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See detailDynamical atomic charges: The case of ABO(3) compounds
Ghosez, Philippe ULg; Michenaud, J. P.; Gonze, X.

in Physical Review. B : Condensed Matter (1998), 58(10), 6224-6240

Based on recent first-principles computations in perovskite compounds, especially BaTiO3, we examine the significance of the Born effective charge concept and contrast it with other atomic charge ... [more ▼]

Based on recent first-principles computations in perovskite compounds, especially BaTiO3, we examine the significance of the Born effective charge concept and contrast it with other atomic charge definitions, either static (Mulliken, Bader, etc.) or dynamical (Callen, Szigeti, etc.). It is shown that static and dynamical charges are not driven by the same underlying parameters. A unified treatment of dynamical charges in periodic solids and large clusters is proposed. The origin of the difference between static and dynamical charges is discussed in terms of local polarizability and delocalized transfers of charge: local models succeed in reproducing anomalous effective charges thanks to large atomic polarizabilities but, in ABO(3) compounds, ab initio calculations favor the physical picture based upon transfer of charges. Various results concerning barium and strontium titanates are presented. The origin of anomalous Born effective charges is discussed thanks to a band-by-band decomposition which allows us to identify the displacement of the Wannier center of separated bands induced by an atomic displacement. The sensitivity of the Born effective charges to microscopic and macroscopic strains is examined. Finally, we estimate the spontaneous polarization in the four phases of barium titanate. [less ▲]

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See detailDynamical behaviour of electro-mechanical coupled problem
Rochus, Véronique ULg; rixen, Daniel; Golinval, Jean-Claude ULg

Conference (2004)

MEMS are very small devices in which electric as well as mechanical dynamics phenomena appear. Because of the microscopic scale, some strong coupling effects between the different physical fields appear ... [more ▼]

MEMS are very small devices in which electric as well as mechanical dynamics phenomena appear. Because of the microscopic scale, some strong coupling effects between the different physical fields appear, and some forces, which are negligible at macroscopic scales, have to be taken into account. In order to make a good design of these micro-systems, it is important to analyse the coupling between the electrical and mechanical fields. This paper concerns the modelling of the strong electromechanical coupling appearing in micro-electro-mechanical systems (MEMS). The finite element method (FEM) is used to perform dynamical analysis taking into account large mesh displacements. Analysing the vibration of microsystems is a fundamental issues in the design of a broad range of sensors and actuators. The state of the art currently consists in using staggered procedures to compute quasi-static configurations based on the iteration between a structural model loaded by electrostatic forces and an electrostatic model defined on a domain following the deformation of the structure. Staggered iteration then leads to a static equilibrium position. Performing a perturbation analysis around the static equilibrium yields the electromechanical linearized stiffness needed for computing the eigenfrequencies. Obviously, performing the perturbation analysis to evaluate the tangent stiffness for every degree of freedom leads to very high computing costs and therefore onlythe tangent stiffness associated with presumed modes (typically some purely structural modes) are computed. Such a procedure can lead to important inaccuracies for designs where the electrostatic coupling is not quasi-uniform. In our work, we have developed a fully coupled electro-mechanical formulation that allows to find static equilibrium positions in a non-staggered way and which provides fully consistent tangent stiffness matrices for vibration analysis. The efficiency of the approach will be illustrated on modes of micro-electromechanical devices. The results obtained indicate that using this approach pull-in can be computed very accurately and at low computational cost. Also the coupled electromechanical modes obtained in the vicinity of equilibrium positions can be significantly different from the approximations obtained using a structural reduction at forehand. Numerical results are checked against analytical results where appropriate. The formulation developed for the strongly coupled electromechanical problem allows consistent vibration analysis of the system and yields more accurate vibration eigenmodes and frequencies than the classical staggered approaches. A second interest of the coupled tangent matrix is the computation of the dynamical behaviour of the coupled problem when we apply suddenly a voltage to the electrodes. Even under the pull-in voltage, the overshoot of the dynamical response may reduce the distance between the plate so that the electric force becomes dominant and the plates stick together. This phenomenon is called the dynamical pull-in. We will also treat it in this research. [less ▲]

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See detailDynamical clustering in driven granular gas
Opsomer, Eric ULg; Ludewig, François ULg; Vandewalle, Nicolas ULg

in Europhysics Letters [=EPL] (2012), 99

Driven granular gases present rich dynamical behaviors. Due to inelastic collisions, particles may form dense and slow regions. These clusters emerge naturally during a cooling phenomenon but another ... [more ▼]

Driven granular gases present rich dynamical behaviors. Due to inelastic collisions, particles may form dense and slow regions. These clusters emerge naturally during a cooling phenomenon but another dynamical clustering is observed when the system is continuously excited. In this paper, the physical processes that trigger the transition from a granular gas to a dynamical cluster are evidenced through numerical simulations. At the granular scale, the transition is evidenced by the observation of caging effects. At the scale of the system, the transition is emphasized by density fluctuations. Physical arguments, based on relaxation times, provide an analytical prediction for the edge between dynamical regimes. [less ▲]

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See detailA dynamical energy-based hysteresis model for iron loss calculation in laminated cores
Steentjes, S.; Henrotte, F.; Geuzaine, Christophe ULg et al

in International Journal of Numerical Modelling (2014), 27(3), 433-443

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See detailDynamical evolution of titanium, strontium, and yttrium spots on the surface of the HgMn star HD 11753
Briquet, Maryline ULg; Korhonen, H.; González, J. F. et al

in Astronomy and Astrophysics (2010), 511

<BR /> Aims: We gathered about 100 high-resolution spectra of three typical HgMn (mercury-manganese) stars, <ASTROBJ>HD 11753</ASTROBJ>, <ASTROBJ>HD 53244</ASTROBJ>, and <ASTROBJ>HD 221507</ASTROBJ>, to ... [more ▼]

<BR /> Aims: We gathered about 100 high-resolution spectra of three typical HgMn (mercury-manganese) stars, <ASTROBJ>HD 11753</ASTROBJ>, <ASTROBJ>HD 53244</ASTROBJ>, and <ASTROBJ>HD 221507</ASTROBJ>, to search for slowly pulsating B-like pulsations and surface inhomogeneous distribution of various chemical elements. <BR /> Methods: Classical frequency analysis methods were used to detect line profile variability and to determine the variation period. Doppler imaging reconstruction was performed to obtain abundance maps of chemical elements on the stellar surface. <BR /> Results: For <ASTROBJ>HD 11753</ASTROBJ>, which is the star with the most pronounced variability, distinct spectral line profile changes were detected for Ti, Sr, Y, Zr, and Hg, whereas for <ASTROBJ>HD 53244</ASTROBJ> and <ASTROBJ>HD 221507</ASTROBJ> the most variable line profiles belong to the elements Hg and Y, respectively. We derived rotation periods for all three stars from the variations of radial velocities and equivalent widths of spectral lines belonging to inhomogeneously distributed elements: P[SUB]rot[/SUB] (<ASTROBJ>HD 11753</ASTROBJ>) = 9.54 d, P[SUB]rot[/SUB] (<ASTROBJ>HD 53244</ASTROBJ>) = 6.16 d, and P[SUB]rot[/SUB] (<ASTROBJ>HD 221507</ASTROBJ>) = 1.93 d. For <ASTROBJ>HD 11753</ASTROBJ> the Doppler imaging technique was applied to derive the distribution of the most variable elements Ti, Sr, and Y using two datasets separated by ~65 days. Results of Doppler imaging reconstruction revealed noticeable changes in the surface distributions of Ti II, Sr II, and Y II between the datasets, indicating the hitherto not well understood physical processes in stars with radiative envelopes that cause a rather fast dynamical chemical spot evolution. Based on observations obtained with the CORALIE Echelle Spectrograph on the 1.2-m Euler Swiss telescope, situated at La Silla, Chile.Postdoctoral Fellow of the Fund for Scientific Research, Flanders. [less ▲]

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See detailA dynamical model with hysteresis for the homogenization of ferromagnetic laminated cores
Henrotte, F.; Niyonzima, Innocent ULg; Steentjes, S. et al

in Proceedings of the 7th European Conference on Numerical Methods in Electromagnetism (NUMELEC2012) (2012, July)

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See detailDynamical Modeling of the Deep Impact Dust Ejecta Cloud
Bonev, T.; Ageorges, N.; Bagnulo, S. et al

in Käufl, H. U.; Sterken, C. (Eds.) Deep Impact as a World Observatory Event: Synergies in Space, Time, and Wavelength (2009)

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its ... [more ▼]

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its position and shape are governed by the physical properties of the dust grains. We use a Monte Carlo model to describe the evolution of the post-impact dust plume. The results of our dynamical simulations are compared to the data obtained with FORS2footnote{FORS stands for \underline{FO}cal Reducer and low dispersion Spectrograph for the Very Large Telescope (VLT) of the European Southern Observatory (ESO).} to derive the particle size distribution and the total amount of material contained in the dust ejecta cloud. [less ▲]

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See detailDynamical modeling of the Deep Impact dust ejecta cloud
Bonev, Tanyu; Ageorges, Nancy; Bagnulo, Stefano et al

Report (2007)

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its ... [more ▼]

The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud of dust which dissipated during several days after the impact. The brightness variations of this cloud and the changes of its position and shape are governed by the physical properties of the dust grains. We use a Monte Carlo model to describe the evolution of the post-impact dust plume. The results of our dynamical simulations are compared to the data obtained with FORS2, the FOcal Reducer and low dispersion Spectrograph for the VLT of the European Southern Observatory (ESO), to derive the particle size distribution and the total amount of material contained in the dust ejecta cloud. [less ▲]

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See detailDynamical problems for dust particles
Lemaitre, Anne; Jancart, Sylvie ULg

Conference (1996)

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See detailDynamical properties of DNA-ligand complexes under shear stress: insights from classical molecular dynamics
Fresch, Barbara ULg

Conference (2013, June 19)

Nucleic acids are flexible molecules: their dynamical properties play an essential role in molecular recognition and self-assembly. In the biological environment, because of mechanical forces acting at ... [more ▼]

Nucleic acids are flexible molecules: their dynamical properties play an essential role in molecular recognition and self-assembly. In the biological environment, because of mechanical forces acting at the molecular level, DNA is transiently deformed, cut and resealed, damaged and repaired, and the strands pulled apart and then re-annealed. These unique features make short DNA oligonucleotides promising building blocks in the development of “bottom-up” nano-devices and molecular logic machines. Single molecule manipulation techniques (Atomic Force Microscopy/ Optical Tweezers) allow detailed investigation of nucleic acids response to the application of controlled mechanical stress. Interpretations of these data in terms of molecular structural changes and dynamical properties call for a collaborative effort between experiments and theoretical/computational modeling. We have theoretically investigated the dynamical properties a DNA dodecamer and its complex with two different binders (Hoechst 33258 and Ethidium cation) by performing fully atomistic classical Molecular Dynamics (MD) simulations. We focused on the modeling of the so-called overstretching transition occurring when double stranded DNA is subjected to a shear stress until separation of the two strands occurs. The results of our analysis reveal the molecular details of the overstretching dynamics and point out the effects of the binders on the structure and the dynamics of the oligonucleotide under stress. The minor groove binder Hoechst 33258 acts as a zip between the two strands enhancing the lifetime of some base-pairs during the pulling experiment while ethidium cation, which is an intercalator, facilitates the separation of the double helix at high elongations. The understanding of the interactions between the binders and the helix at the molecular level gives insights into the unbinding pathways probed by Single Molecule Force Spectroscopy (SMFS). [less ▲]

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See detailDynamical Regimes of a Granular Gas in Microgravity : a Molecular Dynamics Study
Opsomer, Eric ULg; Ludewig, François ULg; Vandewalle, Nicolas ULg

in Journal of Physics: Conference Series (2011)

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See detailDynamical Spot Evolution in HD 11753
Korhonen, H.; Hubrig, S.; Briquet, Maryline ULg et al

in Magnetic Stars. Proceedings of the International Conference, held in the Special Astrophysical Observatory of the Russian AS, August 27- September 1, 2010, Eds: I. I. Romanyuk and D. O. Kudryavtsev (2011)

Our recent studies of HD 11753, a late B-type star showing a HgMn peculiarity for the first time revealed the presence of a fast dynamical evolution of chemical spots on the surface of this chemically ... [more ▼]

Our recent studies of HD 11753, a late B-type star showing a HgMn peculiarity for the first time revealed the presence of a fast dynamical evolution of chemical spots on the surface of this chemically peculiar early-type star. These observations suggest a hitherto unknown physical process operating in stars with outer radiative envelopes. Furthermore, we have also discovered existence of magnetic fields on HgMn stars that were up to now considered non-magnetic. Here we will discuss the dynamical spot evolution in HD 11753 in detail, and also summarize our new results on the magnetic fields of the AR Aur binary system. [less ▲]

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See detailDynamical study of non adiabatic unimolecular reactions: The conical intersection between the B 2B2 and à 2A1 states of H2O+.
Dehareng, Dominique ULg; Chapuisat, Xavier; Lorquet, Jean-Claude ULg et al

in Journal of Chemical Physics (1983), 78(3), 1246-1264

The conical intersection conecting the B 2A' and A 2A' states of the H2O+ ion is studied. The two potential energy surfaces are calculated ab initio by the SCF/CI method within the Cs point group. The ... [more ▼]

The conical intersection conecting the B 2A' and A 2A' states of the H2O+ ion is studied. The two potential energy surfaces are calculated ab initio by the SCF/CI method within the Cs point group. The nonadiabatic elements <A|d/dq|B> are computed for several cross sections throughout the potential energy surfaces. A transformation to the diabatic representation is performed. The linear model is found to be a good approximation in the region close to the apex of the cone. The global functions t(s) and T(S) governing the nonadiabatic transition probability are calculated; their shapes are those predicted by the Landau-Zener model (in the Nikitin bidimensional version). A dynamical study is undertaken by means of classical trajectory calculations on the upper adiabatic potential energy surface. An average transition probability Ptr is derived. Excitation of rotation or of the bending mode of H2O before photon impact has no influence on Ptr. Excitation of the symmetrical or antisymmetrical valence mode of H2O lowers Ptr. The shape of ln(1-Ptr) as a function of time indicates the existence of two distinct regimes at short and intermediate time ranges, characterized by two different rate constants k1 and k2 respectively. The rate constants are of the order of 10exp(14) s-1. k1 exhibits a maximum as a function of the absorbed energy Eabs whereas k2 decreases as a function of Eabs. [less ▲]

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See detailDynamical study of the pentaquark antidecuplet
Stancu, Floarea ULg

in Physics Letters B (2004), 595

Dynamical calculations are performed for all isomultiplets of the flavour antidecuplet to which the newly discovered pentaquark Theta(+) belongs. The framework is a constituent quark model where the short ... [more ▼]

Dynamical calculations are performed for all isomultiplets of the flavour antidecuplet to which the newly discovered pentaquark Theta(+) belongs. The framework is a constituent quark model where the short-range interaction has a flavour-spin structure. In this model the lowest pentaquarks have positive parity. Each antidecuplet member is described by a variational solution with the Pauli principle properly taken into account. By fitting the mass of Theta(+) of minimal content uudd, the mass of Xi(--), of minimal content ddss (u) over bar, is predicted at approximately 1960 MeV. The influence of the octet-antidecuplet mixing on the masses of the Y = I and 0 pentaquarks is considered within the same model and the role of the hyperfine interaction in this mixing is pointed out. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailDynamical Tunneling - Theory and Experiment
Keshavamurthy, Srihari; Schlagheck, Peter ULg

Book published by CRC Press (2011)

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See detailDynamical, dielectric, and elastic properties of GeTe investigated with first-principles density functional theory
Shaltaf, R.; Durgun, Engin ULg; Raty, Jean-Yves ULg et al

in Physical Review. B, Condensed Matter and Materials Physics (2008), 78

The dynamical, dielectric, and elastic properties of GeTe, a ferroelectric material in its low-temperature rhombohedral phase, have been investigated using first-principles density functional theory. We ... [more ▼]

The dynamical, dielectric, and elastic properties of GeTe, a ferroelectric material in its low-temperature rhombohedral phase, have been investigated using first-principles density functional theory. We report the electronic energy bands, phonon-dispersion curves, electronic and low-frequency dielectric tensors, infrared reflectivity, Born effective charges, and elastic and piezoelectric tensors and compare them with the existing theoretical and experimental results, as well as with similar quantities available for other ferroelectric materials, when appropriate. [less ▲]

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See detailDynamically constrained ensemble perturbations - application to tides on the West Florida Shelf
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Beckers, Jean-Marie ULg et al

in Ocean Science (2009), 5(3), 259-270

A method is presented to create an ensemble of perturbations that satisfies linear dynamical constraints. A cost function is formulated defining the probability of each perturbation. It is shown that the ... [more ▼]

A method is presented to create an ensemble of perturbations that satisfies linear dynamical constraints. A cost function is formulated defining the probability of each perturbation. It is shown that the perturbations created with this approach take the land-sea mask into account in a similar way as variational analysis techniques. The impact of the land-sea mask is illustrated with an idealized configuration of a barrier island. Perturbations with a spatially variable correlation length can be also created by this approach. The method is applied to a realistic configuration of the West Florida Shelf to create perturbations of the M2 tidal parameters for elevation and depth-averaged currents. The perturbations are weakly constrained to satisfy the linear shallow-water equations. Despite that the constraint is derived from an idealized assumption, it is shown that this approach is applicable to a non-linear and baroclinic model. The amplitude of spurious transient motions created by constrained perturbations of initial and boundary conditions is significantly lower compared to perturbing the variables independently or to using only the momentum equation to compute the velocity perturbations from the elevation. [less ▲]

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See detailDynamically constrained ensemble perturbations. Application to tides on the West Florida Shelf
Barth, Alexander ULg; Alvera Azcarate, Aïda ULg; Beckers, Jean-Marie ULg et al

Conference (2009)

A method is presented to create an ensemble of perturbations that satisfies linear dynamical constraints. A cost function is formulated defining the probability of each perturbation. It is shown that the ... [more ▼]

A method is presented to create an ensemble of perturbations that satisfies linear dynamical constraints. A cost function is formulated defining the probability of each perturbation. It is shown that the perturbations created with this approach take the land-sea mask into account in a similar way as variational analysis techniques. The impact of the land-sea mask is illustrated with an idealized configuration of a barrier island. Perturbations with a spatially variable correlation length can be also created by this approach. The method is applied to a realistic configuration of the West Florida Shelf to create perturbations of the M2 tidal parameters for elevation and depth-averaged currents. The perturbations are weakly constrained to satisfy the linear shallow-water equations. Despite that the constraint is derived from an idealized assumption, it is shown that this approach is applicable to a non-linear and baroclinic model. The amplitude of spurious transient motions created by constrained perturbations of initial and boundary conditions is significantly lower compared to perturbing the variables independently or to using only the momentum equation to compute the velocity perturbations from the elevation [less ▲]

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See detailThe DynaMICCS perspective. A mission for a complete and continuous view of the Sun dedicated to magnetism, space weather and space climate
Turck-Chièze, S.; Lamy, P.; Carr, C. et al

in Experimental Astronomy (2009), 23

The DynaMICCS mission is designed to probe and understand the dynamics of crucial regions of the Sun that determine solar variability, including the previously unexplored inner core, the radiative ... [more ▼]

The DynaMICCS mission is designed to probe and understand the dynamics of crucial regions of the Sun that determine solar variability, including the previously unexplored inner core, the radiative/convective zone interface layers, the photosphere/chromosphere layers and the low corona. The mission delivers data and knowledge that no other known mission provides for understanding space weather and space climate and for advancing stellar physics (internal dynamics) and fundamental physics (neutrino properties, atomic physics, gravitational moments...). The science objectives are achieved using Doppler and magnetic measurements of the solar surface, helioseismic and coronographic measurements, solar irradiance at different wavelengths and in-situ measurements of plasma/energetic particles/magnetic fields. The DynaMICCS payload uses an original concept studied by Thalès Alenia Space in the framework of the CNES call for formation flying missions: an external occultation of the solar light is obtained by putting an occulter spacecraft 150 m (or more) in front of a second spacecraft. The occulter spacecraft, a LEO platform of the mini sat class, e.g. PROTEUS, type carries the helioseismic and irradiance instruments and the formation flying technologies. The latter spacecraft of the same type carries a visible and infrared coronagraph for a unique observation of the solar corona and instrumentation for the study of the solar wind and imagers. This mission must guarantee long (one 11-year solar cycle) and continuous observations (duty cycle > 94%) of signals that can be very weak (the gravity mode detection supposes the measurement of velocity smaller than 1 mm/s). This assumes no interruption in observation and very stable thermal conditions. The preferred orbit therefore is the L1 orbit, which fits these requirements very well and is also an attractive environment for the spacecraft due to its low radiation and low perturbation (solar pressure) environment. This mission is secured by instrumental R and D activities during the present and coming years. Some prototypes of different instruments are already built (GOLFNG, SDM) and the performances will be checked before launch on the ground or in space through planned missions of CNES and PROBA ESA missions (PICARD, LYRA, maybe ASPIICS). [less ▲]

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See detailDynamics and constraints of livestock production systems in Cam Giang district, Hai Duong Province, North Vietnam
Han Quang, Hanh ULg; Vu Dinh, Ton; Lebailly, Philippe ULg

in Livestock Research for Rural Development (2013), 25(9),

In Northern Vietnam, the livestock production sector has been strongly encouraged to develop by the government for many years as an important livelihood strategy to alleviate household poverty. Over the ... [more ▼]

In Northern Vietnam, the livestock production sector has been strongly encouraged to develop by the government for many years as an important livelihood strategy to alleviate household poverty. Over the last few decades, it has been developed quickly, but remained unsustainable. This study aims to identify the dynamics of livestock production systems during the economic transformation period and their current constraints as the basic for setting up sustainable development policies. A survey, which is based on participatory and retrospective approaches, was conducted at 38 households in two communes of Hai Duong province in 2010. The results indicated a significant evolution of livestock production systems from a traditional small-scale production system into a specialized intensive one due to the land law and the rice land conversion program in 1990s and the industrialization and urbanization process in 2000s. The intensification of livestock production system, which is accompanied by the increasing dependence on imported inputs and the limited knowledge and skills in adequate techniques and disease management, poses a huge difficulty to producers in developing their livestock production systems. Therefore, the priority of development policies should be given to the promotion of the local resource utilisation as feed for animals and to the improvement of farmers’ ability to manage their production through not only government supports but also participation of social organisations and farmers. [less ▲]

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