Santiago Rojas - Academia.edu (original) (raw)

Papers by Santiago Rojas

Research paper thumbnail of Enhanced dipolar transport in one-dimensional waveguide arrays

We experimentally study the transport properties of dipolar and fundamental modes on one dimensio... more We experimentally study the transport properties of dipolar and fundamental modes on one dimensional (1D) coupled waveguide arrays. By carefully modulating a wide optical beam, we are able to effectively excite dipolar or fundamental modes to study discrete diffraction (single-site excitation) and gaussian beam propagation (multi-site excitation plus a phase gradient). We observe that dipolar modes experience a larger spreading area due to an effective larger coupling constant, which is found to be more than two times larger than the one for fundamental modes. Additionally, we study the effect of non-diagonal disorder and find that while fundamental modes are already trapped on a weakly disorder array, dipoles are still able to propagate across the system.

Research paper thumbnail of Analytical model for waveguide light propagation and applications

arXiv: Optics, 2014

We study the polarization properties of elliptical femtosecond-laser-written waveguides arrays. A... more We study the polarization properties of elliptical femtosecond-laser-written waveguides arrays. A new analytical model is presented to explain the asymmetry of the spatial transverse profiles of linearly polarized modes in these waveguides. This asymmetry produces a polarization dependent coupling coefficient, between adjacent waveguides, which strongly affects the propagation of light in a lattice. Our analysis explains how this effect can be exploited to tune the final intensity distribution of light propagated through the array, and links the properties of a polarizing beam splitter in integrated optical circuits to the geometry of the waveguides.

Research paper thumbnail of Evaluating the coupling efficiency of OAM beams into ring-core optical fibers

Optics Express, 2021

In optical communications, space-division multiplexing is a promising strategy to augment the fib... more In optical communications, space-division multiplexing is a promising strategy to augment the fiber network capacity. It relies on modern fiber designs that support the propagation of multiple spatial modes. One of these fibers, the ring-core fiber (RCF), is able to propagate modes that carry orbital angular momentum (OAM), and has been shown to enhance not only classical but also quantum communication systems. Typically, the RCF spatial modes are used as orthogonal transmission channels for data streams that are coupled into the fiber using different free space beams. Free space beams commonly used are Laguerre-Gaussian (LG) and perfect vortex (PV) beams. Here, we study the optimal conditions to multiplex information into ring-core fibers in this scheme. We study the beam coupling efficiency using the overlap between free space beams and RCF bound beams and determine which are the most relevant LG beams to be considered and how their coupling efficiency can be maximized by properly...

Research paper thumbnail of Manipulation of multimode squeezing in a coupled waveguide array

Physical Review A, 2019

We present a scheme for generating and manipulating three-mode squeezed states with genuine tripa... more We present a scheme for generating and manipulating three-mode squeezed states with genuine tripartite entanglement by injecting single-mode squeezed light into an array of coupled optical waveguides. We explore the possibility to selectively generate single-mode squeezing or multimode squeezing at the output of an elliptical waveguides array, determined solely by the input light polarization. We study the effect of losses in the waveguides array and show that quantum correlations and squeezing are preserved for realistic parameters. Our results show that arrays of optical waveguides are suitable platforms for generating multimode quantum light, which could lead to novel applications in quantum metrology.

Research paper thumbnail of Quantum localized states in photonic flat-band lattices

Physical Review A, 2017

The localization of light in flat-band lattices has been recently proposed and experimentally dem... more The localization of light in flat-band lattices has been recently proposed and experimentally demonstrated in several configurations, assuming a classical description of light. Here, we study the problem of light localization in the quantum regime. We focus on quasi one-dimensional and two-dimensional lattices which exhibit a perfect flat-band inside their linear spectrum. Localized quantum states are constructed as eigenstates of the interaction Hamiltonian with a vanishing eigenvalue and a well defined total photon number. These are superpositions of Fock states with probability amplitudes given by positive as well as negative square roots of multinomial coefficients. The classical picture can be recovered by considering poissonian superpositions of localized quantum states with different total photon number. We also study the separability properties of flat band quantum states and apply them to the transmission of information via multi-core fibers, where these states allow for the total passive suppression of photon crosstalk and exhibit robustness against photon losses. At the end, we propose a novel on-chip setup for the experimental preparation of localized quantum states of light for any number of photons.

Research paper thumbnail of Observation of dipolar transport in one-dimensional photonic lattices

Science Bulletin, 2017

We experimentally study the transport properties of dipolar and fundamental modes on one dimensio... more We experimentally study the transport properties of dipolar and fundamental modes on one dimensional (1D) coupled waveguide arrays. By carefully modulating a wide optical beam, we are able to effectively excite dipolar or fundamental modes to study discrete diffraction (single-site excitation) and gaussian beam propagation (multi-site excitation plus a phase gradient). We observe that dipolar modes experience a larger spreading area due to an effective larger coupling constant, which is found to be more than two times larger than the one for fundamental modes. Additionally, we study the effect of non-diagonal disorder and find that while fundamental modes are already trapped on a weakly disorder array, dipoles are still able to propagate across the system.

Research paper thumbnail of Cerebrospinal fluid sTREM2 levels are associated with gray matter volume increases and reduced diffusivity in early Alzheimer's disease

Alzheimer's & Dementia, 2016

IntroductionTREM2 is involved in the regulation of inflammatory response and phagocytosis. A solu... more IntroductionTREM2 is involved in the regulation of inflammatory response and phagocytosis. A soluble fragment (sTREM2) is often found abnormally increased in cerebrospinal fluid (CSF) in Alzheimer's disease (AD).MethodsOne hundred fourteen participants (45 control, 19 preclinical, 27 mild cognitive impairment [MCI], and 23 AD) underwent CSF sTREM2 determination and magnetic resonance imaging (MRI). We studied the association between CSF sTREM2, gray matter volume, and water motion diffusivity and anisotropy across groups.ResultsIn MCI patients, a positive correlation between CSF sTREM2 and gray matter volume was found in the bilateral inferior and middle temporal cortices, precuneus, the supramarginal, and angular gyri, after controlling by age, sex, and p‐tau. A negative correlation with mean diffusivity was detected in overlapping regions, among others.DiscussionIn early AD, augmented CSF sTREM2 levels correspond with cerebral MRI features typical of brain swelling, supporting...

Research paper thumbnail of CSF YKL-40 and pTau181 are related to different cerebral morphometric patterns in early AD

Neurobiology of Aging, 2016

Cerebrospinal fluid (CSF) concentrations of YKL-40 that serve as biomarker of neuroinflammation a... more Cerebrospinal fluid (CSF) concentrations of YKL-40 that serve as biomarker of neuroinflammation are known to be altered along the clinico-biological continuum of Alzheimer's disease (AD). The specific structural cerebral correlates of CSF YKL-40 were evaluated across the early stages of AD from normal to preclinical to mild dementia. Nonlinear gray matter (GM) volume associations with CSF YKL-40 levels were assessed in a total of 116 subjects, including normal controls and those with preclinical AD as defined by CSF Ab < 500 pg/mL, mild cognitive impairment (MCI) due to AD, or mild AD dementia. Agecorrected YKL-40 levels were increased in MCIs versus the rest of groups and showed an inverse ushaped association with p-tau values. A similar nonlinear relationship was found between GM volume and YKL-40 in inferior and lateral temporal regions spreading to the supramarginal gyrus, insula, inferior frontal cortex, and cerebellum in MCI and AD. These findings for YKL-40 remained unchanged after adjusting for p-tau, which was found to be associated with GM volumes in distinct anatomic areas. CSF YKL-40, a biomarker of glial inflammation, is associated with a cerebral structural signature distinct from that related to p-tau neurodegeneration at the earliest stages of cognitive decline due to AD.

Research paper thumbnail of A new model for waveguide light propagation and applications: tuning light distribution in elliptical waveguide arrays and a compact deterministic 50: 50 PBS

We study the polarization properties of elliptical femtosecond-laser-written waveguides arrays. A... more We study the polarization properties of elliptical femtosecond-laser-written waveguides arrays. A new analytical model is presented to explain the asymmetry of the spatial transverse profiles of linearly polarized modes in these waveguides. This asymmetry produces a polarization dependent coupling coefficient, between adjacent waveguides, which strongly affects the propagation of light in a lattice. Our analysis explains how this effect can be exploited to tune the final intensity distribution of light propagated through the array, and links the properties of a polarizing beam splitter in integrated optical circuits to the geometry of the waveguides.

Research paper thumbnail of Delocalization enhancement induced by weak disorder and nonlinearity

Conference on Lasers and Electro-Optics 2012, 2012

ABSTRACT We show theoretically and experimentally for planar and square lattices, that during the... more ABSTRACT We show theoretically and experimentally for planar and square lattices, that during the initial diffractive broadening of a narrow excitation, small amounts of disorder may enhance delocalization. This effect is amplified by nonlinear propagation.

Research paper thumbnail of In vivo evaluation of amyloid deposition and brain glucose metabolism of 5XFAD mice using positron emission tomography

Neurobiology of Aging, 2013

Positron emission tomography (PET) has been used extensively to evaluate the neuropathology of Al... more Positron emission tomography (PET) has been used extensively to evaluate the neuropathology of Alzheimer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease (AD) in vivo. Radiotracers directed toward the amyloid deposition such as [(18)F]-FDDNP (2-(1-{6-[(2-[F]Fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile) and [(11)C]-PIB (Pittsburg compound B) have shown exceptional value in animal models and AD patients. Previously, the glucose analogue [(18)F]-FDG (2-[(18)F]fluorodeoxyglucose) allowed researchers and clinicians to evaluate the brain glucose consumption and proved its utility for the early diagnosis and the monitoring of the progression of AD. Animal models of AD are based on the transgenic expression of different human mutant genes linked to familial AD. The novel transgenic 5XFAD mouse containing 5 mutated genes in its genome has been proposed as an AD model with rapid and massive cerebral amyloid deposition. PET studies performed with animal-dedicated scanners indicate that PET with amyloid-targeted radiotracers can detect the pathological amyloid deposition in transgenic mice and rats. However, in other studies no differences were found between transgenic mice and their wild type littermates. We sought to investigate in 5XFAD mice if the radiotracers [(11)C]-PIB, and [(18)F]-Florbetapir could quantify the amyloid deposition in vivo and if [(18)F]-FDG could do so with regard to glucose consumption. We found that 5XFAD animals presented higher cerebral binding of [(18)F]-Florbetapir, [(11)C]-PIB, and [(18)F]-FDG. These results support the use of amyloid PET radiotracers for the evaluation of AD animal models. Probably, the increased uptake observed with [(18)F]-FDG is a consequence of glial activation that occurs in 5XFAD mice.

Research paper thumbnail of Analytical model for polarization-dependent light propagation in waveguide arrays and applications

Research paper thumbnail of Modest MRI Signal Intensity Changes Precede Delayed Cortical Necrosis After Transient Focal Ischemia in the Rat

Stroke, 2006

Background and Purpose— Diffusion-weighted imaging (DWI) hyperintensities and apparent diffusion ... more Background and Purpose— Diffusion-weighted imaging (DWI) hyperintensities and apparent diffusion coefficient (ADC) hypointensities are MRI features of acute stroke. DWI alterations during ischemia recover with early reperfusion, but they can reappear later. Pronounced signal abnormalities early after stroke are associated with infarction, but the significance of subtle changes is unclear. Here we evaluated the degree and time course of regional signal intensity changes during the first 24 hours of reperfusion after transient ischemia, and we related them to the progression of the histopathological damage. Methods— Rats (n=54) were subjected to 1-hour intraluminal middle cerebral artery occlusion to assess the dynamics of MRI signal intensity changes during the initial 24 hours and their correspondent histopathological features: 2,3,5-triphenyltetrazolium chloride (TTC) staining, and hematoxylin and eosin, and immunoreactivity to 70-kDa heat shock protein and to astroglial and microg...

Research paper thumbnail of Modalidad narrativa en Aura: realidad y enajenación

Revista Iberoamericana, 1980

Desde la publicaci6n de Aura la critica se ha ocupado con frecuencia de esta novela corta de Carl... more Desde la publicaci6n de Aura la critica se ha ocupado con frecuencia de esta novela corta de Carlos Fuentes y en muchas oportunidades se han emitido juicios que realmente sorprenden por su disparidad. Para Luis Harss y Barbara Dohmann, Aura no pasa de ser una elusiva novelita de mnisterio, que adolece de flagrantes deslices de estructura y estilo y por todo ello no alcanza a convencer positivamente al lector 1. Rene Jara opina que <>, agregando a rengl6n seguido este comentario con relaci6n al novelista: <> 2 Manuel Durin, en cambio, cataloga a Aura como <, y Emir Rodriguez Monegal, sin dejar de hacer hincapi6 en las dificultades que el relato depara al critico y al lector, la considera como una de las obras rns logradas del conocido escritor mexicano 3. El propio Fuentes, ademis, segin Daniel de Guzmin, tiene a Aura en alta estima y tambi6n la reconoce como una de sus mejores creaciones 4. Enmanuel Carballo, en una entrevista sostenida con el escritor, haciendo un par6ntesis a los comentarios autocriticos de Fuentes, anota esta elogiosa valoraci6n: Se ha dicho, y con raz6n, que Aura (1962) es una obra maestra de la narrativa mexicana. Obra maestra porque en ella no se distin

Research paper thumbnail of Nonlinear localized modes in dipolar Bose-Einstein condensates in optical lattices

Research paper thumbnail of Enhanced distribution of a wave-packet in lattices with disorder and nonlinearity

Optics Express, 2013

We show, theoretically and experimentally, the counterintuitive result that an increase of disord... more We show, theoretically and experimentally, the counterintuitive result that an increase of disorder can result in an enhanced spreading of an initially localized excitation. Moreover, we find that adding a focusing nonlinearity facilitates the expansion of the wave-packet even further by increasing its effective size. We find a clear transition between between the regions of enhanced spreading (weak disorder) and localization (strong localization) described by a "diffusion peak."

Research paper thumbnail of β-catenin confers resistance to PI3K and AKT inhibitors and subverts FOXO3a to promote metastasis in colon cancer

Nature Medicine, 2012

Wnt/β-catenin and PI3K/AKT pathways play a central role in cancer. We describe the function of th... more Wnt/β-catenin and PI3K/AKT pathways play a central role in cancer. We describe the function of their corresponding transcriptional effectorsβ-catenin and FOXO3a-in colon cancer progression. Their simultaneous nuclear accumulation and activation promotes cell scattering and metastasis, by regulating a defined set of target genes. Unexpectedly, the anti-tumoral AKT inhibitor API-2 promotes nuclear FOXO3a accumulation and metastasis of cells with high nuclear β-catenin. β-catenin confers resistance to FOXO3a-mediated apoptosis induced by PI3K and AKT inhibitors in patient-derived primary cultures and in corresponding xenograft tumors in mice. This resistance is reverted by Wnt/β-catenin signaling inhibitor XAV-939. FOXO3a does not behave as a tumor suppressor but rather as a metastasis inductor activated by PI3K or AKT inhibitory drugs when acting in concert with β-catenin. We show that it is possible to evaluate βcatenin status and the response of patient-derived cells to these target-directed drugs before deciding on treatment. We also consider that this evaluation could be essential to the provision of a safer and more effective personalized treatment.

Research paper thumbnail of Evaluation of Hypoxic Tissue Dynamics with 18F-FMISO PET in a Rat Model of Permanent Cerebral Ischemia

Molecular Imaging and Biology, 2010

Research paper thumbnail of Simultaneous Dual-tracer PET Imaging of the Rat Brain and its Application in the Study of Cerebral Ischemia

Molecular Imaging and Biology, 2010

Research paper thumbnail of Differential role of tumor necrosis factor receptors in mouse brain inflammatory responses in cryolesion brain injury

Journal of Neuroscience Research, 2005

Tumor necrosis factor-alpha (TNF-alpha) is one of the mediators dramatically increased after trau... more Tumor necrosis factor-alpha (TNF-alpha) is one of the mediators dramatically increased after traumatic brain injury that leads to the activation, proliferation, and hypertrophy of mononuclear, phagocytic cells and gliosis. Eventually, TNF-alpha can induce both apoptosis and necrosis via intracellular signaling. This cytokine exerts its functions via interaction with two receptors: type-1 receptor (TNFR1) and type-2 receptor (TNFR2). In this work, the inflammatory response after a freeze injury (cryolesion) in the cortex was studied in wild-type (WT) animals and in mice lacking TNFR1 (TNFR1 KO) or TNFR2 (TNFR2 KO). Lack of TNFR1, but not of TNFR2, significantly decreased the inflammatory response and tissue damage elicited by the cryolesion at both 3 and 7 days postlesion, with decreased gliosis, lower IL-1beta immunostaining, and a reduction of apoptosis markers. Cryolesion produced a clear induction of the proinflammatory cytokines interleukin (IL)-1alpha, IL-1beta, IL-6, and TNF-alpha; this induction was significantly lower in the TNFR1 KO mice. Host response genes (ICAM-1, A20, EB22/5, and GFAP) were also induced by the cryolesion, but to a lesser extent in TNFR1 KO mice. Lack of TNFR1 signaling also affected the expression of apoptosis/cell death-related genes (Fas, Rip, p53), matrix metalloproteinases (MMP3, MMP9, MMP12), and their inhibitors (TIMP1), suggesting a role of TNFR1 in extracellular matrix remodeling after injury. However, GDNF, NGF, and BDNF expression were not affected by TNFR1 deficiency. Overall, these results suggest that TNFR1 is involved in the early establishment of the inflammatory response and that its deficiency causes a decreased inflammatory response and tissue damage following brain injury.

Research paper thumbnail of Enhanced dipolar transport in one-dimensional waveguide arrays

We experimentally study the transport properties of dipolar and fundamental modes on one dimensio... more We experimentally study the transport properties of dipolar and fundamental modes on one dimensional (1D) coupled waveguide arrays. By carefully modulating a wide optical beam, we are able to effectively excite dipolar or fundamental modes to study discrete diffraction (single-site excitation) and gaussian beam propagation (multi-site excitation plus a phase gradient). We observe that dipolar modes experience a larger spreading area due to an effective larger coupling constant, which is found to be more than two times larger than the one for fundamental modes. Additionally, we study the effect of non-diagonal disorder and find that while fundamental modes are already trapped on a weakly disorder array, dipoles are still able to propagate across the system.

Research paper thumbnail of Analytical model for waveguide light propagation and applications

arXiv: Optics, 2014

We study the polarization properties of elliptical femtosecond-laser-written waveguides arrays. A... more We study the polarization properties of elliptical femtosecond-laser-written waveguides arrays. A new analytical model is presented to explain the asymmetry of the spatial transverse profiles of linearly polarized modes in these waveguides. This asymmetry produces a polarization dependent coupling coefficient, between adjacent waveguides, which strongly affects the propagation of light in a lattice. Our analysis explains how this effect can be exploited to tune the final intensity distribution of light propagated through the array, and links the properties of a polarizing beam splitter in integrated optical circuits to the geometry of the waveguides.

Research paper thumbnail of Evaluating the coupling efficiency of OAM beams into ring-core optical fibers

Optics Express, 2021

In optical communications, space-division multiplexing is a promising strategy to augment the fib... more In optical communications, space-division multiplexing is a promising strategy to augment the fiber network capacity. It relies on modern fiber designs that support the propagation of multiple spatial modes. One of these fibers, the ring-core fiber (RCF), is able to propagate modes that carry orbital angular momentum (OAM), and has been shown to enhance not only classical but also quantum communication systems. Typically, the RCF spatial modes are used as orthogonal transmission channels for data streams that are coupled into the fiber using different free space beams. Free space beams commonly used are Laguerre-Gaussian (LG) and perfect vortex (PV) beams. Here, we study the optimal conditions to multiplex information into ring-core fibers in this scheme. We study the beam coupling efficiency using the overlap between free space beams and RCF bound beams and determine which are the most relevant LG beams to be considered and how their coupling efficiency can be maximized by properly...

Research paper thumbnail of Manipulation of multimode squeezing in a coupled waveguide array

Physical Review A, 2019

We present a scheme for generating and manipulating three-mode squeezed states with genuine tripa... more We present a scheme for generating and manipulating three-mode squeezed states with genuine tripartite entanglement by injecting single-mode squeezed light into an array of coupled optical waveguides. We explore the possibility to selectively generate single-mode squeezing or multimode squeezing at the output of an elliptical waveguides array, determined solely by the input light polarization. We study the effect of losses in the waveguides array and show that quantum correlations and squeezing are preserved for realistic parameters. Our results show that arrays of optical waveguides are suitable platforms for generating multimode quantum light, which could lead to novel applications in quantum metrology.

Research paper thumbnail of Quantum localized states in photonic flat-band lattices

Physical Review A, 2017

The localization of light in flat-band lattices has been recently proposed and experimentally dem... more The localization of light in flat-band lattices has been recently proposed and experimentally demonstrated in several configurations, assuming a classical description of light. Here, we study the problem of light localization in the quantum regime. We focus on quasi one-dimensional and two-dimensional lattices which exhibit a perfect flat-band inside their linear spectrum. Localized quantum states are constructed as eigenstates of the interaction Hamiltonian with a vanishing eigenvalue and a well defined total photon number. These are superpositions of Fock states with probability amplitudes given by positive as well as negative square roots of multinomial coefficients. The classical picture can be recovered by considering poissonian superpositions of localized quantum states with different total photon number. We also study the separability properties of flat band quantum states and apply them to the transmission of information via multi-core fibers, where these states allow for the total passive suppression of photon crosstalk and exhibit robustness against photon losses. At the end, we propose a novel on-chip setup for the experimental preparation of localized quantum states of light for any number of photons.

Research paper thumbnail of Observation of dipolar transport in one-dimensional photonic lattices

Science Bulletin, 2017

We experimentally study the transport properties of dipolar and fundamental modes on one dimensio... more We experimentally study the transport properties of dipolar and fundamental modes on one dimensional (1D) coupled waveguide arrays. By carefully modulating a wide optical beam, we are able to effectively excite dipolar or fundamental modes to study discrete diffraction (single-site excitation) and gaussian beam propagation (multi-site excitation plus a phase gradient). We observe that dipolar modes experience a larger spreading area due to an effective larger coupling constant, which is found to be more than two times larger than the one for fundamental modes. Additionally, we study the effect of non-diagonal disorder and find that while fundamental modes are already trapped on a weakly disorder array, dipoles are still able to propagate across the system.

Research paper thumbnail of Cerebrospinal fluid sTREM2 levels are associated with gray matter volume increases and reduced diffusivity in early Alzheimer's disease

Alzheimer's & Dementia, 2016

IntroductionTREM2 is involved in the regulation of inflammatory response and phagocytosis. A solu... more IntroductionTREM2 is involved in the regulation of inflammatory response and phagocytosis. A soluble fragment (sTREM2) is often found abnormally increased in cerebrospinal fluid (CSF) in Alzheimer's disease (AD).MethodsOne hundred fourteen participants (45 control, 19 preclinical, 27 mild cognitive impairment [MCI], and 23 AD) underwent CSF sTREM2 determination and magnetic resonance imaging (MRI). We studied the association between CSF sTREM2, gray matter volume, and water motion diffusivity and anisotropy across groups.ResultsIn MCI patients, a positive correlation between CSF sTREM2 and gray matter volume was found in the bilateral inferior and middle temporal cortices, precuneus, the supramarginal, and angular gyri, after controlling by age, sex, and p‐tau. A negative correlation with mean diffusivity was detected in overlapping regions, among others.DiscussionIn early AD, augmented CSF sTREM2 levels correspond with cerebral MRI features typical of brain swelling, supporting...

Research paper thumbnail of CSF YKL-40 and pTau181 are related to different cerebral morphometric patterns in early AD

Neurobiology of Aging, 2016

Cerebrospinal fluid (CSF) concentrations of YKL-40 that serve as biomarker of neuroinflammation a... more Cerebrospinal fluid (CSF) concentrations of YKL-40 that serve as biomarker of neuroinflammation are known to be altered along the clinico-biological continuum of Alzheimer's disease (AD). The specific structural cerebral correlates of CSF YKL-40 were evaluated across the early stages of AD from normal to preclinical to mild dementia. Nonlinear gray matter (GM) volume associations with CSF YKL-40 levels were assessed in a total of 116 subjects, including normal controls and those with preclinical AD as defined by CSF Ab < 500 pg/mL, mild cognitive impairment (MCI) due to AD, or mild AD dementia. Agecorrected YKL-40 levels were increased in MCIs versus the rest of groups and showed an inverse ushaped association with p-tau values. A similar nonlinear relationship was found between GM volume and YKL-40 in inferior and lateral temporal regions spreading to the supramarginal gyrus, insula, inferior frontal cortex, and cerebellum in MCI and AD. These findings for YKL-40 remained unchanged after adjusting for p-tau, which was found to be associated with GM volumes in distinct anatomic areas. CSF YKL-40, a biomarker of glial inflammation, is associated with a cerebral structural signature distinct from that related to p-tau neurodegeneration at the earliest stages of cognitive decline due to AD.

Research paper thumbnail of A new model for waveguide light propagation and applications: tuning light distribution in elliptical waveguide arrays and a compact deterministic 50: 50 PBS

We study the polarization properties of elliptical femtosecond-laser-written waveguides arrays. A... more We study the polarization properties of elliptical femtosecond-laser-written waveguides arrays. A new analytical model is presented to explain the asymmetry of the spatial transverse profiles of linearly polarized modes in these waveguides. This asymmetry produces a polarization dependent coupling coefficient, between adjacent waveguides, which strongly affects the propagation of light in a lattice. Our analysis explains how this effect can be exploited to tune the final intensity distribution of light propagated through the array, and links the properties of a polarizing beam splitter in integrated optical circuits to the geometry of the waveguides.

Research paper thumbnail of Delocalization enhancement induced by weak disorder and nonlinearity

Conference on Lasers and Electro-Optics 2012, 2012

ABSTRACT We show theoretically and experimentally for planar and square lattices, that during the... more ABSTRACT We show theoretically and experimentally for planar and square lattices, that during the initial diffractive broadening of a narrow excitation, small amounts of disorder may enhance delocalization. This effect is amplified by nonlinear propagation.

Research paper thumbnail of In vivo evaluation of amyloid deposition and brain glucose metabolism of 5XFAD mice using positron emission tomography

Neurobiology of Aging, 2013

Positron emission tomography (PET) has been used extensively to evaluate the neuropathology of Al... more Positron emission tomography (PET) has been used extensively to evaluate the neuropathology of Alzheimer&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s disease (AD) in vivo. Radiotracers directed toward the amyloid deposition such as [(18)F]-FDDNP (2-(1-{6-[(2-[F]Fluoroethyl)(methyl)amino]-2-naphthyl}ethylidene)malononitrile) and [(11)C]-PIB (Pittsburg compound B) have shown exceptional value in animal models and AD patients. Previously, the glucose analogue [(18)F]-FDG (2-[(18)F]fluorodeoxyglucose) allowed researchers and clinicians to evaluate the brain glucose consumption and proved its utility for the early diagnosis and the monitoring of the progression of AD. Animal models of AD are based on the transgenic expression of different human mutant genes linked to familial AD. The novel transgenic 5XFAD mouse containing 5 mutated genes in its genome has been proposed as an AD model with rapid and massive cerebral amyloid deposition. PET studies performed with animal-dedicated scanners indicate that PET with amyloid-targeted radiotracers can detect the pathological amyloid deposition in transgenic mice and rats. However, in other studies no differences were found between transgenic mice and their wild type littermates. We sought to investigate in 5XFAD mice if the radiotracers [(11)C]-PIB, and [(18)F]-Florbetapir could quantify the amyloid deposition in vivo and if [(18)F]-FDG could do so with regard to glucose consumption. We found that 5XFAD animals presented higher cerebral binding of [(18)F]-Florbetapir, [(11)C]-PIB, and [(18)F]-FDG. These results support the use of amyloid PET radiotracers for the evaluation of AD animal models. Probably, the increased uptake observed with [(18)F]-FDG is a consequence of glial activation that occurs in 5XFAD mice.

Research paper thumbnail of Analytical model for polarization-dependent light propagation in waveguide arrays and applications

Research paper thumbnail of Modest MRI Signal Intensity Changes Precede Delayed Cortical Necrosis After Transient Focal Ischemia in the Rat

Stroke, 2006

Background and Purpose— Diffusion-weighted imaging (DWI) hyperintensities and apparent diffusion ... more Background and Purpose— Diffusion-weighted imaging (DWI) hyperintensities and apparent diffusion coefficient (ADC) hypointensities are MRI features of acute stroke. DWI alterations during ischemia recover with early reperfusion, but they can reappear later. Pronounced signal abnormalities early after stroke are associated with infarction, but the significance of subtle changes is unclear. Here we evaluated the degree and time course of regional signal intensity changes during the first 24 hours of reperfusion after transient ischemia, and we related them to the progression of the histopathological damage. Methods— Rats (n=54) were subjected to 1-hour intraluminal middle cerebral artery occlusion to assess the dynamics of MRI signal intensity changes during the initial 24 hours and their correspondent histopathological features: 2,3,5-triphenyltetrazolium chloride (TTC) staining, and hematoxylin and eosin, and immunoreactivity to 70-kDa heat shock protein and to astroglial and microg...

Research paper thumbnail of Modalidad narrativa en Aura: realidad y enajenación

Revista Iberoamericana, 1980

Desde la publicaci6n de Aura la critica se ha ocupado con frecuencia de esta novela corta de Carl... more Desde la publicaci6n de Aura la critica se ha ocupado con frecuencia de esta novela corta de Carlos Fuentes y en muchas oportunidades se han emitido juicios que realmente sorprenden por su disparidad. Para Luis Harss y Barbara Dohmann, Aura no pasa de ser una elusiva novelita de mnisterio, que adolece de flagrantes deslices de estructura y estilo y por todo ello no alcanza a convencer positivamente al lector 1. Rene Jara opina que <>, agregando a rengl6n seguido este comentario con relaci6n al novelista: <> 2 Manuel Durin, en cambio, cataloga a Aura como <, y Emir Rodriguez Monegal, sin dejar de hacer hincapi6 en las dificultades que el relato depara al critico y al lector, la considera como una de las obras rns logradas del conocido escritor mexicano 3. El propio Fuentes, ademis, segin Daniel de Guzmin, tiene a Aura en alta estima y tambi6n la reconoce como una de sus mejores creaciones 4. Enmanuel Carballo, en una entrevista sostenida con el escritor, haciendo un par6ntesis a los comentarios autocriticos de Fuentes, anota esta elogiosa valoraci6n: Se ha dicho, y con raz6n, que Aura (1962) es una obra maestra de la narrativa mexicana. Obra maestra porque en ella no se distin

Research paper thumbnail of Nonlinear localized modes in dipolar Bose-Einstein condensates in optical lattices

Research paper thumbnail of Enhanced distribution of a wave-packet in lattices with disorder and nonlinearity

Optics Express, 2013

We show, theoretically and experimentally, the counterintuitive result that an increase of disord... more We show, theoretically and experimentally, the counterintuitive result that an increase of disorder can result in an enhanced spreading of an initially localized excitation. Moreover, we find that adding a focusing nonlinearity facilitates the expansion of the wave-packet even further by increasing its effective size. We find a clear transition between between the regions of enhanced spreading (weak disorder) and localization (strong localization) described by a "diffusion peak."

Research paper thumbnail of β-catenin confers resistance to PI3K and AKT inhibitors and subverts FOXO3a to promote metastasis in colon cancer

Nature Medicine, 2012

Wnt/β-catenin and PI3K/AKT pathways play a central role in cancer. We describe the function of th... more Wnt/β-catenin and PI3K/AKT pathways play a central role in cancer. We describe the function of their corresponding transcriptional effectorsβ-catenin and FOXO3a-in colon cancer progression. Their simultaneous nuclear accumulation and activation promotes cell scattering and metastasis, by regulating a defined set of target genes. Unexpectedly, the anti-tumoral AKT inhibitor API-2 promotes nuclear FOXO3a accumulation and metastasis of cells with high nuclear β-catenin. β-catenin confers resistance to FOXO3a-mediated apoptosis induced by PI3K and AKT inhibitors in patient-derived primary cultures and in corresponding xenograft tumors in mice. This resistance is reverted by Wnt/β-catenin signaling inhibitor XAV-939. FOXO3a does not behave as a tumor suppressor but rather as a metastasis inductor activated by PI3K or AKT inhibitory drugs when acting in concert with β-catenin. We show that it is possible to evaluate βcatenin status and the response of patient-derived cells to these target-directed drugs before deciding on treatment. We also consider that this evaluation could be essential to the provision of a safer and more effective personalized treatment.

Research paper thumbnail of Evaluation of Hypoxic Tissue Dynamics with 18F-FMISO PET in a Rat Model of Permanent Cerebral Ischemia

Molecular Imaging and Biology, 2010

Research paper thumbnail of Simultaneous Dual-tracer PET Imaging of the Rat Brain and its Application in the Study of Cerebral Ischemia

Molecular Imaging and Biology, 2010

Research paper thumbnail of Differential role of tumor necrosis factor receptors in mouse brain inflammatory responses in cryolesion brain injury

Journal of Neuroscience Research, 2005

Tumor necrosis factor-alpha (TNF-alpha) is one of the mediators dramatically increased after trau... more Tumor necrosis factor-alpha (TNF-alpha) is one of the mediators dramatically increased after traumatic brain injury that leads to the activation, proliferation, and hypertrophy of mononuclear, phagocytic cells and gliosis. Eventually, TNF-alpha can induce both apoptosis and necrosis via intracellular signaling. This cytokine exerts its functions via interaction with two receptors: type-1 receptor (TNFR1) and type-2 receptor (TNFR2). In this work, the inflammatory response after a freeze injury (cryolesion) in the cortex was studied in wild-type (WT) animals and in mice lacking TNFR1 (TNFR1 KO) or TNFR2 (TNFR2 KO). Lack of TNFR1, but not of TNFR2, significantly decreased the inflammatory response and tissue damage elicited by the cryolesion at both 3 and 7 days postlesion, with decreased gliosis, lower IL-1beta immunostaining, and a reduction of apoptosis markers. Cryolesion produced a clear induction of the proinflammatory cytokines interleukin (IL)-1alpha, IL-1beta, IL-6, and TNF-alpha; this induction was significantly lower in the TNFR1 KO mice. Host response genes (ICAM-1, A20, EB22/5, and GFAP) were also induced by the cryolesion, but to a lesser extent in TNFR1 KO mice. Lack of TNFR1 signaling also affected the expression of apoptosis/cell death-related genes (Fas, Rip, p53), matrix metalloproteinases (MMP3, MMP9, MMP12), and their inhibitors (TIMP1), suggesting a role of TNFR1 in extracellular matrix remodeling after injury. However, GDNF, NGF, and BDNF expression were not affected by TNFR1 deficiency. Overall, these results suggest that TNFR1 is involved in the early establishment of the inflammatory response and that its deficiency causes a decreased inflammatory response and tissue damage following brain injury.