483 research outputs found
Evidence for anthropogenic <sup>14</sup>C-enrichment in estuarine waters adjacent to the North Sea
[1] The isotopic composition (d13C and D14C) of high
molecular weight dissolved organic carbon (HMW DOC)
was studied in the Tyne and Tweed estuaries, NE England.
Despite significant removal of terrigenous HMW DOC in
the low salinity regions (S < 15), D14C remained modern
with little variation around 115%. This lack of apparent age
discrimination was attributed to either non-oxidative
removal or the absence of a significant proportion of old
refractory C in the HMW DOC pool. At S < 15, we
observed seaward increases in d13C and D14C. With no
documented local 14C inputs, we attributed non-bomb
related 14C-enrichment at S < 15 to a possible âlingering
effectâ of distal anthropogenic sources in near-coastal North
Sea HMW DOC. Given the global distribution of potential
sources, we propose that anthropogenic 14C should be
considered in assigning ages of DOC pools in near-coastal
waters and suggest its possible use as a tracer for DOC
transformations
A generalized definition of dosimetric quantities
The current definitions of microdosimetric and dosimetric quantities use the notion of 'ionizing radiation'. However, this notion is not rigorously defined, and its definition would require the somewhat arbitrary choice of specified energy cut-off values for different types of particles. Instead of choosing fixed cut-off values one can extend the system of definitions by admitting the free selection of a category of types and energies of particles that are taken to be part of the field. In this way one extends the system of dosimetric quantities. Kerma and absorbed dose appear then as special cases of a more general dosimetric quantity, and an analogue to kerma can be obtained for charged particle fields; it is termed cema. A modification that is suitable for electron fields is termed reduced cema
A new species of Corydoras LacépÚde (Siluriformes: Callichthyidae) from the Rio Tapajós basin and its phylogenetic implications
A new species of Corydoras is described from tributaries of the rio Arinos, rio Teles Pires and rio Preto, all in the rio TapajĂłs basin. The new species is a member of a group that includes 36 species with spots on the body. Within this group, the new species can be readily distinguished by having a smaller dorsal-fin spine than the first three subsequent soft dorsal-fin rays; pectoral, pelvic and anal fins hyaline; dorsal-fin interradial membrane hyaline; rounded spots on trunk restricted to dorsolateral body plates and dorsal portion of ventrolateral body plates, not reaching the base of pelvic and anal fins. The new species can be further distinguished from Corydoras xinguensis by having spots with diffuse edges, and from all other species of spotted Corydoras except C.multimaculatus, by the absence of ventral platelets. A phylogenetic analysis recovered the new species plus Corydoras metae and C.araguaiensis in a clade sharing the presence of a pointed process on the maxilla for insertion of the retractor tentaculi muscle. In addition, the presence in the new species of an elongated anterior portion of the mesethmoid and a triangular uncinate process of the epibranchial 3 suggests a close relationship with Corydoras metae.Uma nova espĂ©cie de Corydoras Ă© descrita dos tributĂĄrios dos rios Arinos, Teles Pires e Preto, bacia do rio TapajĂłs. A nova espĂ©cie Ă© membro de um grupo com pontilhados no corpo que inclui 36 espĂ©cies. Dentro desse grupo, a nova espĂ©cie pode ser facilmente distinguida pelo espinho dorsal menor que os trĂȘs primeiros raios ramificados da nadadeira dorsal; nadadeiras peitorais, pĂ©lvicas e anal hialinas; membranas inter-radiais da nadadeira dorsal hialina; presença de pontilhados redondos no tronco restritas as placas dorsolaterais do corpo e porçÔes dorsais das placas ventrolaterais nĂŁo alcançando a base das nadadeiras pĂ©lvicas e anal. A nova espĂ©cie pode ser distinguida de Corydoras xinguensis por pontilhados com margens difusas e das demais espĂ©cies de Corydoras com pontilhado, exceto em C.multimaculatus, pela ausĂȘncia de pequenas placas ventrais. Uma anĂĄlise filogenĂ©tica recuperou a nova espĂ©cie mais Corydoras metae e C.araguaiensis em um agrupamento compartilhando a presença de um processo pontiagudo para inserção do mĂșsculo retractor tentaculi no maxilar. A porção anterior do mesetmĂłide alongada e o processo uncinado do epibranquial 3 triangular indicam uma relação mais prĂłxima com Corydoras metae
Experimental and numerical investigations of oil film formation and friction in a piston ring-liner contact
The piston ringâcylinder liner contact is a major source of the total parasitic losses in an internal combustion engine. The lubrication process of this contact highly influences the amount of friction, oil consumption and wear that occurs. In this work, a reciprocating test rig combined with an ultrasonic film thickness measurement system was developed and then used for tribological investigation of the piston ringâcylinder liner contact under idealised cold conditions. A special piston ring and cylinder liner holder were designed and five sensors were glued on to the back side of the liner specimen. Ultrasonic reflections captured by the sensors, used to obtain the film thickness, and friction were continuously recorded as the piston ring section reciprocated over the liner. Several experiments were performed at different speed and load conditions. Furthermore, a numerical model has been developed to predict film thickness and friction in all lubrication regimes. The experimentally measured film thickness and friction were compared with the output from the numerical model and good correlation was found. The parameters affecting the accuracy of the ultrasound measurements and numerical simulations of film thickness and friction are then discussed
An experimental and numerical investigation of frictional losses and film thickness for four cylinder liner variants for a heavy duty diesel engine
The piston ring pack is the single greatest contributor to mechanical losses in a heavy duty diesel engine, accounting for 1.1â6.8% of the total losses. Therefore, the piston ring-cylinder liner contact is potentially the most rewarding area to study when attempting to reduce mechanical losses in a heavy duty diesel engine. In this work, four different heavy duty diesel engine cylinder liner variants have been tested to evaluate the lubricating conditions that occur when a section of top compression ring is reciprocated against them in a lubricated environment. Two of the cylinder liners were traditional grey cast iron and plateau honed with different honing angles, one had ANS TriboconditioningÂź applied and the last was plasma sprayed with a stainless steel and ceramic coating, then honed. An experimental test rig was used where friction and film thickness was recorded, by means of an ultrasonic technique. A numerical model was also developed to calculate the friction and film thickness. Comparisons are made between the simulation and experiment, and the four cylinder liner variants are also evaluated. It was found that both simulation and experiment could differentiate between all surfaces and the results from the model and experiment also correlated well with each other. A lower plateau average surface roughness, as exhibited by the ANS TriboconditioningÂź and plasma liners, led to a significant reduction in friction
A "Littlest Higgs" Model with Custodial SU(2) Symmetry
In this note, a ``littlest higgs'' model is presented which has an
approximate custodial SU(2) symmetry. The model is based on the coset space
. The light pseudo-goldstone bosons of the theory
include a {\it single} higgs doublet below a TeV and a set of three
triplets and an electroweak singlet in the TeV range. All of these scalars
obtain approximately custodial SU(2) preserving vacuum expectation values. This
model addresses a defect in the earlier moose
model, with the only extra complication being an extended top sector. Some of
the precision electroweak observables are computed and do not deviate
appreciably from Standard Model predictions. In an S-T oblique analysis, the
dominant non-Standard Model contributions are the extended top sector and higgs
doublet contributions. In conclusion, a wide range of higgs masses is allowed
in a large region of parameter space consistent with naturalness, where large
higgs masses requires some mild custodial SU(2) violation from the extended top
sector.Comment: 22 pages + 8 figures; JHEP style, added references and extra
discussion on size of T contributions, as well as some other minor
clarifications. Version to appear in JHE
Continuous twin screw rheo-extrusion of an AZ91D magnesium alloy
© The Minerals, Metals & Materials Society and ASM International 2012The twin screw rheo-extrusion (TSRE) is designed to take advantage of the nondendritc microstructure and thixotropic characterization of semisolid-metal slurries and produce simple metal profiles directly from melts. The extrusion equipment consists of a rotor-stator high shear slurry maker, a twin screw extruder, and a die assembly. The process is continuous and has a potential for significantly saving energy, manufacturing cost, and enhancing efficiency. The present investigation was carried out to study the process performance for processing rods of an AZ91D magnesium alloy and the microstructure evolution during processing. The semisolid slurry prepared by the process was characterized by uniformly distributed nondendritic granular primary phase particles. AZ91D rods with uniform and fine microstructures and moderate mechanical properties were produced. For the given slurry making parameters, decreasing extrusion temperature was found to improve microstructures and properties. The mechanisms of particle granulation and refinement and the effect of processing parameters on process performance and thermal management are discussed. © 2012 The Minerals, Metals & Materials Society and ASM International.EPSRC (UK) and Rautomead Lt
A New Mechanism for ÎČâLactamases: Class D Enzymes Degrade 1ÎČâMethyl Carbapenems through Lactone Formation
ÎČâLactamases threaten the clinical use of carbapenems, which are considered antibiotics of last resort. The classical mechanism of serine carbapenemase catalysis proceeds through hydrolysis of an acylâenzyme intermediate. We show that classâ
D ÎČâlactamases also degrade clinically used 1ÎČâmethylâsubstituted carbapenems through the unprecedented formation of a carbapenemâderived ÎČâlactone. ÎČâLactone formation results from nucleophilic attack of the carbapenem hydroxyethyl side chain on the ester carbonyl of the acylâenzyme intermediate. The carbapenemâderived lactone products inhibit both serine ÎČâlactamases (particularly classâ
D) and metalloâÎČâlactamases. These results define a new mechanism for the classâ
D carbapenemases, in which a hydrolytic water molecule is not required.FWN â Publicaties zonder aanstelling Universiteit Leide
A New Mechanism for ÎČâLactamases: Class D Enzymes Degrade 1ÎČâMethyl Carbapenems through Lactone Formation
ÎČâLactamases threaten the clinical use of carbapenems, which are considered antibiotics of last resort. The classical mechanism of serine carbapenemase catalysis proceeds through hydrolysis of an acylâenzyme intermediate. We show that classâ
D ÎČâlactamases also degrade clinically used 1ÎČâmethylâsubstituted carbapenems through the unprecedented formation of a carbapenemâderived ÎČâlactone. ÎČâLactone formation results from nucleophilic attack of the carbapenem hydroxyethyl side chain on the ester carbonyl of the acylâenzyme intermediate. The carbapenemâderived lactone products inhibit both serine ÎČâlactamases (particularly classâ
D) and metalloâÎČâlactamases. These results define a new mechanism for the classâ
D carbapenemases, in which a hydrolytic water molecule is not required.FWN â Publicaties zonder aanstelling Universiteit Leide
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