Sparse solutions of linear Diophantine equations

We present structural results on solutions to the Diophantine system $A{\boldsymbol y} = {\boldsymbol b}$, ${\boldsymbol y} \in \mathbb Z^t_{\ge 0}$ with the smallest number of non-zero entries. Our tools are algebraic and number theoretic in nature and include Siegel's Lemma, generating functions, and commutative algebra. These results have some interesting consequences in discrete optimization

The Support of Integer Optimal Solutions

The support of a vector is the number of nonzero-components. We show that given an integral $m\times n$ matrix $A$, the integer linear optimization problem $\max\left\{\boldsymbol{c}^T\boldsymbol{x} : A\boldsymbol{x} = \boldsymbol{b}, \, \boldsymbol{x}\ge\boldsymbol{0}, \,\boldsymbol{x}\in\mathbb{Z}^n\right\}$ has an optimal solution whose support is bounded by $2m \, \log (2 \sqrt{m} \| A \|_\infty)$, where $\| A \|_\infty$ is the largest absolute value of an entry of $A$. Compared to previous bounds, the one presented here is independent on the objective function. We furthermore provide a nearly matching asymptotic lower bound on the support of optimal solutions

Was hätte man sonst machen können? Alternativszenarien zur rot-grünen Einkommensteuerreform

We employ a rich sample of individual tax returns data to simulate alternatives to the income tax reform introduced in Germany by the governmental coalition of Social Democrats and Greens in 1998. We characterize three reforms that would have been fiscally equivalent to the actual one: a distributionally neutral tax reform, one with a maximal basic allowance, and a flat tax. By comparing the individual tax burdens under each alternative, we simulate majority voting on the tax reform. The actual reform loses against both the distributionally neutral reform and the one with maximal basic allowance; however, it wins against the flat tax. The Condorcet winner turns out to be the reform with maximal basic allowance. --

Implementation and Assessment of a Tele-Dermatology Strategy for Identification and Treatment of Skin Lesions in Elderly People

Introduction: The world’s population is living longer which is resulting in a higher incidence of pressure ulcers. Objectives: (1) To describe the implementation of a teledermatology strategy to identify and treat skin lesions in institutionalised elderly patients; (2) To evaluate the established teledermatology strategy. Method: This study was carried out in a geriatric home (AMP) in Brazil, and included: (1) Implementation of a teledermatology method;  (2) Evaluation of the strategy through: a) professional knowledge assessment, b) professional satisfaction, c) clinical aspects evaluation. Results: (1) The team consisted of a remote consulting team, local care team, dermatologist and infectologist. Digital records of skin lesions and weekly monitoring was implemented and was standardised using the iPhone 5’s camera coupled with a dermatoscope in cases of minor lesions. Data were stored in the cloud using FotoFinder HubⓇ. (2) Professionals' knowledge (n=24): age 34.6±7.3 years; 16 responded to the post-test and there was no difference between the 2 tests (86.8± 7.1 and 84.5±9.5, P=0.38). Professional satisfaction (n=17): 16 (94.2%) showed interest in indicating this type of assistance modality to another professional. Clinical aspects’ evaluation: hypertension had the highest prevalence, 9 (50%). Pressure ulcers were identified in 18 patients (83.3%), the heels, 7 cases, were the most affected area (39%). Healing Process: 4 lesions (22.2%) took over 3 months to complete the re-epithelialisation and 6 patients (33.3%) died before the end of treatment. Conclusion: The proposed teledermatology strategy has resulted in better assistance for elderly patients

Effective Maxwell's equations in general periodic microstructures

We study the time harmonic Maxwell equations in a meta-material consisting of perfect conductors and void space. The meta-material is assumed to be periodic with period $\eta > 0$; we study the behaviour of solutions $(E^{\eta}, H^{\eta})$ in the limit $\eta \to 0$ and derive an effective system. In geometries with a non-trivial topology, the limit system implies that certain components of the effective fields vanish. We identify the corresponding effective system and can predict, from topological properties of the meta-material, whether or not it permits the propagation of waves

Role of Correlation and Exchange for Quasi-particle Spectra of Magnetic and Diluted Magnetic Semiconductors

Theoretical foundation and application of the generalized spin-fermion (sp-d) exchange lattice model to magnetic and diluted magnetic semiconductors are discussed. The capabilities of the model to describe spin quasi-particle spectra are investigated. The main emphasis is made on the dynamic behavior of two interacting subsystems, the localized spins and spin density of itinerant carriers. A nonperturbative many-body approach, the Irreducible Green Functions (IGF) method, is used to describe the quasi-particle dynamics. Scattering states are investigated and three branches of magnetic excitations are calculated in the regime, characteristic of a magnetic semiconductor. For a simplified version of the model (Kondo lattice model) we study the spectra of quasi-particle excitations with special attention given to diluted magnetic semiconductors. For this, to include the effects of disorder, modified mean fields are determined self-consistently. The role of the Coulomb correlation and exchange is clarified by comparing of both the cases.Comment: 34 page

Ética, vida e conhecimento

Transcrição do evento temas em debate 24 de agosto de 2012

Kafka e Josefina ou: a solidão da singularidade

O texto tem como objetivo avançar na direção de uma interpretação mais ampla da última grande obra de Kafka, “Josefina a cantora ou O povo dos camundongos”, nosentido de compreender a posição de Josefina na narrativa não apenas como prototípica em relação ao artista ou escritor na solidão do exercício de seu métier, mas, muito mais, como uma lógica da narratividade da solitária singularidade do intelectual como tal