Mode Width Research Articles

The effects of angiotensin II on the coupled microstructural and biomechanical response of C57BL/6 mouse aorta

RationaleAbdominal aortic aneurysm (AAA) is a complex disease that leads to a localized dilation of the infrarenal aorta, the rupture of which is associated with significant morbidity and mortality. Animal models of AAA can be used to study how changes in the microstructural and biomechanical behavior of aortic tissues develop as disease progresses in these animals. We chose here to investigate the effect of angiotensin II (AngII) in C57BL/6 mice as a first step towards understanding how such changes occur in the established ApoE−/− AngII infused mouse model of AAA. ObjectiveThe objective of this study was to utilize a recently developed device in our laboratory to determine how the microstructural and biomechanical properties of AngII-infused C57BL/6 wildtype mouse aorta change following 14 days of AngII infusion. MethodsC57BL/6 wildtype mice were infused with either saline or AngII for 14 day. Aortas were excised and tested using a device capable of simultaneously characterizing the biaxial mechanical response and load-dependent (unfixed, unfrozen) extracellular matrix organization of mouse aorta (using multiphoton microscopy). Peak strains and stiffness values were compared across experimental groups, and both datasets were fit to a Fung-type constitutive model. The mean mode and full width at half maximum (FWHM) of fiber histograms from two photon microscopy were quantified in order to assess the preferred fiber distribution and degree of fiber splay, respectively. ResultsThe axial stiffness of all mouse aorta was found to be an order of magnitude larger than the circumferential stiffness. The aortic diameter was found to be significantly increased for the AngII infused mice as compared to saline infused control (p=0.026). Aneurysm, defined as a percent increase in maximum diameter of 30% (defined with respect to saline control), was found in 3 of the 6 AngII infused mice. These three mice displayed adventitial collagen that lacked characteristic fiber crimp. The biomechanical response in the AngII infused mice showed significantly reduced circumferential compliance. We also noticed that the ability of the adventitial collagen fibers in AngII infused mice to disperse in reaction to circumferential loading was suppressed. ConclusionsCollagen remodeling is present following 14 days of AngII infusion in C57BL/6 mice. Aneurysmal development occurred in 50% of our AngII infused mice, and these dilatations were accompanied with adventitial collagen remodeling and decreased circumferential compliance.

Long-range dielectric-loaded surface plasmon polariton waveguides operating at telecommunication wavelengths

We report on the realization of long-range dielectric-loaded surface plasmon polariton waveguides (LR-DLSPPWs) consisting of straight and bent subwavelength dielectric ridges deposited on thin and narrow metal stripes supported by a dielectric buffer layer covering a low-index substrate. Using imaging with a near-field optical microscope and end-fire coupling with a tapered fiber connected to a tunable laser at telecommunication wavelengths (1425-1545 nm), we demonstrate low-loss (propagation length ∼500 μm) and well-confined (mode width ∼1 μm) LR-DLSPPW mode guiding and determine the propagation and bend loss.

Metal Nanoparticle Ensembles: Tunable Laser Pulses Distinguish Monomer from Dimer Vibrations

Resonant interaction of laser pulses with plasmons is used to identify vibrations associated with isolated spheres and pairs of contacting spheres in a system of gold nanoparticles. The optical pulses generate coherent mechanical oscillations of both monomers and dimers in the 5-150 GHz range, the amplitudes of which exhibit a strong enhancement when the laser central wavelength is tuned to resonate with the corresponding plasmon. Because of the resonant selection in the excitation process, the widths of the acoustic modes are significantly smaller than broadening caused by the spread in radii in the ensemble.

Dispersion of strongly confined channel plasmon polariton modes

We report on experimental (by use of scanning near-field optical microscopy) and theoretical investigations of strongly confined (∼λ/5) channel plasmon polariton (CPP) modes propagating at telecom wavelengths (1425–1630 nm) along V-grooves cut in a gold film. The main CPP characteristics (mode index, width, and propagation length) are determined directly from the experimental near-field images and compared to theoretical results obtained using an analytic description of CPP modes supported by (infinitely deep) V-grooves and finite-element simulations implemented in COMSOL.

Accurate p-mode measurements of the G0V metal-rich CoRoT target HD 52265

The star HD 52265 is a G0V metal-rich exoplanet-host star observed in the seismology field of the CoRoT space telescope from November 2008 to March 2009. The satellite collected 117 days of high-precision photometric data on this star, showing that it presents solar-like oscillations. HD 52265 was also observed in spectroscopy with the Narval spectrograph at the same epoch. We characterise HD 52265 using both spectroscopic and seismic data. The fundamental stellar parameters of HD 52265 were derived with the semi-automatic software VWA, and the projected rotational velocity was estimated by fitting synthetic profiles to isolated lines in the observed spectrum. The parameters of the observed p modes were determined with a maximum-likelihood estimation. We performed a global fit of the oscillation spectrum, over about ten radial orders, for degrees l=0 to 2. We also derived the properties of the granulation, and analysed a signature of the rotation induced by the photospheric magnetic activity. Precise determinations of fundamental parameters have been obtained: Teff = 6100 +- 60 K, log g = 4.35 +- 0.09, [M/H] = 0.19 +- 0.05, as well as vsini = 3.6 +0.3 -1.0 km/s. We have measured a mean rotation period P_rot = 12.3 +- 0.15 days, and find a signature of differential rotation. The frequencies of 31 modes are reported in the range 1500-2550 micro-Hz. The large separation exhibits a clear modulation around the mean value <Dnu> = 98.3 +- 0.1 micro-Hz. Mode widths vary with frequency along an S-shape with a clear local maximum around 1800 micro-Hz. We deduce lifetimes ranging between 0.5 and 3 days for these modes. Finally, we find a maximal bolometric amplitude of about 3.96 +- 0.24 ppm for radial modes.

Theoretical Analysis of Long-Range Dielectric-Loaded Surface Plasmon Polariton Waveguides

A structure for guiding surface plasmon polaritons (SPPs) over millimeter distances with tight mode confinement is presented and analyzed in detail using the finite element method. The proposed long-range plasmonic waveguide consists of a dielectric ridge deposited on a narrow metal stripe supported by a dielectric buffer layer covering a low-index substrate. It is shown that such an asymmetric waveguide structure can be designed to support a long-range symmetric SPP mode, featuring a propagation length of ≈ 3.1 mm and lateral mode width of ≈ 1.6nμ m at telecom wavelengths of ~ 1.55 μm. Our analysis covers a broad spectrum of parameters: ridge dimensions, buffer layer parameters (refractive index and thickness), as well as metal stripe width, considering in detail the underlying mechanisms of SPP waveguiding in this configuration. The suggested configuration offers easy connection to electrodes enabling, e.g., thermo-optic or electro-optic control, and is technologically simple, making fabrication possible using only a few lithography steps. Additionally, a new figure of merit is introduced, which is related to a number of plasmonic components allowed for a given mode confinement and propagation loss, aiming thereby at the evaluation of the application potential of plasmonic waveguides.

Vibration Spectra and Structural Characteristics of Ba[(Zn1-x Mg x )1/3Nb2/3]O3 Solid Solutions

The Ba[(Zn1-x Mg x )1/3Nb2/3]O3 (BZMN, x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0) solid solution ceramics were synthesized by the conventional solid-state reaction method. Vibration spectra (Raman spectroscopy and Fourier transform far-infrared reflection [FTIR] spectroscopy) and X-ray diffraction (XRD) were employed to evaluate the correlation between crystal structures and vibration modes of these solid solutions as a function of Zn2+ ions replaced by Mg2+ ions. Spectroscopic and structural data show sensitivity to the sample structural evolution with Mg2+ concentration, and a 1:2 ordered structure appears for Mg-rich samples where x ≥ 0.6. The Ba[(Zn0.4Mg0.6)1/3Nb2/3]O3 has a 1:2 ordered monoclinic unit cell, which is distorted by the antiphase tilting of the oxygen octahedra. The phonon modes were assigned, and a correlation of phonon vibrations with the microstructure was found. The position and width of the phonon modes were determined and correlated to the ionic radii, mass, and tolerance factors for the different atoms substituted in the B′-site.

Gyrokinetic analysis of tearing instabilities in a collisionless plasma

Using a gyrokinetic description, an analytic investigation of tearing instabilities is carried out for a collisionless tokamak plasma, with particular emphasis on delineating the effects associated with Landau and ∇B resonances. The linear characteristics of Δ′-driven tearing modes are studied by including short wavelength variations across the confining magnetic field and long wavelength variations along the field. For the case when electrons are adiabatic and ions are fluidlike, the dispersion relation is solved analytically for mode widths lying between electron and ion excursion lengths. It is shown that electron Landau damping effect can significantly influence the tearing mode growth rate by making it proportional to (Δ′)1/2 in contrast to earlier kinetic results, which show a linear dependence on Δ′. The growth rate can further slow down when compressional mode coupling effects are taken into account. Likewise, analytic conditions for the growth of the gyrokinetic tearing mode in the presence of electron ∇B resonance effect are obtained for both the Δ′ driven global mode as well as the large Δ′ branch of this instability and expressions for the real frequency and growth rate of the modes are given. Our analytic results, besides providing physical insights into the influence of these ‘resonance’ effects, can also serve as useful benchmark signatures to look for in large scale numerical gyrokinetic simulations.

On the Stability of Oligo(ethylene glycol) (C11EG6OMe) SAMs on Gold: Behavior at Elevated Temperature in Contact with Water

In this study the temperature dependent confor-mation of hexa(ethylene glycol) self-assembling monolayers (SAMs) under aqueous conditions (in situ) is investigated. To this end characteristic absorption modes in the fingerprint region (1050-1500 cm(-1)) were monitored with real-time polarization modulation infrared spectroscopy. We found a temperature induced conformational change from predominantly helical to helical/all-trans. The process may be divided into two temperature regimes. Up to 40 °C the process is reversible after drying the monolayers in air and successive reimmersion in water, indicating a strong binding of the water molecules to the SAM. At higher temperatures, the conformational change is irreversible. Additionally, a rapid change to a larger mode width and a shift of the mode position to higher wavenumbers (blue-shift) at about 50 °C indicates structural changes caused by decreasing crystallinity of the SAM. While the conformational changes up to 40 °C are supposed to originate from an increased conformational freedom in combination with a stronger interaction with water molecules, the irreversibility and rapid change of mode characteristics at higher temperatures indicate chemical degradation. Complementary measurements in air show a fast and virtually complete reversibility up to 40 °C underlining the effect of the interaction of the ethylene glycol moiety with water. At temperatures above 50 °C modes indicating ester and formate groups appear, supporting the idea of chemical degeneration. Moreover, the temperature behavior is coverage dependent. At incomplete coverage the structural order of the SAM starts decreasing at lower temperatures. This study shows, that the conformational and structural change of hexa(ethylene glycol) SAMs at elevated temperature is an interplay of conformational changes of the SAM, its interaction with water and at higher temperatures its chemical degradation. Our experiments also underline the importance of the in situ analysis on the film structure.

Raman micro-spectroscopic analysis of cultured HCT116 colon cancer cells in the presence of roscovitine

Raman micro-spectroscopic analysis of cultured HCT116 colon cancer cells in the presence of roscovitine, [seliciclib, 2-(1-ethyl-2-hydroxy-ethylamino)-6-benzylamino-9-isopropylpurine], a promising drug candidate in cancer therapy, has been performed for the first time. The aim of this study was to investigate modulations in colon cancer cells induced by roscovitine. Raman spectra of the cultured HCT116 colon cancer cells treated with roscovitine at different concentrations (0, 5, 10, 25 and 50 μM) were recorded in the range 400–1850 cm −1. It was shown that the second derivative profile of the experimental spectrum gives valuable information about the wavenumbers and band widths of the vibrational modes of cell components, and it eliminates the appearance of false peaks arising from incorrect baseline corrections. In samples containing roscovitine, significant spectral changes were observed in the intensities of characteristic protein and DNA bands, which indicate roscovitine-induced apoptosis. Roscovitine-induced apoptosis was also assessed by flow cytometry analysis, and analysis of propidium iodide staining. We observed some modifications in amide I and III bands, which arise from alterations in the secondary structure of cell proteins caused by the presence of roscovitine.

PCF-Based Cavity Enhanced Spectroscopic Sensors for Simultaneous Multicomponent Trace Gas Analysis

A multiwavelength, multicomponent CRDS gas sensor operating on the basis of a compact photonic crystal fibre supercontinuum light source has been constructed. It features a simple design encompassing one radiation source, one cavity and one detection unit (a spectrograph with a fitted ICCD camera) that are common for all wavelengths. Multicomponent detection capability of the device is demonstrated by simultaneous measurements of the absorption spectra of molecular oxygen (spin-forbidden b-X branch) and water vapor (polyads 4v, 4v + δ) in ambient atmospheric air. Issues related to multimodal cavity excitation, as well as to obtaining the best signal-to-noise ratio are discussed together with methods for their practical resolution based on operating the cavity in a “quasi continuum” mode and setting long camera gate widths, respectively. A comprehensive review of multiwavelength CRDS techniques is also given.

Temporal Variations of High-Degree Solar p-Modes from GONG and MDI

We study temporal variations in the amplitudes and widths of high-degree acoustic modes in the quiet and active Sun by applying ring-diagram technique to the GONG+ and MDI Dopplergrams during the declining phase of cycle 23. The increase in amplitudes and decrease in line-widths in the declining phase of the solar activity is in agreement with previous studies. A similar solar cycle trend in the mode parameters is also seen in the quiet-Sun regions but with a reduced magnitude. Moreover, the amplitudes obtained from GONG+ data show long-term variations on top of the solar cycle trend.

High frequency power in HMI ring diagrams

Coherent power above the photospheric acoustic cut-off frequency (at v ~ 5.3mHz) is known to exist in solar helioseismic observations. The arrival of high quality velocity data with high temporal and spatial resolution from the Helioseismic & Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO) spacecraft allows the high frequency regime to be explored with greater precision than previously. We analyse mode frequencies, widths, and amplitudes from HMI ring diagrams at high frequencies, and compare them to earlier results.

Analysis of single-mode condition and high-order modes discrimination in photonic crystal VCSEL

A new technique for analyzing the single-mode condition and mode discrimination of high-order modes in photonic crystal VCSEL is proposed and reported in this paper. The technique proposed is a semi-empirical approach that uses analytical analysis based on experimental data. For that purpose, single- and multimode photonic crystal VCSEL devices are fabricated and characterized for comparison of device performance. The mode width for first- and second-order mode of PhC VCSEL is computed for analyzing the mode behavior. In order to verify the findings, the fabricated single- and multimode devices are analyzed using finite difference frequency domain technique for the purpose of showing the loss as a function of mode order for the PhC VCSEL. The results show close agreement between the computed and experiment findings, justifying the use of the proposed semi-empirical technique for analyzing single-mode condition and of high-order modes discrimination in photonic crystal VCSEL.

Recent developments and applications of hybrid surface plasmon resonance interfaces in optical sensing

Nanostructured noble metals exhibit an intense optical near field due to surface plasmon resonance, therefore promising widespread applications and being of interest to a broad spectrum of scientists, ranging from physicists, chemists, and materials scientists to biologists. A wealth of research is available discussing the synthesis, characterization, and application of noble metal nanoparticles in optical sensing. However, with respect to the sensitivity of the frequency and width of these surface plasmon resonance modes to the particle's shape, size, and environment, in nearly every case, success strongly depends on the availability of highly stable, adhesive, and sensitive nanoparticles. This undoubtedly presents a challenging task to nanofabrication. The past decade has witnessed fascinating advances in this field, in particular, the construction of oxide-based hybrid plasmonic interfaces to overcome the problem addressed above by (1) coating the metallic nanostructures with thin overlayers to form sandwiched structures or (2) embedding metallic nanostructures in a dielectric matrix to obtain metal/dielectric matrix nanocomposite films. In this critical review, we focus on recent work related to this field, beginning with a presentation of hybrid films with enhanced structural and optical stability, readily and selectively designed using chemical and physical techniques. We then illustrate their interesting optical properties and demonstrate exciting evidence for the postulated application in surface plasmon sensing fields. Finally, we survey the work remaining to be done for that potential to be realized.

Resonance modes in rare earth doped microcrystals

Alkaline earth sulfide phosphors doped with Eu 2 + or Ce 3 + are good candidates for wavelength conversion in LEDs for general lighting applications. A very broad emission spectrum can be obtained by preparing SrS:Eu–SrS:Ce core–shell particles. These microcrystals are rectangular cuboids and can also be efficiently excited with electrons in a scanning electron microscope. The broad emission spectrum, ranging from 450 nm to 650 nm, consists of the combined emission of Ce 3 + and Eu 2 + centers. Using cathodoluminescence (CL) in a scanning electron microscope, evaluation of the emission characteristics of individual cuboids was possible. Sharp peaks in the CL-spectra of individual particles could be observed and described as being resonance modes. The spectral positions and the line widths of resonance modes in these core–shell microcrystals are predicted by an extension of the plane wave model, taking into account the dispersion of the refractive index and the existence of open orbits.

Demonstration of submicron square-like silicon waveguide using optimized LOCOS process

We demonstrate the design, fabrication and experimental characterization of a submicron-scale silicon waveguide that is fabricated by local oxidation of silicon. The use of local oxidation process allows defining the waveguide geometry and obtaining smooth sidewalls. The process can be tuned to precisely control the shape and the dimensions of the waveguide. The fabricated waveguides are measured using near field scanning optical microscope at 1550 nm wavelength. These measurements show mode width of 0.4 µm and effective refractive index of 2.54. Finally, we demonstrate the low loss characteristics of our waveguide by imaging the light scattering using an infrared camera.

Smoothed local histogram filters

Local image histograms contain a great deal of information useful for applications in computer graphics, computer vision and computational photography. Making use of that information has been challenging because of the expense of computing histogram properties over large neighborhoods. Efficient algorithms exist for some specific computations like the bilateral filter, but not others. Here, we present an efficient and practical method for computing accurate derivatives and integrals of locally-weighted histograms over large neighborhoods. The method allows us to compute the location, height, width and integral of all local histogram modes at interactive rates. Among other things, it enables the first constant-time isotropic median filter, robust isotropic image morphology operators, an efficient "dominant mode" filter and a non-iterative alternative to the mean shift. In addition, we present a method to combat the over-sharpening that is typical of histogram-based edge-preserving smoothing. This post-processing step should make histogram-based filters not only fast and efficient, but also suitable for a variety of new applications.

Raman spectroscopic study of four Spanish shocked ordinary chondrites: Cañellas, Olmedilla de Alarcón, Reliegos and Olivenza

Shock metamorphism in chondritic parent bodies produces typical textures, visible under the microscope, which are a consequence of structural deformation of the crystals. Such deformations can be studied with Raman spectroscopy. The vibrational characteristics of olivines and pyroxenes, structurally deformed by weak-to-moderate shock metamorphism, have been determined on four Spanish ordinary chondrites (Cañellas, Olmedilla de Alarcón, Reliegos and Olivenza). Such deformations would affect, in principle, the band positions and widths of the Raman spectra peaks. The measured band positions and relative intensities are consistent with chemical composition for olivines and pyroxenes, but show little influence on the degree of shock. However, the full spectral band width of the silicate internal modes shows some dependence on the impact grade, which could be attributed to inhomogeneous effects produced by the impacts.

Electromagnetic effects on geodesic acoustic and beta-induced Alfvén eigenmodes

The local kinetic theory of geodesic acoustic modes and beta-induced Alfvén eigenmodes is developed. The local dispersion relations are derived in two opposite limits: and , where k0 = (m − nq)/qR, m and n are poloidal and toroidal mode numbers, and is the electron thermal velocity. It is shown that the nature of the (m ± 1, n) sideband oscillations depends on the radial modes width. The localized modes are mostly electrostatic, while the meso-scale modes of the radial width larger than c/(ωpiq) have a strong electromagnetic component. It is shown that the dispersion relations are remarkably similar provided the radial mode width of the principal (m, n) harmonic is sufficiently small.