Time-dependent cosmic ray modulation

Time-dependent cosmic ray modulation is calculated over multiple solar cycles using our well established two-dimensional time-dependent modulation model. Results are compared to Voyager 1, Ulysses and IMP cosmic ray observations to establish compatibility. A time-dependence in the diffusion and drift coefficients, implicitly contained in recent expressions derived by , ,  and , is incorporated into the cosmic ray modulation model. This results in calculations which are compatible with spacecraft observations on a global scale over consecutive solar cycles. This approach compares well to the successful compound approach of Ferreira and Potgieter (2004). For both these approaches the magnetic field magnitude, variance of the field and current sheet tilt angle values observed at Earth are transported time-dependently into the outer heliosphere. However, when results are compared to observations for extreme solar maximum, the computed step-like modulation is not as pronounced as observed. This indicates that some additional merging of these structures into more pronounced modulation barriers along the way is needed.     

The comprehensive aerospace index (CASI): Tracking the economic performance of the aerospace industry

In this paper, we described the Comprehensive AeroSpace Index (CASI), a financial index aimed at representing the economic performance of the aerospace industry. CASI is build upon a data set of approximately 20 years of daily close prices set, from January 1987 to June 2007, from a comprehensive sample of leading aerospace-related companies with stocks negotiated on the New York Exchange (NYSE) and on the over-the-counter (OTC) markets. We also introduced the sub-indices CASI-AERO, for aeronautical segment, and CASI-SAT, for satellite segment, and considered the relation between them. These three indices are compared to others aerospace indices and to more traditional general financial indices like DJIA, S&P500 and Nasdaq. Our results have shown that the CASI is an index that describes very well the aerospace sector behavior, since it is able to reflect the aeronautical segment comportment as well as the satellite one. Therefore, in this sense, it can be considered as a representative index of the aerospace sector. Moreover, the creation of two sub-indices, the CASI-AERO and the CASI-SAT, allows to elucidate capital movements within the aerospace sector, particularly those of speculative nature, like the dot.com bubble and crash of 1998–2001.     

Neutral buoyancy and sleep-deprived serum factors alter expression of cytokines regulating osteogenesis

We examined expression of genes associated with cytokine production, and genes implicated in regulating bone metabolism, in bone stromal and osteoblast cells incubated under standard ground conditions and under conditions of neutral buoyancy, and in the presence/absence of serum from normal or sleep-deprived mice. We observed a clear interaction between these two conditions (exposure to neutral buoyancy and serum stimulation) in promoting enhanced osteoclastogenesis. Both conditions independently altered expression of a number of cytokines implicated in the regulation of bone metabolism. However, using stromal cells from IL-1 and TNFx cytokine(r) KO mice, we concluded that the increased bone loss under microgravity conditions was not primarily cytokine mediated.     

Sound insulation performance of plates with interconnected distributed piezoelectric patches

This paper deals with the sound insulation performance of a thin plate with intercon-nected distributed piezoelectric patches. Piezoelectric patches are periodically bonded on the sur-faces of the plate in a collocated fashion, and are interconnected via an inductive circuit network. This piezoelectric system is termed as piezo-electromechanical (PEM) plate in the paper. Homogenization methods are involved under a sub-wavelength assumption to analytically develop the dynamical equations for the PEM plate. The dispersion relationships and energy densities of the wave modes propagating in the PEM plate are studied;the sub-wavelength assumption is verified for the simulations in this paper. The coincidence frequency of the PEM plate is researched, and results show that the coincidence frequency of the PEM plate will disappear at certain circum-stances;mathematical and physical explanations are made for this phenomenon. The disappearance of the coincidence frequency is used to optimize the value of inductance, for the purpose of improv-ing the sound transmission loss of the PEM plate.     

Comparison of Antarctic riometer radio wave absorption and THEMIS mission energetic electron fluxes

Simultaneous observations of in situ plasma properties in the tail of the Earth’s magnetosphere and of ground based instruments, lying on the same geomagnetic field lines, have recently proved to yield significant new results. In most cases magnetosphere ionosphere interactions during the night-time northern hemisphere conditions are studied. Here, observations of energetic electrons in the tail of the Earth’s magnetosphere made by the THEMIS mission satellites are compared with auroral radio wave absorption determined by riometers in the Antarctic for sunlit conditions. Days for which satellites and riometers are connected by the same geomagnetic field line are selected using a geomagnetic field model. The six days analysed show clear associations between fluxes and absorptions in some cases. However, these do not necessarily correspond to conjugacy intervals. Hours of positive associations are 1.65 times those for negative associations, all hours and days considered (1.42–3.6 on five days and 0.58 on the other day). These computations are assumed appropriate since the footprints of the satellites used approximately follow corrected geomagnetic parallels for all six days studied. The use of a finer parameterization of geomagnetic models to determine conjugacy may be needed.     

The challenges facing Galileo

Study of the nascent European satellite navigation system, Galileo, is well underway and a decision by the EU Council of Ministers on whether to proceed with the test satellites is expected by late 2000. Although some believe that current systems, most notably the US GPS, make it unnecessary, the history of satellite navigation so far provides some justification for a European system. Nevertheless, Galileo faces a number of challenges if it is to succeed. These include not only the technical specifications for a new generation of navigation satellites and the ground structure, but also a coherent business plan for funding the launch, operation and maintenance of the system. Lastly, one has to consider the compatibility and interoperability of Galileo with the existing GPS and Glonass satellite systems, as well as the likely competition from GSM and (third generation) UMTS mobile services.     

Two-component Bénard convection: Interfacial deformation,oscillatory instabilities and the onset of turbulence

Instabilities and convection in binary fluid mixtures (liquids with impurities, binary gas mixtures, etc.) have been the subject of intense research over the past decade. The major finding has been that mere ppm impurity concentration can play a drastic role in the stability of fluid layers subjected to thermal gradients. For layers open to ambient air the impurity cooperates or competes according to the sign of its migration in the thermal fields with the interfacial deformation thus leading to convective flows. For a layer enclosed between copper plates, say, the impurity can interplay with the slightest buoyancy or buoyancy variations in the environment thus amplifying this force and bringing instability under circumstances where with pure fluids no instability is expected. Recent predictions reported here refer to oscillatory instabilities with or without interfacial deformation and the onset of turbulence in the form of chaotic flows which correspond to irregular patterns with decaying correlations and broadband noise in their power spectra.     

3D Imaging of the OH mesospheric emissive layer

A new and original stereo imaging method is introduced to measure the altitude of the OH nightglow layer and provide a 3D perspective map of the altitude of the layer centroid. Near-IR photographs of the OH layer are taken at two sites separated by a 645 km distance. Each photograph is processed in order to provide a satellite view of the layer. When superposed, the two views present a common diamond-shaped area. Pairs of matched points that correspond to a physical emissive point in the common area are identified in calculating a normalized cross-correlation coefficient (NCC). This method is suitable for obtaining 3D representations in the case of low-contrast objects. An observational campaign was conducted in July 2006 in Peru. The images were taken simultaneously at Cerro Cosmos (12°09′08.2″ S, 75°33′49.3″ W, altitude 4630 m) close to Huancayo and Cerro Verde Tellolo (16°33′17.6″ S, 71°39′59.4″ W, altitude 2272 m) close to Arequipa. 3D maps of the layer surface were retrieved and compared with pseudo-relief intensity maps of the same region. The mean altitude of the emission barycenter is located at 86.3 km on July 26. Comparable relief wavy features appear in the 3D and intensity maps. It is shown that the vertical amplitude of the wave system varies as exp (Δz/2H) within the altitude range Δz = 83.5–88.0 km, H being the scale height. The oscillatory kinetic energy at the altitude of the OH layer is comprised between 3 × 10⁻⁴ and 5.4 × 10⁻⁴ J/m³, which is 2–3 times smaller than the values derived from partial radio wave at 52°N latitude.