7,815 research outputs found
Optimizing the performance of thermionic devices using energy filtering
Conventional thermionic power generators and refrigerators utilize a barrier
in the direction of transport to selectively transmit high-energy electrons.
Here we show that the energy spectrum of electrons transmitted in this way is
not optimal, and we derive the ideal energy spectrum for operation in the
maximum power regime. By using suitable energy filters, such as resonances in
quantum dots, the power of thermionic devices can, in principle, be improved by
an order of magnitude.Comment: 3 pages, 2 figure
Sprayable birefringent coating enables strain measurements on large surfaces
Birefringent coating for strain measurements on large surfaces contains constituents that can be premixed and sprayed as a single component with conventional paint spray equipment. Elevated temperatures are not required for spraying or curing of the coating material which has long pot life
Rheology of Active Filament Solutions
We study the viscoelasticity of an active solution of polar biofilaments and
motor proteins. Using a molecular model, we derive the constitutive equations
for the stress tensor in the isotropic phase and in phases with liquid
crystalline order. The stress relaxation in the various phases is discussed.
Contractile activity is responsible for a spectacular difference in the
viscoelastic properties on opposite sides of the order-disorder transition.Comment: 4 pages, 1 figur
Nematic and Polar order in Active Filament Solutions
Using a microscopic model of interacting polar biofilaments and motor
proteins, we characterize the phase diagram of both homogeneous and
inhomogeneous states in terms of experimental parameters. The polarity of motor
clusters is key in determining the organization of the filaments in homogeneous
isotropic, polarized and nematic states, while motor-induced bundling yields
spatially inhomogeneous structures.Comment: 4 pages. 3 figure
Concept study for a high-efficiency nanowire-based thermoelectric
Materials capable of highly efficient, direct thermal-to-electric energy
conversion would have substantial economic potential. Theory predicts that
thermoelectric efficiencies approaching the Carnot limit can be achieved at low
temperatures in one-dimensional conductors that contain an energy filter such
as a double-barrier resonant tunneling structure. The recent advances in growth
techniques suggest that such devices can now be realized in heterostructured,
semiconductor nanowires. Here we propose specific structural parameters for
InAs/InP nanowires that may allow the experimental observation of near-Carnot
efficient thermoelectric energy conversion in a single nanowire at low
temperature
Bridging the microscopic and the hydrodynamic in active filament solutions
Hydrodynamic equations for an isotropic solution of active polar filaments
are derived from a microscopic mean-field model of the forces exchanged between
motors and filaments. We find that a spatial dependence of the motor stepping
rate along the filament is essential to drive bundle formation. A number of
differences arise as compared to hydrodynamics derived (earlier) from a
mesoscopic model where relative filament velocities were obtained on the basis
of symmetry considerations. Due to the anisotropy of filament diffusion, motors
are capable of generating net filament motion relative to the solvent. The
effect of this new term on the stability of the homogeneous state is
investigated.Comment: 7 pages, 2 figures, submitted to Europhys. Let
An unusual coordination polymer containing Cu+ ions and featuring possible CuāÆCu `cuprophilic' interĀactions: poly[di-Ī¼-chlorido-(Ī¼4-3,5-diĀaminoĀbenzoato-Īŗ4O:Oā²:N:Nā²)tricopper(I)(3 CuāCu)]
We thank the Higher Education Commission of Pakistan (grant No. 1-3/PM-PDFP-II/2006/22) for financial support.Peer reviewedPublisher PD
Effects of suspended sediments, dissolved inorganic nutrients and salinity on fertilisation and embryo development in the coral Acropora millepora (Ehrenberg, 1834)
Exposure of coral reefs to river plumes carrying increasing loads of nutrients and sediments is a pressing issue for coral reefs around the world including the Great Barrier Reef (GBR). Laboratory experiments were conducted to investigate the effects of changes in inorganic nutrients (nitrate, ammonium and phosphate), salinity and various types of suspended sediments in isolation and in combination on rates of fertilisation and early embryonic development of the scleractinian coral Acropora millepora. Doseāresponse experiments showed that fertilisation declined significantly with increasing sediments and decreasing salinity, while inorganic nutrients at up to 20 Ī¼M nitrate or ammonium and 4 Ī¼M phosphate had no significant effect on fertilisation. Suspended sediments of ā„100 mg lā1 and salinity of 30 ppt reduced fertilisation by >50%. Developmental abnormality occurred in 100% of embryos at 30 ppt salinity, and no fertilisation occurred at ā¤28 ppt. Another experiment tested interactions between sediment, salinity and nutrients and showed that fertilisation was significantly reduced when nutrients and low concentrations of sediments co-occurred, although both on their own had no effect on fertilisation rates. Similarly, while slightly reduced salinity on its own had no effect, fertilisation was reduced when it coincided with elevated levels of sediments or nutrients. Both these interactions were synergistic. A third experiment showed that sediments with different geophysical and nutrient properties had differential effects on fertilisation, possibly related to sediment and nutrient properties. The findings highlight the complex nature of the effects of changing water quality on coral health, particularly stressing the significance of water quality during coral spawning time
Are we seeing accretion flows in a 250kpc-sized Ly-alpha halo at z=3?
Using MUSE on the ESO-VLT, we obtained a 4 hour exposure of the z=3.12 radio
galaxy MRC0316-257. We detect features down to ~10^-19 erg/s/cm^2/arcsec^2 with
the highest surface brightness regions reaching more than a factor of 100
higher. We find Ly-alpha emission out to ~250 kpc in projection from the active
galactic nucleus (AGN). The emission shows arc-like morphologies arising at
150-250 kpc from the nucleus in projection with the connected filamentary
structures reaching down into the circum-nuclear region. The most distant arc
is offset by 700 km/s relative to circum-nuclear HeII 1640 emission, which we
assume to be at the systemic velocity. As we probe emission closer to the
nucleus, the filamentary emission narrows in projection on the sky, the
relative velocity decreases to ~250 km/s, and line full-width at half maximum
range from 300-700 km/s. From UV line ratios, the emission on scales of 10s of
kpc from the nucleus along a wide angle in the direction of the radio jets is
clearly excited by the radio jets and ionizing radiation of the AGN. Assuming
ionization equilibrium, the more extended emission outside of the axis of the
jet direction would require 100% or more illumination to explain the observed
surface brightness. High speed (>300 km/s) shocks into rare gas would provide
sufficiently high surface brightness. We discuss the possibility that the arcs
of Ly-alpha emission represent accretion shocks and the filamentary emission
represent gas flows into the halo, and compare our results with gas accretion
simulations.Comment: 4 pages, 2 figures, 1 table, A&A letters accepte
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