3,824 research outputs found
Threshold Effects And Perturbative Unification
We discuss the effect of the renormalization procedure in the computation of
the unification point for running coupling constants. We explore the effects of
threshold--crossing on the --functions. We compute the running of the
coupling constants of the Standard Model, between and , using a mass
dependent subtraction procedure, and then compare the results with ,
and with the -- function approximation. We also do this for the Minimal
Supersymmetric extension of the Standard Model. In the latter, the bounds on
susy masses that one obtains by requiring perturbative unification are
dependent, to some extent, on the procedure.Comment: 22 pages, REVTEX-2.1, 6 Post-Script figures are include
Non-linear Preheating with Scalar Metric Perturbations
We have studied preheating of field perturbations in a 3-dimensional lattice
including the effect of scalar metric perturbations, in two generic models of
inflation: chaotic inflation with a quartic potential, and standard hybrid
inflation. We have prepared the initial state for the classical evolution of
the system with vanishing vector and tensor metric perturbations, consistent
with the constraint equations, the energy and momentum constraints. The
non-linear evolution inevitably generates vector and tensor modes, and this
reflects on how well the constraint equations are fulfilled during the
evolution. The induced preheating of the scalar metric perturbations is not
large enough to backreact onto the fields, but it could affect the evolution of
vector and tensor modes. This is the case in hybrid inflation for some values
of the coupling and the height of potential . For example with
GeV, preheating of scalar perturbations is such that
their source term in the evolution equation of tensor and vector becomes
comparable to that of the field anisotropic stress.Comment: 15 pages, 12 eps figure
Broadband telecom transparency of semiconductor-coated metal nanowires: more transparent than glass
Metallic nanowires (NW) coated with a high permittivity dielectric are
proposed as means to strongly reduce the light scattering of the conducting NW,
rendering them transparent at infrared wavelengths of interest in
telecommunications. Based on a simple, universal law derived from
electrostatics arguments, we find appropriate parameters to reduce the
scattering efficiency of hybrid metal-dielectric NW by up to three orders of
magnitude as compared with the scattering efficiency of the homogeneous
metallic NW. We show that metal@dielectric structures are much more robust
against fabrication imperfections than analogous dielectric@metal ones. The
bandwidth of the transparent region entirely covers the near IR
telecommunications range. Although this effect is optimum at normal incidence
and for a given polarization, rigorous theoretical and numerical calculations
reveal that transparency is robust against changes in polarization and angle of
incidence, and also holds for relatively dense periodic or random arrangements.
A wealth of applications based on metal-NWs may benefit from such invisibility
Cifosis postraumática progresiva del raquis cervical en un adolescente
Se presenta un caso de cifosis cervical progresiva en un paciente adolescente de 14 años que fue remitido a nuestra unidad con siete meses de evolución, tras un antecedente de hiperflexión por zambullida. ClÃnicamente presentaba dolor, actitud antiálgica y limitación de la movilidad. El estudio radiográfico mostró una cifosis cervical C2-C4. Ante la progresión radiográfica de la cifosis (48º) y la limitación funcional, se decidió la estabilización quirúrgica por vÃa posterior, realizando una artrodesis C2-C4 utilizando el Halifax clamp y aporte de injerto antólogo. Tras dos años de seguimiento, el paciente se encuentra asintomático, con una cifosis residual de 18º (C2-C4), que no limita clÃnicamente la flexión y extensión completas.A 14-year-old boy with progressive cervical kyphosis is reported. The patient was remitted to our hospital 7 months after a diving accident. Clinically, he showed pain, antialgic position and limited mobility. The radiological study showed cervical kyphosis C2-C4. Due to kyphotic radiographic progression (48º) and functional limitation, surgical stabilization through a posterior approach was decide, performing C2-C4 arthrodesis with Halifax Clamp and bone graft. After two years of follow-up, the patient is asympthomatic with 18º remnant kyphosis that clinically does not limit full flexion and extension
On the occurrence of Zenopsis conchifer (Lowe, 1852) (Osteichthyes, Zeidae) in the Mediterranean Sea
Sobre la presència de Zenopsis conchifer (Lowe, 1852) (Osteichthyes, Zeidae) al mar Mediterrani
S’informa de la captura de quatre exemplars de Zenopsis conchifer, espècie que va ser citada per primera vegada al Mediterrani l’any 2007, a las costes de la penÃnsula Ibèrica. Un dels exemplars va ser capturat prop de l’estret de Gibraltar, per la qual cosa probablement es tractava d’un individu errant. Malgrat aquestes captures no hi ha evidència de l’existència d’una població estable, raó per la qual l’espècie ha de continuar sent considerada com a exòtica al Mediterrani.The capture of four specimens of Silvery John Dory (Zenopsis conchifer),a species recorded in the Mediterranean Sea for the first time in 2006, is reported from the Iberian coast (western Mediterranean). One of the specimens was caught near the Strait of Gibraltar and is probably a vagrant. Despite these catches, there is no evidence of a self–sustaining population, so this species should be considered as alien in the Mediterranean.Sobre la presencia de Zenopsis conchifer (Lowe, 1852) (Osteichthyes, Zeidae) in el Mar Mediterráneo
Se informa de la captura de cuatro ejemplares de Zenopsis conchifer, especie cuya primera cita en el Mediterráneo data del año 2007, en las costas de la penÃnsula ibérica. Uno de los ejemplares fue capturado cerca del estrecho de Gibraltar, por lo que probablemente se tratarÃa de un individuo errante. A pesar de estas capturas, no hay evidencia de la existencia de una población
Corrugated velocity patterns in the spiral galaxies: NGC 278, NGC 1058, NGC 2500 & UGC 3574
We address the study of the H α vertical velocity field in a sample of four nearly face-on galaxies using long-slit spectroscopy taken with the Intermediate dispersion Spectrograph and Imaging System (ISIS), attached to the William Herschel Telescope (WHT) at the Roque de los Muchachos Observatory (Spain). The spatial structure of the velocity vertical component shows a radial corrugated pattern with spatial scales higher or within the order of 1 kpc. The gas is mainly ionized by high-energy photons: only in some locations of NGC 278 and NGC 1058 is there some evidence of ionization by low-velocity shocks, which, in the case of NGC 278, could be due to minor mergers. The behaviour of the gas in the neighbourhood of the spiral arms fits, in the majority of the observed cases, with that predicted by the so-called hydraulic bore mechanism, where a thick magnetized disc encounters a spiral density perturbation. The results obtained show that it is difficult to explain the H α large-scale velocity field without the presence of a magnetized, thick galactic disc. Larger samples and spatial covering of the galaxy discs are needed to provide further insight into this problem.We acknowledge financial support from the Spanish Ministry of Economy and Competitiveness through grants AYA2010-17631 and AYA2013-40611-P, and from the Consejeria de Educacion y Ciencia (Junta de Andalucia) through TIC-101, TIC-4075 and TIC-114Peer Reviewe
Effect of haptic geometry in C-loop intraocular lenses on optical quality
The biomechanical stability of intraocular lenses (IOLs) must achieve high-quality optical performance and clinical outcomes after cataract surgery. For this reason, the quality and performance features of the IOLs should be previously analysed following the Standard ISO 11979-2 and ISO 11979-3. The ISO 11979-3 tries to reproduce the behaviour of the IOL in the capsular bag by compressing the lens between two clamps. With this test, it has been demonstrated that the haptic design is a crucial factor to obtain biomechanical stability. Hence, the main goal of this study was to design an aberration-free aspheric IOL and to study the influence of haptic geometry on the optical quality. For that purpose, 5 hydrophobic IOLs with different haptic design were manufactured and their biomechanical stability was compared experimentally and numerically. The IOLs were classified as stiff and flexible designs depending on their haptic geometry. The biomechanical response was measured by means of the compression force, the axial displacement, the angle of contact or contact area, the decentration, the tilt and the strain energy. The results suggest that in vitro and in silico compression tests present similar responses for the IOLs analysed. Furthermore, the flexible IOL designs presented better biomechanical stability than stiff designs. These results were correlated with the optical performance, where the optical quality decreases with worst biomechanical stability. This numerical methodology provides an indisputable advance regarding IOL designs, leading to reduce costs by exploring a feasible space of solutions during the product design process and prior to manufacturing
Generation of a porous scaffold with a starting composition in the CaO-SiO2-MgO-P2O5 system in a simulated physiological environment
Magnesium-based ceramics are involved in orthopedic applications such as bone scaffolds or implant coatings. They provide structural support to cells for bone ingrowth, but highly porous matrices cannot resist severe mechanical stress during implantation. In this study, the laser floating zone (LFZ) technique is used to prepare a dense crystalline material with composition in the CaO-SiO2-MgO-P2O5 system. This material, under physiological conditions, is able to generate a porous scaffold controlled by the dissolution of the MgO phase, meeting the mechanical advantages of a dense material and the biological features of a porous scaffold. FESEM (Field emission scanning electron microscopy), XRD (X-ray Diffraction), EDS (Energy Dispersive X-rays spectroscopy), and ICP ((Inductively Coupled Plasma) analysis were carried out in order to characterize the samples before and after immersion in simulated body fluid (SBF)
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