bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of the CALIPSO Lidar 532 nm attenuated backscatter calibration using the NASA LaRC airborne High Spectral Resolution Lidar
Authors: Rogers R. R. , Hostetler C. A. , Hair J. W. , Ferrare R. A. , Liu Z. , Obland M. D. , Harper D. B. , Cook A. L. , Powell K. A. , Vaughan M. A. , Winker D. M.
Published: February 2011

Abstract. The Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument on the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) spacecraft has provided global, high-resolution vertical profiles of aerosols and clouds since it became operational on 13 June 2006. On 14 June 2006, the NASA Langley Research Center (LaRC) High Spectral Resolution Lidar (HSRL) was deployed aboard the NASA Langley B-200 aircraft for the first of a series of 86 underflights of the CALIPSO satellite to provide validation measurements for the CALIOP data products. To better assess the range of conditions under which CALIOP data products are produced, these validation flights were conducted under both daytime and nighttime lighting conditions, in multiple seasons, and over a large range of latitudes and aerosol and cloud conditions. This paper presents a quantitative assessment of the CALIOP 532 nm calibration (through the 532 nm total attenuated backscatter) using internally calibrated airborne HSRL underflight data and is the most extensive study of CALIOP 532 nm calibration. Results show that HSRL and CALIOP 532 nm total attenuated backscatter agree on average within 2.7% ± 2.1% (CALIOP lower) at night and within 2.9% ± 3.9% (CALIOP lower) during the day, demonstrating the accuracy of the CALIOP 532 nm calibration algorithms. Additionally, comparisons with HSRL show consistency of the CALIOP calibration before and after the laser switch in 2009 as well as improvements in the daytime version 3.01 calibration scheme compared with the version 2 calibration scheme. Potential biases and uncertainties in the methodology relevant to validating satellite lidar measurements with an airborne lidar system are discussed and found to be less than 4.5% ± 3.2% for this validation effort with HSRL. Results from this study are also compared with prior assessments of the CALIOP 532 nm attenuated backscatter calibration.
Production, growth and properties of ultrafine atmospheric aerosol particles in an urban environment
Authors: Salma I. , Borsós T. , Weidinger T. , Aalto P. , Hussein T. , Dal Maso M. , Kulmala M.
Published: February 2011

Abstract. Number concentrations of atmospheric aerosol particles were measured by a flow-switching type differential mobility particle sizer in an electrical mobility diameter range of 6–1000 nm in 30 channels near central Budapest with a time resolution of 10 min continuously from 3 November 2008 to 2 November 2009. Daily median number concentrations of particles varied from 3.8 × 103 to 29 ×103 cm−3 with a yearly median of 11.8 × 103 cm−3. Contribution of ultrafine particles to the total particle number ranged from 58 to 92% with a mean ratio and standard deviation of (79 ± 6)%. Typical diurnal variation of the particle number concentration was related to the major emission patterns in cities, new particle formation, sinks of particles and meteorology. Shapes of the monthly mean number size distributions were similar to each other. Overall mean for the number median mobility diameter of the Aitken and accumulation modes were 26 and 93 nm, respectively, which are substantially smaller than for rural or background environments. The Aitken and accumulation modes contributed similarly to the total particle number concentrations at the actual measurement location. New particle formation and growth unambiguously occurred on 83 days, which represent 27% of all relevant days. Hence, new particle formation and growth are not rare phenomena in Budapest. Their frequency showed an apparent seasonal variation with a minimum of 7.3% in winter and a maximum of 44% in spring. New particle formation events were linked to increased gas-phase H2SO4 concentrations. In the studied area, new particle formation is mainly affected by condensation sink and solar radiation. The formation process seems to be not sensitive to SO2, which was present in a yearly median concentration of 6.7 μg m−3. This suggests that the precursor gas was always available in excess. Formation rate of particles with a diameter of 6 nm varied between 1.65 and 12.5 cm−3 s−1 with a mean and standard deviation of (4.2 ± 2.5) cm−3 s−1. Seasonal dependency for the formation rate could not be identified. Growth curves of nucleated particles were usually superimposed on the characteristic diurnal pattern of road traffic direct emissions. The growth rate of the nucleation mode with a median diameter of 6 nm varied from 2.0 to 13.3 nm h−1 with a mean and standard deviation of (7.7 ± 2.4) nm h−1. There was an indicative tendency for larger growth rates in summer and for smaller values in winter. New particle formation events increased the total number concentration by a mean factor and standard deviation of 2.3 ± 1.1 relative to the concentration that occurred immediately before the event. Several indirect evidences suggest that the new particle formation events occurred at least over the whole city, and were of regional type. The results and conclusions presented are the first information of this kind for the region over one-year long time period.
Transport of anthropogenic emissions during ARCTAS-A: a climatology and regional case studies
Authors: Harrigan D. L. , Fuelberg H. E. , Simpson I. J. , Blake D. R. , Carmichael G. R. , Diskin G. S.
Published: February 2011

Abstract. The National Aeronautics and Space Administration (NASA) conducted the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) mission during 2008 as a part of the International Polar Year (IPY). The purpose of ARCTAS was to study the factors responsible for changes in the Arctic's atmospheric composition and climate. A major emphasis was to investigate Arctic haze, which is most pronounced during winter and early spring. This study focuses on the spring phase of ARCTAS (ARCTAS-A) that was based in Alaska during April 2008. Although anthropogenic emissions historically have been associated with Arctic haze, biomass burning dominated the ARCTAS-A period and has been the focus of many ARCTAS related studies. This study determines the common pathways for anthropogenic emissions during ARCTAS-A. Trajectories (air parcels) are released each day from three historically significant regions of anthropogenic emissions (Asia, North America, and Europe). These fifteen day forward trajectories are calculated using data from the Weather Research and Forecasting (WRF) model at 45 km horizontal resolution. The trajectories then are examined to determine: origins of emissions that reach the Arctic (defined as north of 70° N) within fifteen days, pathways of the emissions reaching the Arctic, Arctic entry locations, and altitudes at which the trajectories enter the Arctic. These results serve as regional "climatologies" for the ARCTAS-A period. Three cases during the ARCTAS-A period (one for each of the regions above) are examined using backward trajectories and chemical fingerprinting based on in situ data sampled from the NASA DC-8. The fingerprinting utilizes volatile organic compounds that represent pure anthropogenic tracers, Asian anthropogenic pollution, incomplete combustion, and natural gas emissions. We determine flight legs containing anthropogenic emissions and the pathways travelled by these emissions. Results show that the DC-8 sampled anthropogenic emissions from Asia, North America, and Europe during the spring phase of ARCTAS. The pathways travelled by these emissions agree with our derived "climatologies" and previous studies of Arctic transport. Meteorological analysis and trajectory calculations indicate that middle latitude cyclones and their associated warm conveyor belts play an important role in lofting the surface based emissions to their sampling altitude in all three cases.
Processing of GRAS/METOP radio occultation data recorded in closed-loop and raw-sampling modes
Authors: Gorbunov M. E. , Lauritsen K. B. , Benzon H.-H. , Larsen G. B. , Syndergaard S. , Sørensen M. B.
Published: February 2011

Abstract. Instrument GRAS (Global Navigation Satellite System Receiver for Atmospheric Sounding) on-board of the Metop-A satellite was activated on 27 October 2006. Currently, Metop-A is a fully operational satellite with GRAS providing from 650–700 measurements per day. We describe our processing of GRAS data based on our OCC software, which was modified to become capable of reading and processing GRAS data. We perform a statistical comparison of bending angles and refractivities derived from GRAS data with those derived from ECMWF analyses. We show that GRAS data have error characteristics close to those of COSMIC data. In the height range 10–30 km, the systematic refractivity difference GRAS-ECMWF is of the order of 0.1–0.2%, and the standard deviation is 0.3–0.6%. In the lower troposphere GRAS refractivity and bending angle indicate a negative bias, which reaches its maximum value in the tropics. In particular, the retrieved refractivity is biased by up to 2.5%. The negative bias pattern is similar to that found in the statistical validation of COSMIC data. This makes it probable that the bias should not be attributed to the instrument design or hardware.
Desert dust and anthropogenic aerosol interactions in the Community Climate System Model coupled-carbon-climate model
Authors: Mahowald N. , Lindsay K. , Rothenberg D. , Doney S. C. , Moore J. K. , Thornton P. , Randerson J. T. , Jones C. D.
Published: February 2011

Abstract. Coupled-carbon-climate simulations are an essential tool for predicting the impact of human activity onto the climate and biogeochemistry. Here we incorporate prognostic desert dust and anthropogenic aerosols into the CCSM3.1 coupled carbon-climate model and explore the resulting interactions with climate and biogeochemical dynamics through a series of transient anthropogenic simulations (20th and 21st centuries) and sensitivity studies. The inclusion of prognostic aerosols into this model has a small net global cooling effect on climate but does not significantly impact the globally averaged carbon cycle; we argue that this is likely to be because the CCSM3.1 model has a small climate feedback onto the carbon cycle. We propose a mechanism for including desert dust and anthropogenic aerosols into a simple carbon-climate feedback analysis to explain the results of our and previous studies. Inclusion of aerosols has statistically significant impacts on regional climate and biogeochemistry, in particular through the effects on the ocean nitrogen cycle and primary productivity of altered iron inputs from desert dust deposition.
An aerosol dynamics model for simulating particle formation and growth in a mixed flow chamber
Authors: Vesterinen M. , Korhonen H. , Joutsensaari J. , Yli-Pirilä P. , Laaksonen A. , Lehtinen K. E. J.
Published: February 2011

Abstract. In this work we model the aerosol size distribution dynamics in a mixed flow chamber in which new particles are formed via nucleation and subsequent condensation of oxidation products of VOCs emitted from Norway spruce seedlings. The microphysical processes included in the model are nucleation, condensation, deposition and coagulation. The aerosol dynamics in the chamber is a competition between aerosol growth and scavenging/deposition which results in a cyclic particle formation process. With a simple 1-product model, in which the formed gas is able to both condense to the particles and nucleate, we are able to catch both the oscillatory features of the particle formation process and the evolution of the number concentration in a reasonable way. The gas-phase chemistry was adjusted using pre-estimated reaction rate constant in the simulations and the particle deposition rate as a function of size was determined experimentally. Despite this, some of the essential features of the physical properties of the aerosol population could still be captured and investigated without the detailed knowledge of the physical processes underlying the problem by using the constructed model. The size dependency of the wall loss coefficient was investigated using a slightly modified measurement set-up.
"A not completely satisfactory attempt" – peak discharges and rainfall-runoff relations for Javanese rivers between 1880 and 1940
Authors: Ertsen M. W.
Published: February 2011

Abstract. In the early 19th century, the Dutch colonial power started to build irrigation works. A main problem for Dutch irrigation engineers on Java was how to ensure that the structures they built remained intact. The peak discharge regime of a river was an issue closely related to dam safety. Modifying the approach of Swiss engineer Lauterburg (1877), Dutch irrigation engineer Melchior developed a methodology to determine design peak flows of Javanese rivers. The Melchior methodology has been the standard method throughout the colonial period, despite sometimes severe criticisms on its appropriateness. In independent Indonesia, the approach developed by Melchior continues to be applied. This paper discusses and explains the endurance of the method developed by Melchior. The focus is on the scientific interaction between different participants. The paper shows how participants from these circles debated and which arguments they exchanged.
Probabilistic coastal vulnerability assessment to storms at regional scale – application to Catalan beaches (NW Mediterranean)
Authors: Bosom E. , Jiménez J. A.
Published: February 2011

Abstract. A methodology to assess storm-induced coastal vulnerability taking into account the different induced processes separately (inundation and erosion) is presented. It is based on a probabilistic approach where hazards time series are built from existing storm data and later used to fit an extreme probability function. This is done for different sectors along the coast defined in terms of the wave climate and for representative beach types of the area to be analyzed. Once probability distributions are available, coastal managers must decide the probability of occurrence to be accepted as well as the period of concern of the analysis in function of the importance of the hinterland. These two variables will determine the return period to be considered in the assessment. The comparison of hazards and vulnerabilities associated with the selected probability of occurrence permit to identify the most hazardous areas along the coast in a robust manner by including the spatial variability in forcing (storm climate) and receptor (beaches). The methodology has been applied to a 50 km long coastal stretch of the Catalonia (NW Mediterranean) where offshore wave conditions can be assumed to be homogeneous. In spite of this spatially constant wave field, obtained results indicate a large variability in hazards intensity and vulnerability along the coast.
Role of multifractal analysis in understanding the preparation zone for large size earthquake in the North-Western Himalaya region
Authors: Teotia S. S. , Kumar D.
Published: February 2011

Abstract. Seismicity has power law in space, time and magnitude distributions and same is expressed by the fractal dimension D, Omori's exponent p and b-value. The spatio-temporal patterns of epicenters have heterogeneous characteristics. As the crust gets self-organised into critical state, the spatio-temporal clustering of epicenters emerges to heterogeneous nature of seismicity. To understand the heterogeneous characteristics of seismicity in a region, multifractal studies hold promise to characterise the dynamics of region. Multifractal study is done on seismicity data of the North-Western Himalaya region which mainly involve seismogenic region of 1905 Kangra great earthquake in the North-Western Himalaya region. The seismicity data obtained from USGS catalogue for time period 1973–2009 has been analysed for the region which includes the October 2005 Muzafrabad-Kashmir earthquake (Mw =7.6). Significant changes have been observed in generalised dimension Dq, Dq spectra and b-value. The significant temporal changes in generalised dimension Dq, b-value and Dq−q spectra prior to occurrence of Muzaffrabad-Kashmir earthquake relates to distribution of epicenters in the region. The decrease in generalised dimension and b-value observed in our study show the relationship with the clustering of seismicity as is expected in self-organised criticality behaviour of earthquake occurrences. Such study may become important in understanding the preparation zone of large and great size earthquake in various tectonic regions.
Nursing care in the Conceptual Model and Theory of Goal Attainment
Authors: Bezerra Sara Taciana Firmino , Silva Lúcia De Fátima da
Published: February 2011

ABSTRACTObjective: to present the conceptual model of open systems and King's Theory of Goals Attainment, as well as its contribution for nursing practice, approaching the need of an health assistance with the objective of attend society needs and develop the critical conscience in order to provide positive changes in people's lifestyle and the care aiming the valorization of the other, in order to stimulate active participation of the clientele in the health-disease-care process. Method: this is a reflection on the theory as support to the nursing interactive assistance. Results: we believe that the presented theory can contribute to the nursing practice. Final considerations: based on the theoretical-conceptual reference we have an alternative of humanized nursing care ruled in the interaction between professional and customer in order to propitiate the improvement of health and well-being of the clientele. Descriptors: health; nursing; nursing theory; models theoretical.RESUMOObjetivos: apresentar o modelo conceitual de sistemas abertos e a Teoria do Alcance de Metas de King; discutir a sua contribuição à prática do (a) enfermeiro (a), abordando a assistência à saúde que atenda às necessidades da sociedade no intuito de desenvolver a consciência crítica proporcionando mudanças positivas no estilo de vida das pessoas e o cuidado com vista à valorização do outro, de modo a estimular a participação ativa da clientela no processo de saúde-doença-cuidado. Método: reflexão sobre a teoria como subsídio para a assistência interativa de enfermagem. Resultados: acredita-se que a teoria apresentada poderá contribuir à prática da enfermagem. Considerações finais: a partir do arbouço teórico-conceitual, tem-se uma alternativa de cuidado de enfermagem humanizado, pautado na interação entre profissional e cliente, de modo a propiciar a melhoria da saúde e o bem-estar da clientela. Descritores: saúde; enfermagem; teoria de enfermagem; modelos teóricos.RESUMENObjetivo: presentar el modelo conceptual de sistemas abiertos y la Teoría de Alcance de Metas de King, y su contribución para la práctica del enfermero, señalando la necesidad de una asistencia de salud con la pretensión de atender a las necesidades de la sociedad y desarrollar la conciencia crítica de modo a proponer câmbios positivos en el estilo de vida de las personas y la atención con objetivo de valorar el otro, para estimular la participación activa de la clientela en el proceso de salud-enfermedad-atención. Método: reflejo sobre la teoría como soporte para la asistencia interativa de enfermería. Resultados: se cre que la teoria presentada podrá contribuir como posibilidad para la atención humanizada. Consideraciones finales: delante de marco teórico-conceptual, se mira una alternativa de atención de enfermería humanizado, basada en la interacción entre el profesional y cliente, para promover la mejoría y el bienestar de la clientela. Descriptores: salud; enfermería; teoría de enfermería; modelos teóricos.
Ozone and Sunlight Effect on Aging of Carbon Black Vulcanizates
Authors: Popp George E. , Harbison Lynn
Published: February 2011

Carbon black, regardless of type, particle size, structure, and physical properties imparted, does not affect the rate or degree of checking or cracking in natural-rubber or low-temperature polymer compounds when subjected to weather or ozone exposure. Natural rubber will withstand much longer periods of exposure than the synthetic polymer studied. A pronounced degree of ozone and weather cracking and checking will result if no antioxidant is compounded into the synthetic polymer. An MAF black-synthetic polymer compound may be substantially improved in its resistance to ozone and weather resistance by selection and application of the proper antichecking ingredients.
Physical Properties of Natural and Synthetic Rubber Materials at Low Temperatures
Authors: Lichtman J. Z. , Chatten C. K.
Published: February 2011

A torsional apparatus and a hardness indentation tester have been found to be essentially equivalent for use in evaluating the stiffness characteristics of elastomers over a range of low temperatures. The torsion apparatus, requiring the use of relatively small specimens, facilitates carrying out various conditioning cycles on a material, such as liquid immersion or atmospheric aging. The indentometer, on the other hand, permits the employment of larger sized specimens or even samples, such as relatively thick gasket stocks. There are, then, individual advantages in each apparatus which would determine the choice to be made in selecting a test method for a particular specification.
Crystallization and Tensile Strength of Vulcanized Natural Rubber Compounds
Authors: Morrell S. H. , Stern Jan
Published: February 2011

The effect which changes in the degree of cross-linking have on the crystallization of stretched rubber has been studied by observing the densities of a series of peroxide-cured natural rubber compounds. It was found that at any one elongation, crystallization first increased and then decreased with increase in the degree of cross-linking. The significance of this maximum and the relation between crystallization and tensile strength are discussed.
A Tentative Explanation of the Weissenberg Effect in Latex Solutions
Authors: Frei E. H. , Katchalsky A.
Published: February 2011

Shearing motion produces in certain liquids, not only shearing stresses but also stresses in other directions. This effect, described by Garner and Nissan and by Weissenberg, was treated theoretically by Oldroyd, Reiner, and Rivlin. It will be shown that the last two theories are an oversimplification and do not describe the more complicated behavior of slightly vulcanized latex solutions.
The Direct Reinforcement of Rubber in Latex. II. Synthetic Resins Formed in Situ by the Addition to Latex of the Starting Materials of Their Resinification
Authors: Piccini Ivan
Published: February 2011

This study makes it clear that fillers ordinarily used in the rubber industry impair the properties of latex mixtures. On the other hand, certain organic fillers, in solution and in dispersion, which are susceptible to certain chemical modifications within the latex mixtures in which they have been incorporated, and with which they are compatible, have a favorable effect. Consequently, by introducing into a latex mixture which can be gelled and vulcanized a suitable quantity of formaldehyde-resorcinol resin, in particular a soluble formaldehyde-resorcinol resin, prepared in slightly alkaline pH medium under certain carefully defined conditions, it was possible : (1) for the first time to obtain reinforced articles directly from natural rubber latex, and (2) to obtain an ensemble of properties superior to those at present known in the rubber world. The reinforcement which has been found does not seem attributable to any chemical combination between rubber and resin, but rather to a specific structure of the resin-rubber mixture. The way is now open to the direct use of latex in applications which were undreamed of previously. In fact, reinforced latex, possessing extremely high qualities, must be considered a new material, and it offers to technologists in the latex industry the opportunity to explore applications to heavy industry, such as belts, pneumatic tires, hose, and mechanical articles which must have high quality. Tests have already been undertaken in this direction, and they have given promising results and are being pursued actively. We may assume that, in the not too distant future, certain articles of reinforced latex will be manufactured on an industrial scale.
The Role of Carbon Black in the Action of Light on Rubber
Authors: Zuyev Y. S.
Published: February 2011

The action of light on rubber was studied with reference to the rate of elongation at constant stress of films, 100–150µ thick, obtained from solutions of rubber to which channel carbon black had been added by milling. The measurements were made in an apparatus, described earlier, which was equipped with a rolling carriage. When structure formation takes place as a result of irradiation of a film, the film stretches more slowly than one that has not been irradiated. If the structure is destroyed, the film elongates at a faster rate. The films were irradiated by a mercury quartz lamp P RK-2 in air at a distance of 5 cm., both when relaxed (preliminary irradiation) and while stretched (continuous irradiation). The light filters listed in Table 1 were used. The average temperature in the experiments was 25° ± 0.1° C. A film was stretched in the quartz apparatus, which was equipped with a jacket, about 1 cm. thick, in which distilled water or a solution of the light-filtering substance was circulated. The water and also the solutions were provided with an ultra-thermostat. The temperature of the water leaving the jacket was measured by a thermometer, and was kept constant within ± 0.1° C.
The Load Dependence of Rubber Friction
Authors: Schallamach A.
Published: February 2011

It is shown experimentally that the load dependence of rubber friction can be explained as being due to the load dependence of the true area of contact between rubber and track if the surface asperities of the rubber are assumed be hemispherical.
Statistical Mechanics of Rubber
Authors: Boggs F. W.
Published: February 2011

It is shown in this paper that, above the second-order transition, the partition function of a rubber can be represented to a reasonably good approximation by the product of the partition function of a liquid formed of molecules similar to the chain elements and the partition function of the noninteracting chains divided by the partition function of a perfect gas. In terms of the free energy this means that the free energy of rubber is equal to the sum of the free energy of the chain network without interactions and that of a liquid formed of the chain elements alone minus the free energy of a perfect gas having the same number of molecules as the rubber has chain elements. This same procedure has made possible the calculation of the free energy and partial pressure of a rubber solution. This is, however, by no means the only possible application. All the thermodynamic properties of elastomer solvent systems can be obtained. This is a generalization of the methods previously used in the statistical studies of rubber and rubber solvent mixtures.
Ideal Copolymers and the Second-Order Transitions of Synthetic Rubbers. I. Noncrystalline Copolymers
Authors: Gordon Manfred , Taylor James S.
Published: February 2011

Theoretical and practical evidence is put forward to show that copolymers can be treated like solutions of small molecules in the interpretation of packing phenomena, and that ideal volume-additivity of the repeating units in copolymers is frequently realized. On this basis equations are derived for predicting θ, the second-order transition temperature, of binary copolymers from the two second-order transition temperatures of the pure polymers and their coefficients of expansion in the glassy and rubbery states. Previous mechanistic theories of the second-order transition temperature of such copolymers are thus superseded by a general reduction of the problem to the mechanism of thermal expansion. Practical applications to the choice of monomers in producing synthetic rubbers are outlined, and attention is drawn to the importance of second-order transitions in kinetic measurements on the reactions of polymers.
Mastication of Rubber. I. Mechanism of Plasticizing by Cold Mastication
Authors: Pike M. , Watson W. F.
Published: February 2011

The process of cold mastication has been rationalized in terms of recognized chemical reactions, and its essential difference from the hot mastication process has been demonstrated. Many apparently unrelated phenomena occurring on cold mastication, as, for example, are collected in a recent survey, can be interpreted as specific manifestations of the general scheme now presented. A clearer understanding of the basic function of the masticator is relevant to the design of such machines, i.e., the provision of high shearing forces for low-temperature chain rupture and the exposure of large surface area for high-temperature autoxidative breakdown. No acceleration of cold plasticization by added compounds is normally obtainable under the shear conditions of the Banbury mixer, but may be encountered under more efficient shear and in oxygen-deficient conditions. Cold mastication is revealed as a versatile method for producing rubbers of a wide variety of physical properties, i.e., softer (linear degraded) rubbers, harder and soluble (branched or cross-linked) rubbers, and insoluble (cross-linked) rubbers.
A Study of the Chlorination of Natural Rubber
Authors: Koningsberger C.
Published: February 2011

In 1939 there appeared a series of very interesting communications dealing with the chlorination of simple olefinic hydrocarbons. In these papers it was shown, in conjunction with other experimental work, that branched-chain hydrocarbons like 2-methylpropene and trimethylethylene are attacked by chlorine, with formation chiefly of substitution products, at least in the first stage of the reaction: This substitution, which was, as a matter of fact, demonstrated long ago by Scheschukov in 1884 and by Kondakov in 1885, predominates at room temperature, and also at elevated temperatures, over the addition reaction. In the works cited above, the experiments are described in detail and quantitative data are presented to show that, by means of fractional distillation of the reaction products, the yields of allyl monochlorides are of the order of 80–90 per cent. Now during the last War, chemical investigations by the British Rubber Producers' Research Association, and independently by the Rubber Foundation at Delft, established the fact that this same primary substitution reaction takes place when natural rubber is treated in solution with chlorine. The researches of the British Rubber Producers' Association have already been published, and the experiments described in the present paper represent some of the results obtained in the laboratory at Delft. As will be seen, the latter work is in good accord with the work described by Bloomfield.
Factors Affecting the Stability of Hevea Latex. II
Authors: Paton F. F. , Peel J. D. , Sutno G.
Published: February 2011

Latex from clone Glenshiels 1 (G.1) is always unstable. It contains insufficient phosphate to precipitate its magnesium on ammoniation. After centrifuging, magnesium remains in the concentrated latex and is partly responsible for its abnormal properties, especially for its low mechanical stability and abnormal gelling characteristics. The properties are improved by the addition of phosphates before processing. The concentration of magnesium on the rubber phase is such that in 60 per cent d.r.c. latex one-third of the magnesium is associated with the rubber particles. By almost completely interchanging the serum of G.1 concentrate with that of a seedling latex, a marked improvement in stability and gelling characteristics is brought about. In preliminary experiments, concentrate prepared from G.1 white fraction showed less abnormality than concentrate from the whole latex.
The Influence of the Test-Specimen on the Results Obtained In Tensile Tests of Soft Vulcanized Rubber Mixtures
Authors: Herzog R. , Burton R. H.
Published: February 2011

The small test-specimen of the VSM-1 type should not be used for measuring the tensile properties of pure-gum vulcanizates; instead, the VSM-1a type of test-specimen should be used for such vulcanizates. Results obtained with the different types of test-specimen differ greatly; hence, in reporting the results of any tests of this kind, the type of test-specimen used should be stated, and only results obtained with one particular type of test-specimen should be compared. For example, substitution of the VSM-2 type of test-specimen by the KTA-II type of test-specimen, which is of approxmately the same size, unfortunately does not result in any better agreement. Based on these differences, which in the case of natural rubber have been found to vary from one type of vulcanizate to another, it is natural to expect corresponding unpredictable differences with various synthetic elastomers. The determination of stress-strain properties of soft rubber vulcanizates is, therefore, fundamentally a problem of agreement on methods of testing, i.e., of standardization.
Determination of Particle Size in Latex
Authors: Cockbain E. G.
Published: February 2011

The soap titration method of determining average particle sizes in synthetic latexes has been modified so as to make it applicable to natural rubber latexes. The method consists essentially in determining the distribution of an added detergent (sodium dodecyl sulfate) between the rubber and aqueous phases at a pH of approximately 6.0, the total dodecyl sulfate concentration being just sufficient for the formation of micelles in the aqueous phase. The average particle sizes of nine ammoniated latexes have been measured, including centrifuged and electrodecanted concentrates, two clonal field latexes and a sample of latex skim.
Polyurethanes. IX. New Types of Highly Elastic Products: Vulcollans. Part 2
Authors: Müller E. , Bayer O. , Petersen S. , Piepenbrink H. F. , Schmidt F. , Weinbrenner E.
Published: February 2011

In the 6th Communication on the general subject of urethanes, it was shown that, in the presence of an excess of a diisocyanate, in particular naphthalene 1,5-diisocyanate, linear polyesters of adipic acid and simple glycols simultaneously lengthen and become converted into so-called polyester isocyanates, with the isocyanate groups as terminal groups of the chains. While this earlier work was concerned with the problem of cross-linking to form the synthetic elastomer, Vulcollan, with water as the agent, the work described in the present paper deals with other cross-linking agents, including glycols, aminoalcohols, diamines, and other bifunctional compounds. The mechanism of cross-linking is discussed for each of these cases, and it is shown that the chemical nature of the cross-linking agent has a decisive influence on the properties of the resulting Vulcollan product. The methods of preparation which are described point the way to new manufacturing processes, particularly the possibility of molding Vulcollan without having to use a solvent.
Effect of Associated Salts on the Polymerization of Butadiene by Organosodium Reagents
Authors: Morton Avery A. , Bolton Frank H. , Collins Frances W. , Cluff Edward F.
Published: February 2011

The alfin catalyst is a combination of sodium salts which causes butadiene to polymerize at extreme rapidity in such a fashion that a greater difference exists between sodium and alfin polymerization than between sodium and emulsion polymerization. Hitherto the combination has been assumed to be binary—allylsodium and sodium isopropoxide—but a new method of preparation has revealed that a halide or pseudohalide salt is essential. Chloride, bromide, and iodide salts of sodium and potassium can be used as the halide component, but fluoride and lithium salts, as a rule, cannot be so employed unless the small size of each ion is compensated by a large cation or anion, respectively, as found in cesium fluoride or lithium iodide. The sodium cation is required for the catalyst. The potassium ion can be tolerated in the alkoxide or halide, but not simultaneousely in both. The lithium ion is in general unsuitable. Alfin polybutadiene is differentiated from sodium-polymerized butadiene by a high proportion of 1,4-structure and by an abnormally high intrinsic viscosity. Iodine chloride causes the polymer to precipitate from solution. All results indicate that polymerization by sodium reagents is in considerable degree controlled by the association of other salts with the sodium reagent.
Effect of Oxygen Concentration on Aging of Rubber Vulcanizates. II. Effect of Partial Pressure of Oxygen on Changes in Physical Properties Accompanying Oxidation
Authors: Shelton J. Reid , Cox William L.
Published: February 2011

The over-all rate of deterioration of physical properties increases with the oxygen concentration, as would be expected from the increased rate of oxygen absorption: The nature of the deterioration resulting from a given amount of oxygen absorbed is influenced also by changes in the partial pressure of oxygen in the aging atmosphere. It appears that chain scission is favored at higher oxygen concentrations, while cross-linking becomes of greater relative importance at lower oxygen concentrations. These data suggest that R⋅ radicals are more effective than RO2⋅ radicals in reacting with double bonds to form crosslinks. Heat aging in the absence of oxygen, as observed by heating a vulcanizate in lamp-grade nitrogen, results in considerable stiffening, particularly in the case of a GR-S black stock. This effect is observed primarily in the first few hours of heating, and may account for some of the erratic behavior observed in the early stages of aging when changes in physical properties are compared on the basis of amount of oxygen absorbed. Higher oxygen concentration brings about a more rapid oxidation, and also results in a higher proportion of chain scission compared to cross-linking for a given amount of oxygen absorbed. As tensile decay is the most evident sign of deterioration of Hevea stocks, it follows that the aging behavior of natural rubber in air at normal storage temperatures will be better than that predicted by high temperature testing in oxygen. In the case of GR-S stocks, on the other hand, oxidative hardening is the most serious result of aging, and consequently, the aging behavior of GR-S stocks in air at normal storage temperatures is poorer than would be expected on the basis of comparative tests in oxygen at higher temperatures.
Technically Classified Rubber—The Non-Rubber Content and the Measurement of Cure Rate
Authors: Veith A. G.
Published: February 2011

The nonrubber content of typical samples of all grades of technically classified rubber has been determined. It is found that the nonrubber content increases in the order: red, yellow, and blue. The chemical analyses performed to determine the nonrubber content were as follows: per cent ash, per cent nitrogen, per cent acetone extract, and per cent fatty acid. The pH of both a slurry of the ash and the aqueous digest indicates that blue rubber is more basic in these respects than are red and yellow rubbers. The measurement of the cure rate of these samples of technically classified rubber has been carried out by means of (1) conventional stress-strain testing, (2) the present ASTM method utilizing the Mooney viscometer, (3) the National Bureau of Standards strain test, (4) a new and more quantitative approach developed by Gee and coworkers, and (5) a utilization of the Mooney viscometer to determine two of the parameters of Gee's equation which gives the time dependence of modulus. All of these methods place the rubbers in the same relative order. The use of the viscometer to determine two of the parameters of Gee's equation was prompted by the degree of correlation between the rate parameter obtained with the present ASTM method and the rate constant k calculated by Gee's methods. As a result of a preliminary investigation as to the causes of viscosity increases at curing temperatures, it was found that, within limits of experimental error, all of the viscosity increase is due to the formation of a cross-linked network, with a linear relationship existing between viscosity increase ΔVc and modulus (at 100 per cent elongation) f. The results of a comparison of the rate constants obtained by the viscometer and by Gee's method indicate that for MBT mixes at 260° F there is good agreement between the methods. Statistical analysis shows that the samples employed for this study are significantly different in their rate of cure. The variance, range, and mean of some of the parameters obtained with the viscometer over a 10-week period are also given. It is suggested that the Mooney viscometer be employed to classify natural rubber according to its cure rate. If this is done, it will be necessary to define the degree of accuracy desired. To determine accurately the cure rate, it is necessary that the viscometer be used in conjunction with a press cure for the estimation of the parameter f∞. If it is not feasible to carry out press cures, an average value for f∞ can be assumed, and then only a short time test with the viscometer is required.
Evaluation of Ozone Protective Agents for Elastomers. Apparatus for the Evaluation under Dynamic Conditions
Authors: Creed K. E. , Hill R. B. , Breed J. W.
Published: February 2011

The widespread acceptance of synthetic elastomers for use in rubber products has greatly magnified the problem of obtaining satisfactory protection against weathering in general and ozone attack in particular. Because the tentative ASTM method of evaluation is not entirely satisfactory, a dynamic apparatus has been developed which provides an effective means for accelerated evaluation of ozone protective agents, using a new mechanical arrangement for flexing the rubber, a new specimen shape, rigid control of the ozone concentration, and a new rating system. The apparatus consists of a series of rotating pulleys within a circular chamber. The test-specimens, circular molded belts, are rotated around two pulleys, which gives them approximately 75 flexes per minute with an elongation of 0 to 20 per cent. The flexing provides a mobile surface, so that rigid waxy films cannot be formed, and the molded specimen eliminates the possibility of freak cracking and anomalies due to minute nicks or imperfections during dieing out. The larger surface available for examination facilitates interpretation of results. Air at a rate of 1 cubic meter per hour passes through the chamber with a controlled ozone concentration of 25 ± 5 parts per 100,000,000 at 30° C. Uniformity is ensured by use of a fan in the chamber. The concentration of ozone is determined by potassium iodide method. By a simplified rating system a non-technical person can rate a large number of specimens rapidly and without elaborate equipment.
Aids in Vulcanization of Lignin-Natural Rubber Coprecipitates. Lead, Copper, and Bismuth Oxides
Authors: Griffith T. R. , MacGregor D. W.
Published: February 2011

No difficulty is experienced in the vulcanization of natural rubber containing lignin added as a dry powder, but this method of addition results in relatively low tensile strengths. When lignin solution was added to latex, however, the masterbatch obtained by coprecipitation was difficult to vulcanize. For example, if conventional acceleration was used, i.e., mercaptobenzothiazole with zinc oxide, the test slabs were soft, tacky, and logy, and could be removed from the mold only with difficulty. Although hydrogen sulfide might be a necessary intermediate in the vulcanization reaction, published experimental evidence shows that an excessive concentration of hydrogen sulfide retards vulcanization, even in the presence of powerful organic accelerators. In order to test the possibility that the retardation of cure with lignin master batches might be due to excessive hydrogen sulfide developed during vulcanization, owing to reaction of sulfur with lignin, various metallic oxides were tried which might react with hydrogen sulfide to form insoluble sulfide, and so reduce the hydrogen sulfide concentration. Lead oxides, copper oxide, and bismuth oxide were successful with lignin masterbatches, particularly when used with a dithiocarbamate accelerator. A lignin compound containing litharge, curing in 20 minutes at 282° F, had a tensile strength about 800 pounds per square inch above that obtainable with MPC carbon black. The Bashore resilience figure for the lignin compound was about double that for MPC carbon black. The aging qualities of vulcanizates containing lead oxide and lignin appear to be good, and even copper oxide, which is normally considered to be detrimental, ages satisfactorily, provided an antioxidant is included. A lignin compound containing 7 parts of copper oxide on 100 parts of rubber and 2 parts of antioxidant showed a drop of less than 20 per cent of its tensile strength after 2 days in an air oven at 90° C.
Cross-Linking in Natural-Rubber Vulcanizates
Authors: Adams H. E. , Johnson B. L.
Published: February 2011

Recently, a method for measuring the average number of cross-links per chain of vulcanized polymer has been developed. It is possible to calculate the degree of cross-linking of the vulcanizate from its amount of swelling in a solvent such as benzene. This method was used by Flory to study the effect of primary molecular weight on the cross-linking of Butyl vulcanizates. An evaluation of the general validity of the method was ascertained by using quantitative cross-linking agents (diazodicarboxylates) to prepare vulcanizates of natural rubber and GR-S. Bardwell and Winkler have also used this technique to study the relationship between the degree of cross-linking and the force of retraction at 300 per cent elongation of GR-S latex vulcanized with potassium persulfate. The formation of cross-linking during the vulcanization by sulfur of several polymers has also been investigated. Gee has compared the formation of cross-linking in natural rubber vulcanizates with the amount of combined sulfur. Carbon-to-carbon cross-links were believed to be formed in a nonsulfur tetramethylthiuram disulfide (TMTD) cure. A similar study of Butyl rubber vulcanizates, cured with sulfur-TMTD, indicates that disulfide cross-links are formed. Scott and Magat have estimated that eight sulfur atoms are associated with each cross-link in Russian SK (sodium polybutadiene). This investigation was undertaken to extend Gee's study on the correlation of the cross-linking of natural-rubber vulcanizates with the amount of combined sulfur.
The Viscometric Detection of Branching in Polymers. I. Branching in GR-S as a Function of Conversion
Authors: Cragg L. H. , Brown A. T.
Published: February 2011

Samples of GR-S were taken from a continuous emulsion-polymerization system at conversions 32.0, 45.1, 61.2, and 73.4 per cent, respectively, and each, after careful drying, was carefully fractionated to give five or six top fractions. For each of these fractions, values of intrinsic viscosity [η] and of the viscosity slope constants, β and k′, were determined. As with normal and cross-linked polystyrene, β and k′ appear to be constant for all linear species, but to have higher values for branched species, the increase being a measure of the extent or degree of branching. From the data obtained it is concluded that in GR-S there is little or no branching at low conversions, that the degree of branching increases markedly with increasing conversion, and that branching occurs to the greatest degree in the species of highest molecular weight. There seemed to be, for this polymer at least, a molecular weight below which branching could not be detected, regardless of conversion, but above which branching increased with increasing molecular weight.