Reconstruction of an unsteady flow from incomplete boundary data:Part I. Theory

Purpose – To propose and investigate a stable numerical procedure for the reconstruction of the velocity of a viscous incompressible fluid flow in linear hydrodynamics from knowledge of the velocity and fluid stress force given on a part of the boundary of a bounded domain. Design/methodology/approach – Earlier works have involved the similar problem but for stationary case (time-independent fluid flow). Extending these ideas a procedure is proposed and investigated also for the time-dependent case. Findings – The paper finds a novel variation method for the Cauchy problem. It proves convergence and also proposes a new boundary element method. Research limitations/implications – The fluid flow domain is limited to annular domains; this restriction can be removed undertaking analyses in appropriate weighted spaces to incorporate singularities that can occur on general bounded domains. Future work involves numerical investigations and also to consider Oseen type flow. A challenging problem is to consider non-linear Navier-Stokes equation. Practical implications – Fluid flow problems where data are known only on a part of the boundary occur in a range of engineering situations such as colloidal suspension and swimming of microorganisms. For example, the solution domain can be the region between to spheres where only the outer sphere is accessible for measurements. Originality/value – A novel variational method for the Cauchy problem is proposed which preserves the unsteady Stokes operator, convergence is proved and using recent for the fundamental solution for unsteady Stokes system, a new boundary element method for this system is also proposed.

G-protein-coupled receptor solubilization and purification for biophysical analysis and functional studies, in the total absence of detergent

G-protein coupled receptors (GPCRs) constitute the largest class of membrane proteins and are a major drug target. A serious obstacle to studying GPCR structure/function characteristics is the requirement to extract the receptors from their native environment in the plasma membrane, coupled with the inherent instability of GPCRs in the detergents required for their solubilization. In the present study, we report the first solubilization and purification of a functional GPCR [human adenosine A2A receptor (A2AR)], in the total absence of detergent at any stage, by exploiting spontaneous encapsulation by styrene maleic acid (SMA) co-polymer direct from the membrane into a nanoscale SMA lipid particle (SMALP). Furthermore, the A2AR-SMALP, generated from yeast (Pichia pastoris) or mammalian cells, exhibited increased thermostability (∼5°C) compared with detergent [DDM (n-dodecyl-β-D-maltopyranoside)]-solubilized A2AR controls. The A2AR-SMALP was also stable when stored for prolonged periods at 4°C and was resistant to multiple freeze-thaw cycles, in marked contrast with the detergent-solubilized receptor. These properties establish the potential for using GPCR-SMALP in receptor-based drug discovery assays. Moreover, in contrast with nanodiscs stabilized by scaffold proteins, the non-proteinaceous nature of the SMA polymer allowed unobscured biophysical characterization of the embedded receptor. Consequently, CD spectroscopy was used to relate changes in secondary structure to loss of ligand binding ([³H]ZM241385) capability. SMALP-solubilization of GPCRs, retaining the annular lipid environment, will enable a wide range of therapeutic targets to be prepared in native-like state to aid drug discovery and understanding of GPCR molecular mechanisms.

Blue-detuned optical ring trap for Bose-Einstein condensates based on conical refraction

We present a novel approach for the optical manipulation of neutral atoms in annular light structures produced by the phenomenon of conical refraction occurring in biaxial optical crystals. For a beam focused to a plane behind the crystal, the focal plane exhibits two concentric bright rings enclosing a ring of null intensity called the Poggendorff ring. We demonstrate both theoretically and experimentally that the Poggendorff dark ring of conical refraction is confined in three dimensions by regions of higher intensity. We derive the positions of the confining intensity maxima and minima and discuss the application of the Poggendorff ring for trapping ultra-cold atoms using the repulsive dipole force of blue-detuned light. We give analytical expressions for the trapping frequencies and potential depths along both the radial and the axial directions. Finally, we present realistic numerical simulations of the dynamics of a 87Rb Bose-Einstein condensate trapped inside the Poggendorff ring which are in good agreement with corresponding experimental results.

On the Asymptotic Distribution of Closed Orbits for a Class of Open Billiards

2000 Mathematics Subject Classification: 37D40.

On the impact of Cu dispersion on CO2 photoreduction over Cu/TiO2

A family of Cu/TiO2 catalysts was prepared using a refined sol–gel method, and tested in the photocatalytic reduction of CO2 by H2O to CH4 using a stirred batch, annular reactor. The resulting photoactivity was benchmarked against pure TiO2 nanoparticles (synthesised by an identical sol–gel route). CO2 photoreduction exhibited a strong volcano dependence on Cu loading, reflecting the transition from 2-dimensional CuOx nanostructures to 3-dimensional crystallites, with optimum CH4 production observed for 0.03 wt.% Cu/TiO2.

GPCR-styrene maleic acid lipid particles (GPCR-SMALPs):their nature and potential

G-protein-coupled receptors (GPCRs) form the largest class of membrane proteins and are an important target for therapeutic drugs. These receptors are highly dynamic proteins sampling a range of conformational states in order to fulfil their complex signalling roles. In order to fully understand GPCR signalling mechanisms it is necessary to extract the receptor protein out of the plasma membrane. Historically this has universally required detergents which inadvertently strip away the annulus of lipid in close association with the receptor and disrupt lateral pressure exerted by the bilayer. Detergent-solubilized GPCRs are very unstable which presents a serious hurdle to characterization by biophysical methods. A range of strategies have been developed to ameliorate the detrimental effect of removing the receptor from the membrane including amphipols and reconstitution into nanodics stabilized by membrane scaffolding proteins (MSPs) but they all require exposure to detergent. Poly(styrene-co-maleic acid) (SMA) incorporates into membranes and spontaneously forms nanoscale poly(styrene-co-maleic acid) lipid particles (SMALPs), effectively acting like a 'molecular pastry cutter' to 'solubilize' GPCRs in the complete absence of detergent at any stage and with preservation of the native annular lipid throughout the process. GPCR-SMALPs have similar pharmacological properties to membrane-bound receptor, exhibit enhanced stability compared with detergent-solubilized receptors and being non-proteinaceous in nature, are fully compatible with downstream biophysical analysis of the encapsulated GPCR.

Synthetic studies of azulenyl and pseudoazulenyl nitrones

Free radicals have been implicated in various pathological conditions such as, stroke, aging and ischemic heart disease (IHD), as well as neurodegenerative diseases like Alzheimer’s, Parkinson’s, and Huntington’s disease. The role of antioxidants in protection from the harmful effects of free radicals has long been recognized. Trapping extremely reactive free radicals and eliminating them from circulation has been shown to be effective in animal models. Nitrone-based free radical traps have been extensively explored in biological systems. Examples include nitrones such as PBN, NXY-059, MDL-101,002, DMPO and EMPO. However, these nitrones have extremely high oxidation potentials as compared to natural antioxidants such as Vitamin E (α-tocopherol), and glutathione. Becker et al. (1995) synthesized novel azulenyl nitrones, which were shown to have oxidation potentials much lower than that of any of the previously reported nitrone based spin traps. Another azulenyl nitrone derivative, stilbazulenyl nitrone (STAZN), was shown to have an even lower oxidation potential within the range of natural antioxidants. STAZN, a second generation free radical trap, was found to be markedly superior than the two most studied nitrones, PBN and NXY-059, in animal models of cerebral ischemia and in an in vitro assay of lipid peroxidation. In this study, a third generation azulenyl nitrone was synthesized with an electron donating group on the previously synthesized STAZN derivative with the aim to lower the oxidation potential even more. Pseudoazulenes, because of the presence of an annular heteroatom, have been reported to possess even lower oxidation potential than that of the azulenyl counterpart. Therefore, pseudoazulenyl nitrones were synthesized for the first time by extracting and elaborating valtrate from the roots of Centranthus ruber (Red valerian or Jupiter’s beard). Several pseudoazulenyl nitrones were synthesized by using a facile experimental protocol. The physical and biological properties of these pseudoazulenyl nitrones can be easily modified by simply changing the substituent on the heteroatom. Cyclic voltammetry experiments have shown that these pseudoazulenyl nitrones do indeed have low oxidation potentials. The oxidation potential of these nitrones was lowered even more by preparing derivatives bearing an electron donating group at the 3-position of the five membered ring of the pseudoazulenyl nitrone.

Ichnology and palaeobiology of Phoebichnus trochoides and Schaubcylindrichnus heberti comb. nov.

The three-dimensional reconstructions of Phoebichnus trochoides and Schaubcylindrichnus (Palaeophycus) heberti created as part of this thesis allow us to fully understand and characterize the three-dimensional morphology and palaeobiology of these common taxa. Three-dimensional reconstructions demonstrate that P. trochoides is a large stellate burrow composed of numerous long galleries produced by a deposit feeding organism. This study reports for the first time that the central zone is composed of stacked disk-shaped layers of highly bioturbated sediment, the radial burrows are composed of a sand-rich lining of pelleted annuli surrounding an active sand-rich fill, and the presence of subtle conical features above the radial galleries that are inferred to result from collapse cone feeding. Reconstructions of heberti demonstrate that the thick walled burrows are composed of sand-rich annular rings, are a broad U-shape, and may be either clustered or isolated. Our observations show that the morphology of heberti is inconsistent with the generic diagnosis of Palaeophycus, but is morphologically comparable to Schaubcylindrichnus, and is herein synonymised with Schaubcylindrichnus to create S. heberti comb. nov. The three-dimensional reconstructions have revealed a number of hitherto unknown morphological elements to both taxa which has facilitated new interpretations of the trace-makers behaviour. The data improves the taxonomic understanding of both P. trochoides and S. heberti which require significant taxonomic change and emendation of diagnoses at the species and genus level.

Synthetic Studies of Azulenyl and Pseudoazulenyl Nitrones

Free radicals have been implicated in various pathological conditions such as, stroke, aging and ischemic heart disease (IHD), as well as neurodegenerative diseases like Alzheimer’s, Parkinson’s, and Huntington’s disease. The role of antioxidants in protection from the harmful effects of free radicals has long been recognized. Trapping extremely reactive free radicals and eliminating them from circulation has been shown to be effective in animal models. Nitrone-based free radical traps have been extensively explored in biological systems. Examples include nitrones such as PBN, NXY-059, MDL-101,002, DMPO and EMPO. However, these nitrones have extremely high oxidation potentials as compared to natural antioxidants such as Vitamin E (á-tocopherol), and glutathione. Becker et al. (1995) synthesized novel azulenyl nitrones, which were shown to have oxidation potentials much lower than that of any of the previously reported nitrone based spin traps. Another azulenyl nitrone derivative, stilbazulenyl nitrone (STAZN), was shown to have an even lower oxidation potential within the range of natural antioxidants. STAZN, a second generation free radical trap, was found to be markedly superior than the two most studied nitrones, PBN and NXY-059, in animal models of cerebral ischemia and in an in vitro assay of lipid peroxidation. In this study, a third generation azulenyl nitrone was synthesized with an electron donating group on the previously synthesized STAZN derivative with the aim to lower the oxidation potential even more. Pseudoazulenes, because of the presence of an annular heteroatom, have been reported to possess even lower oxidation potential than that of the azulenyl counterpart. Therefore, pseudoazulenyl nitrones were synthesized for the first time by extracting and elaborating valtrate from the roots of Centranthus ruber (Red valerian or Jupiter’s beard). Several pseudoazulenyl nitrones were synthesized by using a facile experimental protocol. The physical and biological properties of these pseudoazulenyl nitrones can be easily modified by simply changing the substituent on the heteroatom. Cyclic voltammetry experiments have shown that these pseudoazulenyl nitrones do indeed have low oxidation potentials. The oxidation potential of these nitrones was lowered even more by preparing derivatives bearing an electron donating group at the 3-position of the five membered ring of the pseudoazulenyl nitrone.

Critical bed shear stress and threshold of motion of maërl biogenic gravel

Critical bed shear stress for incipient motion has been determined for biogenic free-living coralline algae known as maërl. Maërl from three different sedimentary environments (beach, intertidal, and open marine) in Galway Bay, west of Ireland have been analysed in a rotating annular flume and linear flume. Velocity profile measurements of the benthic boundary layer, using an Acoustic Doppler Velocimeter, have been obtained in four different velocity experiments. The bed shear stress has been determined using three methods: Law of the Wall, Turbulent Kinetic Energy and Reynolds Stress. The critical Shields parameter has been estimated as a non-dimensional mobility number and the results have been compared with the Shields curve for natural sand. Maërl particles fall below this curve because its greater angularity allows grains to be mobilised easier than hydraulically equivalent particles. From previous work, the relationship between grain shape and the settling velocity of maërl suggests that the roughness is greatest for intertidal maërl particles. During critical shear stress determinations, beds of such rough particles exhibited the greatest critical shear stress probably because the particle thalli interlocked and resisted entrainment. The Turbulent Kinetic Energy methodology gives the most consistent results, agreeing with previous comparative studies. Rarely-documented maërl megaripples were observed in the rotating annular flume and are hypothesised to form at velocities ~10 cm s-1 higher than the critical threshold velocity, where tidal currents, oscillatory flow or combined-wave current interaction results in the preferential transport of maërl. A determination of the critical bed shear stress of maërl allows its mobility and rate of erosion and deposition to be evaluated spatially in subsequent applications to biological conservation management.

Intra-pulse transition between ion acceleration mechanisms in intense laser-foil interactions

Multiple ion acceleration mechanisms can occur when an ultrathin foil is irradiated with an intense laser pulse, with the dominant mechanism changing over the course of the interaction. Measurement of the spatial-intensity distribution of the beam of energetic protons is used to investigate the transition from radiation pressure acceleration to transparency-driven processes. It is shown numerically that radiation pressure drives an increased expansion of the target ions within the spatial extent of the laser focal spot, which induces a radial deflection of relatively low energy sheath-accelerated protons to form an annular distribution. Through variation of the target foil thickness, the opening angle of the ring is shown to be correlated to the point in time transparency occurs during the interaction and is maximized when it occurs at the peak of the laser intensity profile. Corresponding experimental measurements of the ring size variation with target thickness exhibit the same trends and provide insight into the intra-pulse laser-plasma evolution.

Ordered arrays of multiferroic epitaxial nanostructures

Epitaxial heterostructures combining ferroelectric (FE) and ferromagnetic (FiM) oxides are a possible route to explore coupling mechanisms between the two independent order parameters, polarization and magnetization of the component phases. We report on the fabrication and properties of arrays of hybrid epitaxial nanostructures of FiM NiFe(2)O(4) (NFO) and FE PbZr(0.52)Ti(0.48)O(3) or PbZr(0.2)Ti(0.8)O(3), with large range order and lateral dimensions from 200 nm to 1 micron. METHODS: The structures were fabricated by pulsed-laser deposition. High resolution transmission electron microscopy and high angle annular dark-field scanning transmission electron microscopy were employed to investigate the microstructure and the epitaxial growth of the structures. Room temperature ferroelectric and ferrimagnetic domains of the heterostructures were imaged by piezoresponse force microscopy (PFM) and magnetic force microscopy (MFM), respectively. RESULTS: PFM and MFM investigations proved that the hybrid epitaxial nanostructures show ferroelectric and magnetic order at room temperature. Dielectric effects occurring after repeated switching of the polarization in large planar capacitors, comprising ferrimagnetic NiFe2O4 dots embedded in ferroelectric PbZr0.52Ti0.48O3 matrix, were studied. CONCLUSION: These hybrid multiferroic structures with clean and well defined epitaxial interfaces hold promise for reliable investigations of magnetoelectric coupling between the ferrimagnetic / magnetostrictive and ferroelectric / piezoelectric phases.

Combustion Noise

Combustion noise is becoming increasingly important as a major noise source in aeroengines and ground based gas turbines. This is partially because advances in design have reduced the other noise sources, and partially because next generation combustion modes burn more unsteadily, resulting in increased external noise from the combustion. This review reports recent progress made in understanding combustion noise by theoretical, numerical and experimental investigations. We first discuss the fundamentals of the sound emission from a combustion region. Then the noise of open turbulent flames is summarized. We subsequently address the effects of confinement on combustion noise. In this case not only is the sound generated by the combustion influenced by its transmission through the boundaries of the combustion chamber, there is also the possibility of a significant additional source, the so-called ‘indirect’ combustion noise. This involves hot spots (entropy fluctuations) or vorticity perturbations produced by temporal variations in combustion, which generate pressure waves (sound) as they accelerate through any restriction at the exit of the combustor. We describe the general characteristics of direct and indirect noise. To gain further insight into the physical phenomena of direct and indirect sound, we investigate a simple configuration consisting of a cylindrical or annular combustor with a low Mach number flow in which a flame zone burns unsteadily. Using a low Mach number approximation, algebraic exact solutions are developed so that the parameters controlling the generation of acoustic, entropic and vortical waves can be investigated. The validity of the low Mach number approximation is then verified by solving the linearized Euler equations numerically for a wide range of inlet Mach numbers, stagnation temperature ratios, frequency and mode number of heat release fluctuations. The effects of these parameters on the magnitude of the waves produced by the unsteady combustion are investigated. In particular the magnitude of the indirect and direct noise generated in a model combustor with a choked outlet is analyzed for a wide range of frequencies, inlet Mach numbers and stagnation temperature ratios. Finally, we summarize some of the unsolved questions that need to be the focus of future research

Modelagem dinâmica e simulação computacional de poços de petróleo verticais e direcionais com elevação por bombeio mecânico

LINS, Filipe C. A. et al. Modelagem dinâmica e simulação computacional de poços de petróleo verticais e direcionais com elevação por bombeio mecânico. In: CONGRESSO BRASILEIRO DE PESQUISA E DESENVOLVIMENTO EM PETRÓLEO E GÁS, 5. 2009, Fortaleza, CE. Anais... Fortaleza: CBPDPetro, 2009.