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 $\Delta K$, 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 $\alpha$ being non-zero. We find that its ($\alpha$) 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 $\alpha > 0$, hydrodynamic interactions can lead to a homogeneous synchronised state. Numerical simulations for a finite number of oscillators confirm this and, when $\alpha <0$, 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