Recording from two neurons: second order stimulus reconstruction from spike trains and population coding

We study the reconstruction of visual stimuli from spike trains, recording simultaneously from the two H1 neurons located in the lobula plate of the fly Chrysomya megacephala. The fly views two types of stimuli, corresponding to rotational and translational displacements. If the reconstructed stimulus is to be represented by a Volterra series and correlations between spikes are to be taken into account, first order expansions are insufficient and we have to go to second order, at least. In this case higher order correlation functions have to be manipulated, whose size may become prohibitively large. We therefore develop a Gaussian-like representation for fourth order correlation functions, which works exceedingly well in the case of the fly. The reconstructions using this Gaussian-like representation are very similar to the reconstructions using the experimental correlation functions. The overall contribution to rotational stimulus reconstruction of the second order kernels - measured by a chi-squared averaged over the whole experiment - is only about 8% of the first order contribution. Yet if we introduce an instant-dependent chi-square to measure the contribution of second order kernels at special events, we observe an up to 100% improvement. As may be expected, for translational stimuli the reconstructions are rather poor. The Gaussian-like representation could be a valuable aid in population coding with large number of neurons

Effect of levels of polymaleic acid on the structural stability of saline soils.

The effect of levels of polymaleic acid was studied on the structural stability of two saline soils exposed to intensive cultivation. Soil samples with undisturbed structure were collected and placed in containers where levels polymaleic acid (0, 10, 20 and 30L/ha) were applied diluted water, in order to raise the moisture up to field capacity. One week later, controlled drip irrigation was applied using a volume corresponding to the pluviometric precipitation of the areas where the samples were collected. The washed soil samples were taken from the containers with the objective of lowering the moisture and separating the aggregates, considering those which passed through a 4 mm sieve and were retained in a 2 mm sieve. From each soil type, four bags of aggregates weighting 1 kg were taken, received a second application of the same levels of the polymer diluted in the irrigation water, adjusting the moisture of the samples of aggregates to 80% of the field capacity. The plastic bags with the humid samples were weighted and closed to keep the moisture uniform. Three subsamples from each bag were taken every 30 days to determine the weighed mean diameter (WMD) of the aggregates up to 150 days. After washing the soil with distilled water, WMD of the aggregates was reduced in the two soil types, in different proportions. The highest levels caused a lower reduction on the stability grade, showing the role of the polymer on protection of the aggregates against disintegration. After 30 days of the second application of the polymer on washed aggregates, WMD started to increase differently for all the treatments, showing is effect on increasing structural stability of the soils

Susceptibility of Alphitobius diaperinus (Panzer) (Coleoptera, Tenebrionidae) to cypermethrin, dichlorvos and triflumuron in southern Brazil.

Susceptibility of Alphitobius diaperinus (Panzer) (Coleoptera, Tenebrionidae) to cypermethrin, dichlorvos and triflumuron in southern Brazil. The lesser mealworm, Alphitobius diaperinus (Panzer), is an important insect pest in poultry houses in Brazil. Susceptibility of the lesser mealworm collected from eight poultry houses in Paraná state, southern Brazil, was evaluated for cypermethrin, dichlorvos and triflumuron. Adult A. diaperinus were tested in bioassays with cypermethrin and dichlorvos. Larvae were fed rabbit feed wetted with a triflumuron-water solution. Concentration-mortality regressions were estimated using Probit analysis and resistance ratios were calculated based on the susceptible population. Among the field populations evaluated, cypermethrin LC50 values for adults, ranged from 68.1 to 6,263 ng (AI)/cm2. LC50 values for adults challenged with dichlorvos ranged from 10.3 to 1,385 ng (AI)/cm2. One population from Pato Branco showed reduced susceptibility to triflumuron (LC50 = 272 ?g (AI)/ml of solution) when compared to the most susceptible population (LC50 = 109.8 ?g (AI)/ml). Application of cypermethrin and dichlorvos analogues should be managed with caution to minimize insecticide resistance problems. Suscetibilidade de Alphitobius diaperinus (Panzer) (Coleoptera, Tenebrionidae) a cipermetrina, diclorvós e triflumurom no sul do Brasil. O cascudinho, Alphitobius diaperinus (Panzer), é uma importante praga em aviários no Brasil. A suscetibilidade do cascudinho à cipermetrina, diclorvós e triflumurom foi avaliada em oito aviários do Estado do Paraná, Brasil. Adultos de A. diaperinus foram testados mediante bioensaios com cipermetrina e diclorvós. As larvas foram alimentadas com ração para coelhos impregnada com suspensões de triflumurom. As regressões de concentração-mortalidade foram estimadas usando análise de Probit e as razões de resistência calculadas com base na população suscetível. Entre as populações de campo avaliadas, os valores da CL50 para adultos tratados com cipermetrina variaram entre 68,1 to 6.263 ng (IA)/cm2. Os valores da CL50 para adultos tratados com diclorvós variaram de 10,3 to 1.385 ng (IA)/cm2. Uma população de Pato Branco apresentou reduzida suscetibilidade ao triflumurom (CL50 = 272 ?g (IA)/ml), quando comparada à população mais suscetível (CL50 = 109,8 ?g (IA)/ml de solução). Cipermetrina, diclorvós e análogos devem ser manejados e aplicados com cautela para minimizar os problemas de resistência a inseticidas

Factors controlling spatio-temporal variation in carbon dioxide efflux from surface litter, roots, and soil organic matter at four rain forest sites in the eastern Amazon

[1] This study explored biotic and abiotic causes for spatio-temporal variation in soil respiration from surface litter, roots, and soil organic matter over one year at four rain forest sites with different vegetation structures and soil types in the eastern Amazon, Brazil. Estimated mean annual soil respiration varied between 13-17 t C ha(-1) yr(-1), which was partitioned into 0-2 t C ha(-1) yr(-1) from litter, 6-9 t C ha(-1) yr(-1) from roots, and 5-6 t C ha(-1) yr(-1) from soil organic matter. Litter contribution showed no clear seasonal change, though experimental precipitation exclusion over a one-hectare area was associated with a ten-fold reduction in litter respiration relative to unmodified sites. The estimated mean contribution of soil organic matter respiration fell from 49% during the wet season to 32% in the dry season, while root respiration contribution increased from 42% in the wet season to 61% during the dry season. Spatial variation in respiration from soil, litter, roots, and soil organic matter was not explained by volumetric soil moisture or temperature. Instead, spatial heterogeneity in litter and root mass accounted for 44% of observed spatial variation in soil respiration (p < 0.001). In particular, variation in litter respiration per unit mass and root mass accounted for much of the observed variation in respiration from litter and roots, respectively, and hence total soil respiration. This information about patterns of, and underlying controls on, respiration from different soil components should assist attempts to accurately model soil carbon dioxide fluxes over space and time

Effect of extrusion-cooking in total carotenoids content in cream and orange flesh sweet potato cultivars.

Sweet potato (Ipomoea batatas) is a food crop that supplies energy, minerals and vitamins C and B. Some cultivars are very rich in carotenoids (pro-vitamin A). In this study were evaluated and compared the total carotenoids content of two cultivars and the losses on the dehydrated extruded sweet potato flour. Samples from organic and conventional crops were analyzed, in the form of fresh and dehydrated extruded samples. Total carotenoids content of the fresh product, expressed on wet basis, was of 437 µg 100 g-1 for the cream cultivar and 10,12 µg 100 g-1 for the orange cultivar. After dehydration, losses of total carotenoids were of 41% and 38%, respectively. The fresh orange cultivar presented high total carotenoids content in comparison to the cream cultivar. The extruded orange sweet potato flour showed the lowest losses in total carotenoids. Therefore, the processed flour of orange sweet potato could be used to obtain pre-gelatinized extruded flour with high total carotenoids content.A batata-doce (Ipomoea batatas) é um alimento fonte rico em energia, minerais, vitaminas C e B. Algumas cultivares são ricas em pró-vitamina A. O objetivo do presente trabalho foi avaliar e comparar o conteúdo de carotenóides totais em duas cultivares de batata-doce e determinar suas perdas na obtenção da farinha desidratada e processada por extrusão. Foram analisadas amostras de sistema de cultivo orgânico e convencional, tanto as frescas como as extrusadas desidratadas. O conteúdo de carotenóides totais do produto fresco, expressos em base úmida, foi de 437 µg 100 g-1 para a cultivar creme e de 10,120 µg 100g-1 para a cultivar alaranjada. Após o processo de desidratação das amostras, as perdas de carotenóides totais foram de 41% para a batata-doce creme e 38% para a alaranjada, respectivamente. Os resultados indicaram alto conteúdo de carotenóides totais para a cultivar alaranjada fresca, quando comparado com a cultivar creme. A amostra de farinha de batata-doce extrusada apresentou menor perda de carotenóides totais. Desta forma, verifica-se que a farinha de batata-doce alaranjada pode ser utilizada na obtenção de uma farinha pré-gelatinizada com alto conteúdo de carotenóides totais

On composite systems of dilute and dense couplings

Composite systems, where couplings are of two types, a combination of strong dilute and weak dense couplings of Ising spins, are examined through the replica method. The dilute and dense parts are considered to have independent canonical disordered or uniform bond distributions; mixing the models by variation of a parameter $\gamma$ alongside inverse temperature $\beta$ we analyse the respective thermodynamic solutions. We describe the variation in high temperature transitions as mixing occurs; in the vicinity of these transitions we exactly analyse the competing effects of the dense and sparse models. By using the replica symmetric ansatz and population dynamics we described the low temperature behaviour of mixed systems.Comment: 35 pages, 9 figures, submitted to JPhys

Semiclassical Evolution of Dissipative Markovian Systems

A semiclassical approximation for an evolving density operator, driven by a "closed" hamiltonian operator and "open" markovian Lindblad operators, is obtained. The theory is based on the chord function, i.e. the Fourier transform of the Wigner function. It reduces to an exact solution of the Lindblad master equation if the hamiltonian operator is a quadratic function and the Lindblad operators are linear functions of positions and momenta. Initially, the semiclassical formulae for the case of hermitian Lindblad operators are reinterpreted in terms of a (real) double phase space, generated by an appropriate classical double Hamiltonian. An extra "open" term is added to the double Hamiltonian by the non-hermitian part of the Lindblad operators in the general case of dissipative markovian evolution. The particular case of generic hamiltonian operators, but linear dissipative Lindblad operators, is studied in more detail. A Liouville-type equivariance still holds for the corresponding classical evolution in double phase, but the centre subspace, which supports the Wigner function, is compressed, along with expansion of its conjugate subspace, which supports the chord function. Decoherence narrows the relevant region of double phase space to the neighborhood of a caustic for both the Wigner function and the chord function. This difficulty is avoided by a propagator in a mixed representation, so that a further "small-chord" approximation leads to a simple generalization of the quadratic theory for evolving Wigner functions.Comment: 33 pages - accepted to J. Phys.