Derivation of the transport equation for electrons moving through random impurities

A single (nonrelativistic, spinless) electron subject to a constant external electric field interacts with impurities located on an infinitely extended lattice by a potential of random strength. The random strength is given by a field of Gaussian random variables. We show the existence of the averaged dynamics and prove that in the weak coupling limit, 0, ₂ t= fixed, one obtains the usual transport equation for the velocity distribution.Work supported by a Max Kade Foundation fellowship.On leave of absence of the Fachbereich Physik der Universität München.     

Effects of processing parameters on the mechanical properties of polypropylene random copolymer

The mechanical properties of polypropylene random copolymer (PP-R) with different processing parameters were studied. Special attention is devoted to the investigation of the influence of masterbatch addition on the variation in the mechanical properties of injection moulded PP-R. Tensile, instrumented Charpy impact, Shore D hardness, differential scanning calorimeter (DSC) and Vicat softening temperature (VST) tests were conducted on the test samples containing different colour masterbatches varying from 0.5 to 10 wt%. The observed changes in the mechanical behaviour are explained by the type and level of masterbatch content. The natural UV weathering performance of the PP-R material was studied from the masterbatch type point of view. The effect of processing parameters on material performance was studied on samples which were directly obtained from extruded pipes and on injection moulded samples.

Finally, the effects of storage time on the polymer properties were investigated.     

Cationic copolymerization of indene with styrene derivatives: Synthesis of random copolymers of indene with high molecular weight

Random copolymers with high molecular weights of indene and p‐methylstyrene (pMeSt) were synthesized by cationic polymerization with trichloroacetic acid/tin tetrachloride in CH₂Cl₂ at low temperatures. When indene and pMeSt (1:1 v/v), for example, were polymerized at ?40 °C, both monomers were consumed at very similar rates to give a copolymer with high molecular weight [number‐average molecular weight (M_n): 8–9 × 10⁴]. This is indeed quite unexpected behavior for the combination of these two monomers because pMeSt polymerized over 1000 times faster than indene in the homopolymerization under the reaction conditions previously described. The product copolymer of indene and pMeSt had a random monomer sequence in it that was confirmed by NMR analyses and thermal‐property measurements. In sharp contrast with pMeSt, styrene and p‐chlorostyrene, which have no electron‐donating groups on the phenyl ring, led to low molecular weight polymers (M_n < 10,000) in the copolymerization with indene (1:1 v/v). © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2449–2457, 2002     

The size distribution for theA g RB f−g Model of polymerization

This paper gives the equilibrium distribution of polymer sizes for Flory'sA _g RB _f–g model of polymerization. In this model, the polymers are composed of structural units withg functional groups of the typeA and (f-g) functional groups of the typeB. Reaction is subject to three conditions: (1) Functional groups of the typeA react only with those of typeB, and vice versa. (2) Intramolecular reactions do not occur [and therefore only branched-chain (noncyclic) polymers and formed]. (3) Subject to conditions (1) and (2), all functional groups are equally reactive. The derivation employs Stockmayer's statistical mechanical method (first used on Flory'sRA _f model), coupled with a recursion giving the number of distinct polymers which may be assembled fromk units of theA _g RB _f–g type. We also give distributions for a limiting case of theA _g RB _f–g model, the so-calledA _g RB model. This paper completes the solution of the Smoluchowski coagulation equation (monodisperse case) for the kernelsa _ij =A + B(i +j)+ Cij. The proof will be given in another publication.     

酿造酱油、配制酱油及酿造食醋、配制食醋的鉴别

乙酰丙酸是配制酱油的特有成分，在硫酸溶液中，乙酰丙酸可与香草醛反应而呈现蓝绿色。掺有尿素的酱油在与丁二酮肟、磷酸混合后，加热煮沸会呈现红色。用酱色、食盐等配制的劣质酱油可用测定氨基酸态氮和酱色含量的方法进行鉴别。酿造食醋和配制食醋的常用鉴别方法是碘液法和高锰酸钾法。     

Individual determination of ortho and non-ortho substituted polychlorobiphenyls (PCBs) in sediments by high performance liquid chromatographic pre-separation and gas chromatography/ECD detection

Summary An analytical procedure for the individual determination of ortho and non-ortho PCB congeners in sediments, using high performance liquid chromatography (HPLC) preseparation and gas chromatography/ECD detection, is described. Gas chromatography/FTIR spectrometry (GC/FTIR) and gas chromatography/mass spectrometry (GC/MS) were employed for individual congener identification and determination. Sample extraction, clean-up of extract and selective elution procedures were optimized by using reference certified marine sediment samples. Recovery and precision were typically 83% and 16% respectively at 2 ng/g of total PCB content. The proposed procedure, tested by analyzing real sediment samples, showed a reproducibility better than 20% at 13 ng/g PCB level.     

Selective hydrogenation of butadiene-styrene copolymers using a Ziegler-Natta type catalyst 2. Thermal properties

Three types of butadiene-styrene copolymers, diblock, triblock and random, were partially hydrogenated in their elastomeric units in order to determine the influence of hydrogenation extent on their thermal properties. The hydrogenation reactions were carried out using a Ziegler-Natta type catalyst and the extent of hydrogenation was evaluated by FTIR spectroscopic technique. The percentage of crystallinity was determined by differential scanning calorimetry (DSC), considering the low density polyethylene (LDPE) as reference since the saturation of elastomeric units with low content of 1,2-vinyl bonds gives a structure which resembles to LDPE, thus semi-crystalline polymers were obtained. On the other hand, the glass transition temperature (T_g) for the hydrogenated and non-hydrogenated copolymers as well as their heat of fusion, were also determined by DSC. An equation to evaluate the T_g of partially hydrogenated random copolymers is proposed considering both the saturated and unsaturated fractions. The thermo-oxidative behaviour of certain hydrogenated and non-hydrogenated copolymers was evaluated by thermogravimetric analyses (TGA). The results obtained by TGA suggest that a minimum saturation level is necessary in order to improve the thermo-oxidative resistance of the polymers.     

Identification of low molecular weight proteins isolated by 2-D liquid separations

Proteins with molecular mass (M(r)) <20 kDa are often poorly separated in 2-D sodium dodecyl sulfate polyacrylamide gel electrophoresis. In addition, low-M(r) proteins may not be readily identified using peptide mass fingerprinting (PMF) owing to the small number of peptides generated in tryptic digestion. In this work, we used a 2-D liquid separation method based on chromatofocusing and non-porous silica reversed-phase high-performance liquid chromatography to purify proteins for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) analysis and protein identification. Several proteins were identified using the PMF method where the result was supported using an accurate M(r) value obtained from electrospray ionization TOFMS. However, many proteins were not identified owing to an insufficient number of peptides observed in the MALDI-TOF experiments. The small number of peptides detected in MALDI-TOFMS can result from internal fragmentation, the few arginines in its sequence and incomplete tryptic digestion. MALDI-QTOFMS/MS can be used to identify many of these proteins. The accurate experimental M(r) and pI confirm identification and aid in identifying post-translational modifications such as truncations and acetylations. In some cases, high-quality MS/MS data obtained from the MALDI-QTOF spectrometer overcome preferential cleavages and result in protein identification.     

A comparison of electron ionization mass spectra obtained at 70 eV,low electron energies,and with cold EI and their NIST library identification probabilities

Electron ionization (EI) mass spectra of 46 compounds from several different compound classes were measured. Their molecular ion abundances were compared as obtained with 70‐eV EI, with low eV EI (such as 14 eV), and with EI mass spectra of vibrationally cold molecules in supersonic molecular beams (Cold EI). We further compared these mass spectra in their National Institute of Standards and Technology (NIST) library identification probabilities. We found that

1. Low eV EI is not a soft ionization method, and it has little or no influence on the molecular ion relative abundances for large molecules and those with weak or no molecular ions.
2. Low eV EI for compounds with abundant or dominant molecular ions in their 70 eV mass spectra results in the reduction of low mass fragment ions abundances thereby reducing their NIST library identification probabilities thus rarely justifies its use in real‐world applications.
3. Cold EI significantly enhances the relative abundance of the molecular ions particularly for large compounds; yet, it retains the low mass fragment ions; hence, Cold EI mass spectra can be effectively identified by the NIST library.
4. Different standard EI ion sources provide different 70 eV EI mass spectra. Among the Agilent technologies ion sources, the “Extractor” exhibits relatively abundant molecular ions compared with the “Inert” ion source, while the “High efficiency source” (HES) provides mass spectra with depleted molecular ions compared with the “Inert” ion source or NIST library mass spectra.

These conclusions are demonstrated and supported by experimental data in nine figures and two tables.     

Application of diode array detectors for solute identification in toxicological analysis

Summary The possibilities and limitation of automated solute identification via UV/VIS spectroscopy in HPLC are demonstrated and applications in toxicologic analysis are described. A standard isocratic system is used. The influence of various chromatographic parameters on retention time is shown. A retention time window of ±15% is required. In addition to retention time, derived spectral data are calculated (minima and maxima of derivatives, area counts under standardized spectral ranges, absorption at various wavelength) and used for positive solute identification. It is possible to identify solutes with a high degree of certainty in urine and plasma if their concentration is at least 10 ppm.