Stellar infrared astronomy with EDISON

In this review the IR emission from circumstellar material is discussed, both of ionized gas and dust grains, and the astrophysical information that can be extracted from such observations. Some emphasis is placed on the possibilities of stellar IR astronomy using a large space-borne telescope, especially with respect to the much better spatial and spectral resolution of such a telescope compared to the current generation of ground-based and space IR telescopes.     

Circumstellar chemistry from microwave and mm-wave spectroscopy.

Stars in their late stages of evolution often shed matter in the form of a cool wind which is molecular in composition. These winds are a major source of replenishment of the interstellar gas and dust, so they furnish a large part of the raw materials for new generations of stars and planets. The chemistry of the circumstellar envelope depends strongly on the photospheric abundances of the elements, especially C and O. If C/O > 1, a rich organic chemistry is observable in the microwave and mm-wavelength emission lines of the reactions products. This paper reviews the observational evidence for the presence of organic molecules and their formation pathways in circumstellar envelopes, with special emphasis on rotational spectra at microwave and millimeter wavelengths.     

MTI data clustering and formation recognition

Image exploitation technology approaches have generally focused on the detection and spatial analysis of stationary groups of objects on the ground using various sensors. While spatial arrangement is clearly necessary in analyzing military formations, it is usually not sufficient. Typically the arrangement must be examined within some context in order to interpret a pattern of deployment. For moving objects the spatial arrangement of the group relative to the direction of motion is key to recognizing the formation. By examining ground moving target indicator (MTI) radar data over time, motion can be inferred and used to establish a context for interpreting the spatial arrangement of the data. New techniques that exploit the multitemporal nature of MTI data are described. The first is a space-time clustering technique that locates compact groups of objects that persist in time. The technique Is an application of Marr and Hildreth's edge detection methodology to the dual problem of region segmentation, or more accurately, volumetric segmentation of space-time. The second technique is based on the use of the Hough transform for recognizing moving formations such as columns, wedges, and lines abreast by analyzing the shape of clustered MTI detections (specifically the orientation of linear arrangements within the group) with respect to their direction of motion. Preliminary results from simulated MTI data sets are presented     

Lower and upper limits to comet p/halley solid material loss rate

A radiative hydrodynamic model of comet P/Halley is used to investigate quantitatively the constraints imposed onto the Comet loss rate in solids by both the in-situ data and the remote sensing data. In particular, for the first time, the in-situ data are used to fit composite spectra extending from near-IR wavelengths to the microwave region. Also, for the first time the uncertainty affecting the ejection velocity of large grains is taken into account. The results suggest that only future rendez-vous studies of the grain density in the vicinity of a comet would be able to provide definitely reliable values of the comet loss rate.     

EUV emission from normal galaxies

Using data from the Wide Field Camera EUV all-sky survey, we have established upper limits to the EUV flux from a sample of 30 bright, nearby, non-active spiral galaxies. These galaxies were chosen to be those most likely to be detected in the EUV on the basis of (i) low interstellar absorption within our own galaxy, (ii) brightness in other wavebands, (iii) high star formation activity, and (iv) proximity. The derived EUV upper limits are restrictive, and establish for the first time that the EUV flux escaping from galaxies does not constitute a major component of their bolometric luminosity, and in particular that it cannot be the sink for the energy injected into the interstellar medium by supernova explosions, as had been suggested following the failure to detect this power in the X-ray band.     

The INFRARED SPACE OBSERVATORY (ISO)

The INFRARED SPACE OBSERVATORY (ISO), a project of the European Space Agency (ESA), will make various astronomical observations in the wavelength range of 2 to 200 μm. Two-thirds of its observing time will be available to guest observers via the traditional route of proposal submission. ISO will be launched in 1995 by an Ariane 4 from Kourou (Guyana) and be brought into a very elongated orbit with a 24hr period of which 16 hr can be used for astronomical observations. The payload module is essentially a large cryostat with a tank that will be filled with over 2000 litres of superfluid helium to keep the instruments cold (2 to 4 K) during an expected lifetime of 18 months. Inside the dewar, there is a Ritchey-Chretien telescope with a primary mirror of diameter 60cm. Four instruments, each provided by a different PI consortium, share the ISO focal plane. These instruments are : a photometer, a camera and two spectrometers — one for the wavelength range 2–45 μm and the other for 45–180 μm.     

Reconfigurable NDI controller using inertial sensor failuredetection & isolation

A modified derivation of nonlinear dynamic inversion provides the theoretical underpinnings for a reconfigurable control law for aircraft that have suffered combinations of actuator failures, missing effector surfaces, and aerodynamic changes. The approach makes use of acceleration feedback to extract information pertaining to any aerodynamic change and thus does not require a complete aerodynamic model of the aircraft. The control law does require feedback of effector positions to accommodate actuator dynamics. Both accelerometer and rate gyro failure detection and isolation (FDI) systems are implemented, allowing up to three independent failures for each FDI system as long as they are in different axes. Nonlinear simulation results show that the FDI systems improve the robustness to accelerometer/rate gyro uncertainties. An advanced tailless aircraft model is used to demonstrate the concepts. The simulation includes accelerometer and rate gyro noise and bias, failures due to accelerometers, rate gyros, and actuators, and modeled missing surfaces that cause airplane aerodynamic changes     

Extracting multiple frequencies from phase-only data

The problem of extracting multiple frequencies from phase-only data is addressed. Multiple frequency estimation is accomplished by reconstructing the Fourier transform of the complex-valued time signal and then finding peaks in the frequency domain. We present a set of conditions under which a discrete-time complex sequence can be completely specified by its phase-only information. Two candidate multiple frequency estimation schemes are introduced, one based on a closed-form least-squares inverse, the other an iterative reconstruction algorithm. The uniqueness of the closed-form solution and the convergence of the iterative scheme have been proven under certain conditions. Several examples are given, including the case where the phase is quantized as would happen in an analog-to-digital (A/D) converter. Extensions to the multidimensional case, and to the case of real-part only reconstruction are straightforward.     

Electric currents induced inside biological cells by geomagnetic and atmospheric phenomena.

An increasing number of studies have appeared in the last ten years indicating that some pathologies may correlate with geomagnetic activity and cosmic rays. However a physical mechanism binding both phenomena has not been proposed. In the present work we obtain the amplitude of the magnetic fields at different frequencies, that may induce inside biological cells currents of the same magnitude of the currents generated by the cells themselves. We compare these values with the wave amplitudes produced in geomagnetic and atmospheric phenomena, and found that micropulsations, whistlers and lightning are capable of produce the same or larger values.