Showing papers by "University of Lisbon published in 1987"

On the ranks of certain finite semigroups of transformations

Abstract: It is well-known (see [2]) that the finite symmetric group Sn has rank 2. Specifically, it is known that the cyclic permutationsgenerate Sn,. It easily follows (and has been observed by Vorob'ev [9]) that the full transformation semigroup on n ( = Singn. This is of course potentially greater than the rank, but in fact the two numbers turn out to be equal.

Finding parts within figures: a developmental study.

Abstract: Preschool children, primary school children, and unschooled adults were tested on the part-probe task designed by Palmer. Relatively high scores were obtained with all groups on parts which had a 'good' relationship with the figure. However, the ability to find more deeply embedded segments was not present in the preschool children or in the unschooled adults. This indicates that the processes of postperceptual analysis necessary to find a part in a figure are neither built-in nor the consequence of mere cognitive growth, but depend on the instruction or experience usually provided in school. Such processes should not be confused with those that lead to form perception. Inspection of the part-figure pairs and of the corresponding detection scores suggests the importance of several stimulus properties.

The Kibaran cycle in Angola — a discussion

Abstract: Three sedimentary formations of Kibaran age have been identified in SW Angola: the Cahama-Otchinjau Formation, the Chela Group and the Leba-Tchamalindi Formation. The Cahama-Otchinjau Formation is intruded by red granites which are also found as boulders within the Chela Group basal conglomerate. These granites yielded the following Rb-Sr ages: Matala region t = 1350 ± 65 Ma, 87Sr/86Sri = 0.716 ± 0.003; Ompupa region t = 1407 ± 26 Ma, 87Sr/86Sri = 0.7058 ± 0.0020; Otchinjau region t = 1411 ± 24 Ma, 87Sr/86Sri = 0.7052 ± 0.0012; Chitado region t = 1302 ± 20 Ma, 87Sr/86Sri = 0.7075 ± 0.0016. The red granites are cut by basic dykes of different compositions and ages. The noritic dolerites which are intrusive in the Chela Group yielded a good Rb-Sr isochron at t = 1119 ± 27 Ma, 87Sr/86Sri = 0.7044 ± 0.0010. This age postdates the deposition of the Chela Group and of the Leba Tchamalindi Formation. These formations of Kibaran age extend to Namibia where they outcrop near the border. Their extension to the central and northeastern Angola is not yet well defined. Regarding the centralwestern region some metasediments outcrops are considered by several authors to belong to the Bale Group of Eburnean age or to the Oendolongo (s.s.) Group. It is assumed in this paper that some of the referred metasediments outcrops belong to the Bale Group while the others belong to the Oendolongo (s.s.) Group to which we suggest a Kibaran age. Concerning the eastern region we admit that the metasediments belonging to the Malombe and Luana Groups which are intruded by basic and granitoid rocks may be of Kibaran age. A more accurate establishment of the stratigraphy of this area will only be possible after isotope determinations, mainly on the basic rocks to define whether they belong to one or other of the two thermotectonic events already detected in Zaire at 2000–2220 Ma and 991 ± 30 Ma.

Nilpotents in finite symmetric inverse semigroups

Abstract: In semigroup theory as in other algebraic theories a significant part of the total effort is appropriately applied to the study of certain standard examples occurring, as it were, “in nature”. The most obvious such semigroup is the full transformation semigroup (X) (see [3]) and about this semigroup a great deal is known in both the finite and infinite cases.

Palaeomagnetism and isotopic age data from Upper Cretaceous igneous rocks of W. Portugal; geological correlation and plate tectonic aspects

Abstract: Summary Palaeomagnetic results and K–Ar age data for the Sintra and Sines intrusive complexes (W. Portugal), and further details on the palaeomagnetic structure of the Lisbon volcanics are reported. The Sintra complex consists of two main intrusive phases having been emplaced in the Upper Cretaceous at around 90 Ma and 75 Ma respectively. The radiometric results show that the Sines complex formed concurrently with the second Sintra magmatism. The early (main) Sintra pluton has a characteristic magnetization of D = 358°, I = 27° (α95= 3.3°). This remanence direction is defined by gabbros and diorites as the granitic rocks (constituting the bulk of the complex) are shown to possess stable secondary magnetization imposed during Quaternary weathering. The characteristic magnetization of the younger intrusive event, as defined by the Sines rocks, has a mean direction of D = 041°, I = 41° (α95= 3.3°). These two Upper Cretaceous palaeomagnetic directions are significantly different at the 95 per cent probability level. The Lisbon volcanics show the presence of the ‘75 Ma’ magnetization suggesting that also this volcanic complex dates from the Upper Cretaceous. In addition, the palaeomagnetic results from the Lisbon complex have given further substance to a previously reported magnetization component with shallow inclination and north-northwest declination, now defined by D = 333° I = 14° (α95= 7.4°). It is inferred that this magnetization which has a dual-polarity structure formed through low temperature oxidation in late Cretaceous to Lower Tertiary time. The declination difference between the ‘90 Ma’ and ‘75 Ma’ magnetizations may be interpreted in terms of a two-phase rotation of Iberia in the Upper Cretaceous prior to the assumed late Cretaceous–early Tertiary secondary magnetic imprint, implying a counterclockwise rotation of minimum 40° followed by a clockwise rotation of similar magnitude. However, if the relevant palaeomagnetic reference frame for Iberia, before and after its independent tectonic movements in the late Cretaceous, is the African plate, then the clockwise rotation is about 20° larger than the counterclockwise one, apparently accounting for the compressive tectonism in the Bay of Biscay.

Currency Incontrovertibility, Trade Taxes and Smuggling

Abstract: In the classic analysis of smuggling importers choose the optimal mix of legal and illegal trade, given trade taxes and the technology of detection. This paper introduces an inconvertible currency in the framework, so that illegal trade is valued at a rate higher than the (fixed) official exchange rate. Sections 1 and 2 show how the smuggling ratio and the domestic price markup for the import and export good are simultaneously determined. With balanced legal and illegal trade, changes in the (long-run) black market premium are a weighted average of changes in trade taxes, whereas changes in the smuggling ratios depend on the ratio of trade taxes. Thus, an import tariff and an export subsidy rising at the same rate would keep smuggling ratios constant but imply a rising black market premium (section 3 and 4). To determine the quantity of exports and imports, a model of the economy is presented in section 5, featuring the production of exports and non-traded goods and the consumption of imports and non-traded goods, as well as a government confiscating the amounts of traded goods unsuccessfully smuggled. Then export production may fall, and welfare may rise, if trade taxes have a negative effect on the relative price of exports and imports stronger than the positive effect on smuggled exports and imports, which is always welfare-reducing. Section 6 introduces the short-run determination of the black market premium via portfolio balance. In this case, rising rade taxes may be associated with a premium rising even faster if there is unreported capital flight and conversely.

Regulation of water use by four species of Cistus in the scrub vegetation of the Serra da Arrábida, Portugal

Abstract: Plants of mediterranean ecosystems are subjected annually to prolonged periods of drought. The drought resistance of individual species occurring in these regions is conferred on them by both morphological and physiological adaptations which provide both drought avoidance and drought tolerance mechanisms (Levitt 1980). In parts of the Serra da Arrabida region, Cistus salvifolius, Cistus monspeliensis, Cistus albidus, and Cistus ladanifer are sympatric species, although in general, differences in habitat preference have been identified based on moisture availability. Cistus salvifolius, for example, is the most prevalent species on less exposed north facing mountain slopes. It occurs in a smaller growth form on drier south facing slopes together with the other three more thermophilic species. The present comparative study was undertaken to examine possible differences in drought resistance among these four Cistus species more closely. Over an annual cycle, the water relations and stomatal response of all four species were observed at monthly intervals in an attempt to identify differential responses to stress conditions.

Late onset coeliac disease in the monozygotic twin of a coeliac child.

Abstract: A case of late onset coeliac disease (confirmed by serial intestinal biopsies) is described in the monozygotic twin of a coeliac patient. This is the second case reported in literature. The permanent discordance for coeliac disease in monozygotic twins is questioned.

On the distribution equivalence in cluster analysis

Abstract: One of the first problems to be solved in cluster analysis particularly when using hierarchical clustering methods is to choose adequate measures of comparison between entities to be clustered.

Geodetic measurements of plate motions across the central Gulf of California, 1982-1986

Abstract: A trilateration network was set up in early 1982 by a team of French and Mexican institutions across the central part of the Gulf of California in order to study the plate boundary related movements in this transition area between the San Andreas fault system and the East Pacific Rise. The reobservation of this network in March 1986 provides a first set of data on the present day deformations in this area. Both surveys used AGA8 Laser geodimeter measurements between 11 stations located on elevated points of Baja California and Sonora and on the islands between the peninsula and mainland coasts. Deformation patterns during the 1982-1986 interval, obtained through three different methods indicate mainly a right lateral shear movement in the Gulf axis direction N46°W. Between Baja California Peninsula and Angel de la Guarda Island 17 ± 4 cm of dextral slip occurred. Between the coast of Sonora and the central islands of the Gulf the mean displacement amount to about 23 ± 12 cm. In the southwestern part of the network, weaker movements seem to have occurred, and are smaller than estimated errors. This may indicate either that the boundary is locked in this part or is deflected towards the ESE. These results, which give an estimation of the relative plate velocity of 8 ± 3 cm/a, are consistent with the generally accepted relative movement between North American and Pacific plates (about 6 cm/a).

Enthalpies of solution oft-butyl chloride and bromide and carbon tetrachloride and tetrabromide in alcohols

Abstract: Standard enthalpies of solution of t-BuX and CX4 (X=Cl and Br) in several alcohols are reported as measured by a calorimetric method. The corresponding transfer functions from the gas phase were calculated.

Smuggler's Blues at the Central Bank: Lessons from Sudan

Abstract: The ineffectiveness of real devaluation as stabilization policy does not imply that the nominal exchange rate should be held constant in the face of a domestic inflation. In this circumstance, import duties and export subsidies would have to be escalated to counter the potential erosion of the trade balance. This escalation of trade barriers generates a rising black market premium and offers increasing incentives to smuggling, already a pervasive problem in the African countries. As a consequence, the central bank would find it more and more difficult to hold the nominal exchange rate constant. This leads us to consider a passive exchange rate policy of stabilizing the exchange rate by moving the nominal rate in line with domestic inflation. If such passive policy is not accompanied by the elimination of trade barriers, however, the black market premium will not disappear. Unless exchange rate policy and trade policy are consistent with each other, the smuggler's blues will reach the central bank. Indeed, this is not just a theoretical possibility, it is the major lesson from the recent experience of Sudan.

Simulation of the development of individual interactional patterns

Abstract: The questions of how and why individuals develop normal or abnormal interpersonal patterns have received nonconsistent answers in the behavioral sciences, perhaps because they were too much concerned with the semantics and the syntax aspects of the communication process that mediates human interaction. This paper demonstrates that a pragmatic approach is necessary and sufficient to answer the above questions. The information processing aspect of the “single bit of information exchange” model (P. De Giacomo and A. Silvestri, 1979) is developed to create a computer simulation procedure. Using both clinical data and normal population measurements of KALTEST (O. G. Pereira and C. P. Ferreira, 1984) as the basic criteria, it is found that the development of a stable normal pattern of interaction depends on the ability to share proposals with the other significant person in the environment and that the development of an abnormal pattern depends on refusal to share coupled with a tendency to escape from the ring...

Annealing and internal oxidation of hafnium implanted magnesium single crystals

Abstract: Using the time differential perturbed angular correlations technique studies of the Hf-Mg system formed by implanting a low fluence of 181Hf in magnesium single crystals were carried out. The temperature dependence of the system was studied in the range between 10 K and 750 K. Experimental evidence was obtained for the occurrence of an “internal oxidation” process of the implanted hafnium.

Red child syndrome.

Abstract: An acute overdose of rifampicin in an 18 month old white infant is described. The characteristic signs of the syndrome: orange-red discolouration of the skin, urine, and tears, facial pruritus, and periorbital oedema were present and the outcome was uneventful. Paediatricians should be aware of this peculiar yet easily identifiable syndrome.

Currency Inconvertibility, Trade Taxes and Smuggling

Abstract: In the classic analysis of smuggling, importers choose the optimal mix of legal and illegal trade, given trade taxes and the technology of detection. This paper introduces an inconvertible currency into the framework, so that illegal trade is valued at a rate higher than the (fixed) official exchange rate. Sections 1 and 2 show how the smuggling ratio and the domestic price mark-up for the import and export good are simultaneously determined. With balanced legal and illegal trade, changes in the (long-run) black market premium are a weighted average of changes in trade taxes, whereas changes in the smuggling ratios depend on the ratio of trade taxes. Thus, an import tariff and an export subsidy rising at the same rate would keep smuggling ratios constant but would lead to a rising black market premium (sections 3 and 4). In Section 5 we present a model explaining the determination of export and import quantities. The model explains the production of exports and non-traded goods and the consumption of imports and non-traded goods, and assumes that the government confiscates traded goods that are unsuccessfully smuggled. Export production may fall and welfare may rise if trade taxes have a negative effect on the relative price of exports and imports which is stronger than the positive effect on smuggled exports and imports (which is always welfare-reducing). Section 6 introduces a portfolio balance model explaining the short-run behaviour of the black market premium. In this model, rising trade taxes may be associated with a premium which increases even more rapidly if there is unreported capital flight.

Effects of Stimulus Dynamics on Frequency Discrimination

Abstract: Physiological data shows that for certain stimulation levels, the discharge rate of an auditory-nerve fiber is roughly proportional to the level of stimulation. However, the same data shows as well that this proportional response attains a plateau if the stimulus level is increased above a certain limit (Schalk and Sachs, 1980). In other words, an auditory-nerve fiber has a certain dynamic range within which it can represent variations in the intensity of stimulation by varying its discharge rate, but for intensities above a certain level the discharge rate saturates and all the stimulation above that level is represented by the same firing rate. The dynamic range of a single fiber is small (of the order of a few tens of dB), although it varies somewhat with the fiber’s spontaneous rate (SR) (Schalk and Sachs, 1980). As a consequence, the dynamic range of a frequency channel-even considering the combined action of fibers with different SRs — is rather small, and the auditory patterns that can be predicted on the basis of the single-fiber responses will appear with very broad spectral peaks even at moderate levels.