Surface Impedance Determination via Numerical Resolution of the Inverse Helmholtz Problem

Assigning boundary conditions, such as acoustic impedance, to the frequency domain thermoviscous wave equations (TWE), derived from the linearized Navier-Stokes equations (LNSE) poses a Helmholtz problem, solution to which yields a discrete set of complex eigenfunctions and eigenvalue pairs. The proposed method -- the inverse Helmholtz solver (iHS) -- reverses such procedure by returning the value of acoustic impedance at one or more unknown impedance boundaries (IBs) of a given domain, via spatial integration of the TWE for a given real-valued frequency with assigned conditions on other boundaries. The iHS procedure is applied to a second-order spatial discretization of the TWEs on an unstructured staggered grid arrangement. Only the momentum equation is extended to the center of each IB face where pressure and velocity components are co-located and treated as unknowns. The iHS is finally closed via assignment of the surface gradient of pressure phase over the IBs, corresponding to assigning the shape of the acoustic waveform at the IB. The iHS procedure can be carried out independently for different frequencies, making it embarrassingly parallel, and able to return the complete broadband complex impedance distribution at the IBs in any desired frequency range to arbitrary numerical precision. The iHS approach is first validated against Rott's theory for viscous rectangular and circular ducts. The impedance of a toy porous cavity with a complex geometry is then reconstructed and validated with companion fully compressible unstructured Navier-Stokes simulations resolving the cavity geometry. Verification against one-dimensional impedance test tube calculations based on time-domain impedance boundary conditions (TDIBC) is also carried out. Finally, results from a preliminary analysis of a thermoacoustically unstable cavity are presented.Comment: As submitted to AIAA Aviation 201

Surmounting collectively oscillating bottlenecks

We study the collective escape dynamics of a chain of coupled, weakly damped nonlinear oscillators from a metastable state over a barrier when driven by a thermal heat bath in combination with a weak, globally acting periodic perturbation. Optimal parameter choices are identified that lead to a drastic enhancement of escape rates as compared to a pure noise-assisted situation. We elucidate the speed-up of escape in the driven Langevin dynamics by showing that the time-periodic external field in combination with the thermal fluctuations triggers an instability mechanism of the stationary homogeneous lattice state of the system. Perturbations of the latter provided by incoherent thermal fluctuations grow because of a parametric resonance, leading to the formation of spatially localized modes (LMs). Remarkably, the LMs persist in spite of continuously impacting thermal noise. The average escape time assumes a distinct minimum by either tuning the coupling strength and/or the driving frequency. This weak ac-driven assisted escape in turn implies a giant speed of the activation rate of such thermally driven coupled nonlinear oscillator chains

Ecological design of a crayfishing program to control population density of the invasive species Procambarus Clarkii in Doñana National Park freshwater marsh (Spain)

The exploitation of Procambarus clarkii in Doñana National Park’s freshwater marsh (DNP) has been economically important to the local human population since the 1970s. The high density of this crayfish species has been causing a major environmental impact in the Park by the substantial reduction of submerging aquatic macrophytes prairies due to its broad trophic spectrum and feeding habits, which turned the environmental frame (consisting in clear water equilibrium) into a turbid water balance. Differences in population dynamics of three population groups of P. clarkii in the DNP freshwater marsh were compared and analyzed from a fishery perspective. The objective is to reduce their ecological impact using optimal crayfishing management. Maximum growth curves showed that crayfish have different growth optimums. Recruitment of young crayfish varies between different populations; when there is an excessive increase in the density of juveniles in a population and conditions are stressful, their growth is deficient. If these conditions persist, the population could become stunted. Fishery for commercial gain is banned in DNP; however, a model of fisheries program aimed at controlling the excess population of crayfish can be effective in halting the ecological impact of this invasive species while providing an opportunity for poachers to have viable productive options. The model proposed can help to solve the problem of crayfish “poaching” through the legalization and strict control of harvesting practicesPedro J. Gutiérrez-Yurrita also thanks the ICI (Spain) for a subvention grant and CONACyT (México) for a financial complement of the former grant that enabled him to complete this researc

Mesoscopic scale modeling of concrete under triaxial loading using X-ray tomographic images

This paper focuses on the discrete modeling of triaxial behaviour of concrete. The originality of this work comes from two points. The first one concerns the predictive feature of the model developed for simulating the response of concrete specimens; the behaviour of mortar, rock, and their interaction being identified a priori or by means of experimental tests on the mortar and the rock. The second originality relates to the construction method of the discrete element assembly based on the 3D segmentation of tomographic images. Such a method allows modeling of concrete at the mesoscopic scale with an internal structure similar to the one of the concrete tested experimentally. The comparisons between numerical and experimental results show the model is capable to reproduce the triaxial behavior of concrete for confining pressure varying from 0 to 650 MPa

Evapotranspiration and CROP COEFFICIENTS of a Coffee Plantation in Southern Brazil.

Coffee plants have been cultivated in Brazil since 1727 and have a great importance for the economy of the country. Brazil has more than 2,400,000 ha of commercial plantations of coffee, and in the last 15 years they have been expanded to regions where drought is more intense and normally coincides with fruit expansion, what became irrigation very important and somewhat essential in such regions (Camargo, 1985). Currently, it is estimated that about 200,000 ha of coffee plantations are being grown under irrigation in the country. In spite of great advances in technologies for water supply and the economic importance of coffee crop, irrigation management have been made inadequately in the most Brazilian coffee regions due to the large amount of water applied, which normally exceeds the crop needs (Camargo, 2002). Regarding this point, Carr (2001) postulated that estimates of water requirements for irrigation purposes are still imprecise for this crop and, probably, subject to large errors depending on the local circumstances and the system of irrigation used. The objective of this study was to assess the water use by a drip-irrigated coffee plantation in Southern Brazil using different measurement techniques in order to determine the two components of crop coefficients (Kc), i.e. basal (Kcb) and evaporative (Kce) components. The study also evaluated the micrometeorological factors affecting transpiration, crop and reference evapotranspiration relationships and its implications on actual rates of water use and on irrigation management

An effective theory of accelerated expansion

We work out an effective theory of accelerated expansion to describe general phenomena of inflation and acceleration (dark energy) in the Universe. Our aim is to determine from theoretical grounds, in a physically-motivated and model independent way, which and how many (free) parameters are needed to broadly capture the physics of a theory describing cosmic acceleration. Our goal is to make as much as possible transparent the physical interpretation of the parameters describing the expansion. We show that, at leading order, there are five independent parameters, of which one can be constrained via general relativity tests. The other four parameters need to be determined by observing and measuring the cosmic expansion rate only, H(z). Therefore we suggest that future cosmology surveys focus on obtaining an accurate as possible measurement of $H(z)$ to constrain the nature of accelerated expansion (dark energy and/or inflation).Comment: In press; minor changes, results unchange

Processo de automação de planilhas para cálculo de balanço hídrico em escalas mensal, decendial e diária.

Um dos fatores essenciais para se conseguir uma máxima produção agrícola é a disponibilidade hídrica no solo, e em razão da sua relevância, foi necessária a criação de ferramentas para realizar o seu monitoramento. Uma destas ferramentas é o balanço hídrico climatológico que consiste na contabilidade de água no solo em um dado período, que pode ser realizado em diversas escalas mediante a disponibilidade dos dados necessários, que variam em função da escala e do método utilizado para cálculo da evapotranspiração potencial. Este trabalho propõe o aperfeiçoamento de planilhas para cálculo do balanço hídrico a fim de proporcionar maior rapidez, exatidão e confiabilidade nos resultados. Todos os cálculos são feitos utilizando-se macros, sendo necessário informar apenas dados de temperatura, precipitação, latitude e período referentes ao local para onde o balanço hídrico será calculado. As ferramentas desenvolvidas foram desenvolvidas para ambiente Windows e Linux, visto que foram implementadas duas versões distintas, para utilização nas ferramentas Microsoft Excel e LibreOffice. Adicionalmente, as planilhas foram divididas em função da temperatura para cálculo da evapotranspiração, esta divisão permite que o cálculo seja feito utilizando a temperatura média e a temperatura efetiva, que é resultado de uma fórmula, onde a exatidão da determinação da temperatura para ambientes superúmidos e áridos é maior em relação à temperatura média.CIIC 2012. No 12618

Balanço de energia e consumo hídrico em pomar de Lima Ácida "Tahiti".

O método da razão de Bowen foi utilizado para avaliar a partição da energia disponível em fluxos de calor latente e sensível, e estimar a evapotranspiração de um pomar irrigado em duas estações do ano: verão (úmido) e inverno (seco). Sensores construídos de acordo com o método do balanço de calor do caule foram empregados na determinação do fluxo de seiva de duas árvores do pomar, e a evapotranspiração de referência foi estimada de acordo com o FAO Irrigation and Drainage Paper 56. A disponibilidade de água no solo da entrelinha foi a principal causa da variação na partição da energia disponível, bem como nas relações entre a transpiração das plantas e evapotranspiração do pomar. No verão, a transpiração representou 41% do consumo hídrico do pomar, enquanto, no inverno, representou 93% do total da evapotranspiração, o que indica a possibilidade de se determinar a transpiração das plantas a partir de estimativas de evapotranspiração do pomar com métodos micrometeorológicos e, assim, tornar mais racional o manejo da irrigação em pomares. A relação entre a evapotranspiração de referência e a evapotranspiração do pomar foi de 0,44 no verão e de 0,27 no inverno, permitindo aplicação desses dados em outros pomares de citros

Internal Anisotropy of Collision Cascades

We investigate the internal anisotropy of collision cascades arising from the branching structure. We show that the global fractal dimension cannot give an adequate description of the geometrical structure of cascades because it is insensitive to the internal anisotropy. In order to give a more elaborate description we introduce an angular correlation function, which takes into account the direction of the local growth of the branches of the cascades. It is demonstrated that the angular correlation function gives a quantitative description of the directionality and the interrelation of branches. The power law decay of the angular correlation is evidenced and characterized by an exponent and an angular correlation length different from the radius of gyration. It is demonstrated that the overlapping of subcascades has a strong effect on the angular correlation.Comment: RevteX, 8 pages, 6 .eps figures include

Validação de marcadores moleculares microssatélites ligados ao gene Rps1-k de resistência à podridão radicular de fitóftora em soja.

O fungo Phytophthora sojae constitui uma das principais doenças que limitam a produtividade da soja. Com isso esse trabalho objetivou a validação de marcadores moleculares microssatélites ligados ao gene Rps1-k, que confere resistência a P. sojae, para serem utilizados no programa de seleção assistida ao melhoramento. Para identificar marcadores ligados ao gene que confere resistência a fitófora, uma população segregante F2 de 138 individuos foram produzidos a partir do cruzamento entre Williams82 (Rps1-k) e BRS133 (suscetível). Os resultados das análises fenotípicas apresentaram 108 individuos resistentes e 30 suscetíveis na geração F2, e o teste de qui-quadrado se ajustou de acordo com a proporção esperada de 3 resistentes: 1 suscetível, sugerindo que a herança de Rps1-k é controlada por um gene dominante de herança monogênica. Cinco marcadores microssatélites foram analisados como ligados ao gene Rps1-k, no cromossomo 3 da soja, sendo o marcador Satt641 posicionado o mais próximo do gene com distância genética de 6,4cM. Assim este marcador pode conferir uma importante estratégia na seleção de genótipos brasileiros de soja resistentes à podridão radicular por fitóftora