Formal Reasoning Using an Iterative Approach with an Integrated Web IDE

This paper summarizes our experience in communicating the elements of reasoning about correctness, and the central role of formal specifications in reasoning about modular, component-based software using a language and an integrated Web IDE designed for the purpose. Our experience in using such an IDE, supported by a 'push-button' verifying compiler in a classroom setting, reveals the highly iterative process learners use to arrive at suitably specified, automatically provable code. We explain how the IDE facilitates reasoning at each step of this process by providing human readable verification conditions (VCs) and feedback from an integrated prover that clearly indicates unprovable VCs to help identify obstacles to completing proofs. The paper discusses the IDE's usage in verified software development using several examples drawn from actual classroom lectures and student assignments to illustrate principles of design-by-contract and the iterative process of creating and subsequently refining assertions, such as loop invariants in object-based code.Comment: In Proceedings F-IDE 2015, arXiv:1508.0338

Packing Fractions and Maximum Angles of Stability of Granular Materials

In two-dimensional rotating drum experiments, we find two separate influences of the packing fraction of a granular heap on its stability. For a fixed grain shape, the stability increases with packing fraction. However, in determining the relative stability of different grain shapes, those with the lowest average packing fractions tend to form the most stable heaps. We also show that only the configuration close to the surface of the pile figures prominently.Comment: 4 pages, 4 figure

Modeling Physiological Processes That Relate Toxicant Exposure and Bacterial Population Dynamics

Quantifying effects of toxicant exposure on metabolic processes is crucial to predicting microbial growth patterns in different environments. Mechanistic models, such as those based on Dynamic Energy Budget (DEB) theory, can link physiological processes to microbial growth. Here we expand the DEB framework to include explicit consideration of the role of reactive oxygen species (ROS). Extensions considered are: (i) additional terms in the equation for the ‘‘hazard rate’’ that quantifies mortality risk ; (ii) a variable representing environmental degradation ; (iii) a mechanistic description of toxic effects linked to increase in ROS production and aging acceleration, and to non-competitive inhibition of transport channels ; (iv) a new representation of the ‘‘lag time’’ based on energy required for acclimation. We estimate model parameters using calibrated Pseudomonas aeruginosa optical density growth data for seven levels of cadmium exposure. The model reproduces growth patterns for all treatments with a single common parameter set, and bacterial growth for treatments of up to 150 mg(Cd)/L can be predicted reasonably well using parameters estimated from cadmium treatments of 20 mg(Cd)/L and lower. Our approach is an important step towards connecting levels of biological organization in ecotoxicology. The presented model reveals possible connections between processes that are not obvious from purely empirical considerations, enables validation and hypothesis testing by creating testable predictions, and identifies research required to further develop the theory

AVALIAÇÃO DA RELAÇÃO DA QUALIDADE MICROBIOLOGICA DA AGUA DE CONSUMO NO MUNICIPIO DE SANTA CECÍLIA E DOENÇAS VEICULADAS POR AGUA CONTAMINADA

O presente estudo avaliou a relação entre a qualidade microbiológica da água da rede de abastecimento para o consumo humano do município de Santa Cecília e as doenças veiculadas por eventual contaminação. Foram analisadas vinte amostras de água, coletadas diretamente da rede de distribuição em cinco bairros com diferentes condições sócio-econômicas, em períodos alternados. Estas amostras foram coletadas em trabalho conjunto com a Vigilância Sanitária sendo após, encaminhadas para análise de cloro residual, pH, características organolépticas, físico-químicas e microbiológicas. No período da primeira coleta foram registrados, 80 casos de diarréia. As primeiras amostras de água coletadas no presente estudo foram na segunda semana do mês sendo que a amostra do Bairro Vila Nova apresentou contaminação significativa por E.coli com presença em 100 mL, período no qual foi registrado o maior número de casos de diarréia (26). Na segunda coleta, o número de casos de diarréia foi de 222, sendo a maioria na primeira semana deste (79). As amostras apresentaram coliformes totais em 100 mL de amostra no Bairro Vila Nova, exatamente na semana em que foi registrado o maior número de doentes por diarréia. No terceiro ponto de coleta para estudo, foram registrados 136 casos de diarréia. As amostras coletadas neste mês foram na segunda semana, sendo que nos Bairros Vila Nova e Guilherme Rauen, as mesmas apresentaram coliformes totais em 100 mL de amostra, e nesta foram registrados 37 casos, embora na terceira e quarta semanas, este número de casos foi semelhante. Nas últimas coletas para estudo, foram notificados 79 casos. As coletas de água para análise deste intervalo foram na terceira semana, a qual teve um maior número de casos (27), sendo detectada presença de coliformes totais em 100 mL de amostra no Bairro Guilherme Rauen. Embora os dados aqui apresentados demonstrem ser possível a relação de um maior número de casos em períodos onde foram detectados coliformes fecais e ou totais, para afirmar a relação entre o aparecimento de coliformes e doenças diarréicas veiculadas pela água em determinados períodos, é necessário obter mais dados e estudos como coleta nos diversos pontos semana a semana, estabelecimento do bairro onde ocorreu a notificação da diarréia, e se possível, a causa da mesma (veiculada por água, alimentos ou outras causas). O que pode ser realizado com este estudo é repassar aos setores de Vigilância Sanitária e Epidemiológica estes dados obtidos e a sua discussão, a fim de determinar estratégias para melhorar a obtenção de estatísticas, pois isto auxilia enormemente no conhecimento dos locais de maior ocorrência de doenças e estabelecimento de suas causas

Conformally coupled dark matter

Dark matter is obtained from a scalar field coupled conformally to gravitation; the scalar being a relict of Dirac's gauge function. This conformally coupled dark matter includes a gas of very light ($m\approx 2.25\times 10^{-34} eV$) neutral bosons having spin 0, as well as a time-dependent global scalar field, both pervading all of the cosmic space. The time-development of this dark matter in the expanding F-R-W universe is investigated, and an acceptable cosmological behaviour is obtained.Comment: LaTEX File 10 pages, no figure

On the exciton binding energy in a quantum well

We consider a model describing the one-dimensional confinement of an exciton in a symmetrical, rectangular quantum-well structure and derive upper and lower bounds for the binding energy $E_b$ of the exciton. Based on these bounds, we study the dependence of $E_b$ on the width of the confining potential with a higher accuracy than previous reports. For an infinitely deep potential the binding energy varies as expected from $1 Ry$ at large widths to $4 Ry$ at small widths. For a finite potential, but without consideration of a mass mismatch or a dielectric mismatch, we substantiate earlier results that the binding energy approaches the value $1 Ry$ for both small and large widths, having a characteristic peak for some intermediate size of the slab. Taking the mismatch into account, this result will in general no longer be true. For the specific case of a $Ga_{1-x}Al_{x}As/GaAs/Ga_{1-x}Al_{x}As$ quantum-well structure, however, and in contrast to previous findings, the peak structure is shown to survive.Comment: 32 pages, ReVTeX, including 9 figure

Two-phase behavior in strained thin films of hole-doped manganites

We present a study of the effect of biaxial strain on the electrical and magnetic properties of thin films of manganites. We observe that manganite films grown under biaxial compressive strain exhibit island growth morphology which leads to a non-uniform distribution of the strain. Transport and magnetic properties of these films suggest the coexistence of two different phases, a metallic ferromagnet and an insulating antiferromagnet. We suggest that the high strain regions are insulating while the low strain regions are metallic. In such non-uniformly strained samples, we observe a large magnetoresistance and a field-induced insulator to metal transition.Comment: 5 pages ReVTeX, 5 figures included, Figures 3, 4 and 5 low resolution, high resolution figures available on request from authors, submitted to Phys. Rev.