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Width Variation (width + variation)

Distribution by Scientific Domains

Engineering	50%

Selected Abstracts

On linking interannual tree ring variability with observations of whole-forest CO2 flux

GLOBAL CHANGE BIOLOGY, Issue 8 2006
ADRIAN V. ROCHA
Abstract We used a 10-year record of the CO2 flux by an old growth boreal forest in central Manitoba (the Northern Old Black Spruce Site (NOBS)), a ,150-year-old Picea mariana [Mill.] stand) to determine whether and how whole-forest CO2 flux is related to tree ring width. We compared a 37-year ring width chronology collected at NOBS to a second chronology that was collected at a nearby Black Spruce stand with a different disturbance history, and also to three measures of annual whole-forest photosynthesis [gross ecosystem production (GEP)], two measures of annual respiration (R), and one measure of annual carbon balance [net ecosystem production (NEP)]. The year-to-year ring width fluctuations were well correlated between the two sites; increasing our confidence in the NOBS chronology and implying that ring width variation is driven and synchronized by the physical environment. Both chronologies exhibited serial correlation, with a fluctuation in ring width that had an apparent periodicity of ,7 years. Neither chronology was correlated with variation in annual precipitation or temperature. Ring width and NEP increased, while R decreased from 1995 to 2004. GEP either remained constant or decreased from 1995 to 2004, depending on which measure was considered. The lack of relationship between ring width and GEP may indicate that ring growth is controlled almost entirely by something other than carbon uptake. Alternative explanations for the ring width chronologies include the possibility that wood production varies as a result of shifts in respiration, or that an unidentified aspect of the environment, rather than the balance between GEP and respiration, controls wood production. The serial correlation in ring width may be related to increases and decreases in carbohydrate pools, or to gradual changes in nutrient availability, pathogens, herbivores, soil frost or soil water table. The cause or causes of serial correlation, and the controls on the allocation of photosynthate to wood production, emerge as critical uncertainties for efforts in predicting the carbon balance of boreal ecosystems and inferring past climate from tree rings. [source]

Funnel-and-Gate Performance in a Moderately Heterogeneous Flow Domain

GROUND WATER MONITORING & REMEDIATION, Issue 3 2001
Lacrecia C. Bilbrey
The funnel-and-gate ground water remediation technology (Starr and Cherry 1994) has received increased attention and application as an in situ alternative to the typical pump-and-treat system. Understanding the effects of heterogeneity on system performance can mean the difference between a successful remediation project and one that fails to meet its cleanup goals. In an attempt to characterize and quantify the effects of heterogeneity on funnel-and-gate system performance, a numerical modeling study of 15 simulated heterogeneous flow domains was conducted. Each realization was tested to determine if the predicted capture width met the capture width expected for a homogeneous flow domain with the same hulk properties. This study revealed that the capture width of the funnel-and-gate system varied significantly with the level of heterogeneity of the aquifer. Two possible remedies were investigated for bringing systems with less than acceptable capture widths to acceptable levels of performance. First, it was determined that enlarging the funnel and gate via a factor of safety applied to the design capture width could compensate for the capture width variation in the heterogeneous flow domains. In addition, it was shown that the use of a pumping well downstream of the funnel and gate could compensate for the effects of aquifer heterogeneity on the funnel-and-gate capture width. However, if a pumping well is placed downstream of the funnel and gate to control the hydraulic gradient through the gate, consideration should be given to the gate residence time in relation to the geochemistry of the contaminant removal or destruction process in the gate. [source]

Changes in spectral features with varying mole fractions of anisaldehyde in binary mixtures

JOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2007
A. Anis Fathima
Abstract Raman and IR spectra of neat anisaldehyde (4-methoxybenzaldehyde (4MeOBz)) and its binary mixtures (in polar and nonpolar solvents) with varying mole fraction of 4MeOBz were investigated. The concentration dependence of the wavenumber position and line width (full width at half maximum, FWHM) was analyzed to study the interaction of the solute vibrational modes with the microscopic solvent environment. The wavenumbers of Raman modes of 4MeOBz, namely, the carbonyl stretching, aldehydic , (CH) and ring-breathing modes, showed a linear variation in the peak position for varying concentrations of 4MeOBz in the different solvents. The dependence of Raman line width with concentration of 4MeOBz of these modes was also taken into account. The solute,solvent interaction is stronger in 2-propanol and acetonitrile because of the formation of hydrogen bonds between them, whereas in benzene the interaction is too weak to affect the Raman modes. The modes, , (CO) in 2-propanol and aldehydic , (CH) in acetonitrile, gave a Gaussian-type line width variation, which was explained by the concentration fluctuation model, and the linear variation of the line widths was also interpreted by solute,solvent interactions. IR spectra were taken for these binary mixtures, which also give further support to these data. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Balanced BPSK modulator for Ka-band communication systems

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 12 2007
Ashok Mittal
Abstract This article details the design of balanced PSK modulator using integrated finline coplanar line hybrid junction. The PSK signal output is in suspended stripline with incident wave carrier in unilateral symmetric finline. Schottky barrier diodes MA4E2037 from M/ACom has been used for modulation. The balanced configuration offers high isolation between the carrier input port and the modulated carrier output port and thus the pulse width variations and amplitude deviations are suppressed. An insertion loss imbalance of ±1.5 dB with an average loss of 2.5 dB in the two switching states has been achieved over 37.0 to 38.0 GHz against the estimated loss of 2.0 dB. The phase imbalance is ±10° with phase switching from 165° to 185°. As the PSK output signal is in suspended stripline, two BPSK Modulators can easily be combined together to work as QPSK modulator for point to point millimeter wave radio links. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3046,3049, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22910 [source]