bluuebunny/crossref_metadata_2025 huggingface dataset:
Bend-Brittle and Shatter Points of Rubberlike Materials
Authors: King Glenn E.
Published: February 2011

Within the past two years the performance of rubberlike compositions at low temperatures has become important. A number of tests have been devised to measure the loss of rubberlike properties of many of these compositions. As the temperature is lowered, the first indication of the loss of rubberlike properties is hardening of the material. As the temperature is lowered further, the material continues to stiffen and harden to a point where it becomes quite inflexible; bending or striking with a solid object then causes breaking or shattering, due to the brittleness of the material. Up to this time the temperature at which breaking occurs has been called the “brittle point” of the material, with no distinction between the temperature at which breaking occurs on bending and the temperature at which breaking occurs on striking with a sharp blow from a solid object. It would be easy to assume that the two points occur at the same temperature. Koch tested the brittle point of elastic materials by measuring the bend stress with a micrometer gauge placed in the center of the specimen that was supported at each end. By observing the distortion caused by weights, the elastic modulus could be measured to the breaking point, which occurred at a definite temperature. This bend-brittle temperature was called the “high elasticity” temperature by Houwink and the “elasticity” temperature by Whitby. An apparatus was developed by the Thiokol Corporation for determining the flexibility of rubberlike materials at low temperatures. The samples are mounted between two plates and bent by turning a crank. The apparatus was designed so that the distance between the plates can be varied. The temperature of breaking was called the “brittle point”.
Evaluating Low-Temperature Stiffness and Brittle Point in Elastomers
Authors: Graves Floyd L. , Davis Arnold R.
Published: February 2011

The illustrations indicate some of the possibilities in our method of evaluation. The urgency of the times requires that all workers come forward with any new test methods that may be of value in developing better compounds, without consuming valuable time investigating all of the possibilities and limitations of such methods. Possibly other workers will wish to apply the methods described, in their studies on the effects of plasticizers, curing times and temperatures, reenforcing fillers, etc., in low-temperature compounding of the various new elastomers being pressed into service today.
The Effect of Petroleum Solvents. On the Cold Resistance of Synthetic Vulcanizates
Authors: Morris Ross E. , James Robert R. , Berger Emil H. , Werkenthin Theodore A.
Published: February 2011

It is concluded that immersion in light petroleum solvents improves the cold resistance of synthetic vulcanizates, and that the greater is the aromatic eontent, i.e., the lower the aniline point, of the solvent, the greater will be this improvement.
Determination of Mercury in Rubber
Authors: Luke C. L.
Published: February 2011

A very simple method has been developed for the separation of iodine from mixtures of mercury and iodine previous to determination of the mercury by the Volhard method. The method has been applied successfully to the determination of small amounts of mercury in. rubber samples containing iodine. The Rupp method has been investigated.
The Course of Autoöxidation Reactions in Polyisoprene and Allied Compounds. III. The Oxidation of Rubber in the Presence of Acetic Acid or Acetic Anhydride
Authors: Bloomfield George F.
Published: February 2011

Oxidation of rubber by oxygen in the presence of acetic anhydride leads to formation of highly oxygenated products containing a considerable proportion of acetoxyl groups. The residual unsaturation of the products of highest acetoxyl content, taken in conjunction with other analytical characteristics, indicates that three, rather than two, acetoxyl groups normally combine with each isoprene unit attacked. Although the bulk of the oxygen introduced is present in the form of acetoxyl groups, a portion occurs as carboxyl and carbonyl groups; also, whenever acetic acid is used (partly or wholly) in place of acetic anhydride, some free hydroxyl groups appear in the oxidized rubber. The proportions of carboxyl and carbonyl groups observed can be correlated satisfactorily with the extent of chain-scission occurring during the oxidation, the groups in question forming the new ends of the severed molecules. Hydrolysis of the acetylated products yields hydroxy acids, which readily undergo lactonic elimination of water. Acetic anhydride and acetic acid can clearly act as auxiliary reagents in autoöxidation reactions, and the detailed results obtained with rubber can be best accounted for on the basis of α-methylene peroxidation, followed by decay reactions involving incorporation of the auxiliary reagent as well as oxidative attack at the double bonds of the rubber.
Structure of Copolymers of Isobutylene and Isoprene
Authors: Rehner John
Published: February 2011

By means of ozone degradation experiments it has been shown that the isoprene units in copolymers of isoprene and isobutylene unite in the 1,4 positions. This conclusion is based on negative evidence. Since no evidence was found that would indicate a tendency for the isoprene units to occur in sequences, it is concluded that one isoprene unit cannot exert any directing influence on another, as far as their relative positions along the polymer chain are concerned. The existence of such an influence would necessitate the assumption of unprecedented long-range forces. Hence, the isoprene units must enter the chain in a random manner.
Effect of Diameter and Surface Area of Carbon Black Particles on Certain Properties of Rubber Compounds
Authors: Parkinson D.
Published: February 2011

Carbon blacks can be grouped into different classes according to the way in which their fineness of division relates to different properties in rubber. Within any one class the principal properties vary in a regular manner with particle size. The normal class consists of the furnace carbons, Kosmos (Dixie)-40, Statex, the rubber-grade impingement carbons, and possibly, the color-grade impingement carbons. The subnormal classes consist of thermal carbons and acetylene and lamp blacks. Irrespective of the above classification, the properties which depend more on fineness of division than on other factors are rebound resilience, abrasion resistance, tensile strength and tear resistance. The lower limit of particle diameter for best tensile strength and tear resistance appears to be higher than that for abrasion resistance. B.S.I, hardness and electrical conductivity are properties which depend at least as much on other factors as on particle size. Stiffness (modulus) depends more on other factors than on particle size. Factors modifying the effects of particle size (or specific surface) include the presence of carbon-carbon structures and a reduction in strength of bond in rubber-carbon structures. Carbon black is thought to exist in rubber in four states: agglomerated, flocculated, dispersed, and bonded to the rubber molecules (the reënforcing fraction). Abrasion resistance is regarded as providing the only reliable measure of reënforcement.
Latex Compounding of GR-S
Authors: O'Connor H. F. , Sweitzer C. W.
Published: February 2011

The more important findings in this study can be summarized as follows. (1) A satisfactory technique has been worked out for compounding GR-S in latex form, either with carbon alone or with carbon plus the other compounding ingredients. (2) Latex compounding of GR-S results in notable improvements in stress-strain properties. (3) Latex compounding of GR-S results in outstanding improvements in heat resistance properties, without any loss in rebound. (4) Latex compounding of GR-S results in lower modulus, higher elongation and higher subpermanent set. The increased set is significant, since it is accompanied by maintained rebound. Besides giving improved quality, latex compounding offers practical advantages and possibilities. These are listed below: (1) Latex compounding makes possible a reduction in the total milling time. This saving amounts to at least 10 per cent for carbon latex compounds and up to 50 per cent for complete latex compounds. The mixing time normally required in the Banbury is certainly not required. (2) Latex compounding makes possible cooler handling of the GR-S. Since the carbon is added to the latex at room temperature, no high temperatures are involved during its incorporation as in Banbury mixing. (3) Latex compounding makes possible cleaner handling of carbon, since it is added to the latex and is, therefore, mixed in the rubber before milling. If desired, the handling of carbon black could thus be transferred in toto to the polymer plants. This offers some interesting possibilities. (4) Latex compounding to the black crumb stage, followed by sheeting and baling, should provide a convenient and economical means for shipping black, particularly for transoceanic deliveries. There would also be important savings in containers. (5) The black latex crumb may provide a convenient form of compounded GR-S for extrusion and related operations.
Stress-Strain Data for Vulcanized Rubber under Various Types of Deformation
Authors: Treloar L. R. G.
Published: February 2011

Stress-strain data are given for two types of vulcanized rubber: (1) an 8% S rubber, and (2) a latex rubber. The types of deformation studied were simple elongation, 2-dimensional extension (or compression), pure shear, and combined elongation and shear. Comparison with the theoretical relations based on the molecular-network model shows the agreement to be good for the 2-dimensional extension, but less good for simple elongation and shear. The effect of combined elongation and shear is satisfactorily accounted for. It is concluded that the theory provides a satisfactory explanation of rubberlike elasticity, and forms a useful basis for the description of the mechanical properties of rubber subjected to large deformations of any type.
Pseudo-Plastic Phenomena with Vulcanized Rubber
Authors: Wildschut A. J.
Published: February 2011

It is shown that plastic flow and relaxation of vulcanized natural rubber follow a logarithmic course with time. As a result, it is possible to define rate of flow as the ratio of flow at constant tension to the logarithm of the time, and rate of relaxation as the ratio of the decline in tension at constant elongation to the logarithm of the time. A study of tension-rate of flow diagrams at different temperatures has shown that, at room temperature, a considerable part of the total flow measured is reversible and therefore must be considered as pseudo-flow. This pseudo-flow is caused by a retardation in crystallization, and diminishes with increase in temperature. As a result, with increasing temperature, the total rate of flow passes through a minimum. An analogous situation occurs with the phenomenon of relaxation.
Theory of Filler Reenforcement in Natural and Synthetic Rubber. The Stresses in and about the Particles
Authors: Rehner John
Published: February 2011

An attempt is made to develop a general theory of filler reënforcement by determining the stresses occurring in and about a spherical particle imbedded in a rubberlike medium subjected to an applied tension. For a system containing a single particle rigidly attached to the adjacent medium, an application of the theory of elasticity shows that, for infinitesimal deformations, the stress components within the particle are independent of the radial distance from the origin, taken at the center of the particle. The stress components at a given point in the surrounding medium depend on the elastic constants both of the particle and of the medium, on the radius of the sphere, on the distance from the origin, and on the angle between the direction vector and the applied tension. Expressions are given for the average stresses in media containing many (independent) particles. Theoretical values of the bulk moduli of the synthetic rubbers considered in the treatment are derived from sound velocity data. Curves showing the spatial distribution of radial and shear stresses are presented for a range of values of elastic constants to be expected for different kinds of filler particles and rubberlike materials.
Derivatives of Synthetic Rubber
Authors: Endres Herbert A.
Published: February 2011

By processes of cyclization and chlorination, synthetic elastomers can be converted into derivatives which differ from the parent product in the following respects: 1. Higher specific gravity. 2. Higher softening point. 3. Greater hardness and rigidity. 4. Less flexibility and elongation. 5. Greater chemical resistance. 6. Lower solution-viscosity. 7. Lower moisture-vapor transfer. 8. Lower moisture absorption. 9. Less tackiness. 10. Greater solubility in polar solvents. Thus, many of the desirable features of the commercially important derivatives of natural rubber can be duplicated in synthetic products. It is, furthermore, logical to assume that the field of usefulness of synthetic derivatives will be extended by selection of the proper type of synthetic rubber for cyclization, chlorination, and hydrochlorination to bring out certain desirable characteristics which are not inherent in products made from natural rubber.
Tear Resistance. I. Mechanisms of Tearing of Natural and Synthetic Rubbers
Authors: Buist J. M.
Published: February 2011

(1) Comparative tests have shown the 0.02 in. nick gives the least variable tear resistances for all the rubbers tested. The error of test is higher for synthetic rubbers (±22 per cent for a single test) than for natural rubber (±12 per cent for a single test). These errors of test apply equally at temperatures of 21° C ± 2° C, 50° C, 70° C and 100° C. (2) Adequate data have shown that tear tests are analogous to tensile tests and the width of the sample should be taken into account by expressing the results as kg. per sq. cm. instead of as kg. per cm. (3) Natural rubber is superior to the synthetic rubbers, but when the depth of nick is increased to 0.20 inch it becomes inferior to Butyl and GR-S. (4) The results emphasize the poor resistance of the gum stocks of the synthetic rubbers compared with natural rubber, and this difference is accentuated at elevated temperatures. (5) Experimental results support the theory that higher tear resistance is obtained with rubbers which crystallize on stretching. (6) The mechanism of tearing is not the same for all rubbers, and it has been found that butyl rubber maintains its tear resistance at elevated temperatures due to the development of knotty tearing. Within a more limited temperature range this effect has also been found to a lesser extent with Novoplas-A. (7) The experimental results have emphasized the need for careful examination of the type of tear developed and also the requirements of accurately analyzing and defining the stress and strain distributions within the sample.
Theory of Filler Reinforcement
Authors: Guth Eugene
Published: February 2011

For small loadings (up to about 10 per cent volume parts) colloidal carbon-black spheres may be considered as suspended in a continuous rubber matrix. In the present paper this model is generalized for ellipsoidal (including plate-like and rodlike) filler particles, and it is extended to the computation of various properties of the suspension in terms of the properties of the matrix and of the fillers. Viscosity, Young's modulus, stress-strain curve below crystallization and dielectric constant of the suspension are derived as linear functions of the volume concentration for small, and as quadratic functions for higher loadings. The stress-strain curves for varying proportions of fillers are similar. For small loadings the tensile strength first decreases because of the stress concentrations around the carbon-black spheres when the samples are stretched. The increase in tensile strength observed for greater loadings is caused by the tendency of the carbon-black spheres to form chains and, finally, a type of network. The stiffness increases with loading up to the point where the suspension becomes a dilution of carbon black by rubber. There the tensile strength decreases too. Binding of rubber by carbon black is similar to solvation. The theoretical conclusions were checked experimentally ; in particular, the dependence of Young's modulus on concentration, the similarity of stress-strain curves, and the decrease of the tensile strength for small loadings. The theory of the elastic properties is very similar to the theory of Einstein on the viscosity of colloidal solutions and to Maxwell's and Rayleigh's theory of dielectric properties.
Theory of Filler Reìnforcement
Authors: Dewey Jane M.
Published: February 2011

In a recent paper, Rehner discusses the stresses in the neighborhood of a spherical filler particle in rubber. He finds that all the stresses are discontinuous at the surface of the particle. His work is based on formula derived by Sezawa and Miyazaki on the usual assumption of continuity of displacement and of the surface stresses at the spherical boundary. As the conclusions of Rehner are, therefore, inconsistent with the assumptions on which they are based, the work must contain a mathematical error at some point. A correct solution of the problem of a spherical inclusion of any rigidity in an elastic medium under simple tension has been given by Goodier. Goodier's paper gives formulas for the stresses at any point in the medium or inclusion when the medium is under simple tension. Rehner considers a number of particular cases of filler particles in an elastomer. In each case the imbedded particle is much more rigid than the surrounding medium, and Poisson's ratio of the surrounding medium is very close to 0.5. When these conditions are fulfilled the stresses are the same, to a very high degree of approximation, as if the particle were entirely rigid and the medium incompressible. From Goodier's results it follows that each stress on the surface of the particle is 5/2 the similar stress at a large distance from the particle. Filler particles in elastomers or plastics are always so much more rigid than the surrounding medium that the error introduced by considering them as entirely rigid is much less than the error introduced by the use of Hooke's law.
A Theory of the Calender Effect in Rubberlike Materials
Authors: Bilmes L.
Published: February 2011

The facts relating to the calender effected are briefly stated and illustrated by experimental data obtained with calendered plasticized polyvinyl chloride sheet. The nature of rubberlike deformation is outlined. A theory of the calender effect is proposed in terms of a mechanical model whose relation to molecular structure is indicated. The theory postulates that temperature-dependent yield values be associated with the mechanisms of high elastic deformation and plastic flow.
The State of Polydispersion of Hevea Latex. I
Authors: Hessels J. H. E.
Published: February 2011

The rubber particles in the latex of Hevea brasiliensis are present in the form of a polydispersion, and their diameters lie within the range of 0.1 to 3 microns. The rubber hydrocarbon itself is composed of a mixture of macromolecules of different degrees of polymerization. Rubber latex is, therefore, a system which is at the same time both polydispersed and polymolecular. It is well known that the degree of dispersion of a substance governs to a great extent certain properties of the substance. Moreover, astonishing as it may seem, in the great number of investigations which have been made of the composition and properties of latex and crude rubber, almost no attention has been paid to the part which may be played by the dimensions of the latex particles. However, in an investigation concerned with the centrifugation of latex, Loomis and Stump have called attention to this possibility, and in a study of latex obtained by fractionation, and in which the majority of the latex particles were of large dimensions, McGavack came to the conclusion that the protein content is proportional to the surface area of the globules. This limited knowledge of the subject seemed to warrant a more thorough study of the problem, which is of fundamental importance both from the theoretical and practical points of view. The investigation as a whole divided itself into three essential parts: (1) separation of latex into fractions containing particles of different sizes, and measurement of the state of dispersion in these fractions, (2) a study of the relation of these fractions to the composition of the rubber, i.e., the relation between the content of nonrubber components and the size of the latex particles, and (3) a study of the changes in the properties of the rubber hydrocarbon with change in the size of the latex particles. The latex used in this investigation was ordinary latex, containing 38–40 per cent dry-rubber content and preserved with ammonia. For the most important points, a concentrated latex (creamed latex containing 60 per cent dry-rubber content) was also tested. These two latices were about two years old when the investigation was started, and they gave results which were in good agreement with each other. In the present paper, only the data obtained with the first of the two latices are presented.
Extraction of Rubber from Cryptostegia Grandiflora
Authors: Bhatnagar S. S. , Shankar Karimullah , Shankar Uma
Published: February 2011

In an earlier communication on the subject, it was.stated that an improved method for the extraction of rubber from harvested partially dry twigs of Cryptostegia grandiflora, which has assumed considerable importance as a secondary source of rubber, has been worked out in these laboratories. The facts that (1) its latex is distributed throughout the plant (unlike Hevea, in which the latex cells are localized in a definite region in the cortex), and (2) its latex does not ooze out in a continuous stream, but coagulates very soon at the cut surface, rendered it necessary to develop either a modified tapping technique involving decapitation of shoots and collection of “plugs,” or a process in which the entire plant or the harvested shoots are suitably treated to release their rubber. The Rubber Directorate, it is understood, are experimenting with modified tapping methods, which have proved to be somewhat cumbersome and uneconomical. At the instance of the Supply Department, investigations were undertaken in these laboratories to develop a more convenient and economical process for the extraction of rubber from the plant.
Control of Elongation in Highly Stretched Cotton Tire Cord
Authors: Philipp Howard J. , Conrad Carl M.
Published: February 2011

1. Cotton tire cords, differing with regard to gauge, construction, and variety of cotton, were subjected to stretching treatments involving various combinations of tension, heat, and moisture. It was found that all these treatments increased the strength of the cords but reduced their gauge and elongation at 10 pounds. The greatest increase in strength was obtained when tire cord was stretched in a swollen condition and in the presence of heat. Increases in count-strength product from 48 to 83 per cent were observed. 2. Experiments showed a reciprocal relationship between the strength and the elongation at 10 pounds obtainable by single-stretching treatments of tire cord, which makes impossible the control of elongation, independently of strength. Bone-dry elongations of about 6 per cent at 10 pounds could be obtained only with negligible increase in strength. 3. The original elongation was restored by treating highly stretched tire cord with water at room temperature for 30 minutes or with boiling water for 3 minutes, while most of the increase in strength resulting from stretching was retained. A hot-wet-stretched tire cord after treating with water had equal elongation but greater strength as compared with the untreated cord. 4. A dual-stretching method was devised which makes possible the control of elongation at 10 pounds independently of strength. The treatment consists of two phases : the first imparts to the cord the maximum potential breaking strength and the second serves to adjust the elongation at 10 pounds to a predetermined controlled value while maintaining over 90 per cent of the maximum count-strength product. Control of the elongation is achieved by proper selection of tension and degree of swelling during the second phase of the dual-stretching treatment.
The Nature of the Dynamic Double Refraction of Rubber Solutions and the Shape of Rubber Molecules
Authors: Tsvetkov V. , Petrova A.
Published: February 2011

The work which is described in the present paper is concerned with the development of a method for measuring the double refraction of a flowing liquid, with particular attention to a study of the structure of polymers. The dependence of double refraction and of the angle of extinction on the velocity of flow of solutions of thirty samples of synthetic rubber through a wide range of velocities was studied. For linear polymers having high molecular weights, the relation: Δn=ƒ(g), shows, when represented graphically, an ascending concave curve. This relation is rectilinear for all polymers whose molecular weights lie within the usual range. In all cases investigated, the angle of extinction lay within the limits of 45° and 0°. The dynamic optical constant which characterizes the double refraction of rubber was established experimentally. This dynamic optical constant was calculated for all samples of rubbers which were studied. Three effects on the double refraction of a solution of a polymer during flow were distinguished experimentally: (1) the effect of the shape of the particles; (2) the effect of the anisotropy of the particles ; and (3) the elastic effect. The double refraction of solutions of synthetic rubbers in an electric field was investigated with a view to determining the anisotropy of the molecules of the polymers. On the basis of the experimental data it is concluded that the double refraction of a flowing rubber solution is fundamentally influenced by the effect of tension. The theory of Kuhn and the experimental data obtained in the present work were utilized to calculate the relation between the transverse and longitudinal dimensions of all the rubbers which were studied.
Weathering of Soft Vulcanized Rubber
Authors: Crabtree James , Kemp A. R.
Published: February 2011

When rubber goods are exposed to the agencies which constitute “weather”, they undergo profound changes. The rubber may lose elasticity, it may split or crack, or the surface may take on a crinkled appearance in a wide variety of designs. Figure 1 shows a small selection of such weathered rubbers. The course of deterioration, or the ultimate condition of any particular rubber specimen, moreover, is not always the same, but depends to a considerable extent on the kind of weather encountered which, in turn, depends on geography, topography, and season. The components of weather are air, heat, water, and sunlight, each varying in quantity and quality so that infinite combinations are possible. Among the major (nitrogen and oxygen), minor (carbon dioxide, argon, helium, neon, krypton, xenon), and trace (ozone, nitrogen oxides, ammonia, sulfur dioxide, sulfuric acid, hydrogen sulfide, carbon monoxide, hydrocarbons, hydrogen, mineral salts, hydrogen peroxide, organic peroxides) components of the atmosphere, only oxygen, ozone, and nitrogen oxides are capable of reacting with rubber. Trial shows steadily that, of these, only oxygen and ozone produce any perceptible effect at the concentrations in which they are present.
Evaluation of Serum Human Telomerase Reverse Transcriptase as a Novel Marker for Cervical Cancer
Authors: Porika Mahendar , Tippani Radhika , Mohammad Anwar , Bollam Sekhar R , Panuganti Sree D , Abbagani Sadanandam
Published: February 2011

Human telomerase reverse transcriptase (hTERT) is the catalytic subunit of human telomerase and its rate-limiting component. The purpose of the present study was to investigate the diagnostic value of hTERT in serum of cervical cancer patients. Preoperative values of hTERT, squamous cell carcinoma antigen (SCC-ag) and cancer antigen 125 (CA 125) were measured by enzyme-linked immunosorbent assay (ELISA) in 192 patients with squamous cell carcinoma or adenocarcinoma of the uterine cervix and 38 healthy controls. Elevated pretreatment levels of hTERT were identified in 80.2% of squamous cell carcinoma and 73.8% of adenocarcinoma patients. The expression of serum hTERT was correlated with telomerase activity in cancer tissues of both histological types. Pretreatment serum hTERT levels showed a significant correlation with clinical stage, tumor size and lymph node metastasis, but not with age. Serum hTERT measurement was found to be useful in the diagnosis and assessment of clinical stage of cervical cancer, and to be superior to the conventional tumor markers. Therefore, serum hTERT is a novel and readily available marker for cervical malignancies.
Early Cannulation Prosthetic Graft (Flixene™) for Arteriovenous Access
Authors: Schild A. Frederick , Schuman Earl S. , Noicely Karlene , Kaufman Joyce , Gillaspie Erin , Fuller Joseph , Collier Patrick , Ronfeld Amy , Nair Rakesh Ravikumaran
Published: February 2011

Purpose

Preferred hemodialysis (HD) access is an autologous fistula. Vascular grafts are used in patients with vessels unsuitable to accomplish an arteriovenous fistula (AVF). It is recommended that most current grafts mature in situ for 2–3 weeks before being accessed. Graft complications occur because the structure was not designed for the trauma of repeated cannulation. This study graft has a different structure that enables early use. Its design minimizes weeping through the graft walls and is meant to endure repeated access, thus minimizing the use of HD catheters. The purpose of this study was to show that the Flixene™ graft can be safely placed in patients where fistulas have failed and can be cannulated in 24–72 hr, while maintaining patency rates similar to other polytetrafluoroethylene (PTFE) grafts on the market. Flixene™ configuration should also reduce the incidence of pseudoaneurysms and seromas.

Methods

A prospective two-center study placed 33 grafts in 33 patients; graft efficacy, post-operative complications, and patency were evaluated. Ease of cannulation and dialysis center complications related to early cannulation were documented. Six month follow-up data was analyzed.

Results

Successful access was achieved in all 33 patients within 72 hr (29 patients within 24 hr). Overall primary patency at 6 months was 49%; primary-assisted patency at 6 months was 80%. No pseudoaneurysms or seromas were documented at 6 months. Complications were typical of graft access.

Conclusion

Early cannulation was successful in all patients. Primary and secondary patency rates at 6–months were equivalent to other data reported on PTFE grafts. Flixene™ successfully prevented pseudoaneurysm and seroma formation at 6 months of prospective follow-up. This graft is a better last-resort option for patients who cannot receive a fistula, compared to double-lumen cuffed catheters.
Caco‐2 Cells as a Model for Intestinal Absorption
Authors: Angelis Isabella De , Turco Laura
Published: February 2011

The Caco‐2 cell system, a well characterized intestinal in vitro model, makes it possible to evaluate the ability of chemicals to cross the intestinal barrier, as well as to study their transport mechanisms. Permeability values estimated with this model correlate well with human in vivo absorption data for many drugs and chemicals. As a consequence, the use of the Caco‐2 cellular model as a permeability assay to predict oral absorption in humans is growing, and its importance is increasing as a screening tool in drug‐discovery strategies for the prediction of intestinal drug permeability. Strict observance of the experimental conditions, coupled with careful control of the cell‐culture procedures, are crucial for obtaining a meaningful correlation with in vivo data. Because of the intrinsic variability of this absorption model, it is important to highlight that each experimental system must be calibrated with internal reference compounds, to permit data sharing between different laboratories.Curr. Protoc. Toxicol. 47:20.6.1‐20.6.15. © 2011 by John Wiley & Sons, Inc.
On stable simultaneous input and state estimation for discrete‐time linear systems
Authors: Fang Huazhen , Shi Yang , Yi Jingang
Published: February 2011

This work is devoted to solving simultaneous input and state estimation (SISE) problem for discrete‐time linear systems. Our aim is to develop stable SISE algorithms. By applying the minimum variance unbiased estimation technique, we derive two SISE algorithms in the presence or absence of direct feedthrough, respectively. Riccati‐like equations are formulated and presented to analyze the stability conditions of the proposed algorithms. Simulation examples are provided to further illustrate the effectiveness of the proposed algorithms and support the theoretical findings. Copyright © 2011 John Wiley & Sons, Ltd.
Inborn errors of cobalamin absorption and metabolism
Authors: Watkins David , Rosenblatt David S.
Published: February 2011

Derivatives of cobalamin (vitamin B12) are required for activity of two enzymes in humans. Adenosylcobalamin is required for activity of mitochondrial methylmalonylCoA mutase and methylcobalamin is required for activity of cytoplasmic methionine synthase. Deficiency in cobalamin, or inability to absorb cobalamin normally, can result in accumulation of methylmalonic acid and homocysteine in blood and urine. Methylmalonic acidemia can result in metabolic acidosis which in severe cases may be fatal. Hyperhomocysteinemia along with hypomethioninemia can result in hematologic (megaloblastic anemia, neutropenia, thrombocytopenia) and neurologic (subacute combined degeneration of the cord, dementia, psychosis) defects. Inborn errors affecting cobalamin absorption (inherited intrinsic factor deficiency, Imerslund–Gräsbeck syndrome) and transport (transcobalamin deficiency) have been described. A series of inborn errors of intracellular cobalamin metabolism, designated cblA‐cblG, have been differentiated by complementation analysis. These can give rise to isolated methylmalonic acidemia (cblA, cblB, cblD variant 2), isolated hyperhomocysteinemia (cblD variant 1, cblE, cblG) or combined methylmalonic acidemia and hyperhomocysteinemia (cblC, classic cblD, cblF). All these disorders are inherited as autosomal recessive traits. The genes underlying each of these disorders have been identified. Two other disorders, haptocorrin deficiency and transcobalamin receptor deficiency, have been described, but it is not clear that they have any consistent clinical phenotype. © 2011 Wiley‐Liss, Inc.
What lies beneath? An evaluation of lower molar trigonid crest patterns based on both dentine and enamel expression
Authors: Bailey Shara E. , Skinner Matthew M. , Hublin Jean‐Jacques
Published: February 2011

The nearly ubiquitous presence of a continuous crest connecting the protoconid and metaconid of the lower molars (often referred to as the middle trigonid crest), is one of several dental traits that distinguish Homo neanderthalensis from Homo sapiens. This study examined variation in trigonid crest patterns on the enamel and dentine surfaces to (1) evaluate the concordance between the morphology of trigonid crests at the inner dentine and the outer enamel surfaces; (2) examine their developmental origin(s); and (3) examine trait polarity through comparison with Australopithecus africanus and Pan. The sample included 73 H. neanderthalensis, 67 contemporary H. sapiens, 5 A. africanus, and 24 Pan lower molars. Results indicate general agreement in the morphology observed on the dentine and enamel surfaces. All but one H. neanderthalensis molar shows some trigonid crest development, whereas trigonid crests occur in low frequency in contemporary humans. Pan and A. africanus both also show high frequencies of a continuous trigonid crest. However, the origin of the trigonid crest differs among groups. H. neanderthalensis uniquely possesses a ‘middle’ trigonid crest that originates from the mesial accessory ridge of one or both cusps. Based on our results we suggest that presence of a continuous middle trigonid crest at the dentine surface is primitive and the lack of any trigonid crest is derived. Genetic drift may explain the high frequency of trigonid crests in H.neanderthalensis. However, H. neanderthalensis still appears to be derived relative to Pan and A. africanus in its high frequency of the mesial‐mesial trigonid crestconfiguration. Am J Phys Anthropol, 2011. © 2011 Wiley‐Liss, Inc.
Mitochondrial DNA structure in North Africa reveals a genetic discontinuity in the Nile Valley
Authors: Fadhlaoui‐Zid Karima , Rodríguez‐Botigué Laura , Naoui Nejib , Benammar‐Elgaaied Amel , Calafell Francesc , Comas David
Published: February 2011

Human population movements in North Africa have been mostly restricted to an east‐west direction due to the geographical barriers imposed by the Sahara Desert and the Mediterranean Sea. Although these barriers have not completely impeded human migrations, genetic studies have shown that an east‐west genetic gradient exists. However, the lack of genetic information of certain geographical areas and the focus of some studies in parts of the North African landscape have limited the global view of the genetic pool of North African populations. To provide a global view of the North African genetic landscape and population structure, we have analyzed ∼2,300 North African mitochondrial DNA lineages (including 269 new sequences from Libya, in the first mtDNA study of the general Libyan population). Our results show a clinal distribution of certain haplogroups, some of them more frequent in Western (H, HV0, L1b, L3b, U6) or Eastern populations (L0a, R0a, N1b, I, J) that might be the result of human migrations from the Middle East, sub‐Saharan Africa, and Europe. Despite this clinal pattern, a genetic discontinuity is found in the Libyan/Egyptian border, suggesting a differential gene flow in the Nile River Valley. Finally, frequency of the post‐LGM subclades H1 and H3 is predominant in Libya within the H sequences, highlighting the magnitude of the LGM expansion in North Africa. Am J Phys Anthropol, 2011. © 2011 Wiley‐Liss, Inc.
Preparation and characterization of mesoporous activated carbons from waste tyre
Authors: Song X. H. , Xu R. , Lai A. , Lo H. L. , Neo F. L. , Wang K.
Published: February 2011

Mesoporous activated carbon was prepared from waste tyres via acid wash and steam activation. The effect of synthetic conditions was studied and the surface texture of the tyre carbon was characterized. The optimally obtained carbon sample presents a surface area of ∼1200 m2 g−1 and is predominantly mesoporous. Acid wash was found to play an important role in the structural development of carbon. The advantage of the mesoporous carbon was demonstrated by its excellent sorption capacity towards the bulky molecule of a basic dye (methylene blue). © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.
Cluster analysis of arterial involvement in Takayasu arteritis reveals symmetric extension of the lesions in paired arterial beds
Authors: Arnaud Laurent , Haroche Julien , Toledano Dan , Cacoub Patrice , Mathian Alexis , Costedoat‐Chalumeau Nathalie , Le Thi Huong‐Boutin Du , Cluzel Philippe , Gorochov Guy , Amoura Zahir
Published: February 2011

Objective

The determinants of vessel targeting are largely unknown in vasculitides. This study was undertaken to identify patterns of vascular involvement in Takayasu arteritis (TA), using objective classification of vascular beds. We postulated that cluster analysis could unveil preferential associations between vascular beds commonly affected by TA.

Methods

Peripheral vascular Doppler, computed tomography angiography, and angio–magnetic resonance imaging data from 82 patients with TA (according to the American College of Rheumatology criteria) were studied between January 1995 and May 2006. Cross‐relationships of involvement between 24 main arteries were assessed using the phi correlation coefficient. Identification of patterns of vascular involvement was performed using agglomerative hierarchical cluster analysis.

Results

Data were obtained from 82 patients (68 women [82.9%] and 14 men [17.1%]). The median duration of followup was 5.1 years (range 1 month to 30 years). For 16 (80%) of 20 paired arteries, the highest correlation of involvement was observed with the contralateral artery. Conversely, disease extension was contiguous in the aorta. Cluster analysis further confirmed that all paired arterial beds, except for the internal and external carotid arteries, clustered with their contralateral counterpart and that the aortic arch, the descending thoracic aorta, and the abdominal aorta clustered together.

Conclusion

Our findings reveal that TA lesions mostly develop in a symmetric manner in paired vascular territories and that disease extension is contiguous in the aorta. This may prove useful for improving the radiologic followup of patients with TA and for providing a pattern for further investigations focusing on the mechanisms of vessel specificity in vasculitides.
The effectiveness of pulsed electrical stimulation in the management of osteoarthritis of the knee: Results of a double‐blind, randomized, placebo‐controlled, repeated‐measures trial
Authors: Fary Robyn E. , Carroll Graeme J. , Briffa Tom G. , Briffa N. K.
Published: February 2011

Objective

To determine the effectiveness of subsensory, pulsed electrical stimulation (PES) in the symptomatic management of osteoarthritis (OA) of the knee.

Methods

This was a double‐blind, randomized, placebo‐controlled, repeated‐measures trial in 70 participants with clinical and radiographically diagnosed OA of the knee who were randomized to either PES or placebo. The primary outcome was change in pain score over 26 weeks measured on a 100‐mm visual analog scale (VAS). Other measures included pain on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), function on the WOMAC, patient's global assessment of disease activity (on a 100‐mm VAS), joint stiffness on the WOMAC, quality of life on the Medical Outcomes Study Short‐Form 36 (SF‐36) health survey, physical activity (using the Human Activity Profile and an accelerometer), and global perceived effect (on an 11‐point scale).

Results

Thirty‐four participants were randomized to PES and 36 to placebo. Intent‐to‐treat analysis showed a statistically significant improvement in VAS pain score over 26 weeks in both groups, but no difference between groups (mean change difference 0.9 mm [95% confidence interval −11.7, 13.4]). Similarly, there were no differences between groups for changes in WOMAC pain, function, and stiffness scores (−5.6 [95% confidence interval −14.9, 3.6], −1.9 [95% confidence interval −9.7, 5.9], and 3.7 [95% confidence interval −6.0, 13.5], respectively), SF‐36 physical and mental component summary scores (1.7 [95% confidence interval −1.5, 4.8] and 1.2 [95% confidence interval −2.9, 5.4], respectively), patient's global assessment of disease activity (−2.8 [95% confidence interval −13.9, 8.4]), or activity measures. Fifty‐six percent of the PES‐treated group achieved a clinically relevant 20‐mm improvement in VAS pain score at 26 weeks compared with 44% of controls (12% [95% confidence interval −11%, 33%]).

Conclusion

In this sample of subjects with mild‐to‐moderate symptoms and moderate‐to‐severe radiographic OA of the knee, 26 weeks of PES was no more effective than placebo.
Antibodies interfering with the type 3 muscarinic receptor pathway inhibit gastrointestinal motility and cholinergic neurotransmission in Sjögren's syndrome
Authors: Park Kyungpyo , Haberberger Rainer V. , Gordon Tom P. , Jackson Michael W.
Published: February 2011

Objective

In primary Sjögren's syndrome (SS), impairment of the gastrointestinal (GI) tract is common, and includes reduced esophageal motor function, delayed gastric emptying, and abnormalities in colonic motility; the pathogenesis is as yet unknown. We undertook this study to investigate the role of functional antibodies to the type 3 muscarinic receptor (M3R) in GI dysfunction associated with primary SS.

Methods

Muscle strip and whole‐organ functional assays were used to determine whether IgG with anti‐M3R activity from patients with primary SS disrupted neurotransmission in tissue from throughout the mouse GI tract. Specificity of the autoantibody for the M3R was determined using knockout mice that were deficient in the expression of muscarinic receptor subtypes.

Results

Functional antibodies to the M3R inhibited neuronally mediated contraction of smooth muscle from throughout the GI tract and disrupted complex contractile motility patterns in the colon. The autoantibodies were not active on tissue from mice that lacked the M3R, providing compelling evidence of the direct interaction of patient autoantibodies with the M3R.

Conclusion

Our results indicate that anti‐M3R autoantibodies have the potential to mediate multiple dysfunctions of the GI tract in primary SS, ranging from reduced esophageal motor activity to altered colonic motility. We hypothesize that altered GI motility forms part of a broader autonomic dysfunction mediated by pathogenic anti‐M3R autoantibodies in primary SS.
Experimentelle und theoretische Untersuchungen von Infrarot reflektierenden Dämmmaterialien
Authors: Hauser Gerd , Kersken Matthias , Schade Almuth , Sinnesbichler Herbert
Published: February 2011

Manche Hersteller von Infrarot reflektierenden Dämmmaterialien werben mit hohen Dämmeigenschaften ihrer Produkte, die angeblich nicht mit Hilfe der klassischen Bauphysik beschrieben werden können. Um deren Dämmqualität zu überprüfen, werden In‐situ‐Messungen durchgeführt. Dazu werden zwei verschiedene Dachaufbauten parallel untersucht: einmal mit Mineralwolle, einmal mit IR‐reflektierender Dämmung. Die Ergebnisse werden mit klassischen Labormessungen verglichen. Die Untersuchungen werden durch Simulationsrechnungen ergänzt. Aus allen Untersuchungen resultiert: die Dachkonstruktion mit der IR‐reflektierenden Dämmung zeigt typische Merkmale eines Aufbaus mit geringerer Dämmwirkung. Außerdem lässt sich das Verhalten des Dachaufbaus mit der IR‐reflektierenden Dämmung während der In‐situ‐Messung sehr gut mit den Ergebnissen aus den klassischen Labormessungen in Übereinstimmung bringen.

Experimental and theoretical investigations on infrared reflective insulation. Some manufacturers of IR‐reflective insulation products claim, that their products feature a high insulation quality that cannot be described by traditional methods of building physics. In situ measurements are carried out to verify. Two different roof systems are investigated parallel: one with mineral wool, the other with IR‐reflective insulation. The results of the in situ tests are compared to those of traditional laboratory measurements. Further the examinations are completed by dynamic calculations. As a result it follows from all investigations, that the roof with IR‐reflective insulation shows a typical characteristic of insulation with lower quality. The values of the traditional measurement match with the results of the in situ measurements.