832 research outputs found
New Toroidal Beam Antennas for WLAN Communications
[Abstract] The design of a number of new antennas that radiate linearly polarized toroidal beams is described. The developed procedures are based on the use of a method of moments commercial software tool. Several numerical examples, working at WLAN communication frequencies, are derived and analyzed. Two experimental prototypes validate the numerical result
Synthesis of Multi-Radial Line Antenna for HIPERLAN
This paper is a postprint of a paper submitted to and accepted for publication in journal Electronics Letters and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital Library"[Abstract] We present a new antenna concept - the multi-radial travelling wave line antenna - that achieves a broadband conical radiation pattern suitable for use in multiple C-band wireless
computer networks
Beam Reconfiguration of Linear Arrays Using Parasitic Elements
This paper is a postprint of a paper submitted to and accepted for publication in journal Electronics Letters and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital Library - http://digital-library.theiet.org/content/journals/10.1049/el:20063674[Abstrac] An innovative method for linear arrays beam reconfiguration is presented. This pattern reconfigurability is achieved by a mechanical displacement of a parasitic array located in front of an active one. Two worked examples that use parallel dipoles are presented
Polarization anisotropy in the optical properties of silicon ellipsoids
A new real space quantum mechanical approach with local field effects
included is applied to the calculation of the optical properties of silicon
nanocrystals. Silicon ellipsoids are studied and the role of surface
polarization is discussed in details. In particular, surface polarization is
shown to be responsible for a strong optical anisotropy in silicon ellipsoids,
much more pronounced with respect to the case in which only quantum confinement
effects are considered. The static dielectric constant and the absorption
spectra are calculated, showing that the perpendicular and parallel components
have a very different dependence on the ellipsoid aspect ratio. Then, a
comparison with the classical dielectric model is performed, showing that the
model only works for large and regular structures, but it fails for thin
elongated ellipsoids.Comment: 5 pages, 4 figures, International Conference on NANO-Structures
Self-Assemblin
Complete-arch accuracy of four intraoral scanners: An in vitro study
The purpose of this study is to define the accuracy of four intraoral scanners (IOS) through the analysis of digital impressions of a complete dental arch model. Eight metal inserts were placed on the model as reference points and then it was scanned with a laboratory scanner in order to obtain the reference model. Subsequently, the reference model was scanned with four IOS (Carestream 3600, CEREC Omnicam, True Definition Scanner, Trios 3Shape). Linear measurements were traced on an STL file between the chosen reference points and divided into four categories: three-element mesiodistal, five-element mesiodistal, diagonal, and contralateral measurements. The digital reference values for the measurements were then compared with the values obtained from the scans to analyze the accuracy of the IOS using ANOVA. There were no statistically significant differences between the measurements of the digital scans obtained with the four IOS systems for any of the measurement groups tested
Acute effects of whole-body vibrations on the fatigue induced by multiple repeated sprint ability test in soccer players
Background: We tested the hypothesis that whole-body vibration (WBV) positively affects the fatigue process ensuing from repeated bouts of maximal efforts, as induced by repeated sprints' ability (RSA). Eleven male soccer players performed three sets of six repeated shuttle sprints (40 meters).
Methods: Eleven male soccer players (age 23.6±4.5 years) were cross-randomized to perform WBW before RSA and during the recovery between sets (WBV-with) or to warm-up and passive recovery between sets (WBV-without). The effects of WBV were quantified by sprint time (ST) and blood lactate concentration (LA), collected up to 15 min after completion of tests.
Results: ST during RSA showed a better maintenance of performance in the WBV-with compared to WBV-without condition in all three sets, reaching a statistical significance between-groups during the 2nd and 3rd set (P<0.05). No significant differences in ST over the sets were detected in WBV-with, whereas a significant decrease was observed in the WBV-without condition (P<0.001). LA recovered significantly faster from the 9th to 15th minute of recovery in WBV-with as compared to WBV-without (P<0.05).
Conclusions: These findings would indicate that WBV performed during recovery between RSA sets can delay the onset of muscle fatigue resulting in a better maintenance of sprint performance
Calcium hydroxide removal using four different irrigation systems: A quantitative evaluation by scanning electron microscopy
This study compares conventional endodontic needle irrigation, passive ultrasonic irriga-tion, apical negative pressure irrigation, and mechanical activation to remove calcium hydroxide from single straight root canals. Eighty-four mandibular premolars were prepared in a crown-down manner up to size #40. Two teeth represented a negative control, and another two served as a positive control. Calcium hydroxide paste was placed inside root canals. The remaining eighty samples were analyzed based on the activation techniques, and the cleanliness of the canals was quantified using Fiji’s software on 500× magnified SEM backscattered electron micrographs. Considering the whole canal, all instruments showed better performance than conventional endodontic needle irrigation in removing calcium hydroxide (p < 0.05). Irrisafe and XP-endo Finisher could remove a significantly higher amount of calcium hydroxide than Endovac (p < 0.05). Irrisafe and XP-endo Finisher have been able to remove more calcium hydroxide than EndoVac
Designing Conducting Polymers Using Bioinspired Ant Algorithms
Ant algorithms are inspired in real ants and the main idea is to create
virtual ants that travel into the space of possible solution depositing virtual
pheromone proportional to how good a specific solution is. This creates a
autocatalytic (positive feedback) process that can be used to generate
automatic solutions to very difficult problems. In the present work we show
that these algorithms can be used coupled to tight-binding hamiltonians to
design conducting polymers with pre-specified properties. The methodology is
completely general and can be used for a large number of optimization problems
in materials science
A pseudopotential study of electron-hole excitations in colloidal, free-standing InAs quantum dots
Excitonic spectra are calculated for free-standing, surface passivated InAs
quantum dots using atomic pseudopotentials for the single-particle states and
screened Coulomb interactions for the two-body terms. We present an analysis of
the single particle states involved in each excitation in terms of their
angular momenta and Bloch-wave parentage. We find that (i) in agreement with
other pseudopotential studies of CdSe and InP quantum dots, but in contrast to
k.p calculations, dot states wavefunction exhibit strong odd-even angular
momentum envelope function mixing (e.g. with ) and large
valence-conduction coupling. (ii) While the pseudopotential approach produced
very good agreement with experiment for free-standing, colloidal CdSe and InP
dots, and for self-assembled (GaAs-embedded) InAs dots, here the predicted
spectrum does {\em not} agree well with the measured (ensemble average over dot
sizes) spectra. (1) Our calculated excitonic gap is larger than the PL measure
one, and (2) while the spacing between the lowest excitons is reproduced, the
spacings between higher excitons is not fit well. Discrepancy (1) could result
from surface states emission. As for (2), agreement is improved when account is
taken of the finite size distribution in the experimental data. (iii) We find
that the single particle gap scales as (not ), that the
screened (unscreened) electron-hole Coulomb interaction scales as
(), and that the eccitonic gap sclaes as . These scaling
laws are different from those expected from simple models.Comment: 12 postscript figure
Predicion of charge separation in GaAs/AlAs cylindrical Russian Doll nanostructures
We have contrasted the quantum confinement of (i) multiple quantum wells of
flat GaAs and AlAs layers, i.e. (\GaAs)_{m}/(\AlAs)_n/(\GaAs)_p/(\AlAs)_q,
with (ii) ``cylindrical Russian Dolls'' -- an equivalent sequence of wells and
barriers arranged as concentric wires. Using a pseudopotential plane-wave
calculation, we identified theoretically a set of numbers ( and )
such that charge separation can exist in ``cylindrical Russian Dolls'': the CBM
is localized in the inner GaAs layer, while the VBM is localized in the outer
GaAs layer.Comment: latex, 8 page
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