Laser offset-frequency locking up to 20 GHz using a low-frequency electrical filter technique

A simple, easy-to-implement, and robust technique is reported to offset lock two semiconductor lasers with a frequency difference easily adjustable up to a couple of tens of gigahertz (10 and 19 GHz experimentally demonstrated). The proposed scheme essentially makes use of low-frequency control electronics and may be implemented with any type of single mode semiconductor laser, without any requirement for the laser linewidth. The technique is shown to be very similar to the wavelength modulation spectroscopy method commonly used for laser stabilization onto molecular absorption lines, as demonstrated by experimental results obtained using 935 nm laser diodes.     

Assessment of Design Formulas for In-Plane FRP Strengthening of Masonry Walls

Masonry structures have demonstrated their seismic vulnerability during recent world seismic events. This paper investigates in-plane seismic performance of unreinforced masonry (URM) walls before and after they are retrofit using fiber-reinforced polymer (FRP) materials. An assessment of available design formulas for evaluating both the in-plane performance of URM walls and the contribution of FRP strengthening systems was performed. Walls with two configurations of the FRP reinforcement have been analyzed: one based on FRP strips installed parallel to the mortar joints, the other characterized by FRP strips arranged along the diagonals of the wall. Based on shear–compression tests carried out on FRP-strengthened masonry walls available in the literature, a comparison between theoretical and experimental data is performed. A discussion about the FRP strains at failure of the walls is provided and values of effective FRP strains to be used for design purposes are proposed.     

Benzene exposure in a sample of population residing in a district of Florence, Italy

OBJECTIVE: Personal exposure to airborne benzene is influenced by various outdoor and indoor sources. The first aim of this study was to assess the benzene exposure of a sample of urban inhabitants living in an inner-city neighborhood of Florence, Italy, excluding exposure from active smoking. The secondary objective was to differentiate the personal exposures according to personal usage patterns of the vehicles. METHODS: A sample of 67 healthy non-smokers was monitored by passive samplers during two 4-weekday campaigns in winter and late spring. Simultaneously, benzene measurements were also taken for a subset of participants, inside and outside their houses. A 4-day time microenvironment activity diary was completed by each subject during each sampling period. Other relevant exposure data were collected by a questionnaire before the sampling. Additional data on urban ambient air benzene levels were also available from the public air quality network. The passive samplers, after automated thermal desorption, were analyzed by GC-FID. RESULTS: Benzene personal exposure levels averaged 6.9 (SD=2.1) and 2.3 (SD=0.7) microg/m(3) in winter and spring, respectively. Outdoor and indoor levels showed high correlation in winter and poor in spring. In winter the highest benzene personal exposure levels were for people traveling by more public transport, followed by users of only car and by users of only bus respectively. CONCLUSIONS: The time spent in-transport for work or leisure makes a major contribution to benzene exposure among Florentine non-smoking citizens. Indoor pollution and transportation means contribute significantly to individual exposure levels especially in winter season.     

Assessment of Eurocode-like design equations for the shear capacity of FRP RC members

Fibre reinforced polymer (FRP) bars represent an interesting alternative to conventional steel as internal reinforcement of reinforced concrete (RC) members where some properties such as durability, magnetic transparency, insulation, are of primary concern. The present paper focuses on the assessment of Eurocode-like design equations for the evaluation of the shear strength of FRP RC members, as proposed by the guidelines of the Italian Research Council CNR-DT 203 [CNR-DT 203/2006. Guide for the design and construction of concrete structures reinforced with fiber-reinforced polymer bars. National Research Council, Rome, Italy; 2006]. Both the concrete and the FRP stirrups contributions to shear are taken into account: the new equations derived with reference to Eurocode equations for shear of steel RC members are verified through comparison with the equations given by ACI, CSA and JSCE guidelines, considering a large database of members with and without shear reinforcement failed in shear.     

Invisible computing: automatically using the many bits of data we create

As we go about our work and our daily lives, we leave a trail of bits behind. Every electronic device we interact with can keep a record of our actions. Even the devices themselves can keep track of their location and radio interactions, even without user involvement. The challenge of invisible computing is to make this wealth of data useful. This paper presents two examples of what has come to be known as 'invisible computing', namely, devices recording, distilling and rendering these many bits of data without unduly taxing human users. The first example is focused on a work environment. Labscape automates the record keeping required of experimenters in a cell biology laboratory. The second example looks at more ad hoc interactions. RFID Ecosystem is a collection of radio-frequency identification (RFID) readers and databases that collect the sightings of passive RFID tags, attached to people and objects, as they move throughout a large building. It provides services such as people and object finding as well as diary keeping.     

On POD reduced models of tubular reactor with periodic regimes

The distributed model of a tubular reactor with recycle is reduced by approximating it first with a Continuous Stirred Tank Reactor (CSTR) cascade. Proper orthogonal decomposition (POD) with Galerkin projection is introduced to study oscillatory regimes. The dynamics of the resulting models is studied via numerical simulation, and solutions in the form of time series and phase plot diagrams are compared to those obtained for the original CSTR cascade model. Different methods to choose the minimum number of basis functions are compared and discussed. Solution diagrams built with POD models are compared with those from CSTR cascade, as a function of the Damköhler number. Features and limitations of POD models are discussed for different snapshot sampling policies and for different values of the Péclet number. Qualitative performance increases and quantitative performance decreases as samples from steady states are considered along with periodic solution samples. Performance becomes worse as the Péclet number increases.     

Misfolding and Amyloid Aggregation of Apomyoglobin

Apomyoglobin is an excellent example of a monomeric all α-helical globular protein whose folding pathway has been extensively studied and well characterized. Structural perturbation induced by denaturants or high temperature as well as amino acid substitution have been described to induce misfolding and, in some cases, aggregation. In this article, we review the molecular mechanism of the aggregation process through which a misfolded form of a mutated apomyoglobin aggregates at physiological pH and room temperature forming an amyloid fibril. The results are compared with data showing that either amyloid or aggregate formation occurs under particular denaturing conditions or upon cleavage of the residues corresponding to the C-terminal helix of apomyoglobin. The results are discussed in terms of the sequence regions that are more important than others in determining the amyloid aggregation process.     

Control of silver-polymer aggregation mechanism by primary particle spatial correlations in dynamic fractal-like geometry

Silver nanocrystals have been prepared by reacting silver nitrate with ascorbic acid in aqueous solution containing a low concentration of a commercial polynaphthalene sulfonate polymer (Daxad 19). Various crystalline morphologies have been obtained simply by tuning the reaction temperature. We have investigated the nanoparticle formation mechanism at three different temperatures by in situ and time resolved small angle X-ray scattering measurements. By modeling the scattering intensity with interacting spherical particles in a fractal-like polymer-Ag matrix, we found signatures of nucleation, growth and assembly of primary particles of about 15-20 nm. We observed how the time evolution of both spatial correlations between primary particles and the dynamic fractal geometry of the polymer-Ag matrix could influence and determine both the aggregation mechanism and the morphology of forming nanostructures in solution.     

Iron Chelates: Production Processes and Reaction Evolution Analysis

Nowadays, fertilization using synthetic chelates is the most common technique to address iron chlorosis, a disease that affects plant growth. Ethylenediamine-N,N'-bis(o-hydroxyphenyl) acetic acid (EDDHA) is among the most efficient iron chelating agents. To produce EDDHA, a reaction was performed using as reactants phenol, ethylenediamine, glyoxylic acid, and sodium hydroxide. To study the reaction kinetics, samples were withdrawn from the reactor during the reaction and the kinetics was quantified, evaluating the yield evolution during the reaction phase. This study was useful to optimize the reaction time. Then, a catalyst was added to the reaction mixture to analyze its effect on the reaction evolution. Comparing the reaction evolution of the non-catalyzed and the catalyzed reaction protocols, two main results have to be highlighted: the time to reach the final yield is lower than the one proposed in the literature and the used catalyst has a minimum effect on the reaction rate.     

From energy‐delay metrics to constraints on the design of digital circuits

In this paper, the adoption of general metrics of the energy‐delay tradeoff is investigated to achieve energy‐efficient design of digital CMOS very large‐scale integrated circuits. Indeed, as shown in a preliminary analysis on the performance of various commercial microprocessors, a wide range of EⁱD^j metrics is typically adopted. Physical interpretation and interesting properties for the designs minimizing EⁱD^j metrics are provided together with the adoption of the Logical Effort theory to define practical design constraints. Two design examples in a 65‐nm CMOS technology are also reported to exemplify the theoretical results. Copyright © 2011 John Wiley & Sons, Ltd.