704 research outputs found
Optical emission investigation of laser-produced MgB2 plume expanding in an Ar buffer gas
Optical emission spectroscopy is used to study the dynamics of the plasma
generated by pulsed-laser irradiation of a MgB2 target, both in vacuum and at
different Ar buffer gas pressures. The analysis of the time-resolved emission
of selected species shows that the Ar background gas strongly influences the
plasma dynamics. Above a fixed pressure, plasma propagation into Ar leads to
the formation of blast waves causing both a considerable increase of the
fraction of excited Mg atoms and a simultaneous reduction of their kinetic flux
energy. These results can be particularly useful for optimizing MgB2 thin film
deposition processes.Comment: 11 pages,4 figures, Applied Physics Letters in pres
Teaching teachers: learning through graphic literacy
Graphic design education has a long history of practitioners leading the development of teaching environments. While these practitioners may develop innovative teaching methods during their educational career, many will never engage with the discipline and literature of pedagogy. Ramsden (2003) asserts that pedagogical principles can help create deeper teaching/learning environments, but this research is all too often disseminated in a lexicon that is not familiar to new graphic design teachers. The research just does not get the message across to those who could benefit most from it. Although graphic design has had difficulties in translating the pedagogical lexicon to its context, it could use its expertise in the visual language to help create a broader understanding of teaching and learning theories and principles for itself and others. The very visual communication skills that we teach could be a more effective way to communicate to educators the necessary pedagogical theory that is to be used in the classroom. This exegesis documents my exploration of pedagogical awareness in graphic design education and how graphic literacy can facilitate this awareness. Through a reflective practice of reading, designing, teaching and conversation, I have uncovered my perceptions and conceptions as a teacher and discovered how some pedagogical principles can help the teaching and learning environment. I have used this knowledge to create an awareness of these principles through the comic language
Statistics for the analysis of molecular dynamics simulations : providing P values for agonist-dependent GPCR activation
Molecular dynamics (MD) is the common computational technique for assessing efficacy of GPCR-bound ligands. Agonist efficacy measures the capability of the ligand-bound receptor of reaching the active state in comparison with the free receptor. In this respect, agonists, neutral antagonists and inverse agonists can be considered. A collection of MD simulations of both the ligand-bound and the free receptor are needed to provide reliable conclusions. Variability in the trajectories needs quantification and proper statistical tools for meaningful and non-subjective conclusions. Multiple-factor (time, ligand, lipid) ANOVA with repeated measurements on the time factor is proposed as a suitable statistical method for the analysis of agonist-dependent GPCR activation MD simulations. Inclusion of time factor in the ANOVA model is consistent with the time-dependent nature of MD. Ligand and lipid factors measure agonist and lipid influence on receptor activation. Previously reported MD simulations of adenosine A2a receptor (A2aR) are reanalyzed with this statistical method. TM6-TM3 and TM7-TM3 distances are selected as dependent variables in the ANOVA model. The ligand factor includes the presence or absence of adenosine whereas the lipid factor considers DOPC or DOPG lipids. Statistical analysis of MD simulations shows the efficacy of adenosine and the effect of the membrane lipid composition. Subsequent application of the statistical methodology to NECA A2aR agonist, with resulting P values in consistency with its pharmacological profile, suggests that the method is useful for ligand comparison and potentially for dynamic structure-based virtual screening
Pulsed laser deposition of SrTiO3/LaGaO3 and SrTiO3/LaAlO3: plasma plume effects
Pulsed laser deposition of SrTiO3/LaGaO3 and SrTiO3/LaAlO3 interfaces has
been analyzed with a focus on the kinetic energy of the ablated species. LaGaO3
and LaAlO3 plasma plumes were studied by fast photography and space-resolved
optical emission spectroscopy. Reflection high energy electron diffraction was
performed proving a layer-by-layer growth up to 10-1 mbar oxygen pressure. The
role of the energetic plasma plume on the two-dimensional growth and the
presence of interfacial defects at different oxygen growth pressure has been
discussed in view of the conducting properties developing at such
polar/non-polar interfaces
Experimental and Theoretical Analysis of Non-linear Vibrational Relaxation of Polyatomic Molecules Strongly Excited by Resonant Laser Radiation
We present a very simple theoretical model aimed at the analysis of non-linear relaxation processes in
molecular gases in the presence of partial molecular dissociation induced by vibrational–vibrational
exchange between highly excited molecules. The model has a phenomenological character, since it analyzes the
behavior of a system of anharmonic diatomic molecules, which is a very rough approximation of a polyatomic
molecule such as SF6. Nonetheless, it provides an interesting key for the interpretation of a number
of peculiar features characterizing our experimental observation, with which a comparison is made. In particular,
the model takes realistic account of the influence of dissociation processes on the relaxation time
Growth methods of c-axis oriented MgB2 thin films by pulsed laser deposition
High quality MgB2 thin films have been obtained by pulsed laser deposition
both on MgO and on Al2O3 substrates using different methods. In the standard
two-step procedure, an amorphous precursor layer is deposited at room
temperature starting both from stoichiometric target and from boron target:
after this first step, it is annealed in magnesium atmosphere in order to
crystallize the superconducting phase. The so obtained films show a strong
c-axis orientation, evidenced by XRD analysis, a critical temperature up to 38
K and very high critical fields along the basal planes, up to 22T at 15K. Also
an in situ one step technique for the realization of superconducting MgB2 thin
films has been developed. In this case, the presence of an argon buffer gas
during deposition is crucial and we observe a strong dependence of the quality
of the deposited film on the background gas pressure. The influence of the Ar
atmosphere has been confirmed by time and space-resolved spectroscopy
measurements on the emission spectrum of the plume. The Ar pressure modifies
strongly the plasma kinetics by promoting excitation and ionization of the
plume species, especially of the most volatile Mg atoms, increasing their
internal energy.Comment: Paper presented at Boromag Workshop, Genoa 17-19 June 2002, in press
on SUS
Measurement of the two-photon absorption cross-section of liquid argon with a time projection chamber
This paper reports on laser-induced multiphoton ionization at 266 nm of
liquid argon in a time projection chamber (LAr TPC) detector. The electron
signal produced by the laser beam is a formidable tool for the calibration and
monitoring of next-generation large-mass LAr TPCs. The detector that we
designed and tested allowed us to measure the two-photon absorption
cross-section of LAr with unprecedented accuracy and precision:
sigma_ex=(1.24\pm 0.10stat \pm 0.30syst) 10^{-56} cm^4s{-1}.Comment: 15 pages, 9 figure
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