Bacterias y su implicación en el fallo de implantes de Titanio

Peer Reviewe

Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks

In this paper, a practical multi-user cooperative transmission scheme denoted as Virtual Maximum Ratio Transmission (VMRT) for Multiple-Input Multiple-Output - Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) Relay-based networks is proposed and evaluated in the presence of a realistic channel estimation algorithm. It is shown that this scheme is robust against channel estimation errors and offers diversity and array gain keeping the complexity low, although the multi-user and multi-antenna channel estimation algorithm is simple and efficient. Diversity gains larger than 4 can be easily obtained with reduced number of relays. Thus, this scheme can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays

Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks

In this paper, a practical multi-user cooperative transmission scheme denoted as Virtual Maximum Ratio Transmission (VMRT) for Multiple-Input Multiple-Output - Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) Relay-based networks is proposed and evaluated in the presence of a realistic channel estimation algorithm. It is shown that this scheme is robust against channel estimation errors and offers diversity and array gain keeping the complexity low, although the multi-user and multi-antenna channel estimation algorithm is simple and efficient. Diversity gains larger than 4 can be easily obtained with reduced number of relays. Thus, this scheme can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays

Effects of channel estimation on multiuser virtual MIMO-OFDMA relay-based networks

In this paper, a practical multi-user cooperative transmission scheme denoted as Virtual Maximum Ratio Transmission (VMRT) for Multiple-Input Multiple-Output - Orthogonal Frequency Division Multiple Access (MIMO-OFDMA) Relay-based networks is proposed and evaluated in the presence of a realistic channel estimation algorithm. It is shown that this scheme is robust against channel estimation errors and offers diversity and array gain keeping the complexity low, although the multi-user and multi-antenna channel estimation algorithm is simple and efficient. Diversity gains larger than 4 can be easily obtained with reduced number of relays. Thus, this scheme can be used to extend coverage or increase system throughput by using simple cooperative OFDMA-based relays

Plasma Magnetosphere Formation Around Oscillating Magnetized Neutron Stars

The notion of death line of rotating pulsars is applied to model of oscillating neutron stars. It is shown that the magnetosphere of typical non-rotating oscillating stars may not contain secondary plasma to support the generation of radio emission in the region of open field lines of plasma magnetosphere.Comment: Accepted for publication in Astrophysics & Space Scienc

Force-free magnetosphere of an aligned rotator with differential rotation of open magnetic field lines

Here we briefly report on results of self-consistent numerical modeling of a differentially rotating force-free magnetosphere of an aligned rotator. We show that differential rotation of the open field line zone is significant for adjusting of the global structure of the magnetosphere to the current density flowing through the polar cap cascades. We argue that for most pulsars stationary cascades in the polar cap can not support stationary force-free configurations of the magnetosphere.Comment: 5 pages, 4 figures. Presented at the conference "Isolated Neutron Stars: from the Interior to the Surface", London, April 24-28, 2006; to appear in Astrophysics and Space Science. Significantly revised version, a mistake found by ourselfs in the numerical code was corrected, all presented results are obtained with the correct version of the cod

Wave scattering from self-affine surfaces

Electromagnetic wave scattering from a perfectly reflecting self-affine surface is considered. Within the framework of the Kirchhoff approximation, we show that the scattering cross section can be exactly written as a function of the scattering angle via a centered symmetric Levy distribution for general roughness amplitude, Hurst exponent and wavelength of the incident wave. The amplitude of the specular peak, its width and its position are discussed as well as the power law decrease (with scattering angle) of the scattering cross section.Comment: RevTeX, 4 pages including 2 figures. Submitted Phys. Rev. Let

Comparison of implant primary stability between maxillary edentulous ridges receiving intramembranous origin block grafts

Purpose: The purposes of the present study were: to compare the resonance frequency analysis (RFA) values of implant placed in either ramus or calvaria block grafts; and to determine if implant diameter influences RFA implant stability quotient (ISQ) value. Material and Methods: This was a retrospective study that included 16 consecutives healthy patients treated with autogenous onlay block grafts for horizontal bone reconstruction in maxilla. Ten ramus and ten calvaria block graft treated patients were selected and compared. Results: Totally, 59 implants were placed, 35 (59.3%) were placed on the calvaria bone grafts and the remaining 24 (40.7%) were on the ramus bone graft. Of all the implants studied, 13 (22%), 35 (59.3%), and 11 (18.6%) were 10 mm, 11.5 mm and 13 mm in length respectively. Regarding the diameter, 4 (7%) were 3.3 mm, 3 (5%) were 3.5 mm, 20 (34%) were 3.7 mm and 32 (54%) were 4 mm. Mean ISQ value obtained by RFA was 73.06 ± 6.08, being 72.19 ± 6 and 74.47 ± 6.06 for the calvaria and ramus treated group respectively. No significant differences were noted between the two groups (p= 0.154). Implants were pooled and divided by their diameter. Mean ISQ value obtained for 3.3 mm was 80 ± 5.09, while for 4.0 mm was 72.5 ± 7.19. Again, no significant differences were found among the groups (p= 0.138). Conclusion: For RFA ISQ value, the bone graft origins (calvaria or ramus) or implant diameters did not influence the outcome

A generic estimate of trans-Planckian modifications to the primordial power spectrum in inflation

We derive a general expression for the power spectra of scalar and tensor fluctuations generated during inflation given an arbitrary choice of boundary condition for the mode function at a short distance. We assume that the boundary condition is specified at a short-distance cutoff at a scale $M$ which is independent of time. Using a particular prescription for the boundary condition at momentum $p = M$, we find that the modulation to the power spectra of density and gravitational wave fluctuations is of order $(H/M)$, where $H$ is the Hubble parameter during inflation, and we argue that this behavior is generic, although by no means inevitable. With fixed boundary condition, we find that the shape of the modulation to the power spectra is determined entirely by the deviation of the background spacetime from the de Sitter limit.Comment: 15 pages (RevTeX), 2 figure

Adjustment of the electric current in pulsar magnetospheres and origin of subpulse modulation

The subpulse modulation of pulsar radio emission goes to prove that the plasma flow in the open field line tube breaks into isolated narrow streams. I propose a model which attributes formation of streams to the process of the electric current adjustment in the magnetosphere. A mismatch between the magnetospheric current distribution and the current injected by the polar cap accelerator gives rise to reverse plasma flows in the magnetosphere. The reverse flow shields the electric field in the polar gap and thus shuts up the plasma production process. I assume that a circulating system of streams is formed such that the upward streams are produced in narrow gaps separated by downward streams. The electric drift is small in this model because the potential drop in narrow gaps is small. The gaps have to drift because by the time a downward stream reaches the star surface and shields the electric field, the corresponding gap has to shift. The transverse size of the streams is determined by the condition that the potential drop in the gaps is sufficient for the pair production. This yields the radius of the stream roughly 10% of the polar cap radius, which makes it possible to fit in the observed morphological features such as the "carousel" with 10-20 subbeams and the system of the core - two nested cone beams.Comment: 8 pages, 1 figur