Showing papers on "Wavelength published in 2003"
TL;DR: Sonic crystals are fabricated, based on the idea of localized resonant structures, that exhibit spectral gaps with a lattice constant two orders of magnitude smaller than the relevant wavelength that are shown to break the conventional mass-density law of sound transmission.
Abstract: We have fabricated a new type of composite which displays localized sonic resonances at ∼350– 2000 Hz with a microstructure size in the millimeter to centimeter range. Around the resonance frequencies the composite behaves as a material with effective negative elastic constants and as a total wave reflector—a 2 cm slab of this material is shown to break the conventional mass-law of sound transmission by order(s) of magnitude. When the microstructure is periodic, our composites exhibit large elastic wave band gaps at the sonic frequency range, with a lattice constant order(s) of magnitude smaller than the corresponding sonic wavelength in air. Good agreement is obtained between theory and experiment.
859 citations
TL;DR: It is shown that beaming is due to the formation of electromagnetic surface resonances and that the beam direction, width, and wavelength at which it occurs can be selected by tuning geometrical parameters of the structure.
Abstract: We present a theoretical foundation for the beaming of light displayed by a single subwavelength aperture in an appropriately corrugated metal film [H. J. Lezec et al., Science 297, 820 (2002)]. Good agreement is found between calculations and experimental data. We show that beaming is due to the formation of electromagnetic surface resonances and that the beam direction, width, and wavelength at which it occurs can be selected by tuning geometrical parameters of the structure.
604 citations
TL;DR: In this paper, it was shown that there exist composite media that exhibit strong spatial dispersion even in the very large wavelength limit, where the description of this medium by means of a local dispersive uniaxial dielectric tensor is not complete.
Abstract: It is found that there exist composite media that exhibit strong spatial dispersion even in the very large wavelength limit. This follows from the study of lattices of ideally conducting parallel thin wires (wire media). In fact, our analysis reveals that the description of this medium by means of a local dispersive uniaxial dielectric tensor is not complete, leading to unphysical results for the propagation of electromagnetic waves at any frequencies. Since nonlocal constitutive relations have been usually considered in the past as a second-order approximation, meaningful in the short-wavelength limit, the aforementioned result presents a relevant theoretical interest. In addition, since such wire media have been recently used as a constituent of some discrete artificial media (or metamaterials), the reported results open the question of the relevance of the spatial dispersion in the characterization of these artificial media.
583 citations
TL;DR: In this article, a microring resonator with increased resonance slopes is proposed by introducing two partially reflecting elements implemented by waveguide offsets, which can greatly enhance the sensitivity of the sensor.
Abstract: Photonic microresonators have great potential in the application of highly sensitive sensors due to high Q-factor resonances and steep slopes between zero and unity transmission. A microring resonator with increased resonance slopes is proposed by introducing two partially reflecting elements implemented by waveguide offsets. This configuration produces a Fano-resonant line shape and can greatly enhance the sensitivity of the sensor. Polystyrene microring resonators were fabricated by the nanoimprinting technique, and the optical spectra were measured in glucose solutions of different concentrations. The shift in resonant wavelength and variation of the normalized transmitted intensity are linearly related to the concentration of the glucose solution.
490 citations
TL;DR: In this article, the authors present a spectroscopic stellar library, STELIB, which consists of an homogeneous library of 249 stellar spectra in the visible range (3200 to 9500 A), with an intermediate spectral resolution (<3 A) and sampling (1 A).
Abstract: We present STELIB ? , a new spectroscopic stellar library, available at http://webast.ast.obs-mip.fr/stelib. STELIB consists of an homogeneous library of 249 stellar spectra in the visible range (3200 to 9500 A), with an intermediate spectral resolution (<3 A) and sampling (1 A). This library includes stars of various spectral types and luminosity classes, spanning a relatively wide range in metallicity. The spectral resolution, wavelength and spectral type coverage of this library represents a substantial improvement over previous libraries used in population synthesis models. The overall absolute photo- metric uncertainty is 3%.
481 citations
TL;DR: In this article, the authors proposed a method to recover information regarding the background spectrum on wavelength scales much smaller than a pixel by propagating this better-sampled background spectrum through inverses of the distortion and rectification transformations.
Abstract: In two-dimensional spectrographs, the optical distortions in the spatial and dispersion directions produce variations in the sub-pixel sampling of the background spectrum. Using knowledge of the camera distortions and the curvature of the spectral features, one can recover information regarding the background spectrum on wavelength scales much smaller than a pixel. As a result, one can propagate this better-sampled background spectrum through inverses of the distortion and rectification transformations, and accurately model the background spectrum in two-dimensional spectra for which the distortions have not been removed (i.e. the data have not been rebinned/rectified). The procedure, as outlined in this paper, is extremely insensitive to cosmic rays, hot pixels, etc. Because of this insensitivity to discrepant pixels, sky modeling and subtraction need not be performed as one of the later steps in a reduction pipeline. Sky-subtraction can now be performed as one of the earliest tasks, perhaps just after dividing by a flat-field. Because subtraction of the background can be performed without having to ``clean'' cosmic rays, such bad pixel values can be trivially identified after removal of the two-dimensional sky background.
438 citations
TL;DR: In this article, the maximum of the surface plasmon resonance of elongated gold nanoparticles to a wavelength, the position of which is precisely midway between the exciting laser line and the Raman line, was used to optimize the surface-enhanced Raman scattering effect.
Abstract: In this letter, we show that tuning the maximum of the surface plasmon resonance of elongated gold nanoparticles to a wavelength, the position of which is precisely midway between the exciting laser line and the Raman line, results in an optimization of the surface-enhanced Raman-scattering effect.
417 citations
TL;DR: This work reports on spectral broadening of 100-fs pulses in PCFs with anomalously flat CD profiles, showing how, through appropriate choice of CD, nonlinearities can be efficiently harnessed to generate laser light at new wavelengths.
Abstract: Photonic crystal fibres (PCFs) offer greatly enhanced design freedom compared to standard optical fibres. For example, they allow precise control of the chromatic dispersion (CD) profile—the frequency dependence of propagation speed—over a broad wavelength range. This permits studies of nonlinear pulse propagation in previously inaccessible parameter regimes. Here we report on spectral broadening of 100-fs pulses in PCFs with anomalously flat CD profiles. Maps of the spectral and spatio-temporal behaviour as a function of power show that dramatic conversion (to both longer and shorter wavelengths) can occur in remarkably short lengths of fibre, depending on the magnitude and shape of the CD profile. Because the PCFs used are single-mode at all wavelengths, the light always emerges in a fundamental guided mode. Excellent agreement is obtained between the experimental results and numerical solutions of the nonlinear wave equation, indicating that the underlying processes can be reliably modelled. These results show how, through appropriate choice of CD, nonlinearities can be efficiently harnessed to generate laser light at new wavelengths.
383 citations
Abstract: In this letter, a planar left-handed propagating medium consisting of a coplanar waveguide (CPW) inductively coupled to split ring resonators (SRR) and periodically loaded with narrow metallic wires is proposed. The wires make the structure behave as a microwave plasma with a negative effective permittivity which covers a broad frequency range. The negative permeability required to achieve left-handed wave propagation is provided by the rings in the vicinity of their resonant frequency. The result is a structure which allows negative wave propagation in a narrow frequency band. The transmission coefficient measured in a fabricated prototype device exhibits very low insertion losses in the pass band and high-frequency selectivity. Since rings are much smaller than signal wavelength at resonance and can be easily tuned, SRR-CPW-based structures are of interest for the design of very compact microwave circuits based on left handedness.
375 citations
TL;DR: In this article, the authors presented an analytical model for support loss in clamped-free (C-F) and clampedclamped (C -C) micromachined beam resonators with in-plane flexural vibrations.
Abstract: This paper presents an analytical model for support loss in clamped–free (C–F) and clamped–clamped (C–C) micromachined beam resonators with in-plane flexural vibrations. In this model, the flexural vibration of a beam resonator is described using the beam theory. An elastic wave excited by the shear stress of the beam resonator and propagating in the support structure is described through the 2D elastic wave theory, with the assumption that the beam thickness (h) is much smaller than the transverse elastic wavelength (λT). Through the combination of these two theories and the Fourier transform, closed-form expressions for support loss in C–F and C–C beam resonators are obtained. Specifically, closed-form expression for the support loss in a C–C beam resonator is derived for the first time. The model suggests lower support quality factor (Qsupport) for higher order resonant modes compared to the fundamental mode of a beam resonator. Through comparison with experimental data, the validity of the presented analytical model is demonstrated. © 2003 Elsevier B.V. All rights reserved.
374 citations
TL;DR: It is demonstrated that an optical resonance (whispering gallery mode) excited in a micron-sized silica sphere can be used to detect and measure nucleic acids and each microsphere can be identified by its unique resonance wavelength.
TL;DR: In this article, the authors measured the refractive index of GaAs in the wavelength range from 0.97 to 17 μm, which covers nearly the entire transmission range of the material.
Abstract: The refractive index of GaAs has been measured in the wavelength range from 0.97 to 17 μm, which covers nearly the entire transmission range of the material. Linear and quadratic temperature coefficients of the refractive index have been fitted to data measured between room temperature and 95 °C. In the midinfrared, the refractive index and temperature dependence are obtained from analysis of etalon fringes measured by Fourier-transform spectroscopy in undoped GaAs wafers. In the near infrared, the refractive index is deduced from the quasiphasematching (QPM) wavelengths of second-harmonic generation in orientation-patterned GaAs crystals. Two alternative empirical expressions are fitted to the data to give the refractive index as a function of wavelength and temperature. These dispersion relations agree with observed QPM conditions for midinfrared difference-frequency generation and second-harmonic generation. Predictions for various nonlinear optical interactions are presented, including tuning curves f...
TL;DR: Photonic crystals (PCs) are optical materials of periodic refractive index, designed to block light of certain wavelengths, and artificial defects can be introduced into PCs to allow light to be manipulated.
Abstract: Photonic crystals (PCs) are optical materials of periodic refractive index, designed to block light of certain wavelengths ( [1][1] – [5][2] ). Artificial defects such as line- and/or point-defects can be introduced into PCs to allow light to be manipulated. Ultrasmall photonic devices, with sizes
TL;DR: The results show that laser pulse duration need not limit the time resolution of a spectroscopic measurement, provided the process studied involves the formation of correlated wave packets, one of which can be controlled; spatial resolution is likewise not limited to the focal spot size or laser wavelength.
Abstract: Spectroscopic measurements with increasingly higher time resolution are generally thought to require increasingly shorter laser pulses, as illustrated by the recent monitoring of the decay of core-excited krypton1 using attosecond photon pulses2,3. However, an alternative approach to probing ultrafast dynamic processes might be provided by entanglement, which has improved the precision4,5 of quantum optical measurements. Here we use this approach to observe the motion of a D2+ vibrational wave packet formed during the multiphoton ionization of D2 over several femtoseconds with a precision of about 200 attoseconds and 0.05 angstroms, by exploiting the correlation between the electronic and nuclear wave packets formed during the ionization event. An intense infrared laser field drives the electron wave packet, and electron recollision6,7,8,9,10,11 probes the nuclear motion. Our results show that laser pulse duration need not limit the time resolution of a spectroscopic measurement, provided the process studied involves the formation of correlated wave packets, one of which can be controlled; spatial resolution is likewise not limited to the focal spot size or laser wavelength.
TL;DR: In this article, a simplified version of the National Center for Atmospheric Research (NCAR) Tropospheric Ultraviolet-Visible (TUV) model was developed and coupled into the NCAR/Atmospheric Chemistry Division global transport chemical model (Model for Ozone and Related Chemical Tracers (MOZART-2)).
Abstract: [1] Cloud layers in the troposphere influence photolysis rates (J values) and hence concentrations of chemical species. In order to study the impact of clouds on photolysis rates and oxidants, we have developed a simplified version of the National Center for Atmospheric Research (NCAR) Tropospheric Ultraviolet-Visible (TUV) model and have coupled the simplified TUV (otherwise known as the fast TUV (FTUV)) into the NCAR/Atmospheric Chemistry Division global transport chemical model (Model for Ozone and Related Chemical Tracers (MOZART-2)). The FTUV model has the same physical processes as the TUV model, except that the wavelength bins between 121 and 750 nm are reduced from 140 to 17. As a result, FTUV is about 8 times faster than the original TUV. Differences in the calculated photolysis rates between TUV and FTUV are generally less than 5% in the troposphere. Subgrid vertical distributions of clouds are also considered in the calculation of photolysis rates in MOZART-2. The method used in this study is a mixed maximum and random overlap scheme. The subgrid method increases the computation time for photolysis rates by a factor of 3 compared to a simple method in which clouds are uniformly distributed over the MOZART-2 grids. Our calculation shows that the uniform cloud distribution method tends to significantly overestimate back scattering on the top of clouds and overestimates the impact on photochemistry in the troposphere. The results suggest that clouds have important impacts on tropospheric chemistry. Global mean OH concentration increases by about 20% due to the impact of clouds. As a result, the calculated CH4 lifetime changes to 11 years for clear sky and 9 years for cloudy sky. The latter value is closer to the methane lifetime estimated from previous studies. Calculated CO surface concentrations are compared with observed values, showing an improvement when the impact of clouds on the photolysis rates is taken into account. Clouds also have important impacts on tropospheric ozone budget. Our calculation suggest that because of clouds, the globally averaged photolysis rates of J[O3], J[CH2O], and J[NO2] are enhanced in the troposphere by about 12, 13, and 13%, respectively, leading to an 8% increase in the tropospheric O3 concentrations. Our study suggests that clouds strongly influence photolysis rates and hence play an important role in controlling the concentrations of the tropospheric oxidants. Such effects should be carefully considered and included in regional and global chemical transport models.
TL;DR: In this article, a physical model that takes into account not only the Bragg mechanism, but also the non-Bragg scattering mechanism associated with wave breaking was developed to explain the background behavior of the NRCS and the wave radar Modulation Transfer Function (MTF) at HH and VV polarization.
Abstract: [1] Multiscale composite models based on the Bragg theory are widely used to study the normalized radar cross-section (NRCS) over the sea surface. However, these models are not able to correctly reproduce the NRCS in all configurations and wind wave conditions. We have developed a physical model that takes into account, not only the Bragg mechanism, but also the non-Bragg scattering mechanism associated with wave breaking. A single model was built to explain on the same physical basis both the background behavior of the NRCS and the wave radar Modulation Transfer Function (MTF) at HH and VV polarization. The NRCS is assumed to be the sum of a Bragg part (two-scale model) and of a non-Bragg part. The description of the sea surface is based on the short wind wave spectrum (wavelength from few millimeters to few meters) developed by Kudryavtsev et al. [1999] and wave breaking statistics proposed by Phillips [1985]. We assume that non-Bragg scattering is supported by quasi-specular reflection from very rough wave breaking patterns and that the overall contribution is proportional to the white cap coverage of the surface. A comparison of the model NRCS with observations is presented. We show that neither pure Bragg nor composite Bragg model is able to reproduce observed feature of the sea surface NRCS in a wide range of radar frequencies, wind speeds, and incidence and azimuth angles. The introduction of the non-Bragg part in the model gives an improved agreement with observations. In Part 2, we extend the model to the wave radar MTF problem.
TL;DR: In this article, the authors developed an action spectrum for growth responses of light-grown oat (Avena sativa L. cv. Otana) seedlings exposed to narrowband UV radiation from a large double water-prism monochromator.
Abstract: Biological spectral weighting functions (BSWF) play a key role in assessing implications of stratospheric ozone reduction. They are used to calculate the increase in biologically effective solar UV radiation due to ozone reduction (radiation amplification factor, RAF), assess current latitudinal gradients of solar UV radiation, and compare solar UV radiation with that from lamps and filters used in experiments. As a basis for a BSWF, we developed an action spectrum for growth responses of light-grown oat (Avena sativa L. cv. Otana) seedlings exposed to narrowband UV radiation from a large double water-prism monochromator. Five UV wavelength peaks were used (275, 297, 302, 313 and 366 nm) in the absence of any visible radiation. Growth responses were measured from 1 to 10 days after the treatments. At all these wavelengths, the UV radiation inhibited height growth, including the height at which the first leaf separated from the stem. Radiation at all wavelengths used, except the one UV-A wavelength, promoted the length of the second leaf. The resulting action spectrum closely resembles the commonly used generalized plant response function except that it indicates continued sensitivity into the UV-A region. When used as a BSWF for the ozone depletion problem, this new function for plant growth would suggest substantially less impact of ozone depletion because it results in only a modest increment of biologically effective UV for a given level of ozone depletion (a lower RAF). Yet this new BSWF also suggests that experimental treatments based on previous BSWF with less emphasis on the UV-A may have resulted in simulations of less pronounced ozone depletion than intended. The validity of this new BSWF with UV-A sensitivity, designated the UV plant growth weighting function, was verified in field experiments as described in the companion paper.
Patent•
02 Jun 2003
TL;DR: A linear metamaterial comprises a transmission line, having a linear dimension, and is loaded with capacitors, and shunted with an inductor such that for an electromagnetic wave having a wavelength greater than the linear dimension and traveling along the axis of the transmission line is simultaneously negative as mentioned in this paper.
Abstract: A linear metamaterial comprises a transmission line, having a linear dimension, and is loaded with capacitors, and shunted with an inductor such that for an electromagnetic wave, having a wavelength greater than the linear dimension and traveling along the axis of the transmission line, the effective permeability and permittivity of the metamaterial are simultaneously negative. Applications for the metameterial are also disclosed.
TL;DR: In this article, a transverse resonance model of the effective medium material model is used to obtain a simple picture of the design space available when the desired operating frequency is fixed, and it is shown that Sievenpiper high-impedance surfaces exist that can suppress TE surface waves alone, or both TE and TM surface waves at the same time, when the distance between the vias in the via array is as close as possible to /spl lambda//2.
Abstract: The Sievenpiper high-impedance surface is a periodic structure characterized by a substrate filled with an array of vertical vias, capped by a capacitive frequency selective surface (FSS). It functions as the ideal antenna groundplane for wireless applications because it simultaneously enhances the gain of the antenna as it suppresses the surface waves associated with it (thus reducing the undesired back-lobe and the reactive coupling to nearby circuits). These two properties are known to occur approximately over the frequency bandwidth where the phase of the reflection coefficient of the surface changes from +90/spl deg/ to -90/spl deg/. Since this behavior takes place at frequencies where the unit cell of the structure is small compared to the wavelength, it can be modeled in terms of a layered homogeneous material where each layer has an anisotropic magneto-dielectric tensor. These tensors, readily derived using an effective medium model, can be designed to obtain independent control of the bandwidths of gain increase and surface wave suppression. Based on a transverse resonance model of the effective medium material model, it is shown that Sievenpiper high-impedance surfaces exist that can suppress TE surface waves alone or TM surface waves alone, or both TE and TM surface waves at the same time. Maximum TM surface wave suppression bandwidth is obtained when the distance between the vias in the via array is as close as possible to /spl lambda//2. Maximum TE bandwidth is obtained when the conductors of the capacitive FSS offer maximum blockage to the normal magnetic field of the wave. A reduction of the transverse resonance solution to nearly closed form is used to obtain a simple picture of the design space available when the desired operating frequency is fixed.
TL;DR: Investigations showed that it was possible to eliminate the influence of depth dependent dispersion by water in tissue by choosing a light source with a center wavelength near 1.0 microm.
Abstract: The influence of depth dependent dispersion by the main component of biological tissues, water, on the resolution of OCT was studied. Investigations showed that it was possible to eliminate the influence of depth dependent dispersion by water in tissue by choosing a light source with a center wavelength near 1.0 microm. Ultrahigh resolution ophthalmic imaging was performed at this wavelength range with a microstructure fiber light source.
TL;DR: In this paper, the effects of surface gravity waves on pore-water release from permeable sediment (k = 1.3-1.8 × 10-11 m 2 ) in shallow water were studied in a wave tank and tracer experiments demonstrated that shallow-water waves can increase fluid exchange between sandy sediment and overlying water 50-fold relative to the exchange by molecular diffusion.
Abstract: The effects of surface gravity waves on pore-water release from permeable sediment (k = 1.3-1.8 × 10 -11 m 2 ) in shallow water were studied in a wave tank Our tracer experiments demonstrated that shallow-water waves can increase fluid exchange between sandy sediment and overlying water 50-fold, relative to the exchange by molecular diffusion. The main driving force for this increased exchange are the pressure gradients generated by the interaction of oscillating boundary flows and sediment wave ripples. These gradients produce a pore-water flow field, with a regular pattern of intrusion and release zones, that migrates with ripple propagation. The ensuing topography-related filtering rates in the wave tank ranged from 60 to 590 L m -2 d -1 and exceeded the solute exchange rates caused by hydrostatic wave pumping (38 L m -2 d -1 ) and initial molecular diffusion (corresponding to 10-12 L m -2 d -1 ). Wave-induced filtration is ecologically relevant because permeable sandy sediments are very abundant on the continental margins and can be converted into effective filter systems, which suggests that these sediments are sites for rapid mineralization and recycling. We propose that the wave influenced continental shelf may be subdivided into two zones; a shallow zone (water depth < wavelength/2), where wave orbital motion at the sea floor creates ripples and causes topography related advective filtering; and a deeper zone (wavelength/2 < water depth < wavelength), where wave pumping enhances interfacial exchange by hydrostatic pressure oscillations.
Journal Article•
TL;DR: In this paper, a physical model that takes into account not only the Bragg mechanism, but also the non-Bragg scattering mechanism associated with wave breaking was developed to explain the background behavior of the NRCS and the wave radar Modulation Transfer Function (MTF) at HH and VV polarization.
Abstract: [1] Multiscale composite models based on the Bragg theory are widely used to study the normalized radar cross-section (NRCS) over the sea surface. However, these models are not able to correctly reproduce the NRCS in all configurations and wind wave conditions. We have developed a physical model that takes into account, not only the Bragg mechanism, but also the non-Bragg scattering mechanism associated with wave breaking. A single model was built to explain on the same physical basis both the background behavior of the NRCS and the wave radar Modulation Transfer Function (MTF) at HH and VV polarization. The NRCS is assumed to be the sum of a Bragg part (two-scale model) and of a non-Bragg part. The description of the sea surface is based on the short wind wave spectrum (wavelength from few millimeters to few meters) developed by Kudryavtsev et al. [1999] and wave breaking statistics proposed by Phillips [1985]. We assume that non-Bragg scattering is supported by quasi-specular reflection from very rough wave breaking patterns and that the overall contribution is proportional to the white cap coverage of the surface. A comparison of the model NRCS with observations is presented. We show that neither pure Bragg nor composite Bragg model is able to reproduce observed feature of the sea surface NRCS in a wide range of radar frequencies, wind speeds, and incidence and azimuth angles. The introduction of the non-Bragg part in the model gives an improved agreement with observations. In Part 2, we extend the model to the wave radar MTF problem.
TL;DR: The spectrum of the body-centered cubic phase shows an instability at zero temperature over a broad region of the wave vectors, indicating that this phase is highly anharmonic and can be stabilized at high temperatures by its phonon entropy.
Abstract: We constructed computer-based simulations of the lattice dynamical properties of plutonium using an electronic structure method, which incorporates correlation effects among the f-shell electrons and calculates phonon spectra at arbitrary wavelengths. Our predicted spectrum for the face-centered cubic δ phase agrees well with experiments in the elastic limit and explains unusually large shear anisotropy of this material. The spectrum of the body-centered cubic phase shows an instability at zero temperature over a broad region of the wave vectors, indicating that this phase is highly anharmonic and can be stabilized at high temperatures by its phonon entropy.
TL;DR: In this article, the authors proposed that the body force that accompanies wave breaking is potentially an important linear mechanism for generating secondary waves that propagate into the mesosphere and lower thermosphere, which can explain some of the mean wind and secondary wave features generated from wave breaking in a 2D nonlinear model study.
Abstract: The authors propose that the body force that accompanies wave breaking is potentially an important linear mechanism for generating secondary waves that propagate into the mesosphere and lower thermosphere. While the focus of this paper is on 3D forcings, it is shown that this generating mechanism can explain some of the mean wind and secondary wave features generated from wave breaking in a 2D nonlinear model study. Deep 3D body forces, which generate secondary waves very efficiently, create high-frequency waves with large vertical wavelengths that possess large momentum fluxes. The efficiency of this forcing is independent of latitude. However, the spatial and temporal variability/intermittency of a body force is important in determining the properties and associated momentum fluxes of the secondary waves. High spatial and temporal variability accompanying a wave breaking process leads to large secondary wave momentum fluxes. If a body force varies slowly with time, negligible secondary wave fluxes result. Spatial variability is important because distributing ‘‘averaged’’ body forces over larger regions horizontally (as is often necessary in GCM models) results in waves with smaller frequencies, larger horizontal wavelengths, and smaller associated momentum fluxes than would otherwise result. Because some of the secondary waves emitted from localized body force regions have large vertical wavelengths and large intrinsic phase speeds, the authors anticipate that secondary wave radiation from wave breaking in the mesosphere may play a significant role in the momentum budget well into the thermosphere.
13 Oct 2003
TL;DR: In this article, a simple approximation of water refractive index in dependence on temperature and wavelength in the spectral range from 200 to 1000 nm is presented, which is important for different applications in biomedical optics and optics of tissues.
Abstract: Water is the most important biological liquid. On the basis of literature data we present a simple approximation of water refractive index in dependence on temperature and wavelength in the spectral range from 200 to 1000 nm. The approximation is important for different applications in biomedical optics and optics of tissues.
Patent•
24 Jul 2003TL;DR: In this article, a method and apparatus for non-invasively determining the blood oxygen saturation level within a subject's tissue is provided that utilizes a near infrared spectrophotometric (NIBS) sensor capable of transmitting a light signal into the tissue of a subject and sensing the light signal once it has passed through the tissue via transmittance or reflectance.
Abstract: A method and apparatus for non-invasively determining the blood oxygen saturation level within a subject's tissue is provided that utilizes a near infrared spectrophotometric (NIBS) sensor capable of transmitting a light signal into the tissue of a subject and sensing the light signal once it has passed through the tissue via transmittance or reflectance. The method includes the steps of: (1) transmitting a light signal into the subject's tissue, wherein the transmitted light signal includes a first wavelength, a second wavelength, and a third wavelength; (2) sensing a first intensity and a second intensity of the light signal, along the first, second, and third wavelengths after the light signal travels through the subject at a first and second predetermined distance; (3) determining an attenuation of the light signal for each of the first, second, and third wavelengths using the sensed first intensity and sensed second intensity of the first, second, and third wavelengths; (4) determining a difference in attenuation of the light signal between the first wavelength and the second wavelength, and between the first wavelength and the third wavelength; and (5) determining the blood oxygen saturation level within the subject's tissue using the difference in attenuation between the first wavelength and the second wavelength, and the difference in attenuation between the first wavelength and the third wavelength.
TL;DR: By fixing charged colloidal crystals in a poly(acrylamide) hydrogel matrix, this paper fabricated photonic crystals whose diffraction peak wavelengths were tunable by applying mechanical stress.
Abstract: By fixing charged colloidal crystals in a poly(acrylamide) hydrogel matrix, we fabricated photonic crystals whose diffraction peak wavelengths were tunable by applying mechanical stress. The reflection spectrum for a single crystal grain was measured by applying microspectroscopy under compression. The photonic band gap wavelength shifted linearly and reversibly over almost the entire visible light wavelength region (460−810 nm).
TL;DR: A number of spectroscopic techniques have been used to study the properties of natural and synthetic (pure and doped) zircon (ZrSiO4) as mentioned in this paper.
Abstract: Natural and synthetic (pure and doped) zircon (ZrSiO4) have been studied with a variety of spectroscopic techniques. These techniques are based on different physical phenomena, for instance transitions between spin states of nuclei and electrons, energetic transitions of valence electrons, intra-molecular vibrations, or vibrations of atoms and molecular units in the lattice. All of the diverse spectroscopic techniques, however, have in common that they probe energy differences between a ground and excited states, mostly upon interaction of the mineral with incident radiation. Such interactions are not only determined by the excited elementary particles or molecules themselves but depend greatly on their local environments (i.e. number, type, valence and geometrical arrangement of neighboring atoms). Spectroscopic techniques are thus sensitive to the local structure and provide information on the short-range order.
Most research on zircon crystals using spectroscopic techniques was done to study their “real structures,” that is the characterization of deviations from “perfect” zircon. Such features include the incorporation of non-formula elements, structural defects and the presence of inclusions and other impurities. Correspondingly, most of the spectroscopic investigations can be assigned to two major groups. The first group represents studies done to characterize the structural position and local environment of non-formula elements when incorporated in the zircon lattice, and accompanying effects on physical properties. The second group comprises studies subjected to the real structures of “metamict” zircon samples, i.e., changes of the zircon structure caused by the impact of self-irradiation and upon recovery from radiation damage (Ewing et al., this volume).
It is most obvious that a spectroscopic bulk or point analysis will first of all yield a spectrum (i.e. a plot of the intensity of the respective physical parameter versus wavelength, frequency or wavenumber), and this is what is used in most studies. In addition, image generation based on …
TL;DR: An analytic solution is derived for acoustic streaming generated by a standing wave in a viscous fluid that occupies a two-dimensional channel of arbitrary width with main restriction that the boundary layer thickness is a small fraction of the acoustic wavelength.
Abstract: An analytic solution is derived for acoustic streaming generated by a standing wave in a viscous fluid that occupies a two-dimensional channel of arbitrary width. The main restriction is that the boundary layer thickness is a small fraction of the acoustic wavelength. Both the outer, Rayleigh streaming vortices and the inner, boundary layer vortices are accurately described. For wide channels and outside the boundary layer, the solution is in agreement with results obtained by others for Rayleigh streaming. As channel width is reduced, the inner vortices increase in size relative to the Rayleigh vortices. For channel widths less than about 10 times the boundary layer thickness, the Rayleigh vortices disappear and only the inner vortices exist. The obtained solution is compared with those derived by Rayleigh, Westervelt, Nyborg, and Zarembo.
TL;DR: In this paper, a theory for surface optical (SO) phonons in cylindrical wires is presented, and the SO mode dispersion ω(q) and the experimental peak frequency are then used to predict the wavelength of the dominant Fourier component of the surface potential responsible for activating SO mode.
Abstract: Raman scattering studies of crystalline GaP nanowires reveal a strong additional peak in the first order spectrum that can be clearly assigned to surface optical (SO) phonons. The frequency of this SO peak is found to be sensitive to the dielectric constant of the surrounding medium in which the nanowire is embedded. A theory for the SO phonons in cylindrical wires is presented, the SO mode dispersion ω(q) and the experimental peak frequency are then used to predict the wavelength of the dominant Fourier component of the surface potential responsible for activating the SO mode. Interestingly, this SO phonon wavelength is found to agree with the wavelength of diameter modulation observed for some nanowires.