733 research outputs found
Solar Dynamics, Rotation, Convection and Overshoot
We discuss recent observational, theoretical and modeling progress made in
understanding the Sun's internal dynamics, including its rotation, meridional
flow, convection and overshoot. Over the past few decades, substantial
theoretical and observational effort has gone into appreciating these aspects
of solar dynamics. A review of these observations, related helioseismic
methodology and inference and computational results in relation to these
problems is undertaken here.Comment: 31 pages, 10 figures, Space Science Review
Frequency comb vernier spectroscopy in the near infrared
We perform femtosecond frequency comb vernier spectroscopy in the near
infrared with a femtosecond Er doped fiber laser, a scanning high-finesse
cavity and an InGaAs camera. By utilizing the properties of a frequency comb
and a scanning high-finesse cavity such spectroscopy provides broad spectral
bandwidth, high spectral resolution, and high detection sensitivity on a short
time scale. We achieved an absorption sensitivity of ~8E-8 cm-1Hz-1/2
corresponding to a detection limit of ~70 ppbv for acetylene, with a resolution
of ~1.1 GHz in single images taken in 0.5 seconds and covering a frequency
range of ~5 THz. These measurements have broad applications for sensing other
greenhouse gases in this fingerprint near IR region with a simple apparatus.Comment: 14 pages, 5 figure
Equitable Access in Education: Access to Joy, Choice Options, and Strong Neighborhood Schools
The purpose of this co-authored dissertation was to understand equitable access of quality educational opportunities in St. Louis, Missouri. Through the following research, we present a better understanding of equity and access in education from a classroom level, on a school level, and finally, on a regional level. This collection of research is the effort of a group of committed and concerned educators seeking to understand the ways of making quality education accessible for all families, specifically in the areas of school choice, quality neighborhood schools, and play in the classroom. By equitable access, we mean all families being able to participate in and take advantage of appropriate learning opportunities that they need or that are desired. Hollenkamp’s mixed methods research asked the question of how an increase in play and experiential education would impact early childhood learners both academically and social-emotionally and found that students who had opportunities to play at school grew at the same academic rate as peers who did not get to play while also showing higher levels of character development than their non-playing peers. Sanders’ mixed methods research examined enrollment trends in a neighborhood school and the effect of marketing and promoting strategies that work to make the school the desired choice for families in the neighborhood and found definitive ways to attract and retain families in a neighborhood school among other choice options. Schuessler’s mixed methods research examined how school enrollment processes impact equitable access to school choice options for traditionally underserved populations and found a range in the complexity of enrollment practices across schools that resulted in certain choice options being more accessible to underserved families and other options being less accessible. The collective impact of this research has the potential to improve educational outcomes for students on a variety of levels
Oxidation state of iron in hydrous phono-tephritic melts
The oxidation state of iron in hydrous ultrapotassic (phono-tephritic) melts coexisting with mixed H2O-CO2 fluids was experimentally studied at 1200 and 1250{degree sign}C and pressures from 50 to 500 MPa. The oxygen fugacity (fO2) varied from NNO-2.9 to NNO+2.6 in logfO2, relative to the Ni-NiO oxygen buffer (NNO), as imposed by external redox conditions in experimental vessels and internal variations in water activity from 0.05 to 1 inside the capsules. The iron redox state of the quenched melts was determined by colorimetric wet-chemical analysis. This analytical method was optimized to measure the Fe2+/ΣFe ratio of mg-sized samples within ±0.03 (2σ). The accuracy and precision was tested with international reference materials and with standards analyzed by other methods. The Fe2+/ΣFe ratio of the experimental glasses covered a range of 0.41 to 0.85. A small negative effect of dissolved water on Fe2+/ΣFe at given fO2 was found, consistent with the thermodynamic model of Moretti (2005). No effect of pressure and temperature on the redox state of iron was resolvable in the investigated P-T range. Compared to hydrous ferrobasaltic melts that were studied previously under similar conditions, systematically lower Fe2+/ΣFe ratios were found for the phono-tephritic melts, in particular at low oxygen fugacities. This effect is attributed to the much higher K2O contents of the phono-tephrite (7.5 compared to 0.3 wt%), but the difference in ΣFeO (7.8 wt% in the phono-tephrite and 12.9 wt% in the ferrobasalt) may have an influence as well. Comparison of the experimentally obtained relationship between logfO2 and Fe3+/Fe2+ for the studied hydrous ultrapotassic melts with commonly used empirical and thermodynamic models suggest that these models can be successfully applied to phono-tephritc melts, although such compositions were not implemented in the model calibrations. Furthermore, the new data can be used to improve the models with respect to the effects of compositional variables, such as H2O or K2O, on the redox state of iron in silicate melts
Surface plasmon resonance study of the actin-myosin sarcomeric complex and tubulin dimers
Biosensors based on the principle of surface plasmon resonance (SPR)
detection were used to measure biomolecular interactions in sarcomeres and
changes of the dielectric constant of tubulin samples with varying
concentration. At SPR, photons of laser light efficiently excite surface
plasmons propagating along a metal (gold) film. This resonance manifests itself
as a sharp minimum in the reflection of the incident laser light and occurs at
a characteristic angle. The dependence of the SPR angle on the dielectric
permittivity of the sample medium adjacent to the gold film allows the
monitoring of molecular interactions at the surface. We present results of
measurements of cross-bridge attachment/detachment within intact mouse heart
muscle sarcomeres and measurements on bovine tubulin molecules pertinent to
cytoskeletal signal transduction models.Comment: Submitted to Journal of Modern Optics *Corresponding author: Andreas
Mershin ([email protected]
Oxidation state of iron in hydrous phono-tephritic melts
The oxidation state of iron in hydrous ultrapotassic (phono-tephritic) melts coexisting with mixed H2O-CO2 fluids was experimentally studied at 1200 and 1250{degree sign}C and pressures from 50 to 500 MPa. The oxygen fugacity (fO2) varied from NNO-2.9 to NNO+2.6 in logfO2, relative to the Ni-NiO oxygen buffer (NNO), as imposed by external redox conditions in experimental vessels and internal variations in water activity from 0.05 to 1 inside the capsules. The iron redox state of the quenched melts was determined by colorimetric wet-chemical analysis. This analytical method was optimized to measure the Fe2+/ΣFe ratio of mg-sized samples within ±0.03 (2σ). The accuracy and precision was tested with international reference materials and with standards analyzed by other methods. The Fe2+/ΣFe ratio of the experimental glasses covered a range of 0.41 to 0.85. A small negative effect of dissolved water on Fe2+/ΣFe at given fO2 was found, consistent with the thermodynamic model of Moretti (2005). No effect of pressure and temperature on the redox state of iron was resolvable in the investigated P-T range. Compared to hydrous ferrobasaltic melts that were studied previously under similar conditions, systematically lower Fe2+/ΣFe ratios were found for the phono-tephritic melts, in particular at low oxygen fugacities. This effect is attributed to the much higher K2O contents of the phono-tephrite (7.5 compared to 0.3 wt%), but the difference in ΣFeO (7.8 wt% in the phono-tephrite and 12.9 wt% in the ferrobasalt) may have an influence as well. Comparison of the experimentally obtained relationship between logfO2 and Fe3+/Fe2+ for the studied hydrous ultrapotassic melts with commonly used empirical and thermodynamic models suggest that these models can be successfully applied to phono-tephritc melts, although such compositions were not implemented in the model calibrations. Furthermore, the new data can be used to improve the models with respect to the effects of compositional variables, such as H2O or K2O, on the redox state of iron in silicate melts
Reconstruction of ionization probabilities from spatially averaged data in N-dimensions
We present an analytical inversion technique which can be used to recover
ionization probabilities from spatially averaged data in an N-dimensional
detection scheme. The solution is given as a power series in intensity. For
this reason, we call this technique a multiphoton expansion (MPE). The MPE
formalism was verified with an exactly solvable inversion problem in 2D, and
probabilities in the postsaturation region, where the intensity-selective
scanning approach breaks down, were recovered. In 3D, ionization probabilities
of Xe were successfully recovered with MPE from simulated (using the ADK
tunneling theory) ion yields. Finally, we tested our approach with
intensity-resolved benzene ion yields showing a resonant multiphoton ionization
process. By applying MPE to this data (which was artificially averaged) the
resonant structure was recovered-suggesting that the resonance in benzene may
have been observable in spatially averaged data taken elsewhere.Comment: 19 pages and 3 figure
Viscosity of andesite melts and its implication for magma mixing prior to Unzen 1991-1995 eruption
The viscosity of an iron-bearing melt with composition similar to Unzen andesite was
determined experimentally in the high (109-1010.5 Pa·s) and low (5-1000 Pa·s) viscosity range
using a parallel plate viscometer and the falling sphere method, respectively. Falling sphere
experiments were carried out in an internally heated argon pressure vessel and in a piston
cylinder apparatus at 1323 to 1573 K and 200 to 2000 MPa. Creep experiments were
performed in the temperature range of 747 - 845 K at 300 MPa. The water content of the melt
varies from nominally dry to 6.2 wt% H2O. The Fe2+/Fetot ratio was determined for each
sample in the quenched glass using a colorimetric method. Pressure has minor influence on
the viscosity compared with the effect of temperature, water content (main compositional
parameter controlling the viscosity) or with the Fe2+/Fetot ratio (especially important at low
water content of the melt). Based on our new viscosity data and literature data with measured
Fe2+/Fetot ratio we propose a new empirical equation to estimate the viscosity η (in Pa·s) of
andesitic melts as a function of temperature T (in K), water content w (in wt%) and Fe2+/Fetot
ratio. The derived relationship reproduces the experimental data (87 in total) in the viscosity
range from 100.5 to 1013 Pa·s with a 1σ standard deviation of 0.17 log units. However,
application of this calculation model is limited to Fe2+/Fetot>0.3 and to temperatures above Tg.
Moreover, in the high viscosity range the variation of viscosity with water content is
constrained only by few experimental data and needs verification by additional
measurements.
The viscosity data are used to interpret mixing processes in the Unzen magma chamber prior
to 1991-1995 eruption. We demonstrate that the viscosities of the rhyolite and andesite melts
from the two end-member magmas are nearly identical prior and during mixing, enabling
efficient magma mixing
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