bluuebunny/crossref_metadata_2025 huggingface dataset:
A parametric library for the simulation of a Union Internationale des Chemins de Fer (UIC) pneumatic braking system
Authors: Pugi L , Malvezzi M , Allotta B , Banchi L , Presciani P
Published: July 2004

European trains are equipped with a pneumatic braking system that has to respect severe specifications concerning both performances and safety. The pneumatic braking system is composed of hundreds of different pneumatic components that reproduce the prescribed response by a complex logic of pneumatic and mechanical elements. In this paper a tool for a complete simulation of the pneumatic braking system is described, it was developed using the Matlab-Simulink numerical environment.

The tool is composed of three different libraries of pneumatic components. The first includes the elementary components such as pipes, orifices, valves and the reservoir. By assembling elementary components, an advanced user can build a customized version of general pneumatic components or plants. Complex components of general use for railway pneumatic brake such as brake cylinders, distributors, pressure transformers and brake valves are available in a second library that can be used to assemble a customized braking plant for a vehicle. The last library is composed of macro-pneumatic subsystems that reproduce the braking system of a typical railway vehicle. Many common plant layouts are reproduced in this library (freight car, passenger coaches, locomotives, etc.).

The pneumatic brake system of a train can be simulated by assembling in a single Matlab-Simulink model the elements of the library.

In this paper the main features of this numerical tool and the test procedures developed to validate the software are described. Experimental data have been kindly supplied by Trenitalia SPA and they are referred to several test campaigns managed by Italian railway in order to verify and release existing components of the pneumatic brake.
Design synthesis of non-symmetrically loaded high-performance disc brakes: Part 3: Verification and optimization
Authors: Tirovic M , Sarwar G A
Published: July 2004

Two successful wheel-hub-mounted disc designs and main problems related to this type of disc are presented in Part 1 of the paper. Following material properties measurements, different types of finite element (FE) analyses were performed in Part 2 and thermoelastic instability and disc plasticity modelled for the TGV powercar disc. The results showed that different FE analyses give very similar disc deflection during braking. Following previous work, in this paper (Part 3), full verification of disc temperatures, permanent deflections and stresses have been conducted. Very good correlation of FE results with dynamometer and vehicle service data was achieved. By proving the validity of the proposed modelling procedures, an optimization methodology was developed and applied, leading to the development of a new disc design. The comparison with the existing disc showed the advantages and limitations of both designs. The recommendations for a successful wheel-hub-mounted disc design are also given. The analytical and experimental work confirmed the efficiency and robustness of the developed methodology, making it suitable for industrial use, by offering substantial savings and reducing development risks.
Parameter determination for a rail system simulator by an intelligent genetic algorithm
Authors: Ruan W , Giras T C , Lin Z , Ou Y
Published: July 2004

This paper reports on a successful determination of the train travel schedule parameters for a rail system based on limited data, and thus provides a verification of the axiomatic safety-critical assessment process (ASCAP), a rail system simulator developed at the Center of Rail Safety-Critical Excellence at the University of Virginia. The train system considered is a corridor encompassing a territory of over 127 miles. It is divided into 37 train speed zones, with nine sidings. The only data available are the actual trip times of 171 trains dispatched over a period of 14 days. The problem of determining the 37 train-speed-zone average speeds and nine siding delay times was formulated as a constrained optimization problem. The cost to be minimized is the accumulated errors between the actual train trip times and the ASCAP simulated trip times resulting from a particular set of train-speed-zone average speeds and siding delay times. The constraints include allowable siding delays, permissible train-speed-zone average speeds and prohibition of southbound trains from entering the sidings. This large-scale non-linear optimization problem was then solved by a genetic algorithm developed by the present authors and referred to as the intelligent genetic algorithm. Simulation results demonstrate the effectiveness of this intelligent genetic algorithm.
Design synthesis of non-symmetrically loaded high-performance disc brakes: Part 2: Finite element modelling
Authors: Tirovic M , Sarwar G A
Published: July 2004

The prediction of the behaviour of wheel-mounted disc brakes is particularly complex due to non-symmetrical heat input, making disc coning during braking inevitable. Furthermore, severe brake applications cause high local temperatures and stresses, resulting in disc material yielding and permanent disc coning. To ensure adequate brake operation, disc coning during braking and permanent disc coning must be kept within acceptable limits. Obviously, excessive hub stresses must also be avoided, to ensure structural integrity throughout expected brake life. In order to predict disc permanent coning, it is necessary to model macro thermal effects, i.e. thermoelastic instability. The paper deals with different finite element (FE) modelling techniques and measurements of disc material properties, establishing efficient methodology for the prediction of wheel-mounted disc performance. The procedure developed is widely based on a standard FE code, with subroutines developed for data preparation, processing and visualization. This approach, combined with the efficiency and robustness of the methodology, is very suitable for industrial use, reducing risks, costs and development time.
Timoshenko beam finite element for vehicle—track vibration analysis and its application to jointed railway track
Authors: Koro K , Abe K , Ishida M , Suzuki T
Published: July 2004

A Timoshenko beam finite element suitable for vehicle-track vibration analysis is proposed and is applied to a jointed railway track. In several simulation models, the track vibration excited by a train running on the rail is formulated as a dynamic problem where a sequence of concentrated loads moves on the discretely supported Timoshenko beam. The external force is then defined by the concentrated load. The Timoshenko beam subjected to concentrated loads deforms with the slope discontinuity at the loading points. This deformation cannot be represented by the usual finite elements, which causes the fictitious responses of the beam. The present finite element model removes the undesirable response by completely modelling the slope discontinuity. This is achieved by the TIM7 element with the piecewise-linear hat functions. The jointed track model constructed by this finite element is employed to predict the impulsive wheel—track contact force excited by the wheel passage on rail joints. The rail joints with fishplates are of great concern to track deterioration, the settlement of ballast track and the failure of track components. In the present paper the effects of train speed and gap size of the joints on the impact force are assessed from simulation results.
Effect of number of ribs and spar load ratio on the wing mass for light aircraft
Authors: Marczi T , Smrcek L
Published: July 2004

This paper presents a calculation process for the estimation of the gross mass of a twospar wing, due to the influence of a number of uniformly distributed ribs along the span. The proposed method is only suitable for preliminary design of light aircraft wings, particularly when the design engineer does not have a clear conception of the dimensions nor a detailed layout of the internal wing structure. The calculation process is developed for a simple rectangular wing model with an unstiffened skin. The estimation of the effect of the number of uniformly distributed ribs on the gross wing mass is based on the calculation of the minimized dimensions of the internal structural components of the wing, i.e. spar booms, spar webs, skin and ribs. Results are presented for three different spar load ratios.
Multiobjective wing design using genetic algorithms and fuzzy logic
Authors: Saggiani G M , Caligiana G , Persiani F
Published: July 2004

The designer frequently faces problems in which the project depends on many parameters and the final solution must be evaluated according to several optimization objectives. This may be the case for the aeroelastic and aeromechanical design of lifting surfaces. The aim of the present paper is to show how the combined techniques of genetic algorithms (GAs) and fuzzy logic can be useful in these situations. The leading idea is the development of a tool to assist the designer in the preliminary phase of activity by assigning a genetic code to every possible solution and assessing its performance by means of a fuzzy controller in order to handle simultaneously different design criteria. Examples are given for some typical problems in aeronautical design.
Numerical analysis of the airfoil flow fields and transonic blade-vortex interaction noise
Authors: Cao Yihua , Kang Pengbin , Li Xiaoyong
Published: July 2004

The flow fields around NACA0012, NACA23012 and OA207 airfoils can be calculated by solving the Euler-Navier-Stokes equations. The far-field noise generated by NACA0012 airfoil- vortex interaction is predicted using the combined Euler-Kirchhoff method. The Kirchhoff surface is selected as one of the grid surfaces. Firstly, the result of flow field under airfoil-vortex interaction can be obtained by solving the Euler equations. Then the result of far-field noise can be obtained by the Kirchhoff method. Finally, the combined Euler-Kirchhoff method developed here is proved to be good for studying blade-vortex interaction noise through sample calculations.
A spacecraft attitude stabilization system with low-power magnetic torquers
Authors: Polites M , Quarles C , Kadebek D , Clements J , Mentch D
Published: July 2004

This paper describes a spacecraft attitude stabilization system that uses a set of 12 low-power magnetic torquers. The low-power magnetic torquer consists of a hard magnetic-material rod inside a solenoid. Discharging a capacitor through the solenoid winding generates a current pulse that changes the magnetic dipole moment of the rod when required. The interaction of this magnetic dipole moment with the Earth' magnetic field creates a torque on the rod that can stabilize the attitude of a spacecraft in a low Earth orbit. Computer simulation results show that a system of 12 low-power magnetic torquers with a combined mass of 3.5 kg or about 8 lb can stabilize a 1400 kg or 3000 lb spacecraft in a 600 km circular orbit to a local vertical orientation in five to ten orbits. With initial rates of 1 deg/s or less in each axis, the peak power dissipated in the low-power magnetic torquers is 440 mW or less, the average power prior to settling is 125 mW or less and the average power after settling is about 2 mW or less.
An engineering approach to the dynamic control of space robotic on-orbit servicers
Authors: Ellery A
Published: July 2004

Robotic on-orbit servicing is the key to the commercial development of a space robotics infrastructure. A major technical difficulty has been the problem of control of the robotic manipulators mounted onto a freeflying platform in space. The problem of control is directly related to the fact that manipulator motions exert reaction effects on the mounting spacecraft. A solution to this problem is outlined-one in which no fuel is expended and that demands no excessive computational resources that would otherwise preclude real-time performance.
Rule-based guidance for flight vehicle flocking
Authors: Crowther W J
Published: July 2004

Within nature, mobile organisms often exhibit a form of emergent behaviour known as flocking. Flocking is adaptive because, for a given population density, the information processing required for collision avoidance is minimized. Within human activities, the problem of increasing civil air traffic is leading to consideration of decentralized traffic management methodologies, such as free flight. On the other hand, for military flight vehicles, safe operation of flight vehicles at high air space densities is seen as an opportunity. The present paper considers the use of guidance based on flocking rules to support the management of flight vehicles in situations of high airspace density. Three elemental flocking schemes are identified based on guidance tasks and a simple analytical framework is developed that allows insight into the fundamental flocking behaviour for all three schemes. Flight vehicles are modelled as point masses moving with constant speed in the horizontal plane. A non-dimensional approach is used throughout to provide generality. The proposed flocking algorithm is implemented within Matlab and numerical simulation results are used to validate analytical predictions of steady state flock size and entropy. Results show that a simple parameter based on the ratio of rule weights is sufficient to predict flock behaviour.
Prediction of elastic deformation of acetabular cups and femoral heads for lubrication analysis of artificial hip joints
Authors: Wang F. C. , Jin Z. M.
Published: July 2004

Fluid film lubrication analysis for artificial hip joints often requires the determination of the elastic deformation of the bearing surfaces of both the acetabular cup and the femoral head. This is generally not a trivial task, because of the complex spherical geometries and non-uniform structural supports due to the bone and cement involved. It is particularly important that an efficient numerical method is employed, with a reasonably small amount of computing time required. The normal elastic deformation of spherical bodies, with particular reference to the acetabular cup and the femoral head for artificial hip joints, was determined in the present study using the two-dimensional spherical fast Fourier transform (SFFT) technique. A cobalt-chromium alloy femoral head was considered, in combination with either an ultra-high molecular weight polyethylene acetabular cup fixed to a metallic (rigid) backing or a cobalt-chromium alloy cup fixed to an equivalent layer representing bone and cement. A representative pressure distribution was applied around both the central region of the cup and the anatomical position with a 45° inclination angle. The elastic deformation determined from the SFFT method was compared with that directly calculated from the finite element method, and excellent agreement was found when the pressure distribution was applied around the central region. Even when the pressure distribution was applied anatomically and extended to the edge of the cup, reasonably good overall agreement of the predicted elastic deformation was achieved. Furthermore, both the computing time and the storage space required for the SFFT method were significantly reduced, compared with the conventional direct summation method used by Jagatia and Jin.
Cavitation development in the lubricant film of a reciprocating piston-ring assembly
Authors: Dellis P , Arcoumanis C
Published: July 2004

The onset and development of cavitation in the lubrication film present throughout the stroke between the piston ring and the cylinder liner in a reciprocating test rig was visualized by a charge-coupled device (CCD) camera and monitored by a miniature pressure sensor. Various transient cavitation patterns were identified during the stroke, ranging from developing fern-shaped cavities to string cavities extending gradually up to the trailing edge of the piston ring. Both the onset and the development of these cavities seem to be affected by piston speed and load; at higher speeds cavities appear later in the stroke and are larger in size, while at higher loads they appear earlier, are more numerous and, thus, smaller in size.
Experimental simulation of impact and sliding wear in the top piston ring groove of a gasoline engine
Authors: Barrell D. J. W. , Priest M , Taylor C. M.
Published: July 2004

The influence of normal impact and sliding on wear and surface damage at the lubricated interface between the top piston ring and the piston was investigated using a specially adapted tribometer. Standard production components were tested, the piston rings being nitrocarburized steel with a production lapped finish and the pistons a hypereutectic aluminium-silicon alloy, either tin-plated or hard anodized. Experiments were undertaken at loads, velocities and temperatures comparable with a modern automotive, four-stroke, gasoline engine, either dry or lubricated with a fully formulated SAE 10W30 engine oil. Lubricant starvation was found to be the most critical operational parameter leading to surface damage and wear. An important phenomenon observed was the tendency of piston material to transfer and adhere to the ring surface, so-called ‘microwelding’. Anodizing was shown to be a very effective treatment to resist microwelding, although it is regarded as an expensive solution by the automotive industry. The experimental observations are consistent with fatigue wear of the piston groove, followed by material transfer to the piston ring flank and accelerated wear during sliding.
In-situ piston measurements
Authors: Taylor R. I. , Evans P. G.
Published: July 2004

Measurements are reported of piston secondary motion, piston ring motion, piston ring oil-film thicknesses, piston ring pack oil chemistry, piston friction and piston temperatures, using a variety of experimental techniques on running engines. These in-situ measurements have highlighted a number of interesting effects, of importance to both the piston designer and the lubricant formulator.
Fracture dominated wear of sharp abrasive grains and grinding wheels
Authors: Jackson M. J.
Published: July 2004

Fracture-dominated wear of abrasive grains is the most important mechanism of material removal from an abrasive wheel during the grinding process. Fracture occurs as a consequence of tensile stresses induced in the abrasive grains by grinding forces to which they are subjected. Experimental work is extracted from the literature and compared with a model abrasive grain using a variety of abrasive grain materials such as alumina, silicon carbide, cubic boron nitride and diamond, with loads applied to the apex and the rake face of an abrasive wedge. The relationship between the wear of grinding wheels, component grinding forces and induced stresses in the model abrasive grains is described in detail. A significant correlation is found between the maximum value of tensile stress induced in the abrasive grain material and the appropriate wheel-wear parameter (grinding ratio). It is concluded that the magnitude of tensile stresses induced in the grain material by grinding forces at the rake face is the best indicator of wheel wear during the grinding process.
Transient elastohydrodynamic analysis of elliptical contacts. Part 1: Isothermal and Newtonian lubricant solution
Authors: Jin Z. M. , Yang P , Cui J , Dowson D
Published: July 2004

Transient elastohydrodynamic lubrication of general elliptical point contacts was analysed in the present study based on multi-level techniques. Both entrainment directions along the major and minor axes of the contact ellipse were considered, together with transient load and speed impulses. In this study, only a Newtonian lubricant and isothermal conditions were assumed. The computing time required for a typical case took only approximately 2 h on a personal computer with a 2.8 GHz central processing unit. The predicted film thickness and the pressure were found to be mainly governed by the squeeze-film or separation actions. A sudden load increase resulted in an increase in the contact conjunction and a significant development of the squeeze-film action. Consequently the lubricant film thickness was increased initially around the inlet region and then moved along in the entraining direction towards the exit. A significant increase in the predicted central film thickness was observed, long after the load impulse had ceased. Such a process was found to be mainly governed by the time period of the impulse, and the time taken for the lubricant to move through the contact conjunction in the entraining direction. The speed impulse had similar effects. However, a sudden speed decrease was found to have negligible effect on the predicted film thickness, due to the powerful squeeze-film action.
Dopamine, through the Extracellular Signal-Regulated Kinase Pathway, Downregulates CD4+CD25+Regulatory T-Cell Activity: Implications for Neurodegeneration
Authors: Kipnis Jonathan , Cardon Michal , Avidan Hila , Lewitus Gil M. , Mordechay Sharon , Rolls Asya , Shani Yael , Schwartz Michal
Published: July 2004

Fighting off neuronal degeneration requires a well controlled T-cell response against self-antigens residing in sites of the CNS damage. The ability to evoke this response is normally suppressed by naturally occurring CD4+CD25+regulatory T-cells (Treg). No physiological compound that controls Treg activity has yet been identified. Here, we show that dopamine, acting via type 1 dopamine receptors (found here to be preferentially expressed by Treg), reduces the suppressive activity and the adhesive and migratory abilities of Treg. Treg activity was correlated with activation of the ERK1/2 (extracellular signal-regulated kinase 1/2) signaling pathway. Systemic injection of dopamine or an agonist of its type 1 receptors significantly enhanced, via a T-cell-dependent mechanism, protection against neuronal death after CNS mechanical and biochemical injury. These findings shed light on the physiological mechanisms controlling Treg and might open the way to novel therapeutic strategies for downregulating Treg activity (e.g., in neuronal degeneration) or for strengthening it (in autoimmune diseases).
The Y99C Mutation in Guanylyl Cyclase-Activating Protein 1 Increases Intracellular Ca2+and Causes Photoreceptor Degeneration in Transgenic Mice
Authors: Olshevskaya Elena V. , Calvert Peter D. , Woodruff Michael L. , Peshenko Igor V. , Savchenko Andrey B. , Makino Clint L. , Ho Ye-Shih , Fain Gordon L. , Dizhoor Alexander M.
Published: July 2004

Guanylyl cyclase-activating proteins (GCAPs) are Ca2+-binding proteins that activate guanylyl cyclase when free Ca2+concentrations in retinal rods and cones fall after illumination and inhibit the cyclase when free Ca2+reaches its resting level in the dark. Several forms of retinal dystrophy are caused by mutations inGUCA1A,the gene coding for GCAP1. To investigate the cellular mechanisms affected by the diseased state, we created transgenic mice that express GCAP1 with a Tyr99Cys substitution (Y99C GCAP1) found in human patients with a late-onset retinal dystrophy (Payne et al., 1998). Y99C GCAP1 shifted the Ca2+sensitivity of the guanylyl cyclase in photoreceptors, keeping it partially active at 250 nmfree Ca2+, the normal resting Ca2+concentration in darkness. The enhanced activity of the cyclase in the dark increased cyclic nucleotide-gated channel activity and elevated the rod outer segment Ca2+concentration in darkness, measured by using fluo-5F and laser spot microscopy. In different lines of transgenic mice the magnitude of this effect rose with the Y99C GCAP1 expression. Surprisingly, there was little change in the rod photoresponse, indicating that dynamic Ca2+-dependent regulation of cGMP synthesis was preserved. However, the photoreceptors in these mice degenerated, and the rate of the cell loss increased with the level of the transgene expression, unlike in transgenic mice that overexpressed normal GCAP1. These results provide the first direct evidence that a mutation linked to congenital blindness increases Ca2+in the outer segment, which may trigger the apoptotic process.
Nogo Receptor Antagonism Promotes Stroke Recovery by Enhancing Axonal Plasticity
Authors: Lee Jung-Kil , Kim Ji-Eun , Sivula Michael , Strittmatter Stephen M.
Published: July 2004

After ischemic stroke, partial recovery of function frequently occurs and may depend on the plasticity of axonal connections. Here, we examine whether blockade of the Nogo-NogoReceptor (NgR) pathway might enhance axonal sprouting and thereby recovery after focal brain infarction. Mutant mice lacking NgR or Nogo-AB recover complex motor function after stroke more completely than do control animals. After a stroke, greater numbers of axons emanating from the undamaged cortex cross the midline to innervate the contralateral red nucleus and the ipsilateral cervical spinal cord; this axonal plasticity is enhanced inngr-/- ornogo-ab-/- mice. In rats with middle cerebral artery occlusion, both the recovery of motor skills and corticofugal axonal plasticity are promoted by intracerebroventricular administration of a function-blocking NgR fragment. Behavioral improvement occurs when therapy is initiated 1 week after arterial occlusion. Thus, delayed pharmacological blockade of the NgR promotes subacute stroke recovery by facilitating axonal plasticity.
Rapid Axoglial Signaling Mediated by Neuregulin and Neurotrophic Factors
Authors: Esper Raymond M. , Loeb Jeffrey A.
Published: July 2004

During peripheral nervous system development, Schwann cells are precisely matched to the axons that they support. This is mediated by axonal neuregulins that are essential for Schwann cell survival and differentiation. Here, we show that sensory and motor axons rapidly release heparin-binding forms of neuregulin in response to Schwann cell-derived neurotrophic factors in a dose-dependent manner. Neuregulin release occurs within minutes, is saturable, and occurs from axons that were isolated using a newly designed chamber slide apparatus. Although NGF and glial cell line-derived neurotrophic factor (GDNF) were the most potent neurotrophic factors to release neuregulin from sensory neurons, GDNF and BDNF were most potent for motor neurons and were the predominant neuregulin-releasing neurotrophic factors produced by cultured Schwann cells. Comparable levels of neuregulin could be released at a similar rate from neurons after protein kinase C activation with the phorbol ester, phorbol 12-myristate 13-acetate, which has also been shown to promote the cleavage and release of neuregulin from its transmembrane precursor. The rapid release of neuregulin from axons in response to Schwann cell-derived neurotrophic factors may be part of a spatially restricted system of communication at the axoglial interface important for proper peripheral nerve development, function, and repair.
Sodium and Sodium Alloys
Authors: Lemke Charles H. , Markant Vernon H.
Published: July 2004

Of all the alkali metals, sodium has had perhaps the greatest commercial success, owing to its relative ease of manufacture and its important role worldwide in the manufacture of organolead compounds for use as gasoline octane enhancers. The decline of organoleads in North America has greatly affected U.S. production. Other sodium uses exist, but none requiring the massive quantities needed for lead antiknock compounds. Most sodium is made electrolytically. Various electrochemical cells are described. Sodium continues to have an important role in the manufacture of many organic chemicals as a reducing agent.
Has the transition to agriculture reshaped the demographic structure of prehistoric populations? New evidence from the Levant
Authors: Eshed Vered , Gopher Avi , Gage Timothy B. , Hershkovitz Israel
Published: July 2004

This paper presents the demographic changes that followed the transition from a hunting‐gathering way of life (Natufian) to an agricultural, food‐producing economy (Neolithic) in the southern Levant. The study is based on 217 Natufian (10,500–8,300 BC) skeletons and 262 Neolithic (8,300–5,500 BC) skeletons. Age and sex identification were carried out, and life tables were constructed. A five‐parameter competing hazard model developed by Siler ([1979] Ecology 60:750–757) was used to smooth life‐table data. No indication of increased mortality with the advent of agriculture was noted. On the contrary, both life expectancy at birth (24.6 vs. 25.5 years) and adults' mean age at death (31.2 vs. 32.1 years) increased slightly from the Natufian to the Neolithic period (assuming stationary populations). Yet the transition to agriculture affected males and females differently: mean age at death in the Natufian was higher for adult females compared to adult males, while in the Neolithic, it was the reverse. One interpretation given to the distribution of female ages at death is that with the onset of the Neolithic period, maternal mortality increased as a result of a concomitant increase in fertility. If the adoption of agriculture in the Levant increased the rate of population growth at the beginning of the Neolithic, expectation of life may have increased dramatically. Am J Phys Anthropol, 2003. © 2003 Wiley‐Liss, Inc.
Circadian rhythms in diet and habitat use in red ruffed lemurs (Varecia rubra) and white‐fronted brown lemurs (Eulemur fulvus albifrons)
Authors: Vasey Natalie
Published: July 2004

Daily variation in niche use among vertebrates is attributed to a variety of factors, including thermoregulatory, reproductive, and nutritional requirements. Lemuriform primates exhibit many behavioral and physiological adaptations related to thermoregulation and sharp, seasonal reproduction, yet they have rarely been subjects of a quantitative analysis of circadian (or daily) rhythms in niche use. In this study, I document daily rhythms in diet and microhabitat use over an annual cycle in two sympatric, frugivorous lemurs, Varecia rubra and Eulemur fulvus albifrons. Data on diet, forest site, and forest height were recorded at 5‐min time points on focal animals and divided into three time blocks for analysis (06:00–10:00 hr, 10:00–14:00 hr, and 14:00–18:00 hr). I employed multivariate tests of independence to examine daily rhythms in diet and microhabitat use according to sex, season, and reproductive stage. Throughout the day, V. rubra is frugivorous and dwells in the upper canopy, with notable departures (especially for females) during the hot seasons, gestation, and lactation. E. f. albifrons has heterogeneous daily rhythms of food choice and microhabitat use, particularly across seasons, and both sexes are equally variable. These daily rhythms in diet and microhabitat use appear related to thermoregulatory and nutritional requirements, seasonal food availability and circadian rhythms of plant (and possibly insect) palatability, predator avoidance tactics, and in the case of Varecia, to reproduction. Daily rhythms of food choice in V. rubra support two previously suggested hypotheses explaining why primates consume more nonfruit items late in the day, whereas those of E. f. albifrons are too variable to lend support to these hypotheses. Am J Phys Anthropol, 2003. © 2003 Wiley‐Liss, Inc.
Genetic signatures of pre‐expansion bottleneck in the Choctaw population of Oklahoma
Authors: Wang Ning , Zhou Xiaodong , Tan Filemon K. , Foster Morris W. , Arnett Frank C. , Chakraborty Ranajit
Published: July 2004

Previous research showed that the Choctaw Indians of Oklahoma exhibit considerable linkage disequilibria (LD) in a number of regions of the genome that has allowed genetic fine mapping for potential susceptibility genes for the autoimmune connective tissue disease scleroderma, or systemic sclerosis (SSc). In principle, such enhanced background LD in the Choctaws could be caused by population bottleneck event(s) followed by recent population expansion. This investigation utilizes genome‐scan data on 175 dinucleotide loci from 76 Choctaw individuals to seek genetic evidence of the demographic history of the Choctaw Nation. Of the 175 loci examined, 105 are in Hardy‐Weinberg equilibrium. The average unbiased homozygosity over the 105 loci for the Choctaws (29.3%) is significantly higher than that in the European descent group (20.9%); and when adjusted for sample‐size differences, the Choctaw also exhibit a significantly smaller number of segregating alleles (6.65 vs. 8.14) at these loci. Both of these observations are consistent with the trend expected in an isolated population. Comparison of the allele size variance and gene diversity yields an imbalance index (lnβ) of 0.811 in the Choctaw. Of the 105 loci examined, 93 exhibit excess expected homozygosity in comparison to the expectations of a stepwise mutation model in a population of constant size. Taken together, these observations are consistent with a signature of the recent population size expansion of the Choctaws, preceded by bottleneck event(s). Am J Phys Anthropol, 2003. © 2003 Wiley‐Liss, Inc.
Modellreaktionen für die Rhodium‐katalysierte Oxygenierung von Alkenen
Authors: de Bruin Bas , Budzelaar Peter H. M. , Gal Anton W.
Published: July 2004

Die Oxygenierung der C‐H‐ und CC‐Bindungen von Kohlenwasserstoffen, meist mit H2O2 und O2, ist ein wichtiger industrieller Prozess zur Überführung von Mineralöl in hochwertige Chemikalien. Trotz ihrer enormen wirtschaftlichen Bedeutung (und einer entsprechend intensiven Erforschung der Alkenoxygenierung) sind diese Reaktionen aber bislang nur lückenhaft verstanden. Bereits in den frühen 70er Jahren ist eine Anwendung von Rhodium‐ und Iridiumkomplexen in Alkenoxygenierungen eingehend untersucht worden, und einfache anorganische Salze dieser Metalle erwiesen sich verglichen mit dem traditionellen Wacker‐System als weitgehend untauglich. Mit geeigneten Liganden kann andererseits die Oxidation von Alkenen an Rhodium‐ oder Iridiumkomplexen Schritt für Schritt verfolgt werden. Diese Katalysatoren sind daher zur Untersuchung mechanistischer Details der Substratkoordination und der Bildung von C‐O‐Bindungen am Metallzentrum besonders geeignet. Mit den erhaltenen Resultaten lassen sich katalytische Reaktionen mit diesen und eventuell auch mit anderen Metallen besser verstehen. Die Kenntnis der Unterschiede zwischen der Rhodium‐katalysierten Oxidation und der herkömmlichen Wacker‐Oxidation am Palladium könnte zu nützlichen Anwendungen in der Katalyse führen.
Titelbild: Platonic Gold Nanocrystals (Angew. Chem. 28/2004)
Authors: Kim Franklin , Connor Stephen , Song Hyunjoon , Kuykendall Tevye , Yang Peidong
Published: July 2004

Platonischen Körpern gleichen die Formen von Goldnanokristallen, die nach einem modifizierten Polyolprozess in Gegenwart von Oberflächen regulierendem Poly(vinylpyrrolidon) erhalten werden. P. Yang und Mitarbeiter beschreiben in ihrer Zuschrift auf S. 3759 ff., wie diese Polyeder durch die sorgfältige Steuerung der Wachstumsgeschwindigkeiten längs der verschiedenen kristallographischen Richtungen erzeugt werden. Im Zentrum des Titelbilds steht ein Modell des Astronomen Johannes Kepler aus dem 17. Jahrhundert: Zwischen benachbarten Planetenbahnen ist jeweils ein Platonischer Körper einbeschrieben.
Mechanical and aging properties of cross‐linked ethylene propylene diene rubber / styrene butadiene rubber blends
Authors: Nair T. Muraleedharan , Kumaran M. G. , Unnikrishnan G.
Published: July 2004

The mechanical properties and aging characteristics of blends of ethylene propylene diene monomer (EPDM) rubber and styrene butadiene rubber (SBR) were investigated with special reference to the effect of blend ratio and cross‐linking systems. Among the blends, the one with 80/20 EPDM/SBR has been found to exhibit the highest tensile, tear, and abrasion properties at ambient temperature. The observed changes in the mechanical properties of the blends have been correlated with the phase morphology, as attested by scanning electron micrographs (SEMs). The effects of three different cure systems, namely, sulfur (S), dicumyl peroxide (DCP), and a mixed system consisting of sulfur and peroxide (mixed) on the blend properties also were studied. The stress‐strain behavior, tensile strength, elongation at break, and tear strength of the blends were found to be better for the mixed system. The influence of fillers such as high‐abrasion furnace (HAF) black, general‐purpose furnace (GPF) black, silica, and clay on the mechanical properties of 90/10 EPDM/SBR blend was examined. The ozone and water aging studies also were conducted on the sulfur cured blends, to supplement the results from the mechanical properties investigation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2606–2621, 2004
New side‐chain liquid‐crystalline ionomers. I. Synthesis and characterization of a homopolymer derived from ionic mesogenic groups
Authors: Zang Bao‐Ling , Hu Jian‐She , Meng Fan‐Bao , Zhang Bao‐Yan
Published: July 2004

Liquid‐crystalline monomer cholesteryl 4‐allyloxybenzoate (M1), new ionic mesogenic monomer cholesteryl 4‐allyloxy‐3‐(potassium sulfonate)benzoate (M2), and corresponding polymer P1 and ionomer P2 were synthesized. The chemical structures of the monomers and homopolymer were confirmed with Fourier transform infrared and 1H‐NMR spectroscopy. The mesogenic properties were studied with differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. The effect of the ionic units on the phase behavior was examined. M1 showed a cholesteric phase, and M2 revealed a smectic A phase. P1 and P2 displayed smectic A phases. The experimental results demonstrated that the addition of ionic units to the mesogenic molecule not only affected the phase‐transition temperature but also changed the mesogenic phase type. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2511–2516, 2004
Photocontrol of the refractive index of poly(methyl methacrylate) with a nitrone additive
Authors: Tanaka Kenta , Shima Koichi , Kondoh Harunobu , Igarashi Tetsutaro , Sakurai Tadamitsu
Published: July 2004

Hydroxy‐substituted aromatic nitrone derivatives were used for the photochemical control of the refractive index of poly(methyl methacrylate) (PMMA) films. Upon irradiation with 366‐nm light in solution, these derivatives underwent rearrangement reactions, which eventually produced N,N‐diarylformamide derivatives in quantitative yields. Similar photoreactions of the aromatic nitrones in the PMMA films lowered the refractive index of the films by as much as 0.014. The magnitude of the observed refractive‐index change was enough for hydroxy‐substituted nitrones to be used as additives for the fabrication of graded‐index‐type polymer optical fibers. In addition, the refractive index of the PMMA films remained almost constant at any conversion of the starting nitrone derivatives for at least 70 days at room temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2517–2520, 2004
Wood‐fiber/high‐density‐polyethylene composites: Compounding process
Authors: Lu J. Z. , Wu Q. , Negulescu I. I.
Published: July 2004

The compounding process directly influenced the compounding quality of wood–polymer blends and finally affected the interfacial bonding strength and flexural modulus of the resultant composites. With 50 wt % wood fiber, the optimum compounding parameters for the wood‐fiber/high‐density‐polyethylene blends at 60 rpm were a temperature of 180°C and a mixing time of 10 min for the one‐step process with a rotor mixer. The optimum compounding conditions at 90 rpm were a temperature of 165°C and a mixing time of 10 min. Therefore, a short compounding time, appropriate mixing temperatures, and a moderate rotation speed improved the compounding quality of the modified blends and the dynamic mechanical properties of the resultant composites. The melt torque and blend temperature followed a polynomial relationship with the loading ratio of the wood fiber. The highest melt torque and blend temperature were obtained with 50% wood fiber. The coupling treatment was effective for improving the compatibility and adhesion at the interface. The two‐step process was better than the one‐step process because the coupling agents were more evenly distributed at the interface with the two‐step process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2570–2578, 2004
Properties of acrylonitrile–butadiene–styrene/polycarbonate blends with styrene–butadiene–styrene block copolymer
Authors: Taşdemir Münir
Published: July 2004

The importance of alloys and blends has increased gradually in the polymer industry so that the plastics industry has moved toward complex systems. The main reasons for making polymer blends are the strengthening and the economic aspects of the resultant product. In this study, I attempted to improve compatibility in a polymer blend composed of two normally incompatible constituents, namely, acrylonitrile–butadiene–styrene (ABS) and polycarbonate (PC), through the addition of a compatibilizer. The compatibilizing agent, styrene–butadiene–styrene block copolymer (SBS), was added to the polymer blend in ratios of 1, 5, and 10% with a twin‐screw extruder. The morphology and the compatibility of the mixtures were examined by scanning electron microscopy and differential scanning calorimetry. Further, all three blends of ABS/PC/SBS were subjected to examination to obtain their yield and tensile strengths, elasticity modulus, percentage elongation, Izod impact strength, hardness, heat deflection temperature, Vicat softening point, and melt flow index. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2521–2527, 2004
Preparation and characterization of conductive latex based on polyaniline–perlite composite
Authors: Arsalani Nasser , Hayatifar Mohammad
Published: July 2004

The development of polymers with high electrical conductivity has attracted significant research interest because of the possibility of new applications. Electrically conductive latexes have drawn the attention of scientists over the last few years. The present work reports the preparation of composites in which polyaniline was deposited onto perlite particles by oxidative polymerization. Electrically conductive latex was prepared by homogeneously mixing submicron conductive composites with poly(vinylacetate‐co‐butylacrylate‐co‐butylversitate) resin in a desirable ratio. The conductivity of composites and latex was measured by a standard four‐point probe. Morphology of composites was studied by scanning electron microscopy. Adhesion and electroactivity of the latex were also investigated. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2528–2531, 2004
Preparation and properties of a salt‐resistant superabsorbent polymer
Authors: Ma Songmei , Liu Mingzhu , Chen Zhenbin
Published: July 2004

Crosslinked sodium polyacrylate was prepared by solution polymerization with N,N‐methylene‐bisacrylamide (bisAM) as crosslinking agent; it was subsequently surface‐crosslinked by ethylene glycol diglycidyl ether (EGDE) and then was modified with inorganic salt to obtain a superabsorbent with water absorbency in 0.9 wt % NaCl aqueous solution at atmosphere and applied pressure (P ≈ 2 × 103 Pa) of 55 and 20 g.g−1, respectively. Moreover, it also had excellent hydrogel strength. The effects of reaction temperature, reaction time, neutralization degree (ND) of acrylic acid, amount of initiator, crosslinking agent, and surface‐crosslinking agent, mass ratio of inorganic salt to initial superabsorbent, molar ratio of sodium aluminate (NaAlO2) to potassium dihydrogen hyphosphate (KH2PO4) on water absorbency (WA) in 0.9 wt % NaCl aqueous, and the hydrogel modulus were investigated and optimized. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2532–2541, 2004
Syntheses and properties of low‐level melamine‐modified urea–melamine–formaldehyde resins
Authors: No B. Young , Kim Moon G.
Published: July 2004

Syntheses of urea–melamine–formaldehyde (UMF) resins were studied using 2–12% melamine levels and UF base resins that were preadvanced to various different extents. The melamine reaction was carried out at pH 6.3 with F/(U + M) mole ratio of 2.1 until a target viscosity of V was reached (Gardener–Holdt) and then the second urea added at pH 8.0 to give a final F/(U + M) mole ratio of 1.15. Analyses with 13C‐NMR and viscosity measurements showed that MF components react fast and the UF components very slowly in the melamine reaction. Therefore, as the extent of preadvancement of UF base resin was decreased, the reaction time to reach the target viscosity became longer and the MF resin components showed high degrees of polymerization. The overpolymerization of MF components resulted in increasingly more opaque resins, with viscosity remaining stable for more than a month. As the preadvancement of UF base resin was increased, the extent of advancement of MF components decreased, to give clearer resins, with viscosity slowly increasing at room temperature. Overall, preadvancing the UF base resin components to an appropriate extent was found to be a key to synthesizing various low‐level melamine‐modified UMF resins. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2559–2569, 2004
Characterization of crosslinked starch materials with spectroscopic techniques
Authors: Delval Franck , Crini Grégorio , Bertini Sabrina , Morin‐Crini Nadia , Badot Pierre‐Marie , Vebrel Joël , Torri Giangiacomo
Published: July 2004

The structure, mobility, and properties of crosslinked starch materials of various compositions were investigated with FTIR and NMR spectroscopy, and relaxation time measurements were taken with cross‐polarization/magic‐angle‐spinning (CP–MAS) and magic‐angle‐spinning (MAS) spectroscopy. Characterization by Fourier transform infrared spectroscopy confirmed the crosslinking reaction. The CP–MAS and MAS spectra allowed the assignment of the principal 13C signals. The molecular mobility of these polysaccharides was analyzed in terms of the cross‐relaxation time between the protons and carbons, the 1H spin–lattice relaxation time in the rotating frame, and the 1H longitudinal spin–lattice relaxation time. Relaxation studies showed that increasing the crosslinking degree increased the amorphous content, and the material became rigid as an increasing number of covalent bonds in the polymer network reduced mobility. The values of the spin–lattice relaxation in the rotating frame reflected the homogeneous nature of the materials. The correlation between the crosslinking degree, structure, and mobility and the sorption properties of these sorbents was examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2650–2663, 2004