462 research outputs found
Tracer diffusion inside fibrinogen layers
We investigate the obstructed motion of tracer (test) particles in crowded
environments by carrying simulations of two-dimensional Gaussian random walk in
model fibrinogen monolayers of different orientational ordering. The fibrinogen
molecules are significantly anisotropic and therefore they can form structures
where orientational ordering, similar to the one observed in nematic liquid
crystals, appears. The work focuses on the dependence between level of the
orientational order (degree of environmental crowding) of fibrinogen molecules
inside a layer and non-Fickian character of the diffusion process of spherical
tracer particles moving within the domain. It is shown that in general
particles motion is subdiffusive and strongly anisotropic, and its
characteristic features significantly change with the orientational order
parameter, concentration of fibrinogens and radius of a diffusing probe.Comment: 8 pages, 12 figure
Effects of nano-void density, size, and spatial population on thermal conductivity: a case study of GaN crystal
The thermal conductivity of a crystal is sensitive to the presence of
surfaces and nanoscale defects. While this opens tremendous opportunities to
tailor thermal conductivity, a true "phonon engineering" of nanocrystals for a
specific electronic or thermoelectric application can only be achieved when the
dependence of thermal conductivity on the defect density, size, and spatial
population is understood and quantified. Unfortunately, experimental studies of
effects of nanoscale defects are quite challenging. While molecular dynamics
simulations are effective in calculating thermal conductivity, the defect
density range that can be explored with feasible computing resources is
unrealistically high. As a result, previous work has not generated a fully
detailed understanding of the dependence of thermal conductivity on nanoscale
defects. Using GaN as an example, we have combined physically-motivated
analytical model and highly-converged large scale molecular dynamics
simulations to study effects of defects on thermal conductivity. An analytical
expression for thermal conductivity as a function of void density, size, and
population has been derived and corroborated with the model, simulations, and
experiments
The Casimir force on a surface with shallow nanoscale corrugations: Geometry and finite conductivity effects
We measure the Casimir force between a gold sphere and a silicon plate with
nanoscale, rectangular corrugations with depth comparable to the separation
between the surfaces. In the proximity force approximation (PFA), both the top
and bottom surfaces of the corrugations contribute to the force, leading to a
distance dependence that is distinct from a flat surface. The measured Casimir
force is found to deviate from the PFA by up to 15%, in good agreement with
calculations based on scattering theory that includes both geometry effects and
the optical properties of the material
Metabolic profiles of six African cultivars of cassava (Manihot esculenta Crantz) highlight bottlenecks of root yield
Open Access Article; Published online: 17 Jan 2020Cassava is an important staple crop in subâSaharan Africa, due to its high productivity even on nutrient poor soils. The metabolic characteristics underlying this high productivity are poorly understood including the mode of photosynthesis, reasons for the high rate of photosynthesis, the extent of source/sink limitation, the impact of environment, and the extent of variation between cultivars. Six commercial African cassava cultivars were grown in a greenhouse in Erlangen, Germany, and in the field in Ibadan, Nigeria. Source leaves, sink leaves, stems and storage roots were harvested during storage root bulking and analyzed for sugars, organic acids, amino acids, phosphorylated intermediates, minerals, starch, protein, activities of enzymes in central metabolism and yield traits. High ratios of RuBisCO:phosphoenolpyruvate carboxylase activity support a C3 mode of photosynthesis. The high rate of photosynthesis is likely to be attributed to high activities of enzymes in the CalvinâBenson cycle and pathways for sucrose and starch synthesis. Nevertheless, source limitation is indicated because root yield traits correlated with metabolic traits in leaves rather than in the stem or storage roots. This situation was especially so in greenhouseâgrown plants, where irradiance will have been low. In the field, plants produced more storage roots. This was associated with higher AGPase activity and lower sucrose in the roots, indicating that feedforward loops enhanced sink capacity in the high light and low nitrogen environment in the field. Overall, these results indicated that carbon assimilation rate, the K battery, root starch synthesis, trehalose, and chlorogenic acid accumulation are potential target traits for genetic improvement
A novel, aerosol-nanocrystal floating-gate device for non-volatile memory applications
This paper describes the fabrication, and structural and electrical characterization of a new, aerosol-nanocrystal floating-gate FET, aimed at non-volatile memory (NVM) applications. This aerosol-nanocrystal NVM device features program/erase characteristics comparable to conventional stacked gate NVM devices, excellent endurance (>l0^5 P/E cycles), and long-term non-volatility in spite of a thin bottom oxide (55-60Ă
). In addition, a very simple fabrication process makes this aerosol-nanocrystal NVM device a potential candidate for low cost NVM applications
Stepwise quantum decay of self-localized solitons
The two-phonon decay of self-localized soliton in a one-dimensional monatomic
anharmonic lattice caused by cubic anharmonicity is considered. It is shown
that the decay takes place with emission of phonon bursts. The average rate of
emission of phonons is of the order of vibrational quantum per vibrational
period. Characteristic time of the relaxation is determined by the quantum
anharmonicity parameter; this time may vary from a few (quantum lattices, large
anharmonicity) to thousands (ordinary lattices, small anharmonicity) of
vibrational periods.Comment: 6 pages, 3 figure
Measurement of the Casimir force between a gold sphere and silicon surface with nanoscale trench arrays
We report measurements of the Casimir force between a gold sphere and a
silicon surface with an array of nanoscale, rectangular corrugations using a
micromechanical torsional oscillator. At distance between 150 nm and 500 nm,
the measured force shows significant deviations from the pairwise additive
formulism, demonstrating the strong dependence of the Casimir force on the
shape of the interacting bodies. The observed deviation, however, is smaller
than the calculated values for perfectly conducting surfaces, possibly due to
the interplay between finite conductivity and geometry effects.Comment: 5 pages, 3 figure
Master Equation for the Motion of a Polarizable Particle in a Multimode Cavity
We derive a master equation for the motion of a polarizable particle weakly
interacting with one or several strongly pumped cavity modes. We focus here on
massive particles with complex internal structure such as large molecules and
clusters, for which we assume a linear scalar polarizability mediating the
particle-light interaction. The predicted friction and diffusion coefficients
are in good agreement with former semiclassical calculations for atoms and
small molecules in weakly pumped cavities, while the current rigorous quantum
treatment and numerical assessment sheds a light on the feasibility of
experiments that aim at optically manipulating beams of massive molecules with
multimode cavities.Comment: 30 pages, 5 figure
Elastic Spin Relaxation Processes in Semiconductor Quantum Dots
Electron spin decoherence caused by elastic spin-phonon processes is
investigated comprehensively in a zero-dimensional environment. Specifically, a
theoretical treatment is developed for the processes associated with the
fluctuations in the phonon potential as well as in the electron procession
frequency through the spin-orbit and hyperfine interactions in the
semiconductor quantum dots. The analysis identifies the conditions (magnetic
field, temperature, etc.) in which the elastic spin-phonon processes can
dominate over the inelastic counterparts with the electron spin-flip
transitions. Particularly, the calculation results illustrate the potential
significance of an elastic decoherence mechanism originating from the
intervalley transitions in semiconductor quantum dots with multiple equivalent
energy minima (e.g., the X valleys in SiGe). The role of lattice anharmonicity
and phonon decay in spin relaxation is also examined along with that of the
local effective field fluctuations caused by the stochastic electronic
transitions between the orbital states. Numerical estimations are provided for
typical GaAs and Si-based quantum dots.Comment: 57 pages, 14 figure
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