Dual bin packing with items of random sizes

Given a collection of items and a number of unit size bins, the dual bin packing problem requires finding the largest number of items that can be packed in these bins. In our stochastic model, the item sizesX ₁,,X _n are independent identically distributed according to a given probability measure. Denote byN _n =N _n (X ₁,,X _n ) the largest number of these items that can be packed in an bins, where 0<a<1 is a constant. We show thatb = lim _n E(N _n )/n exists, and that the random variable (N _n –nb)/ converges in distribution. The limit is identified as the distribution of the supremum of a certain Gaussian process cannonically attached to. This research is in part supported by NSF grant CCR-8801517 and CCR-9000611.This research is in part supported by NSF grant DMS-8801180.     

测定可见光区分光光度系组成的新方法

本文报道一种测定二元分光光度系组成的新方法,原理新颖,为作者首创,采用双波长分光光度技术消除显色产物的影响,直接测定与显色剂平衡浓度相对应的吸光度,通过简单的计算即可求得产物组成。     

Rapid and ultra-sensitive GC/MS analyses with a microchannel plate array detector Part I: Possibilities of simultaneous ion detection in narrow-bore GC/MS

Identification and detection limits for scanning and non-scanning mass spectrometers are discussed. It is theoretically deduced and experimentally confirmed that these limits are on the low pico-and femtogram levels, respectively, when using conventional secondary electron multiplier-amplifier systems. The sensitivity can be increased at least tenfold by pulse-counting techniques, instead of current amplification, provided the chemical noise is sufficiently low. The potential advantages of a detection system for simultaneous ion detection in a significant mass range, for obtaining complete mass spectra in fast GC/MS analyses, are demonstrated. A double focusing mass spectrometer was constructed, using the well-proven Mattauch-Herzog principles. By application of an “electronic photoplate”, substance identification in the low femtogram range on a millisecond time scale, so far only accessible for single ion monitoring techniques, is feasible.     

Molecular mechanics force field parameterization of the fluorescent probe rhodamine 6G using automated frequency matching

Novel single-molecule fluorescence experimental techniques have prompted a growing need to develop refined computational models of dye-tagged biomolecules. As a necessary first step towards useful molecular simulations of fluorescence-labeled biomolecules, we have derived a force field for the commonly used dye, rhodamine 6G (R6G). A novel automated method is used that includes fitting the molecular mechanics potential to both vibrational frequencies and eigenvector projections derived from quantum chemical calculations. The method is benchmarked on a series of aromatic molecules then applied to derive new parameters for R6G. The force field derived reproduces well the crystal structure of R6G.     

Theoretical evaluation of the collection efficiency at ring-disc microelectrodes

Ring-disc microelectrodes operating as collector-generators are capable of probing multiple aspects of mass transport and are becoming popular electrochemical detectors. In this paper, the key parameters affecting the efficiency of these detectors are modelled and compared to experimental measurements by us and others. The first parameters considered pertain to electrode geometry; the disc radius and inner and outer ring radii. Our model results and experimental measurements show that varying these parameters significantly changes the sensor’s efficiency. The influence of recess and protrusion of the active surfaces from the insulating face of the electrode is also studied over a reasonable range of distances. We find that in general, protrusions will increase the efficiency of the sensor whilst recesses decrease it. The other parameters considered pertain to the flux distribution at the surface of the ring and disc electrodes, focusing on the generator electrode. The flux distribution at the generator is influenced by the voltage applied and the relative rates of mass transport or electron transfer of the species used. We find that the sensor’s efficiency increases with increasing overpotential. When the level of overpotential is sufficiently high, D and k₀ have no effect on the value of the collection efficiency. However, to establish the required level of overpotential needed to ensure a maximum collection efficiency the reaction kinetics and diffusion coefficient of a species need to be specified. Our investigations highlight the best operating modes and points out problems and features of the ring-disc microelectrode and its use as a collector-generator.     

Transition metal complexes coordinated by an NAD(P)H model compound and their enhanced hydride-donating abilities in the presence of a base

The ruthenium(II) and rhenium(I) complexes containing an NAD(P)H model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH), as ligand, [Ru(tpy)(bpy)(BNAH)]2+ (1 a) and [Re(bpy)(CO)3(BNAH)]+ (1 b), were quantitatively produced by the reaction of the corresponding metal hydrido complexes with BNA(+) (1-benzylnicotinamidium cation). In the presence of base with pK(a) = 8.9, 1 a and 1 b have much greater reducing power than "free" BNAH. The oxidation potentials of 1 a in the absence and the presence of triethylamine were 0.55 V and -0.04 V, respectively, versus Ag/AgNO(3), whereas that of "free" BNAH was 0.30 V. Spectroscopic results clearly showed that the base extracts a proton from the carbamoyl group on 1 a and 1 b to give the deprotonated BNAH coordinating to the transition-metal complexes [Ru(tpy)(bpy)(BNAH-H+)]+ (3 a) and [Re(bpy)(CO)3(BNAH-H+)] (3 b); this deprotonation underlies the enhancement in reducing ability. The deprotonated forms 3 a and 3 b can efficiently reduce other NAD(P) models to give the corresponding 1,4-dihydro form, resulting in the deprotonated BNA+ being coordinated to the metal complexes [Ru(tpy)(bpy)(BNA(+)-H+)]2+ (2 a) and [Re(bpy)(CO)3(BNA+-H+)]+ (2 b); "free" BNAH and the protonated adducts 1 a and 1 b cannot act in this way. X-ray crystallography was performed on the PF6- salt of 2 a, and showed that the deprotonated nitrogen atom on the carbamoyl group coordinates to the ruthenium(II) metal center with a bond length of 2.086(3) Angstroms. Infrared spectral data suggested that the deprotonated carbamoyl group on the reduced forms 3 a and 3 b is converted to the imido group, and that the oxygen atom coordinates to the metal center.     

Stabilization of Unusual Oxidation and Coordination States by the Ligands OSF5, OSeF5, and OTeF5

Compounds with the ligands OSF₅, OSeF₅, and OTeF₅ are now known for most of the chemical elements. The ability of these ligands to stabilize the highest valency levels of the central atoms to which they are bound is unsurpassed by any other polyatomic ligand. Examples are Xe(OTeF₅)₆, Te(OTeF₅)₆, W(OTeF₅)₆, and U(OTeF₅)₆ or I(OTeF₅)₅ and Br(OSeF₅)₃. Because of the ligands' size and internal bonding they hardly ever form bridges, and in this respect they differ from fluorine, although they do share the latter's high electronegativity.     

稀土单氧化物发射光谱法的研究I.混合稀土浓集物中钐的双波长测定

报道了空气乙炔火焰中ＳｍＯ蒸气的发射光谱行为，试验了Ｌａ、Ｎｄ、Ｅｕ、Ｙ对ＳｍＯ发射强度增强作用，在大量Ｌａ存在下，ＳｍＯ的发射强度与其浓度成正比关系。用大量Ｌａ作增感剂和干扰抑制剂，借助双波长测定法克服光谱干扰，实现了直接测定高Ｙ混合稀土浓集物中的Ｓｍ，方法准确，快速     

Detecting the Rouse and Sub-Rouse Modes in Poly(Butyl Acrylate) and Poly(Ethyl Acrylate) Through Two-Dimensional Dynamic Mechanical Spectra

The difficulties of observing sub-Rouse modes (SRM) and Rouse modes (RM) in acrylate polymers has resulted in many arguments and disputes concerning the nature of their glass-rubber transition. Because different modes have different sensitivity to external perturbations, the two-dimensional dynamic analysis mechanical spectra (2D-DMS) was introduced to detect the local segments motion (LSM), SRM, and RM in poly(butyl acrylate) (PBA) and poly(ethyl acrylate) (PEA). The results of the asynchronous spectra showed the LSM, SRM, and RM of PBA and PEA are located, respectively, at about (?46 ～ ?29°C), (?28 ～ ?10°C), (?4 ～ 27°C), and about (?12 ～ ?5°C), (?3 ～ 6°C), and (10 ～ 44°C). Furthermore, the LSM and SRM of PBA and PEA have an overlap in the synchronous spectra. This is suggested to be caused by the higher coupling effect in PBA and PEA when compared with strong glass formation polymers, like polyisobutylene (PIB).