45,163 research outputs found
Ferroelectricity and structure of BaTiO3 grown on YBa2Cu3O7-d thin films
We have investigated the crystal structure and the ferroelectric properties
of BaTiO3 thin films with YBa2Cu3O7-d as the bottom and Au as the top
electrode. Epitaxial heterostructures of YBa2Cu3O7-d and BaTiO3 were prepared
by dc and rf sputtering, respectively. The crystal structure of the films was
characterised by x-ray diffraction. The ferroelectric behaviour of the BaTiO3
films was confirmed by hysteresis loop measurements using a Sawyer Tower
circuit. We obtain a coercive field of 30 kV/cm and a remanent polarisation of
1.25 \muC/cm. At sub-switching fields the capacitance of the films obeys a
relation analogous to the Rayleigh law. This behaviour indicates an interaction
of domain walls with randomly distributed pinning centres. At a field of 5 MV/m
we calculate 3% contribution of irreversible domain wall motion to the total
dielectric constant.Comment: 12 pages and 9 figure
Transient lateral photovoltaic effect in patterned metal-oxide-semiconductor films
The time dependent transient lateral photovoltaic effect has been studied
with us time resolution and with chopping frequencies in the kHz range, in
lithographically patterned 21 nm thick, 5, 10 and 20 um wide and 1500 um long
Co lines grown over naturally passivated p-type Si (100). We have observed a
nearly linear dependence of the transitorial response with the laser spot
position. A transitorial response with a sign change in the laser-off stage has
been corroborated by numerical simulations. A qualitative explanation suggests
a modification of the drift-diffusion model by including the in uence of a
local inductance. Our findings indicate that the microstructuring of position
sensitive detectors could improve their space-time resolution.Comment: 4 pages, 4 figure
AnĂĄlisis, diseño e implementaciĂłn de un sistema de informaciĂłn geogrĂĄfico web turĂstico
In the competitive world in which we live today, technology has been fundamental basis for the creation of new applications that help make this growth will parallel the progression of time. Applications such as Geographic Information Systems changed its original objective of a tool for handling large amounts of information to an analysis tool for management orientation, becoming a Systems for Decision Making.
This project shows the importance of developing a GIS application, such as digital tool for query and location of various tourist attractions of Guayaquil city, allowing amicably provide general knowledge of the streets, distances and routes displacement of habitants of the city to certain place.
This tool lets collect and store through of a graphical interface, the media information centers and tourist points of the sectors defined in Guayaquil, as well as providing routes of origin / destination for the transfer of visitors according to the start address , destination address and road sense
A Critical Realist Reflection on the Use of Social Media as Third Space for Rights Education in Early Childhood
The promotion and advancement of Rights Education in Early Childhood ought to be supported through the development of spaces that allow for interdisciplinary discourses among different stakeholders. The project #ChildRightsChat emerged from interactions between the authors to use a digital space to promote the advancement of an interdisciplinary and global discussion about childrenâs rights. A primary aim was to facilitate adult learning about the protection and promotion of childrenâs rights in practice. Chats in Twitter, through structured and moderated interactions, were designed to share knowledge and experiences around specific topics. The present paper presents the authorsâ reflections, as moderators of #ChildRightsChat, through a critical realist analysis. The findings explore how social media can be understood as a learning environment in âthird spaceâ, with respect to the nature of interactions that occurred, the context as a learning space, and the voices heard in the chat. The implications of social media to include global perspectives for the advancement of rights-based practice in early childhood education and care are considered
Testing Relativity at High Energies Using Spaceborne Detectors
(ABRIDGED) The Gamma-ray Large Area Space Telescope (GLAST) will measure the
spectra of distant extragalactic sources of high energy gamma-rays. GLAST can
look for energy dependent propagation effects from such sources as a signal of
Lorentz invariance violation (LIV). Such sources should also exhibit high
energy spectral cutoffs from pair production interactions with low energy
photons. The properties of such cutoffs can also be used to test LIV. Detectors
to measure gamma-ray polarization can look for the depolarizing effect of
space-time birefingence predicted by loop quantum gravity. A spaceborne
detector array looking down on Earth to study extensive air showers produced by
ultrahigh energy cosmic rays can study their spectral properties and look for a
possible deviation from the predicted GZK effect as another signal of LIV.Comment: 14 pages, Text of invitated talk presented at the "From Quantum to
Cosmos: Fundamental Physics Studies from Space" meeting. More references
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Extended coherence time on the clock transition of optically trapped Rubidium
Optically trapped ensembles are of crucial importance for frequency
measurements and quantum memories, but generally suffer from strong dephasing
due to inhomogeneous density and light shifts. We demonstrate a drastic
increase of the coherence time to 21 s on the magnetic field insensitive clock
transition of Rb-87 by applying the recently discovered spin self-rephasing.
This result confirms the general nature of this new mechanism and thus shows
its applicability in atom clocks and quantum memories. A systematic
investigation of all relevant frequency shifts and noise contributions yields a
stability of 2.4E-11 x tau^(-1/2), where tau is the integration time in
seconds. Based on a set of technical improvements, the presented frequency
standard is predicted to rival the stability of microwave fountain clocks in a
potentially much more compact setup.Comment: 5 pages, 4 figure
Dynamics of hard-sphere suspension using Dynamic Light Scattering and X-Ray Photon Correlation Spectroscopy: dynamics and scaling of the Intermediate Scattering Function
Intermediate Scattering Functions (ISF's) are measured for colloidal hard
sphere systems using both Dynamic Light Scattering (DLS) and X-ray Photon
Correlation Spectroscopy (XPCS). We compare the techniques, and discuss the
advantages and disadvantages of each. Both techniques agree in the overlapping
range of scattering vectors. We investigate the scaling behaviour found by
Segre and Pusey [1] but challenged by Lurio et al. [2]. We observe a scaling
behaviour over several decades in time but not in the long time regime.
Moreover, we do not observe long time diffusive regimes at scattering vectors
away from the peak of the structure factor and so question the existence of a
long time diffusion coefficients at these scattering vectors.Comment: 21 pages, 11 figure
Geometric Hamilton-Jacobi Theory
The Hamilton-Jacobi problem is revisited bearing in mind the consequences
arising from a possible bi-Hamiltonian structure. The problem is formulated on
the tangent bundle for Lagrangian systems in order to avoid the bias of the
existence of a natural symplectic structure on the cotangent bundle. First it
is developed for systems described by regular Lagrangians and then extended to
systems described by singular Lagrangians with no secondary constraints. We
also consider the example of the free relativistic particle, the rigid body and
the electron-monopole system.Comment: 40 page
Some remarks on particle size effects on the abrasion of a range of Fe based alloys
The low-stress three body abrasion behaviour of a range of steels was investigated. The tests were carried out in a rubber wheel tester (according to ASTM G65-94, reapproved in 2000) at room temperature. The abrasive particles used were angular alumina particles of four different sizes. The results showed that, in general, the smaller particles (50 8m and 125 8m average size) caused more damage. With these particles, observations of surface morphology indicarted a more intense cutting and ploughing action, leading to more damage, whereas bigger particles i.e. larger 250 8m and 560 8m particles produced less damage, and their action involved more plastic deformation type wear. The 304 SS had a lower abrasion resistance than the 310 SS. For the austentic and ferritic steels the subsurface deformation was larger for impact with the coarser particles. Variations in substrate hardness had no effect on the abrasive behaviour observed. On the whole, the hardest steel (mild steel in martensitic condition) showed the higher extent of damage, irrespective of particle size
Analysis of CMB maps with 2D wavelets
We consider the 2D wavelet transform with two scales to study sky maps of
temperature anisotropies in the cosmic microwave background radiation (CMB). We
apply this technique to simulated maps of small sky patches of size 12.8 \times
12.8 square degrees and 1.5' \times 1.5' pixels. The relation to the standard
approach, based on the cl's is established through the introduction of the
scalogram. We consider temperature fluctuations derived from standard, open and
flat-Lambda CDM models. We analyze CMB anisotropies maps plus uncorrelated
Gaussian noise (uniform and non-uniform) at idfferent S/N levels. We explore in
detail the denoising of such maps and compare the results with other techniques
already proposed in the literature. Wavelet methods provide a good
reconstruction of the image and power spectrum. Moreover, they are faster than
previously proposed methods.Comment: latex file 7 pages + 5 postscript files + 1 gif file; accepted for
publication in A&A
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