Spatial Demultiplexing in the sub-millimeter wave band using multlayer free-standing frequency selective surfaces

In this paper, we show that a multilayer freestanding slot array can be designed to give an insertion loss which is significantly lower than the value obtainable from a conventional dielectric backed printed frequency selective surface (FSS). This increase in filter efficiency is highlighted by comparing the performance of two structures designed to provide frequency selective beamsplitting in the quasioptical feed train of a submillimeter wave space borne radiometer. A two layer substrateless FSS providing more than 20 dB of isolation between the bands 316.5â??325.5 GHz and 349.5â??358.5 GHz, gives an insertion loss of 0.6 dB when the filter is orientated at 45 incidence in the TM plane, whereas the loss exhibited by a conventional printed FSS is in excess of 2 dB. A similar frequency response can be obtained in the TE plane, but here a triple screen structure is required and the conductor loss is shown to be comparable to the absorption loss of a dielectric backed FSS. Experimental devices have been fabricated using a precision micromachining technique. Transmission measurements performed in the range 250â??360 GHz are in good agreement with the simulated spectral performance of the individual periodic screens and the two multilayer freestanding FSS structures.

Las Comisiones del Mapa de España en la década de 1850

La necesidad de contar con un mapa de base científica que cubriera todo el territorio español llevó al Estado a crear en paralelo varias Comisiones con cometidos geodésicos, topográficos y cartográficos durante la década de 1850. La labor simultánea de estas Comisiones se prolongó hasta 1859, cuando se aprobó la Ley de Medición del Territorio, que las fusionó en un único organismo. Este artículo analiza aspectos técnicos de los trabajos que realizaron estas Comisiones a partir de la información contenida en algunos documentos que custodia el Archivo Topográfico del IGN. Las conclusiones que se extraen son que estas Comisiones acometieron operaciones geodésicas que resultaron cruciales en el establecimiento ulterior de la red de triangulación peninsular, realizaron mediciones topográficas que fueron reutilizadas veinte años después en el levantamiento del Mapa Topográfico Nacional, e idearon las características catastrales que fueron adoptadas durante todo el siglo posterior para el Catastro de España.

Exile or emigrant? Female ex-prisoners who left Ireland 1850-1921

In the popular mind, the concept of 'emigration' usually refers to people voluntarily leaving one country to go to another in search of a new and better life. It presupposes some degree of choice, although it is accepted that for many emigrants, such as those who left Ireland during the nineteenth century, there were few incentives to stay at home. Current scholarship on voluntary and forced movements of people demonstrates that the distinction between the categories of 'voluntary emigrant' and 'forced exile' is often blurred. Orm Overland's study of refugee communities in the United States highlights the fact that, although the differences between the 'emigrant' and the 'exile' may be clear in extreme cases, this is not always true, as there may be 'pressing political or economic reasons behind a decision to emigrate'. Migration scholars Jan Lucassen and Leo Lucassen also question the adequacy of conceptual models of migration based on what Lindsay Proudfoot and Dianne Hall refer to as the 'straightforward binarism between free and unfree emigration'. The questions raised by these scholars are very relevant to the study of Irish people who left their country during the second half of the nineteenth century immediately after they had been discharged from prison or from Dundrum. Their stories are discussed here against a background of substantial scholarship on emigration from Ireland and on the criminal justice system within Ireland. According to David Fitzpatrick, at least eight million men, women and children emigrated from Ireland between 1801 and 1921. This large-scale movement of people was generally characterised by the voluntary emigration of individuals who funded their own passages. However, it also included schemes of assisted emigration, funded variously by governments, landlords, the poor law authorities, earlier emigrants, and philanthropists. In addition, it included people who were transported from Ireland by means of the criminal justice system a practice that had originated in the seventeenth century. What is less well known is that after the end of transportation from Ireland to eastern Australia in 1853, to Bermuda in 1863 and to Western Australia in 1868, Irish convicts continued to be channelled towards emigration by being offered early release if they agreed to leave Ireland. These people, and especially the women among them, are the subject of this article.

Can we characterise ‘openness’ in the Holocene palaeoenvironmental record? Modern analogue studies of insect faunas and pollen spectra from Dunham Massey deer park and Epping Forest, England

This paper examines the degree to which tree-associated Coleoptera (beetles) and pollen could be used to predict the degree of ‘openness’ in woodland. The results from two modern insect and pollen analogue studies from ponds at Dunham Massey, Cheshire and Epping Forest, Greater London are presented. We explore the reliability of modern pollen rain and sub-fossil beetle assemblages to represent varying degrees of canopy cover for up to 1000m from a sampling site. Modern woodland canopy structure around the study sites has been assessed using GIS-based mapping at increasing radial distances as an independent check on the modern insect and pollen data sets. These preliminary results suggest that it is possible to use tree-associated Coleoptera to assess the degree of local vegetation openness. Additionally, it appears that insect remains may indicate the relative intensity of land use by grazing animals. Our results also suggest most insects are collected from within a 100m to 200m radius of the sampling site. The pollen results suggest that local vegetation and density of woodland in the immediate area of the sampling site can have a strong role in determining the pollen signal.