bluuebunny/crossref_metadata_2025 huggingface dataset:
The abundance, distribution, and correlation of viruses, phytoplankton, and prokaryotes along a Pacific Ocean transect
Authors: Culley Alexander I. , Welschmeyer Nicholas A.
Published: June 2010

Concentrations of virus‐like particles (VLP), prokaryote‐like particles (PLP), chlorophyll a, and zeaxanthin were determined at 9–12 depths (0–250 m) for each of 13 stations along a 3,800‐km transect from the coastal waters of Monterey Bay, California (36.62°N, 122.25°W) to the open ocean Hawaii Ocean Time‐Series (HOTS) station near Hawaii (22.69°N, 158.12°W). We collected VLP and PLP, the latter of which included heterotrophic bacteria and cyanobacteria, in glutaraldehyde‐fixed samples on 0.02‐µm Anodisc filters. The samples were stained with the nucleic acid dye Yo‐Pro‐1 and quantified by epifluorescence microscopy. Measurements of Chl a and zeaxanthin were used as indicators of total phytoplankton and cyanobacteria biomass, respectively.With the exception of the most coastal station, depth‐integrated VLP and PLP abundance was similar at all stations along the transect; all stations showed a decrease of VLP and PLP with depth. Standard multiple regression analysis showed that logarithmically
Silicate and labile DOC interfere in structuring the microbial food web via algal—bacterial competition for mineral nutrients: Results of a mesocosm experiment
Authors: Havskum Harry , Thingstad T. Frede , Scharek Renate , Peters Francesc , Berdalet Elisa , Sala M. Montserrat , Alcaraz Miquel , Bangsholt Jan C. , Zweifel Ulla Li , Hagström Åke , Perez Maite , Dolan John R.
Published: June 2010

The effects of organic and inorganic nutrient enrichments on algal‐bacterial competition were investigated using mesocosms. Interactions were followed over 10 d in 12, 3−m3 seawater mesocosms in the Isefjord, Denmark. Two sets of four mesocosms were given the same daily addition of “phytoplankton nutrients” (phosphate and nitrate) but received different amounts of glucose, and one set was kept in excess with respect to silicate. Four additional mesocosms served as controls and received either no additions, silicate alone, or glucose alone. In the mesocosm set where no silicate was added, enrichment with phytoplankton nutrients and glucose led to a replacement of diatoms, not by other algae, but by heterotrophic bacteria, mainly bacteria > 2 µ. In the mesocosm set where silicate was kept replete, diatoms competed successfully with bacteria for the uptake of mineral nutrients. Even in mesocosms enriched with high amounts of glucose, primary production increased throughout the experimental period, while bacterial production, after an initial increase, leveled off. In addition, turnover time of glucose increased in the silicate‐replete mesocosm set, consistent with the idea that bacterial consumption was hampered by diatoms competing successfully for phosphate and nitrate. The size and shape of different algal and bacterial groups in relation to nutrient uptake and grazer avoidance are discussed. Both accumulation and consumption of dissolved organic carbon could depend on the structure of the microbial food web.
Transport of dissolved inorganic carbon from a tidal freshwater marsh to the York River estuary
Authors: Neubauer Scott C. , Anderson Iris C.
Published: June 2010

The cycling of dissolved inorganic carbon (DIC) and the role of tidal marshes in estuarine DIC dynamics were studied in a Virginia tidal freshwater marsh and adjacent estuary. DIC was measured over diurnal cycles in different seasons in a marsh tidal creek and at the junction of the creek with the adjacent Pamunkey River. In the creek, DIC concentrations around high tide were controlled by the same processes affecting whole‐estuary DIC gradients. Near low tide, DIC concentrations were 1.5–5‐fold enriched relative to high tide concentrations, indicating an input of DIC from the marsh. Similar patterns (although dampened in magnitude) were observed at the creek mouth and indicated that DIC was exported from the marsh. Marsh pore‐water DIC concentrations were up to 5 mmol L−1 greater than those in the creek and suggested a significant input of sediment pore water to the creek. A model of tidal marsh DIC export showed that, on a seasonal basis, DIC export rates were influenced by water temperature. The composition of exported DIC averaged 19% dissolved CO2 and 81% HCO3− and CO32−. Although CO2 can be lost to the atmosphere during transit through the estuary, DIC in the form of carbonate alkalinity is subject to export from the estuary to the coastal ocean. When extrapolated to an estuarywide scale, the export of marsh‐derived DIC to the York River estuary explained a significant portion (47 ± 23%) of excess DIC production (i.e., DIC in excess of that expected from conservative mixing between seawater and freshwater and equilibrium with the atmosphere) in this system. Therefore, CO2 supersaturation, by itself, does not indicate that an estuary is net heterotrophic.
Illumination and turbidity effects on observing faceted bottom elements with uniform Lambertian albedos
Authors: Carder, Kendall L. , Liu, Cheng-Chien , Lee, Zhongping , English, David C. , Patten, James , Chen, F. Robert , Ivey James E. , Curtiss O. Davis
Published: June 2010

Aircraft images were collected near Lee Stocking Island (LSI), Bahamas, with wavelike features for bright sand bottoms during times when solar zenith angles were large. The image contrast between leading and trailing wave facets approached a 10–15% difference because of algae accumulations in wave troughs or topographic variations of the bottom. Reflectance contrast for blue light was greater than for red and green wavelengths when algae or detritus was present in the troughs. However, the contrast at green and red wavelengths was greater than at blue wavelengths when caused by the interplay between bottom topography and oblique illumination. A three‐dimensional backwards Monte Carlo (BMC) model was developed to evaluate the effect of oblique illumination on wavelike topographic features for various values of water clarity and bottom albedo. An inverse optical modeling approach, previously developed for flat, horizontally homogeneous bottoms, was applied to the BMC results. Bathymetric estimates for bright facets tilted 10° toward the sun were slightly smaller than actual depths, whereas shaded facet depth estimates were too high by about 5%. Larger errors were associated with albedo retrievals, where shaded facets produced albedo estimates up to 15% lower than actual values. Errors increased with tilt angles up to 20° but decreased with sea and sky turbidity. Averaging sunlit and shaded pixels before running the inverse model reduced the uncertainty of bathymetric and albedo estimates to about 2 and 5%, respectively, comparable to previous field evaluations of the inversion model.
A biooptical model of irradiance distribution and photosynthesis in seagrass canopies
Authors: Zimmerman Richard C.
Published: June 2010

Although extremely vulnerable to coastal eutrophication, seagrasses represent important structuring elements and sources of primary production in shallow waters. They also generate an optical signature that can be tracked remotely. Accurate knowledge of light absorption and scattering by submerged plant canopies permits the calculation of important plant‐ and ecosystem‐level properties, including rates of photosynthesis, vegetation abundance, and distribution. The objectives of this study were to develop a realistic, yet simply parameterized two‐flow model of plane irradiance distribution through a seagrass canopy submerged in an optically active water column, to evaluate its performance against in situ measurements, and to explore the impacts of variations in canopy architecture on irradiance distribution and photosynthesis within the canopy. Allometric functions derived from leaf length‐frequency data enabled simple parameterization of canopy architecture. Model predictions of downwelling spectral irradiance distributions in seagrass canopies growing in both oligotrophic and eutrophic waters were within 15% of field measurements. Thus, the model provides a robust tool for investigating photosynthetic performance of seagrass canopies as functions of water quality, depth distribution, canopy architecture, and leaf orientation. Model predictions of upwelling irradiance were less reliable, particularly in the upper half of the canopies. The model was more sensitive to leaf orientation than leaf optical properties, seabed reflectance, or the average cosine of downwelling irradiance. Better knowledge of leaf orientation appears to be a fruitful avenue for improving our understanding of the interaction between seagrasses and the submarine light environment.
Study of the precipitation evolution in Catalonia using a mesoscale model (1971–2000)
Authors: Barrera-Escoda A. , Cunillera J.
Published: June 2010

Abstract. In this work the MM5 mesoscale model is used in order to analyse the temporal evolution of the precipitation for the period 1971–2000 in Catalonia (NE Iberian Peninsula). Three one-way nested domains with 135, 45 and 15 km horizontal grid resolution and 23 vertical levels have been used. The simulation is performed nesting MM5 into the ERA40 reanalyses. Dynamical nudging is applied to the first domain. However, nudging is not applied in the second and third domains. In order to assess the performance of the developed methodology (main spatio-temporal precipitation characteristics), the results obtained in each simulation are compared with those obtained from ERA40 and observational data. The results show a climatologically reliable distribution of the simulated precipitation spatial patterns for annual, semi-annual, spring and summer precipitation compared to those obtained from 1100 rain gauges covering the whole study area. For winter and autumn the goodness of the results is much lower. Furthermore, the results for 15-km outputs are better than the 45-km ones. The simulations also reproduce well the evolution of annual anomalies for Catalonia and the probability density function (PDF) of monthly mean precipitation. They also improve the precipitation outputs from ERA40, which present an important negative trend and a drier PDF for the period 1971–2000. On the other hand, extreme values are not well reproduced by the simulation. Despite this fact, hydric extremes derived from extreme values (i.e. extreme rainy days and flood records) are well captured by the model.
On some relationships between storms and plankton dynamics
Authors: Peters F.
Published: June 2010

Abstract. The physico-chemical fields of the pelagic environment are constantly fluctuating at different spatial and temporal scales. Storms are extreme events of such fluctuations that cascade down to small scales to alter nutrient availability to microscopic algae or swimming and mating behaviour of motile plankton. Mediterranean storms sometimes are also responsible for the transport of micro and macronutrients from Saharan origin, albeit the significance for marine production is still under question. In coastal ecosystems, storms represent dissolved nutrient injections via run-off and resuspension that trigger planktonic succession events. Storms may also have a role in the development and mitigation of harmful algal blooms, events with economic and health consequences that are of growing societal concern. Based on laboratory experiments on the effects of turbulence on swimming behaviour and population growth of dinoflagellates, a conceptual sequence of events is proposed for bloom initiation. Overall, storms affect, directly or indirectly, the dynamics of plankton and hence ecosystem production and cannot be considered catastrophic or hazardous in this context. The full potential of such relationships will be evidenced once biological time series match the resolution and spatial coverage of meteorological and oceanic data. As the frequency and intensity of storms is subject to global change, future oceanic ecosystem production should be affected as well.
Der Eurocode 2 für Deutschland – Erläuterungen und Hintergründe
Authors: Fingerloos Frank
Published: June 2010

Der neue Eurocode 2: “Bemessung und Konstruktion von Stahlbeton‐ und Spannbetontragwerken – Teil 1‐1: Allgemeine Bemessungsregeln und Regeln für den Hochbau” (EC2‐1‐1) mit seinem Nationalen Anhang ist nach einer ausführlichen Erprobungsphase bereit zur bauaufsichtlichen Einführung in Deutschland. In mehreren Beiträgen sollen Erläuterungen und Hintergründe zu einigen Regelungen im Eurocode 2 und zu den Entscheidungen für Regeln im Nationalen Anhang vorgestellt werden, die entweder zu Änderungen gegenüber DIN 1045‐1 oder zu Abweichungen vom Eurocode 2 führten. Teil 2 enthält Erläuterungen zu den Grundlagen der Tragwerksplanung, zur Sicherstellung der Dauerhaftigkeit, zu den Baustoffeigenschaften und zu den Spannungs‐ Dehnungslinien.

The Eurocode 2 for Germany – Explanations and Backgrounds Part 2: Basics, Durability, Materials, Stress‐Strain‐Relationships

The new Eurocode 2 “Design of concrete structures – Part 1‐1: General rules and rules for buildings” (EC2‐1‐1) and its National Annex has undergone a phase of detailed testing and is now ready for the implementation in Germany. In some articles should be given explanations and backgrounds of some rules in Eurocode 2 and of decisions for rules in the National Annex, which have been taken either to changes compared with DIN 1045‐1 or to differences to Eurocode 2. Article 2 contains explanations for the basis of design, for the durability, for the material properties and for the stress‐strain‐relationships.
ChemInform Abstract: Lipases: Interfacial Enzymes with Attractive Applications
Authors: SCHMID R. D. , VERGER R.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Carbohydrate‐Based Combinatorial Libraries
Authors: SOFIA M. J.
Published: June 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Identification and characterization of high‐molecular‐weight secalins from triticale seeds by capillary zone electrophoresis
Authors: Salmanowicz Boleslaw P.
Published: June 2010

A rapid and reliable method for separation and characterization of the variability of high‐molecular‐weight secalin subunits (HMW‐SS) in hexaploid triticale (× Triticosecale Wittmack) by CZE has been developed. In this method, a mixture of two poly(ethylene oxide) polymers differing in molecular weight and a high concentration of ACN in isoelectric buffer was applied as the running electrolyte. For dynamic coating of the capillary inner wall, a low‐concentration mixture of poly(vinylpyrrolidone) and hydroxypropylmethylcellulose was employed. Wide allelic variations in rye HMW‐SS composition, including some novel x‐ and y‐type HMW‐SS, were detected by CZE. The CZE electropherograms of HMW‐SS showed two groups of peaks in accordance with y‐ and x‐type subunits, with migration times of 8.0–8.8 and 11.0–13.3 min, respectively. HMW‐SS differed in migration times from the simultaneously resolved HMW glutenin subunits, but frequently had very similar electrophoretic mobilities during separation by SDS‐PAGE. Each of the two rye subunits 2r and 6.5r detected by SDS‐PAGE represents in fact two subunits (5.1r or 5.2r, and 6.4r or 6.5r, respectively). After analyzing 106 European triticale cultivars, 12 HMW‐SS were identified (six x‐type and six y‐type). They form six allelic variants of these subunits. The simultaneous separation and identification of triticale HMW glutenin and secalin subunits by CZE is an efficient alternative to SDS‐PAGE and should facilitate breeding of valuable cultivars.
Development of CE–dual opposite carbon‐fiber micro‐disk electrode detection for peak purity assessment of polyphenols in red wine
Authors: Du Fuying , Fung Ying Sing
Published: June 2010

A new dual opposite carbon‐fiber micro‐disk electrode detector was fabricated and tested for hyphenation with CE in the polyphenol determination. Under optimized conditions, CE–dual opposite carbon‐fiber micro‐disk electrode was found able to baseline separate and determine five important polyphenols (trans‐resveratrol, (+)‐catechin, (−)‐epicatechin, quercetin and gallic acid) in red wine within 16 min with low detection limit (0.031–0.21 mg/L) and satisfactory repeatability (2.0–3.3% RSD, n=5). The opposite dual electrode enables simultaneous determination of CE eluents for current ratio measured at +0.8 and +1.0 V versus Ag/AgCl for the peak purity assessment. The capability to identify the presence of co‐migrating impurities in given polyphenol peaks was demonstrated in a mixed standard solution with overlapping (+)‐catechin and (−)‐epicatechin peaks and in commercial red wine with unknown impurities and confirming the reliability for polyphenol quantitation in red wine with matching migration time and current ratio.
Determination of endocrine disruptors in honey by CZE‐MS using restricted access materials for matrix cleanup
Authors: Rodríguez‐Gonzalo Encarnación , Domínguez‐Álvarez Javier , García‐Gómez Diego , García‐Jiménez María‐Guadalupe , Carabias‐Martínez Rita
Published: June 2010

An analytical method based on CZE coupled to ESI‐MS is proposed for the identification and simultaneous quantification of several endocrine‐disrupting chemicals in honey. The target compounds were the chlorophenols: 2,4‐dichlorophenol, 2,4,5‐trichlorophenol and pentachlorophenol, and bisphenol‐A, 4‐tert‐butylphenol, and 4‐tert‐butylbenzoic acid. A two‐step optimization of the ESI‐MS detection was carried out. First, the organic solvent present in the sheath liquid was selected and its effect on the analytical signal was studied. The best results in terms of the intensity of the MS signals were obtained with methanol. Thus, an experimental design technique (Doehlert type) was used for the optimization of the other parameters: the NH3 concentration in the sheath liquid, the flow of the sheath liquid, the nebulizer pressure in ESI, and the drying gas temperature and flow. Here, we developed a new sample treatment based on the combined use of a restricted access material and a polymeric sorbent for SPE. The LOD achieved were in the range of 5–31 ng/g. The intraday precision of the proposed method was determined from replicate analyses (n=4) at a concentration level of 50 ng/g, with RSD values in the range of 15–23%. The results revealed that the proposed method is suitable for the reliable quantification of endocrine‐disrupting chemicals in honey at nanograms per gram levels.
Determination of melatonin in wine and plant extracts by capillary electrochromatography with immobilized carboxylic multi‐walled carbon nanotubes as stationary phase
Authors: Stege Patricia W. , Sombra Lorena L. , Messina Germán , Martinez Luis D. , Silva María F.
Published: June 2010

The finding of melatonin, the often called “hormone of darkness” in plants opens an interesting perspective associated to the plethora of health benefits related to the moderate consumption of red wine. In this study, the implementation of a new method for the determination of melatonin in complex food matrices by CEC with immobilized carboxylic multi‐walled carbon nanotubes as stationary phase is demonstrated. The results indicated high electrochromatographic resolution, good capillary efficiencies and improved sensitivity respect to those obtained with conventional capillaries. In addition, it was demonstrated highly reproducible results between runs, days and columns. The LOD for melatonin was 0.01 ng/mL. The method was successfully applied to the determination of melatonin in red and white wine, grape skin and plant extracts of Salvia officinalis L.
CE and CEC of nucleosides and nucleotides in food materials
Authors: Chen Xiao‐Jia , Yang Feng‐Qing , Wang Yi‐Tao , Li Shao‐Ping
Published: June 2010

Dietary nucleosides and nucleotides play an important role in the maintenance of functions of bone marrow hematopoietic cells, intestinal mucosa, and brain. Therefore, analysis of those compounds in food is very important for improving and assuring food quality. This review summarized the application of CE and CEC in the analysis of nucleosides and nucleotides in food. The sample preparation and detection are also discussed.
On‐line preconcentration for the determination of aflatoxins in rice samples by micellar electrokinetic capillary chromatography with laser‐induced fluorescence detection
Authors: Arroyo‐Manzanares Natalia , Gámiz‐Gracia Laura , García‐Campaña Ana M. , Soto‐Chinchilla Jorge J. , García‐Ayuso Luis Enrique
Published: June 2010

MEKC coupling with LIF detection has been used for the determination of four aflatoxins (B1, B2, G1 and G2). Separations were performed in an uncoated fused‐silica capillary (70 cm×75 μm id, 55 cm effective length), using 20 mM borate buffer with 30 mM SDS (pH 8.5) and 7% ACN. In order to increase sensitivity, an on‐line preconcentration procedure was applied, based on sweeping, using the same separation buffer without SDS as solvent of the sample. The precision of the method was evaluated in terms of repeatability and intermediate precision and the results were acceptable in all cases (RSD<12%). With the on‐line preconcentration LODs (obtained as 3×S/N) were as low as 0.11, 0.52, 0.04 and 0.10 μg/L for G2, G1, B2 and B1, respectively. Recovery studies were developed with extracts of rice samples spiked with aflatoxins, being in the range between 93.0 and 105.4%. The method has also been applied to the determination of aflatoxins in rice samples, and the results compared with those obtained by a standard method, being in good agreement.
Hydrogels for the Detection and Management of Protease Levels
Authors: Patrick Alison G. , Ulijn Rein V.
Published: June 2010

The design of hydrogels that simultaneously report protease activity and remove excess protease from solution is elucidated. The hydrogels, based on amino‐PEGA, combine enzyme‐specific peptides flanked with FRET complimented by charged amino acid residues that facilitate protease uptake via short range electrostatic interactions. Enzymatic response was analysed using a combination of fluorescence spectroscopy, two‐photon microscopy and UV/Vis spectroscopy. An optimised elastase‐responsive hydrogel resulted in lowering of elastase levels below those typical of chronic wounds. The versatility of the modular‐design approach was demonstrated by development of matrix metalloprotease and chymotrypsin sensitive systems.

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Understanding the Ring‐Opening Reaction of α‐Amino Acid N‐Carboxyanhydride in an Amine‐Mediated Living Polymerization: A DFT Study
Authors: Ling Jun , Huang Yanxin
Published: June 2010

The primary‐amine‐initiated polymerization of α‐amino acid N‐carboxyanhydride (NCA) is a widely‐used and promising way to synthesize polypeptide‐involved materials with various applications. The nucleophilic attack mechanism, also known as normal amine mechanism of ring opening reaction of NCA is investigated in detail by means of the DFT calculation in this work. Three steps, i.e., addition, ring opening and decarboxylation are discussed. The addition of C5 carbonyl group of NCA by NH2 group of initiator requires the highest activation energy (≈60 kcal · mol−1) and is regarded as the rate‐determining step. These results are compatible with the experimental studies reported previously and provide an inside view of the normal amine mechanism.

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Synthesis of Optically Active Polymer with P‐Stereogenic Phosphine Units
Authors: Morisaki Yasuhiro , Suzuki Kentaro , Imoto Hiroaki , Chujo Yoshiki
Published: June 2010

Optically active polymer containing P‐stereogenic bisphosphine as a repeating unit in the main was successfully synthesized. A coordinated borane on the phosphorus atom could be completely removed by an organic base under mild condition, and the successive reaction with Pd afforded the corresponding polymer complex. The chirality of P‐stereogenic centers was transferred to the m‐phenylene‐ethynylene linkers by complexation because of the prohibition of the rotary motion of the bisphosphine‐Pd unit.

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Size‐Dependent Interfacial Tension of Polymer Blends with Broad Composition Polydispersity
Authors: Groenewold Jan , Remerie Klaas
Published: June 2010

The surface tension as a function of system size of a pure blend with chemically polydisperse compatibilizer is investigated by simulation. The main finding is that such compatibilizers adsorb readily at the interface between the bulk phases giving rise to very broad interfacial zones. This phenomenon leads to a marked size dependence of the interfacial tension. However the adsorption only leads to a decrease of 40% of the interfacial tension of the blend without compatibilizer. The limited effect on interfacial tension is explained by the observation that a considerable fraction of the compatibilizing chains do not contribute to the interfacial tension, instead these chains become part of an inhomogeneous phase with extensive thermodynamic properties.

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Stress‐strain‐time‐birefringence relations in photoelastic plastics with creep
Authors: Amba‐Rao Chintakindi L.
Published: June 2010

The above is an exploratory study started in September 1961 with a view to solving the time dependent stress and strain distributions in structural problems through optical model analysis. The present analysis, however, is restricted to monotonically increasing uniaxial loading. Finally, “optical creep parallels mechanical creep” is the basis on which this analysis is built.
Dynamic birefringence of amorphous polymers
Authors: Read B. E.
Published: June 2010

The principles underlying the dynamic birefringence method are outlined, giving particular emphasis to the use of this technique in investigating the molecular mechanism of relaxation in amorphous polymers. Data are presented for amorphous polyacetaldehyde in the frequency range 1‐20 cycles/sec. and temperature range 0 to −25°C. The results are discussed and compared briefly with dielectric data for poly‐acetaldehyde and also with earlier dynamic birefringence data obtained for polymethyl‐acrylate.
Investigation of polymer order by X‐ray diffraction
Authors: Roldan L. G. , Rahl F. , Paterson A. R.
Published: June 2010

The determination of per cent crystallinity in polymers by x‐ray diffraction techniques is generally based on a two‐phase system. Complications arise when intermediate phases are present reducing the significance of the value obtained, To overcome this difficulty, a procedure is described which yields the maximum information from the x‐ray diagram of a polymer. The use of this procedure with oriented nylon 6 establishes the presence of a paracrystalline a phase. The effect of this phase on the density of oriented materials is emphasized. In conclusion, it is suggested that crystallinity, as a degree of order, can best be represented as a tensor rather than a scalar property.
Gel permeation chromatography. II. The nature of the separation
Authors: Moore J. C. , Hendrickson J. G.
Published: June 2010

Gel permeation chromatography is a special type of liquid‐solid elution chromatography based on the permeation of solute molecules into a rigid gel particle. The large molecules penetrate less into the small void spaces of the gel, and they are eluted first. Ideally, the entire separation is due to the size barriers that exist within the gel. Gel columns were readily calibrated with a series of polymer samples with a narrow molecular weight distribution. Elution curves of single components were found to be symmetrical, fitting closely the normalized probability function. Peak widths divided by their elution volumes correlated well with their heights. Complete resolution of the elution curve of a low polymer was demonstrated with these correlations. Calibration curves for polystyrenes and polyglycols were brought into coincidence by plotting elution volume against chain length on a logarithmic scale. These curves were not affected by column temperature changes or by changes to other good solvents as eluants.
Numerical analysis and kinetic interpretation of molecular weight distribution data
Authors: Goodrich Frank C. , Cantow Manfred J. R.
Published: June 2010

A novel numerical method is described for calculating both the distribution moments and the molecular weight distribution curve from fractional on data. The method is based upon Gauss‐Laguerre integration techniques and enables the user to calculate six distribution moments by finite algebraic operations on the cumulative distribution curve. Results obtained by this method on a sample of thermally polymerized polystyrene are described and compared with the theoretical predictions of polymerization kinetics. The data are found to be equally consistent with an initiation mechanism which is either second‐ or third‐order in monomer concentration. The calculated activation energy for second‐order initiation compares favorably with values already reported in the literature, but insufficient data are available to make the same comparison for third‐order initiation.
Some viewpoints on polymer physics
Authors: Tobolsky Arthur V.
Published: June 2010

The following sections attempt a brief survey of the structure and properties of polymers. Many of the views that are discussed here in summary form are those that have been developed in this laboratory during the past five years. This review can therefore be regarded as a brief supplement to reference 1.
Transport through polymer films
Authors: Kumins C. A.
Published: June 2010

A brief summary of some of the factors influencing the transport of gases, vapors and ions through polymeric films is presented. The activated transition suite theory of diffusion and the application of Fick's law to the movement of molecules are discussed. The part played by the glass transition temperature and its relation to segmental mobility in determining the diffusion coefficients and hence the permeability characteristics of organic films is described. It will also be shown how the degree of crosslinking, hydrogen bonding, plasticization, and polymer adsorption in heterogeneous systems affect the chain mobility with subsequent effects on transport phenomena. In the case of the transport of ionic species through membranes, investigations are discussed which relate the permselectivity characteristics of polymers to their ability to act as barriers.
Ionic conduction in polymer films and related systems
Authors: Barker R. E. , Sharbaugh A. H.
Published: June 2010

In polymer films, electrical conduction by ion transport is a significant process which is potentially capable of revealing various aspects of the film's morphology. In this report, further details and consequences of conduction experiments with ion‐doped cellulose 2.5 acetate will be discussed along with some corroborating evidence for a large number of organic liquids. The most important conclusions are: (1) sorbed moisture provides charge carriers by dissociation to H+ and OH−, and (2) the effective dielectric constant ϵ′ is increased by sorbed moisture to a value above that of the pure polymer, or organic liquid, so that barriers to the dissociation of ionic species are greatly reduced. Furthermore, the theory of weak electrolytes may be applied to “strong electrolytes” within solid polymeric and/or liquid organic systems.
The polymerization of 1,4‐anhydro sugar derivatives
Authors: Kops Jorgen , Schuerch Conrad
Published: June 2010

1,4‐Anhydro‐2,3,6‐tri‐O‐methyt‐D‐galactose has been synthesized and positively identified for the first time. 1,4‐Anhydro‐2,3‐di‐O‐methyl‐L‐arabinose was obtained in nearly pure form by an analogous reaction sequence. Both of these compounds undergo addition polymerization under the influence of Lewis acid catalysts to yield amorphous polymers with maximum degrees of polymerization of approximately 90. The chain propagation proceeds in each case with nearly equal amounts of 5‐ and 6‐mernbered ring opening leading to a mixture of furanosidic and pyranosidic unite in the polymer backbone. The resulting configurations at the anomeric centers under various conditions of polymerization, as elucidated mainly by degradation studies, can be explained only by a carbonium ion rather than a trialkyl oxonium ion polymerization mechanism and with the assistance of conformations analysis. The C‐5 substituent in the 1,4‐anhydro‐2,3,6‐tri‐O‐methyl‐D‐gitlactose was found to influence the stereochemistry of the chain propagation.
Mechanical loss mechanisms for polymers at very low temperatures
Authors: Woodward Arthur E.
Published: June 2010

Results of dynamic mechanical investigations for various polymers in the temperature region from 4.2–77°K. or above are reviewed, and the mechanisms believed to be responsible for the various loss maxima are discussed. Dynamic mechanical data, obtained at ∼104 cps with a longitudinal vibrational apparatus, are presented for an un‐annealed polypropylene sample, for a commercial poly(methyl methacrylate) specimen, for a sample of purified poly(methyl methacrylate) containing 1% water, for three poly(vinyl toluene) samples (in the 200–300°K. range), and for a 76% styrene‐24% acrylonitrile copolymer.
Dielectric study of the transition temperature regions for poly (vinyl chloride) and some chlorinated poly(vinyl chlorides)
Authors: Reddish W.
Published: June 2010

Audio frequency dielectric constant data versus temperature data for poly(vinyl chloride) exhibit a high temperature (glass) transition which becomes steeper and reaches higher values as the frequency is reduced. The same trend is demonstrated for a series of chlorinated poly(vinyl chlorides) although the transition decreases in magnitude and moves to higher temperatures systematically with increasing chlorine content. Corresponding loss data are presented. Dielectric constant values for poly(vinyl chloride), determined in the high temperature transition region from reversible (d.c.) polarization experiments, show that the trend to steeper and larger transitions continues as polarization lime increases. For 10,000 sec. polarization the curve exhibits a sharp peak with lambda point character and twice the highest a.c. value is reached. This dielectric constant peak is interpreted as a cooperative interaction in noncrystalline regions of long‐rod dipoles with moments perpendicular to the chain axes. This model is related to Natta's crystal structure for syndiotactic PVC where the assembly of planar molecules form an antipolar array. For PVC all the chlorines are on the same side of the axis but for chlorinated PVC, dipolar balancing due to 1,2‐dichloro groupings is responsible for the reduced transition magnitude. The high temperature process involves equilibrium of macroscopic volumes, whereas the low temperature transition, which is little affected by chlorination, involves local equilibrium only.
Non‐newtonian intrinsic viscosity and streaming birefringence of polymer solutions
Authors: Peterlin A.
Published: June 2010

The gradient dependence of intrinsic viscosity and streaming birefringence is a function of the orientation and deformation of the randomly coiled macromolecule in the viscous force field of the laminar flow. Orientation decreases the contribution of the coil to the shearing stress and deformation increases it. The anisotropy of hydrodynamic interaction favors orientation and slightly decreases deformation. Free deformation first increases and then decreases the hydrodynamic interaction thus causing the hydrodynamic resistance of the average chain segment and hence the intrinsic viscosity to pass through a minimum point. Finite chain length limits the expansion of coil and introduces saturation effects in viscosity and streaming birefringence. In the former it may eventually completely mask the effect of coil expansion on hydrodynamic interaction so that the minimum in the gradient dependence of viscosity may be observable with very long macromolecules only in good agreement with experimental data. In addition, the finite resistance of molecules to rapid change of coil shape also reduces the deformation and hence suppresses the up‐turn effect. The influence of coil rigidity is larger with low solvent viscosity and may be negligibly small with a very viscous solvent. Indeed, experiments with poly(methyl methacrylate) in Aroclor show effects characteristic for large‐coil deformation, i.e., a minimum in intrinsic viscosity and a subsequent increase with increasing gradient.
Synthesis of Polymers with Charged Heteroatoms in the Chain by the “Onium Polymerization” Method
Authors: Berlin A. A. , Razvodovskii E. F.
Published: June 2010

The method of “onium polymerization” was used for the preparation of conjugated polymers with quaternary nitrogen atoms in the main chain. The polymerization was studied for the case of 4‐chloropyridine, 4‐bromopyridine, and 4‐chloromethylpyridine. Poly‐4‐chloropyridine has increased electroconductivity and contains a considerable number of paramagnetic particles. The introduction of methylene groups between pyridinium nuclei results in the disappearance of this property. Poly‐4‐chloropyridine is soluble only in water, hydrolyzing rapidly to form pyridylpyridone and hydroxypyridine. Under the action of ammonia poly‐4‐chloromethylpyridine is transformed to the polymeric ilide.
Cooperative Interactions of Bound Ions and Sulfhydryl Groups in Hemerythrin
Authors: Keresztes‐Nagy S. , Klotz I. M.
Published: June 2010

Hemerythrin, the oxygen‐carrying protein of sipunculids, has been known in three forms: deoxy, oxy, met. A characteristic spectrum has been associated with each form. We have now found, from electrophoretic mobilites, that anions are bound to hemerythrin with concomitant large shifts in spectra. All of the ions showing these effects, N3−, HS−, SCN−, CNO−, Cl−, F−, and OH−, are known to form coordination complexes with Fe(III). Association constants have been evaluated for several of these complexes by spectrophotometric titration. The association is stronger with the protein in which the sulfhydryl group has been previously blocked. In a complementary manner, the reaction of hemerythric with mercaptan reagents, such as N‐ethylmaleimide, is very slow in the absence of iron‐coordinating ligands but rapid in the presence of ions such as N3− or SCN−. This cooperative interaction can be accounted for in either of two ways: (I) if under normal conditions hemerythrin is in equilibrium with a very small amount of its subunits (in which mercaptan groups are more accessible), bound ions would shift this equilibrium toward subunits; (Q) bound ions may produce a change of conformation in the macromolecule. Hybridization experiments provide strong evidence that the octamer → monomer equilibrium is the actual mechanism of the cooperative interactions.
Slereospecific copolymers 1,3‐butadiene‐2‐phenylbutadiene
Authors: Marconi W. , Mazzei A. , Lugli G. , Bruzzone M.
Published: June 2010

The results obtained in the stereospecific copolymerization of 1,3‐butadiene with 2‐phenylbutadiene are reported. The copolymers were generally obtained using catalysts prepared from substituted aluminum hydrides, AlI3 and TiCl4. Homopolymerization of 2‐phenylbutadiene with such catalysts gives an amorphous, low M.W. polymer having prevailing 1,4‐cis structure. In the copolymers the 2‐phenylbutadiene units still have a substantially cis structure; also the butadiene units are mainly 1,4‐cis up to 90‐95%. The 1,2 content in the copolymers is always very low. The content of 2‐phenylbutadiene units in the copolymers varies in a broad range from 10 to 80% and the reaction rate and the average molecular weight diminish as the phenylbutadiene increases. The monomer reactivity ratios were calculated and the distribution of sequence lengths in the copolymer chains was made by statistical analysis. The copolymer composition was determined by IR and NMR analysis and the results compared with spectra obtained from mechanical mixtures of the homopolymers. The formation of a true copolymer was confirmed by extractions, fractionations, and glass transition temperature determinations. Mechanical properties of the copolymers are given and compared with those of other polymers, in particular with those of 1,4‐cis polybutadiene.
Large deformation tensile properties of elastomers. I. Temperature dependence of c1 and c2 in the mooney‐rivlin equation
Authors: Smith Thor L.
Published: June 2010

Tensile stress‐strain data were determined at various extension rates and temperatures on unfilled butyl and silicone vulcanizates and on six hydrofluorocarbon (Viton A‐HV) vulcanizates that contain between 0.90 and 12.2 × 10−5 mole of effective network chains per unit volume of gel rubber. From 1‐min. isochronal data, values of C1 and C2 in the Mooney‐Rivlin equation were derived. For the butyl and silicone vulcanizates from, respectively, −20 to 150°C. and −45 to 200°C., C1 increases with temperature at a rate which is in reasonable agreement with published data from forcetemperature measurements. Because C2 is sensibly temperature independent over these extended temperature ranges, it is concluded that C2 is a finite quantity under equilibrium conditions. Time‐dependent behavior was observed on the Viton A‐HV vulcanizates between −5 and 230°C. For each vulcanizate between about 25 and 230°C., C1273/T is temperature independent, but it increases with decreasing temperature below about 25°C. Except at the lowest temperatures, C2273/T decreases with increasing temperature, the rate of decrease becoming progressively less with an increase in crosslink density. Above 25°C. the ratio C2/C1, which ranges from about 90 to 0.6, decreases with an increase in either temperature or crosslink density. The time‐dependent behavior of C2273/T appears to arise primarily from molecular processes whose relaxation times are considerably longer than the terminal relaxation time of individual chains.
Electrical and mechanical properties of anhydride‐cured epoxy resins
Authors: Shito Nobuhiko , Sato Mikio
Published: June 2010

A diglycidyl ether of bisphenol A was crosslinked with several acid anhydrides of different structures, such as the homologs of succinic anhydride and the acid anhydrides with a double bond or a ring structure. Dilatometric, dielectric, and dynamic mechanical measurements were carried out on the cured resins. The glass transition temperature is shown to be influenced by the presence of double bonds or ring structures in the chain backbones. The specific volume at the glass transition temperature can be predicted as a sum of atomic volumes. Two dielectric relaxation processes were observed in all the resins. The temperature dependence of the relaxation time for the α‐process can be represented by the WLF equation. The mechanical retardation time for the α‐process generally agrees with the dielectric relaxation time. The observed dynamic Young's modulus in the glassy state is nearly one‐third of the value calculated from the cohesive heat density. A good correspondence is obtained between the observed dynamic Young's modulus in the rubbery state and the Young's modulus calculated from the crosslinking density, but the deviation increases with decreasing crosslinking density.
A light‐scattering study of degradation of polyisoprenes
Authors: Vavra J.
Published: June 2010

The molecular weights of natural and synthetic polyisoprenes have been measured by the light‐scattering method. The changes of intensity of scattered light caused by heat aging of these rubbers in air have been investigated. During aging of natural rubber considerable depolymerization takes place, with simultaneous formation of new macromolecules with a higher degree of branching, as confirmed by the unusual shapes of Zimm diagrams. The experimental values of the Pθ functions have been compared with theoretical ones calculated from the combined Debye and Mie theories.
New transparent plastics of polyacrylonitrile
Authors: Shavit Nehemia , Konigsbuch Mordechai , Oplatka Avraham
Published: June 2010

The ordinary bulk polymerization of acrylonitrile (AN) yields a powdery precipitate or an aggregated white polyacrylonitrile (PAN). Only one case has been reported, previous to our work (presented in this and in another paper5), in which AgNO3 catalyst yielded a transparent PAN gel containing, however, 50% salt. We have found that conventional initiators can be employed in a bulk polymerization process, carried out under controlled conditions, to yield transparent rigid plastics of pure PAN. The process found involves a phenomenon of spontaneous transformation of the polymerizing system at high conversions from a heterogeneous polymer‐monomer mixture to a homogeneous transparent solid polymer. Processes employing benzoyl peroxide, α,α‐azobisiso‐butyronitrile, p‐toluene sulfinic acid, and mixtures of these, other catalysts, co‐catalysts, and additives are described. The transformation was found to depend on catalyst type and concentration, temperature, volume, and shape of the system as well as on the presence and supply of oxygen above the reaction mixture.
Laws of mechanical relaxation processes in polymers
Authors: Slonimsky G. L.
Published: June 2010

Certain distinctive characteristics of relaxation processes in polymers due to a chain structure of macromolecules and supermolecular structure of a polymeric body call for a new approach to their quantitative description. A mathematical method of description of relaxation processes based on the use of fractional integral operators is proposed.
Reactivities of alkyl methacrylates in their radical polymerization
Authors: Otsu T. , Ito T. , Imoto M. , Otsu Takayuki , Ito Toshio , Imoto Minoru
Published: June 2010

The effect of the alkyl group on radical polymerizations of alkyl methacrylates (RMA) has been investigated. From the results on copolymerizations of RMA(M2) with styrene or B‐chloroethyl methacrylate (M1), the relative reactivities (lr1) of RMA toward attack of polymer radicals were plotted by the Taft's equation: log (1/r1) = ρ* σ*+δE8. The plot could correlate with polar substituent constants (σ*), but not steric substituent constants (E8) of the alkyl substituents in RMA. These results might strongly indicate that the radical reactivities of RMA depended on the polar character of the alkyl groups, but not on their steric character. This conclusion is compared with other experimental results and discussed.
The relationship between unpaired spin concentration, structure, and electrical conduction of a pyrolytic aromatic polyimide
Authors: Bruck Stephen D.
Published: June 2010

When films of poly[N,N′‐(p,p′‐oxydiphenylene)pyromellitimide] are pyrolyzed in vacuum between 575 and 800°C., they are converted into products having electrical conductivities as high as 20 (ohm‐cm.)−1 measured at 25°C. This transformation of the polymer from an insulator into an electroconductor is accompanied by distinct changes in the electron paramagnetic resonance absorption (EPR) vs. time curves, x‐ray diffraction, elemental composition, and density. From the rates of EPR absorption, a tentative activation energy of 25 ± 3 kcal./mole was calculated for this internal transformation. The absence of polarization effects and the fact that repeated thermal cycling does not significantly diminish the observed electrical conduction suggest that it is electronic rather than ionic in character. The development of electrical conduction in the pyrolyzed polymer occurs well below the graphitization temperature and with the retention of considerable quantities of nitrogen and oxygen. Apparently a fused conjugated network with a large pool of π‐electrons and π‐orbital overlap develops and the reduction of interboundary resistance at sufficiently high temperatures causes the appearance of electrical conduction.