Dynamics of dark hollow Gaussian laser pulses in relativistic plasma

Optical beams with null central intensity have potential applications in the field of atom optics. The spatial and temporal evolution of a central shadow dark hollow Gaussian (DHG) relativistic laser pulse propagating in a plasma is studied in this article for first principles. A nonlinear Schrodinger-type equation is obtained for the beam spot profile and then solved numerically to investigate the pulse propagation characteristics. As series of numerical simulations are employed to trace the profile of the focused and compressed DHG laser pulse as it propagates through the plasma. The theoretical and simulation results predict that higher-order DHG pulses show smaller divergence as they propagate and, thus, lead to enhanced energy transport. © 2013 American Physical Society.

Optimised extraction of heterocyclic aromatic amines from blood using hollow fibre membrane liquid-phase microextraction and triple quadrupole mass spectrometry

Heterocyclic aromatic amines (HCA) are carcinogenic mutagens formed during cooking of proteinaceous foods, particularly meat. To assist in the ongoing search for biomarkers of HCA exposure in blood, a method is described for the extraction from human plasma of the most abundant HCAs: 2-Amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx) (and its isomer 7,8-DiMeIQx), using Hollow Fibre Membrane Liquid-Phase Microextraction. This technique employs 2.5 cm lengths of porous polypropylene fibres impregnated with organic solvent to facilitate simultaneous extraction from an alkaline aqueous sample into a low volume acidic acceptor phase. This low cost protocol is extensively optimised for fibre length, extraction time, sample pH and volume. Detection is by UPLC-MS/MS using positive mode electrospray ionisation with a 3.4 min runtime, with optimum peak shape, sensitivity and baseline separation being achieved at pH 9.5. To our knowledge this is the first description of HCA chromatography under alkaline conditions. Application of fixed ion ratio tolerances for confirmation of analyte identity is discussed. Assay precision is between 4.5 and 8.8% while lower limits of detection between 2 and 5 pg/mL are below the concentrations postulated for acid-labile HCA-protein adducts in blood.

The hydraulics and resulting bed scour within the vicinity of Submerged Single Span Arch Bridges

As a consequence of climate change there is now a more frequent occurrence of extreme rainfall events where, with higher rates of urbanisation, the built environment has become increasingly affected by flooding.. This is of particular importance in relation to the stability of bridge structures that span rivers and canals etc. In November 2009, the UK and Ireland were subjected to extraordinarily severe weather conditions for several days. The rainfall was logged as the highest level of rainfall ever recorded within the UK, and as a direct consequence, unprecedented flooding occurred in Cumbria. This flooding led to the collapse of three road bridges which were generally 19th century masonry arch bridges, with relatively shallow foundations. In the UK, knowledge of the combined effect of bridge scouring and inundation has been not been particularly widely studied. Research carried out by Hamill et al [1] considered the hydraulic analysis of single arch bridges under flood conditions, but no consideration was given towards the likely damage to these structures due to scouring. Prior to this, Bierry and Delleur [2] produced a classic paper in predicting the discharge downstream of an inundated arch, focussing on predicting afflux as opposed to bridge scour. Further work on backwater effects was carried out by Martin-Vide & Prio [3] in semi-circular arch bridges. Both pressurized and free-surface flows at the bridge were investigated. Flows on a mobile bed in clear-water conditions were compared to those with a rigid bed, but no predictive equation for scour under pressurised conditions was considered. This paper will present initial findings from an experimental investigation into the effects of surcharged flow and subsequent scour within the vicinity of single span arch bridges. Velocities profiles will be shown within the vicinity of the arch, in addition to the depth of clear water scour, for a series of flows and model spans. The data will be presented, where results will be correlated to the most recent predictive equations that are proposed.

Is the shortened dental arch an underused treatment strategy in the Republic of Ireland?

OBJECTIVES: To determine the proportion of Republic of Ireland 35-44 and 65+ year-olds currently satisfying the criteria for a classic shortened dental arch (SDA) of 20 anterior teeth.

RESEARCH DESIGN: Secondary analysis of data collected in the 2000/02 epidemiological survey of the oral health of Irish adults.

CLINICAL SETTING: Participants underwent a clinical oral examination in health board dental clinics and completed a detailed interview pertaining to dental and general health.

PARTICIPANTS: The analysis is based on a random sample of adults, aged 35 to 44 years (n = 978), and 65 years and older (n = 714).

MAIN OUTCOME MEASURES: The SDA was measured as 20 teeth in the mouth in the positions normally described as from the left second premolar to the right second premolar in each arch.

RESULTS: Only one of the 35-44 year-olds and none of the 65+ year-olds had teeth in their mouths in positions normally described as a classic SDA. However, of the 35-44 year old age group only five patients who had at least a premolar dentition of 20 contiguous teeth had been provided with a removable denture compared to one patient from the 65+ years group.

CONCLUSIONS: Very few older patients in the Republic of Ireland have a SDA based on the measure used. However, very few have been provided with removable dentures where they already possess at least a premolar dentition of 20 contiguous teeth. Suggested reasons for this may include limitations of the data recorded, patient preferences and economic factors.

Preparation of La2NiO4+δ powders as a cathode material for SOFC via a PVP-assisted hydrothermal route

Uniform submicron La₂NiO_4+δ (sm-LNO) powders have been synthesized by a facile polyvinylpyrrolidone (PVP)-assisted hydrothermal route. In the presence of PVP, sm-LNO of pure phase has been obtained by calcination at the relatively low temperature of 900 °C for 8 h. Compared micron-sized LNO (m-LNO) particles obtained at 1,000 °C by hydrothermal synthesis route without PVP assisted, the sm-LNO-PVP displays regularly shaped and well-distributed particles in the range of 0.3–0.5 μm. The scanning electron microscopy (SEM) results showed that the sm-LNO sample is submicronic and that the m-LNO sample shows agglomerates with a broad size distribution. The electrochemical performance of m-LNO and sm-LNO-PVP has been investigated by electrochemical impedance spectroscopy. The polarization resistance of the sm-LNO-PVP cathode reaches a value of 0.40 Ω cm² at 750 °C, which is lower than that of m-LNO (0.62 Ω cm²). This result indicates that a fine electrode microstructure with submicron particles can help to increase the active sites, accelerate oxygen diffusion, and reduce polarization resistance. An anode-supported single cell with sm-LNO cathode has been fabricated and tested over a temperature range from 650 to 800 °C. The maximum power density of the cell has achieved 834 mW cm⁻² at 750 °C. These results therefore show that this PVP-assisted hydrothermal method is an effective approach to construct submicron-structured cathode and enhance the performance of intermediate temperature solid oxide fuel cell.

A design strategy of large grain lithium-rich layered oxides for lithium-ion batteries cathode

Li-rich materials are considered the most promising for Li-ion battery cathodes, as high capacity can be achieved. However, poor cycling stability is a critical drawback that leads to poor capacity retention. Here a strategy is used to synthesize a large-grain lithium-rich layered oxides to overcome this difficulty without sacrificing rate capability. This material is designed with micron scale grain with a width of about 300 nm and length of 1-3 μm. This unique structure has a better ability to overcome stress-induced structural collapse caused by Li-ion insertion/extraction and reduce the dissolution of Mn ions, which enable a reversible and stable capacity. As a result, this cathode material delivered a highest discharge capacity of around 308 mAh g^-1 at a current density of 30 mA g^-1 with retention of 88.3% (according to the highest discharge capacity) after 100 cycles, 190 mAh g^-1 at a current density of 300 mA g^-1 and almost no capacity fading after 100 cycles. Therefore, Lithium-rich material of large-grain structure is a promising cathode candidate in Lithium-ion batteries with high capacity and high cycle stability for application. This strategy of large grain may furthermore open the door to synthesize the other complex architectures for various applications.

Facile synthesis of nanocrystalline LiFePO4/graphene composite as cathode material for high power lithium ion batteries

We describe a simple strategy, which is based on the idea of space confinement, for the synthesis of carbon coating on LiFePO₄ nanoparticles/graphene nanosheets composites in a water-in-oil emulsion system. The prepared composite displayed high performance as a cathode material for lithium-ion battery, such as high reversible lithium storage capacity (158 mA h g^-1 after 100 cycles), high coulombic efficiency (over 97%), excellent cycling stability and high rate capability (as high as 83 mA h g ^-1 at 60 C). Very significantly, the preparation method employed can be easily adapted and be extended as a general approach to sophisticated compositions and structures for the preparation of highly dispersed nanosized structure on graphene. 

In situ synthesis of LiV3O8 nanorods on graphene as high rate-performance cathode materials for rechargeable lithium batteries

We developed a facile two-step hydrothermal procedure to prepare hybrid materials of LiV₃O₈ nanorods on graphene sheets. The special structure endows them with the high-rate transportation of electrolyte ions and electrons throughout the electrode matrix, resulting in remarkable electrochemical performance when they were used as cathodes in rechargeable lithium batteries. © 2013 The Royal Society of Chemistry.

Electrochemical promotion of a Pt catalyst supported on La 0.6Sr 0.4Co 0.2Fe 0.8O 3 - δ hollow fibre membranes

The use of wireless electrochemical promotion of catalysis (EPOC) of a Pt catalyst supported on a mixed ionic electronic conducting hollow fibre membranes is investigated. This reactor configuration offers high surface areas per unit volume and is ideally suited for scaled-up applications. The MIEC membrane used is the La _0.6Sr _0.4Co _0.2Fe _0.8O ₃ perovskite (LSCF) with a Pt catalyst film deposited on the outer surface of the LSCF membrane. Experimental results showed that after initial catalyst deactivation (in the absence of an oxygen chemical potential difference across the membrane) the catalytic rate can be enhanced by using an oxygen sweep and wireless EPOC can be used for the in situ regeneration of a deactivated catalyst. © 2012 Elsevier B.V.

Issues in fe modelling of FRP strengthened masonry arch bridges

Externally bonding of FRP composites is an effective technique for retrofitting historical masonry arch structures. A major failure mode in such strengthened structures is the debonding of FRP from the masonry. The bond behaviour between FRP and masonry thus plays a crucial role in these structures. Major challenges exist in the finite element modelling of such structures, such as modelling of mixed Mode-I and Mode-II bond behaviour between the FRP and the curved masonry substrate, modelling of existing damages in the masonry arches, consideration of loading history in the unstrengthened and strengthened structure etc. This paper presents a rigorous FE model for simulating FRP strengthened masonry arch structures. A detailed solid model was developed for simulating the masonry and a mixed-mode interface model was used for simulating the FRP-to-masonry bond behaviour. The model produces results in very close agreement with test results.

The linear elastic in-plane bending of curved hollow profiles having a thin-walled rectangular section

This paper presents a simple solution for the flexibility calculation of curved profiles having a rectangular thin-walled cross-section. Some assumptions related to geometric details about the shape of the deformed structure are included in the present analysis, aiming at an economic and accurate solution. Results concerning the distortion of the transverse section are compared with the corresponding data from the solution with a thin shell finite element analysis. A flexibility factor for the structure analysed here is presented as a graphical result.