Recristalización de bandas de aluminio procedentes de colada continua, laminadas en frío

Este artículo revisa la bibliografía existente sobre los problemas que la banda de colada continua, laminada en frío, presenta en su recristalización. Se examinan los impedimentos que presenta la precipitación de elementos de aleación o impurezas, previa o simultánea a la recristalización, para la nucleación de la recristalización y por tanto para ésta. Se explica el uso de las curvas TTT (Temperatura, Tiempo, Transformación) para la determinación de temperatura y velocidad de calentamiento críticas para llegar a la recristalización sin pasar por la zona de precipitación. Se explica también la obtención de curvas CTT (Concentración, Tiempo, Transformación) y "diagramas de tamaño de grano" para aleaciones Al-Mn en función de la velocidad de calentamiento y contenido de manganeso en solución sólida.

Compressive membrane action in composite floor slabs in the Cardington LBTF

This paper presents the results of an experimental study (the ultimate load capacity of composite metal decking/concrete floor slabs. Full-scale in situ testing of composite floor slabs was carried out in the Building Research Establishment's Large Building Test Facility (LBTF) at Cardington. A parallel laboratory test programme, which compared the behaviour of composite floor slabs strips, also carried out at Queen's University Belfast (QUB). Articular attention was paid to the contribution of compressive membrane action to the load carrying capacity. The results of both test programmes were compared with predictions by yield line theory and a theoretical prediction method in which the amount of horizontal restraint mid be assessed. The full-scale tests clearly demon-wed the significant contribution of compressive membrane effects to the load capacity of interior floor panels with a lesser contribution to edge/corner panels.

Arching action in high strength concrete slabs

The corrosion of reinforcement in bridge deck slabs has been the cause of major deterioration and high costs in repair and maintenance.This problem could be overcome by reducing the amount of reinforcement and/or altering the location.This is possible because, in addition to the strength provided by the reinforcement, bridge deck slabs have an inherent strength due to the in-plane arching forces set up as a result of restraint provided by the slab boundary conditions. This is known as arching action or Compressive Membrane Action (CMA). It has been recognised for some time that laterally restrained slabs exhibit strengths far in excess of those predicted by most design codes but the phenomenon has not been recognised by the majority of bridge design engineers. This paper presents the results of laboratory tests on fifteen reinforced concrete slab strips typical of a bridge deck slab and compares them to predicted strengths using the current codes and CMA theory. The tests showed that the strength of laterally restrained slabs is sensitive to both the degree of external lateral restraint and the concrete compressive strength.The tests particularly highlighted the benefits in strength obtained from very high strength concrete slabs. The theory extends the existing knowledge of CMA in slabs with concrete compressive strengths up to 100 N/mm[2] and promotes more economical and durable bridge deck construction by utilising the benefits of high strength concrete.

Cholinergic-induced Ca2+ signaling in interstitial cells of Cajal from the guinea pig bladder.

Acetylcholine released from parasympathetic excitatory nerves activates contraction in detrusor smooth muscle. Immunohistochemical labeling of guinea pig detrusor with anti-c-Kit and anti-VAChT demonstrated a close structural relationship between interstitial cells of Cajal (ICC) and cholinergic nerves. The ability of guinea pig bladder detrusor ICC to respond to the acetylcholine analog, carbachol, was investigated in enzymatically dissociated cells, loaded with the Ca(2+) indicator fluo 4AM. ICC fired Ca(2+) transients in response to stimulation by carbachol (1/10 microM). Their pharmacology was consistent with carbachol-induced contractions in strips of detrusor which were inhibited by 4-DAMP (1 microM), an M(3) receptor antagonist, but not by the M(2) receptor antagonist methoctramine (1 microM). The source of Ca(2+) underlying the carbachol transients in isolated ICC was investigated using agents to interfere with influx or release from intracellular stores. Nifedipine (1 microM) or Ni(2+) (30-100 microM) to block Ca(2+) channels or the removal of external Ca(2+) reduced the amplitude of the carbachol transients. Application of ryanodine (30 microM) or tetracaine (100 microM) abolished the transients. The phospholipase C inhibitor, U-73122 (2.5 microM), significantly reduced the responses. 2-Aminoethoxydiethylborate (30 microM) caused a significant reduction and Xestospongin C (1 microM) was more effective, almost abolishing the responses. Intact in situ preparations of guinea pig bladder loaded with a Ca(2+) indicator showed distinctively different patterns of spontaneous Ca(2+) events in smooth muscle cells and ICC. Both cell types responded to carbachol by an increase in frequency of these events. In conclusion, guinea pig bladder detrusor ICC, both as isolated cells and within whole tissue preparations, respond to cholinergic stimulation by firing Ca(2+) transients. PMID: 18171995 [PubMed - indexed for MEDLINE]

Isolation and preliminary biological assessment of AADGAPLIRFamide and SVPGVLRFamide from Caenorhabditis elegans

To date, 9 FMRFamide-related peptides (FaRPs) have been structurally characterised from Caenorhabditis elegans. Radioimmunometrical screening of an ethanolic extract of C. elegans revealed the presence of two additional FaRPs that were purified by reverse-phase HPLC and subjected to Edman degradation analysis and gas-phase sequencing. Unequivocal primary structures for the two FaRPs were determined as Ala-Ala-Asp-Gly-Ala-Pro-Leu-Ile-Arg-Phe-NH2 and Ser-Val-Pro-Gly-Val-Leu-Arg-Phe-NH2. Using MALDI-TOF mass. spectrometry, the molecular masses of the peptides were found to be 1032 Da (MH) and 875 Da (MH)(+), respectively. Two copies of AADGAPLIRFamide are predicted to be encoded on the precursor gene termed flp-13, while one copy of SVPGVLRFamide is located on flp-18. Synthetic replicates of the peptides were tested on Ascaris suum somatic muscle to assess bioactivity. ADDGAPLIRFamide had inhibitory effects on A. suum muscle strips, which occurred over a range of concentrations from a threshold for activity of 10 nM to 10 muM. SVPGVLRFamide was excitatory on A. suum somatic musculature from a threshold concentration for activity of 1 nM to 10 muM. The inhibitory and excitatory effects of AADGAPLIRFamide and SVPGVLRFamide, respectively, were the same for dorsal and ventral muscle strips as well as innervated and denervated preparations, suggesting that these physiological effects are not nerve cord dependent. Addition of ADDGAPLIRFamide (10 muM) to muscle strips preincubated in high-K+ and -Ca2+-free medium resulted in a normal inhibitory response. Peptide addition to muscle strips preincubated in Cl--free medium showed no inhibitory response, suggesting that the inhibitory response of the peptide may be chloride mediated. A normal excitatory response was noted following the addition of 10 muM SVPGVLRFamide to muscle strips preincubated in high-K+, Ca2+- and Cl--free media. (C) 2001 Academic Press.

Flatworm nerve-muscle: structural and functional analysis

Platyhelminthes occupy a unique position in nerve-muscle evolution, being the most primitive of metazoan phyla. Essentially, their nervous system consists of an archaic brain and associated pairs of longitudinal nerve cords cross-linked as an orthogon by transverse commissures. Confocal imaging reveals that these central nervous system elements are in continuity with an array of peripheral nerve plexuses which innervate a well-differentiated grid work of somatic muscle as well as a complexity of myofibres associated with organs of attachment, feeding, and reproduction. Electrophysiological studies of flatworm muscles have exposed a diversity of voltage-activated ion channels that influence muscle contractile events. Neuronal cell types are mainly multi- and bi-polar and highly secretory in nature, producing a heterogeneity of vesicular inclusions whose contents have been identified cytochemically to include all three major types of cholinergic, aminergic, and peptidergic messenger molecules. A landmark discovery in flatworm neurobiology was the biochemical isolation and amino acid sequencing of two groups of native neuropeptides: neuropeptide F and FMRFamide-related peptides (FaRPs). Both families of neuropeptide are abundant and broadly distributed in platyhelminths, occurring in neuronal vesicles in representatives of all major flatworm taxa. Dual localization studies have revealed that peptidergic and cholinergic substances occupy neuronal sets separate from those of serotoninergic components. The physiological actions of neuronal messengers in flatworms are beginning to be established, and where examined, FaRPs and 5-HT are myoexcitatory, while cholinomimetic substances are generally inhibitory. There is immunocytochemical evidence that FaRPs and 5-HT have a regulatory role in the mechanism of egg assembly. Use of muscle strips and (or) muscle fibres from free-living and parasitic flatworms has provided baseline information to indicate that muscle responses to FaRPs are mediated by a G-protein-coupled receptor, and that the signal transduction pathway for contraction involves the second messengers cAMP and protein kinase C.

The impact and recovery of asteroid 2008 TC3

In the absence of a firm link between individual meteorites and their asteroidal parent bodies, asteroids are typically characterized only by their light reflection properties, and grouped accordingly into classes. On 6 October 2008, a small asteroid was discovered with a flat reflectance spectrum in the 554-995nm wavelength range, and designated 2008 TC3 (refs 4-6). It subsequently hit the Earth. Because it exploded at 37km altitude, no macroscopic fragments were expected to survive. Here we report that a dedicated search along the approach trajectory recovered 47 meteorites, fragments of a single body named Almahata Sitta, with a total mass of 3.95kg. Analysis of one of these meteorites shows it to be an achondrite, a polymict ureilite, anomalous in its class: ultra-fine-grained and porous, with large carbonaceous grains. The combined asteroid and meteorite reflectance spectra identify the asteroid as F class, now firmly linked to dark carbon-rich anomalous ureilites, a material so fragile it was not previously represented in meteorite collections.

Dales, long lands, and the medieval division of land in eastern England

The long, parallel fields of the marshlands between the Fens and the Humber estuary in eastern England, which are recorded on nineteenth-century maps, were the result of the division of the wetlands that occurred particularly during the twelfth and early thirteenth centuries. Areas of common fen pasture were partitioned between tenants to provide land for grazing and arable. Similar division also took place on the coastal strip and in the peat fen for land for salt-making and cutting fuel. These long strips, known as dales, are compared to similar areas in open fields in parts of Yorkshire and Northamptonshire, which have been discussed elsewhere. It is argued that the field shape is the result of a type of division in eastern England in which considerable emphasis was placed on case of partitioning land equitably.

Sensor technologies based on a cellulose supported platform

A simple approach to sensor development based on encapsulating a probe molecule in a cellulose support followed by regeneration from an ionic liquid solution is demonstrated here by the codissolution of cellulose and 1-(2-pyridylazo)-2-naphthol in 1-butyl-3-methylimidazolium chloride followed by regeneration with water to form strips which exhibit a proportionate (1 : 1) response to Hg(II) in aqueous solution.

Specialised pacemaking cells in the rabbit urethra.

1. Collagenase dispersal of strips of rabbit urethra yielded, in addition to normal spindle-shaped smooth muscle cells, a small proportion of branched cells which resembled the interstitial cells of Cajal dispersed from canine colon. These were clearly distinguishable from smooth muscle in their appearance under the phase-contrast microscope, their immunohistochemistry and their ultrastructure. They had abundant vimentin filaments but no myosin, a discontinuous basal lamina, sparse rough endoplasmic reticulum, many mitochondria and a well-developed smooth endoplasmic reticulum. 2. Interstitial cells were non-contractile but exhibited regular spontaneous depolarisations in current clamp. These could be increased in frequency by noradrenaline and blocked by perfusion with calcium-free solution. In voltage clamp they showed abundant calcium-activated chloride current and spontaneous transient inward currents which could be blocked by chloride channel blockers. 3. The majority of smooth muscle cells were vigorously contractile when stimulated but did not show spontaneous electrical activity in current clamp. In voltage clamp, smooth muscle cells showed very little calcium-activated chloride current. 4. We conclude that there are specialised pacemaking cells in the rabbit urethra that may be responsible for initiating the slow waves recorded from smooth muscle cells in the intact syncitium.

Effects of Geometrical Discontinuities on Distributed Passive Intermodulation in Printed Lines

This paper presents the results of experimental study of passive intermodulation (PIM) generation in microstrip lines with U-shaped and meandered strips, impedance tapers, and strips with the profiled edges. It is shown that the geometrical discontinuities in printed circuits may have a noticeable impact on distributed PIM generation even when their effect is indiscernible in the linear regime measurements. A consistent interpretation of the observed phenomena has been proposed on the basis of the phase synchronism in the four-wave mixing process. The results of this study reveal new features of PIM production important for the design and characterization of low-PIM microstrip circuits. © 2010 IEEE.

Perturbed frequency-selective surfaces fabricated on large thin polymer membranes for multiband infrared applications

The design, fabrication, and characterization of single-screen perturbed frequency-selective surfaces (FSS) at infrared frequencies for single and multiband applications are reported. Single-band FSS based on parallel strips have been perturbed by decreasing the length of every second strip within the array in order to achieve dual band-stop responses. The same principle has been extended to design FSS exhibiting tri- and quadreflection bands. In addition, strip FSSs have been perturbed by replacing every second strip for a metallic ring, resulting in dual-band filters with different polarization responses of the bands. These designs have been fabricated on large thin polyimide membranes using sacrificial silicon wafers. An oxide interlayer between the sacrificial silicon wafer and the polyimide membrane is employed to stop the silicon etching and is wet etched subsequently by a solution of ammonium fluoride and acetic acid that does not attack either the polyimide membrane or the aluminium FSS elements. Fourier transform infrared spectroscopy measurements are presented to validate the predicted responses of the fabricated prototypes.

Comparison of mechanical and electrical activity and interstitial cells of Cajal in urinary bladders from wild-type and W/W-v mice

Background and purpose: W/Wv and wild-type murine bladders were studied to determine whether the W/Wv phenotype, which causes a reduction in, but not abolition of, tyrosine kinase activity, is a useful tool to study the function of bladder interstitial cells of Cajal (ICC).

Experimental approach: Immunohistochemistry, tension recordings and microelectrode recordings of membrane potential were performed on wild-type and mutant bladders.

Key results: Wild-type and W/Wv detrusors contained c-Kit- and vimentin-immunopositive cells in comparable quantities, distribution and morphology. Electrical field stimulation evoked tetrodotoxin-sensitive contractions in wild-type and W/Wv detrusor strips. Atropine reduced wild-type responses by 50% whereas a 25% reduction occurred in W/Wv strips. The atropine-insensitive component was blocked by pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid in both tissue types. Wild-type and W/Wv detrusors had similar resting membrane potentials of -48 mV. Spontaneous electrical activity in both tissue types comprised action potentials and unitary potentials. Action potentials were nifedipine-sensitive whereas unitary potentials were not. Excitatory junction potentials were evoked by single pulses in both tissues. These were reduced by atropine in wild-type tissues but not in W/Wv preparations. The atropine-insensitive component was abolished by pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid in both preparations.

Conclusions and implications: Bladders from W/Wv mice contain c-Kit- and vimentin-immunopositive ICC. There are similarities in the electrical and contractile properties of W/Wv and wild-type detrusors. However, significant differences were found in the pharmacology of the responses to neurogenic stimulation with an apparent up-regulation of the purinergic component. These findings indicate that the W/Wv strain may not be the best model to study ICC function in the bladder.

Passive Intermodulation in Printed Lines: Effects of Trace Dimensions and Substrate

A comprehensive experimental study was performed to identify and discriminate mechanisms contributing to passive intermodulation (PIM) in microstrip transmission lines. The effects of strip length and width, and substrate materials on PIM performance of printed lines were investigated in the GSM900, DCS1800 and UMTS frequency bands. The major features of the experiment design, sample preparation and test setup are discussed in detail. The measurement results have demonstrated that the PIM level cumulatively grows on the longer microstrip lines and decreases on wider strips and, thus, indicated that the distributed resistive nonlinearity of the printed traces represents the dominant mechanism of intermodulation generation in the printed lines on PTFE-based substrates. © 2009 The Institution of Engineering and Technology.

Preconditioning protects the guinea-pig urinary bladder against ischaemic conditions in vitro

Aims: To investigate the ability of ischaemic preconditioning (IPC) to protect guinea-pig detrusor from damage caused by a subsequent more prolonged exposure to ischaemic conditions.

Materials and Methods: Smooth muscle strips were mounted for tension recording in small organ baths continuously superfused with Krebs' solution at 37 degrees C. Ischaemia was mimicked by removing oxygen and glucose from the superfusing solution. Contractile responses to electrical field stimulation (EFS) and carbachol were monitored. Three regimes of preconditioning were examined: 15, 10, and 5 min of ischaemic conditions followed by 15, 10, and 5 min of normal conditions, respectively.

Results: Without preconditioning, nerve-mediated responses were significantly and proportionally reduced by periods of ischaemic conditions lasting for 45, 60, and 90 min, but recovered fully after exposure to ischaemic conditions for 30 min. The recovery of the responses to EFS was significantly improved in preconditioned strips when the period of ischaemic conditions was 45 or 60 min. However, no significant differences were seen with preconditioning when the period of ischaemic conditions was 90 min. The recovery of responses to carbachol was much greater than for the responses to EFS, and no significant differences were found between control and preconditioned strips.

Conclusions: It is suggested that in vivo short periods of transient ischaemia may be able to protect the guinea-pig bladder from the impairment associated with longer periods of ischaemia and reperfusion, which might happen in obstructed micturition. Our results also indicate that the phenomenon affects mainly the intrinsic nerves, which are more susceptible to ischaemic damage than the smooth muscle.