Temporal scale and spatial resolution effects on Amazon forest fragmentation assessment in Rondônia

The Amazon has been under an intense deforestation process for the last 30 years, causing landscape fragmentation in many different regions and at distinct stages. The fragmentation process is commonly assessed by land‐use maps derived from satellite sensor data and analysed at a landscape context. The analysis of fragmentation depends on an adequate choice of spatial resolution of land‐use maps, and temporal scale in landscape dynamics studies. In this study, spatial–temporal resolution variation effects on fragmentation assessment were analysed in the Quatro Cachoeiras watershed, located at central Rondônia, Brazilian Amazon. Land‐use maps derived from 1984 to 2002 satellite sensor data at 2‐year intervals were used for landscape structure analysis on 12 samples randomly distributed along the watershed. In the spatial resolution variation analysis, landscape metrics obtained at 30 m resolution were compared with those obtained at coarser spatial resolutions. Effects of temporal scale variation were tested by comparison of landscape metrics calculated at 2‐, 4‐ and 6‐year intervals in the studied period. Results show that fragmentation stage influences sensitivity of landscape metrics for spatial resolution and at initial stages of fragmentation finer spatial resolution is required. Also, coarser resolutions up to 100 m could be used to assess landscape fragmentation at regions and the adequate time interval for landscape dynamics studies should be between 3 and 4 years.     

Distributing and revoking access authorizations on abstract objecs: A capability approch

In this paper a capability addressing environment is presented, based on the concept of extended capability. First of all it is shown that such an environment is well suited for implementing objects of abstract type. Then the problem of distributing and revoking access authorizations on abstract objects is considered and an efficient solution is presented. The revocation mechanism results in being selective, transitive and deferred.     

Dielectric behavior of a rubber-toughened epoxy resin

The dielectric behavior of amine-terminated butadiene acrylonitrile rubber/DGEBA epoxy resin bleuds of different formulations has been studied in the temperature range ?120–160°C at 10kHz. As indicated by the constancy of the glass transition temperatures of the two components, the degree of segmental mixing was very low or nil, irrespective of cure schedules. The intensity of the α-relaxation of the rubber was much less than that predicted by the simple series model (lower bound). This has been attributed to incomplete phase separation at gelation. Measurements carried out with a nonreactive rubber support this conclusion. Part of the rubber remains molecularly dispersed within the glassy matrix, thus contributing to the modification of the mechanical properties of epoxy resins brought about by reactive rubbers.     

Automated module placement and wire routeing according to a structured biplanar scheme in printed boards

Heuristic procedures are proposed for solving the module placement and the wire routeing problems in printed boards with the primary objective of reducing the area covered by the conductor paths. A structured biplanar scheme has been adopted, into which the modules are placed on the nodes of an array and the conductor paths are realized by means of horizontal and vertical connections, printed on the different sides of the card and electrically connected via holes. The proposed method is well suited for implementation on a small computer.     

Use of the dielectrometer for the determination of the complex dielectric constant in the microwave region in organic high polymers at various temperatures

A commercial type dielectrometer has been utilized for determining the complex dielectric constant of insulating materials as a function of temperature. For low-temperature measurements, modifications of the apparatus have been made, by which the lower section of the guide, containing the specimen, is insulated from the upper section by means of a Teflon disk, in order to permit measurements under vacuum without difficulties arising from moisture condensation. Taking into account the modifications made, relations between the experimentally measured quantities and the complex dielectric constant have been elaborated, and error analysis made, and best conditions to perform experimental measurements determined. For high- and medium-loss materials, in the low-temperature range, an accuracy of the order of 1% in ?′ and of 10% in ?″ have been calculated. Better results can be obtained for measurements at high temperature. The apparatus performance and the accuracy of measurements have been checked through measurements of the complex dielectric constant of different polar polymers at frequencies of the order of 9 × 10⁹ Hz, at temperatures between ?150 and 200°C. The experimental results are in good agreement with literature data derived from experimental measurements with other techniques and with the behavior expected on the basis of the results from radiofrequency measurements through considerations of molecular mobility in relation to molecular structure.     

The Use of Size Functions for Comparison of Shapes Through Differential Invariants

For comparison of shapes under subgroups of the projective group, we can use a lot of invariants and especially differential invariants coming from multiscale analysis. But such invariants, as we have to compute curvature, are very sensitive to the noise induced by the dicretization grid. In order to resolve this problem we use size functions which can recognize the qualitative similarity between graphs of functions that should be theorically coinciding but, unfortunately, change their values due to the presence of noise. Moreover, we focus this study on a projective differential invariant which allows to decide if one shape can be considered as the deformation of another one by a rotation of the camera.     

Dielectric behavior of some polar high polymers at ultra-high frequencies (microwaves)

The dielectric behavior of different polar high polymers at ultra-high frequencies has been investigated by means of a dielectrometer, suitably modified to permit measurements at different temperatures. Experimental measurements were made at about 9 × 10⁹ cps over the temperature range of ?150 to 200°C. for polyoxymethylene, polythiomethylene, poly(3,3′-chloromethyl)oxetane (Penton), polycarbonate of 4,4′-dioxydiphenyl-2,2′-propane (Makrolon), poly(vinyl alcohol), poly(vinyl acetate), poly(vinyl chloride), vinyl chloride–vinyl acetate copolymer, and two ABS plastics, type B (blend) and type G (graft). On comparing the dielectric behavior of the examined materials at ultra-high frequencies with the corresponding ones determined at low or at radiofrequencies, it is observed that, in the microwave region, all relaxation peaks, either connected with cooperative motions in main chain (primary processes) or with local motions in the backbone or in side chains (secondary processes), usually observed at lower frequencies, tend to disappear; the corresponding relaxation effects, however, manifest themselves through a progressive increase of losses with increasing temperature, which is particularly marked above the glass transition temperature T_g. The latter transition, in spite of the very high frequency, is easily distinguished, in most cases, by the sudden change of slope in the tan δ versus temperature curve which accompanies its onset. This is explained on the basis of the very wide distribution times of molecular relaxation processes in polymers and the increase in strength of the secondary relaxation effects, which is verified at T_g, as a consequence of the increased kinetic energy of macromolecules and of the larger free volume for orientation of side chains. Each case is discussed separately and the experimental results interpreted on the basis of the molecular structure and chain mobility of the examined polymers.