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The linear polarization degree of the cosmological background has been investigated at angular scales ranging between 0.5/sup 0/ and 40/sup 0/ by means of a balloon-borne far-infrared polarimeter. An upper limit has been found of 8 x 10/sup -/4 at 40/sup 0/ (at one standard deviation). Some cosmological implications are discussed.

For Assess II, the Spacelab mission simulation conducted in mid-1977, four payload specialists aboard a Convair 990 research aircraft performed six American and six European experiments during nine research flights each of six hours duration in order to evaluate the compatibility of training and experimental design. Mission organization and some initial data from the European experiments are reported. The experiments, conducted over the western U.S., involved infrared astronomy, solar brightness temperature, lidar, airglow TV, and a medical experiment for which physiological parameters were monitored. Conclusions concerning general principles of experiment design are discussed.

We review the measurements of the cosmic background anisotropies at all angular scales. Special attention is devoted to experimental problems and questions concerning the data analysis.

We investigate the rotation of the polarization planes for radiation freely traveling in homogeneous anisotropic spaces (Brans effect). Solving the parallel-transport equations in Bianchi type-I and type-V spaces, we find that the rotation angle is at most about 1 rad. The scrambling of the polarization states due to the Brans effect and the finite thickness of the last-scattering surface is negligible in any realistic model, so that any primeval polarization can survive up to the present epoch.

Noise measurements in the frequency regions 5-200 HZ and 5.2 x 10/sup -4/ -8.3 x 10/sup -3/ Hz have been performed in the wavelength region between 300 and 3000 mu m from the high altitude observatory of Tests Grigia, Italy (3.500 m). In the high frequency region a specially designed Ge bolometer operating in background-limited-infrared-photoconductor conditions matched to a 1.5-m telescope has been used, while at low frequency a radiometer designed for atmospheric transmittance measurements was employed. In both regions no excess noise with respect to the photon noise relative to 300-K blackbody has been detected.

The possibility of detecting diffuse sky radiation in the (250÷3000) μm range is discussed on the basis of recent measurements performed at the mountain observatory of Testa Grigia (3500 m a.s.l.) on the atmospheric emission and on the atmospheric noise. It is shown how, in many cases, the limits assigned by the residual atmospheric emission are well below the sensitivity of the available infra-red detectors; as a consequence some new experiments of background astronomy are suggested.

Observations carried out from an Alpine location (3500 m) using a Dicke- type radiometer with a broad-band germanium bolometer have proved that the cosmic background radiation in the 900-1400 micron band can be measured from mountain altitudes with a precision comparable with that obtained in the 3.3-mm band. The inaccuracy in the measurements is attributed to calibration rather than to the atmospheric disturbances. The upper limit of 2.7 degreeK observed is more stringent than that of previously reported balloon-borne and rocket-borne observations in the same band. (AIP)

The cosmic-background anisotropy has been investigated at the angular scale of 25 minutes of arc by means of a special isotropometer at the alpine station of Testa Grigia (3500 m above sea level) through the atmospheric window 1.0-1.4 mm. We found an upper limit $\frac{\ensuremath{\Delta}T}{T}\ensuremath{\lesssim}1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ at two standard deviations. Some physical implications about the origin and the rotation of superclusters and about the secondary ionization of plasma are discussed.

We measured the anisotropy of the cosmic background radiation at the angular scale of 2/sup 0/ in the millimetric wavelength region, in the course of the NASA-ESA ASSESS II Mission. We set upper limits on the anisotropy in several sky regions, the most stringent one being ..delta..T/T

A study has been made of the optical properties of thirty compounds suitable for making far infrared filters of the Yoshinaga type. The transmission curve of each compound in the far infrared is given for various thicknesses of the sample. The transmittance in the near infrared is also given in order to allow an appropriate choice of the materials capable of cutting off the near infrared radiation.

The photocurrent pinch-off, observed in high resistivity thin CdS crystals subject to a high electric field (field effect), is strongly dependent on the atmosphere surrounding the crystal. The minimum pinch-off voltage has been measured in different atmospheres. This gives a method for the evaluation of several physical quantities relevant to the surface and bulk properties of CdS.

The investigation of hole mobilityμp in CdS has shown a number of apparently contradictory experimental results. In the present work we examine in some detail the kinetics of the photocurrent under field effect. One finds that the photocurrent pinch-off and the complete recovery give respectivelyμp=0 andμp ≠ 0. The contradiction can be overcome assuming a «surface hole mobility»μps=0 and 24 bulk hole mobility»μpb≠0. Based on this assumption, a simple mathematical model has been developed which appears to describe correctly the photocurrent kinetics under field effect. Furthermore, the results of various authors are well interpreted separating the observations into two groups according to whether the measurement ofμp is done moving the holes at the surface of CdS (μps=0) or through the bulk only (μpb≠0).

We report preliminary results relative to a balloon-borne search for the large-scale anisotropy carried out in 1980 by means of two far infrared photometers centered at 400 and 1100 microns. While these results are consistent with those obtained in an earlier flight, the second, shorter wavelength channel included in the 1980 work provides interesting insights into the influence of galactic dust on such far infrared observations.

We have evaluated the accuracy in maintaining the differential modulation parallel to the horizon, which is required to reduce the atmospheric background below the detector noise in an infrared telescope operating under optimized conditions.

Results concerning zodiacal dust emission are reported from an IR sky survey experiment performed during a balloon flight on July 30, 1984 which explored five wavelength bands centered at 11, 19, 50, 108, and 225 microns. The dust density n decreases at a rate slower than r exp -1.3 with increasing heliocentric distance. The trend of n depends critically on the radial variation of the temperature which, in turn, depends on the chemical composition of the grains. The spatial distribution of the dust is in good agreement with that previously inferred from IR measurements. A comparison between IR and optical observations points out the uncertainties affecting the estimates of the dust density obtained with both methods. The emission spectrum of the dust is used to discriminate among the different species of grains, showing that the observations can be accounted for by an appropriate mixture of graphite and silicates. 18 references.

We have measured the sky temperature trough the 7-10cm−1 atmospheric window from the Alpine station of Testa Grigia(3500m. a.s.l.). An upper limit of 2.7°K has been found.

Weber's theoretical calculations concerning photoconductivity of semiconductors in a transverse electric field are extended to two particular models for CdS single crystals. An agreement with experiment is found when photoexcitation is weak; the presence of surface states is pointed out.