1,337 research outputs found
sj-docx-1-qjp-10.1177_17470218221111789 – Supplemental material for Cognitive control mechanisms in language processing: are there both within- and across-task conflict adaptation effects?
No full textSupplemental material, sj-docx-1-qjp-10.1177_17470218221111789 for Cognitive control mechanisms in language processing: are there both within- and across-task conflict adaptation effects? by Nicoletta Simi, Ian Grant Mackenzie, Hartmut Leuthold, Markus Janczyk and Carolin Dudschig in Quarterly Journal of Experimental Psychology</p
An analysis of building behaviour of the termite Macrotermes subhyalinus (Rambur)
No full textAlthough the work presented in this study is little more than a first survey of the causal factors involved in construction behaviour of Macrotermessubhyalinus , it clearly indicates a fertile field of research which has scarcely been explored. Past studies have concentrated on the release of building behaviour and have done little (with the exception of Grassé, 1959) to account for the formation of the various types of structural elements present in termite nests. The present study gives a general account of building behaviour and of the formation of several structural elements: volatile chemical cues in concerted action with tactile stimuli provided by physical objects, cause workers to grasp soil pellets, transport them, and subsequently deposit them at a building site. The ability of termite workers to employ pheromones in a versatile way in their orientation is the underlying condition which gives rise to the formation of a variety of structural elements.Building behaviour in this species is predominantly released by chemical stimuli like the building pheromone of the queen, the 'cement' pheromone and the trail pheromone (Bruinsma, unpublished). In view of the fact that the active space of the latter two pheromones directly depends on the number abd distribution of workers, it would appear, then, that the building latency time is inversely related to the workers group size. Grassé, (1959) has described such a density dependent effect on building activity in Cubitermes.The orientation required by building workers is mediated by trail- and 'cement' pheromone (directional orientation) and in the appropriate situation also by the building pheromone emanating from the queen (providing distance orientation). Other authors have documented examples of chemical orientation among termites. Leuthold (1975) has reviewed a body of evidence which shows that termites to a great extent rely on odour trail orientation. Stuart (1967) discovered that Zootermopsis is recruited to building sites by chemical trails. Grassé, (1959), Wilson (1971) and Deneubourg (1977) indicated the possibility of odours emanating from construction sites, orienting nearby motivated workers to such sites. This study furnishes convincing authentication of a pheromone emanating from a building site and confirms its rôle in worker orientation. Soil transporting workers arriving at a building site, e.g. located along a trail or in a deposition zone around the queen, attain a stable orientation with respect to that site prior to and during cementing their load. This response is probably to be due to the perception of a local stimulus, or stimulus complex. Such a mechanism of orientation is named telotaxis (Schöne, 1973), and implies as already emphasized by Fraenkel and Gunn (1961), simultaneous perception and evaluation of several stimuli.The results obtained with physical objects (small spheres) are in accordance with those of Stuart (1967) who demonstrated that surface irregularities release building behaviour in Nasutitermes. In respect of the ability of M . subhyalinus to perceive spatial relations between the discussed stimuli, it is of interest to mention a mechanism of orientation which has been described by Forel as: "By topochemical I mean a sense of smell which informs the ant as to the topography of the places surrounding it by means of chemical emanations which give an odour to objects" (Forel, 1928; cit. by Wilson, 1971, p252). To date such a mechanism integrating olfactory and mechanical information has been only demonstrated in honey bees (Martin, 1965) and the termites referred to in this study.Grassé, (1959, 1967) described in detail building behaviour in M . bellicosus , M . mülleri and Cubitermes sp. According to this author, it is the product of work previously accomplished, which constitutes the social stimulus for the workers to perform additional work (the concept of 'stigmergy'). In summary, two stages are distinguished: 1) A phase of 'unco-ordination' during which the workers first explore the container they are placed in, and after a certain time lapse start depositing soil pellets anywhere in the arena. When at some place the deposited material reaches a 'critical density' that is when several soil pellets are stuck together, this incipient structure proves to be very attractive to the workers compared to single pellets. 2) Subsequently the phase of 'co-ordination' is started during which workers transform the incipient structures into pillars, which, when a neighbouring one is within a critical distance, are combined to form arches. The concept of 'stigmergy' can be very well viewed in terms of the mechanism treated in the present study, except the observation that, initially, building is random. This observation is at variance with that of Stuart (1969), and the finding in the current study that workers employ the edge of a pheromone trail as a zone to co-ordinate soil depositions.Stuart (1967, 1969, and 1972) concludes that the behavioural basis of building is a response to a 'low level excitatory' stimulus, like air movement, odour, light, temperature etc., deviating from the normal nest environment. The subsequent building activity gradually eliminates the causal stimulus, and when no more environmental stimuli are forthcoming, building will stop. In conclusion, the immediate function of building is a homeostatic one. Since termites like most other social insects control the environment within the nest by actively maintaining several steady states, based on behavioural and physiological regulation (this phenomenon has been named 'social homeostasis' by Emerson, 1956), it is important to know whether the building mechanism proposed in this study is compatible with homeostatic regulation. At present it is only possible to indicate that there are several negative feedback mechanisms operating during building activity. At first, the ephemeral activity of both the trail- and the 'cement' pheromone is likely to modify the number of workers recruited to building sites. Secondly, it could be shown that major and minor workers during subsequent building runs loose between 20 - 40% of their fresh weight. In case workers are not allowed to compensate this loss by drinking at the water supply, they invariably stop building (Bruinsma, unpublished).The fact that pheromones, together with structural signals, are involved in the initiation and co-ordination of building behaviour in termites constitutes a plausible mechanism which accounts for most aspects of nest building behaviour in M . subhyalinus . The findings presented in this study may serve a useful purpose, increasing the understanding of the way in which termites perform such remarkable engineering feats as the construction of their impressive nest mounds.</TT
CASH AND FUTURES PRICE RELATIONSHIPS FOR NONSTORABLE COMMODITIES: AN EMPIRICAL ANALYSIS USING A GENERAL THEORY
No full textEmpirical analysis examines the presence of basis risk, speculative component, and expected maturity basis component in basis relationships for nonstorable commodities. The results indicate that all three above components exist in both cattle and hog markets. The basis risk and speculative components vary across contracts. Hog markets showed seasonality, which helps explain the hog basis more accurately. Flexibility in making the marketing decision strengthens the explanation of intertemporal price relationships for both cattle and hogs beyond that previously attributed to only feed prices.Demand and Price Analysis, Marketing,
NONPARAMETRIC KERNEL ESTIMATION OF MULTIPLE HEDGE RATIOS
No full textIt is possible for the traditional hedge ratio estimation to produce erroneous guidance to risk managers because of the restrictive assumptions. This study adopts nonparametric locally polynomial kernel estimation to exclude the assumptions. Results from the hog complex find that hedge ratios estimated by local polynomial kernel regression outperform naïve and GARCH models. Because of the potential assumption violations associated with the estimation and implementation of hedge ratios by GARCH models, LPK is a reasonable alternative for estimating hedge ratios to manage price risks.Marketing, Research Methods/ Statistical Methods, Risk and Uncertainty,
Lehramtsstudierende in prekärer Konstellation? Empirische Analysen zu widersprüchlichen Erwartungen und ambivalenten Adressierungen im Praxissemester
No full textHeinrich M, Dietz M, Ihmig K-N, Mergelkuhl T, Schlingmeyer K. Lehramtsstudierende in prekärer Konstellation? Empirische Analysen zu widersprüchlichen Erwartungen und ambivalenten Adressierungen im Praxissemester. In: Lähnemann C, Leuthold-Wergin A, Hagelgans H, Ritschel L, eds. Professionelle Kooperation in und mit der Schule – Erkenntnisse aus der Praxisforschung. Tagungsband der 20. Jahrestagung Nordverbund Schulbegleitforschung. Schriftenreihe Forschungspraxis - Praxisforschung . Vol 5. Münster: Monsenstein und Vannerdat; 2016: 221-232
OPTIMAL HEDGING STRATEGIES FOR THE U.S. CATTLE FEEDER
No full textMultiproduct optimal hedging for simulated cattle feeding is compared to alternative hedging strategies using weekly price data for 1983-95. Out-of-sample means and variances of hedged feeding margins using estimated hedge ratios for four commodities suggest that there is no consistent domination pattern among the alternative strategies, leaving the hedging decision up to the agent's degree of risk aversion. However, all hedging strategies significantly reduce the feeding margin's means and variances compared to no hedging, with variance reduction always exceeding 50%. Hedging results appear quite sensitive to the data set and its size.cattle feeding, hedge ratios, hedging strategies, multiproduct hedging, optimal hedging, Marketing,
Local Polynomial Kernel Forecasts and Management of Price Risks using Futures Markets
No full textThis study contributes to understanding price risk management through hedging strategies in a forecasting context. A relatively new forecasting method, nonparametric local polynomial kernel (LPK), is used and applied to the hog sector. The selective multiproduct hedge based on the LPK price and hedge ratio forecasts is, in general, found to be better than continuous hedge and alternative forecasting procedures in terms of reduction of variance of unhedged return. The findings indicate that combining hedging with forecasts, especially when using the LPK technique, can potentially improve price risk management.Marketing,
High-speed low-voltage electro-optic modulator with a polymer-infiltrated silicon photonic crystal waveguide
No full textThe paper concerns the design and the study of a silicon-based electro-optical modulator, using a photonic crystal waveguide containing a slot which is infiltrated with a nonlinear polymer. The research topic is important for the physics of photonic systems and for applications to integrated optics and to telecommunications.
Abstract: A novel electro-optic silicon-based modulator with a bandwidth of 78GHz, a drive voltage amplitude of 1V and a length of only 80 μm is proposed. Such record data allow 100Gbit/s transmission and can be achieved by exploiting a combination of several physical effects. First, we rely on the fast and strong nonlinearities of polymers infiltrated into silicon, rather than on the slower free-carrier effect in silicon. Second, we use a Mach-Zehnder interferometer with slotted slow-light waveguides for minimizing the modulator length, but nonetheless providing a long interaction time for modulation field and optical mode. Third, with this short modulator length we avoid bandwidth limitations by RC time constants. The slow-light waveguides are based on a photonic crystal. A polymer-filled narrow slot in
the waveguide center forms the interaction region, where both the optical mode and the microwave modulation field are strongly confined to. The waveguides are designed to have a low optical group velocity and negligible dispersion over a 1THz bandwidth.With an adiabatic taper we significantly enhance the coupling to the slow light mode. The feasibility of broadband slow-light transmission and efficient taper coupling has been previously demonstrated by us with calculations and microwave model experiments, where fabrication-induced disorder of the photonic crystal was taken into account
THE DISTRIBUTIONAL BEHAVIOR OF FUTURES PRICE SPREADS
No full textThe distributional behavior of futures price spreads is examined for four commodities: corn, live cattle, gold and T-bonds. Remarkably different results are found over commodities, time period, and sample size. Actual spread changes for the smaller sample size of gold and T-bonds and for corn produce more normal distributions for weekly than for daily differencing intervals, while all live cattle spreads for actual changes are normally distributed. However, the larger sample size of both gold and T-bonds and the relative spread changes for corn and live cattle do not become more normally distributed under temporal aggregation of the data.corn, futures price spreads, gold, goodness of fit, live cattle, normality tests, spread distributions, T-bonds, Marketing,
- …
