Free isometric actions on the affine space Qn

AbstractWe will show that for every integer n ≧ 3 there exists a free non-abelian group of linear isometries of the vector space Qn such that any subgroup fixing any point v ≠ 0 of Qn is cyclic. Recall that two elements of F2 commute if and only if they belong to a cyclic subgroup of F2

Experimentelle Studien uber die akute Pankreasnekrose. I. Mitteilnug Ueber den Reststickstoff

Bei Hunden hat der Verf. durch Eingiessung von Galle sowie Olivenöl in den Pankreasgang experimentell eine akute Pankreasnekrose hervorgerufen und den Wert des Rest-N bestimmt. 1) Eine erhebliche Erhöhung erfährt der Rest-N im Blut, der bei moribunden Versuchstieren sogar bis zum ca. 3 fachen seiner normalen Menge gesteigert ist. 2) Auch der Rest-N der Organgewebe wird an Menge beträchtlich gesteigert, was in der Leber und den Nieren mit seiner ungefähr 2 fachen Vermehrung als die Norm besonders stark zum Ausdruck kommt. 3) Beim-erkrankten Pankreas erléidet der Rest-N hingegen eine Verringerung und die um so stärker, je erheblicher die pathologischen Veränderungen stattfinden. 4) Ileus und Perforationsperitonitis, welche beide in der vorliegenden Untersuchung ale Kontrolle dienten, weisen ebenfalls eine auffällige Steigerung der Rest-N-Menge. Vom Wert des Rest-N im Blut betrachtet nimmt die akute Pankreasnekrose eine mittlere Stelle zwischen dem Ileus und der Perforationsperitonitis ein; wenn es sich aber um den Rest-N-Wert der Organgewebe handelt, so steht die akute Pankreasnekrose hinter den beiden anderen zurück. 5) Es liegt die Annahme nahe, dass man die Ursache der Vermehrung des Rest-N bei akuter Pankreasnekrose nicht in der Autodigestion durch das Trypsin, sondern in demselben Verhältnis wie bei akuter Perfosationsperitonitis und dem Ileus zu suchen hat

Source inversion of W phase: speeding up seismic tsunami warning

W phase is a long period phase arriving before S wave. It can be interpreted as superposition of the fundamental, first, second and third overtones of spheroidal modes or Rayleigh waves and has a group velocity from 4.5 to 9 km s^−1 over a period range of 100–1000 s. The amplitude of long period waves better represents the tsunami potential of an earthquake. Because of the fast group velocity of W phase, most of W phase energy is contained within a short time window after the arrival of the P wave. At a distance of 50°, W phase energy is contained within 23 min after the origin time which is the distinct advantage of using W phase for rapid tsunami warning purposes. We use a time domain deconvolution method to extract W phases from the broad-band records of global seismic networks. The bandwidth of W phase is approximately from 0.001 to 0.01 Hz, and we bandpass filter the data from 0.001 to 0.005 Hz in most cases. Having extracted W phase from the vertical component records, we perform a linear inversion using a point source to determine Mw and the source mechanism for several large earthquakes including the 2004 Sumatra–Andaman earthquake, the 2005 Nias earthquake, the 2006 Kuril Is. earthquake and the 2007 Sumatra earthquake. W phase inversion yields reliable solutions and holds promise of the use of W phase for rapid assessment of tsunami potential

Explicit asymptotic modelling of transient Love waves propagated along a thin coating

The official published version can be obtained from the link below.An explicit asymptotic model for transient Love waves is derived from the exact equations of anti-plane elasticity. The perturbation procedure relies upon the slow decay of low-frequency Love waves to approximate the displacement field in the substrate by a power series in the depth coordinate. When appropriate decay conditions are imposed on the series, one obtains a model equation governing the displacement at the interface between the coating and the substrate. Unusually, the model equation contains a term with a pseudo-differential operator. This result is confirmed and interpreted by analysing the exact solution obtained by integral transforms. The performance of the derived model is illustrated by numerical examples.This work is sponsored by the grant from Higher Education of Pakistan and by the Brunel University’s “BRIEF” research award

Analysis of Laser Ultrasonic Measurements of Surface Waves on Elastic Spheres

In conventional ultrasonic nondestructive evaluation studies, piezoelectric transducers are used to generate sound waves in solids via a couplant that transmits the mechanical motions. In recent years, a different method of generating sound in solids, pulsed laser heating, was introduced by White [1,2]. This method is noncontacting, requires no coupling medium, and operates directly on the surface of the specimen. Noncontacting ultrasonic detection using laser interferometers of several types has also been developed [3]. Laser techniques can achieve essentially point source and point detection of ultrasonic motion through focusing. Laser ultrasonics can, therefore, be used on objects with complex shapes, e.g. curved surfaces, and are applicable to material shapes more commonly found in industry. Often the goal of ultrasonic measurements is to determine material properties such as Lame’s elastic constants. The conventional approach measures longitudinal and shear wave speeds between two parallel flat surfaces. The work reported here demonstrates the versatility of laser ultrasonics by directly measuring the surface motion of a solid sphere generated by ablation from a pulsed laser beam. The results compare well with elastodynamic theoretical calculations, where the ablation source is approximated as a normal impulse on the surface. This work suggests that an algorithm could be formulated to measure elastic properties of targets with curved surfaces

DESIGN AND DEVELOPMENT OF THE AFRICAN PLASMODIUM FALCIPARUM DATABASE – (afriPFdb)

The detailed investigation of mantle structure from the dispersion of surface waves is a young but vigorous field of study. Observations have been accumulating rapidly in the past few years because of the wide-spread installation of long-period instruments. Modern methods of data analysis used in conjunction with high-speed digital computers have made it possible to determine dispersion with greater precision and over a broader spectrum than has previously been possible. Observations now extend out to the fundamental periods of free oscillations of the whole earth. Interpretation has lagged behind observation because of the difficulties inherent in the problem of dispersion over realistic models of a spherical earth. This problem is now well in hand and dispersion appropriate to the standard earth models suggested by earlier body waves studies has been calculated. Even with digital computers, however, the computations are so formidable that until recently only the most tentative efforts have been made to modify the standard earth structures to give a more satisfactory fit to the data. A review as recent as the one by Bolt in the preceding volume of this series was, of necessity, limited to a discussion of the various standard earth models with no attempt made to use the full power of surface waves as an independent technique. Recent developments have made detailed surface wave interpretations possible and new information, rather than generalized verification of old information, should be rapidly forthcoming. Project Mohole and the International Upper Mantle Project have focused the attention of many earth scientists on the upper mantle. Because of this renewed emphasis present information and speculation on the properties of the mantle based on a variety of sources is summarized and re-examined in some detail. This provides the guide-lines for potentially fruitful further research and points out the nature of some of the discrepancies and limitations in our present knowledge that may be resolved by the surface wave method