Search results for "Dispersion."
showing 10 items of 1094 documents
Characterization of fiber nonuniformities with ppm resolution using time-resolved in-fiber acousto-optics
2014
Time-resolved acousto-optic interaction using flexural waves enables the characterization of fiber nonuniformities along sections of about 1-2 m. A resolution better than 10 ppm of fiber diameter and core refractive index is demonstrated.
Design and optimization of broadband tapered optical fibers with a nanofiber waist
2010
The control over the transmission properties of tapered optical fibers (TOFs) is an important requirement for a whole range of applications. Using a carefully designed flame pulling process that allows us to realize preset fiber radius profiles, we fabricate TOFs with a nanofiber waist. We study the spectral transmission properties of these TOFs as a function of the taper profile and the waist length and show how the transmission band of the TOF can be tuned via different fiber profile parameters. Based on these results, we have designed a nanofiber-waist TOF with broadband transmission for surface spectroscopy of organic molecules. Moreover, our method allows us to analyze the loss mechani…
Accurate modal characterization of optical fibers using acousto-optics
2016
In-fiber acousto-optics enable accurate and broadband characterization of two mode optical fibers. Differential effective index, group index and dispersion are reported for two-mode optical fibers. Small phase differences between the quasi-degenerated vector modes comprising the LP 11 mode are also measured. In addition, a fine analysis of fiber axial non-uniformities can be performed using a time-resolved acousto-optic technique. In this case, sub-ppm changes of effective index are measured with few cm resolution along fiber sections of about 2 m.
Carbon nanorings: A challenge to theoretical chemistry
2006
High-level quantum-chemical methods show that the binding in the inclusion complex of hexamethylbenzene (HMB) in 6-cycloparaphenilacetylene (6-CPPA) cannot be explained only in terms of electrostatic interactions - caused by the polarization associated to curved Ï-conjugated systems - and the inclusion of dispersion forces is definitely needed. The theoretical description of van der Waals interactions is notoriously complicated and in fact some DFT methods cannot even predict the existence of the relatively small supramolecular nanoring studied here. However, ab initio MP2 calculations agree with experimental data and show that, in the considered complex, the HMB fragment is placed at the …
Kinetic interpretation of influence of sodium chloride concentration and temperature on xanthan gum dispersion flow model
2001
The present study derives a fixed-concentration (0.4%) xanthan gum dispersion flow model for different molar concentrations of sodium chloride (0–0.25M) and different temperatures (20–70°C). The Ostwald–de Waele model is used in all cases. A temperature rise reduces the shear-thinning characteristics of the systems, although the power law index is much less sensitive to changes in temperature when NaCl is added, even in very small amounts. The lowest consistency values correspond to the dispersions formulated in the absence of salt, the highest values are observed for molar values of ≥0.15, and there are decreases in consistency upon raising the temperature in all cases. The viscous behavio…
Elastic properties of CsCN
1983
The temperature dependence of the elastic constants of CsCN exhibiting the CsCl structure was measured with ultrasonic and neutron techniques. The room temperature values were found to bec11=18.8,c12=10.7 andc44=2.95 1010 dyn/cm2. The sound waves inT2g andEg symmetries exhibit anomalous temperature effects which are similar but definitively weaker than those in the NaCl type cyanides. In addition we measured the acoustic phonon dispersion along [100] and [110]. These results are compared with recent molecular dynamics calculations.
Return Dispersion and Cross-Sectional Asset Pricing Anomalies
2015
Recent research finds that cross-sectional return dispersion provides a risk-based explanation for some investment anomalies, including accrual, investment, and momentum strategies. This study extends the analyses of return dispersion to a broad set of anomalies by testing whether the state of return dispersion is associated with anomalous returns. Empirical results for 12 well-known anomalies indicate a robust link between good and bad states of return dispersion and most anomalies. Also, return dispersion helps to explain a number anomalies regardless of their association with investor sentiment. We conclude that market risk related to return dispersion plays an important role in many inv…
Risk-Managed 52-Week High Industry Momentum, Momentum Crashes, and Hedging Macroeconomic Risk
2017
This is the first study that investigates the profitability of Barroso and Santa-Clara’s (2015) risk managing approach for George and Hwang’s (2004) 52-week high momentum strategy in an industrial portfolio setting. The findings indicate that risk-managing adds value as the Sharpe ratio increases, and the downside risk remarkably decreases. Even after controlling for the spread of the traditional 52-week high industry momentum strategy in association with standard risk-factors, the risk-managed version generates economically and statistically significant payoffs. Notably, the risk-managed strategy is partially explained by changes in cross-sectional return dispersion, whereas the traditiona…
Performances and morphology of polyamide/carbonaceous structures based fibers
2014
In this work the influence of carbonaceous particles with different particle sizes and shapes on the morphology and mechanical performances of polyamide (PA) based fibers was investigated. Graphene nanoplatelets (GNP) are compared with spherical and rod-like carbon fillers such as carbon black (CB) and multiwall carbon nanotubes (MWCNT). The different morphologies of the particles control their dispersion and their alignment in PA fibers upon elongational flow action and play a key role in structure-property relationships.
Taking advantage of the functional synergism between carbon nanotubes and graphene nanoplatelets to obtain polypropylene-based nanocomposites with en…
2020
Carbon Nanotubes (CNT) and Graphene Nanoplatelets (GNP) were incorporated in Polypropylene (PP) as single filler (CNT=1, 2 and 4 %wt. and GNP=2, 4, and 6 %wt.) and in hybrid form (CNT:GNP weight ratio 2:2, 2:4 and 4:2) using a prototype miniature Twin Screw Extruder (TSE) coupled with a double slit rheological die, in order to assess in-line the extent of nanofiller dispersion and to deliver PP-based nanocomposites with enhanced thermo-oxidative stability. The morphological, electrical and mechanical properties, as well as the resistance to thermal and photo degradation of the composites containing single nanofillers (PP/CNT and PP/GNP) were compared with those of hybrid PP based nanocompos…