Robustness margin for attitude control of a four rotor mini-rotorcraft: Case of study

In this paper we present new results to compute the robustness margin of an attitude control algorithm for a quad-rotor mini-rotorcraft known as X4-flyer. The maximum parametric uncertainty is calculated when multivariable PD controller is used to stabilize the attitude of the aerial vehicle. This work is based on the value set characterization approach of the mathematical model for the closed-loop control system, which is represented by an interval plant with time delay. The zero exclusion principle is used to compute the robustness margin of the closed-loop system. This approach transforms the original robust stability problem into simple problem of graphic inspection, where we only needed to verify if a graph on the complex plane does not contain the origin of the plane. Additionally, different experiments were made in order to validate theoretical results; these experimental results will be presented at the end of this work.     

创意设计“六诫律”

德国设计大师Dieter Rams在上世纪八十年代初期曾对其当时所出的现实环境深感忧虑，他形容设计行业仿佛是一个“充斥着奇异形状，色彩和噪音的让人无法理解的混沌世界”。而他始终在考虑着一个问题：“我的设计到底是不是好设计？”带着这个问题他开始重新审视自己和同时代设计师所走过的轨迹，在进行了大量的考察研究后，总结出了优秀设计的十大诫律。     

Testing a social-cognitive model of HIV transmission risk behaviors in HIV-infected MSM with and without depression.

Objective: Social-cognitive models have been used to explain health risk behaviors in numerous populations, including people with HIV. However, these models generally do not account for the influence of clinically significant psychological problems such as major depression. Design: This study examined whether a social-cognitive model would explain recent sexual transmission risk behavior among sexually active HIV-infected men who have sex with men (MSM) who meet or do not meet screening criteria for major depression. Main Outcome Measures: Participants (n = 403) completed self-report assessments of negative expectancy, social models, and self-efficacy (SE) related to condom use, as well as recent STRB and a screening measure for major depression. Multiple group modeling was used to examine whether condom use SE explained associations of negative expectancy and social models for condom use with recent STRB among participants who screened positive (n = 47) or negative (n = 356) for major depression. Results: The multiple group model fit the data well (χ2(36) = 30.55, p = .73; CFI = 1.00; RMSEA     

Further validation of a cigarette purchase task for assessing the relative reinforcing efficacy of nicotine in college smokers.

The authors sought to further validate a cigarette purchase task (CPT), a self-report analogue of a progressive-ratio operant schedule, for the assessment of the relative reinforcing efficacy (RRE) of nicotine in smokers. The measure was assessed in terms of its correspondence to typically observed operant behavior, convergent validity, and divergent validity. Participants were 33 individuals (58% male, age M = 19.30 years) who smoked at least weekly (M = 5.31 cigarettes/day) and underwent a single assessment session. Data from the CPT exhibited the predicted inverse relationship between consumption and price, the predicted relationship between consumption and expenditure, and a heterogeneous pattern of interrelationships among the indices of reinforcement. In addition, 2 indices from the measure, intensity of demand and maximum expenditure for cigarettes, exhibited robust convergent and divergent validity. Although this is an incipient research area and the current study used a relatively small sample, these findings support the validity of a CPT as a time- and cost-efficient method for assessing nicotine reinforcement. Theoretical implications of the findings, limitations, and future directions are also discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The quantum square well with moving boundaries: A numerical analysis

We present some numerical discussions concerning the infinite square well in one dimension with moving boundaries. Our results show that if the speed of displacement is small, objects of physical relevance like probability density, averaged position or mean value of the energy have a smooth behavior. On the contrary, if this speed becomes large, many irregularities arise, which has a difficult qualitative explanation. These irregularities manifest themselves as sharp bumps on the probability distribution or a chaotic shape on the averaged values of position and energy. None of these patterns is the result of numerical errors and, therefore, we conclude that an unknown and very nontrivial effect is produced at high speeds of the moving wall.     

Microbial spoilage of meats offered for retail sale in Mexico City

Causes of the food borne epidemics in Mexico City have usually been ascribed to poor handling and preparation of foods. In this work, presence of microorganisms indicative of contamination were analysed in meat sold in Mexico City's retail outlets. Enterobacteriaceae, psycorothrophs, mould and yeast, and mesophile counts, were evaluated in meat from five animal species (beef, sheep, chicken, rabbit and horse). pH, recorded as spoilage indicator, was not significantly different among days of storage nor animal species, conversely, water holding capacity was significantly higher for horse meat. Mesophiles, psychrothrophs and Enterobacteriaceae counts were above legal limits in beef after 5 days of storage at 4°C. This was not observed in rabbit nor chicken meat. Mould and yeast populations remained constant until day 4. Moulds are seldom a problem, whereas yeasts play an important role in the alteration of flavour characteristics. In general, horse had the highest initial microbial counts.     

From Molecular Machines to Stimuli-Responsive Materials

Artificial molecular machines are able to produce and exploit precise nanoscale actuations in response to chemical or physical triggers. Recent scientific efforts have been devoted to the integration, orientation, and interfacing of large assemblies of molecular machines in order to harness their collective actuations at larger length scale and up to the generation of macroscopic motions. Making use of such “hierarchical mechanics” represents a fundamentally new approach for the conception of stimuli-responsive materials. Furthermore, because some molecular machines can function as molecular motors—which are capable of cycling a unidirectional motion out of thermodynamic equilibrium and progressively increasing the work delivered to their environment—one can expect unique opportunities to design new kinds of mechanically active materials and devices capable of autonomous behavior when supplied by an external source of energy. Recently reported achievements are summarized, including the integration of molecular machines at surfaces and interfaces, in 3D self-assembled materials, as well as in liquid crystals and polymer materials. Their detailed functioning principles as well as their functional properties are discussed along with their potential applications in various domains such as sensing, drug delivery, electronics, optics, plasmonics, and mechanics.     

HCS: A New Local Search Strategy for Memetic Multiobjective Evolutionary Algorithms

In this paper, we propose and investigate a new local search strategy for multiobjective memetic algorithms. More precisely, we suggest a novel iterative search procedure, known as the Hill Climber with Sidestep (HCS), which is designed for the treatment of multiobjective optimization problems, and show further two possible ways to integrate the HCS into a given evolutionary strategy leading to new memetic (or hybrid) algorithms. The pecularity of the HCS is that it is intended to be capable both moving toward and along the (local) Pareto set depending on the distance of the current iterate toward this set. The local search procedure utilizes the geometry of the directional cones of such optimization problems and works with or without gradient information. Finally, we present some numerical results on some well-known benchmark problems, indicating the strength of the local search strategy as a standalone algorithm as well as its benefit when used within a MOEA. For the latter we use the state of the art algorithms Nondominated Sorting Genetic Algorithm-II and Strength Pareto Evolutionary Algorithm 2 as base MOEAs.      

Parallel modular exponentiation using load balancing without precomputation

The modular exponentiation operation of the current algorithms for asymmetric cryptography is the most expensive part in terms of computational cost. The RSA algorithm, for example, uses the modular exponentiation algorithm in encryption and decryption procedure. Thus, the overall performance of those asymmetric cryptosystems depends heavily on the performance of the specific algorithm used for modular exponentiation. This work proposes new parallel algorithms to perform this arithmetical operation and determines the optimal number of processors that yields the greatest speedup. The optimal number is obtained by balancing the processing load evenly among the processors. Practical implementations are also performed to evaluate the theoretical proposals.     

Progressive crushing of fiber-reinforced composite structural components of a Formula One racing car

The present paper describes an experimental and numerical investigation on energy absorbers for Formula One side impact and steering column impact. The crash tests are performed measuring the load-shortening diagram and the energy absorbed by the structure. A finite element model is then developed using the non-linear, explicit dynamic code LS-DYNA. To set up the numerical model, tubes crushing testing are conducted to determine the material failure modes and to characterise them with LS-DYNA. The results presented in this study show that the composite structural components of the investigated Formula One racing car possess high value of specific absorbed energy and crash load efficiency around 1.1. The finite element simulations accurately predict the overall shape, magnitude and pulse duration in all the types of impact as well as the deformation and failure of the structures. Comparing the numerical data of the specific absorbed energy to the experimental results, the differences are around 10%.