5,979 research outputs found
Short-range stationary patterns and long-range disorder in an evolution equation for one-dimensional interfaces
A novel local evolution equation for one-dimensional interfaces is derived in
the context of erosion by ion beam sputtering. We present numerical simulations
of this equation which show interrupted coarsening in which an ordered cell
pattern develops with constant wavelength and amplitude at intermediate
distances, while the profile is disordered and rough at larger distances.
Moreover, for a wide range of parameters the lateral extent of ordered domains
ranges up to tens of cells. This behavior is new in the context of dynamics of
surfaces or interfaces with morphological instabilities. We also provide
analytical estimates for the stationary pattern wavelength and mean growth
velocity
Theoretical calculations of an osmium molecular switch
IndexaciĂłn: Web of Science; Scielo.ABSTRACT
We have investigated the molecular, electronic and optical properties of the [Os(tpy-py)2]2+ complex (tpy-py = 4'-(4-pyridyl)-2,2':6',2"-terpyridine) and its protonated derivative [Os(tpy-pyH)2]4+ through Density Functional Relativistic calculations including Scalar and Spin Orbit corrections. The molecular geometry of the parent complex is not strongly modified by the protonation at the basic nitrogen atoms of the pyridine moieties of the terpyridine ligands in the complex. On the other hand, the optical properties of these complexes can be controlled by a change in the chemical acid-base environment, converting them into suitable materials to act as molecular switches or pH sensor devices.http://ref.scielo.org/54hzc
Non-linear ripple dynamics on amorphous surfaces patterned by ion-beam sputtering
Erosion by ion-beam sputtering (IBS) of amorphous targets at off-normal
incidence frequently produces a (nanometric) rippled surface pattern, strongly
resembling macroscopic ripples on aeolian sand dunes. Suitable generalization
of continuum descriptions of the latter allows us to describe theoretically for
the first time the main nonlinear features of ripple dynamics by IBS, namely,
wavelength coarsening and non-uniform propagation velocity, that agree with
similar results in experiments and discrete models. These properties are seen
to be the anisotropic counterparts of in-plane ordering and (interrupted)
pattern coarsening in IBS experiments on rotating substrates and at normal
incidence.Comment: 5 pages, 3 figure
The predictive functional control and the management of constraints in GUANAY II autonomous underwater vehicle actuators
Autonomous underwater vehicle control has been a topic of research in the last decades. The challenges addressed vary depending on each research group's interests. In this paper, we focus on the predictive functional control (PFC), which is a control strategy that is easy to understand, install, tune, and optimize. PFC is being developed and applied in industrial applications, such as distillation, reactors, and furnaces. This paper presents the rst application of the PFC in autonomous underwater vehicles, as well as the simulation results of PFC, fuzzy, and gain scheduling controllers. Through simulations and navigation tests at sea, which successfully validate the performance of PFC strategy in motion control of autonomous underwater vehicles, PFC performance is compared with other control techniques such as fuzzy and gain scheduling control. The experimental tests presented here offer effective results concerning control objectives in high and intermediate levels of control. In high-level point, stabilization and path following scenarios are proven. In the intermediate levels, the results show that position and speed behaviors are improved using the PFC controller, which offers the smoothest behavior. The simulation depicting predictive functional control was the most effective regarding constraints management and control rate change in the Guanay II underwater vehicle actuator. The industry has not embraced the development of control theories for industrial systems because of the high investment in experts required to implement each technique successfully. However, this paper on the functional predictive control strategy evidences its easy implementation in several applications, making it a viable option for the industry given the short time needed to learn, implement, and operate, decreasing impact on the business and increasing immediacy.Peer ReviewedPostprint (author's final draft
Solid flow drives surface nanopatterning by ion-beam irradiation
Ion Beam Sputtering (IBS) is known to produce surface nanopatterns over
macroscopic areas on a wide range of materials. However, in spite of the
technological potential of this route to nanostructuring, the physical process
by which these surfaces self-organize remains poorly under- stood. We have
performed detailed experiments of IBS on Si substrates that validate dynamical
and morphological predictions from a hydrodynamic description of the
phenomenon. Our results elucidate flow of a nanoscopically thin and highly
viscous surface layer, driven by the stress created by the ion-beam, as a
description of the system. This type of slow relaxation is akin to flow of
macroscopic solids like glaciers or lead pipes, that is driven by defect
dynamics.Comment: 12 pages, 4 figure
Redes DWDM usando configurações Raman com fibras DCF
En el presente artĂculo se abordan los fundamentos teĂłricos básicos respecto de una red DWDM [MultiplexaciĂłn Densa por DivisiĂłn de Longitud de Onda] al usar configuraciones Raman con Fibras Compensadoras de DispersiĂłn [DCF], mediante el estudio de: efectos lineales, como ruido, pĂ©rdidas, dispersiĂłn cromática y DispersiĂłn por Modo de PolarizaciĂłn [PMD]; y efectos no lineales, como ModulaciĂłn de Auto-Fase [SPM], ModulaciĂłn de Fase Cruzada [XPM] y Mezcla de Cuarta Onda, frente a los Parámetros de Monitoreo Ă“ptico [OPM]. In this paper, the basic theoretical foundations regarding a DWDM [Dense Wavelength Division Multiplexing] network when using Raman configurations with DCF [Dispersion Compensation Fiber] are studied, through the revision of: linear effects, such as noise, loss, chromatic dispersion and PMD [Polarization Mode Dispersion]; and nonlinear effects, such as Self-Phase Modulation [SPM], Cross-Phase Modulation [XPM] and Four-Wave Mixing [FWM], compared to Optical Monitoring Parameters [OPM].Neste artigo sĂŁo apresentados os fundamentos teĂłricos básicos a respeito de uma rede DWDM [Multiplexação Densa por DivisĂŁo de Comprimento de Onda] usando fibras de configuração Raman com Fibras Compensadoras de DispersĂŁo [DCF] atravĂ©s do estudo de: efeitos lineares, tais como o ruĂdo, perdas, dispersĂŁo cromática e DispersĂŁo por Modo de Polarização por [PMD]; e efeitos nĂŁo lineares tais como Auto Modulação de Fase [SPM], Modulação de Fase Cruzada [XPM] e Mistura de Quatro Ondas [FWM], em comparação com a Monitorização Ă“ptica do Desempenho [OPM]
Tensor mesons produced in tau lepton decays
Light tensor mesons (T = a_2, f_2 and K_2^*) can be produced in decays of tau
leptons. In this paper we compute the branching ratios of tau --> T pi nu
decays by assuming the dominance of intermediate virtual states to model the
form factors involved in the relevant hadronic matrix element. The exclusive
f_2(1270) pi^- decay mode turns out to have the largest branching ratio, of
O(10^-4) . Our results indicate that the contributions of tensor meson
intermediate states to the three-pseudoscalar channels of tau decays are rather
small.Comment: 10 pages, 1 figure. Version accepted for publication in PRD, some
typos are corrected and comments are added in section 4. Conclusions remain
unchange
Ion induced solid flow
Amorphous solids can flow over very long periods of time. Solid flow can also
be artificially enhanced by creating defects, as by Ion Beam Sputtering (IBS)
in which collimated ions with energies in the 0.1 to 10 keV range impact a
solid target, eroding its surface and inducing formation of nanometric
structures. Recent experiments have challenged knowledge accumulated during the
last two decades so that a basic understanding of self-organized nano-pattern
formation under IBS is still lacking. We show that considering the irradiated
solid to flow like a highly viscous liquids can account for the complex IBS
morphological phase diagram, relegating erosion to a subsidiary role and
demonstrating a controllable instance of solid flow at the nanoscale. This new
perspective can allow for a full harnessing of this bottom-up route to
nanostructuring.Comment: 17 pages, 5 figure
Field experimental study of traffic-induced turbulence on highways
This paper is focused on traffic-induced turbulence (TIT) analysis from a field campaign performed in 2011, using ultrasonic anemometers deployed in the M-12 Highways, Madrid (Spain). The study attempts to improve knowledge about the influence of traffic-related parameters on turbulence. Linear relationships between vehicle speed and turbulent kinetic energy (TKE) values are found with coefficients of determination (R2) of 0.75 and 0.55 for the lorry and van respectively. The vehicle-induced fluctuations in the wind components (u', v' and w') showed the highest values for the longitudinal component (v) because of the wake-passing effect. In the analysis of wake produced by moving vehicles it is indicated how the turbulence dissipates in relation to a distance d and height h. The TKE values were found to be higher at the measuring points closer to the surface during the wake analysis.This work was supported by the OASIS Research Project that was co financed by CDTI (Spanish Science and Innovation Ministry) and developed with the Spanish companies: Iridium, OHL Concesiones, Abertis, Sice, Indra, Dragados, OHL, Geocisa, GMV, Asfaltos Augusta, Hidrofersa, Eipsa, PyG, CPS, AEC and Torre de Comares Arquitectos s.l and 16 research centres
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