Primary Formation Mechanism Research Articles

Voluntary Associations, Trust, and Civic Engagement: A Multilevel Approach

This article argues that the scope of the voluntary sector is more important than the activity level of members for the formation of social capital. The intensity and scope of 13 European voluntary sectors are analyzed on both the individual and aggregate levels. This reveals no additional effect of face-to-face contact (active participation) over passive membership. Thus, the primary mechanism of social capital formation in the voluntary sector cannot be socialization of individual members. Furthermore, effects at the aggregate level are much stronger than at the individual level. This indicates that social capital is constructed through institutional (macro), not social (micro) processes. It is not face-to-face encounters but awareness of strong and visible voluntary organizations in society that generate a belief in the utility and rationality of collective action. Thus, voluntary organizations institutionalize rather than generate social capital.

Ion irradiation of H 2O ice on top of sulfurous solid residues and its relevance to the Galilean satellites

In this paper we present the results of new experiments of ion irradiation of water ice deposited on top of a solid sulfurous residue to study the potential formation of SO 2 at the interface ice/refractory material and discuss the possibility that this mechanism accounts for the sulfur dioxide ice detected on the surfaces of the Galilean satellites. In situ infrared spectroscopy was the used experimental technique. We have irradiated a thin film of H 2O frost on a sulfurous layer with 200 keV of He + at 80 K. The used sulfurous residue was obtained by irradiation of frozen SO 2 at 16 K and it is used as a template of sulfur bearing solid materials. We have not found evidences of the efficient formation of SO 2 after irradiation of H 2O ice on top of the sulfurous residue. An upper limit to the production yield of SO 2, Y ⩽ 6.3 × 10 −7 molecules cm −2 of interface area for each 100 eV of energy absorbed in 1 cm 3 of ice-covered residue, has been estimated. These results have relevance in the context of the surfaces of the icy Galilean satellites in which SO 2 was detected. Our results show that radiolysis of mixtures of water ice and refractory sulfurous materials is not the primary formation mechanism responsible for the SO 2 present on the surfaces of the Galilean satellites.

A new route for synthesizing VO 2(B) nanoribbons and 1D vanadium-based nanostructures

This paper demonstrated the large-scale fabrication of metastable single crystal VO 2(B) nanoribbons with a home-made vanadium (IV, V) compound as a precursor. The influence factors on the morphology and a primary formation mechanism were presumably studied. Furthermore, the capability fabricating other vanadium-based 1D nanostructures was also explored from the precursor.

OH(AΣ+2) and rare gas-deuteride (NeD, ArD) excimers generated in microcavity plasmas: Ultraviolet emission spectra and formation kinetics

Emission in the ultraviolet from the AΣ+2 electronic excited states of OH, NeD, and ArD, and the formation kinetics of these excited heteronuclear diatomics, have been investigated in microcavity plasmas generated in rare gas/H2O or D2 gas mixtures. Excitation transfer from the aΣu+3(1u,0u−) Rydberg state of Ar2 appears to be the dominant pathway to OH(AΣ+2) formation in Ar∕H2O vapor mixtures with total pressures of 400–800Torr and H2O partial pressures of 100mTorr–3Torr. Maximum emission on the (v′,v″)=(0,0) vibrational band of the OH(A→X) transition is observed in a 25μm, 45nl microcavity for 600–800Torr Ar∕0.5Torr H2O mixtures. Comparisons of experimental and simulated fluorescence spectra show the OH[AΣ+2(v′=0)] state rotational temperature to be 425K for 600Torr Ar∕100mTorr H2O mixtures but to rise linearly with the H2O partial pressure and exhibit a slope of 170K∕Torr H2O for 100mTorr⩽pH2O⩽3Torr. Excitation of Ne or Ar∕D2 gas mixtures in 50×50 arrays of Si microplasma devices generates broadband spectra, peaking in the mid-ultraviolet (λ∼280–320nm), which are attributed to the A→X transition of the ArD or NeD excimers. The optimal D2 concentration is observed to be ∼0.5% and the primary kinetic formation mechanism for the deuterides involves D atom transfer in collisions between Ar(4sP3) and D2.

Binary asteroid population: 1. Angular momentum content

We compiled a list of estimated parameters of binary systems among asteroids from near-Earth to trojan orbits. In this paper, we describe the construction of the list, and we present results of our study of angular momentum content in binary asteroids. The most abundant binary population is that of close binary systems among near-Earth, Mars-crossing, and main belt asteroids that have a primary diameter of about 10 km or smaller. They have a total angular momentum very close to, but not generally exceeding, the critical limit for a single body in a gravity regime. This suggests that they formed from parent bodies spinning at the critical rate (at the gravity spin limit for asteroids in the size range) by some sort of fission or mass shedding. The Yarkovsky–O'Keefe–Radzievskii–Paddack (YORP) effect is a candidate to be the dominant source of spin-up to instability. Gravitational interactions during close approaches to the terrestrial planets cannot be a primary mechanism of formation of the binaries, but it may affect properties of the NEA part of the binary population.

The Use of Statins in Postoperative Adhesion Prevention

The Use of Statins in Postoperative Adhesion Prevention

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion in semi-solid isothermal treatment

Microstructure evolution of processed Mg-Al-Zn alloy by equal channel angular extrusion(ECAE) in semi-solid isothermal treatment was investigated. The results show that with increasing semi-solid isothermal treatment temperature, the α phase solid grain size of processed Mg-Al-Zn alloy by ECAE increases firstly due to coarsening of α phase solid grains, then decreases due to melting of α phase solid grains. With the increase of extrusion passes during ECAE, the α phase solid grain size in the following semi-solid isothermal treatment decreases. The α phase solid grain size of processed Mg-Al-Zn alloy by ECAE under route B c is the smallest, while the α phase solid grain size of processed material by ECAE under route A is the largest. The primary mechanism of spheroid formation depends on the melting of recrystallizing boundaries and diffusion of solute atoms in the semi-solid state.

Mechanisms of pit formation at strained crystallineSi(111)∕Si3N4(0001)interfaces: Molecular-dynamics simulations

Molecular-dynamics simulations of the crystalline silicon-silicon nitride interfaces are performed to investigate the mechanical failure mechanisms at the interfaces under external strain. At 8% applied tensile strain, parallel to the interface, regular crack initiation and propagation in silicon nitride and dislocation emission and propagation in silicon are observed. At larger 16% strain, however, the formation of a pit similar to that in experiments with lattice-mismatched systems is observed. The simulation results suggest the primary mechanism of pit formation is interaction of a local compressional pinch of the film at the interface with the close proximity to the arrival of a dislocation at the interface in the highly strained silicon.

Formation of nickel nanodots on GaN

We examine the annealing-induced formation of nickel nanodots on GaN substrates. The initial Ni layer thickness is 2 nm. Annealing temperatures range from 550 to 930 °C. The islands are well defined at the highest temperatures. Island formation kinetics provide an activation energy of 0.34±0.07eV. Time dependence of the nanodot island areas, annealed at 750 °C, is consistent with a t2∕3. These observations are indicative of diffusion-limited ripening as the primary formation mechanism. X-ray diffraction results show that nickel gallides form at anneal temperatures 750 °C and above.

CO 2 production by ion irradiation of H 2O ice on top of carbonaceous materials and its relevance to the Galilean satellites

In this work we report on new experiments of ion irradiation of water ice deposited on top of solid carbonaceous materials to study the production of CO 2 at the interface ice/refractory material and discuss the possibility that this mechanism accounts for the quantity of CO 2 ice detected on the surfaces of the Galilean satellites. The used experimental technique has been in situ infrared spectroscopy. We have irradiated thin films of H 2O frost on carbonaceous layers with 200 keV of He + and Ar +, and 30 keV of He + at 16 and 80 K. The used carbonaceous layers have been asphaltite, a natural bitumen, and solid organic residues obtained by irradiation of frozen benzene. In both cases the results show that CO 2 is produced very efficiently after irradiation obtaining a maximum quantity of the order of 6 × 10 15 molecules cm −2 . These results are, also quantitatively similar, to those recently obtained for water ice deposited on amorphous carbon films [Mennella, V., Palumbo, M.E., Baratta, G.A., 2004. Formation of CO and CO 2 molecules by ion irradiation of water ice covered hydrogenated carbon grains. Astrophys. J. 615, 1073–1080]. Thus we suggest that, whatever is the carbonaceous residue, CO 2 will be produced efficiently by the studied process. These results have interest in the context of the surfaces of the icy Galilean satellites in which CO 2 has been detected mainly trapped in the non-ice material, not in the pure water ice. We suggest that radiolysis of mixtures of water ice and refractory carbonaceous materials is the primary formation mechanism responsible for the CO 2 formation on the surfaces of the Galilean satellites.

Nucleation studies in the Martian atmosphere

We developed models for unary nucleation of water and carbon dioxide in the Martian atmosphere. Both homogeneous and heterogeneous nucleation on dust particles were studied. Our models are based on classical theory. We compare results of different adsorption approaches. Heterogeneous nucleation on the abundant dust particles seems to be the primary mechanism of both H2O and CO2 cloud formation in the Martian atmosphere. Heterogeneous nucleation is obtained at a saturation ratio of about 1.18 for H2O and 1.32 for CO2. Homogeneous nucleation is not likely to occur since it would require high supersaturations. We use our models to study nucleation as a function of height at different locations on Mars where ice fog or clouds have been observed. H2O ice nucleation results are in good agreement with surface fog observations and previous model studies. CO2 ice nucleation simulations in the polar hood cloud areas suggest that negative temperature perturbations caused by, e.g., adiabatic cooling in orographic waves or in convective plumes are required for the formation of CO2 clouds.

Flame synthesis of single-walled carbon nanotubes

Flames offer potential for synthesis of carbon nanotubes in large quantities at considerably lower costs than that of other methods currently available. This study aims to examine conditions for carbon nanotube formation in premixed flames and to characterize the morphology of solid carbon deposits and their primary formation mechanisms in the combustion environment. Single-walled nanotubes have been observed in the post-flame region of a premixed acetylene/oxygen/15 mol% argon flame operated at 6.7 kPa with Fe(CO) 5 vapor used as a source of metallic catalyst necessary for nanotube growth. Thermophoretic sampling and transmission electron microscopy were used to characterize the solid material present in the flame at various heights above burner (HAB), giving a resolution of formation dynamics within the flame system. Catalyst particle formation and growth is observed to dominate the immediate post-flame region (10–40 mm HAB). Nanotubes were observed to be present after 40 mm HAB with nanotube inception occurring as early as 30 mm HAB. Between 40 and 70 mm HAB, nanotubes are observed to coalesce into clusters. A nanotube formation ‘window’ is evident with formation limited to fuel equivalence ratios between 1.5 and 1.9. A continuum of morphologies ranging from relatively clean clusters of nanotubes to amorphous material is observed between these lower and upper limits. High-resolution TEM and Raman spectroscopy revealed nanotube bundles with each nanotube being single-walled with diameters between 0.9 and 1.5 nm.

Flame synthesis of single-walled carbon nanotubes

Flames offer potential for synthesis of carbon nanotubes in large quantities at significantly lower cost than that of other methods currently available. This study aimed to examine conditions for carbon nanotube formation in premixed flames and to characterize the morphology of solid carbon deposits and their primary formation mechanisms in the combustion environment. Single-walled nanotubes were observed in the post-flame region of a premixed acetylene/oxygen/15 mol% argon flame operated at 6.7 kPa with Fe(CO) 5 vapor used as a source of metallic catalyst necessary for nanotube growth. Thermophoretic sampling and transmission electron microscopy were used to characterize the solid material present in the flame at various heights above burner (HAB), providing a quantitative description of formation dynamics within the flame system. Catalyst particle formation and growth is observed to dominate the immediate post-flame region (10–40 mm HAB). Nanotubes were observed to be present after 40 mm HAB with nanotube inception occurring as early as 30 mm HAB. Between 40 and 70 mm HAB, nanotubes were observed to coalesce into clusters. A nanotube formation `window' was evident with formation limited to fuel equivalence ratios between 1.5 and 1.9. A continuum of morphologies ranging from relatively clean clusters of nanotubes to amorphous material was observed between these lower and upper limits. High-resolution transmission electron microscopy and Raman spectroscopy revealed nanotube bundles with each nanotube being single-walled with diameters between 0.9 and 1.5 nm. Particles associated with nanotube bundles were identified as primarily Fe 2O 3. The estimated yield of nanotubes per unit of material fed to the flame was 0.1 wt% of carbon and 2.5 wt% of iron. A mechanistic interpretation of nanotube formation processes in the premixed flame clearly identifies the role of iron oxide particles and suggests ways for significantly improving the yield of nanotubes from the flame.

The formation mechanisms of turbidity maximum in the Pearl River estuary, China

The formation and dynamics of turbidity maxima (TM) in the Pearl River estuary (PRE) are not well understood but the existence of TM in the estuary have great potential engineering and environmental impacts. Based on the measurements of two large-scale field surveys conducted in the wet season of 1978 (July of 1978) and the dry season of 1979 (March of 1979), the existence and seasonal variations of TM in the PRE focusing on the two major natural navigation channels have been studied. The sediment transport fluxes over two consecutive tidal cycles have been analyzed in detail. The analysis results reveal that the formation mechanisms of TM in the estuary are rather complex. In general, gravitational circulation, tidal trapping, and sediment resuspension and deposition processes are the primary TM formation mechanisms in the PRE. The clockwise back flow pattern around Lingding Island also leads to the formation of TM in the West channel of the PRE. The occurrence of TM far upstream of the salt water wedge is the result of the complex hydrodynamic and sediment transport processes generated by the runoff of the major rivers.

Integrating lateral expansion into models of peatland development in temperate New England

Summary As peatlands form they create a temporal archive of community development, allowing the reconstruction of vegetation dynamics through the analysis of sediments and the development of detailed chronologies of successional change. Peatland formation occurs through two mechanisms: (i) terrestrialization, when a water body fills with sediments and peat; and (ii) paludification, the conversion of dry land to peatland. In temperate regions, where high summer temperatures may limit peat accumulation, general models of peatland development suggest that allogenic factors such as climate change control peatland development and that terrestrialization is the primary mechanism of formation. This study evaluates this widely accepted model by comparing the developmental histories of three peatlands within the same climate region in New England in order to: (i) describe the development and timing of successional events among peatlands; (ii) document the roles of paludification and terrestrialization as developmental mechanisms; and (iii) evaluate the importance of climate change vs. autogenic factors in peatland development in this temperate region. Basin morphometry, sediment stratigraphies, and chronologies of community change determined through radiocarbon dating indicate that peatland development at each site involved terrestrialization followed by paludification, with no apparent influence of broad‐scale climate change on the timing of these processes. Paludification was consistently initiated coincident with the consolidation of a shrub mat across each lake‐basin, and was controlled in extent and rate by the topography of the adjoining uplands. The timing of stratigraphic changes varied among sites, suggesting that autogenic factors associated with the accumulation of peat rather than regional climate change controlled development. These results provide the foundation for a model of temperate peatland development driven by autogenic factors and caution against the use of temperate peatland development as a proxy for climatic reconstruction.

Flame Synthesis of Carbon Nanotubes

AbstractFlames offer a potential for the synthesis of carbon nanotubes in large quantities at modest costs. This study aims to examine the conditions for carbon nanotube formation in premixed flames and to characterize the morphology of solid carbon deposits and their primary formation mechanisms in the combustion environment. Single walled nanotubes have been observed in the post-flame region of a premixed acetylene/oxygen/argon flame operated at 50 Torr (6.7 kPa) with iron pentacarbonyl vapor used as a source of metallic catalyst. A thermophoretic sampling method and transmission electron microscopy were used to characterize the solid material present in the flame at various heights above burner (HAB), giving resolution of formation dynamics within the flame system. Catalyst particle formation and growth are observed in the immediate post-flame region, 10 to 40 mm HAB, with coagulation leading to typical particle sizes on the order of 5 to 10 nm. Nanotubes were observed to be present after 40 mm HAB (∼34 milliseconds) with nanotube inception occurring as early as 30mm HAB (∼25 ms). Between 40 and 70 mm HAB (∼30 ms), nanotubes are observed to form and coalesce into clusters. Based on the rapid appearance of nanotubes in this region, it appears that once initiated, the nanotube growth occurs quite rapidly, on the order of 10 νm/s. A nanotube formation ‘envelope’ is evident with a formation limited to fuel equivalence ratios between a lower limit of 1.5 and an upper limit of 1.9. A continuum of morphologies ranging from relatively clean clusters of nanotubes to amorphous material is observed between the lower and upper limits. We suggest that the diversity of morphologies is due to competition between carbon precipitation pathways. High resolution TEM revealed the nanotubes to be primarily single walled. Raman spectroscopy confirmed the presence of single wall nanotubes and indicated a broad range of diameters and differences in chirality to plasma-arc generated material.

The Precipitation Process in Convective Cells Embedded in Deep Snow Bands over the Sea of Japan

Convective cells in two deep snow bands were examined over the Sea of Japan with an instrumented aircraft and dual-Doppler radars. A combination of the relatively warm air stream (westerly) at lower levels secluded near the center of the low and the polar air stream (west-southwesterly) at middle and upper levels produced a deep unstable stratification to the southwestern quadrant of a well-developed low, where snow bands A1 and B1 were respectively observed at around 1600 and 1700 JST on 28 Jan. 1993. Radar data showed that both snow bands were in quasi-steady state within a dual Doppler radar observation area. However, the two snow bands showed quite different development; the maximum re-flectivities in bands A1 and B1 were 15 dBZ and 30 dBZ, respectively. Aircraft data showed that the accretional growth of snow particles was the primary precipitation formation mechanism in the convective cells embedded in both snow bands. From aircraft and radar data, it appears that vertical wind shear within the cloud layer influenced the precipitation process. In the cell embedded in snow band A1, the updraft at middle and upper levels tilted downshear due to a strong wind shear and precipitation embryos initiated in the updraft were advected downshear from the main supercooled cloud water region. Therefore, these embryos did not grow to large graupel particles. By comparison, in the cell embedded in snow band B1, the updraft tilted upshear at lower levels and stood almost erect at middle and upper levels due to weak wind shear. Therefore, precipitation embryos initiated in the updraft grew into 5 mm graupel particles as they descended through the main supercooled cloud water region. In addition, re-circulation of graupel particles, which had descended in a vicinity of the updraft core, seemed to play an important role to efficiently produce larger graupel particles.

Suppression of Prostaglandin Synthesis with NS-398 Has Different Effects on Endocortical and Periosteal Bone Formation Induced by Mechanical Loading

Prostaglandins mediate adaptive bone formation induced by mechanical loading. Inhibition of cyclooxygenase-2 (COX-2) with NS-398 effectively blocks loading-induced osteogenesis on the endocortical bone surface of the tibia. In this study, we compared the effects of selective inhibition of COX-2 with NS-398 on mechanically induced osteogenesis at the endocortical surface (tibia) with that on the periosteal surface (ulna). We further tested the effect of NS-398 administered at different times before (3 hrs or 30 min) or after (30 min) mechanical loading. Mechanical loading induced lamellar bone formation on the endocortical surface of the tibia and the periosteal surface of the ulna. Oral administration of either indomethacin or NS-398 3 hrs before loading significantly decreased loading-induced bone formation rate (BFR) and mineralizing surface (MS/BS), but not mineral apposition rate (MAR), at the endocortical surface of the tibia and the periosteal surface of the ulna. NS-398 reduced loading-induced MS/BS by 96% on the endocortical surface of the tibia, but only by 37% on the periosteal surface of the ulna (significantly different from endocortical, P <0.05). Indomethacin reduced MS/BS and BFR to a lesser extent than NS-398 and did not have different effects on the periosteal and endocortical surfaces. These data suggest that the endocortical bone adaptive response to mechanical loading is more dependent upon COX-2 activity than is the periosteal bone response. Intraperitoneal injection of NS-398 3 hrs before loading suppressed load-induced bone formation rate at the endocortical surface of the tibia significantly more (27%) than when administered 30 min before loading. When NS-398 was given 30 min after loading, bone formation was not significantly suppressed. These data suggest that a primary cellular mechanism of bone formation following brief bouts of mechanical loading involves release of prostaglandins from cells at the time mechanical loading is applied, rather than new prostaglandin synthesis associated with a mechanically induced COX-2 expression.

Stellar Metallicity and the Formation of Extrasolar Gas Giant Planets

Spectroscopic searches for extrasolar planets are most successful when the target star has high metallicity, a trend that may be caused by observational selection effects, pollution by ingested planetary material, or a requirement of high metallicity for gas giant planet formation. We show that in the scenario of the disk instability mechanism for forming gas giant protoplanets, clump-forming gravitational instabilities proceed in much the same manner in protoplanetary disks with metallicities that vary by factors of 10 greater or less than that of a standard disk model. This remarkable insensitivity to the dust grain opacity is attributed to radiative energy losses from the disks being controlled more by their being embedded in a thermal bath determined by their central protostar than by radiative fluxes deep within the disks' optically thick midplanes. This result suggests that if disk instability is the primary formation mechanism for extrasolar gas giant planets, even relatively low-metallicity galactic disk stars should harbor gas giant planets.

Exploring polar stratospheric cloud and ozone minihole formation: The primary importance of synoptic‐scale flow perturbations

The formation of polar stratospheric clouds (PSCs) is sometimes attributed to cooling induced by mountain waves. Some examples of PSCs explained by this mechanism are found in the literature. Other studies show that the cooling producing PSCs is of synoptic scale. In this paper we use data from Polar Ozone Aerosol Measurement (POAM) II and from TIROS Operational Vertical Sounder (TOVS) showing coincident occurrences of PSCs and ozone miniholes over the sea and land. Using European Centre for Medium‐Range Weather Forecasts (ECMWF) analyses, we show that when both PSCs and localized ozone minima appear, they are associated primarily with anticyclonic potential vorticity anomalies near the tropopause. The flow anomaly penetrates upward and downward, inducing an upward displacement of isentropic surfaces above and a downward displacement below, the upward and downward penetration being consistent with the deformation scale. These flow anomalies result in synoptic‐scale quasi‐adiabatic uplift through the lower stratosphere. The adiabatic cooling of the air masses creates the conditions for PSC formation. Coincidentally, the ozone partial pressure decreases, and the localized ozone minimum appears. Our purpose in this paper is to show that the primary PSC formation mechanism in the Arctic is the same as for minihole formation: synoptic‐scale dynamics. We show three multiday sequences of PSCs and localized ozone minima. We reveal the robustness of the PSC/dynamics link by showing multiyear, monthly statistics of POAM II PSC sighting fraction compared with PSC formation temperature and isentropic geopotential.