The causal differential scattering approach to calculating the effective properties of random composite materials with a particle size distribution

An implementation of the Causal Differential Method (CDM) for modelling the effective properties of a random two-phase composite material is presented. Such materials are commonly used as ultrasonic transducer matching layersor backing layers. The method is extended to incorporate a particle size distribution in the inclusion phase. Numerical issues regarding the implementation and convergence of the method are discussed. It is found that, for a given frequency of excitation, the calculated velocity for the composite has a distribution whose variance increases as the volume fraction of inclusions increases. The model predictions would suggest that to reliably and repeatedly manufacture these composites, with a desired mechanical impedance, a low volume fraction of inclusions should be used

Relativistic Iron lines at high redshifts

The shape and the intensity of the 6.4 keV iron line bring unique information on the geometrical and physical properties of the supermassive black hole and the surrounding accreting gas at the very center of Active Galactic Nuclei. While there are convincing evidences of a relativistically broadened iron line in a few nearby bright objects, their properties at larger distances are basically unknown. We have searched for the presence of iron line by fully exploiting Chandra observations in the deep fields. The line is clearly detected in the average spectra of about 250 sources stacked in several redshift bins over the range z=0.5-4.0. We discuss their average properties with particular enphasys on the presence and intensity of a broad component.Comment: 6 pages, 4 figures. To appear in the proceedings of "Relativistic Astrophysics and Cosmology - Einstein's Legacy" (Eds.: B. Aschenbach, V. Burwitz, G. Hasinger, and B. Leibundgut), 7 - 11 November 2005, Munich, German

Cortisol levels are positively associated with pup-feeding rates in male meerkats

In societies of cooperative vertebrates, individual differences in contributions to offspring care are commonly substantial. Recent attempts to explain the causes of this variation have focused on correlations between contributions to care and the protein hormone prolactin, or the steroid hormone testosterone. However, such studies have seldom considered the importance of other hormones or controlled for non-hormonal factors that are correlative with both individual hormone levels and contributions to care. Using multivariate statistics, we show that hormone levels explain significant variation in contributions to pup-feeding by male meerkats, even after controlling for non-hormonal effects. However, long-term contributions to pup provisioning were significantly and positively correlated with plasma levels of cortisol rather than prolactin, while plasma levels of testosterone were not related to individual patterns of pup-feeding. Furthermore, a playback experiment that used pup begging calls to increase the feeding rates of male helpers gave rise to parallel increases in plasma cortisol levels, whilst prolactin and testosterone levels remained unchanged. Our findings confirm that hormones can explain significant amounts of variation in contributions to offspring feeding, and that cortisol, not prolactin, is the hormone most strongly associated with pup-feeding in cooperative male meerkats

A mixed life-cycle stage bloom of Syracosphaera bannockii (Borsetti and Cati, 1976) Cros et al. 2000 (Bay of Biscay, April 2010)

High concentrations (464 cells mL-1) of Syracosphaera bannockii have been identified for the first time, in the Bay of Biscay during April 2010. These high concentrations combined with coccolithophore community dominance (~87%) indicated that a bloom of S. bannockii had formed. While the bloom consisted mostly of heterococcolith coccospheres, both holococcolith coccospheres and holococcolith-heterococcolith combination coccospheres were observed. This is only the second time that combination coccospheres of S. bannockii have been observed

High power magnetic stimulation of the peripheral nervous system and the upper urinary tract.

In theory many of the physiological effects of electrical stimulation should be repeatable with magnetic stimulation. The aim of this study was to investigate some of the potentially clinically relevant actions of high power magnetic stimulation on the mammalian peripheral nervous system. This investigation can be separated into 3 parts. Firstly, experiments examining the ability of 'wide pulse' electrical stimulation to produce complete reversible block of peripheral nerve were undertaken at both the compound and single unit level. The findings were used to estimate the magnitude of an impulse magnetic field required to produce 'magnetic nerve block'. Secondly, the design and construction of two prototype high power magnetic stimulators (HPMS) and their associated filed coils was carried out. Theoretical predictions and practical measurements of the output of each stimulator were undertaken. Thirdly physiological experiments with the HPMS's were performed, examining magnetic stimulation of unmyelinated nerve fibres in the upper renal tract. The aim of stimulating the kidney was to generate ureteric peristalsis, which may have a role in aiding stone excretion, especially post lithotripsy. For the electrical nerve block study the saphenous nerve in anaesthetized rats and rabbits was exposed. Either the whole nerve or fine filaments dissected from the cut proximal end of the nerve were studied. A-ap, A- 5 and C fibres were stimulated and blocked by wide electrical pulses with an exponential decay. The strength duration relationship of this response was studied and block was confirmed by failure of conduction of a proximally generated action potential to pass through the blocked region. Two HPMS's were designed and constructed in conjunction with Digitimer Ltd. and the department of Electrical and Electronic Engineering at Loughborough University. The first prototype was rated at 4.3 KJ and the second at 96KJ. Early on in structural testing it was found that conventional coil design was insufficient to allow repetitive shots, particularly with the 96KJ device. Redesign of the coil housing allowed multiple stimuli without failure. Finally physiological experiments with the prototype HPMS's demonstrated stimulation of C-fibres in the upper renal tract in a pig model. Magnetic stimulation of the kidney was able to generate ureteric peristalsis in the in-situ and exteriorized kidney preparations studied. Local anaesthetic applied topically to the renal pelvis and calyces blocked this response indicating that magnetic stimulation of ureteric peristalsis is a neurally mediated phenomenon. This thesis demonstrates that high power magnetic stimulation is technically feasible from both an engineering and physiological perspective. It can activate all classes of nerve fibre allowing the extracorporeal stimulation of internal organs