Modeling methods for high-fidelity rotorcraft flight mechanics simulation

The cooperative effort being carried out under the agreements of the United States-Israel Memorandum of Understanding is discussed. Two different models of the AH-64 Apache Helicopter, which may differ in their approach to modeling the main rotor, are presented. The first model, the Blade Element Model for the Apache (BEMAP), was developed at Ames Research Center, and is the only model of the Apache to employ a direct blade element approach to calculating the coupled flap-lag motion of the blades and the rotor force and moment. The second model was developed at the Technion-Israel Institute of Technology and uses an harmonic approach to analyze the rotor. The approach allows two different levels of approximation, ranging from the 'first harmonic' (similar to a tip-path-plane model) to 'complete high harmonics' (comparable to a blade element approach). The development of the two models is outlined and the two are compared using available flight test data

Solving Medium-Density Subset Sum Problems in Expected Polynomial Time: An Enumeration Approach

The subset sum problem (SSP) can be briefly stated as: given a target integer $E$ and a set $A$ containing $n$ positive integer $a_j$, find a subset of $A$ summing to $E$. The \textit{density} $d$ of an SSP instance is defined by the ratio of $n$ to $m$, where $m$ is the logarithm of the largest integer within $A$. Based on the structural and statistical properties of subset sums, we present an improved enumeration scheme for SSP, and implement it as a complete and exact algorithm (EnumPlus). The algorithm always equivalently reduces an instance to be low-density, and then solve it by enumeration. Through this approach, we show the possibility to design a sole algorithm that can efficiently solve arbitrary density instance in a uniform way. Furthermore, our algorithm has considerable performance advantage over previous algorithms. Firstly, it extends the density scope, in which SSP can be solved in expected polynomial time. Specifically, It solves SSP in expected $O(n\log{n})$ time when density $d \geq c\cdot \sqrt{n}/\log{n}$, while the previously best density scope is $d \geq c\cdot n/(\log{n})^{2}$. In addition, the overall expected time and space requirement in the average case are proven to be $O(n^5\log n)$ and $O(n^5)$ respectively. Secondly, in the worst case, it slightly improves the previously best time complexity of exact algorithms for SSP. Specifically, the worst-case time complexity of our algorithm is proved to be $O((n-6)2^{n/2}+n)$, while the previously best result is $O(n2^{n/2})$.Comment: 11 pages, 1 figur

Ternary Syndrome Decoding with Large Weight

The Syndrome Decoding problem is at the core of many code-based cryptosystems. In this paper, we study ternary Syndrome Decoding in large weight. This problem has been introduced in the Wave signature scheme but has never been thoroughly studied. We perform an algorithmic study of this problem which results in an update of the Wave parameters. On a more fundamental level, we show that ternary Syndrome Decoding with large weight is a really harder problem than the binary Syndrome Decoding problem, which could have several applications for the design of code-based cryptosystems

Relationship between Structure, Entropy and Diffusivity in Water and Water-like Liquids

Anomalous behaviour of the excess entropy ($S_e$) and the associated scaling relationship with diffusivity are compared in liquids with very different underlying interactions but similar water-like anomalies: water (SPC/E and TIP3P models), tetrahedral ionic melts (SiO$_2$ and BeF$_2$) and a fluid with core-softened, two-scale ramp (2SRP) interactions. We demonstrate the presence of an excess entropy anomaly in the two water models. Using length and energy scales appropriate for onset of anomalous behaviour, the density range of the excess entropy anomaly is shown to be much narrower in water than in ionic melts or the 2SRP fluid. While the reduced diffusivities ($D^*$) conform to the excess entropy scaling relation, $D^* =A\exp (\alpha S_e)$ for all the systems (Y. Rosenfeld, Phys. Rev. A {\bf 1977}, {\it 15}, 2545), the exponential scaling parameter, $\alpha$, shows a small isochore-dependence in the case of water. Replacing $S_e$ by pair correlation-based approximants accentuates the isochore-dependence of the diffusivity scaling. Isochores with similar diffusivity scaling parameters are shown to have the temperature dependence of the corresponding entropic contribution. The relationship between diffusivity, excess entropy and pair correlation approximants to the excess entropy are very similar in all the tetrahedral liquids.Comment: 24 pages, 4 figures, to be published in Journal of Physical Chemistry

A magnanimidade da teoria: interpretar a ética em teoria da literatura

Tese de doutoramento, Teoria da Literatura, Universidade de Lisboa, Faculdade de Letras, 2003Um dos pressupostos desta tese consiste na ideia segundo a qual o pensamento ético só adquire propriedade conceptual se preliminarmente pudermos definir ‘acção’. Como se procura demonstrar no capítulo I, saber o que é uma acção não se constitui, no entanto, como tarefa que descobre e estabelece propriedades intrínsecas e estáveis, mas como descrição de certas ocorrências, nos termos das pessoas que procuram explicar e descrever acções. Assim, o pensamento ético é algo que se constitui a partir da coerência e racionalidade de certas descrições de acções particulares e não um sistema de regras ou prescrições. Defende-se que a coerência estrutural destas descrições determina não apenas a consideração moral das acções, mas também a possibilidade do conhecimento entre as pessoas e a certeza, mais poética do que epistemológica, da sua existência. Se uma certa estabilidade do texto ético e uma certeza suficiente acerca do conhecimento humano dependem da configuração mais ou menos padronizada das acções humanas e do funcionamento mental, assumem especial relevância cognitiva e ética os casos e fenómenos de irracionalidade na realização de acções e formação de crenças. De facto, como se sugere no capítulo II, estes casos suscitam perplexidades éticas e cognitivas e assinalam o carácter provisório e conceptualmente circunscrito das nossas descrições sobre acções e pessoas, no contexto restrito do pensamento filosófico e ético. Importa por isso considerar outros textos em que a acção se constitui como motivo de estrutura argumentativa e objecto de análise. A consideração da tragédia e, sobretudo, a análise da teorização poética de Aristóteles acerca do texto trágico formam o capítulo III desta tese. A determinação ética da argumentação técnica da Poética é tão relevante para o entendimento da tragédia quanto, para a ética, conduta moral e compreensão da irracionalidade, é de absoluta pertinência uma particular descrição da acção trágica e da peculiaridade de certas actividades interpretativas exigidas não só por esse entendimento trágico de acção, mas por qualquer texto.ABSTRACT - One of the central ideas of this thesis is that ethical thinking acquires conceptual accuracy only when we can define ‘action’. As it is suggested in chapter I, to know what an action is is not, nevertheless, an activity which finds and establishes intrinsic and stable properties, but a description of some phenomena, in the vocabulary of those who seek to explain and to describe actions. Thus, ethical thinking is derived from the coherence and rationality of descriptions of particular actions and is not, therefore, a system of rules and prescriptions. It is argued that the structural coherence of these descriptions determines not only the moral apprehension of actions, but also the possibility of knowledge of persons and the assurance, more poetical than epistemological, of their existence. If a certain stability of the ethical text and a sufficient certainty about human knowledge depend on a more or less standard configuration of human actions and of mental functioning, then irrational episodes and phenomena in action and belief assume a particular cognitive and ethical relevance. As proposed in chapter II, these cases excite some ethical and cognitive perplexities and show the provisional and conceptually circumscribed character of our descriptions of actions and persons, in the strict realm of philosophy and ethics. It is necessary, therefore, to consider other texts in which action is constituted as the cause for the argumentative structure and object of analysis. The consideration of tragedy and, mostly, of the treatment of the tragic text in Aristotle’s Poetics constitutes an important part of this task and is sketched in chapter III. The ethical influence of the technical arguments of the Poetics is therefore relevant to the understanding of tragedy. A particular description of tragic action and of the specificity of interpretative activities is required not only by the understanding of action in tragedy as by the description of ethical patterns of moral behaviour and the comprehension of irrationality in any text.Fundação Calouste Gulbenkian: Bolsa de Curta Duraçã

Peptide:lipid ratio and membrane surface charge determine the mechanism of action of the antimicrobial peptide BP100. Conformational and functional studies

The cecropin-melittin hybrid antimicrobial peptide BP100 (H-KKLFKKILKYL-NH2) is selective for Gram-negative bacteria, negatively charged membranes, and weakly hemolytic. We studied BP100 conformational and functional properties upon interaction with large unilamellar vesicles, LUVs, and giant unilamellar vesicles, GUVs, containing variable proportions of phosphatidylcholine (PC) and negatively charged phosphatidylglycerol (PG). CD and NMR spectra showed that upon binding to PG-containing LUVs BP100 acquires a-helical conformation, the helix spanning residues 3-11. Theoretical analyses indicated that the helix is amphipathic and surface-seeking. CD and dynamic light scattering data evinced peptide and/or vesicle aggregation, modulated by peptide: lipid ratio and PG content. BP100 decreased the absolute value of the zeta potential () of LUVs with low PG contents; for higher PG, binding was analyzed as an ion-exchange process. At high salt, BP100-induced LUVS leakage requires higher peptide concentration, indicating that both electrostatic and hydrophobic interactions contribute to peptide binding. While a gradual release took place at low peptide:lipid ratios, instantaneous loss occurred at high ratios, suggesting vesicle disruption. Optical microscopy of GUVs confirmed BP100-promoted disruption of negatively charged membranes. the mechanism of action of BP100 is determined by both peptide:lipid ratio and negatively charged lipid content While gradual release results from membrane perturbation by a small number of peptide molecules giving rise to changes in acyl chain packing, lipid clustering (leading to membrane defects), and/or membrane thinning, membrane disruption results from a sequence of events large-scale peptide and lipid clustering, giving rise to peptide-lipid patches that eventually would leave the membrane in a carpet-like mechanism. (C) 2014 Elsevier B.V. All rights reserved.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Institut Nacional de Ciencia e Tecnologia de fluidos complexos (INCTFCx)Nude de Apoio Pesquisa de Fluidos Complexos (NAPFCx)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Univ São Paulo, Inst Chem, Dept Biochem, BR-05513970 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Biophys, BR-04044020 São Paulo, BrazilUniv Fed Rio de Janeiro, Inst Med Biochem, Nucl Magnet Resonance Natl Ctr, Rio de Janeiro, BrazilEmbrapa Recursos Genet & Biotecnol, BR-70770917 Brasilia, DF, BrazilUniversidade Federal de São Paulo, Dept Biophys, BR-04044020 São Paulo, BrazilFAPESP: 2007/50970-5FAPESP: 2013/08166-5Web of Scienc

Influence of Molecular Dipole Orientations on Long-Range Exponential Interaction Forces at Hydrophobic Contacts in Aqueous Solutions

Strong and particularly long ranged (>100 nm) interaction forces between apposing hydrophobic lipid monolayers are now well understood in terms of a partial turnover of mobile lipid patches, giving rise to a correlated long-range electrostatic attraction. Here we describe similarly strong long-ranged attractive forces between self-assembled monolayers of carboranethiols, with dipole moments aligned either parallel or perpendicular to the surface, and hydrophobic lipid monolayers deposited on mica. We compare the interaction forces measured at very different length scales using atomic force microscope and surface forces apparatus measurements. Both systems gave a long-ranged exponential attraction with a decay length of 2.0 +/- 0.2 nm for dipole alignments perpendicular to the surface. The effect of dipole alignment parallel to the surface is larger than for perpendicular dipoles, likely due to greater lateral correlation of in-plane surface dipoles. The magnitudes and range of the measured interaction forces also depend on the surface area of the probe used: At extended surfaces, dipole alignment parallel to the surface leads to a stronger attraction due to electrostatic correlations of freely rotating surface dipoles and charge patches on the apposing surfaces. In contrast, perpendicular dipoles at extended surfaces, where molecular rotation cannot lead to large dipole correlations, do not depend on the scale of the probe used. Our results may be important to a range of scale-dependent interaction phenomena related to solvent/water structuring on dipolar and hydrophobic surfaces at interfaces