11,233 research outputs found
On uniformly rotating fluid drops trapped between two parallel plates
This contribution is about the dynamics of a liquid bridge between two fixed parallel plates. We consider a mathematical model and present some results from the doctoral thesis [10] of the first author. He showed that there is a Poisson bracket and a corresponding Hamiltonian, so that the model equations are in Hamiltonian form. The result generalizes previous results of Lewis et al. on the dynamics of free boundary problems for "free" liquid drops to the case of a drop between two parallel plates, including, especially the effect of capillarity and the angle of contact between the plates and the free fluid surface. Also, we prove the existence of special solutions which represent uniformly rotating fluid ridges, and we present specific stability conditions for these solutions. These results extend work of Concus and Finn [2] and Vogel [18],[19] on static capillarity problems (see also Finn [5]). Using the Hamiltonian structure of the model equations and symmetries of the solutions, the stability conditions can be derived in a systematic way. The ideas that are described will be useful for other situations involving capillarity and free boundary problems as well
Persistent quantum interfering electron trajectories
The emission of above-ionization-threshold harmonics results from the
recombination of two electron wavepackets moving along a "short" and a "long"
trajectory in the atomic continuum. Attosecond pulse train generation has so
far been attributed to the short trajectory, attempted to be isolated through
targeted trajectory-selective phase matching conditions. Here, we provide
experimental evidence for the contribution of both trajectories to the harmonic
emission, even under phase matching conditions unfavorable for the long
trajectory. This is finger printed in the interference modulation of the
harmonic yield as a function of the driving laser intensity. The effect is also
observable in the sidebands yield resulting from the frequency mixing of the
harmonics and the driving laser field, an effect with consequences in
cross-correlation pulse metrology approaches.Comment: 13 pages, 3 figure
Plant neighbor interactions of a native goldenrod impact abundance and composition of pollinator communities
The development of a solar powered residential heating and cooling system
A solar energy collector design is disclosed that would be efficient for both energy transfer and fluid flow, based upon extensive parametric analyses. Thermal design requirements are generated for the energy storage systems which utilizes sensible heat storage in water. Properly size system components (including the collector and storage) and a practical, efficient total system configuration are determined by means of computer simulation of system performance
Pyrolysis kinetics of hydrochars produced from brewer’s spent grains
The current market situation shows that large quantities of the brewer's spent grains (BSG)-the leftovers from the beer productions-are not fully utilized as cattle feed. The untapped BSG is a promising feedstock for cheap and environmentally friendly production of carbonaceous materials in thermochemical processes like hydrothermal carbonization (HTC) or pyrolysis. The use of a singular process results in the production of inappropriate material (HTC) or insufficient economic feasibility (pyrolysis), which hinders their application on a larger scale. The coupling of both processes can create synergies and allow the mentioned obstacles to be overcome. To investigate the possibility of coupling both processes, we analyzed the thermal degradation of raw BSG and BSG-derived hydrochars and assessed the solid material yield from the singular as well as the coupled processes. This publication reports the non-isothermal kinetic parameters of pyrolytic degradation of BSG and derived hydrochars produced in three different conditions (temperature-retention time). It also contains a summary of their pyrolytic char yield at four different temperatures. The obtained KAS (Kissinger-Akahira-Sunose) average activation energy was 285, 147, 170, and 188 kJ mol(-1) for BSG, HTC-180-4, HTC-220-2, and HTC-220-4, respectively. The pyrochar yield for all hydrochar cases was significantly higher than for BSG, and it increased with the severity of the HTC's conditions. The results reveal synergies resulting from coupling both processes, both in the yield and the reduction of the thermal load of the conversion process. According to these promising results, the coupling of both conversion processes can be beneficial. Nevertheless, drying and overall energy efficiency, as well as larger scale assessment, still need to be conducted to fully confirm the concept
Active contractility in actomyosin networks
Contractile forces are essential for many developmental processes involving
cell shape change and tissue deformation. Recent experiments on reconstituted
actomyosin networks, the major component of the contractile machinery, have
shown that active contractility occurs above a threshold motor concentration
and within a window of crosslink concentration. We present a microscopic
dynamic model that incorporates two essential aspects of actomyosin
self-organization: the asymmetric load response of individual actin filaments
and the correlated motor-driven events mimicking myosin-induced filament
sliding. Using computer simulations we examine how the concentration and
susceptibility of motors contribute to their collective behavior and interplay
with the network connectivity to regulate macroscopic contractility. Our model
is shown to capture the formation and dynamics of contractile structures and
agree with the observed dependence of active contractility on microscopic
parameters including the contractility onset. Cooperative action of
load-resisting motors in a force-percolating structure integrates local
contraction/buckling events into a global contractile state via an active
coarsening process, in contrast to the flow transition driven by uncorrelated
kicks of susceptible motors.Comment: 15 pages, 4 main figures, 4 supplementary figure
Effective operators from exact many-body renormalization
We construct effective two-body Hamiltonians and E2 operators for the p-shell
by performing ab initio no-core shell model (NCSM) calculations
for A=5 and A=6 nuclei and explicitly projecting the many-body Hamiltonians and
E2 operator onto the space. We then separate the effective E2
operator into one-body and two-body contributions employing the two-body
valence cluster approximation. We analyze the convergence of proton and neutron
valence one-body contributions with increasing model space size and explore the
role of valence two-body contributions. We show that the constructed effective
E2 operator can be parametrized in terms of one-body effective charges giving a
good estimate of the NCSM result for heavier p-shell nuclei.Comment: 9 pages, 8 figure
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