Comparison of microwave-assisted acid leaching techniques for the determination of heavy metals in sediments, soils, and sludges

Microwave-assisted EPA method 3051 for nitric acid leaching of environmentally key elements from sediments, soils, and sludges was tested, and the influence of leaching temperature and time on element recovery for an estuarine sediment (CRM 277) was investigated. The extraction efficiencies for four certified reference materials applying EPA method 3051, an optimized nitric acid procedure, and an aqua regia (HCl/HNO₃ 3:1) procedure were compared. Digestions were carried out in a high-pressure microwave system offering simultaneous temperature and pressure control for all digestion vessels employed. Eight elements (Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn) were determined by ICP-AES and ICP-MS. Extraction efficiency strongly depended on the applied leaching parameters and varied for certain elements among different materials when a nitric acid procedure was applied. In general, element recoveries obtained from the aqua regia procedure were superior to those obtained from nitric acid procedures and showed good agreement with the 95% confidence interval of the certified value for most of the elements investigated. Received: 27 March 1998 / Revised: 29 June 1998 / Accepted: 3 July 1998     

Vapor-liquid equilibria for the nitrogen-isobutane system

Vapor-liquid equilibria have been investigated experimentally for the nitrogen-isobutane system at temperatures from 120 K to 220 K and at pressures up to 150 bar. Below 126.5 K, two liquid phases were observed as pressure was increased to near the vapor pressure of pure nitrogen. The equilibrium ratio of nitrogen in the binary system and the Henry’s law constants for nitrogen in isobutane were determined from experimental data. The experimental phase equilibrium data were correlated by means of the Peng-Robinson equation of state.     

Redox potentials of chlorophylls and beta-carotene in the antenna complexes of photosystem II

Electron transfer (ET) processes in reaction centers (RC) of photosystem II (PSII) are prerequisites of oxygen generation. They are promoted by energy transfer from antenna to RC. Here, we calculated the redox potentials of chlorophylla/beta-carotene (Chla/Car) in PSII CP43/CP47 antenna complexes, solving the linearized Poisson-Boltzmann (LPB) equation based on the PSII crystal structure. The majority of antenna Chla redox potentials for reduction/oxidation were lower than those of RC Chla. Hence, ET events with excess electrons remain localized in the RC. Simultaneously antenna Chla can serve as an efficient cation sink to rereduce RC Chla if normal PSII function is inhibited. Especially three antenna Chla (Chl-47, Chl-18, and Chl-12) and two Car bridging the space between Chl(Z(D1)) and cytochrome (cyt) b559 have the same level of oxidation redox potential. Together with Chl(Z(D2)) they form an electron hole transfer pathway and temporary storage device guiding from the oxidized P680(+.) Chla to the cyt b559. This path may play a photoprotective role as efficient electron hole quencher.     

Angle-resolved photoemission and valence band dispersions for GaAs: Direct vs indirect models

Angle-resolved photoemission measurements for GaAs(110) have been extended to hv= 100 eV. These results show that dominant emission peaks are due to direct transitions. Weaker one-dimensional density of states features sometimes observed are due to surface umklapp/secondary cone and lifetime effects. Accurate band dispersions

for all four valence bands GaAs along the [110] direction are given using simple normal emission and off-normal emission methods. Electron and hole lifetimes are directly determined.     

MODs vs. NPs: Vying for the Future of Printed Electronics

This Minireview compares two distinct ink types, namely metal-organic decomposition (MOD) and nanoparticle (NP) formulations, for use in the printing of some of the most conductive elements: silver, copper and aluminium. Printing of highly conductive features has found purpose across a broad array of electronics and as processing times and temperatures reduce, the avenues of application expand to low-cost flexible substrates, materials for wearable devices and beyond. Printing techniques such as screen, aerosol jet and inkjet printing are scalable, solution-based processes that historically have employed NP formulations to achieve low resistivity coatings printed at high resolution. Since the turn of the century, the rise in MOD inks has vastly extended the range of potentially applicable compounds that can be printed, whilst simultaneously addressing shelf life and sintering issues. A brief introduction to the field and requirements of an ink will be presented followed by a detailed discussion of a wide array of synthetic routes to both MOD and NP inks. Unindustrialized materials will be discussed, with the challenges and outlook considered for the market leaders: silver and copper, in comparison with the emerging field of aluminium inks.     

Differential geometric analysis of alterations in MH α‐helices

Antigen presenting cells present processed peptides via their major histocompatibility (MH) complex to the T cell receptors (TRs) of T cells. If a peptide is immunogenic, a signaling cascade can be triggered within the T cell. However, the binding of different peptides and/or different TRs to MH is also known to influence the spatial arrangement of the MH α‐helices which could itself be an additional level of T cell regulation. In this study, we introduce a new methodology based on differential geometric parameters to describe MH deformations in a detailed and comparable way. For this purpose, we represent MH α‐helices by curves. On the basis of these curves, we calculate in a first step the curvature and torsion to describe each α‐helix independently. In a second step, we calculate the distribution parameter and the conical curvature of the ruled surface to describe the relative orientation of the two α‐helices. On the basis of four different test sets, we show how these differential geometric parameters can be used to describe changes in the spatial arrangement of the MH α‐helices for different biological challenges. In the first test set, we illustrate on the basis of all available crystal structures for (TR)/pMH complexes how the binding of TRs influences the MH helices. In the second test set, we show a cross evaluation of different MH alleles with the same peptide and the same MH allele with different peptides. In the third test set, we present the spatial effects of different TRs on the same peptide/MH complex. In the fourth test set, we illustrate how a severe conformational change in an α‐helix can be described quantitatively. Taken together, we provide a novel structural methodology to numerically describe subtle and severe alterations in MH α‐helices for a broad range of applications. © 2013 Wiley Periodicals, Inc.     

Mono-Triflation of Carbohydrate Diols and Triols

ABSTRACT

For five carbohydrate substrates [methyl 4,6-O-(phenylmethylene)-1-thio-α-D-glucopyranoside 1a, 1-cyano-1-deoxy-4,6-O-(phenylmethylene)-α-D-galactopyranose 2a, methyl α-D-xylopyranoside 3a, methyl β-D-arabinopyranoside 4a, and methyl 5-O-(tert-butyldiphenylsilyl)-α-D-ribofuranoside 5a], selective mono-triflation was achieved where the reacting hydroxyl is cis and vicinal to a heteroatom.     

Quantum‐Chemical and Electrochemical Investigation of the Electrochemical Windows of Halogenated Carborate Anions

The range of electrochemical stability of a series of weakly coordinating halogenated (Hal=F, Cl, Br, I) 1‐carba‐closo‐dodecaborate anions, [1‐R‐CB₁₁X₅Y₆]^? (R=H, Me; X=H, Hal, Me; Y=Hal), has been established by using quantum chemical calculations and electrochemical methods. The structures of the neutral and dianionic radicals, as well as the anions, have been optimized by using DFT calculations at the PBE0/def2‐TZVPP level. The calculated structures are in good agreement with existing experimental data and with previous calculations. Their gas‐phase ionization energies and electron affinities were calculated based on their optimized structures and were compared with experimental (cyclic and square‐wave) voltammetry data. Electrochemical oxidation was performed in MeCN at room temperature and in liquid sulfur dioxide at lower temperatures. All of the anions show a very high resistance to the onset of oxidation (2.15–2.85 V versus Fc^0/+), with only a minor dependence of the oxidation potential on the different halogen substituents. In contrast, the reduction potentials in MeCN are strongly substituent dependent (?1.93 to ?3.32 V versus Fc^0/+). The calculated ionization energies and electron affinities correlate well with the experimental redox potentials, which provide important verification of the thermodynamic validity of the mostly irreversible redox processes that are observed for this series. The large electrochemical windows that are afforded by these anions indicate their suitability for electrochemical applications, for example, as supporting electrolytes.     

单矢量水听器估计目标方位的方法与实验

为评估基于单矢量水听器的方位估计能力,在黄海海域对矢量水听器进行实验。矢量水听器吊放于接收船尾部,采用平均声强器和复声强器方位估计方法,并提出以概率密度值最大的方位角作为目标方位估计值的具体处理准则,对恒定方向、匀速行驶的目标船方位进行估计,并求出两种方法的方位估计误差。结果表明,水听器布放深度10 m时,对正横距离为0.42 km的航速10 kn的目标船,平均声强器方法的水平方位角估计误差18°,极角估计误差为5°,可以在离目标船最远1.17 km处估计其方位;复声强法的水平方位角估计误差为13°,极角估计误差为8°,可以在离目标船最远2.35 km处估计其方位。在有接收船的噪声干扰情况下,复声强器比平均声强器方法估计的方位更准确,可以对更远处的噪声源进行方位估计。     

Optimal spin squeezing inequalities detect bound entanglement in spin models

We determine the complete set of generalized spin squeezing inequalities. These are entanglement criteria that can be used for the experimental detection of entanglement in a system of spin-1/2 particles in which the spins cannot be individually addressed. They can also be used to show the presence of bound entanglement in the thermal states of several spin models.