Formation mechanism of levoglucosan and formaldehyde during cellulose pyrolysis

Biomass pyrolysis is an efficient way to transform raw biomass or organic waste materials into useable energy, including liquid, solid, and gaseous materials. Levoglucosan (1,6-anhydro-β-d-glucopyranose) and formaldehyde are two important products in biomass pyrolysis. The formation mechanism of these two products was investigated using the density functional theory (DFT) method based on quantum mechanics. It was found that active anhydroglucose can be obtained from a cellulose homolytic reaction during high-temperature steam gasification of the biomass process. Anhydroglucose undergoes a hydrogen-donor reaction and forms an intermediate, which can transform into the products via three pathways, one (path 1) for the formation of levoglucosan and two (paths 2 and 3) for formaldehyde. A total of six elementary reactions are involved. At a pressure of 1 atm, levoglucosan can be formed at all of the temperatures (450-750 K) considered in this simulation, whereas formaldehyde can be formed only when the temperature is higher than 475 K. Moreover, the energy barrier of levoglucosan formation is lower than that of formaldehyde, which is in agreement with the mechanism proposed in the experiments. © 2011 American Chemical Society.

Broadband XUV polarimetry of high harmonics from plasma surfaces using multiple Fresnel reflections

High-harmonic generation (HHG) by nonlinear interaction of intense laser pulses with gases or plasma surfaces is the most prominent way of creating highly coherent extreme ultraviolet (EUV/XUV) pulses. In the last years, several scientific applications have been found which require the measurement of the polarization of the harmonic radiation. We present a broadband XUV polarimeter based on multiple Fresnel reflections providing an extinction rate of 5-25 for 17-45 nm which is particularly suited for surface harmonics. The device has first been tested at a gas harmonic source providing linearly polarized XUV radiation. In a further experiment using HHG from plasma surfaces, the XUV polarimeter allowed a polarization measurement of high harmonic radiation from plasma surfaces for the first time which reveals a linear polarization state as predicted for our generation parameters. The generation and control of intense polarized XUV pulses-together with the availability of broadband polarizers in the XUV-open the way for a series of new experiments. For instance, dichroism in the XUV, elliptically polarized harmonics from aligned molecules, or the selection rules of relativistic surface harmonics can be studied with the broadband XUV polarimeter.

Bdellovibrio predation in the presence of decoys:Three-way bacterial interactions revealed by mathematical and experimental analyses

Bdellovibrio bacteriovorus is a small, gram-negative, motile bacterium that preys upon other gram-negative bacteria, including several known human pathogens. Its predation efficiency is usually studied in pure cultures containing solely B. bacteriovorus and a suitable prey. However, in natural environments, as well as in any possible biomedical uses as an antimicrobial, Bdellovibrio is predatory in the presence of diverse decoys, including live nonsusceptible bacteria, eukaryotic cells, and cell debris. Here we gathered and mathematically modeled data from three-member cultures containing predator, prey, and nonsusceptible bacterial decoys. Specifically, we studied the rate of predation of planktonic late-log-phase Escherichia coli S17-1 prey by B. bacteriovorus HD100, both in the presence and in the absence of Bacillus subtilis nonsporulating strain 671, which acted as a live bacterial decoy. Interestingly, we found that although addition of the live Bacillus decoy did decrease the rate of Bdellovibrio predation in liquid cultures, this addition also resulted in a partially compensatory enhancement of the availability of prey for predation. This effect resulted in a higher final yield of Bdellovibrio than would be predicted for a simple inert decoy. Our mathematical model accounts for both negative and positive effects of predator-prey-decoy interactions in the closed batch environment. In addition, it informs considerations for predator dosing in any future therapeutic applications and sheds some light on considerations for modeling the massively complex interactions of real mixed bacterial populations in nature.

Quantifying heritable variation in fitness-related traits of wild, farmed and hybrid Atlantic salmon families in a wild river environment

Farmed fish are typically genetically different from wild conspecifics. Escapees from fish farms may contribute one-way gene flow from farm to wild gene pools, which can depress population productivity, dilute local adaptations and disrupt coadapted gene complexes. Here, we reanalyse data from two experiments (McGinnity et al., 1997, 2003) where performance of Atlantic salmon (Salmo salar) progeny originating from experimental crosses between farm and wild parents (in three different cohorts) were measured in a natural stream under common garden conditions. Previous published analyses focussed on group-level differences but did not account for pedigree structure, as we do here using modern mixed-effect models. Offspring with one or two farm parents exhibited poorer survival in their first and second year of life compared with those with two wild parents and these group-level inferences were robust to excluding outlier families. Variation in performance among farm, hybrid and wild families was generally similar in magnitude. Farm offspring were generally larger at all life stages examined than wild offspring, but the differences were moderate (5–20%) and similar in magnitude in the wild versus hatchery environments. Quantitative genetic analyses conducted using a Bayesian framework revealed moderate heritability in juvenile fork length and mass and positive genetic correlations (>0.85) between these morphological traits. Our study confirms (using more rigorous statistical techniques) previous studies showing that offspring of wild fish invariably have higher fitness and contributes fresh insights into family-level variation in performance of farm, wild and hybrid Atlantic salmon families in the wild. It also adds to a small, but growing, number of studies that estimate key evolutionary parameters in wild salmonid populations. Such information is vital in modelling the impacts of introgression by escaped farm salmon.

The signature of fine scale local adaptation in Atlantic salmon revealed from common garden experiments in nature

Understanding the extent, scale and genetic basis of local adaptation is important for conservation and management. Its relevance in salmonids at microgeographic scales, where dispersal (and hence potential gene flow) can be substantial, has however been questioned. Here we compare the fitness of communally-reared offspring of local and foreign Atlantic salmon Salmo salar from adjacent Irish rivers and reciprocal F1 hybrid crosses between them, in the wild ‘home’ environment of the local population. Experimental groups did not differ in wild smolt output but a catastrophic flood event may have limited our ability to detect freshwater performance differences, which were evident in a previous study. Foreign parr exhibited higher, and hybrids intermediate, emigration rates from the natal stream relative to local parr, consistent with genetically-based behavioural differences. Adult return rates were lower for the foreign compared to the local group. Overall lifetime success of foreigners and hybrids relative to locals was estimated at 31% and 40% (mean of both hybrid groups), respectively. The results imply a genetic basis to fitness differences among populations separated by only 50km, driven largely by variation in smolt to adult return rates. Hence even if supplementary stocking programs obtain broodstock from neighbouring rivers, the risk of extrinsic outbreeding depression may be high.

Interpreting signals from astrophysical transient experiments

Time domain astronomy has come of age with astronomers now able to monitor the sky at high cadence both across the electromagnetic spectrum and using neutrinos and gravitational waves. The advent of new observing facilities permits new science, but the ever increasing throughput of facilities demands efficient communication of coincident detections and better subsequent coordination among the scientific community so as to turn detections into scientific discoveries. To discuss the revolution occurring in our ability to monitor the Universe and the challenges it brings, on 2012 April 25-26 a group of scientists from observational and theoretical teams studying transients met with representatives of the major international transient observing facilities at the Kavli Royal Society International Centre, UK. This immediately followed the Royal Society Discussion meeting "New windows on transients across the Universe" held in London. Here we present a summary of the Kavli meeting at which the participants discussed the science goals common to the transient astronomy community and analysed how to better meet the challenges ahead as ever more powerful observational facilities come on stream.

Deep Salience: Visual Salience Modeling via Deep Belief Propagation

Visual salience is an intriguing phenomenon observed in biological neural systems. Numerous attempts have been made to model visual salience mathematically using various feature contrasts, either locally or globally. However, these algorithmic models tend to ignore the problem’s biological solutions, in which visual salience appears to arise during the propagation of visual stimuli along the visual cortex. In this paper, inspired by the conjecture that salience arises from deep propagation along the visual cortex, we present a Deep Salience model where a multi-layer model based on successive Markov random fields (sMRF) is proposed to analyze the input image successively through its deep belief propagation. As a result, the foreground object can be automatically separated from the background in a fully unsupervised way. Experimental evaluation on the benchmark dataset validated that our Deep Salience model can consistently outperform eleven state-of-the-art salience models, yielding the higher rates in the precision-recall tests and attaining the best F-measure and mean-square error in the experiments.

Electrochemical promotion of a metal catalyst supported on a mixed-ionic conductor

It has been found that the catalytic activity and selectivity of a metal film deposited on a solid electrolyte could be enhanced dramatically and in a reversible way by applying an electrical current or potential between the metal catalyst and the counter electrode (also deposited on the electrolyte). This phenomenon is know as NEMCA [S. Bebelis, C.G. Vayenas, Journal of Catalysis, 118 (1989) 125-146.] or electrochemical promotion (EP) [J. Prichard, Nature, 343 (1990) 592.] of catalysis. Yttria-doped barium zirconate, BaZr_0.9Y_0.1O_{3 - α} (BZY), a known proton conductor, has been used in this study. It has been reported that proton conducting perovskites can, under the appropriate conditions, act also as oxide ion conductors. In mixed conducting systems the mechanism of conduction depends upon the gas atmosphere that to which the material is exposed. Therefore, the use of a mixed ionic (oxide ion and proton) conducting membrane as a support for a platinum catalyst may facilitate the tuning of the promotional behaviour of the catalyst by allowing the control of the conduction mechanism of the electrolyte. The conductivity of BZY under different atmospheres was measured and the presence of oxide ion conduction under the appropriate conditions was confirmed. Moreover, kinetic experiments on ethylene oxidation corroborated the findings from the conductivity measurements showing that the use of a mixed ionic conductor allows for the tuning of the reaction rate. © 2006 Elsevier B.V. All rights reserved.

Strategic behaviour in choice experiments.

Practitioners of environmental economics sometimes use repeated trinary choice experiment surveys to estimate the value of environmental policies and programs for use in policy evaluation. These surveys have several advantages over simpler forms of non-market valuation: (1) researchers can estimate the marginal value of attributes of the good or service in question, making the results useful for benefits transfer; and (2) because respondents make several choices and choose from choice sets containing three options, efficiency of the willingness to pay estimate is improved over one-shot, binary choice formats. Despite these benefits, such surveys may have incentive properties which cause the resulting value estimates to be biased. This paper presents a theoretical demonstration that subjects often have an incentive to choose the second-best option in a repeated trinary choice survey. The model shows that due to the nature of factorial choice set design, the second-best option in the choice set will often be the status quo option. The paper reports a set of experiments designed to test these theoretical predictions in an induced-value setting. The experimental results are consistent with the theoretical predictions, demonstrating that repeated trinary choice experiment surveys can generate biased value estimates under a wide range of conditions.

Split Converter-Fed SRM Drive for Flexible Charging in EV/HEV Applications

Electric vehicles (EVs) and hybrid EVs are the way forward for green transportation and for establishing low-carbon economy. This paper presents a split converter-fed four-phase switched reluctance motor (SRM) drive to realize flexible integrated charging functions (dc and ac sources). The machine is featured with a central-tapped winding node, eight stator slots, and six rotor poles (8/6). In the driving mode, the developed topology has the same characteristics as the traditional asymmetric bridge topology but better fault tolerance. The proposed system supports battery energy balance and on-board dc and ac charging. When connecting with an ac power grid, the proposed topology has a merit of the multilevel converter; the charging current control can be achieved by the improved hysteresis control. The energy flow between the two batteries is balanced by the hysteresis control based on their state-of-charge conditions. Simulation results in MATLAB/Simulink and experiments on a 150-W prototype SRM validate the effectiveness of the proposed technologies, which may provide a solution to EV charging issues associated with significant infrastructure requirements.

Paving the way to nanoionics: atomic origin of barriers for ionic transport through interfaces

The blocking of ion transport at interfaces strongly limits the performance of electrochemical nanodevices for energy applications. The barrier is believed to arise from space-charge regions generated by mobile ions by analogy to semiconductor junctions. Here we show that something different is at play by studying ion transport in a bicrystal of yttria (9% mol) stabilized zirconia (YSZ), an emblematic oxide ion conductor. Aberration-corrected scanning transmission electron microscopy (STEM) provides structure and composition at atomic resolution, with the sensitivity to directly reveal the oxygen ion profile. We find that Y segregates to the grain boundary at Zr sites, together with a depletion of oxygen that is confined to a small length scale of around 0.5 nm. Contrary to the main thesis of the space-charge model, there exists no evidence of a long-range O vacancy depletion layer. Combining ion transport measurements across a single grain boundary by nanoscale electrochemical strain microscopy (ESM), broadband dielectric spectroscopy measurements, and density functional calculations, we show that grain-boundary-induced electronic states act as acceptors, resulting in a negatively charged core. Ultimately, it is this negative charge which gives rise to the barrier for ion transport at the grain boundary

Multi-pair two-way AF relaying with massive arrays and imperfect CSI

We consider a multi-pair two-way amplify-and-forward relaying system with a massive antenna array at the relay and estimated channel state information, assuming maximum-ratio combining/transmission processing. Closed-form approximations of the sum spectral effi- ciency are developed and simple analytical power scaling laws are presented, which reveal a fundamental trade-off between the transmit powers of each user/the relay and of each pilot symbol. Finally, the optimal power allocation problem is studied.

Magnetic collimation of petawatt driven fast electron beam for prospective fast ignition studies

Collimated transport of fast electron beam through solid density matter is one of the key issues behind the success of the fast ignition scheme by means of which the required amount of ignition energy can be delivered to the hot spot region of the compressed fuel. Here we report on a hot electron beam collimation scheme in solids by tactfully using the strong magnetic fields generated by an electrical resistivity gradient according to Faraday's law. This was accomplished by appropriately fabricating the targets in such a way that the electron beam is directed to flow in a metal which is embedded in a much lower resistivity and atomic number metal. Experimental results showed guided transport of hot electron beam over hundreds of microns length inside solid density plasma, which were obtained from two experiments examining the scheme for petawatt laser driven hot electron beam while employing various target configurations.

Sistemas de informação para DNA microarrays

O projecto de sequenciação do genoma humano veio abrir caminho para o surgimento de novas áreas transdisciplinares de investigação, como a biologia computacional, a bioinformática e a bioestatística. Um dos resultados emergentes desde advento foi a tecnologia de DNA microarrays, que permite o estudo do perfil da expressão de milhares de genes, quando sujeitos a perturbações externas. Apesar de ser uma tecnologia relativamente consolidada, continua a apresentar um conjunto vasto de desafios, nomeadamente do ponto de vista computacional e dos sistemas de informação. São exemplos a optimização dos procedimentos de tratamento de dados bem como o desenvolvimento de metodologias de interpretação semi-automática dos resultados. O principal objectivo deste trabalho consistiu em explorar novas soluções técnicas para agilizar os procedimentos de armazenamento, partilha e análise de dados de experiências de microarrays. Com esta finalidade, realizou-se uma análise de requisitos associados às principais etapas da execução de uma experiência, tendo sido identificados os principais défices, propostas estratégias de melhoramento e apresentadas novas soluções. Ao nível da gestão de dados laboratoriais, é proposto um LIMS (Laboratory Information Management System) que possibilita a gestão de todos os dados gerados e dos procedimentos realizados. Este sistema integra ainda uma solução que permite a partilha de experiências, de forma a promover a participação colaborativa de vários investigadores num mesmo projecto, mesmo usando LIMS distintos. No contexto da análise de dados, é apresentado um modelo que facilita a integração de algoritmos de processamento e de análise de experiências no sistema desenvolvido. Por fim, é proposta uma solução para facilitar a interpretação biológica de um conjunto de genes diferencialmente expressos, através de ferramentas que integram informação existente em diversas bases de dados biomédicas.

Desenvolvimento profissional e educação em línguas: potencialidades e constrangimentos em contexto escolar

Este trabalho, desenvolvido por uma professora em contexto académico, movida por uma vontade de intervenção em contexto escolar para melhoria da qualidade do desempenho profissional e das aprendizagens dos alunos, assenta: por um lado, num entendimento de desenvolvimento profissional (DP) enquanto processo contínuo que se articula com e inscreve na prática do quotidiano docente; e, por outro lado, num entendimento da educação em línguas como um processo que valoriza a diversidade e enfatiza o plurilinguismo como valor e competência, enriquecendo os repertórios linguístico-comunicativos dos sujeitos, de modo a facilitar a abertura ao Outro, num processo de construção e recriação de significado sobre o mundo e sobre si na relação com esse Outro. Pretendeu-se, neste estudo, compreender o processo de desenvolvimento profissional de professores de línguas, tentando identificar potencialidades e constrangimentos que se colocam a esse desenvolvimento profissional em contexto. Para tal, foi desenvolvido um projecto de formação para a educação plurilingue numa escola Secundária com 3º Ciclo do Ensino Básico com um grupo de cinco professoras ao longo de dois anos. A formação, promovida através de um Centro de Formação de Escolas e acreditada pelo Conselho- Científico da Formação Contínua desenvolveu-se em duas fases. A primeira fase (2004/2005), na modalidade Oficina de Formação com 10 sessões de formação num total de 50 horas, e a segunda fase (2005/2006), na modalidade Projecto com nove sessões de formação, num total de 50 horas. O estudo seguiu uma metodologia de cariz qualitativo e de inspiração interpretativa/fenomenológica, pretendendo colocar em evidência o sujeito e sublinhando a interacção que estabelece consigo e com os outros, a partir das práticas discursivas que vai construindo. A estratégia investigativa desenhou-se em torno do estudo de caso no qual procurámos analisar a (des/re)construção de conhecimento profissional no contexto de um grupo de professoras em formação. Esta análise assumiu duas vertentes, uma tomando a interacção entre o grupo como alvo de análise, outra olhando para o percurso de cada formanda na sua singularidade. Os dados recolhidos e analisados incluem um inquérito por questionário inicial, a transcrição das sessões de formação e as reflexões escritas ao longo das duas fases da formação, bem como um inquérito por entrevista semiestruturada, após o terminus da formação, em Julho de 2007. Os resultados da análise indicam que os processos formativos que promovem o questionamento de si e das suas práticas, ajudando a identificar representações e a analisar o modo como as representações interferem ou não nas práticas para, em seguida, estas poderem ser reconstruídas, são facilitadores de DP. Evidenciaram-se, nestes processos, dois tempos de formação distintos, mas complementares, o tempo da observação e da análise e o tempo da apropriação e da acção, que englobam espaços de trabalho individual e colectivo. Nestes dois tempos de formação identificámos quatro modos facilitadores da reconstrução do conhecimento profissional, nomeadamente: a articulação da teoria com a prática; a tomada do objecto de trabalho em objecto de análise e de experimentação, incluindo a visualização, a análise e a reflexão sobre as experiências realizadas; a colocação do aluno no centro do processo de ensino; e o alargamento da consciencialização do trabalho com as línguas e das suas finalidades educativas. Estes quatro modos constituem-se como impulsionadores ou inibidores de DP, dependendo a sua percepção de factores, tanto de carácter individual como de carácter colectivo. Os factores de carácter individual dizem respeito ao comprometimento, ao empenho, ao modo como cada sujeito se vê como pessoa e como profissional, bem como à fase da carreira em que se situa. Os factores de carácter colectivo dizem respeito aos contextos nos quais o sujeito se move, nomeadamente a cultura da escola em que exerce funções, às relações interpessoais e profissionais que estabelece com os colegas de trabalho e às possibilidades e espaços de formação que cada sujeito encontra com os outros. Tendo constatado que o desenvolvimento profissional é fruto da intersecção da acção individual com a acção colectiva, concluímos que, na constituição de ambientes facilitadores de DP, importa ter em conta seis componentes: a apropriação individual da construção do conhecimento profissional pelos sujeitos, a construção de oportunidades de desenvolvimento, a construção da capacidade de intervenção em contexto, a promoção da colegialidade, a monitorização e avaliação de processos e resultados do trabalho no âmbito do DP e a criação de espaços e tempos próprios para esse trabalho. Os resultados da análise indicam também que a formação em contexto permite iniciar um trabalho de DP porque cria condições de auto/hetero/eco e coformação que incluem um potencial de aprendizagem profissional transformativa. Enquanto constrangimentos ao DP em contexto destacam-se aspectos contextuais que se relacionam com o tempo e a sua gestão, bem como com a visibilidade, o reconhecimento e o impacto do trabalho realizado no contexto. Através da descrição e análise de uma experiência de formação contínua em contexto, este trabalho revela possibilidades de ultrapassar os constrangimentos contextuais, sublinhando as potencialidades de desenvolvimento profissional em contexto, pelo modo como professoras, predispostas à mudança e comprometidas com a profissão, onde os alunos têm um papel particular, são capazes de inscrever transformação nas suas práticas, evidenciando a urgência não só de um apoio concreto e explícito, mas também de reconhecimento do trabalho desenvolvido em cada sala de aula, com cada turma, à descoberta de si e do outro, através das línguas para a construção de um mundo mais plural.