340 research outputs found
A simple E-learning system based on classroom competition
The final publication is available at Springer via http://dx.doi.org/10.1007/978-3-642-16020-2_42Proceedings of 5th European Conference on Technology Enhanced Learning, EC-TEL 2010, Barcelona, Spain, September 28 - October 1, 2010.We present an e-learning system based on online forms that allows teachers to easily organise competitions in a classroom. This system is used in a preliminary study to evaluate whether cooperative competition is positive or not in education, and to identify which are the characteristics this kind of activity should have to be no harmful for students, motivating and helping them in their learning process.This work was supported by the Spanish Ministry of Science
and Innovation (TIN2008-06566-C04-02), and the Community of Madrid (S2009TIC-
1542)
Analysis and design of power management scheme for an on-board solar energy storage system
This paper investigates the power management issues in a mobile solar energy storage system. A multi-converter based energy storage system is proposed, in which solar power is the primary source while the grid or the diesel generator is selected as the secondary source. The existence of the secondary source facilitates the battery state of charge detection by providing a constant battery charging current. Converter modeling, multi-converter control system design, digital implementation and experimental verification are introduced and discussed in details. The prototype experiment indicates that the converter system can provide a constant charging current during solar converter maximum power tracking operation, especially during large solar power output variation, which proves the feasibility of the proposed design
Quasicondensate and superfluid fraction in the 2D charged-boson gas at finite temperature
The Bogoliubov - de Gennes equations are solved for the Coulomb Bose gas
describing a fluid of charged bosons at finite temperature. The approach is
applicable in the weak coupling regime and the extent of its quantitative
usefulness is tested in the three-dimensional fluid, for which diffusion Monte
Carlo data are available on the condensate fraction at zero temperature. The
one-body density matrix is then evaluated by the same approach for the
two-dimensional fluid with e^2/r interactions, to demonstrate the presence of a
quasi-condensate from its power-law decay with increasing distance and to
evaluate the superfluid fraction as a function of temperature at weak coupling.Comment: 9 pages, 2 figure
The superconductivity at 18 K in LiFeAs system
A new iron arsenide superconducting system LiFeAs was found that crystallizes
into a tetragonal structure with space group P4/nmm. The superconductivity with
Tc up to 18 K was observed in the compounds. This simple 111 type layered iron
arsenide superconductor can be viewed as an analogue of the infinite layer
structure of copper oxides.Comment: 11 pages 3 Figure
Cosmic histories of star formation and reionization: An analysis with a power-law approximation
With a simple power-law approximation of high-redshift () star
formation history, i.e., , we
investigate the reionization of intergalactic medium (IGM) and the consequent
Thomson scattering optical depth for cosmic microwave background (CMB) photons.
A constraint on the evolution index is derived from the CMB optical
depth measured by the {\it Wilkinson Microwave Anisotropy Probe} (WMAP)
experiment, which reads ,
where the free parameter is the number of the escaped
ionizing ultraviolet photons per baryon. Moreover, the redshift for full
reionization, , can also be expressed as a function of as well as
. By further taking into account the implication of the
Gunn-Peterson trough observations to quasars for the full reionization
redshift, i.e., , we obtain
and .
For a typical number of of ionizing photons released per baryon of
normal stars, the fraction of these photons escaping from the stars, , can be constrained to within the range of .Comment: 10 pages, 4 figures, accepted for publication in JCA
High pressure synthesis of a new superconductor Sr2CuO2+xCl2-y induced by apical oxygen doping
Using the apical oxygen doping mechanism, i.e. a partial substitution of
divalence O for the monovalence Cl, a p-type oxychloride cuprate
superconductor, Sr2CuO2+xCl2-y, was synthesized at high pressure high
temperature. The x-ray diffraction refinement suggests the superconductor
crystallizes into a 0201 structure with space group I4/mmm and lattice
parameters being a=3.92A, c=15.6 A. The magnetic susceptibility as well as
resistance measurements indicated that the bulk superconductivity with
transition temperature 30K was achieved in the sample.Comment: accepted by physica
Resonance Fluorescence Spectrum of a Trapped Ion Undergoing Quantum Jumps
We experimentally investigate the resonance fluorescence spectrum of single
171Yb and 172Yb ions which are laser cooled to the Lamb-Dicke regime in a
radiofrequency trap. While the fluorescence scattering of 172Yb is continuous,
the 171Yb fluorescence is interrupted by quantum jumps because a nonvanishing
rate of spontaneous transitions leads to electron shelving in the metastable
hyperfine sublevel 2D3/2(F=2). The average duration of the resulting dark
periods can be varied by changing the intensity of a repumping laser field.
Optical heterodyne detection is employed to analyze the fluorescence spectrum
near the Rayleigh elastic scattering peak. It is found that the stochastic
modulation of the fluorescence emission by quantum jumps gives rise to a
Lorentzian component in the fluorescence spectrum, and that the linewidth of
this component varies according to the average duration of the dark
fluorescence periods. The experimental observations are in quantitative
agreement with theoretical predictions.Comment: 14 pages including 4 figures, pdf file, fig.1 replace
Natural product derivative Gossypolone inhibits Musashi family of RNA-binding proteins
Background: The Musashi (MSI) family of RNA-binding proteins is best known for the role in post-transcriptional regulation of target mRNAs. Elevated MSI1 levels in a variety of human cancer are associated with up-regulation of Notch/Wnt signaling. MSI1 binds to and negatively regulates translation of Numb and APC (adenomatous polyposis coli), negative regulators of Notch and Wnt signaling respectively. Methods: Previously, we have shown that the natural product (-)-gossypol as the first known small molecule inhibitor of MSI1 that down-regulates Notch/Wnt signaling and inhibits tumor xenograft growth in vivo. Using a fluorescence polarization (FP) competition assay, we identified gossypolone (Gn) with a > 20-fold increase in Ki value compared to (-)-gossypol. We validated Gn binding to MSI1 using surface plasmon resonance, nuclear magnetic resonance, and cellular thermal shift assay, and tested the effects of Gn on colon cancer cells and colon cancer DLD-1 xenografts in nude mice. Results: In colon cancer cells, Gn reduced Notch/Wnt signaling and induced apoptosis. Compared to (-)-gossypol, the same concentration of Gn is less active in all the cell assays tested. To increase Gn bioavailability, we used PEGylated liposomes in our in vivo studies. Gn-lip via tail vein injection inhibited the growth of human colon cancer DLD-1 xenografts in nude mice, as compared to the untreated control (P < 0.01, n = 10). Conclusion: Our data suggest that PEGylation improved the bioavailability of Gn as well as achieved tumor-targeted delivery and controlled release of Gn, which enhanced its overall biocompatibility and drug efficacy in vivo. This provides proof of concept for the development of Gn-lip as a molecular therapy for colon cancer with MSI1/MSI2 overexpression
- …