1,617 research outputs found
Hybrid Approach in Microscale Transport Phenomena: Application to Biodiesel Synthesis in Micro-reactors
A hybrid engineering approach to the study of transport phenomena, based on the
synergy among computational, analytical, and experimental methodologies is
reviewed. The focus of the chapter is on fundamental analysis and proof of concept
developments in the use of nano- and micro-technologies for energy efficiency and
heat and mass transfer enhancement applications. The hybrid approach described
herein combines improved lumped-differential modeling, hybrid numericalanalytical solution methods, mixed symbolic-numerical computations, and
advanced experimental techniques for micro-scale transport phenomena. An
application dealing with micro-reactors for continuous synthesis of biodiesel is
selected to demonstrate the instrumental role of the hybrid approach in achieving
improved design and enhanced performance
Image Processing of Temperature Fields from Infrared Termography of Micro-Mixers with Polymeric Substrates
International audienceThe present work deals with the image processing and thermal analysis of micro-mixers from the data provided by an infrared camera thermography system. The micro-mixers are prepared by photolitography on a polymeric substrate and the camera employed is the FLIR SC645 with the proprietary software ThermaCam Researcher Pro v2.10. The thermal analysis is aimed at understanding the direct contact heat transfer between two fluid streams and the polymeric substrate at different inlet temperatures and mass flow rates, within mixers of various geometric configurations. Infrared thermography is thus employed to measure the external wall temperatures fields along the mixer length. Water at different inlet temperatures has been used as the working fluid in all cases and the mass flow rates of the two streams have been imposed through independent syringe pumps. The image processing and analysis of the experimental results show the basic qualitative and quantitative features of the heat transfer phenomena and indicates that a conjugated heat transfer formulation of the micro-mixer structure should be pursued for accurate quantitative analysis in theoretical predictions
Link Invariants of Finite Type and Perturbation Theory
The Vassiliev-Gusarov link invariants of finite type are known to be closely
related to perturbation theory for Chern-Simons theory. In order to clarify the
perturbative nature of such link invariants, we introduce an algebra V_infinity
containing elements g_i satisfying the usual braid group relations and elements
a_i satisfying g_i - g_i^{-1} = epsilon a_i, where epsilon is a formal variable
that may be regarded as measuring the failure of g_i^2 to equal 1.
Topologically, the elements a_i signify crossings. We show that a large class
of link invariants of finite type are in one-to-one correspondence with
homogeneous Markov traces on V_infinity. We sketch a possible application of
link invariants of finite type to a manifestly diffeomorphism-invariant
perturbation theory for quantum gravity in the loop representation.Comment: 11 page
Dissolved organic matter indicates changes in temperature and plant communities in peatlands
Though northern peatlands cover only 3 % of the land surface they count as one of the largest terrestrial organic C pools. This huge C pool is threatened by increasing temperatures, related microbial degradation and indirect effects of climate change leading to vascular plant dominance over sphagnum mosses and a shift from graminoids to shrubs. Effects of these changes in vegetation on peat degradation are unknown. Dissolved organic matter (DOM) as an important component of the C cycle in peatlands might be used as a sensitive indicator of enhanced peat degradation. Furthermore, peatlands are the major source of DOM in many surface waters and understanding the mechanisms of peat degradation will help to elucidate the reasons for the ongoing trends of increasing concentrations of dissolved organic carbon (DOC) in surface waters. In this study we aimed to determine effects of temperature and plant functional types (PFT: graminoids, shrubs) on amounts and composition of DOM allowing conclusions about ongoing changes in peat degradation. We selected two ombrotrophic peatlands in the Italian Alps, reflecting a temperature gradient where we manipulated the vascular plant cover by selective clipping. On the established plant functional type plots we collected DOM directly after plant removal and during the following seasons over a period of one year. Besides DOC concentrations we determined DOM composition by C-13 of DOC and UV and fluorescence spectroscopy. The short term response (2-24h) of DOM to the plant clipping enabled us to estimate the C input of vascular plants via roots. The medium to long term data showed a clear relation of DOM to the temperature gradient and the PFT. All in all our results indicated a substantial contribution of the roots from vascular plants to DOM in peatlands. The release of DOM from peat clearly increased with temperature and vascular plant biomass. The difference between graminoids and shrubs seems to be marginal. We conclude that higher temperatures and greater vascular plant biomass result in increasing peat degradation as one likely reason for increasing DOC concentrations in many surface waters across Europe and North America
Determining Ratios of WIMP-Nucleon Cross Sections from Direct Dark Matter Detection Data
Weakly Interacting Massive Particles (WIMPs) are one of the leading
candidates for Dark Matter. So far the usual procedure for constraining the
WIMP-nucleon cross sections in direct Dark Matter detection experiments have
been to fit the predicted event rate based on some model(s) of the Galactic
halo and of WIMPs to experimental data. One has to assume whether the
spin-independent (SI) or the spin-dependent (SD) WIMP-nucleus interaction
dominates, and results of such data analyses are also expressed as functions of
the as yet unknown WIMP mass. In this article, I introduce methods for
extracting information on the WIMP-nucleon cross sections by considering a
general combination of the SI and SD interactions. Neither prior knowledge
about the local density and the velocity distribution of halo WIMPs nor about
their mass is needed. Assuming that an exponential-like shape of the recoil
spectrum is confirmed from experimental data, the required information are only
the measured recoil energies (in low energy ranges) and the number of events in
the first energy bin from two or more experiments.Comment: 33 pages, 20 eps figures; v2: typos fixed, references added and
updated, revised version for publicatio
4-Dimensional BF Theory as a Topological Quantum Field Theory
Starting from a Lie group G whose Lie algebra is equipped with an invariant
nondegenerate symmetric bilinear form, we show that 4-dimensional BF theory
with cosmological term gives rise to a TQFT satisfying a generalization of
Atiyah's axioms to manifolds equipped with principal G-bundle. The case G =
GL(4,R) is especially interesting because every 4-manifold is then naturally
equipped with a principal G-bundle, namely its frame bundle. In this case, the
partition function of a compact oriented 4-manifold is the exponential of its
signature, and the resulting TQFT is isomorphic to that constructed by Crane
and Yetter using a state sum model, or by Broda using a surgery presentation of
4-manifolds.Comment: 15 pages in LaTe
Braneworld Flux Inflation
We propose a geometrical model of brane inflation where inflation is driven
by the flux generated by opposing brane charges and terminated by the collision
of the branes, with charge annihilation. We assume the collision process is
completely inelastic and the kinetic energy is transformed into the thermal
energy after collision. Thereafter the two branes coalesce together and behave
as a single brane universe with zero effective cosmological constant. In the
Einstein frame, the 4-dimensional effective theory changes abruptly at the
collision point. Therefore, our inflationary model is necessarily 5-dimensional
in nature. As the collision process has no singularity in 5-dimensional
gravity, we can follow the evolution of fluctuations during the whole history
of the universe. It turns out that the radion field fluctuations have a steeply
tilted, red spectrum, while the primordial gravitational waves have a flat
spectrum. Instead, primordial density perturbations could be generated by a
curvaton mechanism.Comment: 11 pages, 6 figures, references adde
Screening of endoglucanase-producing bacteria in the saline rhizosphere of Rhizophora mangle.
Abstract: In screening the culturable endoglucanase-producing bacteria in the rhizosphere of Rhizophora mangle, we found a prevalence of genera Bacillus and Paenibacillus. These bacteria revealed different activities in endoglucolysis and biofilm formation when exposed to specific NaCl concentrations, indicating modulated growth under natural variations in mangrove salinity
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