Comments on “School Integration Policies in Northern Cities”

This study develops a research method of assessing people's satisfaction with housing. Instead of the old approaches which consider in fragmented ways the characteristics of the dwelling, or the neighborhood, or the social environment, the author proposes a systems approach in which various interdependent factors are studied in relation to one another. Using the techniques developed, the relative satisfaction of tenants in public housing projects in certain areas of Canada is identified, analyzed, and discussed.     

Emissions of perfluorinated alkylated substances (PFAS) from point sources--identification of relevant branches

Effluents of wastewater treatment plants are relevant point sources for the emission of hazardous xenobiotic substances to the aquatic environment. One group of substances, which recently entered scientific and political discussions, is the group of the perfluorinated alkylated substances (PFAS). The most studied compounds from this group are perfluorooctanoic acid (PFOA) and perfluorooctane sulphonate (PFOS), which are the most important degradation products of PFAS. These two substances are known to be persistent, bioaccumulative and toxic (PBT). In the present study, eleven PFAS were investigated in effluents of municipal wastewater treatment plants (WWTP) and in industrial wastewaters. PFOS and PFOA proved to be the dominant compounds in all sampled wastewaters. Concentrations of up to 340 ng/L of PFOS and up to 220 ng/L of PFOA were observed. Besides these two compounds, perfluorohexanoic acid (PFHxA) was also present in nearly all effluents and maximum concentrations of up to 280 ng/L were measured. Only N-ethylperfluorooctane sulphonamide (N-EtPFOSA) and its degradation/metabolisation product perfluorooctane sulphonamide (PFOSA) were either detected below the limit of quantification or were not even detected at all. Beside the effluents of the municipal WWTPs, nine industrial wastewaters from six different industrial branches were also investigated. Significantly, the highest emissions or PFOS were observed from metal industry whereas paper industry showed the highest PFOA emission. Several PFAS, especially perfluorononanoic acid (PFNA), perfluorodecanoic acid (PFDA), perfluorododecanoic acid (PFDoA) and PFOS are predominantly emitted from industrial sources, with concentrations being a factor of 10 higher than those observed in the municipal WWTP effluents. Perfluorodecane sulphonate (PFDS), N-Et-PFOSA and PFOSA were not detected in any of the sampled industrial point sources.     

A dielectric-free superconducting coaxial cable

The theoretical properties of a dielectric-free superconducting coaxial cable with a magnetically levitated inner conductor are studied. It is found that at 100 GHz the intrinsic attenuation along such a cable is on the order of a 0.1 dB per kilometer. Furthermore, for a given cable, the loss is proportional to the square of the frequency. This low loss, coupled with a generous signal to noise ratio (≈80 dB at 100-GHz bandwidth), provides bit rates of 100 Gb/s over 600 km. At 10 Gb/s the distance increases to over 60000 km. Such a high-bandwidth, extremely-low-loss electronic transmission medium might be of interest for very-long distance repeaterless communications. In addition, since efficient means of tapping coaxial media already exist, local area network applications with an excess of 10⁴ users could be supported. The two properties of superconductors central to this application are very low intrinsic loss and expulsion of magnetic flux. Low loss allows high-bandwidth dispersionless transmission, and magnetic flux expulsion permits magnetic support of the inner conductor, thereby avoiding the large dielectric losses associated with any support material     

Zur adsorptiven Abscheidung von Isocyanaten aus Abgasen

Ohne Zusammenfassung Reihe 3 Nr. 100 (1985) der FORTSCHRITT-BERICHTE VDI gibt den vollen Wortalut der Arbeit als Manuskript gedruckt wieder. 84 Seiten, Preis 58 DM. Bestellungen an die VDI-Verlag GmbH, Postfach 1139, 4000 Düsseldrof 1.     

On Limits of Wireless Communications in a Fading Environment when Using Multiple Antennas

This paper is motivated by the need for fundamental understanding of ultimate limits of bandwidth efficient delivery of higher bit-rates in digital wireless communications and to also begin to look into how these limits might be approached. We examine exploitation of multi-element array (MEA) technology, that is processing the spatial dimension (not just the time dimension) to improve wireless capacities in certain applications. Specifically, we present some basic information theory results that promise great advantages of using MEAs in wireless LANs and building to building wireless communication links. We explore the important case when the channel characteristic is not available at the transmitter but the receiver knows (tracks) the characteristic which is subject to Rayleigh fading. Fixing the overall transmitted power, we express the capacity offered by MEA technology and we see how the capacity scales with increasing SNR for a large but practical number, n, of antenna elements at both transmitter and receiver.We investigate the case of independent Rayleigh faded paths between antenna elements and find that with high probability extraordinary capacity is available. Compared to the baseline n = 1 case, which by Shannon's classical formula scales as one more bit/cycle for every 3 dB of signal-to-noise ratio (SNR) increase, remarkably with MEAs, the scaling is almost like n more bits/cycle for each 3 dB increase in SNR. To illustrate how great this capacity is, even for small n, take the cases n = 2, 4 and 16 at an average received SNR of 21 dB. For over 99% of the channels the capacity is about 7, 19 and 88 bits/cycle respectively, while if n = 1 there is only about 1.2 bit/cycle at the 99% level. For say a symbol rate equal to the channel bandwith, since it is the bits/symbol/dimension that is relevant for signal constellations, these higher capacities are not unreasonable. The 19 bits/cycle for n = 4 amounts to 4.75 bits/symbol/dimension while 88 bits/cycle for n = 16 amounts to 5.5 bits/symbol/dimension. Standard approaches such as selection and optimum combining are seen to be deficient when compared to what will ultimately be possible. New codecs need to be invented to realize a hefty portion of the great capacity promised.     

Propagation measurements for fixed wireless loops (FWL) in asuburban region with foliage and terrain blockages

We present the results of propagation measurements at 2.485 GHz for fixed wireless loops. Path loss measurements were performed and characterized at 43 subscriber locations around a base station antenna located on top of Crawford Hill in Holmdel, NJ. This suburban location is characterized by rolling hills, foliage, and terrain blockages. Temporal and horizontal motion path loss fluctuations were found to be uncorrelated, each characterized by a different Ricean distribution. Lower r.m.s. delay spreads were obtained with directive subscriber antennas than with omni-directional antennas. No substantial gain loss (less than 2 dB) of subscribers' directive antennas was observed. The effects of trees, with foliage, surrounding the base station upon the path loss and the ratio of scattered power to specular power are also examined. The distance exponent of path loss versus distance (about 1.5) was observed to be less than free-space. Diffraction loss from hilltop trees, shadowing the base station, are suspected to be the cause. This loss decreases as the remote moves further away and comes out of the shadow. Scattered power from directions other than line-of-sight was observed to be as high as one half of the specular contribution when tree scattering near the base station was significant     

Microcells in personal communications systems

Research projects involving fiber-connected microcell base units, measurements and models of propagation in urban microcells, and radio link performance in urban microcells are summarized. Developments in microcell system issues, such as channel assignments and handoff in microcells and architectures for combining microcells with traditional macrocells, are discussed. Research on both indoor radio propagation and wireless indoor systems is reviewed