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The cosmic microwave background radiation provides unique constraints on cosmological models. In this Letter we present a summary of the spatial properties of the cosmic microwave background radiation based on the full 4 years of COBE DMR observations, as detailed in a set of companion Letters. The anisotropy is consistent with a scale-invariant power law model and Gaussian statistics. With full use of the multi-frequency 4-year DMR data, including our estimate of the effects of Galactic emission, we find a power-law spectral index of n = 1.2 ± 0.3 and a quadrupole normalization Q rms−P S = 15.3 +3.8 −2.8 µK. For n = 1 the best-fit normalization is Q rms−P S | n=1 = 18 ± 1.6 µK. These values are consistent with both our previous 1-year and 2-year results. The results include use of the ℓ = 2 quadrupole term; exclusion of this term gives consistent results, but with larger uncertainties. The 4-year sky maps, presented in this Letter, portray an accurate overall visual impression of the anisotropy since the signal-to-noise ratio is ∼ 2 per 10 • sky map patch. The improved signal-to-noise ratio of the 4-year maps also allows for improvements in Galactic modeling and limits on non-Gaussian statistics.Subject headings: cosmic microwave background -cosmology: observations 1 NASA/GSFC is responsible for the design, development, and operations of the COBE. Scientific guidance is provided by the COBE Science Working Group. GSFC is also responsible for the development of the analysis software and the delivery of the mission data sets.

We present a determination of the cosmic microwave background dipole amplitude and direction from the COBE Di erential Microwave Radiometers (DMR) rst year of data. Data from the six DMR channels are consistent with a Dopplershifted Planck function of dipole amplitude T = 3:365 0:027 mK toward direction (l II ; b II ) = (264:4 0:3 ; 48:4 0:5 ). The implied velocity of the Local Group with respect to the CMB rest frame isṽ LG = 627 22 km s 1 toward (l II ; b II ) = (276 3 ; 30 3 ). DMR has also mapped the dipole anisotropy resulting from the Earth's orbital motion about the Solar system barycenter, yielding a measurement of the monopole CMB temperature T 0 at 31.5, 53, and 90 GHz, T 0 = 2:75 0:05 K. Subject headings: cosmic microwave background | cosmology: observations 2

A laboratory investigation has been made of formation factor‐porosity relationships (formation factor being the ratio of the resistivity of a porous medium to the resistivity of the pore‐fluid), using natural and artificial sand samples whose grains varied widely in both size and shape. All samples obeyed Archie’s law, [Formula: see text] (where FF is the formation factor and n is the porosity) including mixtures of two differently shaped particle types. The exponent m was dependent on the shape of the particles, increasing as they became less spherical, while variations in size and spread of sizes appeared to have little effect. The results have been combined to produce an FF/n relationship, with an error “envelope”, which may be applicable to marine sediments in general, being in agreement with published data for marine clays. It is also suggested that the exponent m may be a better measure of the “tortuosity” of porous media than the formulas quoted in the literature.

The rst two years of COBE Di erential Microwave Radiometers (DMR) observations of the cosmic microwave background (CMB) anisotropy are analyzed and compared with our previously published rst year results. The results are consistent, but the addition of the second year of data increases the precision and accuracy of the detected CMB temperature uctuations. The two-year 53 GHz data are characterized by RMS temperature uctuations of ( T) rms (7 ) = 44 7 K and ( T) rms (10 ) = 30:5 2:7 K at 7 and 10 angular resolution respectively. The 53 90 GHz cross-correlation amplitude at zero lag is C(0) 1=2 = 36 5 K (68% CL) for the unsmoothed (7 resolution) DMR data.A likelihood analysis of the cross correlation function, including the quadrupole anisotropy, gives a most likely quadrupole-normalized amplitude, Q rms PS , of 12:4 +5:2 3:3 K (68% CL) and a spectral index n = 1:59 +0:49 0:55 (68% CL) for a power law model of initial density uctuations, P(k) / k n . With n xed to 1.0 the most likely amplitude is 17:4 1:5 K (68% CL). Excluding the quadrupole anisotropy we nd Q rms PS = 16:0 +7:5 5:2 K (68% CL), n = 1:21 +0:60 0:55 (68% CL), and, with n xed to 1.0 the most likely amplitude is 18:2 1:6 K (68% CL). Monte Carlo simulations indicate that these derived estimates of n may be biased by +0:3 (with the observed low value of the quadrupole included in the analysis) and +0:1 (with the quadrupole excluded). Thus the most likely bias-corrected estimate of n is between 1.1 and 1.3. Our best estimate of the dipole from the two-year DMR data is 3:363 0:024 mK towards Galactic coordinates (`; b) = (264:4 0:2 ; +48:1 0:4 ), and our best estimate of the RMS quadrupole amplitude in our sky is 6 3 K (68% CL).Subject headings: cosmology: cosmic microwave background -large scale structure of the universe -observations { 3 {

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A 1-km 2 area located 2 km off the Florida Panhandle (30 22 6 N; 86 38 7 W) was selected as the site to conduct high-frequency acoustic seafloor penetration, sediment propagation, and bottom scattering experiments [1]. Side scan, multibeam, and normal incidence chirp acoustic surveys as well Manuscript