2,290 research outputs found
Synchronisation and liquid crystalline order in soft active fluids
We introduce a phenomenological theory for a new class of soft active fluids,
with the ability to synchronise. Our theoretical framework describes the
macroscopic behaviour of a collection of interacting anisotropic elements with
cyclic internal dynamics and a periodic phase variable. This system (i) can
spontaneously undergo a transition to a state with macroscopic orientational
order, with the elements aligned: a liquid crystal, (ii) attain another broken
symmetry state characterised by synchronisation of their phase variables or
(iii) a combination of both types of order. We derive the equations describing
a spatially homogeneous system and also study the hydrodynamic fluctuations of
the soft modes in some of the ordered states. We find that synchronisation can
promote the transition to a state with orientational order; and vice-versa.
Finally, we provide an explicit microscopic realisation: a suspension of
micro-swimmers driven by cyclic strokes.Comment: 5 pages, 3 figure
Dynamics and interactions of active rotors
We consider a simple model of an internally driven self-rotating object; a
rotor, confined to two dimensions by a thin film of low Reynolds number fluid.
We undertake a detailed study of the hydrodynamic interactions between a pair
of rotors and find that their effect on the resulting dynamics is a combination
of fast and slow motions. We analyse the slow dynamics using an averaging
procedure to take account of the fast degrees of freedom. Analytical results
are compared with numerical simulations. Hydrodynamic interactions mean that
while isolated rotors do not translate, bringing together a pair of rotors
leads to motion of their centres. Two rotors spinning in the same sense rotate
with an approximately constant angular velocity around each other, while two
rotors of opposite sense, both translate with the same constant velocity, which
depends on the separation of the pair. As a result a pair of counter-rotating
rotors are a promising model for controlled self-propulsion.Comment: 6 pages, 6 figure
Formation of light exotic nuclei in low-energy multinucleon transfer reactions
Low-energy multinucleon transfer reactions are shown to be very effective
tool for the production and spectroscopic study of light exotic nuclei. The
corresponding cross sections are found to be significantly larger as compared
with high energy fragmentation reactions. Several optimal reactions for the
production of extremely neutron rich isotopes of elements with Z=6-14 are
proposed.Comment: 8 figure
Violation and persistence of the K-quantum number in warm rotating nuclei
The validity of the K-quantum number in rapidly rotating warm nuclei is
investigated as a function of thermal excitation energy U and angular momentum
I, for the rare-earth nucleus 163Er. The quantal eigenstates are described with
a shell model which combines a cranked Nilsson mean-field and a residual
two-body interaction, together with a term which takes into account the angular
momentum carried by the K-quantum number in an approximate way. K-mixing is
produced by the interplay of the Coriolis interaction and the residual
interaction; it is weak in the region of the discrete rotational bands (U
\lesim 1MeV), but it gradually increases until the limit of complete violation
of the K-quantum number is approached around U \sim 2 - 2.5 MeV. The calculated
matrix elements between bands having different K-quantum numbers decrease
exponentially as a function of , in qualitative agreement with recent
data.Comment: 29 pages, 7 figure
Swimmers in thin films: from swarming to hydrodynamic instabilities
We investigate theoretically the collective dynamics of a suspension of low
Reynolds number swimmers that are confined to two dimensions by a thin fluid
film. Our model swimmer is characterized by internal degrees of freedom which
locally exert active stresses (force dipoles or quadrupoles) on the fluid. We
find that hydrodynamic interactions mediated by the film can give rise to
spontaneous continuous symmetry breaking (swarming), to states with either
polar or nematic homogeneous order. For dipolar swimmers, the stroke averaged
dynamics are enough to determine the leading contributions to the collective
behaviour. In contrast, for quadrupolar swimmers, our analysis shows that
detailed features of the internal dynamics play an important role in
determining the bulk behaviour. In the broken symmetry phases, we investigate
fluctuations of hydrodynamic variables of the system and find that these
destabilize order. Interestingly, this instability is not generic and depends
on length-scale.Comment: 4 pages, 2 figures, references added, typos corrected, new
introductio
Hydrodynamic synchronisation of non-linear oscillators at low Reynolds number
We introduce a generic model of weakly non-linear self-sustained oscillator
as a simplified tool to study synchronisation in a fluid at low Reynolds
number. By averaging over the fast degrees of freedom, we examine the effect of
hydrodynamic interactions on the slow dynamics of two oscillators and show that
they can lead to synchronisation. Furthermore, we find that synchronisation is
strongly enhanced when the oscillators are non-isochronous, which on the limit
cycle means the oscillations have an amplitude-dependent frequency.
Non-isochronity is determined by a nonlinear coupling being non-zero.
We find that its () sign determines if they synchronise in- or
anti-phase. We then study an infinite array of oscillators in the long
wavelength limit, in presence of noise. For , hydrodynamic
interactions can lead to a homogeneous synchronised state. Numerical
simulations for a finite number of oscillators confirm this and, when , show the propagation of waves, reminiscent of metachronal coordination.Comment: 4 pages, 2 figure
Effect of Supplementary Irrigation on Yield of Chickpea Genotypes in a Mediterranean Climate
Rosana G. Moreira, Editor-in-Chief; Texas A&M UniversityThis is a paper from International Commission of Agricultural Engineering (CIGR, Commission Internationale du Genie Rural) E-Journal Volume 8 (2006): Effect of Supplementary Irrigation on Yield of Chickpea Genotypes in a Mediterranean Climate. Manuscript LW 04 005. Vol. VIII. May, 2006
Electronic reconstruction of hexagonal FeS: a view from density functional dynamical mean-field theory
We present a detailed study of correlation- and pressure-induced electronic reconstruction in hexagonal iron monosulfide, a system which is widely found in meteorites and one of the components of Earth's core. Based on a perusal of experimental data, we stress the importance of multi-orbital electron-electron interactions in concert with first-principles band structure calculations for a consistent understanding of its intrinsic Mott–Hubbard insulating state. We explain the anomalous nature of pressure-induced insulator-metal-insulator transition seen in experiment, showing that it is driven by dynamical spectral weight transfer in response to changes in the crystal-field splittings under pressure. As a byproduct of this analysis, we confirm that the electronic transitions observed in pristine FeS at moderated pressures are triggered by changes in the spin state which causes orbital-selective Kondo quasiparticle electronic reconstruction at low energies
Soilless system with supplementary LED light to obtain a high-quality out-of-season production of green beans
Green bean (Phaseolus vulgaris L.) is one of the most important sources of vegetable proteins in the world and it is cultivated all year round, but the light availability, during the dark sea-son, limited its growth. Nevertheless, recent studies conducted on greenhouse horticulture demonstrated that, with the application of light emitting diodes (LEDs) as supplementary light (SL) technology, it is possible to overcome this limitation. Consequently, during the experiment conducted, two cultivars of green bean (‘Saporro’ and ‘Maestrale’) were grown with a soilless system in a cold greenhouse during the fall-winter period. To increase the photoperiod and the daily light integral (DLI), early in the morning, four hours of red (R), blue (B) and red+blue (R+B) supplementary light were supplied by LEDs at 180 μmol·m−2·s−1 (PPFD) at plants level. Plants grown under LEDs improved the yield and the gas exchange system compared with the plants grown under natural light; when B light was supplied as a sole source of SL, it increased the dry matter content and the bright-ness (L*) of the pods. Between the cultivars, ‘Maestrale’ produced 20 g·plant−1 of pods more than ‘Saporro’ but the latter’s colour was brighter (L*) and greener (a*), and ‘Saporro’ also showed the highest photosynthetic efficiency (ΦPSII). In conclusion, ‘Maestrale’ and ‘Saporro’ obtained encouraging out-of-season yields under different LED spectra, but among those B light seems to improve overall crop performances and pods quality
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