Study of a mode-locked erbium-doped frequency-shifted-feedback fiber laser incorporating a broad bandpass filter: Numerical results

Vazquez-Zuniga, Luis Alonso,Jeong, Yoonchan Elsevier 2014 OPTICS COMMUNICATIONS - Vol.322 No.-

We present a comprehensive numerical study on the spectral and temporal behaviors of a mode-locked erbium-doped frequency-shifted-feedback fiber laser as a function of the frequency shift and optical bandwidth of the laser cavity. For this we develop a numerical model which is based on the rate equation and nonlinear Schrodinger equation for the fiber-based active cavity. We numerically verify that if the ratio of the filter bandwidth to the frequency-shift value is higher than 400 times, the spectral broadening of the laser output tends to break up and form a secondary spectral band (SSB) on the wavelength side of the spectrum where the spectral components of the cavity modes are constantly shifted by the intracavity frequency shifter. We also verify that the SSB forms a satellite pulse in the time domain, traveling on either the trailing edge or leading edge of the main pulse, depending on whether the SSB is formed on the shorter or longer wavelength side of the pulse spectrum. We emphasize that these numerical results are also in good agreement with the experimental results discussed in our previous report [251. (c) 2014 Elsevier B.V. All rights reserved.

Inhibitory Neuron Activity Contributions to Hemodynamic Responses and Metabolic Load Examined Using an Inhibitory Optogenetic Mouse Model

Vazquez, Alberto L,Fukuda, Mitsuhiro,Kim, Seong-Gi Oxford University Press 2018 Cerebral cortex Vol.28 No.11

<P><B>Abstract</B></P><P>Hemodynamic signals are routinely used to noninvasively assess brain function in humans and animals. This work examined the contribution of inhibitory neuron activity on hemodynamic responses captured by changes in blood flow, volume and oxygenation in the cortex of lightly anesthetized mice. Because cortical activity is not commonly initiated by inhibitory neurons, experiments were conducted to examine the neuronal activity properties elicited by photo-stimulation. We observed comparable increases in neuronal activity evoked by forelimb and photo-stimulation; however, significantly larger increases in blood flow and volume were produced by photo-stimulation of inhibitory neurons compared with forelimb stimulation. Following blockade of glutamate and GABA-A receptors to reduce postsynaptic activity contributions, neuronal activity was reliably modulated and hemodynamic changes persisted, though slightly reduced. More importantly, photo-stimulation-evoked changes in blood flow and volume were suppressed by 75–80% with the administration of a nitric oxide synthase inhibitor, suggesting that inhibitory neurons regulate blood flow mostly via nitric oxide. Lastly, forelimb and photo-stimulation of excitatory neurons produced local decreases in blood oxygenation, while large increases were generated by photo-stimulation of inhibitory neurons. Estimates of oxygen metabolism suggest that inhibitory neuron activity has a small impact on tissue metabolic load, indicating a mismatch between the metabolic demand and blood flow regulation properties of inhibitory and excitatory neurons.</P>

Backstepping Control of a Buck-Boost Converter in an Experimental PV-System

Vazquez, Jesus R.,Martin, Aranzazu D. The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.6

This paper presents a nonlinear method to control a DC-DC converter and track the Maximum Power Point (MPP) of a Photovoltaic (PV) system. A backstepping controller is proposed to regulate the voltage at the input of a buck-boost converter by means of Lyapunov functions. To make the control initially faster and avoid local maximum, a regression plane is used to estimate the reference voltages that must be obtained to achieve the MPP and guarantee the maximum power extraction, modifying the conventional Perturb and Observe (P&O) method. An experimental platform has been designed to verify the validity and performance of the proposed control method. In this platform, a buck-boost converter has been built to extract the maximum power of commercial solar modules under different environmental conditions.

Neuronal and Physiological Correlation to Hemodynamic Resting-State Fluctuations in Health and Disease

Vazquez, Alberto L.,Murphy, Matthew C.,Kim, Seong-Gi Mary Ann Liebert 2014 Brain connectivity Vol.4 No.9

Adaptive broadband continuum source at 1200-1400 nm based on an all-fiber dual-wavelength master-oscillator power amplifier and a high-birefringence fiber.

Vazquez-Zuniga, L A,Kim, Hong Sig,Kwon, Youngchul,Jeong, Yoonchan Optical Society of America 2013 Optics express Vol.21 No.6

<P>We experimentally analyze the stimulated Raman scattering characteristics of a high-birefringence fiber (HBF), which presents an extraordinary level of spectral broadening incurred by the strong nonlinear interaction between the pump and Stokes pulses via the polarization-mode dispersion and group-velocity dispersion of the fiber. We also investigate the impact of the inter-pulse time-delay on the additional spectra broadening when dual-wavelength pump pulses are used. Exploiting these unique SRS properties of the HBF, we develop a novel Raman continuum source based on an all-fiber dual-wavelength master-oscillator power amplifier that can generate a dip-free spectrum in the 1200-1400-nm spectral range. We finally obtain a broadband continuum having an average power of ~840 mW and a 3-dB bandwidth of ~240 nm centered at 1200-1400 nm, which also represents a good spectral flatness and conversion efficiency. This type of source is very useful and important for optical coherence tomography applications, for example.</P>

Super-Broadband Noise-Like Pulse Erbium-Doped Fiber Ring Laser With a Highly Nonlinear Fiber for Raman Gain Enhancement

Vazquez-Zuniga, Luis A.,Jeong, Yoonchan IEEE 2012 IEEE Photonics Technology Letters Vol.24 No.17

<P>We present a compact all-fiberized erbium-doped fiber ring laser, which generates linearly polarized picosecond pulses with a maximum bandwidth of 135 nm and excellent spectral flatness. The pulse energy and width are reconfigurable from 0.7 to 1.1 nJ and from 6.5 to 220 ps, respectively, via controlling the pumping power and/or the cavity finesse. We also analyze the relative intensity noise (RIN) characteristics of the source that results in <TEX>${-}{\rm 97}~{\rm dB}$</TEX> at low frequencies (up to 100 kHz) and <TEX>${-}{\rm 104}~{\rm dB}$</TEX> at high frequencies (up to 5 MHz), respectively. In particular, the high-frequency RIN is attributed to the spontaneous Raman scattering generated in the laser and of a comparable level with that of a commercial supercontinuum source based on a mode-locked fiber laser.</P>

Effect of Fodder Tree Species with Condensed Tannin Contents on In vitro Methane Production

Vazquez, Ernestina Gutierrez,Medina, Leonardo Hernandez,Benavides, Liliana Marquez,Caratachea, Aureliano Juarez,Razo, Guillermo Salas,Burgos, Armin Javier Ayala,Rodriguez, Ruy Ortiz Asian Australasian Association of Animal Productio 2016 Animal Bioscience Vol.29 No.1

The objective was to evaluate the effect of fodder tree species (FTS) with condensed tannin contents: Cordia elaeagnoides, Platymiscium lasiocarpum, Vitex mollis, and Haematoxylon brasiletto, on in vitro methane ($CH_4$) production at 24 h post incubation. The analysis was performed using the in vitro gas production technique, with three levels of inclusion/species: 600, 800, and 1,000 mg and with 4 replicates/species/level of inclusion. The substrate was incubated at $39^{\circ}C$, and the gas and $CH_4$ production were recorded at 4, 8, 12, and 24 h post incubation. The data collected was analyzed through Pearson correlation, polinomial regression and fixed effects models. There were negative correlations between FTS-total gas volume (r = -0.40; p<0.001); FTS-volume of $CH_4$ produced (r = -0.40; p<0.001) and between the inclusion level-volume of $CH_4$ produced (r = -0.20; p<0.001). As well as a positive correlation between hours post incubation-total gas volume (r = 0.42; p<0.001) and between hours post incubation-volume of $CH_4$ produced (r = 0.48; p<0.001). The FTS: C. elaeagnoides, V. mollis, and H. brasiletto have potential, in the three inclusion levels analyzed, to reduce $CH_4$ emission on in vitro trials (>32.7%), taking into account the total $CH_4$ production at 24 h of the forage used as reference (Avena sativa). It's suggested that C. elaeagnoides-according to its crude protein, neutral detergent fiber, and condensed tannins content- is the best alternative within the FTS analyzed, for feeding ruminants and for the control of $CH_4$ emissions during the dry season.

Aerodynamic forces on fixed and rotating plates

Martinez-Vazquez, P.,Baker, C.J.,Sterling, M.,Quinn, A.,Richards, P.J. Techno-Press 2010 Wind and Structures, An International Journal (WAS Vol.13 No.2

Pressure measurements on static and autorotating flat plates have been recently reported by Lin et al. (2006), Holmes, et al. (2006), and Richards, et al. (2008), amongst others. In general, the variation of the normal force with respect to the angle of attack appears to stall in the mid attack angle range with a large scale separation in the wake. To date however, no surface pressures have been measured on auto-rotating plates that are typical of a certain class of debris. This paper presents the results of an experiment to measure the aerodynamic forces on a flat plate held stationary at different angles to the flow and allowing the plate to auto-rotate. The forces were determined through the measurement of differential pressures on either side of the plate with internally mounted pressure transducers and data logging systems. Results are presented for surface pressure distributions and overall integrated forces and moments on the plates in coefficient form. Computed static force coefficients show the stall effect at the mid range angle of attack and some variation for different Reynolds numbers. Normal forces determined from autorotational experiments are higher than the static values at most pitch angles over a cycle. The resulting moment coefficient does not compare well with current analytical formulations which suggest the existence of a flow mechanism that cannot be completely described through static tests.

EMPRESAS TRANSNACIONALES Y EVOLUCION DE LA INTEGRACION COMERCIAL EN AMERICA LATINA: 1995-2008

Raul Vazquez Lopez Institute of Iberoamerican Studies Pusan Universit 2011 International Journal of Latin American Studies Vol.1 No.1

This article assesses the commerce evolution among the most important Latin American countries in the 1995-2008 periods, using as reference the existing theoretical debate on economic integration literature in terms of static versus dynamic competitive advantages. It is highlighted in particular, the historical role of the transnational enterprises as a barrier to build a project configured according to the ECLA (Economic Commission for Latin America ?CEPAL is the Spanish acronym?) theoretical propositions. Our main findings shows that the consolidation of global value chains promoted by large corporations accentuates the existing asymmetries between the nations and opposes to the development of a real complementarity among the productive structures of the Latin American economies. We also characterize the growing commercial deficit on service trade of the stronger economies as a new form of dependence. The article concludes then, by estimating the viability of an alternative economic integration project for the region.

Pressure field of a rotating square plate with application to windborne debris

Martinez-Vazquez, P.,Kakimpa, B.,Sterling, M.,Baker, C.J.,Quinn, A.D.,Richards, P.J.,Owen, J.S. Techno-Press 2012 Wind and Structures, An International Journal (WAS Vol.15 No.6

Traditionally, a quasi steady response concerning the aerodynamic force and moment coefficients acting on a flat plate while 'flying' through the air has been assumed. Such an assumption has enabled the flight paths of windborne debris to be predicted and an indication of its potential damage to be inferred. In order to investigate this assumption in detail, a series of physical and numerical simulations relating to flat plates subject to autorotation has been undertaken. The physical experiments have been carried out using a novel pressure acquisition technique which provides a description of the pressure distribution on a square plate which was allowed to auto-rotate at different speeds by modifying the velocity of the incoming flow. The current work has for the first time, enabled characteristic pressure signals on the surface of an auto-rotating flat plate to be attributed to vortex shedding.