipophilic organic acid into the solution of 1 in NB, sodium extraction was selectively enhanced due to the initiation of an exchange reaction between the aqueous sodium ion and the ionizable proton of the organic acid. A series of weak lipophilic hydroxy acids (HA) including fluorinated alcohols and phenols was tested. The resulting synergistic pseudo-hydroxide extraction correlates with the pKa of the employed HA; the most acidic cation exchangers provide the greatest synergism. The synergistic factor obtained using a fluorinated benzyl alcohol 7 was as high as 256. Ion-pair extraction of neutral sodium salts was not changed or only mildly enhanced by addition of HA into the NB solution of 1. This enhancement was explained by hydrogen bonding of HA with the anion as related to the hardness of the anion and the acidity of HA. In comparison with the synergism observed for NaOH, this enhancement was weak and unable to overcome the Hofmeister effect. Examination of extraction selectivity revealed that the combination of 1 and 7 preferentially extracted NaOH over all other sodium salts, including the normally preferred nitrate and perchlorate salts. Quantitative recovery of NaOH from the NB phase was demonstrated via hydrolysis of the organic acid upon a single contact of the loaded solvent with water.     

Design criteria and optical characteristics of one-dimensional photonic crystals based on periodically grooved silicon

Photonic bandgap (PBG) regions have been calculated for periodically grooved Si structures, acting as a one-dimensional photonic crystal. The wavelength range of the PBG as a function of the ratio (DSi/A) is presented, where DSi is the width of the Si walls and A is the grooved silicon lattice constant. The influence of the parameter DSi, the refractive index of the space between the Si walls and the number of structure periods, m, on the forming of PBG regions is discussed. A good correlation between the calculated and the experimentally observed PBG regions is obtained.     

Acute public health consequences associated with hazardous substances released during transit, 1993-2000

Massive quantities of hazardous substances are transported each day throughout the United States. While most arrive safely at their destination, uncontrolled releases of substances in transit do occur and have the potential of causing acute public health consequences for those individuals at or near the release. Data from 16 state health departments participating in the Agency for Toxic Substances and Disease Registry's (ATSDR) Hazardous Substances Emergency Events Surveillance (HSEES) system were analyzed to determine the public health consequences that occurred from actual releases in transit. Of the 9392 transportation events analyzed, 9.1% resulted in 2008 victims, including 115 deaths. The population groups injured most often were employees and the general public. The most common injury sustained was respiratory irritation. Evacuations were ordered in 5.5% of events effecting at least 63,686 people. Human error and equipment failure were the most common factors leading to events. These findings underscore the importance of job safety training, community planning, and effective emergency response to prevent adverse public health consequences from occurring or lessen their effect on the public.     

A 3-GHz 70-mb SRAM in 65-nm CMOS technology with integrated column-based dynamic power supply

Column-based dynamic power supply has been integrated into a high-frequency 70-Mb SRAM design that is fabricated on a high-performance 65-nm CMOS technology. The fully synchronized design achieves a 3-GHz operating frequency at 1.1-V power supply. The power supply at SRAM cell array is dynamically switched between two different voltage levels during READ and WRITE operations. Silicon measurement has proven this method to be effective in achieving both good cell READ and WRITE margins, while lowering the overall SRAM leakage power consumption.     

The effects of pick density on order picking areas with narrow aisles

The cost and service performance of an order fulfillment center are determined partly by how workers are organized into an order picking system. One common approach is batch picking, in which workers circumnavigate a picking area with other workers, gathering items on a pick list. In some systems with high space utilization, narrow aisles prohibit workers from passing one another when in the same aisle, and this leads to congestion. We build analytical and simulation models of these systems to investigate their behavior under different levels of activity. Among other things, our results suggest that when the system is busier and pick density is high (that is, when workers stop often to make picks) congestion is less of a problem and workers are more productive.     

Response of seasonal vegetation development to climatic variations in eastern central Asia

Meteorological records show that central Asia has experienced one of the strongest warming signals in the world over the last 30 years. The objective of this study was to examine the seasonal vegetation response to the recent climatic variation on the Mongolian steppes, the third largest grassland in the world. The onset date of green-up for central Asia was estimated using time-series analysis of advanced very high resolution radiometer (AVHRR) normalized difference vegetation index (NDVI) biweekly composite data collected between January 1982 and December 1991. Monthly precipitation and mean temperature data (1982-1990) were acquired from 19 meteorological stations throughout the grasslands of the eastern Mongolian steppes in China. Our results showed that while the taiga forest north of the Mongolian steppes (>50°N) experienced an earlier onset of green-up during the study period, a later onset was observed at the eastern and northern edges of the Gobi Desert (40°N-50°N). Responses of different vegetation types to climatic variability appeared to vary with vegetation characteristics and spring soil moisture availability of specific sites. Plant stress caused by drought was the most significant contributor to later vegetation green-up as observed from satellite imagery over the desert steppe. Areas with greater seasonal soil moisture greened up earlier in the growing season. Our results suggested that water budget limitations determine the pattern of vegetation responses to atmospheric warming.     

Collaborative jamming and collaborative defense in cognitive radio networks

In cognitive radio networks, cognitive nodes operate on a common pool of spectrum where they opportunistically access and use parts of the spectrum not being used by others. Though cooperation among nodes is desirable for efficient network operations and performance, there might be some malicious nodes whose objective could be to hinder communications and disrupt network operations. The absence of a central authority or any policy enforcement mechanism makes these kinds of open-access network more vulnerable and susceptible to attacks.In this paper, we analyze a common form of denial-of-service attack, i.e., collaborative jamming. We consider a network in which a group of jammers tries to jam the channels being used by legitimate users who in turn try to evade the jammed channels. First, we compute the distribution of the jamming signal that a node experiences by considering a random deployment of jammers. Then, we propose different jamming and defending schemes that are employed by the jammers and legitimate users, respectively. In particular, we model and analyze the channel availability when the legitimate users randomly choose available channels and the jammers jam different channels randomly. We propose a multi-tier proxy-based cooperative defense strategy to exploit the temporal and spatial diversity for the legitimate secondary users in an infrastructure-based centralized cognitive radio network. Illustrative results on spectrum availability rates show how to improve resiliency in cognitive radio networks in the presence of jammers.     

Efficiently Testing Sparse <Emphasis Type="Italic">GF</Emphasis>(2) Polynomials

We give the first algorithm that is both query-efficient and time-efficient for testing whether an unknown function f:{0,1} ⁿ →{−1,1} is an s-sparse GF(2) polynomial versus ε-far from every such polynomial. Our algorithm makes poly(s,1/ε) black-box queries to f and runs in time n⋅poly(s,1/ε). The only previous algorithm for this testing problem (Diakonikolas et al. in Proceedings of the 48th Annual Symposium on Foundations of Computer Science, FOCS, pp. 549–558, 2007) used poly(s,1/ε) queries, but had running time exponential in s and super-polynomial in 1/ε.     

Marking student programs using graph similarity

We present a novel approach to the automated marking of student programming assignments. Our technique quantifies the structural similarity between unmarked student submissions and marked solutions, and is the basis by which we assign marks. This is accomplished through an efficient novel graph similarity measure (AssignSim). Our experiments show good correlation of assigned marks with that of a human marker.     

资产管理软件帮助节省成本

最近,一家厂商的自动润滑系统在人为地进行了一次未知的定时改动之后,损失了超过100,000美元与停工相关的费用。一个定时器之前是每20分钟注入一次润滑油,后来被设定为每8小时注入一次润滑油,导致机械轴承需要进行一次提前到来的改装。