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Natural convection heat transfer effects with micro finned structures
This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.Micro-scale natural convection plays an important role in heat removal from microelectronic components and Micro-Electro-Mechanical Systems (MEMS) devices. Natural convection of macrofin arrays has been extensively studied by many researchers over the past several decades; however analysis of free convection around microfin arrays is less well researched. The objective of this work was to experimentally investigate the effects of micro fin height and spacing for a horizontally mounted heat sink on heat transfer coefficient when operating under steady state natural convection conditions. An array of micro finned copper heat sinks was fabricated using micro-electro discharge wire machining (μ-EDWM) with fin height ranging from 0.25 to 1.0mm and fin spacing from 0.5 to 1.0mm respectively. Results showed that values of the convective heat transfer coefficient increased with increased fin spacing and decreased as fin height increased.This study is funded by Advantage West Midlands (AWM)
Massive torsion modes, chiral gravity, and the Adler-Bell-Jackiw anomaly
Regularization of quantum field theories introduces a mass scale which breaks
axial rotational and scaling invariances. We demonstrate from first principles
that axial torsion and torsion trace modes have non-transverse vacuum
polarization tensors, and become massive as a result. The underlying reasons
are similar to those responsible for the Adler-Bell-Jackiw (ABJ) and scaling
anomalies. Since these are the only torsion components that can couple
minimally to spin 1/2 particles, the anomalous generation of masses for these
modes, naturally of the order of the regulator scale, may help to explain why
torsion and its associated effects, including CPT violation in chiral gravity,
have so far escaped detection. As a simpler manifestation of the reasons
underpinning the ABJ anomaly than triangle diagrams, the vacuum polarization
demonstration is also pedagogically useful. In addition it is shown that the
teleparallel limit of a Weyl fermion theory coupled only to the left-handed
spin connection leads to a counter term which is the Samuel-Jacobson-Smolin
action of chiral gravity in four dimensions.Comment: 7 pages, RevTeX fil
A finite element simulation for orthogonal cutting of UD-CFRP incorporating a novel fibre - matrix interface model
AbstractThe rapid increase in industrial utilisation of carbon fibre reinforced plastic (CFRP) composites in recent years has led to growing interest in numerical modelling of material behaviour and defect formation when machining CFRP. The inhomogeneous/anisotropic nature of CFRP however presents considerable challenges in accurately modelling workpiece defects such as debonding between the matrix and fibre phase following cutting operations. Much of the published literature has involved the use of zero thickness cohesive elements to represent the fibre-matrix interface, despite the inability of such elements to model compressive stresses. This paper details a new approach for characterising the interface region in a two-dimensional explicit finite element simulation when orthogonal machining unidirectional (UD) CFRP laminates. A cohesive zone model based on a traction-separation law is applied to small thickness (0.25μm) interface elements in order to accommodate compressive failure, which is implemented via a bespoke user subroutine. Fibre fracture is based on a maximum principal stress criterion while elastic-plastic behaviour to failure is used to represent matrix damage. The influence of varying fibre orientations (45°, 90°, 135°) on predicted cutting and thrust forces were validated against published experimental data. While the former was generally within 5% of experimental data for workpieces with 90° and 135° fibre directions, predicted thrust forces were typically underestimated by ∼30-60%. The corresponding chip formation mechanisms and sub-surface damage due to the different material phases were also investigated. The proposed model was able to predict composite behaviour and defect formation that was comparable to experimental high speed camera images outlined in the literature
On the determination of local instantaneous averages in particulate flow measurements
Determination of instantaneous local average particle density of a gas-particle suspension requires satisfying both the time scale relation and the volume scale relation or its continuum counter part of time averaging. This procedure was validated by comparing simultaneous velocity and mass flux measurements and the laser phase Doppler measurements
Directional interacting whispering gallery modes in coupled dielectric microdisks
We study the optical interaction in a coupled dielectric microdisks by
investigating the splitting of resonance positions of interacting whispering
gallery modes (WGMs) and their pattern change, depending on the distance
between the microdisks. It is shown that the interaction between the WGMs with
odd parity about y-axis becomes appreciable at a distance less than a
wavelength and causes directional emissions of the resulting interacting WGMs.
The directionality of the interacting WGMs can be understood in terms of an
effective boundary deformation in ray dynamical analysis. We also discuss about
the oscillation of the splitting when the distance is greater than a
wavelength.Comment: 7 pages, 10 figure
Nonequilibrium plasmons and transport properties of a double--junction quantum wire
We study theoretically the current-voltage characteristics, shot noise, and
full counting statistics of a quantum wire double barrier structure. We model
each wire segment by a spinless Luttinger liquid. Within the sequential
tunneling approach, we describe the system's dynamics using a master equation.
We show that at finite bias the non-equilibrium distribution of plasmons in the
central wire segment leads to increased average current, enhanced shot noise,
and full counting statistics corresponding to a super-Poissonian process. These
effects are particularly pronounced in the strong interaction regime, while in
the non-interacting case we recover results obtained earlier using detailed
balance arguments.Comment: 22 pages, RevTex 2-column, 11 figure
Double-Well Potential : The WKB Approximation with Phase Loss and Anharmonicity Effect
We derive a general WKB energy splitting formula in a double-well potential
by incorporating both phase loss and anharmonicity effect in the usual WKB
approximation. A bare application of the phase loss approach to the usual WKB
method gives better results only for large separation between two potential
minima. In the range of substantial tunneling, however, the phase loss approach
with anharmonicity effect considered leads to a great improvement on the
accuracy of the WKB approximation.Comment: 14 pages, revtex, 1 figure, will appear at Phys. Rev.
Selenium Biotransformations in an Engineered Aquatic Ecosystem for Bioremediation of Agricultural Wastewater via Brine Shrimp Production
An engineered aquatic ecosystem was specifically designed to bioremediate selenium (Se), occurring as oxidized inorganic selenate from hypersalinized agricultural drainage water while producing brine shrimp enriched in organic Se and omega-3 and omega-6 fatty acids for use in value added nutraceutical food supplements. Selenate was successfully bioremediated by microalgal metabolism into organic Se (seleno-amino acids) and partially removed via gaseous volatile Se formation. Furthermore, filterfeeding brine shrimp that accumulated this organic Se were removed by net harvest. Thriving in this engineered pond system, brine shrimp (Artemia franciscana Kellogg) and brine fly (Ephydridae sp.) have major ecological relevance as important food sources for large populations of waterfowl, breeding, and migratory shore birds. This aquatic ecosystem was an ideal model for study because it mimics trophic interactions in a Se polluted wetland. Inorganic selenate in drainage water was metabolized differently in microalgae, bacteria, and diatoms where it was accumulated and reduced into various inorganic forms (selenite, selenide, or elemental Se) or partially incorporated into organic Se mainly as selenomethionine. Brine shrimp and brine fly larva then bioaccumulated Se from ingesting aquatic microorganisms and further metabolized Se predominately into organic Se forms. Importantly, adult brine flies, which hatched from aquatic larva, bioaccumulated the highest Se concentrations of all organisms tested
Transport properties of a molecule embedded in an Aharonov-Bohm interferometer
We theoretically investigate the transport properties of a molecule embedded
in one arm of a mesoscopic Aharonov-Bohm interferometer. Due to the presence of
phonons the molecule level position () and the electron-electron
interaction () undergo a \emph{polaronic shift} which affects dramatically
the electronic transport through the molecular junction. When the
electron-phonon interaction is weak the linear conductance presents Fano-line
shapes as long as the direct channel between the electrodes is opened. The
observed Fano resonances in the linear conductance are originated from the
interference between the spin Kondo state and the direct path. For strong
enough electron-phonon interaction, the electron-electron interaction is
renormalized towards negative values, {\it i.e.} becomes effectively
attractive. This scenario favors fluctuations between the empty and doubly
occupied charge states and therefore promotes a charge Kondo effect. However,
the direct path between the contacts breaks the electron-hole symmetry which
can efficiently suppress this charge Kondo effect. Nevertheless, we show that a
proper tuning of the gate voltage is able to revive the Kondo resonance. Our
results are obtained by using the Numerical Renormalization approximation to
compute the electronic spectral function and the linear conductance.Comment: 17 pages, 12 figure
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