Source as a controlling factor on the quality and interpretation of sediment magnetic records from the northern North Atlantic

Magnetic properties of eight particle size ranges from nine locations in Iceland and 26 locations in southern Greenland reveal the importance of source variation for our understanding of paleomagnetic and environmental magnetic records in the marine environment. These terrestrial samples show varying degrees of particle size dependence with all samples showing that the silt fraction possesses greater concentrations of ferrimagnetic minerals than either clay or sand. Fine pseudo-single domain (PSD) size magnetic grains dominate the magnetic assemblage of all Icelandic fractions. In contrast, Greenlandic samples possess greater variation in magnetic grain size; only fine silt and clay are as magnetically fine as the Icelandic PSD grains, while Greenlandic silts and sands are dominated by coarser PSD and multi-domain grains. These observations from potential marine sediment sources suggest that the silt size fraction is a likely driver for much of the concentration-dependent parameters derived from bulk magnetic records and that the magnetic grain size of the silt fraction can be used to discriminate between Icelandic and Greenlandic sources. Using these results to examine magnetic grain size records from marine sediment cores collected across the northern North Atlantic suggests that source, not just transport-controlled physical grain-size, has a significant impact on determining the magnetic grain size at a particular location. Homogeneity of magnetic grain size in Icelandic sediments at least partially explains the consistent quality of paleomagnetic records derived from cores surrounding Iceland and their ability to buffer large environmental changes. © 2013 Elsevier B.V.

A generalized functional response for predators that switch between multiple prey species

We develop a theory for the food intake of a predator that can switch between multiple prey species. The theory addresses empirical observations of prey switching and is based on the behavioural assumption that a predator tends to continue feeding on prey that are similar to the prey it has consumed last, in terms of, e.g., their morphology, defences, location, habitat choice, or behaviour. From a predator's dietary history and the assumed similarity relationship among prey species, we derive a general closed-form multi-species functional response for describing predators switching between multiple prey species. Our theory includes the Holling type II functional response as a special case and makes consistent predictions when populations of equivalent prey are aggregated or split. An analysis of the derived functional response enables us to highlight the following five main findings. (1) Prey switching leads to an approximate power-law relationship between ratios of prey abundance and prey intake, consistent with experimental data. (2) In agreement with empirical observations, the theory predicts an upper limit of 2 for the exponent of such power laws. (3) Our theory predicts deviations from power-law switching at very low and very high prey-abundance ratios. (4) The theory can predict the diet composition of a predator feeding on multiple prey species from diet observations for predators feeding only on pairs of prey species. (5) Predators foraging on more prey species will show less pronounced prey switching than predators foraging on fewer prey species, thus providing a natural explanation for the known difficulties of observing prey switching in the field. (C) 2013 Elsevier Ltd. All rights reserved.

Autonomic scheduling of tasks from data parallel patterns to CPU/GPU core mixes

We propose a methodology for optimizing the execution of data parallel (sub-)tasks on CPU and GPU cores of the same heterogeneous architecture. The methodology is based on two main components: i) an analytical performance model for scheduling tasks among CPU and GPU cores, such that the global execution time of the overall data parallel pattern is optimized; and ii) an autonomic module which uses the analytical performance model to implement the data parallel computations in a completely autonomic way, requiring no programmer intervention to optimize the computation across CPU and GPU cores. The analytical performance model uses a small set of simple parameters to devise a partitioning-between CPU and GPU cores-of the tasks derived from structured data parallel patterns/algorithmic skeletons. The model takes into account both hardware related and application dependent parameters. It computes the percentage of tasks to be executed on CPU and GPU cores such that both kinds of cores are exploited and performance figures are optimized. The autonomic module, implemented in FastFlow, executes a generic map (reduce) data parallel pattern scheduling part of the tasks to the GPU and part to CPU cores so as to achieve optimal execution time. Experimental results on state-of-the-art CPU/GPU architectures are shown that assess both performance model properties and autonomic module effectiveness. © 2013 IEEE.

Performance of polarisation functionals for linear and nonlinear optical properties of bulk zinc chalcogenides ZnX (X=S,Se,Te).

We calculated the frequency dependent macroscopic dielectric function and second-harmonic generation of cubic ZnS, ZnSe and ZnTe within time-dependent density-polarisation functional theory. The macroscopic dielectric function is calculated in a linear response framework, and second-harmonic generation in a real-time framework. The macroscopic exchange–correlation electric field that enters the time-dependent Kohn–Sham equations and accounts for long range correlation is approximated as a simple polarisation functional αP, where P is the macroscopic polarisation. Expressions for α are taken from the recent literature. The performance of the resulting approximations for the exchange–correlation electric field is analysed by comparing the theoretical spectra with experimental results and results obtained at the levels of the independent particle approximation and the random-phase approximation. For the dielectric function we also compare with state-of-the art calculations at the level of the Bethe–Salpeter equation.

Aplicação de métodos de customer relationship management ao tratamento de dados para o desenvolvimento de negócios

Tese de Doutoramento, Gestão, na especialidade de Marketing, Faculdade de Economia, Universidade do Algarve, 2007

Effect of rufinamide on gating properties of voltage-gated sodium channel Na(v)1.7

Background: Voltage-gated sodium channels (Nav1.x) are important players in chronic pain. A particular interest has grown in Nav1.7, expressed in nociceptors, since mutations in its gene are associated to two inherited pain syndromes or insensitivity to pain. Rufinamide, a drug used to treat refractory epilepsy such as the Lennox-Gastaut syndrome, has been shown to reduce the number of action potentials in cortical neurons without completely blocking Na channels. Aim: The goal of this study was to investigate the effect of rufinamide on Nav1.7 current. Methods and results: Whole-cell patch clamp experiments were performed using HEK293 cells stably expressing Nav1.7. Rufinamide significantly decreased peak sodium current by 28.3, 21.2 and 12.5% at concentrations of 500, 100 and 50μM respectively (precise EC50 could not be calculated since higher rufinamide concentrations could not be achieved in physiological buffer solution). No significant difference on the V1/2 of voltage-dependence of activation was seen; however a shift in the steady-state inactivation curve was observed (-82.6 mV to -88.8 mV and -81.8 to -87.6 mV for 50 and 100 μM rufinamide respectively, p <0.005). Frequency-dependent inhibition of Nav1.7 was also influenced by the drug. One hundred μM rufinamide reduced the peak sodium current (in % of the peak current taken at the first sweep of a train of 50) from 90.8 to 80.8% (5Hz), 88.7 to 71.8% (10 Hz), 69.1 to 49.2% (25 Hz) and 22.3 to 9.8% (50 Hz) (all p <0.05). Onset of fast inactivation was not influenced by the drug since no difference in the time constant of current decay was observed. Conclusion: In the concentration range of plasma level in human treated for epilepsy, 15 μM, rufinamide only minimally blocks Nav1.7. However, it stabilizes the inactivated state and exerts frequencydependent inhibition of Nav1.7. These pharmacological properties may be of use in reducing ectopic discharges as a causal and symptom related contributor of neuropathic pain syndrome.

Evolutionary branching in deme-structured populations.

Adaptive dynamics shows that a continuous trait under frequency dependent selection may first converge to a singular point followed by spontaneous transition from a unimodal trait distribution into a bimodal one, which is called "evolutionary branching". Here, we study evolutionary branching in a deme-structured population by constructing a quantitative genetic model for the trait variance dynamics, which allows us to obtain an analytic condition for evolutionary branching. This is first shown to agree with previous conditions for branching expressed in terms of relatedness between interacting individuals within demes and obtained from mutant-resident systems. We then show this branching condition can be markedly simplified when the evolving trait affect fecundity and/or survival, as opposed to affecting population structure, which would occur in the case of the evolution of dispersal. As an application of our model, we evaluate the threshold migration rate below which evolutionary branching cannot occur in a pairwise interaction game. This agrees very well with the individual-based simulation results.

The infared optical properties of Sr2RuO4 and SmTiO3 including an object-oriented resistivity interface /

The perovskite crystal structure is host to many different materials from insulating to superconducting providing a diverse range of intrinsic character and complexity. A better fundamental description of these materials in terms of their electronic, optical and magnetic properties undoubtedly precedes an effective realization of their application potential. SmTiOa, a distorted perovskite has a strongly localized electronic structure and undergoes an antiferromagnetic transition at 50 K in its nominally stoichiometric form. Sr2Ru04 is a layered perovskite superconductor (ie. Tc % 1 K) bearing the same structure as the high-tem|>erature superconductor La2_xSrrCu04. Polarized reflectance measurements were carried out on both of these materials revealing several interesting features in the far-infrared range of the spectrum. In the case of SmTiOa, although insulating, evidence indicates the presence of a finite background optical conductivity. As the temperature is lowered through the ordering temperature a resonance feature appears to narrow and strengthen near 120 cm~^ A nearby phonon mode appears to also couple to this magnetic transition as revealed by a growing asymmetry in the optica] conductivity. Experiments on a doped sample with a greater itinerant character and lower Neel temperature = 40 K also indicate the presence of this strongly temperature dependent mode even at twice the ordering temperature. Although the mode appears to be sensitive to the magnetic transition it is unclear whether a magnon assignment is appropriate. At very least, evidence suggests an interesting interaction between magnetic and electronic excitations. Although Sr2Ru04 is highly anisotropic it is metallic in three-dimensions at low temperatures and reveals its coherent transport in an inter-plane Drude-like component to the highest temperatures measured (ie. 90 K). An extended Drude analysis is used to probe the frequency dependent scattering character revealing a peak in both the mass enhancement and scattering rate near 80 cm~* and 100 cm~* respectively. All of these experimental observations appear relatively consistent with a Fermi-liquid picture of charge transport. To supplement the optical measurements a resistivity station was set up with an event driven object oriented user interface. The program controls a Keithley Current Source, HP Nano-Voltmeter and Switching Unit as well as a LakeShore Temperature Controller in order to obtain a plot of the Resistivity as a function of temperature. The system allows for resistivity measurements ranging from 4 K to 290 K using an external probe or between 0.4 K to 295 K using a Helium - 3 Cryostat. Several materials of known resistivity have confirmed the system to be robust and capable of measuring metallic samples distinguishing features of several fiQ-cm.

Calculation of the optical conductivity for the Anderson impurity model using the slave boson technique

The optical conductivity of the Anderson impurity mode l has been calculated by emp l oying the slave boson technique and an expansion in powers of l i N, where N is the d egeneracy o f the f electron level . This method has been used to find the effective mass of the conduction electrons for temperatures above and below the Kondo tempera ture. For low temperatures, the mass enhancement is f ound to be large while a t high t emperatures, the mass enhancement is sma ll. The conductivity i s f ound to be Drude like with frequency dependent effective mass and scattering time for low independent effective mass and temperatures and scattering time f requency for high t emperatures. The behavior of both the effective mass and the conductivity is in qualitative agreement with experimental r esul t s .

Far-infrared optical properties of the heavy fermion superconductor UB[E13]

Temperature dependent resistivity, p, magnetic susceptibility, X, and far-infrared reflectance measurements were made on the low Tc superconductor UBe13. Two variants of UBe13 have been proposed, named 'L'- (for low Tc ) and 'H'-type (for high Tc ). Low temperature resistivity measurements confirmed that our sample was of H-type and that the transition temperature was at 0.9 K. This was further confirmed with the observation of this transition in the AC-susceptibility. Low temperature reflectance measurements showed a decrease in the reflectivity as the temperature is lowered from 300 to 10 K, which is in qualitative agreement with the increasing resistivity in this temperature range as temperature is lowered. No dramatic change in the reflectivity was observed between 10 and 0.75 K. A further decrease of the reflectance was observed for the temperature of 0.5 K. The calculated optical conductivity shows a broad minimum near 80 cm-1 below 45 K. Above 45 K the conductivity is relatively featureless. As the temperature is lowered, the optical conductivity decreases. The frequency dependent scattering rate was found to be flat for temperatures between 300 and 45 K. The development of a peak, at around 70 cm-1 was found for temperatures of 45 K and below. This peak has been associated with the energy at which the transition to a coherent state occurs from single impurity scattering in other heavy fermion systems. The frequency dependent mass enhancement coefficient was found to increase at low frequencies as the frequency decreases. Its' magnitude as frequency approaches zero also increased as the temperature decreased.

Transmission measurements using a new far-infrared set-up

A system comprised of a Martin-Puplett type polarizing interferometer and a Helium-3 cryostat was developed to study the transmission of materials in the very-far-infrared region of the spectrum. This region is of significant interest due to the low-energy excitations which many materials exhibit. The experimental transmission spectrum contains information concerning the optical properties of the material. The set-up of this system is described in detail along with the adaptations and improvements which have been made to the system to ensure the best results. Transmission experiments carried out with this new set-up for two different varieties of materials: superconducting thin films of lead and biological proteins, are discussed. Several thin films of lead deposited on fused silica quartz substrates were studied. From the ratio of the transmission in the superconducting state to that in the normal state the superconducting energy gap was determined to be approximately 25 cm-1 which corresponds to 2~/kBTc rv 5 in agreement with literature data. Furthermore, in agreement with theoretical predictions, the maximum in the transmission ratio was observed to increase as the film thickness was increased. These results provide verification of the system's ability to accurately measure the optical properties of thin low-Tc superconducting films. Transmission measurements were carried out on double deionized water, and a variety of different concentrations by weight of the globular protein, Bovine Serum Albumin, in the sol, gel and crystalline forms. The results of the water study agree well with literature values and thus further illustrate the reproducibility of the system. The results of the protein experiments, although preliminary, indicate that as the concentration increases the samples become more transparent. Some weak structure in the frequency dependent absorption coefficient, which is more prominent in crystalline samples, may be due to low frequency vibrations of the protein molecules.

L'influence de la sélection fréquence-dépendante sur le choix de partenaire chez le diamant mandarin (Taeniopygia guttata)

La sélection fréquence-dépendante est un mécanisme d’évolution selon lequel l’aptitude d'un type varie en fonction de sa fréquence dans la population. Ce mécanisme joue un rôle important dans de nombreuses interactions autant interspécifiques (parasitisme, prédation, compétition), qu'intra-spécifiques entre les différents phénotypes d'une même espèce. La sélection fréquence-dépendante peut être positive ou négative et favoriser alors les phénotypes communs ou rares, respectivement. Elle a été mise en évidence dans le contexte du choix de partenaire chez plusieurs espèces, notamment chez certaines espèces d'insectes (ex.: demoiselles, drosophiles, cantharide de Pennsylvanie) et de poissons (ex.: guppys, xiphos), mais elle a été aussi récemment découverte chez l’humain. L'importance de la sélection fréquence-dépendante dans le choix de partenaire chez les espèces monogames reste tout de même peu explorée et cette étude vise à combler cette lacune en utilisant le diamant mandarin, un passereau monogame, comme modèle biologique. Nous avons étudié l'importance de ce mécanisme lorsqu'un trait est neutre et lorsque celui-ci constitue un indicateur de qualité. De plus, nous avons tenté de déterminer si la présence de rivales peut modifier la préférence initiale des femelles pour les phénotypes rares ou communs.

Dynamic characterization of olfactory receptors in the fruit fly Drosophila melanogaster

Temporal changes in odor concentration are vitally important to many animals orienting and navigating in their environment. How are such temporal changes detected? Within the scope of the present work an accurate stimulation and analysis system was developed to examine the dynamics of physiological properties of Drosophila melanogaster olfactory receptor organs. Subsequently a new method for delivering odor stimuli was tested and used to present the first dynamic characterization of olfactory receptors at the level of single neurons. Initially, recordings of the whole antenna were conducted while stimulating with different odors. The odor delivery system allowed the dynamic characterization of the whole fly antenna, including its sensilla and receptor neurons. Based on the obtained electroantennogram data a new odor delivery method called digital sequence method was developed. In addition the degree of accuracy was enhanced, initially using electroantennograms, and later recordings of odorant receptor cells at the single sensilla level. This work shows for the first time that different odors evoked different responses within one neuron depending on the chemical structure of the odor. The present work offers new insights into the dynamic properties of olfactory transduction in Drosophila melanogaster and describes time dependent parameters underlying these properties.

Left preference for sport tasks does not necessarily indicate left-handedness

In the elite domain of interactive sports, athletes who demonstrate a left preference (e.g., holding a weapon with the left hand in fencing or boxing in a ‘southpaw’ stance) seem overrepresented. Such excess indicates a performance advantage and was also interpreted as evidence in favour of frequency-dependent selection mechanisms to explain the maintenance of left-handedness in humans. To test for an overrepresentation, the incidence of athletes’ lateral preferences is typically compared with an expected ratio of left- to right-handedness in the normal population. However, the normal population reference values did not always relate to the sport-specific tasks of interest, which may limit the validity of reports of an excess of ‘left-oriented’ athletes. Here we sought to determine lateral preferences for various sport-specific tasks (e.g., baseball batting, boxing) in the normal population and to examine the relationship between these preferences and handedness. To this end, we asked 903 participants to indicate their lateral preferences for sport-specific and common tasks using a paper-based questionnaire. Lateral preferences varied considerably across the different sport tasks and we found high variation in the relationship between those preferences and handedness. In contrast to unimanual tasks (e.g., fencing or throwing), for bimanually controlled actions such as baseball batting, shooting in ice hockey or boxing the incidence of left preferences was considerably higher than expected from the proportion of left-handedness in the normal population and the relationship with handedness was relatively low. We conclude that (i) task-specific reference values are mandatory for reliably testing for an excess of athletes with a left preference, (ii) the term ‘handedness’ should be more cautiously used within the context of sport-related laterality research and (iii) observation of lateral preferences in sports may be of limited suitability for the verification of evolutionary theories of handedness.

Field-induced coordinates for the determination of dynamic vibrational nonlinear optical properties

Three conjugated organic molecules that span a range of polarity and valence-bond/charge transfer characteristics were studied. It was found that dispersion can be insignificant, and that adequate treatment can be achieved with frequency-dependent field-induced vibrational coordinates (FD-FICs)