A discontinuous Galerkin method for the wave equation

We present a new discontinuous Galerkin method for solving the second-order wave equation using the standard continuous finite element method in space and a discontinuous method in time directly applied to second-order ode systems. We prove several optimal a priori error estimates in space–time norms for this new method and show that it can be more efficient than existing methods. We also write the leading term of the local discretization error in terms of Lobatto polynomials in space and Jacobi polynomials in time which leads to superconvergence points on each space–time cell. We discuss how to apply our results to construct efficient and asymptotically exact a posteriori estimates for space–time discretization errors. Numerical results are in agreement with theory.     

A new climatology of aerosols in the middle and upper stratosphere by alternative analysis of GOMOS observations during 2002–2006

Recent works have shown how the study of stratospheric background aerosol (i.e. in periods uninfluenced by major volcanic eruption) seems more complex as it is now performed by more accurate means. We propose a re-analysis of Global Ozone Monitoring by Occultation of Stars (GOMOS) level 1b data for the period August 2002–July 2006, using the LPC2E processor algorithm, which was developed for the retrieval of aerosol extinction in the middle and upper stratosphere. The main differences with regard to the ‘official’ algorithm are the correction of chromatic scintillation, the spectral domain (which has been restricted to the 400–700 nm region), the use of a Differential Optical Absorption Spectroscopy (DOAS) method for species retrieval, and the use of a fourth-order polynomial to reproduce the wavelength dependence of extinction. Since GOMOS observations are performed using stars of different magnitude and colour, discrepancy in signal-to-noise ratio between several profiles exists, and a data selection concerning standard deviation of aerosol extinction and other parameters becomes necessary. In the middle stratosphere, aerosol extinction profiles obtained with the LPC2E processor seem to be in better agreement with the SAGE III observations and sparse balloon-borne measurements than the ‘official products’. We present global coverage of the 500 nm extinction values from around 15–60 km, and the wavelength dependence in the 400–675 nm spectral range which gives information about the nature of the particles. The well-known layer of liquid aerosols can be observed in the lower stratosphere, where the value of extinction is greater for blue than for red wavelengths, as is typical for small droplets. In the middle stratosphere, relatively high extinction values are found, probably due to the presence of solid particles above 30 km at all latitudes. The presence of soot and interplanetary material in the middle atmosphere is discussed, as well as seasonal patterns common to the several years of analysis, such as the stratospheric cleansing of aerosols above 30 km during polar winters.     

Effect of wood powder on polymer foam nucleation

It is usually reported that wood particles in wood/polymer composite foams can act as nucleating sites. Since high wood contents are used, it is difficult to determine exactly the effect of wood particles. In this study, LDPE was chemically foamed in a twin‐screw extruder, and small amounts of wood (0–5 phr) were added to determine their effect. Particle size was investigated by using three mesh sizes: 45–61, 104–125, and 180–210 μm. As expected, wood particles acted as nucleating agents that substantially reduced cell size and increased cell density. J. VINYL. ADDIT. TECHNOL., 12:19–24, 2006. © 2006 Society of Plastics Engineers     

Photonics based on carbon nanotubes

Among direct-bandgap semiconducting nanomaterials, single-walled carbon nanotubes (SWCNT) exhibit strong quasi-one-dimensional excitonic optical properties, which confer them a great potential for their integration in future photonics devices as an alternative solution to conventional inorganic semiconductors. In this paper, we will highlight SWCNT optical properties for passive as well as active applications in future optical networking. For passive applications, we directly compare the efficiency and power consumption of saturable absorbers (SAs) based on SWCNT with SA based on conventional multiple quantum wells. For active applications, exceptional photoluminescence properties of SWCNT, such as excellent light-emission stabilities with temperature and excitation power, hold these nanometer-scale materials as prime candidates for future active photonics devices with superior performances.     

Comparison of different oxidation techniques on single-crystal and nanocrystalline diamond surfaces

Various oxidation techniques (plasma-beam, sulfo-chromic acid, UV-ozone, heating in air) were applied to single-crystalline (111) and (100) diamond surfaces as well as nanocrystalline diamond (NCD) films and analyzed by X-ray photoelectron spectroscopy (XPS) with respect to oxygen content and type of carbon–oxygen groups formed upon oxidation. Due to their increased surface, NCD films show a significantly higher oxygen uptake as compared to their single-crystal counterparts. No marked differences were observed between the different oxidation techniques. For all oxidation techniques used, several carbon–oxygen groups are simultaneously present on the surface. The relative fraction of singly-oxidized carbon atoms (attributed to isolated ether or epoxy-like groups) generally decreases slightly with increasing oxygen content, but always remains the dominating species.     

Degenerative complications of diabetes. Value of systematic Doppler echocardiography

Autonomic neuropathy in diabetes mellitus can cause alterations of the motor function of various segments of the gastroenteric apparatus. With hepatocholangio-cholecystiscintigraphy-HIDA we have studied the motility of the biliary system in patients with diabetes mellitus type II. The research has been carried out in 29 patients with diabetic autonomic neuropathy; 12 healthy volunteers have been studied to compare the results obtained. The results showed a delay in the appearance of radionucleotide in the small intestine of diabetic subjects compared to controls with statistical significance. Moreover the diabetic subjects with a serious neuropathic injury showed increased intestinal transit time. These results match those obtained by other authors that have studied the cholecystic emptying in diabetic subjects with other methods. Consequently the biliary system is also affected by the diabetic autonomic neuropathy that can be in its turn the cause of other pathologies such as biliary lithiasis.