1,606 research outputs found
Design considerations for micromechanical sensors using encapsulated built-in resonant strain gauges
This paper describes the various design aspects for micromechanical sensors consisting of a structure with encapsulated built-in resonant strain gauges. Analytical models are used to investigate the effect of device parameters on the behaviour of a pressure sensor and a force sensor. The analyses indicate that the sealing cap can have a strong degrading effect on the device performance if the thicknesses of the cap and of the supporting structure are of the same order of magnitude. A novel design, employing bossed structures, is described, which reduces the design complexity and virtually eliminates the influence of the cap on the sensitivity of the sensor
Valorisation of lignin – Achievements of the LignoValue project
Lignocellulosic biorefinery for production of biofuels, materials and chemicals requires valorization of all fractions including lignin. As a consequence of its poly-aromatic structure, lignin potentially serves as a source for aromatic chemicals. The developed biorefinery concept of the LignoValue project comprises two major steps: (1) Organosolv fractionation of wheat straw and willow into (hemi)cellulose and high purity lignin. (2) Further conversion of the isolated lignin via catalytic pyrolysis, supercritical depolymerization and partial hydrodeoxygenation (HDO) into different components like low molecular phenolic compounds, wood adhesives and fuel additives. The cellulose fraction resulting after organosolv fractionation is effectively hydrolysed by enzymes for biofuel production. Quality assessment of the liberated lignins shows interesting characteristics for follow-up chemistry such as high purity, relatively low molar mass and polydispersity. Catalytic pyrolysis in a fluidised bed at 400-500°C was found to convert organosolv lignin in 35-55% phenolic oil, 10% identified monomeric phenolic compounds, 10-20% water, 5-20% gas and 35-55% char. Supercritical depolymerisation of lignin in carbon dioxide based solvents resulted in a similar spectrum of products, however, at a lower temperature (ca 300°C) but at higher pressures. In both thermochemical processes the use of promotors or catalysts lead to an improved yield of the target monomeric aromatic products. Also the residual char fraction shows interesting properties for use in bio-char applications. Catalytic semi-continuous HDO of lignin in hydrogen atmosphere can be manipulated to yield both light oils or heavy oils as potential additives to fuels. Suitable catalysts were found to convert depolymerised lignin to phenolic oils in high yields. In this process no char formation is observed. The lignin oils were successfully tested on lab scale as partial substitution of phenol in resins for gluing wood panels. The LignoValue concept is critically reviewed in a techno-economic analysis demonstrating the potential for further commercial development and adoptation of this innovative biorefinery process in Europe
The ASK Network: developing a virtuous cycle of subsurface data and knowledge exchange
Knowledge of the subsurface is essential in delivering successful construction and regeneration projects. Inadequate understanding of subsurface ground conditions can constrain effective development of urban areas and is a key factor in project delay and overspending. Improving this situation demands much better use, and re-use, of subsurface data and knowledge. The establishment of ASK subsurface data and knowledge exchange network has led to substantial improvements in how urban subsurface data is reported and exchanged between the public and private sectors. Implementation of the GSPEC standardised digital data reporting format has improved the integrity and accessibility of data. ASK and GSPEC are enabling the expansion and exchange of high quality systematic subsurface datasets, improving development of robust 3D ground models which can be used to promote more cost effective and better informed ground engineering investigations, and monitoring and regulation of resources in the urban environment. The work underway in Glasgow is acting as a standard for change, both within the UK and Europe
Dilatancy transition in a granular model
We introduce a model of granular matter and use a stress ensemble to analyze
shearing. Monte Carlo simulation shows the model to exhibit a second order
phase transition, associated with the onset of dilatancy.Comment: Future versions can be obtained from:
http://www.ma.utexas.edu/users/radin/papers/shear2.pd
Community structure and ethnic preferences in school friendship networks
Recently developed concepts and techniques of analyzing complex systems
provide new insight into the structure of social networks. Uncovering recurrent
preferences and organizational principles in such networks is a key issue to
characterize them. We investigate school friendship networks from the Add
Health database. Applying threshold analysis, we find that the friendship
networks do not form a single connected component through mutual strong
nominations within a school, while under weaker conditions such
interconnectedness is present. We extract the networks of overlapping
communities at the schools (c-networks) and find that they are scale free and
disassortative in contrast to the direct friendship networks, which have an
exponential degree distribution and are assortative. Based on the network
analysis we study the ethnic preferences in friendship selection. The clique
percolation method we use reveals that when in minority, the students tend to
build more densely interconnected groups of friends. We also find an asymmetry
in the behavior of black minorities in a white majority as compared to that of
white minorities in a black majority.Comment: submitted to Physica
Spatial and temporal variations in Pb concentrations and isotopic composition in road dust, farmland soil and vegetation in proximity to roads since cessation of use of leaded petrol in the UK
Results are presented for a study of spatial distributions and temporal trends in concentrations of lead (Pb) from different sources in soil and vegetation of an arable farm in central Scotland in the decade since the use of leaded petrol was terminated. Isotopic analyses revealed that in all of the samples analysed, the Pb conformed to a binary mixture of petrol Pb and Pb from industrial or indigenous geological sources and that locally enhanced levels of petrol Pb were restricted to within 10 m of a motorway and 3 m of a minor road. Overall, the dominant source of Pb was historical emissions from nearby industrial areas. There was no discernible change in concentration or isotopic composition of Pb in surface soil or vegetation over the decade since the ban on the sale of leaded petrol. There was an order of magnitude decrease in Pb concentrations in road dust over the study period, but petrol Pb persisted at up to 43% of the total Pb concentration in 2010. Similar concentrations and spatial distributions of petrol Pb and non petrol Pb in vegetation in both 2001 and 2010, with enhanced concentrations near roads, suggested that redistribution of previously deposited material has operated continuously over that period, maintaining a transfer pathway of Pb into the biosphere. The results for vegetation and soil transects near minor roads provided evidence of a non petrol Pb source associated with roads/traffic, but surface soil samples from the vicinity of a motorway failed to show evidence of such a source
Fractal Structures and Scaling Laws in the Universe: Statistical Mechanics of the Self-Gravitating Gas
Fractal structures are observed in the universe in two very different ways.
Firstly, in the gas forming the cold interstellar medium in scales from 10^{-4}
pc till 100 pc. Secondly, the galaxy distribution has been observed to be
fractal in scales up to hundreds of Mpc. We give here a short review of the
statistical mechanical (and field theoretical) approach developed by us. We
consider a non-relativistic self-gravitating gas in thermal equilibrium at
temperature T inside a volume V. The statistical mechanics of such system has
special features and, as is known, the thermodynamical limit does not exist in
its customary form. Moreover, the treatments through microcanonical, canonical
and grand canonical ensembles yield different results.We present here for the
first time the equation of state for the self-gravitating gas in the canonical
ensemble. We find that it has the form p = [N T/ V] f(eta), where p is the
pressure, N is the number of particles and \eta \equiv {G m^2 N \over V^{1/3}
T}. The N \to\infty and V \to\infty limit exists keeping \eta fixed. We compute
the function f(\eta) using Monte Carlo simulations and for small eta
analytically. We compute the thermodynamic quantities of the system as free
energy, entropy, chemical potential, specific heat, compressibility and speed
of sound. We reproduce the well-known gravitational phase transition associated
to the Jeans' instability. Namely, a gaseous phase for eta < eta_c and a
condensed phase for eta > eta_c. Moreover, we derive the precise behaviour of
the physical quantities near the transition. In particular, the pressure
vanishes as p \sim(eta_c-eta)^B with B \sim 0.2 and eta_c \sim 1.6 and the
energy fluctuations diverge as \sim(eta_c-eta)^{B-1}. The speed of sound
decreases monotonically and approaches the value sqrt{T/6} at the transition.Comment: Invited paper to the special issue of the `Journal of Chaos, Solitons
and Fractals': `Superstrings, M, F, S...theory', M. S El Naschie and C.
Castro, Editors. Latex file, 16 pages plus three .ps figure
Continuous Quantum Measurement and the Quantum to Classical Transition
While ultimately they are described by quantum mechanics, macroscopic
mechanical systems are nevertheless observed to follow the trajectories
predicted by classical mechanics. Hence, in the regime defining macroscopic
physics, the trajectories of the correct classical motion must emerge from
quantum mechanics, a process referred to as the quantum to classical
transition. Extending previous work [Bhattacharya, Habib, and Jacobs, Phys.
Rev. Lett. {\bf 85}, 4852 (2000)], here we elucidate this transition in some
detail, showing that once the measurement processes which affect all
macroscopic systems are taken into account, quantum mechanics indeed predicts
the emergence of classical motion. We derive inequalities that describe the
parameter regime in which classical motion is obtained, and provide numerical
examples. We also demonstrate two further important properties of the classical
limit. First, that multiple observers all agree on the motion of an object, and
second, that classical statistical inference may be used to correctly track the
classical motion.Comment: 12 pages, 4 figures, Revtex
Modal satisfiability via SMT solving
Modal logics extend classical propositional logic, and they are robustly decidable. Whereas most existing decision procedures for modal logics are based on tableau constructions, we propose a framework for obtaining decision procedures by adding instantiation rules to standard SAT and SMT solvers. Soundness, completeness, and termination of the procedures can be proved in a uniform and elementary way for the basic modal logic and some extensions.Fil: Areces, Carlos Eduardo. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina.Fil: Areces, Carlos Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina.Fil: Fontaine, Pascal. Université de Lorraine; Francia.Fil: Fontaine, Pascal. National Institute for Research in Digital Science and Technology; Francia.Fil: Merz, Stephan. Université de Lorraine; Francia.Fil: Merz, Stephan. National Institute for Research in Digital Science and Technology; Francia.Ciencias de la Computació
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