Open Arrangement Research Articles

Conformation and orientation effects in the X-ray photoelectron spectra of organic polymers

Conformation and orientation effects in the XPS spectra of organic polymers are small but can be observed with modern high performance equipment. This paper discusses some of the experimental factors that should be considered when attempting to detect such effects, and describes several recent studies which illustrate the subtle phenomena that can now be observed. Conformation effects, revealed by melting semi-crystalline polymer samples in the analysis chamber of an XPS spectrometer, are reported for the valence band and C 1s spectra of nylon 12 and poly(ethylene adipate), and for the valence band spectrum of poly(ethylene succinate). For nylon 12 the changes in the C 2s region of the valence band spectrum are interpreted in terms of disordering of the planar zig-zag conformation of the (CH 2) 11 segments of the polymer chain. Pendant group surface orientation effects, detected by angle resolved XPS (with emission angles as low as 5° relative to the sample surface), are reported for poly(2-chloroethyl methacrylate) (PCEMA), poly(lauryl methacrylate) (PLMA) and poly(2-hydroxyethyl methacrylate) (PHEMA). For PCEMA and PLMA the uppermost surfaces are enriched with –CH 2CH 2Cl and –(CH 2) 11CH 3 pendant groups, respectively, whereas for PHEMA the data suggest relatively few –CH 2CH 2OH pendant groups at the surface. The C 1s and Cl 2p spectra of PCEMA reveal surface core level binding energy shifts of about +0.2 eV, and the Cl L 23M 23M 23 spectrum a surface Auger kinetic energy shift of about −0.6. The C 1s spectra of PLMA and PHEMA also reveal surface core level shifts and for PLMA this is interpreted in terms of a disordered and open arrangement of the –(CH 2) 11CH 3 pendant groups at the polymer surface.

SE—Structures and Environment: Analysis of Thermally Driven Ventilation in Tunnel Greenhouses using Small Scale Models

A laboratory method for studying natural ventilation by thermal effects was applied to a single-span tunnel greenhouse with different opening arrangements. One-tenth scale models of the tunnel greenhouse were made of Perspex and immersed in a water tank. The buoyancy flux due to solar heating of the floor in real greenhouses was simulated in the laboratory by adding a salty solution through the floor of the inverted scale model. Tests were video recorded and images digitized so that the temperature distribution in a cross-section could be obtained. Dimensional analysis and the scaling laws established relationships between variables in the model and at full scale.First, the method was verified by comparing laboratory results on temperature rise and air exchange rate with measurements from a 3 m wide tunnel greenhouse. The effect of insect-proof screens on the air exchange rate was also investigated in the laboratory and compared to full-scale results. After verification, tests were conducted on a scale model of 6m wide tunnel greenhouses. Four vent arrangements were considered: 16 and 33% of sidewall openings, 8% sidewall opening plus 10% roof opening and 16% sidewall opening plus 10% roof openings. For each configuration, expressions of the temperature rise as a function of the sensible heat given to the greenhouse air are presented. Also, the air exchange rate of all configurations studied with three types of net over the openings is given. The results show the importance of combining roof and sidewall ventilation, especially when netting of reduced permeability covers the openings.

Oocyte donation in infertility treatment

Oocyte donation in infertility treatment

Serine Acetyltransferase from Escherichia coli Is a Dimer of Trimers

Equilibrium sedimentation studies show that the serine acetyltransferase (SAT) of Escherichia coli is a hexamer. The results of velocity sedimentation and quasi-elastic light scattering experiments suggest that the identical subunits are loosely packed and/or arranged in an ellipsoidal fashion. Chemical cross-linking studies indicate that the fundamental unit of quaternary structure is a trimer. The likelihood, therefore, is that in solution SAT exists as an open arrangement of paired trimers. Crystals of SAT have 32 symmetry, consistent with such an arrangement, and the cell density function is that expected for a hexamer. Electron microscopy with negative staining provides further evidence that SAT has an ellipsoidal subunit organization, the dimensions of the particles consistent with the proposed paired trimeric subunit arrangement. A bead model analysis supports the view that SAT has a low packing density and, furthermore, indicates that the monomers may have an ellipsoidal shape. Such a view is in keeping with the ellipsoidal subunit shape of trimeric LpxA, an acyltransferase with which SAT shares contiguous repeats of a hexapeptide motif.

Effect of Aperture Geometry on Heat Transfer in Tilted Partially Open Cavities

Free convection from a square, tilted partially open cavity was investigated experimentally. The experiment was carried out to study the effect of the aperture geometry on the heat transfer between the cavity and the surrounding air. Four different geometrical arrangements for the opening were investigated: (1) high wall slit, (2) low wall slit, (3) centered wall slit, and (4) uniform wall slots. Each opening arrangement was studied at opening ratios (i.e., ratio of opening height to cavity height) of 0.25, 0.5, and 0.75. The average heat transfer coefficient between the cavity and the surrounding air was estimated for each geometrical arrangement for tilt angles ranging from −90 deg to +90 deg with increments of 15 deg and at a constant heat flux Grashof number of 5.5 × 108. The results showed that for tilt angles between 90 and 75 deg, the heat transfer coefficient has a small value that is independent of the geometrical arrangement of the opening. The value of the heat transfer coefficient increases sharply with decreasing tilt angle until an angle value of zero degrees is reached. The increase in the heat transfer coefficient continues in the negative range of tilt angle but not in the same rate as in the positive range of the tilt angle. The uniform slot arrangement gave in general higher heat transfer coefficient than the other three arrangements of the opening. Large differences in the heat transfer coefficient were observed between the high and the low wall slits where the high wall slit is found to transfer more heat to the surroundings than the low wall slit. Correlations were developed to predict the average Nusselt number of the cavity in terms of the opening ratio and the cavity tilt angle for cavities with high wall slit, low wall slit, centered wall slit, and the uniform wall slots.

The structural basis for the susceptibility of gangliosides to enzymatic degradation.

The conformational properties of GM2, GalNacbeta-4(Neu5Acalpha-3) Galbeta-4Glcbeta-1Cer have been compared to those of 6'-GM2, in which the linkage between the GalNAc and Gal was altered from GalNacbeta-4Galbeta- to GalNacbeta-6Galbeta-, and to those of GD1a, Neu5Acalpha-3Galbeta-3GalNAcbeta-4(Neu5Acalpha-3 )Galbeta-4Glcbeta-1Cer, and GalNAc-GD1a. Our results revealed that unlike the compact and rigid oligosaccharide head group found in GM2, where the Neu5Ac and the GalNAc residues interact, the sugar chain of 6'-GM2 is in an open spatial arrangement, with the Neu5Ac no longer interacting with GalNAc, freely accessible to external interactions. The structure of GD1a can be regarded as that of GM2 with an extension of the terminal Neu5Acalpha-3Galbeta-disaccharide. The inner portion of GD1a is that of GM2 comprising the very rigid GalNAc-[Neu5Ac-]Gal trisaccharide. The terminal Neu5Ac-Gal linkage is flexible and fluctuates between two limiting conformations. In GalNAc-GD1a the outer sialic acid gains conformational rigidity due to the presence of the outer GalNAc in position 4 of galactose. This ganglioside has two 'core' GalNAc-[Neu5Ac-]Gal trisaccharide linked in tandem.

Structural Basis for the Resistance of Tay-Sachs Ganglioside GM2 to Enzymatic Degradation

To understand the reason why, in the absence of GM2 activator protein, the GalNAc and the NeuAc in GM2 (GalNAcbeta1-->4(NeuAcalpha2-->3)Galbeta1-->4Glcbet a1-1'Cer) are refractory to beta-hexosaminidase A and sialidase, respectively, we have recently synthesized a linkage analogue of GM2 named 6'GM2 (GalNAcbeta1-->6(NeuAcalpha2-->3)Galbeta1-->4Glcbet a1-1'Cer). While GM2 has GalNAcbeta1-->4Gal linkage, 6'-GM2 has GalNAcbeta1-->6Gal linkage (Ishida, H., Ito, Y., Tanahashi, E., Li, Y.-T., Kiso, M., and Hasegawa, A. (1997) Carbohydr. Res. 302, 223-227). We have studied the enzymatic susceptibilities of GM2 and 6'GM2, as well as that of the oligosaccharides derived from GM2, asialo-GM2 (GalNAcbeta1-->4Galbeta1--> 4Glcbeta1-1'Cer) and 6'GM2. In addition, the conformational properties of both GM2 and 6'GM2 were analyzed using NMR spectroscopy and molecular mechanics computation. In sharp contrast to GM2, the GalNAc and the Neu5Ac of 6'GM2 were readily hydrolyzed by beta-hexosaminidase A and sialidase, respectively, without GM2 activator. Among the oligosaccharides derived from GM2, asialo-GM2, and 6'GM2, only the oligosaccharide from GM2 was resistant to beta-hexosaminidase A. Conformational analyses revealed that while GM2 has a compact and rigid oligosaccharide head group, 6'GM2 has an open spatial arrangement of the sugar units, with the GalNAc and the Neu5Ac freely accessible to external interactions. These results strongly indicate that the resistance of GM2 to enzymatic hydrolysis is because of the specific rigid conformation of the GM2 oligosaccharide.

Conformational changes in myocardial actin in heart failure caused by toxic allergic myocarditis

The fluorescence resonance energy transfer method was used to study myocardial actin in rabbits with severe heart failure caused by toxic allergic myocarditis. It caused changes in orientation and microenvironment and increased excitation lifetime of fluorophores at the labels to Cys374 and Cys10 (subdomain 1), as well as at Lys61 and Tyr69 (subdomain 2). In addition, it increased the distance between Cys374 and Lys61, Cys10, and Tyr69, as well as between Tyr69 and Cys10. This attests to enlargement of the outer actin domain and more exposed and open arrangement of the tertiary structures of the N- and C-terminal regions and subdomain 2, accompanied by reduced conformational mobility. The relationships between actin conformation changes and decrease in contractile force and rate, as well as efficiency of actomyosin contraction are revealed, which agrees with the hypothesis on the leading role of actin in disturbances of contractile activity and energy transduction in the system of contractile proteins in heart failure.

The habitat of nesting whooping cranes

Through a spatial, multi-scale approach I compared available habitat with habitat used by whooping cranes ( Grus americana) on their nesting grounds in Wood Buffalo National Park, Canada. Thirty-two study sites (16 used, 16 available) were established in the nesting area in August 1996. Data were gathered by (a) plots of 9.8 m radius which provided detailed site data and served as ground truth for (b) concentric circular plots of 25, 50, 100, 200, and 500 m radius in which 21 cover types were mapped onto false color infrared 1:15,840 airphotos. Whooping cranes chose habitat that differed from a random sample. Habitat selection was strongest at the nest site, where many attributes of habitat type and structure were evident. Beyond 200 m radius from the nest site, selection was evident solely as avoidance of unsuitable habitat. At the nest site scale (9.8 m radius), the preferred habitat was visually open, with large amounts of open water (median depth 7 cm in August), nearby which there were a few abundant vegetation species in an open spatial arrangement. Habitat types used by whooping cranes were diatom ponds, bulrush ( Scirpus validus) marshes, bulrush/cattail ( Typha latifolia) mixed marshes with aquatic macrophytes, and shrubby mixed marshes with water sedge ( Carex aquatilis) and cattail. Plant species diversity of the entire crane area is low, particularly that of nesting sites. In contrast, spatial diversity of community types is a marked characteristic of the area; average patch size is <1 ha. At the 78.5 ha scale (500 m radius), there were no apparent differences in landscape structure or diversity between used vs available habitats. MANOVA/repeated measures and multi-response permutation procedures were used to examine habitat selection at five spatial scales. Whooping cranes selected bulrush marsh out to a radius of 200 m from the nest, and avoided featureless shrub bogs and fens out to a radius of at least 500 m from nests. Historical and present nesting habitat share the following characteristics: small shallow lakes and ponds, willow communities, marshes of bulrush and cattail, mudflats, and perhaps sedge meadows. The present nesting habitat may be atypical compared to the core of the historical range in its diatom ponds, gypsum karst-groundwater discharge hydrogeology, and permafrost. Cranes appear to use only a small portion of the total available area of their nesting grounds. The Wood Buffalo–Aransas whooping crane population should not be limited by available breeding habitat in the near future.

Voids Investigation of Amorphous Carbon Films Deposited by DC-Magnetron Sputtering: A Small Angle x-ray Scattering and Gas Thermal Effusion Study

ABSTRACTAmorphous carbon films were deposited onto (100) Si crystals and onto ultra-pure Al foils by dc-magnetron sputtering with different Ar plasma pressures, from 0.17 to 1.4 Pa. We investigate the voids structure and the voids density in these films by means of small angle x-ray scattering (SAXS) and mass spectrometry of effused gases. The analysis of the effusion spectra provided clear evidence that films deposited at lower pressures are compact, while the films deposited at higher pressure present a more open structural arrangement, confirming density results obtained by using ion beam techniques. SAXS results reveal that the fraction of open volumes increases with the plasma pressure: a direct correlation between film density and open volume fraction is found. These different film microstructures could be explained by the existence of different bombarding regimes during film growth

Mutations and modifications support a ‘pitted-flexiball’ model for α-crystallin

α-Crystallin is renown for resisting crystallization and electron microscopic image analysis. The spatial conformation thus remaining elusive, the authors explored the structure and chaperone functioning by analyzing the effects of site-directed mutagenesis, the properties of naturally occurring aberrant forms of α-crystallin and the influence of chemical modifications. The authors observed that the globular multimeric structure, as well as the chaperoning capacity are remarkably tolerant towards changes and modifications in the primary structure. The essential features of the quaternary structure—globular shape, flexibility, highly polar exterior and accessible hydrophobic surface pockets—support a ‘pitted-flexiball’ model, which combines tetrameric subunit building blocks in an open micelle-like arrangement.

PHOTOACOUSTIC SPECTROSCOPY OF CORROSION PRODUCTS OF COPPER FORMED IN TROPICAL ENVIRONMENTS

The evolution of thermal properties of copper samples, as a function of exposure time to a corroding atmosphere, is investigated in detail. The samples were exposed to a natural marine environment of the Yucatan Peninsula in Mexico and were analyzed without any additional pretreatment. The study is mainly based upon the measurements of thermal and optical properties of the sample, using the non-destructive photoacoustic technique. The thermal diffusivity was measured with a conventional open photoacoustic cell arrangement, whereas the thermal effusivity was determined using a new experimental configuration.

Foster Placement

For children who require placement, individual assessment can reveal whether return to the parents, termination of parental rights and adoption, relative placement, transfer of guardianship, or innovative placement and open adoption arrangements, such as the neighborhood program of The Center for Family Life, represents the least harmful option for the child. Nevertheless, certain guiding principles should prevail: psychological continuity of at least one significant nurturing protective adult and decisions based on the least detrimental alternative, according to the child's sense of time.

ARRANJOS ESPACIAIS E AGRUPAMENTOS DE CRIANÇAS PEQUENAS EM CRECHES

Este trabalho verificou a formação de agrupamentos em duos, trios, quadras e com cinco ou mais elementos, utilizando a mesma coleta de dados do estudo anterior, realizado com crianças de 2-3 anos de duas creches da região de Ribeirão Preto (SP) que atendem famílias de baixa renda. Os dados foram obtidos por duas câmeras fotográficas com funcionamento automático e simultâneo a cada 30 segundos, em três fases: I - arranjo aberto: habitual (4 sessões): II - arranjo aberto: introdução de pequenas estantes de madeira nas laterais (6 sessões); III - arranjo semi-aberto: montagem de duas zonas circunscritas (6 sessões). Proximidade física (distância de até 1 m) foi utilizada para registrar os agrupamentos, verificando-se: (1) maior estruturação espacial acarreta acréscimo na ocorrência de agrupamentos entre crianças e redução daqueles com o adulto; (2) maior freqûência de díades; (3) maior ocorrência de agrupamentos. especialmente com três ou mais crianças, em áreas mais estruturadas de cada fase. Salienta-se a importância do arranjo espacial na formação de agrupamentos infantis e no planejamento de ambientes infantis coletivos.

Syntheses and Reactivity of Heterometallic Oxo−Acetylide Cluster Compounds. Skeletal Rearrangement and Conversion of Acetylide to Alkenyl, Alkylidene, and Allenyl Ligands on a WRe2 Framework

Oxidation of the mixed-metal cluster Cp*WRe2(CCR)(CO)9 (1, Cp* = C5Me5; R = Ph and C(Me)CH2) with dioxygen in solution at 100 °C affords the oxo clusters Cp*W(O)Re2(CCR)(CO)8, (2a, R = Ph; and 2b, R = C(Me)CH2. Treatment of 2 with CO at 110 °C provides the clusters Cp*W(O)Re2(CCR)(CO)9 (4), which revert back to 2 by removal of one CO upon thermolysis. Both compounds 2 and 4 contain an open triangular skeletal arrangement, a multisite bound acetylide ligand, and a terminal oxo ligand attached to the W atom. Complex 2a reacts with dihydrogen to form a mixture of three cluster complexes: the acetylide cluster Cp*WRe2(μ-O)(μ-H)2(CCPh)(CO)6 (5a), alkenyl cluster Cp*W(O)Re2(CHCHPh)(CO)8 (6a), and the alkylidene cluster Cp*W(O)Re2(μ-H)(CHCH2Ph)(CO)8 (7a), which are formally produced by addition of two H2 and elimination of two CO molecules, transferring one H2 to the acetylide ligand and incorporation of one H2 molecule to 6a, respectively. For the vinylacetylide compound 2b, it reacts with dihydrogen under sim...

Concept study for a combined reinforced concrete containment

A variety of different types of steel and concrete containments have been designed and constructed in the past. Most of the concrete containments had been pre-stressed, offering the advantage of small displacements and a certain leak-tightness of the concrete itself. However, considerable stresses in concrete as well as in the tendons have to be maintained during the whole lifetime of the plant in order to guarantee the required pre-stressing. The long-time behaviour and the ductility in the case of beyond-design-load cases must be verified. Contrary to a pre-stressed containment a reinforced containment will only be significantly loaded during test conditions or when needed in case of an accident. It offers additional margins which can be used especially for dynamic loads such as impacts or for beyond-design events. The aim of this paper is to show the feasibility of a so-called combined containment which means a containment capable of resisting both severe internal accidents and external hazards, mainly the aircraft crash impact as considered in the design of nuclear power plants in Germany. The concept is based on a lined reinforced containment without pre-stressing. The mechanical resistance function is provided by the reinforced concrete and the leak-tightness function is provided by a so-called composite liner made of non-metallic materials. Some results of tests performed at Siemens laboratories and at the University of Karlsruhe which show the capability of a composite liner to bridge over cracks at the concrete surface will be presented in the paper. The study shows that the combined reinforced concrete containment with a composite liner offers a robust concept with high flexibility with respect to load requirements, beyond-design events and geometrical shaping (arrangement of openings, an integration of adjacent structures). The concept may be further optimized by partial pre-stressing at areas of high concentration of stresses such as at transition zones or at disturbances around large openings.

A Triclinic Crystal Form of the Lectin Concanavalin A

The molecular structure of a triclinic crystal form of concanavalin A has been refined at 2.4 Å resolution. The crystals have unit cell dimensionsa= 78.8 Å,b= 79.3 Å,c= 133.3 Å, α = 97.1°, β = 90.2°, and γ = 97.5° and contain two tetramers per asymmetric unit each with approximate 222 symmetry. The final crystallographic R-factor is 0.205 and the free-R-factor is 0.265 in the resolution range 6.0 to 2.4 Å. The conformation of the tetramer is more similar to that found in concanavalin A saccharide complexes than in the previously reported I222 crystal form of uncomplexed concanavalin A. A comparison of the molecular packing between the two crystal forms shows a more open arrangement with large solvent channels through the crystal.

Property Rights, Small Woodlot Owners and Forest Management in Nova Scotia

This paper explores the political, economic and social power structure in the forest of Nova Scotia through the history of forest tenures and forest management, focussing on small woodlot owners. In forest management, one assumption holds that small woodlot owners strongly believe in the notion of private property rights; the other holds that it is unacceptable to interfere with such rights except through educational and voluntary programmes. We question these assumptions. In Nova Scotia, the state’s alleged protection of property rights has been rhetorical and highly selective. Property rights have been contested. Individual property rights, common property rights and open access arrangements have been eroded while corporate property rights have been enhanced. The ascendancy and pre-eminence of the latter are not a function of a natural order. There are precedents for different sets of rules, even within capitalism, as illustrated both by the history of Nova Scotia and by conditions in other jurisdictions.

Selective Catalytic Reactions at the External Surface of Zeolite Crystals

The arrangement of the pore openings serves as a template for the positions of the branchings in the isomerization of n‐alkanes—this is the explanation proposed by Martens et al. (Angew. Chem. Int. Ed. Engl. 1995, 34, 2528) to rationalize their results in the isomerization of n‐heptadecane on the zeolite ZSM‐22. This reaction would thereby be the first example of key–lock catalysis on the external surface of a zeolite.

THE GOLDFIELDS GAS PIPELINE: &amp;apos;OPENING A NEW FRONTIER&amp;apos;

Gas exploration and development in the northwest Pilbara in WA has increased due to the commitment of the Goldfields Gas Transmission Joint Venture to a 1,380 km gas pipeline linking the north west Pilbara to the east Pilbara iron ore region and the northern and central Goldfields. Construction of the GGT pipeline was approved in January 1995 and it is expected the pipeline will be servicing major mining operations in Newman, Mt Keith, Leinster and Kalgoorlie by August 1996. Other existing mining operations located near the pipeline are expected to convert from distillate for power station fuel to gas in 1996-97. Major new mining prospects in these highly prospective minerals provinces also offer potential for increased gas demand and GGT Pipeline throughput.The commercial arrangements for GGT Pipeline services are the first in Australia to be offered under the open access arrangements espoused by the Federal and WA Governments, and have set a benchmark for other pipelines in Australia. The innovative distance related pipeline tariff arrangements offer prospective gas shippers a simple method for evaluating use of the GGT pipeline and securing gas transmission services.The GGT Pipeline has had and will continue to have a major effect on the WA gas scene, stimulating gas exploration by capturing an established base load energy market currently dependent on liquid fuels and stimulating further WA gas demand growth.