bluuebunny/crossref_metadata_2025 huggingface dataset:
An interface‐update‐based implicit algorithm for mold filling simulation of liquid composite molding
Authors: Jiang Shunliang , Duan Yuexin
Published: April 2006

In this article, a new implicit numerical algorithm has been presented for mold filling simulation in liquid composite molding process. The new implicit numerical algorithm is based on the update of flow interface to track flow front for each time step. Nodes of mesh are divided into three groups, i.e. filled nodes, interface nodes (or partially filled nodes), and empty nodes. Governing equations of filled nodes are solved to obtain pressure distribution; filling fractions of interface nodes are checked to determine if any node is needed to be added to filled nodes or be removed from filled nodes. The local LU factorization solver and preconditioned conjugated gradient iterative solver were employed to investigate the new implicit algorithm. Case studies demonstrated the performance of the proposed implicit algorithm. The new implicit algorithm reduced the computational complexity to below 2.0 power order of problem sizes. POLYM. COMPOS., 27:271–281, 2006. © 2006 Society of Plastics Engineers.
The effect of clay particles on film formation from polystyrene latex
Authors: Uğur Şaziye , Alemdar Ayşe , Pekcan Önder
Published: April 2006

Film formation from surfactant‐free polystyrene (PS) latex was performed in the presence of 5% Na‐montmorillonite (NaMMT). The composite films were prepared from pyrene (P)‐labeled PS particles at room temperature and annealed at elevated temperatures above the glass‐transition (Tg) temperature of polystyrene. Scattered light (Is) and fluorescence intensity (IP) from P were measured after each annealing step to monitor the stages of composite film formation. Minimum film formation temperature, T0, and healing temperatures, Th, were determined. Void closure and interdiffusion stages were modeled and related activation energies were measured. From these results, it was found that the presence of NaMMT in the PS latex film only affects the minimum film formation, but does not affect the void closure and backbone motion activities. POLYM. COMPOS., 27:299–308, 2006. © 2006 Society of Plastics Engineers
Structure–properties relations in titanium‐based thermoplastic fiber–metal laminates
Authors: Cortés P. , Cantwell W.J.
Published: April 2006

This paper investigates the interfacial, tensile, and fatigue properties of a titanium alloy fiber–metal laminate (Ti‐FML) based on woven glass‐fiber‐reinforced polyetherimide (GF/PEI). Initial tests, using the single cantilever beam (SCB) geometry have shown that it is not necessary to surface treat the titanium alloy in order to achieve a high value of metal–composite interfacial fracture toughness. Tensile tests have shown that the mechanical properties of the FML lie between those offered by its constituent materials. Tension–tension fatigue tests have shown that the fatigue lives of these laminates are superior to those offered by the plain titanium alloy. The mechanical properties of this glass fiber/PEI FML have also been compared with those offered by an FML based on a unidirectional carbon‐fiber‐reinforced polyetheretherketone (CF/PEEK) composite. Here, it has been shown that although the fatigue properties of this woven GF/PEI composite are inferior to those of the CF/PEEK FML, they do offer a higher temperature capability due to the higher glass transition temperature of the PEI matrix. Polym. Compos. 27:264–270, 2006. © 2006 Society of Plastics Engineers.
Studies of biodegradable thermoplastic amylose/kaolin composites: Fabrication, characterization, and properties
Authors: Huang Mingfu , Wang Hongyuan , Yu Jiugao
Published: April 2006

Biodegradable thermoplastic amylose/kaolin composites (BTAKC) have been fabricated from glycerol‐plasticized amylose (GPA) and inorganic reinforced materials kaolin. Fourier Transform infrared (FTIR) patterns showed that in the BTAKC the CO groups of amylose molecules shifted to the higher wavenumber, while the reactive hydroxyl groups of kaolin in BTAKC shifted to the lower wavenumber. This was caused by the cooperation of strong absorption that existed between kaolin and amylose molecules and hydrogen bonds that formed between the reactive hydroxyl groups of kaolin and the hydroxyl groups of amylose molecules. Kaolin was on the submicron filling transition state and acted as an obstructer. Thermogravimetric analysis (TGA) showed that the mass loss of GPA and BTAKC with 20% kaolin were 15.54 and 13.74% respectively, the thermal stability of BTAKC were improved. When BTAKC was stored for 10 days at Relative Humidity (RH) = 50%, the tensile stress, strain, Young's modulus and breaking energy of BTAKC with 20% kaolin were 9.53 MPa, 65.4%, 149.8 MPa and 1.402 N m respectively. It was obvious that the mechanical properties of BTAKC were greatly improved. X‐ray diffraction revealed that kaolin restrained the crystallization of GPA effectively. Water absorption testing indicated that the introduction of kaolin reduced the water absorption of BTAKC, which greatly improve the application property of BTAKC. Scanning electron microscope (SEM) revealed that kaolin was commendably dispersed in GPA. Polym. Compos. 27:309–314, 2006. © 2006 Society of Plastics Engineers
Synthesis, molecular and optical characterization of polycarbonates containing azobenzene side‐chains
Authors: Lee Jin‐Kook , Park Sang‐Wook , Lee Jae‐Wook , Kim Mi‐Ra
Published: April 2006

In this study, we report the synthesis and holographic characterization of polycarbonates containing an azobenzene group in their side‐chains. The polycarbonate (DR‐PC) was synthesized by the polyaddition reaction of Disperse Red 19 (DR 19) and carbon dioxide in N‐methyl‐2‐pyrrolidone for 24 h in air, and we investigated the mechanism in the presence of potassium carbonate. The film of polycarbonate was obtained by casting onto a slide glass in N,N‐dimethylformamide. The diffraction efficiency of the polycarbonate film was measured as a function of time and intensity of the induced laser. Independently of the intensity of the writing beam, the maximum diffraction efficiency in all DR‐PC films reached about 0.25%. Copyright © 2006 Society of Chemical Industry
Palladium nanoparticles obtained by mechanical milling
Authors: Sampedro B. , Rojas T. C. , Fernández A. , Hernando A.
Published: April 2006

Opposed to the existing chemical methods, we have used a physical one in order to obtain palladium nanoparticles. In this work we present the HRTEM observation of Pd nanoparticles obtained by mechanical milling. These particles are around 6 nm in size. The Pd milled samples have exhaustively been structurally characterized. We have also studied its magnetic properties as a function of the milling time and magnetic measurements are according to those previously carried out by us in palladium nanoparticles obtained by chemical methods. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrochemical synthesis and stabilization of cobalt nanoparticles
Authors: Ledo‐Suárez A. , Rodríguez‐Sánchez L. , Blanco M. C. , López‐Quintela M. A.
Published: April 2006

Cobalt nanoparticles (NPs) were synthesized via an electrochemical method in the presence of tetraalkylammonium salt. The nanometer dimensions of the NPs can be controlled in a simple way by adjustment of the current density. From these particles stable colloidal suspensions are prepared in the presence of a fatty acid (oleic acid) and triphenylphosphine. The colloidal system is stable against oxidation when they are kept in heptane (C7H16).

Transmission electron microscopy (TEM) was employed to determine the core size and the shape of metal nanoparticles. The chemical interaction of the surfactant with the Co nanoparticles was studied by using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Thermogravimetric analysis (TGA) was used to study the thermal stability and the composition of the capped cobalt nanoparticles. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Assessment of body condition in Asian elephants (Elephas maximus)
Authors: Wemmer C. , Krishnamurthy V. , Shrestha S. , Hayek L.‐A. , Thant Myo , Nanjappa K.A.
Published: April 2006

A method of assessing body condition of Asian elephants (Elephas maximus) is presented. The method uses visual assessment to assign numerical scores to six different regions of the body, which are totaled to give a numerical index ranging from 0–11. The relationship between the index and morphometric variables is compared for a sample of 119 juvenile and young adult elephants from southern India, Nepal, and Myanmar. Mean ages of males and females were similar. Mean index of body condition (with standard error [SE]) was 7.3±0.2 points. No significant correlation was found between index of body condition and age over both sexes (r=0.01, n=50). Results were equivalent when sexes were treated separately (females: r=0.03, n=24; males: r=0.01, n=26). Sexes did not differ in height of the shoulder or body condition in our sample, but there was significant sexual dimorphism in breadth of the zygomatic arch and three measures of subcutaneous fat: girth of neck, thickness of cervical fold, and thickness of anal flap. These three measures were also significantly correlated with each other. Our assessment method should prove a practical tool for ecologic studies, but the relationship of the index to percentage of body fat should be determined using heavy water dilution methodology. Zoo Biol 25:187–200, 2006. © 2006 Wiley‐Liss, Inc.
A Two-dimensional Boussinesq equation for water waves and some of its solutions
Authors: Johnson R. S.
Published: April 2006

A two-dimensional Boussinesq equation,
\[u_{tt} - u_{xx} + 3(u^2)_{xx} - u_{xxxx} - u_{yy} = 0,\]
is introduced to describe the propagation of gravity waves on the surface of water, in particular the head-on collision of oblique waves. This equation combines the two-way propagation of the classical Boussinesq equation with the (weak) dependence on a second spatial variable, as occurs in the two-dimensional Korteweg-de Vries (2D KdV) (or KPII) equation. Exact and general solitary-wave, two-soliton and resonant solutions are obtained from the Hirota bilinear form of the equation. The existence of a distributed-soliton solution is investigated, but it is shown that this is not a possibility. However the connection with the classical 2D KdV equation (which does possess such a solution) is explored via a suitable parametric representation of the dispersion relation.

A three-soliton solution is also constructed, but this exists only if an auxiliary constraint among the six parameters is satisfied; thus the two-dimensional Boussinesq equation is not one of the class of completely integrable equations, confirming the analysis of Hietarinta (1987). This constraint is automatically satisfied for the classical Boussinesq equation (which is completely integrable). Graphical reproductions of some of the solutions of the two-dimensional Boussinesq equations are also presented.
The motion of particles near a bubble in a gas-fluidized bed
Authors: Gilbertson M. A. , Yates J. G.
Published: April 2006

Most models of gas bubbles in fluidized beds are based on the assumption of an empty central region, the void, surrounded by a ‘cloud’ or ‘shell’ of particles whose voidage is larger than that of the remote emulsion phase. Batchelor & Nitsche (1994) investigated the formation of a void by tracking the paths of particles initially within a buoyant ‘blob’ of gas that has the form of a toroidal vortex. They showed that the particles dropped through the floor of the blob under the influence of gravity, leaving it empty. This paper extends their method to particles initially outside the blob. It is shown that inertia allows these particles to penetrate the blob and it is the extent of this penetration that determines the size of the void. The void is nearly as large as the blob for small, light particles, but becomes smaller relative to the blob with increasing particle size and weight until it disappears altogether. This provides an explanation for experimental observations of voids smaller than the blob (or ‘cloud’ as it is sometimes known), and suggests that when examining bubbles in a gas-fluidized bed the most significant dimension is the diameter of the blob and not that of the void.
Secondary instability of flow in a curved duct of square cross-section
Authors: Mees Philip A. J. , Nandakumar K. , Masliyah J. H.
Published: April 2006

Experiments and simulations of a travelling wave state of incompressible Newtonian flow in a curved duct of square cross-section are presented. The travelling wave mode develops from the well-documented steady four-cell flow state and is characterized by oscillations of the two Dean vortices near the centre of the outer wall.

The oscillations were induced by a carefully positioned pin at 5° from the inlet of the curved section along the symmetry line of the cross-section. It was shown that the travelling wave state is characteristic for curved duct flow and that the pin made it possible to observe the oscillations within the 270° long curved duct. Travelling waves were observed at flow rates above Dn = 170 (Dn = Re/(R/a)1/2, where Re is the Reynolds number, R is the radius of curvature of the duct and a is the duct dimension. The curvature ratio, R/a, is 15.1).

If no other disturbances are imposed, the oscillations are the result of the selective amplification of random disturbances in the flow, leading to a broad frequency spectrum. The travelling wave was found to lock in to an imposed periodic disturbance at a selected frequency. The flow structure of the locked state was investigated in detail, using flow visualization and a one-component laser Doppler anemometer to measure streamwise or spanwise velocities. Direct numerical simulations using the package CFDS-FLOW3D are in very good agreement with the experiments and confirm the existence of a fully developed, streamwise-periodic travelling wave state.

The inflow region between the two Dean vortices, which transports low-speed fluid away from the outer wall, creates strongly inflectional spanwise profiles of the streamwise velocity. Similarities with twisting vortices in a curved channel and sinuous oscillations of Görtler vortices show that the travelling waves observed here result from a secondary shear instability of these spanwise inflectional profiles.
Resonance gas oscillations in closed tubes
Authors: Goldshtein A. , Vainshtein P. , Fichman M. , Gutfinger C.
Published: April 2006

The problem of gas motion in a tube closed at one end and driven at the other by an oscillating poston is studied theoretically. When the piston vibrates with a finite amplitude at the first acoustic resonance frequency, periodic shock waves are generated, travelling back and forth in the tube. A perturbation method, based on a small Mach number. M and a global mass conservation condition, is employed to formulate a solution of the problem in the form of two standing waves separated by a jump (shock front). By expanding the equations of motion in a series of a small parameter ε = M½, all hydrodynamic properties are predicted with an accuracy to second-order terms, i.e. to ε2. It is found that the first-order solution coincides with the previous theories of Betchov (1958) and Chester (1964), while additional terms predict a non-homogeneous time-averaged pressure along the tube. This prediction compares favourably with experimental results from the literature. The importance of the phenomenon is discussed in relation to different transport processes in resonance tubes.
Interaction of single travelling bubbles with the boundary layer and attached cavitation
Authors: Li Chih-Yang , Ceccio Steven L.
Published: April 2006

Individual travelling cavitation bubbles were examined as they interacted with the flow over a two-dimensional hydrofoil. Each bubble was produced from a single nucleus created upstream of the hydrofoil, and the flow near the hydrofoil was visualized using particle imaging velocimetry (PIV). Travelling bubbles were observed to generate a local region of turbulence as they passed close to an unstable laminar boundary layer. By producing a locally turbulent region, the bubbles could temporarily sweep away a portion of attached cavitation at the foil midchord. Also, the bubbles were observed to strongly interact with a turbulent boundary layer, producing local regions of patch cavitation.
Three-dimensional separated flow structure over a cylinder with a hemispherical cap
Authors: Hsieh T. , Wang K. C.
Published: April 2006

Thin-layer Navier–Stokes solutions are obtained for an incompressible laminar flow over a hemisphere–cylinder at 10°, 30° and 50° incidence to exhibit some three-dimensional separated flow characteristics. Some of the results are compared with a previous water-tunnel investigation for the same body geometry. Good agreement is found, even for some detailed features. Although the geometry is relatively simple, the separated flow surprisingly embraces a number of intricate structural characteristics unique to three-dimensional flows. Particularly noteworthy are the separation sequence at increasing incidence, tornado-like vortices, outward-spiralling vortices, limit cycles, coaxial counter-spiralling patterns and horseshoe vortex systems. Physical insights to these new features are offered.
Effect of laminar chaos on reaction and dispersion in eccentric annular flow
Authors: Bryden Michelle D. , Brenner Howard
Published: April 2006

Generalized Taylor dispersion theory is used to study the chaotic laminar transport of a reactive solute between eccentric rotating cylinders in the presence of an inhomogeneous chemical reaction. The circumstance considered is that of laminar axial ‘Poiseuille’ flow in the annular region between the two non-concentric cylinders, accompanied by a secondary, generally chaotic, flow induced via alternate rotation of the cylinders. A Brownian tracer introduced into the flow is assumed to undergo an instantaneous, irreversible reaction on the surface of the outer cylinder. The resulting effective transversely and time-averaged reaction rate, axial solute velocity, and axial convective dispersivity are computed. When chaos is present, the effective reaction rate is increased to a value several times larger than occurs in the absence of chaotic transport. It is found that an optimum alternation frequency exists, and that this frequency decreases with increasing transverse Péclet number (Peq). It is also observed that the maximum achievable reaction rate increases with (Peq). The effect of laminar chaotic mixing on the mean axial solute/solvent velocity ratio is to drive its value towards the perfectly mixed value of 1.0, despite the removal of solute from the slower-moving axial streamlines near the outer (reactive) cylinder wall. Lastly, in the presence of transverse chaotic transport, the convective Taylor contribution to the axial solute dispersivity acquires a value up to several orders of magnitude smaller than that achievable by means of non-chaotic convection.
Miscible displacements in capillary tubes. Part 2. Numerical simulations
Authors: Chen Ching-Yao , Meiburg Eckart
Published: April 2006

Numerical simulations are presented which, in conjunction with the accompanying experimental investigation by Petitjeans & Maxworthy (1996), are intended to elucidate the miscible flow that is generated if a fluid of given viscosity and density displaces a second fluid of different such properties in a capillary tube or plane channel. The global features of the flow, such as the fraction of the displaced fluid left behind on the tube walls, are largely controlled by dimensionless quantities in the form of a Péclet number Pe, an Atwood number At, and a gravity parameter. However, further dimensionless parameters that arise from the dependence on the concentration of various physical properties, such as viscosity and the diffusion coefficient, result in significant effects as well.

The simulations identify two distinct Pe regimes, separated by a transitional region. For large values of Pe, typically above O(10), a quasi-steady finger forms, which persists for a time of O(Pe) before it starts to decay, and Poiseuille flow and Taylor dispersion are approached asymptotically. Depending on the strength of the gravitational forces, we observe a variety of topologically different streamline patterns, among them some that leak fluid from the finger tip and others with toroidal recirculation regions inside the finger. Simulations that account for the experimentally observed dependence of the diffusion coefficient on the concentration show the evolution of fingers that combine steep external concentration layers with smooth concentration fields on the inside. In the small-Pe regime, the flow decays from the start and asymptotically reaches Taylor dispersion after a time of O(Pe).

An attempt was made to evaluate the importance of the Korteweg stresses and the consequences of assuming a divergence-free velocity field. Scaling arguments indicate that these effects should be strongest when steep concentration fronts exist, i.e. at large values of Pe and At. However, when compared to the viscous stresses, Korteweg stresses may be relatively more important at lower values of these parameters, and we cannot exclude the possibility that minor discrepancies observed between simulations and experiments in these parameter regimes are partially due to these extra stresses.
Breakage of a drop of inviscid fluid due to a pressure fluctuation at its surface
Authors: Shreekumar  , Kumar R. , Gandhi K. S.
Published: April 2006

In this work, an attempt is made to gain a better understanding of the breakage of low-viscosity drops in turbulent flows by determining the dynamics of deformation of an inviscid drop in response to a pressure variation acting on the drop surface. Known scaling relationships between wavenumbers and frequencies, and between pressure fluctuations and velocity fluctuations in the inertial subrange are used in characterizing the pressure fluctuation. The existence of a maximum stable drop diameterdmaxfollows once scaling laws of turbulent flow are used to correlate the magnitude of the disruptive forces with the duration for which they act.

Two undetermined dimensionless quantities, both of order unity, appear in the equations of continuity, motion, and the boundary conditions in terms of pressure fluctuations applied on the surface. One is a constant of proportionality relating root-mean-square values of pressure and velocity differences between two points separated by a distancel. The other is a Weber number based on turbulent stresses acting on the drop and the resisting stresses in the drop due to interfacial tension. The former is set equal to 1, and the latter is determined by studying the interaction of a drop of diameter equal todmaxwith a pressure fluctuation of length scale equal to the drop diameter. The model is then used to study the breakage of drops of diameter greater thandmaxand those with densities different from that of the suspending fluid.

It is found that, at least during breakage of a drop of diameter greater thandmaxby interaction with a fluctuation of equal length scale, a satellite drop is always formed between two larger drops. When very large drops are broken by smaller-length-scale fluctuations, highly deformed shapes are produced suggesting the possibility of further fragmentation due to instabilities. The model predicts that as the dispersed-phase density increases,dmaxdecreases.
Bromeliad species of the Atlantic forest of north-east Brazil: losses of critical populations of endemic species
Authors: Filho José A. Siqueira , Tabarelli Marcelo
Published: April 2006

In this paper we examine the number of known populations of 86 bromeliad species recorded in the Atlantic forest of north-east Brazil, to test the following predictions: (1) the current number of populations of most bromeliad species inhabiting the Atlantic forest of north-east Brazil is critically low, (2) the number of extant populations of a particular species is associated with the ecological attributes of the species, and (3) habitat loss determines, at least in part, the current distribution and number of populations of each species. At present there are at least 535 bromeliad populations in this forest but 61.6% of species have <6 populations and 24.4% have only one known population. The mean number of populations per species was significantly lower among species endemic to this part of the Atlantic forest, species recorded in only one vegetation type, forest and inselberg species, and obligatory epiphytic and terrestrial species. We were unable to relocate 41 populations recorded between 1920 and 1996, and populations of 20 species have become locally extinct. For these bromeliads geographic range, habitat specificity and life form appear to determine which species are more vulnerable to extinction. The species that have <6 extant populations include 27 species that are endemic to this forest. These species need to be evaluated for inclusion on both the IUCN and Brazilian Red Lists. Some of these species will only survive if the fragments containing the last populations are declared as protected areas.
Habitat use by vicuña Vicugna vicugna in Laguna Pozuelos Reserve, Jujuy, Argentina
Authors: Arzamendia Yanina , Cassini Marcelo H. , Vilá Bibiana L.
Published: April 2006

Vicuña Vicugna vicugna are an emblematic species of one of the major arid ecosystems of the neotropics: the puna or altiplano. Excessive commercial hunting of vicuña for their valuable fleece in the past caused a severe decline in the population, with the vicuña almost becoming extinct by the mid 20th century. Effective protection resulted in the recovery of some populations and, recently, limited vicuña exploitation has been allowed. Research is urgently required to underpin the design of the management systems used for this exploitation. We present the results of a 2-year study on habitat utilization of vicuña in Laguna de Pozuelos UNESCO Biosphere Reserve in Argentina. Vicuña did not use the study area homogeneously but preferred vegetation communities dominated by grasses (known locally as pajonal and esporal) and with high overall plant cover. Vicuña were less selective in 2003, when overall habitat quality decreased, than in 2002. This change is predicted by habitat selection theory. We also found that members of family groups spend more time foraging than members of non-reproductive groups. Solitary vicuña spend more time standing up than members of groups, consistent with the observation that herding behaviour is related to protection against predators. Heterogeneous use and habitat selectivity suggest that exploitation of vicuña needs to take spatial behaviour into account in the establishment of the optimal location of capturing sites.
Toward understanding the history and mechanisms of Martian faulting: The contribution of gravitational potential energy
Authors: Dimitrova Lada L. , Holt William E. , Haines A. John , Schultz R. A.
Published: April 2006

Current stress solutions for Mars match the long wavelength signal of present day topography and gravity but fail to match many surface faults, including the normal faults in northern Claritas Fossae north to Tantalus and Alba Fossae. A deviatoric stress field associated with horizontal gradients of gravitational potential energy (GPE) provides an excellent fit, as measured by objective functions, to many of the normal faults in the western Martian hemisphere as well as wrinkle ridges circumferential to Tharsis; ∼70% of the faults have a misfit ≤ 0.1. The fit of faults to the GPE‐derived stress field reflects the thermal state of the planet at the times of faulting, and suggests that at such times elastic thicknesses and membrane stresses were small, and topography was supported by buoyancy forces.
A generalized Rhines effect and storms on Jupiter
Authors: Theiss J.
Published: April 2006

The Rhines effect is an interaction of Rossby waves and two‐dimensional turbulence that induces alternating zonal flows, thereby deforming and eventually destroying coherent vortices that might exist. Large‐scale geophysical flows are not strictly two‐dimensional. To be applicable to these flows the Rhines effect is therefore generalized. A novel aspect of the generalized Rhines effect is its possible suppression. On Jupiter, it is suppressed in the polar regions and at specific lower latitudes. It is remarkable that exactly there storms (vortices) have been observed, suggesting that storms can exist only where Rossby waves cannot interact with them. Thus the Rhines effect plays not only a role in the formation of the alternating zonal winds on Jupiter, as previously suggested, but in its generalized form also dictates the latitudes at which storms can exist.
A quantitative model for the time‐size distribution of eruptions
Authors: Marzocchi Warner , Zaccarelli Lucia
Published: April 2006

The modeling of the statistical distribution of eruptive frequency and volume provides basic information to assess volcanic hazard and to constrain the physics of the eruptive process. We analyze eruption catalogs from volcanoes worldwide in order to find “universal” relationships and peculiarities linked to different eruptive styles. In particular, we test (1) the Poisson process hypothesis in the time domain, looking for significant clustering of events or the presence of almost regular recurrence times, (2) the relationship between the time to the next eruption and the size of the previous event (the “time predictable” model), and (3) the relationship between the size of an event and the previous repose time (the “size predictable” model). The results indicate different behavior for volcanoes with “open” conduit regimes compared to those with “closed” conduit regimes. Open conduit systems follow a time predictable model, with a marked time clustering of events; closed conduit systems have no significant tendency toward a size or a time predictable model, and the eruptions follow mostly a Poisson distribution. These results are used to build general probabilistic models for volcanic hazard assessment of open and closed conduit systems.
On the origin of surface ozone and reactive nitrogen observed at a remote mountain site in the northeastern Qinghai‐Tibetan Plateau, western China
Authors: Wang T. , Wong H. L. A. , Tang J. , Ding A. , Wu W. S. , Zhang X. C.
Published: April 2006

Measurements of surface ozone (O3), carbon monoxide (CO), nitric oxide (NO), and total reactive nitrogen (NOy) were made, in conjunction with other trace gases and fine aerosols, at Mount Waliguan (WLG, 36.28°N, 100.90°E, 3816 m above sea level) in the late spring and summer of 2003 in order to better understand the source(s) of ozone and other chemically active gases over the remote highlands of western China. The average mixing ratio (plus or minus standard deviation) was 58 (±9) ppbv for O3, 155 (±41) ppbv for CO, and 3.83 (±1.46) ppbv for NOy in the spring phase, compared to a summer average value of 54 (±11) ppbv for O3, 125 (±36) ppbv for CO, and 3.60 (±1.13) ppbv for NOy. The daytime (0800–1759 local time) average NO mixing ratios were 72 (±79) pptv and 47 (±32) pptv in the spring and summer, respectively. The ozone mixing ratios exhibited a minimum in late morning, while CO (and NOy in spring) showed enhanced concentrations at night. The latter is in contrast to the diurnal behaviors observed in many remote mountain sites. Analysis of 10‐day back trajectories using output from Fifth‐Generation National Center for Atmospheric Research/Penn State University Mesoscale Model (MM5) simulations shows that air masses from the remote western regions contained the lowest level of CO (121–129 ppbv) but had the highest O3 (60 ppbv), compared to the other three air mass groups that were impacted by anthropogenic emissions in eastern/southern China and in the Indian subcontinent. Ozone correlated negatively with CO (and water vapor content), particularly during summer in air originating in the west, suggesting that the high‐ozone events were mostly derived from the downward transport of the upper tropospheric air and not from anthropogenic pollution. An examination of in situ chemical measurements (CO‐NOy correlation, ethyne/propane, and benzene/propane) as well as Measurements of Pollution in the Troposphere (MOPITT) and Moderate‐Resolution Imaging Spectroradiometer (MODIS) remote‐sensing data revealed some impacts from forest fires in central Asia in the late spring of 2003 on the background concentrations of trace gases over western China. While the O3 and CO levels at WLG are comparable to those at remote continental sites in Europe and North America, the NOy concentrations were substantially higher at WLG. The possible reasons for the abnormally high NOy levels are discussed. While more studies are needed to pin down these sources/causes, including a possible contribution from long‐range transport, we believe that microbial processes in soils and animal wastes associated with animal grazing were an important cause of the elevated NOy. The observed daytime NO concentrations imply a net photochemical production of O3 at WLG, suggesting a positive contribution of photochemistry to the ozone budget.
Role of transition zones in marine ice sheet dynamics
Authors: Pattyn Frank , Huyghe Ann , De Brabander Sang , De Smedt Bert
Published: April 2006

It has been suggested that rapid thinning of the West Antarctic ice sheet is due to increased melting under ice shelves caused by a gradual ocean warming (Shepherd et al., 2004). Payne et al. (2004) showed that such melting could lead to an acceleration of grounded ice flow. In this paper, we analyze the response of a marine ice sheet to different perturbations near the grounding line using a numerical ice sheet model that takes into account longitudinal stress coupling and grounding line migration at subgrid precision, based on a novel technique. Results show that stress transmission or longitudinal coupling across the grounding line plays a decisive role. The grounding line migration is a function of the length scale over which the basal conditions change from frozen to the bed to floating, the “transition zone.” We demonstrate that thinning of the ice shelf due to bottom melting has a negligible effect on the grounded ice mass. Only perturbations at the grounding line or reduction in buttressing of the ice shelf substantially thins the grounded ice sheet. Inclusion of lateral drag does not alter these results qualitatively. Marine ice sheets with large transition zones, such as ice streams, seem highly sensitive to such perturbations compared to ice sheets with small transition zones, such as an abrupt ice sheet/ice shelf junction.
Emissions of carbon from land use change in sub‐Saharan Africa
Authors: Houghton R. A. , Hackler J. L.
Published: April 2006

Previous estimates of the flux of carbon from land use change in sub‐Saharan Africa have been based on highly aggregated data and have ignored important categories of land use. To improve these estimates, we divided the region into four subregions (east, west, central, and southern Africa), each with six types of natural vegetation and five types of land use (permanent crops, pastures, shifting cultivation, industrial wood harvest, and tree plantations). We reconstructed rates of land use change and rates of wood harvest from country‐level statistics reported by the Food and Agriculture Organization (FAO) (1961–2000) and extrapolated the rates from 1961 to 1850 on the basis of qualitative histories of demography, economy, and land use. We used a bookkeeping model to calculate the annual flux of carbon associated with these changes in land use. Country‐level estimates of average forest biomass from the FAO, together with changes in biomass calculated from the reconstructed rates of land use change, constrained the average biomass of forests in 1850. Comparison of potential (predisturbance) forest areas with the areas present in 1850 and 2000 suggests that 60% of Africa's forests were lost before 1850 and an additional 10% lost in the last 150 years. The annual net flux of carbon from changes in land use was probably small and variable before the early 1900s but increased to a source of 0.3 ± 0.2 PgC/yr by the end of the century. In the 1990s the source was equivalent to about 15% of the global net flux of carbon from land use change.
Current distribution of a VLF electric dipole antenna in the plasmasphere
Authors: Bell T. F. , Inan U. S. , Chevalier T.
Published: April 2006

In a recent paper (Inan et al., 2003) a method of remediating enhanced energetic electron fluxes in the radiation belt was proposed in which injection of VLF whistler mode waves from spacecraft within the radiation belts would dramatically increase the pitch angle scattering of the relativistic electrons and cause these particles to be rapidly lost from the belts, thereby mitigating the flux enhancement. The VLF wave transmitting system discussed by Inan et al. (2003) involves electric dipole antennas. One of the most important characteristics of such an antenna is the current distribution along the length of the dipole, since it is this current which ultimately determines the amount of VLF power which can be radiated from the antenna into the plasma. In past work it has been assumed without proof that the dipole current has a triangular distribution. In the present work we determine the dipole antenna current distribution from first principles, constructing an integral equation of the Hallén type relating the current distribution to the wave vector potential. In this development it is assumed that the length of the thin cylindrical dipole antenna is small compared to the wavelength of whistler mode waves which propagate parallel to the Earth's magnetic field Bo. In the case of the dipole antenna oriented parallel to Bo, it is found that the assumption of a triangular current distribution is reasonable for antenna lengths up to hundreds of meters. For the case of the antenna perpendicular to Bo, it is found that the current decays exponentially along the antenna from the feed points to the antenna ends. In this case we find the conditions under which a triangular current distribution is still a reasonable approximation. We also give the conditions under which the quasi‐static model of Balmain (1964) reasonably describes the electric fields associated with the dipole antenna.
Indian Ocean‐monsoon coupled interactions and impending monsoon droughts
Authors: Krishnan R. , Ramesh K. V. , Samala B. K. , Meyers G. , Slingo J. M. , Fennessy M. J.
Published: April 2006

Monsoon droughts over the Indian subcontinent emanate from failures in the seasonal (June–September) monsoon rains. While prolonged dry‐spells (“monsoon‐breaks”) pervade on sub‐seasonal/intra‐seasonal time‐scales, the underlying causes for these long‐lasting anomalies remain elusive. Based on analyses of a suite of observed data sets, we report an ocean‐atmosphere dynamical coupling on intra‐seasonal time‐scales, in the tropical Indian Ocean, which is pivotal in forcing extended monsoon‐breaks and causing droughts over the subcontinent. This coupling involves a feedback between the monsoonal flow and thermocline depth in the Equatorial Eastern Indian Ocean (EEIO), in which an anomaly of the summer monsoon circulation induces downwelling and maintains a higher‐than‐normal heat‐content. The near‐equatorial anomalies induce strong and sustained suppression of monsoon rainfall over the subcontinent. It is concluded that the intra‐seasonal evolution of the ocean‐monsoon coupled system is a vital key to unlocking the dynamics of monsoon droughts.
Seismological insight into the kinematics of the 5 April 2003 vulcanian explosion at Stromboli volcano (southern Italy)
Authors: D'Auria Luca , Giudicepietro Flora , Martini Marcello , Peluso Rosario
Published: April 2006

On 5 April 2003 at 07:13 GMT (09:13 local time) a violent vulcanian explosion occurred at Stromboli volcano. At the time of the event an eruptive crisis was ongoing at the volcano with a lava flow outpouring along the Sciara del Fuoco flank. The seismic signals related to the event were recorded by 8 permanent broadband stations and gives information about the eruption kinematics. An ultra‐long‐period signal (period > 20 s), that we interpret as the effect of the ground tilt on the broadband sensors, starts about 4 min before and terminates about 1 min after the explosion. On the basis of the radial pattern of tilt directions we conclude that this signal is the effect of the deformation of the volcanic edifice, due to the rapid rising of a batch of magma, its ejection and the magma column readjustment. About 1 min before the explosion we observe an high frequency signal (period < 0.1 s) that we believe to be related to the vesiculation of the rising batch of gas‐rich magma. At 07:13:35 GMT a powerful very‐long‐period signal (period 2 ÷ 20 s), marking the onset of the explosive fragmentation, is recorded. This is confirmed by a blast wave following few seconds later. The remaining seismic signal (more than 3 min), shows an higher frequency content being related only to the fall of ballistic ejecta and to landslides along Sciara del Fuoco. We propose the implementation of an early warning system for the short‐term forecast of such explosions, based on the real‐time automatic detection of the tilt signals preceding such events.
Temperature-dependences of the kinetics of reactions of papain and actinidin with a series of reactivity probes differing in key molecular recognition features
Authors: Gul Sheraz , Mellor Geoffrey W. , Thomas Emrys W. , Brocklehurst Keith
Published: April 2006

The temperature-dependences of the second-order rate constants (k) of the reactions of the catalytic site thiol groups of two cysteine peptidases papain (EC 3.4.22.2) and actinidin (EC 3.4.22.14) with a series of seven 2-pyridyl disulphide reactivity probes (R-S-S-2-Py, in which R provides variation in recognition features) were determined at pH 6.7 at temperatures in the range 4–30 °C by stopped-flow methodology and were used to calculate values of ΔS‡, ΔH‡ and ΔG‡. The marked changes in ΔS‡ from negative to positive in the papain reactions consequent on provision of increase in the opportunities for key non-covalent recognition interactions may implicate microsite desolvation in binding site–catalytic site signalling to provide a catalytically relevant transition state. The substantially different behaviour of actinidin including apparent masking of changes in ΔH‡ by an endothermic conformational change suggests a difference in mechanism involving kinetically significant conformational change.
TEF-1 and C/EBPβ are major p38α MAPK-regulated transcription factors in proliferating cardiomyocytes
Authors: Ambrosino Concetta , Iwata Tomoko , Scafoglio Claudio , Mallardo Massimo , Klein Rüdiger , Nebreda Angel R.
Published: April 2006

p38 MAPKs (mitogen-activated protein kinases) play important roles in the regulation of cellular responses to environmental stress. Recently, this signalling pathway has also been implicated in the regulation of processes unrelated to stress, for example, in T lymphocytes and cardiomyocytes. In order to identify molecular targets responsible for the housekeeping functions of p38 MAPKs, we have analysed the differences in the transcriptomes of normally proliferating wild-type and p38α knockout immortalized embryonic cardiomyocytes. Interestingly, many potential components of the myocardium extracellular matrix were found to be upregulated in the absence of p38α. Further analysis of the microarray data identified TEF-1 (transcriptional enhancer factor-1), a known regulator of heart-specific gene expression, and C/EBPβ (CCAAT/enhancer-binding protein β), as the two transcription factors the binding sites of which were most enriched in the promoters of p38α-regulated genes. We have focused on the study of the extracellular matrix component COL1A1 (α1 chain of type I collagen) and found evidence for the involvement of both TEF-1 and C/EBPβ in the p38α-dependent inhibition of COL1A1 transcription. Our data therefore show that p38 MAPKs regulate TEF-1 and C/EBPβ transcriptional activity in the absence of environmental stress and suggests a role for p38α in the expression of extracellular matrix components that maintain organ architecture.
Identification of Ebp1 as a component of cytoplasmicbcl-2mRNP (messenger ribonucleoprotein particle) complexes
Authors: Bose Sudeep K. , Sengupta Tapas K. , Bandyopadhyay Sumita , Spicer Eleanor K.
Published: April 2006

The 3′-UTR (untranslated region) of bcl-2 mRNA contains an ARE (AU-rich element) that potentially regulates the stability of bcl-2 mRNA in a cell specific fashion. Previous studies have demonstrated that multiple proteins interact with bcl-2 mRNA in HL-60 (human leukaemia-60) cells, potentially contributing to the overexpression of Bcl-2 protein. Treatment of HL-60 cells with taxol or okadaic acid has been shown to induce destabilization of bcl-2 mRNA, which was associated with decreased binding of trans-acting factors to bcl-2 mRNA. Nucleolin has been identified as one of the bcl-2 mRNA-binding proteins [Sengupta, Bandyopadhyay, Fernandes and Spicer (2004) J. Biol. Chem. 279, 10855–10863]. In an effort to identify additional bcl-2 mRNA-binding proteins, two polypeptides of approx. 45 kDa and 60 kDa were isolated from HL-60 cells by AREbcl-2 (transcripts that contain bcl-2 AREs) RNA affinity chromatography. These proteins were identified as the human proliferation associated protein, Ebp1, and human DRBP76 (double stranded RNA-binding protein 76) respectively, by MALDI (matrix-assisted laser-desorption ionization)-MS. RNA electrophoretic mobility shift assays indicated that recombinant Ebp1 binds to AREbcl-2 RNA but not to the group 1 ARE present in GM-CSF (granulocyte macrophage-colony stimulating factor) mRNA in vitro. Antibody supershift assays demonstrated that Ebp1 is present in protein–AREbcl-2 RNA complexes formed with cytosolic HL-60 extracts. The interaction of Ebp1 with bcl-2 mRNA in HL-60 cells was also demonstrated by RNA co-immunoprecipitation assays. This interaction was not detected in extracts of taxol-treated HL-60 cells. Immunoprecipitation assays further revealed that Ebp1 co-precipitates with nucleolin from HL-60 cytoplasmic extracts. The observation that co-precipitation was decreased when extracts were treated with RNase suggests that Ebp1 and nucleolin are present in the same bcl-2 mRNP (messenger ribonucleoprotein particle) complexes. RNA-decay assays further demonstrated that Ebp1 decreased the rate of decay of β-globin–AREbcl-2 transcripts in HL-60 cell extracts. Collectively, these results indicate a novel function for Ebp1 in contributing to the regulation of bcl-2 expression in HL-60 cells.