26,888 research outputs found
On the propagation speed of evanescent modes
The group-velocity of evanescent waves (in undersized waveguides, for
instance) was theoretically predicted, and has been experimentally verified, to
be Superluminal (v_g > c). By contrast, it is known that the precursor speed in
vacuum cannot be larger than c. In this paper, by computer simulations based on
Maxwell equations only, we show the existence of both phenomena. In other
words, we verify the actual possibility of Superluminal group velocities,
without violating the so-called (naive) Einstein causality. (Subject classes:
General physics, Classical physics, Optics, Special Relativity; PACS nos.:
73.40Gk, 03.80+z, 03.65Bz; Keywords: evanescent waves; tunnelling photons;
Hartman effect; group velocity; Superluminal waves; precursors; transient
waves; front velocity; Maxwell equations; electromagnetic waves; computer
simulations; Special Relativity; Extended Relativity).Comment: plain LaTeX file (14 pages), plus 15 figures in .jp
Nonleptonic decays and the nature of the orbitally excited charmed-strange mesons
The Belle Collaboration has recently reported a study of the decays and has given also estimates of relevant
ratios between branching fractions of decays
providing important information to check the structure of the
, and mesons. The
disagreement between experimental data and Heavy Quark Symmetry has been used
as an indication that and mesons could
have a more complex structure than the canonical one. We analyze
these ratios within the framework of a constituent quark model, which allows us
to incorporate the effects given by finite -quark mass corrections. Our
findings are that while the meson could have a sizable
non- component, the and mesons
seem to be well described by a pure structure.Comment: 13 pages, 1 figur
Mode stability in delta Scuti stars: linear analysis versus observations in open clusters
A comparison between linear stability analysis and observations of pulsation
modes in five delta Scuti stars, belonging to the same cluster, is presented.
The study is based on the work by Michel et al. (1999), in which such a
comparison was performed for a representative set of model solutions obtained
independently for each individual star considered. In this paper we revisit the
work by Michel et al. (1999) following, however, a new approach which consists
in the search for a single, complete, and coherent solution for all the
selected stars, in order to constrain and test the assumed physics describing
these objects. To do so, refined descriptions for the effects of rotation on
the determination of the global stellar parameters and on the adiabatic
oscillation frequency computations are used. In addition, a crude attempt is
made to study the role of rotation on the prediction of mode instabilities.The
present results are found to be comparable with those reported by Michel et al.
(1999). Within the temperature range log T_eff = 3.87-3.88 agreement between
observations and model computations of unstable modes is restricted to values
for the mixing-length parameter alpha_nl less or equal to 1.50. This indicates
that for these stars a smaller value for alpha_nl is required than suggested
from a calibrated solar model. We stress the point that the linear stability
analysis used in this work still assumes stellar models without rotation and
that further developments are required for a proper description of the
interaction between rotation and pulsation dynamics.Comment: 8 pages, 4 figures, 3 tables. (MNRAS, in press
Temperature dependent dynamic and static magnetic response in magnetic tunnel junctions with Permalloy layers
Ferromagnetic resonance and static magnetic properties of CoFe/Al2O3/CoFe/Py
and CoFe/Al2O3/CoFeB/Py magnetic tunnel junctions and of 25nm thick
single-layer Permalloy(Py) films have been studied as a function of temperature
down to 2K. The temperature dependence of the ferromagnetic resonance excited
in the Py layers in magnetic tunnel junctions shows knee-like enhancement of
the resonance frequency accompanied by an anomaly in the magnetization near
60K. We attribute the anomalous static and dynamic magnetic response at low
temperatures to interface stress induced magnetic reorientation transition at
the Py interface which could be influenced by dipolar soft-hard layer coupling
through the Al2O3 barrier
Tunneling Splittings in Mn12-Acetate Single Crystals
A Landau-Zener multi-crossing method has been used to investigate the tunnel
splittings in high quality Mn-acetate single crystals in the pure
quantum relaxation regime and for fields applied parallel to the magnetic easy
axis. With this method several individual tunneling resonances have been
studied over a broad range of time scales. The relaxation is found to be
non-exponential and a distribution of tunnel splittings is inferred from the
data. The distributions suggest that the inhomogeneity in the tunneling rates
is due to disorder that produces a non-zero mean value of the average
transverse anisotropy, such as in a solvent disorder model. Further, the effect
of intermolecular dipolar interaction on the magnetic relaxation has been
studied.Comment: Europhysics Letters (in press). 7 pages, including 3 figure
Eimeria tenella protein trafficking: differential regulation of secretion versus surface tethering during the life cycle
Eimeria spp. are intracellular parasites that have a major impact on poultry. Effective live vaccines are available and the development of reverse genetic technologies has raised the prospect of using Eimeria spp. as recombinant vectors to express additional immunoprotective antigens. To study the ability of Eimeria to secrete foreign antigens or display them on the surface of the sporozoite, transiently transfected populations of E. tenella expressing the fluorescent protein mCherry, linked to endogenous signal peptide (SP) and glycophosphatidylinositol-anchor (GPI) sequences, were examined. The SP from microneme protein EtMIC2 (SP2) allowed efficient trafficking of mCherry to cytoplasmic vesicles and following the C-terminal addition of a GPI-anchor (from surface antigen EtSAG1) mCherry was expressed on the sporozoite surface. In stable transgenic populations, mCherry fused to SP2 was secreted into the sporocyst cavity of the oocysts and after excystation, secretion was detected in culture supernatants but not into the parasitophorous vacuole after invasion. When the GPI was incorporated, mCherry was observed on the sporozites surface and in the supernatant of invading sporozoites. The proven secretion and surface exposure of mCherry suggests that antigen fusions with SP2 and GPI of EtSAG1 may be promising candidates to examine induction of protective immunity against heterologous pathogens
Preoperative digital three-dimensional planning for rhinoplasty
BACKGROUND: This report describes preoperative digital planning for rhinoplasty using a new three-dimensional (3D) radiologic viewer that allows both patients and surgeons to visualize on a common monitor the 3D real aspect of the nose in its inner and outer sides.
METHODS: In the period 2002 to 2008, 210 patients underwent rhinoplasty procedures in the authors' clinic. The patients were randomly divided into three groups according to the type of preoperative planning used: photos only, a simulated result by Adobe Photoshop, or the 3D radiologic viewer. The parameters evaluated included the number of patients that underwent surgery after the first consultation, the number of patients who asked for a reintervention, patient satisfaction (according to a test given to the patients 12 months postoperatively), the surgical time required for a functional intervention, and the improvement in nasal function by postoperative rhinomanometry and subjective evaluation.
RESULTS: Computer-aided technologies led to a higher number of patients deciding to undergo a rhinoplasty. Simulation of the postoperative results was not as useful in the postoperative period due to the higher number of reintervention requests.
CONCLUSION: The patients undergoing rhinoplasties preferred new technologies in the preoperative period. The advantages of using the 3D radiologic viewer included improved preoperative planning, reduction in intraoperative stress, a higher number of patients undergoing surgery, reduction in postoperative surgical corrections, reduction in surgical time for the functional intervention, a higher rate of improvement in nasal function, a higher percentage of postoperative satisfaction, and reduced costs
Automatic classification of reforested Pinus SPP and Eucalyptus SPP in Mogi-Guacu, SP, Brazil, using LANDSAT data
The author has identified the following significant results. Single date LANDSAT CCTs were processed, by Image-100 to classify Pinus and Eucalyptus species and their age groups. The study area Mogi-Guagu was located in the humid subtropical climate zone of Sao Paulo. The study was divided into ten preliminary classes and featured selection algorithms were used to calculate Bhattacharyya distance between all possible pairs of these classes in the four available channels. Classes having B-distance values less than 1.30 were grouped in four classes: (1) class PE - P. elliottii, (2) class P0 - Pinus species other than P. elliotii, (3) class EY - Eucalyptus spp. under two years, and (4) class E0 - Eucalyptus spp. more than two years old. The percentages of correct classification ranged from 70.9% to 94.12%. Comparisons of acreage estimated from the Image-100 with ground truth data showed agreement. The Image-100 percent recognition values for the above four classes were 91.62%, 87.80%, 89.89%, and 103.30%, respectively
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