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Evolution of a collapsing and exploding Bose-Einstein condensate in different trap symmetries

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PHYSICAL REVIEW A 71, 053603 s2005d Evolution of a collapsing and exploding Bose-Einstein condensate in different trap symmetries Sadhan K. Adhikari Instituto de Física Teórica, Universidade Estadual Paulista, 01.405-900 São Paulo, São Paulo, Brazil sReceived 27 October 2004; published 12 May 2005d Based on the time-dependent Gross-Pitaevskii equation we study the evolution of a collapsing and exploding Bose-Einstein condensate in different trap symmetries to see the effect of confinement on collapse and subsequent explosion, which can be verified in future experiments. We make a prediction for the evolution of the shape of the condensate and the number of atoms in it for different trap symmetries scigar to pancaked as well as in the presence of an optical lattice potential. We also make a prediction for the jet formation in different cases when the collapse is suddenly terminated by changing the scattering length to zero via a Feshbach resonance. In addition to the usual global collapse to the center of the condensate, in the presence of an optical-lattice potential one could also have in certain cases independent collapse of parts of the condensate to local centers, which could be verified in experiments. DOI: 10.1103/PhysRevA.71.053603 PACS numberssd: 03.75.Nt I. INTRODUCTION Since the detection and study of Bose-Einstein condensates sBECsd of 7Li atoms with attractive interaction f1g, such condensates have been used in the study of solitons f2g and collapse f3g. In general an attractive condensate with number of atoms N larger than a critical value Ncr is not dynamically stable f1g. However, if such a strongly attractive condensate is “prepared” or somehow made to exist it experiences a dramatic collapse and explodes emitting atoms. The first demonstration of such a collapse was made with a 7Li condensate by slowly increasing the number of atoms in it from an external source, while the BEC showed a sequence of collapse with the number of atoms N oscillating around Ncr f1g. Such a collapse is driven by a stochastic process. A dynamical study of a much stronger and violent collapse has been performed by Donley et al. f3g on an attractive 85Rb BEC f4g in an axially symmetric trap, where they manipulated the interatomic interaction by changing the external magnetic field exploiting a nearby Feshbach resonance f5g. In the vicinity of a Feshbach resonance the atomic scattering length a can be varied over a huge range by adjusting an external magnetic field. Consequently, they changed the sign of the scattering length, thus transforming a repulsive condensate of 85Rb atoms into an attractive one which naturally evolves into a collapsing and exploding condensate. Donley et al. provided a quantitative estimate of the explosion of this BEC by measuring different properties of the exploding condensate. It has been realized that many features of the experiment by Donley et al. f3g on the collapsing condensate can be described f6–18g by the mean-field Gross-Pitaevskii sGPd equation f19g. To account for the loss of atoms from the strongly attractive collapsing condensate an absorptive nonlinear three-body recombination term is included in the GP equation f6g. However, we are fully aware that there are features of this experiment which are expected to be beyond mean-field description. Among these are the distribution of number and energy of emitted high-energy s,10−7 Kelvind burst atoms reported in the experiment. Although there have 1050-2947/2005/71s5d/053603s8d/$23.00 been some attempts f9–11g to describe the burst atoms using the mean-field GP equation, now there seems to be a consensus that they cannot be described adequately and satisfactorily using a mean-field approach f13–15g. Also, the GP equation did not successfully predict the “time to collapse” sor the time lag to start the collapse after changing the sign of the scattering lengthd in all cases investigated in the experiment, as has been pointed out in Refs. f12,16g. However, the reason for the failure to predict the time to collapse is not clear. The GP equation is supposed to deal with the zero- or very low-energy condensed phase of atoms and has been used to predict the time to collapse, evolution of the collapsing condensate including the very low-energy s; nano Kelvind jet formation f3g when the collapse is suddenly stopped before completion by jumping the scattering length to aquench = 0 snoninteracting atomsd or positive srepulsive atomsd values. The jet atoms are slowly formed in the radial direction when the collapse is stopped in this fashion. In the experiment usually aquench = 0. It is emphasized that unlike the emitted uncondensed “hotter” missing and burst atoms reported in the experiment f3g the jet atoms form a part of the surviving “colder” condensate and hence should be describable by the mean-field GP equation. Saito et al. f9g, Bao et al. f15g and this author f17g presented a mean-field description of jet formation and Calzetta et al. f14g treated jet formation exclusively as a quantum effect. The GP equation has also been used to study the conditions of stability as well as collapse f20g of a coupled condensate. More recently, the present author used successfully the GP equation to describe the essentials of the collapse dynamics of a mixture of a boson and fermion condensates f21g. In this paper we extend the study of the evolution of the collapsing and exploding condensate in different symmetries to see the effect of confinement on collapse and subsequent explosion. Future experiments may verify these predictions and thus provide a more stringent test for the mean-field GP equation. The experiment of Donley et al. was performed for an axially-symmetric cigar-shaped BEC. In the present analysis we extend our study to a spherical as well as an axially-symmetric pancake-shaped BEC. 053603-1 ©2005 The American Physical Society PHYSICAL REVIEW A 71, 053603 s2005d SADHAN K. ADHIKARI Lately, the periodic optical-lattice potential has played an essential role in many theoretical and experimental studies of Bose-Einstein condensation, e.g., in the study of Josephson oscillation f22g and its disruption f23g, interference of matter wave f24g, BEC dynamics on periodic trap f25g, etc. The optical-lattice confinement creates a BEC in an entirely different shape and trapping condition form a conventional harmonic oscillator trapping. Consequently, one could have a collapse of a different nature in the presence of an opticallattice potential. We shall see in our study that under certain conditions of trap symmetry, in addition to the usual global collapse to the center, in the presence of the optical-lattice potential one could have independent local collapse of pieces of the condensate to local centers. In view of this we study the dynamics of a collapsing and exploding BEC of different symmetries prepared on a periodic optical-lattice potential. We study the evolution of the shape and size of the condensate as well as the jet formation upon stopping the collapse by making the BEC repulsive or noninteracting. In Sec. II we present our mean-field model. In Sec. III we present our results that we compare with the experiment and other numerical studies. In Sec. III we also present a physical discussion of our findings and some concluding remarks are given in Sec. IV. II. NONLINEAR GROSS-PITAEVSKII EQUATION The time-dependent Bose-Einstein condensate wave function Csr ; td at position r and time t allowing for atomic loss may be described by the following mean-field nonlinear GP equation f19g, F − i" ] " 2¹ 2 i" + Vsrd + gNuCsr; tdu2 − fK2NuCsr; tdu2 − ]t 2m 2 G + K3N2uCsr; tdu4g Csr; td = 0. s2.1d Here m is the mass and N the number of atoms in the condensate, g = 4p"2a / m the strength of interatomic interaction, with a the atomic scattering length. The terms K2 and K3 denote two-body dipolar and three-body recombination lossrate coefficients, respectively, and include the Bose statistical factors 1 / 2! and 1 / 3! needed to describe the condensate. The trap potential with cylindrical symmetry may be written as Vsrd = 21 mv2sr2 + n2z2d + Vop, where v is the angular frequency in the radial direction r and nv that in the axial direction z of the harmonic trap. The cigar-shaped condensate corresponds to n , 1 and pancake-shaped condensate corresponds to n . 1. The periodic optical-lattice potential in the axial z direction created by a standing-wave laser field of wavelength l is given by Vop = kER cos2skLzd with ER = "2kL2 / s2md, kL = 2p / l and k the strength. The normalization condition of the wave function is edruCsr ; tdu2 = 1. Here we simulate the atom loss via the most important quintic three-body term K3 f6–9g. The contribution of the cubic twobody loss term K2 f26g is expected to be negligible f6,9g compared to the three-body term in the present problem of the collapsed condensate with large density and will not be considered here. In the absence of angular momentum the wave function has the form Csr ; td = csr , z ; td. Now transforming to dimensionless variables defined by x = Î2r / l, y = Î2z / l, t = tv, l ; Î" / smvd, and fsx,y;td ; we get F −i wsx,y;td = x ÎÎ l3 S 8 csr,z; td, s2.2d D U 4 ] ]2 1 ] ]2 1 − 2+ − 2 + x2 + n2y 2 − 2 4 ]t ]x x ]x ] y x +k S D U UG 4p2 l20 − izn2 U 2p wsx,y;td y + 8Î2pn l0 x cos2 wsx,y;td x 2 4 wsx,y;td = 0, s2.3d where n = Na / l, l0 = Î2l / l and z = 4K3 / sa2l4vd. The normalization condition of the wave function becomes E E ` Nnorm ; 2p ` dx 0 dyuwsx,y;tdu2x−1 . s2.4d −` For z = K3 = 0, Nnorm = 1, however, in the presence of loss K3 . 0, Nnorm , 1. The number of remaining atoms N in the condensate is given by N = N0Nnorm, where N0 is the initial number of atoms. In this study the term K3 or z = 4K3sa2l4vd will be used for a description of atom loss in the case of attractive interaction. The choice of K3 has a huge effect on some experimental observables and the fact that it is experimentally not precisely determined is a problem for existing theory on the experiment. As in our previous study f17g we employ z = 2 and K3 , a2 throughout this study. It was found f17g that this value of zs=2d reproduced the time evolution of the condensate in the experiment of Donley et al. f3g satisfactorily for a wide range of variation of an initial number of atoms and scattering lengths f7g. The present value z = 2 with K3 = za2l4v / 4 leads to f7,8g K3 . 8 3 10−25 cm6 / s at a = −340a0 and K3 . 6 3 10−27 cm6 / s at a = −30a0, where a0 is the Bohr radius. The experimental value of the loss rate is f26g K3 . 7 3 10−25 cm6 / s at a = −340a0 which is very close to the present choice. Of the theoretical studies, the K3 values used by Santos et al. f11g sK3 . 7 3 10−25 cm6 / s at a = −340a0d, Savage et al. f12g sK3 . 193 10−27 cm6 / s at a = −30a0d, Bao et al. f15g sK3 . 6.753 10−27 cm6 / s at a = −30a0d and the present author f7g are consistent with each other and describes well the decay of the collapsing condensate. However, it seems unlikely that the much smaller value of K3 sK3 = 2 3 10−28 cm6 / s at a = −30a0d used in Refs. f9,10g will properly describe the decay of the collapsing condensate. III. NUMERICAL RESULT We solve the GP equation s2.3d numerically using a timeiteration method based on the Crank-Nicholson discretization scheme elaborated on in Ref. f27g. We discretize the GP 053603-2 PHYSICAL REVIEW A 71, 053603 s2005d EVOLUTION OF A COLLAPSING AND EXPLODING FIG. 1. sColor onlined Number of remaining atoms Nstd in the condensate of 16 000 85Rb atoms after ramping the scattering length from ain = 7a0 to sad acol = −30a0 and sbd acol = −6.7a0 as a function of evolution time in milliseconds. The unpublished and unanalyzed experimental points of Donley et al. f3g for acol = −6.7a0 are taken from Bao et al. f15g. The curves are labeled by their respective optical lattice strength k and axial trap parameter n. final scattering lengths after collapse acol = −30a0 and −6.7a0, respectively. In both cases the experimental data for k = 0 and n = 0.39 scigar-shaped condensated are in agreement with the theoretical simulation without any adjustable parameter. For acol = −6.7a0, the unpublished experimental data of f3g as shown in Fig. 1sbd are as quoted in Bao et al. f15g. These data are not fully analyzed and for large time are expected to be bigger than the actual number of atoms. This is due to the difficulty in separating the remnant condensate from the oscillating atom cloud surrounding it f3g. In addition, in Figs. 1 we plot the results for k = 4 and n = 0.39 scigar-shaped condensate with optical-lattice potentiald; k = 4 and n = 1 sspherical condensate with optical-lattice potentiald; k = 0 and n = 1 sspherical condensated; and k = 0 and n = 5 spancake-shaped condensated. As the repulsive condensate is quickly turned attractive at t = 0, via a Feshbach resonance, the condensate starts to collapse and once the central density increases sufficiently it loses a significant portion of atoms in an explosive fashion via three-body recombination to form a remnant condensate in about 15 ms as can be seen in Figs. 1. After explosion the number of atoms in the remnant continues to be much larger than the critical number of atoms Ncr and it keeps on losing atoms at a much slower rate without undergoing a violent explosion. However, in some cases the remnant undergoes a smaller secondary explosion while it loses a reasonable fraction of atoms in a small interval of time. This happens when the number of atoms in the remnant is much larger than Ncr so as to initiate a secondary collapse and explosion. Prominent secondary explosions in the presence of optical-lattice potential are found in different cases in Figs. 1 for 40. t . 30. B. Time to collapse equation using time step D = 0.001 and space step 0.1 for both x and y spanning x from 0 to 15 and y from −30 to 30. This domain of space was sufficient to encompass the whole condensate wave function in this study. First, the numerical simulation is performed with the actual parameters of the experiment by Donley et al. f3g, e.g., the initial number of atoms, scattering lengths, etc. Throughout this investigation we take the harmonic oscillator length l = 2607 nm and one unit of time t = 0.009 095 s f7g consistent with the experiment of Donley et al. f3g. When we include an optical-lattice potential, the optical-lattice strength k is taken to be 4, and the reduced wavelength l0 is taken to be 1 throughout this study. These optical-lattice parameters are consistent with the experiment by Cataliotti et al. f22,23g. The numerical simulation using Eq. s2.3d with a nonzero zs=2d immediately yields the remaining number of atoms in the condensate after the jump in scattering length. A. Evolution of the number of atoms in the condensate In the experiment the initial scattering length ains.0d of a repulsive condensate is suddenly jumped to acols,0d to start the collapse. The remaining number Nstd of atoms versus time for an initial number of atoms N0 = 16 000 and an initial scattering length ain = 7a0 are shown in Figs. 1sad and 1sbd for Another important aspect of collapse is the “time to collapse” or the time to initiate the collapse and explosion tcollapse after the repulsive condensate is suddenly made attractive at t = 0. Collapse is characterized by a sudden rapid emission of atoms from the condensate. From Figs. 1 we find that the time to collapse is the shortest for a pancake-shaped symmetry sn . 1d and is the longest for a cigar-shaped symmetry sn , 1d. The inclusion of an optical-lattice potential has no effect on the time to collapse for a spherical or pancake-shaped symmetry. However, its inclusion reduces the time to collapse for a cigar-shaped symmetry. These features of the time to collapse are illustrated in Fig. 2 where we plot tcollapse vs uacollapseu / a0 of the collapse of a condensate of 6000 atoms originally in a noninteracting state with scattering length ainitial = 0. Then suddenly its scattering length is changed to a negative sattractived value acollapse and its tcollapse is obtained. Donley et al. experimentally measured tcollapse in this case for n = 0.39 and k = 0 and here we provide the same for other values of trap symmetry n and also in the presence of a optical lattice potential with k = 4. It should be recalled that the prediction of the GP equation by this author and others f9,12,16g does not very well describe the experimental results of Donley et al. for the time to collapse. The inclusion of the optical-lattice potential has reduced the time to collapse in a cigar-shaped condensate sn = 0.1d. 053603-3 PHYSICAL REVIEW A 71, 053603 s2005d SADHAN K. ADHIKARI FIG. 2. sColor onlined The time to collapse tcollapse vs uacollapseu / a0 for ainitial = 0, N0 = 6000. Solid circle with error bar: experiment f3g with n = 0.39 and k = 0; open circle: mean-field model of f9g with n = 0.39 and k = 0; full line: the present result with n = 0.39 and k = 0; dashed line: the present result with n = 1 and k = 0; dashed-dotted line: the present result with n = 0.1 and k = 4; and dashed-doubled-dotted line: the present result with n = 0.1 and k = 0. The above features of time to collapse could be understood on a physical ground. In a cigar-shaped condensate the average distance among the atoms is larger than that in a pancake-shaped condensate of the same volume. Hence, due to atomic attraction a cigar-shaped condensate has to contract during a larger interval of time than a pancake-shaped condensate before the central density increases sufficiently to start an explosion. This justifies a larger time to collapse for a cigar-shaped condensate. In the presence of an opticallattice potential for cigar-shaped symmetry the optical-lattice divides the condensate in a large number of pieces. What predominates in the collapse of such a condensate is the collapse equilibrium value of MeCpG steps (,+14 deg.) [31,44]. In comparison, methylation has a significantly lower stability cost when happening at major groove positions, such as 211 and 21 base pair from dyad (mutations 9 and 12), where the roll of the nucleosome bound conformation (+10 deg.) is more compatible with the equilibrium geometry of MeCpG steps. The nucleosome destabilizing effect of cytosine methylation increases with the number of methylated cytosines, following the same position dependence as the single methylations. The multiple-methylation case reveals that each major groove meth- PLOS Computational Biology | www.ploscompbiol.org 3 November 2013 | Volume 9 | Issue 11 | e1003354 DNA Methylation and Nucleosome Positioning ylation destabilizes the nucleosome by around 1 kJ/mol (close to the average estimate of 2 kJ/mol obtained for from individual methylation studies), while each minor groove methylation destabilizes it by up to 5 kJ/mol (average free energy as single mutation is around 6 kJ/mol). This energetic position-dependence is the reverse of what was observed in a recent FRET/SAXS study [30]. The differences can be attributed to the use of different ionic conditions and different sequences: a modified Widom-601 sequence of 157 bp, which already contains multiple CpG steps in mixed orientations, and which could assume different positioning due to the introduction of new CpG steps and by effect of the methylation. The analysis of our trajectories reveals a larger root mean square deviation (RMSD) and fluctuation (RMSF; see Figures S2– S3 in Text S1) for the methylated nucleosomes, but failed to detect any systematic change in DNA geometry or in intermolecular DNA-histone energy related to methylation (Fig. S1B, S1C, S4–S6 in Text S1). The hydrophobic effect should favor orientation of the methyl group out from the solvent but this effect alone is not likely to justify the positional dependent stability changes in Figure 2, as the differential solvation of the methyl groups in the bound and unbound states is only in the order of a fraction of a water molecule (Figure S5 in Text S1). We find however, a reasonable correlation between methylation-induced changes in hydrogen bond and stacking interactions of the bases and the change in nucleosome stability (see Figure S6 in Text S1). This finding suggests that methylation-induced nucleosome destabilization is related to the poorer ability of methylated DNA to fit into the required conformation for DNA in a nucleosome. Changes in the elastic deformation energy between methylated and un-methylated DNA correlate with nucleosomal differential binding free energies To further analyze the idea that methylation-induced nucleosome destabilization is connected to a worse fit of methylated DNA into the required nucleosome-bound conformation, we computed the elastic energy of the nucleosomal DNA using a harmonic deformation method [36,37,44]. This method provides a rough estimate of the energy required to deform a DNA fiber to adopt the super helical conformation in the nucleosome (full details in Suppl. Information Text S1). As shown in Figure 2, there is an evident correlation between the increase that methylation produces in the elastic deformation energy (DDE def.) and the free energy variation (DDG bind.) computed from MD/TI calculations. Clearly, methylation increases the stiffness of the CpG step [31], raising the energy cost required to wrap DNA around the histone octamers. This extra energy cost will be smaller in regions of high positive roll (naked DNA MeCpG steps have a higher roll than CpG steps [31]) than in regions of high negative roll. Thus, simple elastic considerations explain why methylation is better tolerated when the DNA faces the histones through the major groove (where positive roll is required) that when it faces histones through the minor groove (where negative roll is required). Nucleosome methylation can give rise to nucleosome repositioning We have established that methylation affects the wrapping of DNA in nucleosomes, but how does this translate into chromatin structure? As noted above, accumulation of minor groove methylations strongly destabilizes the nucleosome, and could trigger nucleosome unfolding, or notable changes in positioning or phasing of DNA around the histone core. While accumulation of methylations might be well tolerated if placed in favorable positions, accumulation in unfavorable positions would destabilize the nucleosome, which might trigger changes in chromatin structure. Chromatin could in fact react in two different ways in response to significant levels of methylation in unfavorable positions: i) the DNA could either detach from the histone core, leading to nucleosome eviction or nucleosome repositioning, or ii) the DNA could rotate around the histone core, changing its phase to place MeCpG steps in favorable positions. Both effects are anticipated to alter DNA accessibility and impact gene expression regulation. The sub-microsecond time scale of our MD trajectories of methylated DNAs bound to nucleosomes is not large enough to capture these effects, but clear trends are visible in cases of multiple mutations occurring in unfavorable positions, where unmethylated and methylated DNA sequences are out of phase by around 28 degrees (Figure S7 in Text S1). Due to this repositioning, large or small, DNA could move and the nucleosome structure could assume a more compact and distorted conformation, as detected by Lee and Lee [29], or a slightly open conformation as found in Jimenez-Useche et al. [30]. Using the harmonic deformation method, we additionally predicted the change in stability induced by cytosine methylation for millions of different nucleosomal DNA sequences. Consistently with our calculations, we used two extreme scenarios to prepare our DNA sequences (see Fig. 3): i) all positions where the minor grooves contact the histone core are occupied by CpG steps, and ii) all positions where the major grooves contact the histone core are occupied by CpG steps. We then computed the elastic energy required to wrap the DNA around the histone proteins in unmethylated and methylated states, and, as expected, observed that methylation disfavors DNA wrapping (Figure 3A). We have rescaled the elastic energy differences with a factor of 0.23 to match the DDG prediction in figure 2B. In agreement with the rest of our results, our analysis confirms that the effect of methylation is position-dependent. In fact, the overall difference between the two extreme methylation scenarios (all-in-minor vs all-in-major) is larger than 60 kJ/mol, the average difference being around 15 kJ/ mol. We have also computed the elastic energy differences for a million sequences with CpG/MeCpG steps positioned at all possible intermediate locations with respect to the position (figure 3B). The large differences between the extreme cases can induce rotations of DNA around the histone core, shifting its phase to allow the placement of the methylated CpG steps facing the histones through the major groove. It is illustrative to compare the magnitude of CpG methylation penalty with sequence dependent differences. Since there are roughly 1.5e88 possible 147 base pairs long sequence combinations (i.e., (4n+4(n/2))/2, n = 147), it is unfeasible to calculate all the possible sequence effects. However, using our elastic model we can provide a range of values based on a reasonably large number of samples. If we consider all possible nucleosomal sequences in the yeast genome (around 12 Mbp), the energy difference between the best and the worst sequence that could form a nucleosome is 0.7 kj/mol per base (a minimum of 1 kJ/mol and maximum of around 1.7 kJ/mol per base, the first best and the last worst sequences are displayed in Table S3 in Text S1). We repeated the same calculation for one million random sequences and we obtained equivalent results. Placing one CpG step every helical turn gives an average energetic difference between minor groove and major groove methylation of 15 kJ/ mol, which translates into ,0.5 kJ/mol per methyl group, 2 kJ/ mol per base for the largest effects. Considering that not all nucleosome base pair steps are likely to be CpG steps, we can conclude that the balance between the destabilization due to CpG methylation and sequence repositioning will depend on the PLOS Computational Biology | www.ploscompbiol.org 4 November 2013 | Volume 9 | Issue 11 | e1003354 DNA Methylation and Nucleosome Positioning Figure 3. Methylated and non-methylated DNA elastic deformation energies. (A) Distribution of deformation energies for 147 bplong random DNA sequences with CpG steps positioned every 10 base steps (one helical turn) in minor (red and dark red) and major (light and dark blue) grooves respectively. The energy values were rescaled by the slope of a best-fit straight line of figure 2, which is 0.23, to por la lectura a través de la lectura de la prensa. La educación en los medios las fuerzas dispersas en función de los soportes mediáticos y orientarse más hacia la educación en medios que al dominio adquiere pleno derecho y entidad en la sección sexta titulada «competencias sociales y cívi- técnico de los aparatos. cas» que indica que «los alum- nos deberán ser capaces de juz- gar y tendrán espíritu crítico, lo que supone ser educados en los las programaciones oficiales, ya que, a lo largo de un medios y tener conciencia de su lugar y de su influencia estudio de los textos, los documentalistas del CLEMI en la sociedad». han podido señalar más de una centena de referencias a la educación de los medios en el seno de disciplinas 4. Un entorno positivo como el francés, la historia, la geografía, las lenguas, Si nos atenemos a las cifras, el panorama de la las artes plásticas : trabajos sobre las portadas de educación en medios es muy positivo. Una gran ope- prensa, reflexiones sobre temas mediáticos, análisis de ración de visibilidad como la «Semana de la prensa y publicidad, análisis de imágenes desde todos los ángu- de los medios en la escuela», coordinada por el CLE- los, reflexión sobre las noticias en los países europeos, MI, confirma año tras año, después de 17 convocato- información y opinión rias, el atractivo que ejerce sobre los profesores y los Esta presencia se constata desde la escuela mater- alumnos. Concebida como una gran operación de nal (2 a 6 años) donde, por ejemplo, se le pregunta a complementariedad entre la escuela y los profesiona- los niños más pequeños si saben diferenciar entre un les de los medios, alrededor del aprendizaje ciudada- periódico, un libro, un catálogo, a través de activida- no de la comunicación mediática, este evento moviliza des sensoriales, si saben para qué sirve un cartel, un durante toda una semana un porcentaje elevado de periódico, un cuaderno, un ordenador si son capa- centros escolares que representan un potencial de 4,3 ces de reconocer y distinguir imágenes de origen y de millones de alumnos (cifras de 2006). Basada en el naturaleza distintas. Podríamos continuar con más voluntariado, la semana permite desarrollar activida- ejemplos en todos los niveles de enseñanza y práctica- des más o menos ambiciosas centradas en la introduc- Páginas 43-48 ción de los medios en la vida de la escuela a través de la instalación de kioscos, organización de debates con profesionales y la confección por parte de los alumnos de documentos difundidos en los medios profesionales. Es la ocasión de dar un empujón a la educación en medios y de disfrutarlos. Los medios –un millar en 2006– se asocian de maneras diversas ofreciendo ejemplares de periódicos, acceso a noticias o a imágenes, proponiendo encuentros, permitiendo intervenir a los jóvenes en sus ondas o en sus columnas Esta operación da luz al trabajo de la educación en medios y moviliza a los diferentes participantes en el proyecto. 5. La formación de los docentes La formación es uno de los pilares principales de la educación en los medios. Su función es indispensable ya que no se trata de una disciplina, sino de una enseñanza que se hace sobre la base del voluntariado y del compromiso personal. Se trata de convencer, de mostrar, de interactuar. En primer lugar es necesario incluirla en la formación continua de los docentes, cuyo volumen se ha incrementado desde 1981 con la aparición de una verdadera política de formación continua de personal. Es difícil dar una imagen completa del volumen y del público, pero si nos atenemos a las cifras del CLEMI, hay más de 24.000 profesores que han asistido y se han involucrado durante 2004-05. 5.1. La formación continua En la mayoría de los casos, los profesores reciben su formación en contextos cercanos a su centro de trabajo, o incluso en este mismo. Después de una política centrada en la oferta que hacían los formadores, se valora más positivamente la demanda por parte del profesorado, ya que sólo así será verdaderamente fructífera. Los cursos de formación se repartieron en varias categorías: desde los formatos más tradicionales (cursos, debates, animaciones), hasta actividades de asesoramiento y de acompañamiento, y por supuesto los coloquios que permiten un trabajo en profundidad ya que van acompañados de expertos investigadores y profesionales. Citemos, por ejemplo en 2005, los coloquios del CLEMI-Toulouse sobre el cine documental o el del CLEMI-Dijon sobre «Políticos y medios: ¿connivencia?». Estos coloquios, que forman parte de un trabajo pedagógico regular, reagrupan a los diferentes participantes regionales y nacionales alrededor de grandes temas de la educación en medios y permiten generar nuevos conocimientos de aproximación y una profundización. Páginas 43-48 Hay otro tipo de formación original que se viene desarrollando desde hace menos tiempo, a través de cursos profesionales, como por ejemplo, en el Festival Internacional de Foto-periodismo «Visa para la imagen», en Perpignan. La formación se consolida en el curso, da acceso a las exposiciones, a las conferencias de profesionales y a los grandes debates, pero añade además propuestas pedagógicas y reflexiones didácticas destinadas a los docentes. Estas nuevas modalidades de formación son también consecuencia del agotamiento de la formación tradicional en las regiones. Los contenidos más frecuentes en formación continua conciernen tanto a los temas más clásicos como a los cambios que se están llevando a cabo en las prácticas mediáticas. Así encontramos distintas tendencias para 2004-05: La imagen desde el ángulo de la producción de imágenes animadas, el análisis de la imagen de la información o las imágenes del J.T. La prensa escrita y el periódico escolar. Internet y la información en línea. Medios y educación de los medios. 5.2 La formación inicial La formación inicial está aun en un grado muy ini- cial. El hecho de que la educación en medios no sea una disciplina impide su presencia en los IUFM (Institutos Universitarios de Formación de Maestros) que dan una prioridad absoluta a la didáctica de las disciplinas. En 2003, alrededor de 1.400 cursillistas sobre un total de 30.000 participaron en un momento u otro de un módulo de educación en medios. Estos módulos se ofrecen en función del interés que ese formador encuentra puntualmente y forman parte a menudo de varias disciplinas: documentación, letras, historia-geografía Estamos aún lejos de una política concertada en este dominio. La optativa «Cine-audiovisual» ha entrado desde hace muy poco tiempo en algunos IUFM destinada a obtener un certificado de enseñanza de la opción audiovisual y cine. Internet tiene cabida también en los cursos de formación inicial, recientemente con la aparición de un certificado informático y de Internet para los docentes, dirigido más a constatar competencias personales que a valorar una aptitud para enseñarlos. 6. ¿Y el futuro? El problema del futuro se plantea una vez más por la irrupción de nuevas técnicas y nuevos soportes. La difusión acelerada de lo digital replantea hoy muchas cuestiones relativas a prácticas mediáticas. Muchos Comunicar, 28, 2007 47 Comunicar, 28, 2007 Enrique Martínez-Salanova '2007 para Comunicar 48 trabajos que llevan el rótulo de la educación en medios solicitan una revisión ya que los conceptos cambian. La metodología elaborada en el marco de la educación en medios parece incluso permitir la inclinación de la sociedad de la información hacia una sociedad del conocimiento, como defiende la UNESCO. En Francia, se necesitaría unir las fuerzas dispersas en función de los soportes mediáticos y orientarse más hacia la educación en medios que al dominio técnico de los aparatos. Los avances recientes en el reconocimiento de estos contenidos y las competencias que supondrían podrían permitirlo. Referencias CLEMI/ACADEMIE DE BORDEAUX (Ed.) (2003): Parcours médias au collège: approches disciplinaires et transdisciplinaires. Aquitaine, Sceren-CRDP. GONNET, J. (2001): Education aux médias. Les controverses fécondes. Paris, Hachette Education/CNDP. SAVINO, J.; MARMIESSE, C. et BENSA, F. (2005): L’éducation aux médias de la maternelle au lycée. Direction de l’Enseignement Scolaire. Paris, Ministère de l’Education Nationale, Sceren/CNDP, Témoigner. BEVORT, E. et FREMONT, P. (2001): Médias, violence et education. Paris, CNDP, Actes et rapports pour l’éducation. – www.clemi.org: fiches pédagogiques, rapports et liens avec les pages régionales/académiques. – www.ac-nancy-metz.fr/cinemav/quai.html: Le site «Quai des images» est dédié à l’enseignement du cinéma et de l’audiovisuel. – www.france5.fr/education: la rubrique «Côté profs» a une entrée «education aux médias». – www.educaunet.org: Programme européen d’éducation aux risques liés à Internet. dResedfeleexliobnuetsacón Páginas 43-48
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