Polymerization of liquid propylene with a fourth‐generation Ziegler–Natta catalyst: Influence of temperature,hydrogen, monomer concentration,and prepolymerization method on powder morphology

Liquid propylene was polymerized in a 5‐L autoclave batch reactor using a commercially available TiCl₄/MgCl₂/Al(ethyl)₃/DCPDMS Ziegler–Natta catalyst, with a phthalate ester as internal electron donor. The powders from these polymerizations were characterized using laser diffraction particle size distribution (PSD) analysis, scanning electron microscopy (SEM), and bulk density measurements. These characteristics were analyzed as a function of the process conditions, including hydrogen and monomer concentration, polymerization temperature, and the prepolymerization method. It was shown that polymerization temperature influences the powder morphology to a large extent. At low temperatures, high‐density particles were obtained, showing regular shaped particle surfaces and low porosities. With increasing temperature, the morphology gradually was transferred into a more open structure, with irregular surfaces and poor replication of the shape of the catalyst particle. When using a prepolymerization step at a relatively low temperature, the morphology obtained was determined by this prepolymerization step and was independent from conditions in main polymerization. The morphology obtained was the same as that observed after a full polymerization at temperature. Even when using a short polymerization at an increasing temperature, the morphology was strongly influenced by the initial conditions. The effect of variation in hydrogen concentration supported the conclusion that the initial polymerization rate determines the powder morphology. In the absence of hydrogen, high bulk densities, and regularly shaped particles were obtained, even at high temperatures. With increasing hydrogen concentration, the reaction rates increased rapidly, and with that changed the morphology. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1421–1435, 2003     

A survey on the history of transaction management: from flat to grid transactions

Transactions have been around since the Seventies to provide reliable information processing in automated information systems. Originally developed for simple ‘debit-credit’ style database operations in centralized systems, they have moved into much more complex application domains including aspects like distribution, process-orientation and loose coupling. The amount of published research work on transactions is huge and a number of overview papers and books already exist. A concise historic analysis providing an overview of the various phases of development of transaction models and mechanisms in the context of growing complexity of application domains is still missing, however. To fill this gap, this paper presents a historic overview of transaction models organized in several ‘transaction management eras’, thereby investigating numerous transaction models ranging from the classical flat transactions, via advanced and workflow transactions to the Web Services and Grid transaction models. The key concepts and techniques with respect to transaction management are investigated. Placing well-known research efforts in historical perspective reveals specific trends and developments in the area of transaction management. As such, this paper provides a comprehensive, structured overview of developments in the area.     

Effects of woody elements on simulated canopy reflectance: Implications for forest chlorophyll content retrieval

An important bio-indicator of actual plant health status, the foliar content of chlorophyll a and b (Cab), can be estimated using imaging spectroscopy. For forest canopies, however, the relationship between the spectral response and leaf chemistry is confounded by factors such as background (e.g. understory), canopy structure, and the presence of non-photosynthetic vegetation (NPV, e.g. woody elements)—particularly the appreciable amounts of standing and fallen dead wood found in older forests. We present a sensitivity analysis for the estimation of chlorophyll content in woody coniferous canopies using radiative transfer modeling, and use the modeled top-of-canopy reflectance data to analyze the contribution of woody elements, leaf area index (LAI), and crown cover (CC) to the retrieval of foliar Cab content. The radiative transfer model used comprises two linked submodels: one at leaf level (PROSPECT) and one at canopy level (FLIGHT). This generated bidirectional reflectance data according to the band settings of the Compact High Resolution Imaging Spectrometer (CHRIS) from which chlorophyll indices were calculated. Most of the chlorophyll indices outperformed single wavelengths in predicting Cab content at canopy level, with best results obtained by the Maccioni index ([R₇₈₀ − R₇₁₀] / [R₇₈₀ − R₆₈₀]). We demonstrate the performance of this index with respect to structural information on three distinct coniferous forest types (young, early mature and old-growth stands). The modeling results suggest that the spectral variation due to variation in canopy chlorophyll content is best captured for stands with medium dense canopies. However, the strength of the up-scaled Cab signal weakens with increasing crown NPV scattering elements, especially when crown cover exceeds 30%. LAI exerts the least perturbations. We conclude that the spectral influence of woody elements is an important variable that should be considered in radiative transfer approaches when retrieving foliar pigment estimates in heterogeneous stands, particularly if the stands are partly defoliated or long-lived.     

Effects of 400 keV electrons flux on two space grade silicone rubbers

Two different space grade silicone rubbers were irradiated by an electron flux of 400 keV. The irradiation impact strongly depends on the chemical structure of rubbers (one reinforced with MQ resins, and the other one functionalized with phenyl groups at the silicon atoms and reinforced with silica). The irradiated rubbers were studied by means of solvent swelling, solid-state ²⁹Si NMR, and ATR–FTIR spectroscopy. Physical properties were evaluated by thermal (differential scanning calorimetry), mechanical (dynamic mechanical analysis), and thermo-optical (ultraviolet–visible–near infrared spectroscopy) analyses. The formation of silicium T units and Si–CH₂–Si networks were evidenced by ²⁹Si NMR, and the increase of the glass transition temperature and of modulus reflect the substantial increase in the macromolecular chain rigidity of the irradiated material. Dramatic damages of mechanical properties were observed, depending on the reinforced materials used. Slight changes of thermo-optical properties were highlighted independently to the initial chemical structure.     

Sustaining leprosy services in the changing context of health sector reform

National leprosy control programmes currently face a number of changes to the environment within which they operate. This paper examines the issues arising from these. It focuses, in particular, on those arising from changes in the structure of the health sector as a result of policies of health sector reform which are being considered or adopted in many developing countries. These include decentralization, financing strategies, greater role for the private and NGO sectors and the integration of vertical programmes. The paper is structured around a number of key steps in the development of a strategy for sustainability of appropriate leprosy services. These are the assessment of the epidemiological, social and health services context, development of programme objectives, planning of human and financial resources, development of the strategy, mapping the roles of potential actors, development of regulatory and incentive mechanism, action planning and managing change and, finally, re-evaluation of the programme objectives and service delivery organization. The paper stresses the importance of process in developing ownership of a strategy. It concludes with a set of key questions which it suggests need to be addressed by leprosy programme managers in the development of a proactive response to the changes.     

Analysis of a modified variable-length tuning post in a rectangular waveguide.

A modified variable-length post for use in high power waveguide tuning networks is analyzed to determine its reactance properties. Theoretical predictions are shown to be in good agreement with experimental results. An investigation of the reactance characteristics and the aperture voltage characteristics of the modified post, as a function of its dimensions, is also reported.     

Speed limits: Orientation and semantic context interactions constrain natural scene discrimination dynamics.

The visual system rapidly extracts information about objects from the cluttered natural environment. In 5 experiments, the authors quantified the influence of orientation and semantics on the classification speed of objects in natural scenes, particularly with regard to object-context interactions. Natural scene photographs were presented in an object-discrimination task and pattern masked with various scene-to-mask stimulus-onset asynchronies (SOAs). Full psychometric functions and reaction times (RTs) were measured. The authors found that (a) rotating the full scenes increased threshold SOA at intermediate rotation angles but not for inversion; (b) rotating object or context degraded classification performance in a similar manner; (c) semantically congruent contexts had negligible facilitatory effects on object classification compared with meaningless baseline contexts with a matching contrast structure, but incongruent contexts severely degraded performance; (d) any object-context incongruence (orientation or semantic) increased RTs at longer SOAs, indicating dependent processing of object and context; and (e) facilitatory effects of context emerged only when the context shortly preceded the object. The authors conclude that the effects of natural scene context on object classification are primarily inhibitory and discuss possible reasons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reference range and repeatability of a combined intestinal permeability and function test in clinically healthy Irish setter dogs

We investigated the influence of nutrition and exercise interventions within cognitive/behavioral and public health formats on weight and blood lipid profiles in obese children. Compliance was also examined as well as the relationship of the compliance measures with clinical outcome variables. Three conditions were compared over 16 sessions: nutrition and eating-habit change followed by exercise (NE), exercise followed by nutrition and eating-habit change (EN), and an information control (INFO). NE and EN were presented in a cognitive/ behavioral framework which focused on the development of self-regulation whereas the INFO condition received the same material in a public health/educational model. NE and EN participants evidenced modest, yet significant, reductions in weight and blood lipids, and the impact of these two interventions endured at a five-year follow-up. In contrast, INFO participants displayed stable weight and blood lipids during the course of the program, and most remained morbidly obese at follow-up. Improved nutrition, increased physical activity and fitness were significantly correlated with weight and lipid reductions.     

Optical fiber coatings: High modulus coatings for fibers with a low microbending sensitivity

An important function of an optical fiber coating is to prevent optical losses due to microbending induced by lateral forces on the fiber. To protect the fiber over a wide temperature range the modulus of the primary and the secondary coating should be low and high, respectively, and temperature independent. However, selecting the most appropriate organic coating materials introduces a new source of optical losses. Since the linear thermal expansion coefficients of silica and the organic coatings differ by about two orders of magnitude, thermal, fluctuations will cause axial stresses. Cooling may then induce bending or buckling of the glass fiber in the soft primary coating, resulting in increased transmission losses. This effect is especially pronounced when a high-modulus secondary coating is selected with a glass transition temperature above 80°C. For this type of coating the difference in radial shrinkage between the buffer and the top coating during cooling from the curing temperature becomes important. The influence of primary coating thickness is discussed.     

Mutational analysis of the C-terminal region of Saccharomyces cerevisiae ribosomal protein L25 in vitro and in vivo demonstrates the presence of two distinct functional elements

A previous analysis of yeast ribosomal protein L25 implicated an evolutionarily conserved motif of seven amino acids near the C terminus (positions 120 to 126) in specific binding of the protein to domain III of 26 S rRNA. We analyzed the effect of various point mutations in this amino acid sequence on the capacity of the protein to interact in vitro with its binding site on the rRNA. Most of the mutations tested, including some conservative replacements, strongly reduced or abolished rRNA binding, further supporting a pivotal role for the motif in the specific interaction between L25 and 26 S rRNA. We have also determined the ability of the various mutant L25 species to complement in vivo for the absence of wild-type protein in cells that conditionally express the chromosomal L25 gene. Surprisingly, up to a fivefold reduction in the in vitro binding capacity of L25 is tolerated without affecting the ability of the mutant protein to support (virtually) wild-type rates of 60 S subunit formation and cell growth. Mutations that completely abolish recognition of 26 S rRNA, however, block the formation of 60 S particles, demonstrating that binding of L25 to this rRNA is an essential step in the assembly of the large ribosomal subunit. Using the same combination of approaches we identified an element, located between positions 133 and 139, that is indispensable for the ability of L25 to support a normal rate of 60 S subunit formation, but plays a relatively minor role in determining the rRNA-binding capacity of the protein. In particular, the presence of a hydrophobic amino acid at position 135 was found to be highly important. These results indicate that the element in question is crucial for a step in the assembly of the 60 S subunit subsequent to association of L25 with 26 S rRNA.