A simple frequency‐domain method for stress analysis of stall‐regulated wind turbines

A simple method, based in the frequency domain, was developed for calculating the dynamic response of a stall‐regulated wind turbine. Emphasis is placed on two aspects of the method, which are necessary in order to obtain a reasonable linearization of behavior when the blades are stalled. First, the tangential (in‐plane) component of turbulence is included, in addition to the axial component. Second, the linearized relationship between lift coefficient and angle‐of‐attack is adjusted to account for the effects of dynamic stall: separate linearizations are used for excitation and damping of vibration. A thorough comparison is made between linear and non‐linear dynamic‐stall methods, with the conclusion that the accuracy of the linear method depends upon the frequency and amplitude of oscillation. The linear dynamic‐stall method is accurate at blade vibrational frequencies, but it can be inaccurate at frequencies in the vicinity of 1P or below, when the angle‐of‐attack oscillates with an amplitude of 3° or more. Load spectra of a Nordtank 500 turbine, calculated using the frequency‐domain method, are compared with measurements. The frequency‐domain method provides estimates of load spectra and aerodynamic damping (stability) that are useful for preliminary design and optimization, but the method lacks sufficient accuracy and generality to be used for certification. Copyright © 2011 John Wiley & Sons, Ltd.     

Biodegradable Frequency‐Selective Magnesium Radio‐Frequency Microresonators for Transient Biomedical Implants

Bioresorbable implantable medical devices show a great potential for applications requiring medical care over well‐defined periods of time. Once their function is fulfilled, such implants naturally degrade and resorb in the body, which eliminates adverse long‐term effects or the need for a secondary surgery to extract the implanted device. Since biodegradable materials are water‐soluble, the fabrication of such transient electronic circuits and devices requires special care and needs to rely solely on dry processing steps without exposure to aqueous solutions. A further challenge is the in vivo powering of medical implants that are only constituted of biodegradable materials. This paper describes the design, fabrication, and testing of radio‐frequency biodegradable magnesium microresonators. To this end, an innovative microfabrication process with minimal exposure to aqueous media is developed to fabricate magnesium‐based, water‐soluble electronic components. It consists of a novel sequence of only three steps: one physical vapor deposition, one photolithography, and one ion beam etching step. The frequency‐selective wireless heating of different resonators is demonstrated. This represents a significant step toward their use as power receivers and microheaters in biodegradable implantable medical devices, for applications such as triggered drug release.     

A Threat Analysis of Human Bond Communications

In this paper we provide a high-level threat analysis of Human Bond Communications, using the STRIDE methodology. To this end, we provide an overview over Human Bond Communications and define a sample set of cases. The Human Bond Communications cases are such that the threats literally may be existential by nature. We also outline the STRIDE threat analysis methodology, and apply it to the sample set of cases previously defined. The threat analysis is carried out at a high abstraction level to highlight the major threats.

     

Benefits of Residual Aluminum in Ductile Iron

Two main chemistry systems of micro-inclusions can be identified in ductile iron: Ca-S-X and Mg-Si-O-X with the majority of the inclusions regardless of treatment type and location being of the second type, silicates. Laboratory investigations have shown that simple silicates were present in the matrix, while more complex silicates were present in conjunction with graphite, probably acting as graphite nucleation sites. In these more complex silicates, elevated levels of Al, Ca, Ce and La were typical. Comparing micro-particles embedded in iron matrix and graphite nodules of iron treated with pure Mg-metal and iron treated with MgFeSi alloy showed a higher amount of complex silicates with elevated Al-levels in the iron treated with MgFeSi. Further laboratory investigation was undertaken to explore which source of Al and which range of residual Al would have a favorable impact on the graphite nucleation in ductile iron. The work showed that a residual aluminum of 0.005 to 0.020 wt.% appears to be beneficial for improving ductile iron solidification characteristics without the incidence of pinholes. Greatest benefits were achieved when introducing the Al into the iron via an inoculant late during processing or via a pre-conditioner to the base iron. Al added via the MgFeSi provided less benefit. Some case studies illustrating the effect of Al in ductile iron are also presented, as Al-containing pre-conditioner or/and Al-bearing, FeSi inoculant application.     

An investigation of late closure: The role of syntax, thematic structure, and pragmatics in initial interpretation.

Four reading-time experiments investigated the application of the late closure principle in Italian. The experiments tested the principle governing the initial attachment of different types of modifiers (relative clause, adjectival phrase, and prepositional phrase) to a complex noun phrase. By manipulating the type of preposition within the complex noun phrase, the authors investigated the role of the thematic structure in initial and final parsing. The results show that the late closure principle applies to initial parsing in Italian without being affected by the thematic structure of the complex noun phrase. Final interpretation, however, shows an effect of pragmatic preference and an effect of thematic structure on syntactic revisions. The results are discussed in terms of a parsing model that adopts syntactic parsing strategies and makes modular use of linguistic information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The slave of the passions: Experiencing problems and selecting solutions.

This article argues that problem solving is motivated by feelings. The proposition is made that a person will experience a problem and engage in problem solving only if the person is in a state that feels aversive or if a mentally represented state becomes a goal by eliciting feelings more pleasurable than those that currently dominate. When people solve problems, the criteria they use in evaluating alternative solutions cannot in themselves motivate the choosing at an alternative. On evaluation, each alternative elicits a feeling that can be placed somewhere on a hedonic continuum. Whether rational or irrational, and even if the problem solver regards another alternative as correct, the alternative that produces the best feeling will always be selected as the solution to the problem. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optimization of Formulation Variables to Increase Antigen Entrapment in PLGA Particles

Efficient antigen entrapment is a key factor in preparation of poly (lactide-co-glycolide) acid (PLGA) vaccine formulations when the antigen is of short supply. This study presents a systematic approach in the testing of formulation variables with the objective to increase antigen entrapment in particles when the antigen stock concentration was low. Some of the experimental variables tested were poly (vinyl) alcohol (PVA) concentration in the inner (W₁) and outer (W₂) aqueous phase, W₁/oil (O) phase ratio and choice of organic solvent. The double emulsion solvent evaporation technique was applied to prepare PLGA particles with sonication as the emulsifying force. To measure antigen entrapment efficiency, the antigen (bovine serum albumin, BSA) was isotope labeled with ¹²⁵iodine (¹²⁵I). Our results demonstrated that a low PVA concentration in the inner aqueous (W₁) phase was beneficial to achieve a high encapsulation efficiency of antigen. On the contrary, in the outer aqueous (W₂) phase, a high PVA concentration favored antigen entrapment. We also demonstrated that decreasing the W₁ to O/polymer ratio contributed to increased entrapment efficiency. Testing different organic solvents (ethyl acetate, dichloromethane and chloroform), either alone or in combination, revealed that using chloroform as solvent resulted in the highest encapsulation of antigen and the highest production yield. Some of the results presented in this work are in disagreement with well-established formulation variables from previous studies.     

The alpha-to-beta conformational transition of Alzheimer's Abeta-(1-42) peptide in aqueous media is reversible: a step by step conformational analysis suggests the location of beta conformation seeding

Current views of the role of beta-amyloid (Abeta) peptide fibrils range from regarding them as the cause of Alzheimer's pathology to having a protective function. In the last few years, it has also been suggested that soluble oligomers might be the most important toxic species. In all cases, the study of the conformational properties of Abeta peptides in soluble form constitutes a basic approach to the design of molecules with "antiamyloid" activity. We have experimentally investigated the conformational path that can lead the Abeta-(1-42) peptide from the native state, which is represented by an alpha helix embedded in the membrane, to the final state in the amyloid fibrils, which is characterized by beta-sheet structures. The conformational steps were monitored by using CD and NMR spectroscopy in media of varying polarities. This was achieved by changing the composition of water and hexafluoroisopropanol (HFIP). In the presence of HFIP, beta conformations can be observed in solutions that have very high water content (up to 99 % water; v/v). These can be turned back to alpha helices simply by adding the appropriate amount of HFIP. The transition of Abeta-(1-42) from alpha to beta conformations occurs when the amount of water is higher than 80 % (v/v). The NMR structure solved in HFIP/H2O with high water content showed that, on going from very apolar to polar environments, the long N-terminal helix is essentially retained, whereas the shorter C-terminal helix is lost. The complete conformational path was investigated in detail with the aid of molecular-dynamics simulations in explicit solvent, which led to the localization of residues that might seed beta conformations. The structures obtained might help to find regions that are more affected by environmental conditions in vivo. This could in turn aid the design of molecules able to inhibit fibril deposition or revert oligomerization processes.     

浅议高层办公建筑的发展

当今高层办公建筑挣脱了20世纪50～60年代“方盒子”的束缚,走向了丰富多变的平面及形体设计时期。转向关注节能设计、创造多元的人性化公共空间及舒适的办公环境,成为设计的目标。