A Qualitative Approach to E-Learning ? A Dynamic Situation in Montpellier Business School

The article proposes a more productive way and approach for an e-learning research methodology. The e-learning tools: the computer and the Internet are serious obstacles for sense making in the student’s behaviour context. Their use defines in a way the user’s behaviour. This article underlines the advantages of qualitative methods for this kind of research and vote for an ethnographic method. Our suggestion has many assets in order to understand and consider interactions. Communication processes tend to have a strong influence on learning behaviour and are almost neglected during quantitative methodology. Accurate and corrective feedback is essential for establishing and performing elearning techniques. Our suggestions are highlighted by lessons learnt from Montpellier Business school experience

Magnetic Properties of a Quantum Ferrimagnet: NiCu(pba)(D_2O)_3 . 2D_2O

We report the results of magnetic measurements on a powder sample of NiCu(pba)(D_2O)_3 \cdot 2D_2O$(pba=1,3-propylenebis(oxamato)) which is one of the prototypical examples of an$S$=1/2 and 1 ferrimagnetic chain. Susceptibility($\chi$) shows a monotonous increase with decreasing temperature (T) and reaches a maximum at about 7 K. In the plot of$\chi T$versus$T$, the experimental data exhibit a broad minimum and are fit to the$\chi T$curve calculated for the ferrimagnetic Heisenberg chain composed of S=1/2 and 1. From this fit, we have evaluated the nearest-neighbor exchange constant$J/k_B=121 K$, the g-values of Ni$^{2+}$and Cu$^{2+}$,$g_{Ni}$=2.22 and$g_{Cu}$=2.09, respectively. Applied external field dependence of$\chi T$ at low temperatures is reproduced fairly well by the calculation for the same ferrimagnetic model.Comment: 7pages, 4 postscript figures, usues REVTEX. appear in J. Phys. Soc. Jpn vol 67 No.7 (1998

Nuclear spin relaxation in ordered bimetallic chain compounds

A theoretical interpretation is given to recent proton spin relaxation-time (T_1) measurements on NiCu(C_7H_6N_2O_6)(H_2O)_3$\cdot$2H_2O, which is an ideal one-dimensional ferrimagnetic Heisenberg model system of alternating spins 1 and 1/2. The relaxation rate T_1^{-1} is formulated in temrs of the spin-wave theory and is evaluated by the use of a quantum Monte Carlo method. Calculations of the temperature and applied-field (H) dependences of T_1^{-1} are in total agreement with the experimental findings. T_1 behaves as $T_1^{-1}\propto H^{-1/2}$, which turns out an indirect observation of the quadratic dispersion relations dominating the low-energy physics of quantum ferrimagnets.Comment: 5 pages, 4 figures embedded, to appear in Phys. Lett.

Magnetic Properties of Quantum Ferrimagnetic Spin Chains

Magnetic susceptibilities of spin-$(S,s)$ ferrimagnetic Heisenberg chains are numerically investigated. It is argued how the ferromagnetic and antiferromagnetic features of quantum ferrimagnets are exhibited as functions of $(S,s)$. Spin-$(S,s)$ ferrimagnetic chains behave like combinations of spin-$(S-s)$ ferromagnetic and spin-$(2s)$ antiferromagnetic chains provided $S=2s$.Comment: 4 pages, 7 PS figures, to appear in Phys. Rev. B: Rapid Commu

Low-energy structure of the intertwining double-chain ferrimagnets A_3_Cu_3_(PO_4_)_4_ (A=Ca,Sr,Pb)

Motivated by the homometallic intertwining double-chain ferrimagnets A_3_Cu_3_(PO_4_)_4_ (A=Ca,Sr,Pb), we investigate the low-energy structure of their model Hamiltonian H=\sum_n_[J_1_(S_{n :1}_+S_{n :3}_) +J_2_(S_{n+1:1}+S_{n-1:3}_)]\cdotS_{n:2}_, where S_{n:l}_ stands for the Cu^{2+}^ ion spin labeled l in the nth trimer unit, with particular emphasis on the range of bond alternation 0<J_2/J_1<1. Although the spin-wave theory, whether up to O(S^1^) or up to O(S^0^), claims that there exists a flat band in the excitation spectrum regardless of bond alternation, a perturbational treatment as well as the exact diagonalization of the Hamiltonian reveals its weak but nonvanishing momentum dispersion unless J_2_=J_1_ or J_2_=0. Quantum Monte Carlo calculations of the static structure factor further convince us of the low-lying excitation mechanism, elucidating similarities and differences between the present system and alternating-spin linear-chain ferrimagnets.Comment: 8 pages, 6 figure

Significance of the direct relaxation process in the low-energy spin dynamics of a one-dimensional ferrimagnet NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O

In response to recent nuclear-magnetic-resonance measurements on a ferrimagnetic chain compound NiCu(C_7H_6N_2O_6)(H_2O)_3 2H_2O [Solid State Commun. {\bf 113} (2000) 433], we calculate the nuclear spin-lattice relaxation rate 1/T_1 in terms of a modified spin-wave theory. Emphasizing that the dominant relaxation mechanism arises from the direct (single-magnon) process rather than the Raman (two-magnon) one, we explain the observed temperature and applied-field dependences of 1/T_1. Ferrimagnetic relaxation phenomena are generally discussed and novel ferrimagnets with extremely slow dynamics are predicted.Comment: 5 pages, 5 figures embedded, Solid State Commun. 117, No. 1 (2000

Structural organization of human replication timing domains

AbstractRecent analysis of genome-wide epigenetic modification data, mean replication timing (MRT) profiles and chromosome conformation data in mammals have provided increasing evidence that flexibility in replication origin usage is regulated locally by the epigenetic landscape and over larger genomic distances by the 3D chromatin architecture. Here, we review the recent results establishing some link between replication domains and chromatin structural domains in pluripotent and various differentiated cell types in human. We reconcile the originally proposed dichotomic picture of early and late constant timing regions that replicate by multiple rather synchronous origins in separated nuclear compartments of open and closed chromatins, with the U-shaped MRT domains bordered by “master” replication origins specified by a localized (∼200–300kb) zone of open and transcriptionally active chromatin from which a replication wave likely initiates and propagates toward the domain center via a cascade of origin firing. We discuss the relationships between these MRT domains, topologically associated domains and lamina-associated domains. This review sheds a new light on the epigenetically regulated global chromatin reorganization that underlies the loss of pluripotency and the determination of differentiation properties

Magnetic properties of M2P4O12 ( M = Ni, Co, Cu)

We have discussed thermodynamic properties from susceptibilities and specific heat mesurements of isostructural one-dimensional M2P4O12 system. The compounds show different magnetic behaviours, varied from ferromagnetic to antiferromagnetic ordering.We have discussed thermodynamic properties from susceptibilities and specific heat mesurements of isostructural one-dimensional M2P4O12 system. The compounds show different magnetic behaviours, varied from ferromagnetic to antiferromagnetic ordering

Nuclear Spin-Lattice Relaxation in One-Dimensional Heisenberg Ferrimagnets: Three-Magnon versus Raman Processes

Nuclear spin-lattice relaxation in one-dimensional Heisenberg ferrimagnets is studied by means of a modified spin-wave theory. We consider the second-order process, where a nuclear spin flip induces virtual spin waves which are then scattered thermally via the four-magnon exchange interaction, as well as the first-order process, where a nuclear spin directly interacts with spin waves via the hyperfine interaction. We point out a possibility of the three-magnon relaxation process predominating over the Raman one and suggest model experiments.Comment: to be published in J. Phys. Soc. Jpn. 73, No. 6 (2004

Non Linearity of the Ball/Rubber Impact in Table Tennis: Experiments and Modeling

AbstractAlong with comfort, the speed is a key metric used to qualify the performance of a table tennis racket. The restitution coefficient which corresponds to the ratio between the velocities of the ball right before and after normally impacting the racket relates to the speed performance: the higher the restitution coefficient, the greater the speed. Thus, understanding the normal impact problem is key and suggests investigating the effects of the intrinsic properties and architectures of the constituents of the racket. In this work, both experimental and numerical studies were pursued. Experimentally, normal impact tests were performed for varying launching velocities on samples made of isolated or associated constituents of a table tennis racket and the restitution coefficients calculated. Numerically, 3D finite elements simulations were conducted to replicate the normal impact conditions while incorporating the time-dependent constitutive behavior of the polymeric elements contributing during the impact: the racket constituents (the foam and the compact) and the ball. The restitution coefficients are seen to decrease with increasing launching velocity, while being minimum when the two racket polymeric constituents are associated. A fair agreement is obtained with the FE simulations in which the sample/ball contact zone is identified as a ring with its mean radius increasing till the maximum crushing. Ultimately, additional FE calculations confirm that the friction plays a key role in the energy dissipation process, alongside with the rate-dependent behavior and architecture of the polymeric constituents