Equivalent Velocities Research Articles

1D System identification of a 54‐story steel frame building by seismic interferometry

SUMMARYA 54‐story steel, perimeter‐frame building in downtown Los Angeles, California, is identified by a wave method using records of the Northridge earthquake of 1994 (ML = 6.4, R = 32 km). The building is represented as a layered shear beam and a torsional shaft, characterized by the corresponding velocities of vertically propagating waves through the structure. The previously introduced waveform inversion algorithm is applied, which fits in the least squares sense pulses in low‐pass filtered impulse response functions computed at different stories. This paper demonstrates that layered shear beam and torsional shaft models are valid for this building, within bands that include the first five modes of vibration for each of the North–South (NS), East–West (EW), and torsional responses (0–1.7 Hz for NS and EW, and 0–3.5 Hz for the torsional response). The observed pulse travel time from ground floor to penthouse level is τ ≈1.5 s for NS and EW and τ ≈ 0.9 s for the torsional responses. The identified equivalent uniform shear beam wave velocities are βeq ≈ 140 m/s for NS and EW responses, and 260 m/s for torsion, and the apparent Q ≈ 25 for the NS and torsional, and ≈14 for the EW response. Across the layers, the wave velocity varied 90–170 m/s for the NS, 80–180 m/s for the EW, and 170–350 m/s for the torsional responses. The identification method is intended for use in structural health monitoring. Copyright © 2013 John Wiley & Sons, Ltd.

Fly Ash Deposition during Oxy-fuel Combustion in a Bench-Scale Fluidized-Bed Combustor

Ash deposition on heat-exchanger surfaces in boiler systems can cause numerous problems, including slagging, fouling, and corrosion. These deleterious processes can be compounded if the boiler combustion process is changed from air to oxy-fuel. In this paper, fly ash deposition characteristics under both air and oxy-fuel combustion conditions were investigated using a bench-scale fluidized-bed combustor (FBC) based on measurements of ash deposition rates via a temperature-controlled probe. Three different combustion atmospheres were studied, and results demonstrated that, under similar combustion temperature profiles and equivalent fluidization velocities, the deposition rate increased when transitioning from combustion atmospheres consisting of 21% O2/79% CO2 to air to 30% O2/70% CO2. To determine the primary factors associated with the observed variations in deposition rates, the chemical compositions and micromorphologies of ash and fly ash deposits were analyzed by inductively coupled plasma–atomic emission spectrometry (ICP–AES) and scanning electron microscopy (SEM). Particulate matter with aerodynamic diameters less than 10 μm (PM10) was measured by an electrical low-pressure impactor (ELPI), and the particle size distributions (PSDs) and carbon contents of the collected filter ash were also ascertained. The results indicate that the higher deposition propensity associated with a 30% O2/70% CO2 atmosphere can be largely attributed to a wider PSD rather than any changes in the chemical compositions of the fly ash or deposited ash, in which there are no obvious differences between air and oxy-fuel combustion. In addition, the slightly higher concentration of fine particles produced under this atmosphere also promotes the deposition of fly ash.

Measuring Seismometer Nonlinearity on a Shake Table

Abstract We have measured the nonlinear distortion in six broadband seismometers on the vertical shake table at the Institute of Geophysics and Planetary Physics La Jolla: a vertical STS1, three STS2s, a CMG‐3T, and a Trillium 240. In each case, low‐frequency intermodulation of a two‐tone signal was observed for six frequency pairs near 0.25, 0.5, 1, 2, 4, and 8 Hz at a beat frequency of 0.02 Hz. The peak velocity amplitude was 6.3 mm/s, which is about half of the operating range of an STS2 or CMG‐3T. We found similar distortion levels in all seismometers: The average over all distortion ratios is −96 dB ±7 dB (standard deviation) in terms of equivalent ground acceleration, with a tendency to higher distortion at higher frequencies. When the same signals are expressed as electric output voltages or equivalent ground velocities, ratios are much higher and increase rapidly with frequency: around −65 dB at 1 Hz and around −40 dB at 8 Hz. The distortion of seismic signals cannot be predicted from the distortion of electrical signals fed into the calibration coil, and the electrical distortion is about 30 dB lower in one of the STS2s. Low‐frequency distortion of the table motion has a level of −140 dB at 1 Hz in terms of acceleration, which is far below that of all seismometers. This number does not indicate a super‐linear table motion but results from expressing the distortion present in the table displacement at −72 dB as a ratio of accelerations. What may seem to be a trivial conversion has a very practical implication: The linearity of seismometers can be tested on moderately performing shake tables.

Time-dependent spectral-feature variations of stars displaying the B[e] phenomenon

Context. B[e] stars are anomalous objects around which extended circumstellar matter is present. The observed properties of the central star are significantly affected by the surrounding material. Therefore, the use of standard synthetic spectra is disputable in this case and our capability to study these objects is limited. One of the possibilities is to analyse variations of the spectral features. Long-term spectroscopic observations are required for this, but are not found in the literature. For our study we choose the B[e] star HD 50138 of the FS CMa type because of the indication that this star is a post-main-sequence star, although still not highly evolved. Therefore, it can be a good object for testing evolutionary models. Currently, HD 50138 is the most extensively observed FS CMa star which makes it an ideal object for modelling. Our observations fill the gap in the available data.Aims. To describe the variability of HD 50138 we have monitored this star spectroscopically over the last twenty years. To search for the periodicity on short-term scales, series of night-to-night observations were also obtained. We were able to obtain 130 spectra from four different telescopes – 1.06 m at Ritter Observatory (echelle, R ~ 26 000, 32 spectra, 1994-2003), the Perek 2 m telescope at Ondrejov Observatory (slit, R ~ 12 500, 56 spectra, 2004-2013), the 2.12 m telescope at Observatorio Astronomico Nacional San Pedro Martir (echelle, R ~ 18 000, 16 spectra, 2005-2013), and the 0.81 m telescope at Three College Observatory (echelle, R ~ 12 000, 26 spectra, 2013-2014).Methods. We describe and analyse variations of the chosen lines. The measurements of the equivalent widths and radial velocities of the Ha, Hs, and [O?i] ?? 6300, 6364 A lines are presented. The set of obtained spectra allows us to describe the changes on timescales from days to years.Results. The long-term quasi-periodic trend was found in the variations of the Ha equivalent width and confirmed by time dependent studies of the relative flux and equivalent width of the [O?i] 6300 A line and radial velocity of the Ha violet peak. The two long periods of 3000 ± 500and 5000 ± 1000 days were detected there. We were able to catch moving humps in the Ha line, which reveal the rotating media around the star. An analysis of the correlation of equivalent widths, radial velocities, relative fluxes, and V/R ratios for various lines is presented in detail.Conclusions. We describe the spectral variability of HD 50138 over the last twenty years. Based on these data, we determine new restrictions for future modelling. We confirm the quasi-periodic behaviour of the object’s spectral variability, which probably reflects mass transfer in a binary system. This behaviour also supports a recently introduced explanation of the nature of FS CMa stars as post-merger systems.

THE MOST METAL-POOR STARS. I. DISCOVERY, DATA, AND ATMOSPHERIC PARAMETERS

We report the discovery of 34 stars in the Hamburg/ESO Survey for metal-poor stars and the Sloan Digital Sky Survey that have [Fe/H] < -3.0. Their median and minimum abundances are [Fe/H] = -3.1 and -4.1, respectively, while 10 stars have [Fe/H] < -3.5. High-resolution, high-S/N spectroscopic data - equivalent widths and radial velocities - are presented for these stars, together with an additional four objects previously reported or currently being investigated elsewhere. We have determined the atmospheric parameters, effective temperature (Teff) and surface gravity (logg), which are critical in the determination of the chemical abundances and the evolutionary status of these stars. Three techniques were used to derive these parameters. Spectrophotometric fits to model atmosphere fluxes were used to derive Teff, logg, and an estimate of E(B-V); Halpha, Hbeta, and Hgamma profile fitting to model atmosphere results provided the second determination of Teff and logg; and finally, we used an empirical Teff-calibrated Hdelta index, for the third, independent Teff determination. The three values of Teff are in good agreement, although the profile fitting may yield systematically cooler Teff values, by ~100K. This collective data set will be analyzed in future papers in the present series to utilize the most metal-poor stars as probes of conditions in the early Universe.

Spectral and photometric studies of the Wolf-Rayet star WR 134 = HD 191765

The results of spectral and photometric observations of the Wolf-Rayet star WR 134 = HD 191765 performed at the N. Tusi Shamakha Astrophysical Observatory (ShAO) of the National Academy of Sciences of Azerbaijan in 2006–2010 are presented. The spectral observations were carried out at the ShAO Zeiss-2000 telescope with an echelle spectrometer. Thirty-four echelle spectrograms of WR 134 were obtained. Profiles of the five strongest emission lines were analyzed: HeII 4859, HeII 5411, CIV 5808, HeI 5875, and (HeII+Hα) 6560. Various parameters of these emission lines are determined: their equivalent widths, radial velocities, central intensities, and half-widths. Only the radial velocity was found to be variable. Variability of the shapes of all emission-line profiles was found, but the largest changes are observed for the (HeII+Hα) 6560 emission band. Photometric observations were carried out at the ShAO Zeiss-600 telescope using an Alta U-47 CCD array (1024 × 1024 pixels) in the V filter of the photometric UBV system. Photometric observations were carried out on 18 nights, with from 100 to 300 measurements made during each night. The mean V magnitudes of WR 134 and a control star were determined for each night. Variability of WR 134 was detected, both within a night and during the entire observation period. The exposure time varied from 1 to 6 s on different nights. A statistical analysis of the mean magnitudes indicated that this series contains a peak at a frequency of ν = 0.530 day−1, corresponding to the period P = 1.887d. This period is interpreted as the manifestation binarity for this star. It is suggested that the secondary component of the system may be a low-mass optical K-M star.

Time-dependent spectral-feature variations of stars displaying the B[e] phenomenon

We present results of nearly six years of spectroscopic observations of the B[e] star V2028 Cyg. The presence of the cold-type absorption lines combined with a hot-type spectrum indicate the binarity of this object. Since B[e] stars are embedded in an extended envelope, the usage of common stellar atmosphere models for the analysis is quite inappropriate. Therefore, we focus on the analysis of the long-term spectral line variations in order to determine the nature of this object. We present the time dependences of the equivalent width and radial velocities of the H alpha line, [O I] 6300 A, Fe II 6427, 6433, and 6456 A lines. The bisector variations and line intensities are shown for the H alpha line. The radial velocities are also measured for the absorption lines of the K component. No periodic variation is found. The observed data show correlations between the measured quantities, which can be used in future modelling.

Large-area manipulation of microdroplets by holographic optical tweezers based on a hybrid diffractive system

We report on large-area manipulation of microdroplets by holographic optical tweezers based on a hybrid diffractive system, in which a static computer-generated hologram and a spatial light modulator (SLM) are used. The hybrid diffractive system is useful to manipulate microdroplets on distant areas with the same manner. Experimental results demonstrated that microdroplets were transported successfully in parallel with approximately equivalent velocities over the entire manipulation area. Fusion of microdroplets was also achieved at a position where the optical pattern generated by the SLM alone did not reach.

The Wolf–Rayet star HD 192163 as a possible evolutionary progenitor of a low-mass X-ray binary

We have used 46 high-resolution echelle spectra of the Wolf-Rayet star HD 192163 taken in 2005–2009 at the Cassegrain focus of the 2-m Zeiss-2000 telescope of the Shamakha Astrophysical Observatory to study profiles of the five strongest emission lines (HeII 4859, HeII 5411, CIV 5808, HeI 5875, (HeII + Hα) 6560). We also obtained four echelle spectrograms of the Wolf-Rayet star HD 191765 for a comparative study of the NaI 5890 (D2) and NaI 5896 (D1) interstellar absorption lines. The echelle spectrograms were reduced using the DECH20 code. We determined the equivalent widths, radial velocities, central intensities, and half-widths of the emission lines. We detected variations in the violetwing of the (HeII + Hα) 6560 emission band (between λ ∼ 6496 A and λ ∼ 6532 A). Our statistical analysis of the radial velocities available for the (HeII + Hα) 6560 emission band reveals a peak at the ∼1% level at the frequency ν = 0.195 d−1, corresponding to the period P = 5.128d. We also studied the NaI 5890 (D2) and NaI 5896 (D1) interstellar absorption lines, which are important for understanding the nature of the nebula NGC 6888, whose origin is related to HD 192163. Asymmetric profiles were found for the NaI 5890 and NaI 5896 interstellar absorption lines, interpreted as reflecting a contribution from NGC 6888 to these lines. We suggest that the detected profile variations of the (HeII + Hα) 6560 emission band and the periodic variations of its Doppler shifts (P = 5.128d) are due to the existence of a low-mass K-M star companion to the Wolf-Rayet star. HD 192163 is a possible evolutionary progenitor of a low-mass X-ray binary.

Modulation of Heme Orientation and Binding by a Single Residue in Catalase HPII of Escherichia coli

Heme-containing catalases have been extensively studied, revealing the roles of many residues, the existence of two heme orientations, flipped 180° relative to one another along the propionate-vinyl axis, and the presence of both heme b and heme d. The focus of this report is a residue, situated adjacent to the vinyl groups of the heme at the entrance of the lateral channel, with an unusual main chain geometry that is conserved in all catalase structures so far determined. In Escherichia coli catalase HPII, the residue is Ile274, and replacing it with Gly, Ala, and Val, found at the same location in other catalases, results in a reduction in catalytic efficiency, a reduced intensity of the Soret absorbance band, and a mixture of heme orientations and species. The reduced turnover rates and higher H(2)O(2) concentrations required to attain equivalent reaction velocities are explained in terms of less efficient containment of substrate H(2)O(2) in the heme cavity arising from easier escape through the more open entrance to the lateral channel created by the smaller side chains of Gly and Ala. Inserting a Cys at position 274 resulted in the heme being covalently linked to the protein through a Cys-vinyl bond that is hypersensitive to X-ray irradiation being largely degraded within seconds of exposure to the X-ray beam. Two heme orientations, flipped along the propionate-vinyl axis, are found in the Ala, Val, and Cys variants.

Spectral properties of type Ia supernovae up toz ~ 0.3

Aims: Spectroscopic observations of Type Ia supernovae obtained at the New Technology Telescope (NTT) and the Nordic Optical Telescope (NOT), in conjunction with the SDSS-II Supernova Survey, are analysed. We use spectral indicators measured up to a month after the lightcurve peak luminosity to characterise the supernova properties, and examine these for potential correlations with host galaxy type, lightcurve shape, colour excess, and redshift. Methods: Our analysis is based on 89 Type Ia supernovae at a redshift interval z = 0.05 - 0.3, for which multiband SDSS photometry is available. A lower-z spectroscopy reference sample was used for comparisons over cosmic time. We present measurements of time series of pseudo equivalent widths and line velocities of the main spectral features in Type Ia supernovae. Results: Supernovae with shallower features are found predominantly among the intrinsically brighter slow declining supernovae. We detect the strongest correlation between lightcurve stretch and the Si ii 4000 absorption feature, which also correlates with the estimated mass and star formation rate of the host galaxy. We also report a tentative correlation between colour excess and spectral properties. If confirmed, this would suggest that moderate reddening of Type Ia supernovae is dominated by effects in the explosion or its immediate environment, as opposed to extinction by interstellar dust.

Bedrock fracturing, threshold hillslopes, and limits to the magnitude of bedrock landslides

Bedrock fracturing and rock strength are widely believed to influence landscape morphology and erosional resistance. Yet, understanding of the quantitative relationship between rock-mass strength and landscape evolution remains limited. Here we present a new application of seismic refraction surveys that uses variations in seismic velocity to interpret differences in bedrock fracture density with depth. We use a comparative study of Fiordland and the western Southern Alps of New Zealand to examine how differences in rock type and bedrock fracturing influence landscape morphology and landslide response to rock uplift. In both regions, slopes appear invariant with differential rock-uplift rates and slope distributions reveal modal hillslope angles of ~ 32°. The majority of landslides initiate on slopes steeper than the modal hillslope angle, however, landslide magnitude–frequency distributions reveal order-of-magnitude differences between the regions, with Fiordland experiencing considerably smaller and less frequent landsliding events. Landslide-driven denudation rates of ~ 9 mm/yr in the western Southern Alps and between ~ 0.1 and 0.3 mm/yr in Fiordland approximate estimates of long-term rock-uplift rates for each region. The invariance of hillslope angles, near-normal slope distributions, predominance of landslide initiation on slopes steeper than modal values, and the apparent balance between rates of uplift and landslide-driven erosion suggest that hillslopes in both regions are at threshold angles. Their similar modal slopes further suggest that both ranges are characterized by equivalent rock-mass strength, despite striking differences in lithology. Additionally, our seismic analysis reveals nearly identical surface p-wave velocities. The unexpected equivalence of both modal slopes and surface velocities between these lithologically distinct ranges is attributed to contrasting degrees of surface fracturing that have differentially affected the intact rock properties, such that they now yield equivalent surface velocities and hillslope-scale strengths. Given that surface fractures help regulate threshold angles by modulating hillslope strength; we propose that shallow seismic velocities may provide a quantitative proxy for rock-mass strength. We define two contrasting fracture and landsliding environments. In Fiordland, dense geomorphic fracturing that is focused within the shallow subsurface appears to limit the depth and magnitude of most bedrock landslides. Conversely, in the western Southern Alps, tectonic forces produce pervasive fracturing with depth that results in larger, and deeper landslides. Our data suggest that bedrock fracturing at the Earth's surface modulates threshold hillslope angles, whereas the depth of bedrock fracturing influences the magnitude and frequency of landslide response to tectonic rock uplift.

A method for direct measurement of ion mobilities using a travelling wave ion guide

The relatively recent introduction of a commercial ion mobility-mass spectrometry instrument has provided access to ion mobility for many investigators for the first time. The mechanism of mobility separation in this instrument differs from classical drift tubes in that travelling voltage waves are used, which has necessitated calibration of the device when collision cross-section (CCS) data are required. Here we present a study into a mode of operation of the travelling wave mobility separator which enables direct determination of mobility and hence CCS values. It is shown that for fixed travelling wave pulse amplitudes and velocities, a minimum mobility is required for an ion species to fully surf on a single wave through the mobility device. For a species with the minimum mobility, the trajectory on the travelling wave front is unique and reproducible. SIMION modelling shows the electric potential profile of the travelling wave to be approximately Gaussian and this is used to establish the field experienced by an ion species on the wave front, ultimately allowing determination of mobility values. With the travelling wave mobility device operating with Helium at 2.5 mbar and equivalent wave velocities of 200–300 m/s, wave amplitudes between 7.9 and 16.2 V were required to establish the mobilities of various singly and multiply charged species ranging in CCS from 147 to 3815 Å 2. We show that using this method, CCS values can be obtained which are within 5% of the results obtained using drift tubes.

Influence of biofilm on the transport of fullerene (C 60) nanoparticles in porous media

The significance of biofilm on fullerene C 60 nanoparticles transport and deposition were examined both in porous media and quartz crystal microbalance with dissipation (QCM-D) systems under a variety of environmentally relevant ionic strength (1–25 mM in NaCl and 0.1–5 mM in CaCl 2) and flow conditions (4–8 m day −1). The magnitudes of deposition rate coefficients ( k d ) were compared between porous media with and without biofilm extracellular polymeric substances (EPS) coating under equivalent fluid velocities and solution chemistries. The observed k d were greater in porous media with biofilm EPS coating relative to those without biofilm EPS coating across the entire solution ionic strengths and fluid velocities examined, demonstrating that the enhancement of C 60 deposition by the biofilm EPS coating is relevant to a wide range of environmental conditions. This greater deposition was also observed on silica surfaces with biofilm EPS coating in QCM-D system. The results clearly showed that biofilm EPS have a great influence on C 60 deposition. Derjaguin–Landau–Verwey–Overbeek (DLVO) theory could not explain the enhanced C 60 deposition by biofilm EPS. Biochemical and physical characteristics of biofilm EPS were responsible for the increased C 60 deposition.

Spectroscopy of the symbiotic binary CH Cygni from 1996 to 2007

Context. Efforts to uncover the nature of the variable star CH Cyg have lasted for decades by now. Recently, the model of a red giant and an accreting white dwarf on a ~5700-day orbit has seemed to have gained an advantage over other ideas, mainly as a result of the investigation of the cool component's absorption lines. In addition to those lines the star's spectrum also presents emission features, which form near the hot component and are therefore a probe of the accretion phenomenon, which in turn could be bound to the orbital motion. Aims. We have monitored a set of emission lines in the optical spectra of CH Cyg over an extended period of time to determine relations between the behaviour of those lines and the photometric data. We are searching for a possible connection with the star's orbital motion, and find hints of the physical phenomena occurring near the white dwarf. Methods. More than 500 observations of CH Cyg were carried out during $1996{-}2007$ using the 1.5-m telescope at the Tartu Observatory, Estonia. Most of the spectra were registered in the H α region, but other Balmer lines and lines of He, N, O, and Fe were also investigated in terms of their equivalent widths, radial velocities, and absolute fluxes. Results. The spectra indicate different stages that CH Cyg has been through in the course of our observations. During quiescence, the strength of the line profiles changes in opposite phase with the star's luminosity. The H α profile becomes double-peaked at times, which may point to the temporary presence of some disk-like structure, but also to absorption in neutral gas surrounding the area of the formation of the emission component. Occasionally the line develops wide wings, which indicate high velocities of the matter. In 1999, when a periastron passage is assumed according to the 5700-day model, the Balmer lines strengthen considerably, as might be expected due to an increase in the accretion rate. The eclipse in 2001, however, is not noticed. At certain episodes, the controversial 756-day period of CH Cyg is seen in our data.

Equivalent viscoelastic solids for heterogeneous fluid-saturated porous rocks

Different theoretical and laboratory studies on the propagation of elastic waves in real rocks have shown that the presence of heterogeneities larger than the pore size but smaller than the predominant wavelengths (mesoscopic-scale heterogeneities) may produce significant attenuation and velocity dispersion effects on seismic waves. Such phenomena are known as “mesoscopic effects” and are caused by equilibration of wave-induced fluid pressure gradients. We propose a numerical upscaling procedure to obtain equivalent viscoelastic solids for heterogeneous fluid-saturated rocks. It consists in simulating oscillatory compressibility and shear tests in the space-frequency domain, which enable us to obtain the equivalent complex undrained plane wave and shear moduli of the rock sample. We assume that the behavior of the porous media obeys Biot’s equations and use a finite-element procedure to approximate the solutions of the associated boundary value problems. Also, because at mesoscopic scales rock parameter distributions are generally uncertain and of stochastic nature, we propose applying the compressibility and shear tests in a Monte Carlo fashion. This facilitates the definition of average equivalent viscoelastic media by computing the moments of the equivalent phase velocities and inverse quality factors over a set of realizations of stochastic rock parameters described by a given spectral density distribution. We analyzed the sensitivity of the mesoscopic effects to different kinds of heterogeneities in the rock and fluid properties using numerical examples. Also, the application of the Monte Carlo procedure allowed us to determine the statistical properties of phase velocities and inverse quality factors for the particular case of quasi-fractal heterogeneities.

D214 大口径管内における気泡流のダイナミクス(OS12 温暖化対策とCO2削減技術)

In order to clarify the characteristics of bubbly flows, we researched the fluctuation of bubbly flow in a large diameter pipe of 400 mm in diameter and 2000 mm in height. The acrylic pipe with water jacket was filled up with water, and bubbles were generated via perforated plate. We employed Four-Tip Optical-fiber Probe (F-TOP) to measure the equivalent bubble diameters, bubble velocities and time-series void fractions. On the basis of the experimental results, we proposed a newly developed method to extract the long-period fluctuations from point-wise void fractions. Analyzing time-series point-wise void fractions measured via F-TOP, we demonstrate the long-period fluctuations are extracted via wave form analysis. As a result, we confirmed that the structure of the bubbly flows has the transition from inhomogeneous structure into homogeneous structure with respect to height. Furthermore, we obtained the correlation between the time-series void fractions and visualization results of the bubbly flows.

Diffuse interstellar bands in M 33

Aims. We investigate the diffuse interstellar band (DIB) spectrum in the interstellar medium of the Local Group spiral galaxy M 33. Methods. Optical spectra of the M 33 supergiant star J013346.96+303642.8 were taken at a resolving power of ~3000 using the DEIMOS spectrograph of the W. M. Keck Observatory. Results. We report the first detection and measurement of DIBs in M 33. The λ λ 5705, 5780, 5797, 6203, 6269, 6283, and 6613 DIBs are detected at velocities matching the M 33 absorption lines. The λ 4428 DIB is tentatively detected. The stellar spectrum is classified as A3 Ia and the line-of-sight interstellar reddening is derived. Diffuse interstellar band (DIB) equivalent widths and radial velocities are presented. Conclusions. The overall spectrum of DIBs observed in M 33 is found to be similar to that observed in the Milky Way. However, along this line-of-sight, the M 33 DIB equivalent widths per unit reddening are large compared with those typically observed in the Galaxy.

Dual femtosecond laser multiheterodyne optical coherence tomography

A time domain optical coherence tomography (OCT) system without moving parts is described, which is based on multiheterodyning utilizing two mode-locked femtosecond lasers. By synchronizing the two lasers to slightly different repetition rates and coupling to an interferometric OCT setup, we obtain amplitude-modulated beat signals representing the structure of the specimen under investigation. Our system is suitable for biological imaging as well as technical applications. We demonstrate high axial imaging depths of 150 mm with up to 5000 axial scans per second, achieving equivalent path scanning velocities of 750 m/s.

Estimate of annual NH 3 dry deposition to a fumigated ombrotrophic bog using concentration-dependent deposition velocities

Estimates of the dry deposition of ammonia (NH 3) gas in a field fumigation experiment on an ombrotrophic bog have been made using the inferential technique, with measured wind speed at 2 m, and air concentrations at two heights above the vegetation. The parameters for a concentration-dependent surface resistance term have been derived from flux measurements over the same vegetation in a chamber study, separating stomatal from non-stomatal resistances. Annual NH 3-N deposition in each of the 4 years 2003–2006 was estimated to increase from 3.0 ± 0.2 kg N ha −1 y −1 in ambient air, with an NH 3 concentration at 0.5 m above the canopy of 0.7 μg m −3, to 50–70 kg N ha −1 y −1 where annual average air concentrations were 70–90 μg m −3 and concentrations during fumigation were up to 1600 μg m −3. The equivalent deposition velocities (at z = 0.5 m) were 0.016 m s −1 in ambient air and 0.003 m s −1 at 100 μg m −3. The differences between annual deposition estimates made from independent air concentration data at 0.1 m and 0.5 m above the canopy were small for distances more than 10 m from the source, after vertical mixing was complete. Over 4 years (2003–2006) and at eight sampling points more than 10 m from the NH 3 source, the mean difference between the dry deposition estimates, using NH 3 concentrations measured independently at 0.1 m and 0.5 m above the canopy, was 2%. Use of a constant surface resistance, with no concentration dependence, as commonly used in inferential models of dry deposition, would have predicted deposition up to eight times too large.