2,150 research outputs found
Experimental and numerical investigation of edge tones
We study both, by experimental and numerical means the fluid dynamical phenomenon of so-called edge tones. Of particular interest is the clarification of certain scaling laws relating the frequency ƒ to geometrical quantities, namely 푑, the height of the jet, 푤, the stand-off distance and the velocity of the jet. We conclude that the Strouhal number S푑 is given by S푑 = C · (푑/푤)푛 with 푛 ≈ 1 in our case. Moreover, the constant C of the experiment agrees within 10-15% with the result of the simulation. As for the frequency dependence on the geometry and on the jet velocity there is a very good agreement of experimental and numerical results
Gap-filling strategies for annual VOC flux data sets
Up to now the limited
knowledge about the exchange of volatile organic compounds (VOCs) between the
biosphere and the atmosphere is one of the factors which hinders more
accurate climate predictions. Complete long-term flux data sets of several
VOCs to quantify the annual exchange and validate recent VOC models are
basically not available. In combination with long-term VOC flux measurements
the application of gap-filling routines is inevitable in order to replace
missing data and make an important step towards a better understanding of the
VOC ecosystem–atmosphere exchange on longer timescales.
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We performed VOC flux measurements above a mountain meadow in Austria during
two complete growing seasons (from snowmelt in spring to snow reestablishment
in late autumn) and used this data set to test the performance of four
different gap-filling routines, mean diurnal variation (MDV), mean gliding
window (MGW), look-up tables (LUT) and linear interpolation (LIP), in terms
of their ability to replace missing flux data in order to obtain reliable VOC
sums. According to our findings the MDV routine was outstanding with regard
to the minimization of the gap-filling error for both years and all
quantified VOCs. The other gap-filling routines, which performed gap-filling
on 24 h average values, introduced considerably larger uncertainties. The
error which was introduced by the application of the different filling
routines increased linearly with the number of data gaps. Although average
VOC fluxes measured during the winter period (complete snow coverage) were
close to zero, these were highly variable and the filling of the winter
period resulted in considerably higher uncertainties compared to the
application of gap-filling during the measurement period.
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The annual patterns of the overall cumulative fluxes for the quantified VOCs
showed a completely different behaviour in 2009, which was an exceptional
year due to the occurrence of a severe hailstorm, compared to 2011. Methanol
was the compound which, at 381.5 mg C m<sup>−2</sup> and 449.9 mg
C m<sup>−2</sup>, contributed most to the cumulative VOC carbon emissions in
2009 and 2011, respectively. In contrast to methanol emissions, however,
considerable amounts of monoterpenes (−327.3 mg C m<sup>−2</sup>) were
deposited onto the mountain meadow during 2009 caused by a hailstorm. Other
quantified VOCs had considerably lower influences on the annual patterns
Rigorous sufficient conditions for index-guided mode in microstructured dielectric waveguides
We derive a sufficient condition for the existence of index-guided modes in a
very general class of dielectric waveguides, including photonic-crystal fibers
(arbitrary periodic claddings, such as ``holey fibers''), anisotropic
materials, and waveguides with periodicity along the propagation direction.
This condition provides a rigorous guarantee of cutoff-free index-guided modes
in any such structure where the core is formed by increasing the index of
refraction (e.g. removing a hole). It also provides a weaker guarantee of
guidance in cases where the refractive index is increased ``on average''
(precisely defined). The proof is based on a simple variational method,
inspired by analogous proofs of localization for two-dimensional attractive
potentials in quantum mechanics.Comment: 15 page
Expression of Rb2/p130 in breast and endometrial cancer: correlations with hormone receptor status
Rb2/p130 is a member of the retinoblastoma family of proteins, consisting of Rb, Rb2 and p107, which are important negative regulators of cell cycle progression and differentiation. While Rb2 downregulation was observed in several malignant tumours including endometrial cancer, the role of p130 in breast carcinomas is still unknown. We investigated Rb2 protein expression in tumour tissue from 68 mammary and 41 endometrial carcinomas, 4 mammary cell lines, and normal tissue samples. Therefore, we performed Western blot experiments for Rb2, Rb, and the oestrogen and progesterone receptors (ER, PR-A, PR-B). Weak or absent Rb2 expression was more often found in endometrial (59%) than in mammary carcinomas (24%). We found significant positive correlations of Rb2 expression with Rb, ER, and PR-B in breast cancer samples, and of Rb2 with Rb, PR-A, PR-B, and younger age in endometrial carcinomas. No significant associations with histological grading, stage, nodal involvement, or Ki67 staining were detected. Rb2 mRNA expression was studied by semi-quantitative RT-PCR in 56 endometrial or mammary tissue samples and correlated significantly with Western blot results. Our results indicate that loss of Rb2 expression, mostly by transcriptional down-regulation, may be associated with the development and dedifferentiation of most endometrial and a subset of mammary carcinomas. © 2001 Cancer Research Campaign http://bjcancer.co
Testing the Resolving Power of 2-D K^+ K^+ Interferometry
Adopting a procedure previously proposed to quantitatively study
two-dimensional pion interferometry, an equivalent 2-D chi^2 analysis was
performed to test the resolving power of that method when applied to less
favorable conditions, i.e., if no significant contribution from long lived
resonances is expected, as in kaon interferometry. For that purpose, use is
made of the preliminary E859 K^+ K^+ interferometry data from Si+Au collisions
at 14.6 AGeV/c. As expected, less sensitivity is achieved in the present case,
although it still is possible to distinguish two distinct decoupling
geometries. The present analysis seems to favor scenarios with no resonance
formation at the AGS energy range, if the preliminary K^+ K^+ data are
confirmed. The possible compatibility of data with zero decoupling proper time
interval, conjectured by the 3-D experimental analysis, is also investigated
and is ruled out when considering more realistic dynamical models with
expanding sources. These results, however, clearly evidence the important
influence of the time emission interval on the source effective transverse
dimensions. Furthermore, they strongly emphasize that the static Gaussian
parameterization, commonly used to fit data, cannot be trusted under more
realistic conditions, leading to distorted or even wrong interpretation of the
source parameters!Comment: 11 pages, RevTeX, 4 Postscript figures include
Centrality dependence of the expansion dynamics in Pb-Pb collisions at 158 A GeV/c
Two-particle correlation functions of negatively charged hadrons from Pb-Pb
collisions at 158 GeV/c per nucleon have been measured by the WA97 experiment
at the CERN SPS. A Coulomb correction procedure that assumes an expanding
source has been implemented. Within the framework of an expanding thermalized
source model the size and dynamical state of the collision fireball at
freeze-out have been reconstructed as a function of the centrality of the
collision. Less central collisions exhibit a different dynamics than central
ones: both transverse and longitudinal expansion velocities are slower, the
expansion duration is shorter and the system freezes out showing smaller
dimensions and higher temperature.Comment: 22 pages, 11 figures, Te
Signaling in Secret: Pay-for-Performance and the Incentive and Sorting Effects of Pay Secrecy
Key Findings: Pay secrecy adversely impacts individual task performance because it weakens the perception that an increase in performance will be accompanied by increase in pay; Pay secrecy is associated with a decrease in employee performance and retention in pay-for-performance systems, which measure performance using relative (i.e., peer-ranked) criteria rather than an absolute scale (see Figure 2 on page 5); High performing employees tend to be most sensitive to negative pay-for- performance perceptions; There are many signals embedded within HR policies and practices, which can influence employees’ perception of workplace uncertainty/inequity and impact their performance and turnover intentions; and When pay transparency is impractical, organizations may benefit from introducing partial pay openness to mitigate these effects on employee performance and retention
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