2,464 research outputs found
Pi Charge Distribution from Molecular Topology and Pi Orbital Electronegativity
The automatic and computer-aided prediction of reactivity by
means of a few basic atomic parameters is achieved. Considering
that only the topology of a molecule is required for the computation
it is evident that PEOE (partial equalization of orbital electronegativity)
and SD-POE (sigma dependent POE) models proposed by
the authors together establish a valid alternative to the presently
available, time consuming quantum mechanical procedures.
Furthermore, this approach gives a new insight into the interaction
between a and it electrons which seems worthy of further
investigation. In addition, we have revived the concept of orbital
electronegativity, especially in the case of the Jt electrons for which
no calculation based on POE (pi orbital electronegativy) has, up to
now, ever been performed
Achievement and Integration of Students with Special Needs (SEN) in the Fifth Grade
In Styria 77.3% of all students with special
needs are educated in integrated classrooms.
Currently, it is not known much either about the
school performance nor the active class
participation of these students. This study
examined 230 fifth grade students – 43 with
and 187 students without special educational
needs (SEN). Moreover, it is important to
acknowledge that the available data for this
study represents the first wave of larger
longitudinal study. The school performance of
the students with SEN ranged one standard
deviation below the level of the students
without SEN. All students felt emotionally well
integrated in the school settings, but the
differences in the degree of social integration
were evident. In fact, the students with SEN
mentioned that they got along well with their
classmates less frequently than the students
without SEN
Pi Charge Distribution from Molecular Topology and Pi Orbital Electronegativity
The automatic and computer-aided prediction of reactivity by
means of a few basic atomic parameters is achieved. Considering
that only the topology of a molecule is required for the computation
it is evident that PEOE (partial equalization of orbital electronegativity)
and SD-POE (sigma dependent POE) models proposed by
the authors together establish a valid alternative to the presently
available, time consuming quantum mechanical procedures.
Furthermore, this approach gives a new insight into the interaction
between a and it electrons which seems worthy of further
investigation. In addition, we have revived the concept of orbital
electronegativity, especially in the case of the Jt electrons for which
no calculation based on POE (pi orbital electronegativy) has, up to
now, ever been performed
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Numerical simulations of optical properties of Saharan dust aerosols with emphasis on lidar applications
In the framework of the Saharan Mineral Dust Experiment (SAMUM) for the first time the spectral dependence of particle linear depolarization ratios was measured by combining four lidar systems. In this paper these measurements are compared with results from scattering theory based on the T-matrix method. For this purpose, in situ measurements—size distribution, shape distribution and refractive index—were used as input parameters; particle shape was approximated by spheroids. A sensitivity study showed that lidar-related parameters—lidar ratio Sp and linear depolarization ratio δp—are very sensitive to changes of all parameters. The simulated values of the δp are in the range of 20% and 31% and thus in the range of the measurements. The spectral dependence is weak, so that it could not be resolved by the measurements. Calculated lidar ratios based on the measured microphysics and considering equivalent radii up to 7.5μm show a range of possible values between 29 and 50 sr at λ = 532 nm. Larger Sp might be possible if the real part of the refractive index is small and the imaginary part is large. A strict validation was however not possible as too many microphysical parameters influence Sp and δp that could not be measured with the required accuracy
Nickel, Manganese, and Cobalt Dissolution from Ni-Rich NMC and Their Effects on NMC622-Graphite Cell
What is the benefit of ceilometers for aerosol remote sensing? An answer from EARLINET
With the establishment of ceilometer networks by national weather services, a discussion commenced to which extent these simple backscatter lidars can be used for aerosol research. Though primarily designed for the detection of clouds it was shown that at least observations of the vertical structure of the boundary layer might be possible. However, an assessment of the potential of ceilometers for the quantitative retrieval of aerosol properties is still missing. In this paper we discuss different retrieval methods to derive the aerosol backscatter coefficient beta(p),with special focus on the calibration of the ceilometers. Different options based on forward and backward integration methods are compared with respect to their accuracy and applicability. It is shown that advanced lidar systems such as those being operated in the framework of the European Aerosol Research Lidar Network (EARLINET) are excellent tools for the calibration, and thus beta(p) retrievals based on forward integration can readily be implemented and used for real-time applications. Furthermore, we discuss uncertainties introduced by incomplete overlap, the unknown lidar ratio, and water vapor absorption. The latter is relevant for the very large number of ceilometers operating in the spectral range around lambda = 905-910 nm. The accuracy of the retrieved beta(p) mainly depends on the accuracy of the calibration and the long-term stability of the ceilometer. Under favorable conditions, a relative error of beta(p) on the order of 10% seems feasible. In the case of water vapor absorption, corrections assuming a realistic water vapor distribution and laser spectrum are indispensable;otherwise errors on the order of 20% could occur. From case studies it is shown that ceilometers can be used for the reliable detection of elevated aerosol layers below 5 km, and can contribute to the validation of chemistry transport models, e. g.,the height of the boundary layer. However, the exploitation of ceilometer measurements is still in its infancy, so more studies are urgently needed to consolidate the present state of knowledge, which is based on a limited number of case studies
Volcanic ash from Iceland over Munich: mass concentration retrieved from ground-based remote sensing measurements
Volcanic ash plumes, emitted by the Eyjafjallajökull volcano (Iceland) in
spring 2010, were observed by the lidar systems MULIS and POLIS in Maisach
(near Munich, Germany), and by a CIMEL Sun photometer and a JenOptik
ceilometer in Munich. We retrieve mass concentrations of volcanic ash from
the lidar measurements; spectral optical properties, i.e. extinction
coefficients, backscatter coefficients, and linear depolarization ratios, are
used as input for an inversion. The inversion algorithm searches for model
aerosol ensembles with optical properties that agree with the measured values
within their uncertainty ranges. The non-sphericity of ash particles is
considered by assuming spheroids. Optical particle properties are calculated
using the T-matrix method supplemented by the geometric optics approach. The
lidar inversion is applied to observations of the pure volcanic ash plume in
the morning of 17 April 2010. We find 1.45 g m−2 for the ratio between
the mass concentration and the extinction
coefficient at λ = 532 nm, assuming an ash density of 2.6 g cm−3.
The uncertainty range for this ratio is from 0.87 g m−2 to
2.32 g m−2. At the peak of the ash concentration over Maisach the
extinction coefficient at λ = 532 nm was 0.75 km−1
(1-h-average), which corresponds to a maximum mass concentration of
1.1 mg m−3 (0.65 to 1.8 mg m−3). Model calculations show that
particle backscatter at our lidar wavelengths (λ ≤ 1064 nm), and
thus the lidar retrieval, is hardly sensitive to large particles
(r ≳ 3 μm); large particles, however, may contain
significant amounts of mass. Therefore, as an independent cross check of the
lidar retrieval and to investigate the presence of large particles in more
detail, we model ratios of sky radiances in the aureole of the Sun and
compare them to measurements of the CIMEL. These ratios are sensitive to
particles up to r ≈ 10 μm. This approach confirms the
mass concentrations from the lidar retrieval. We conclude that synergistic
utilization of high quality lidar and Sun photometer data, in combination
with realistic aerosol models, is recommended for improving ash mass
concentration retrievals
Airborne observations of the Eyjafjalla volcano ash cloud over Europe during air space closure in April and May 2010
© Author(s) 2011. This work is distributed under the Creative Commons Attribution 3.0 LicenseAirborne lidar and in-situ measurements of aerosols and trace gases were performed in volcanic ash plumes over Europe between Southern Germany and Iceland with the Falcon aircraft during the eruption period of the Eyjafjalla1 volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with lidar directly over the volcano and up to a distance of 2700 km downwind, and up to 120 h plume ages. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 μm diameter, with size and age dependent composition. Ash mass concentrations were derived from optical particle spectrometers for a particle density of 2.6 g cm-3 and various values of the refractive index (RI, real part: 1.59; 3 values for the imaginary part: 0, 0.004 and 0.008). The mass concentrations, effective diameters and related optical properties were compared with ground-based lidar observations. Theoretical considerations of particle sedimentation constrain the particle diameters to those obtained for the lower RI values. The ash mass concentration results have an uncertainty of a factor of two. The maximum ash mass concentration encountered during the 17 flights with 34 ash plume penetrations was below 1 mg m-3. The Falcon flew in ash clouds up to about 0.8 mg m-3 for a few minutes and in an ash cloud with approximately 0.2 mg -3 mean-concentration for about one hour without engine damage. The ash plumes were rather dry and correlated with considerable CO and SO2 increases and O3 decreases. To first order, ash concentration and SO2 mixing ratio in the plumes decreased by a factor of two within less than a day. In fresh plumes, the SO2 and CO concentration increases were correlated with the ash mass concentration. The ash plumes were often visible slantwise as faint dark layers, even for concentrations below 0.1 mg m-3. The large abundance of volatile Aitken mode particles suggests previous nucleation of sulfuric acid droplets. The effective diameters range between 0.2 and 3 μm with considerable surface and volume contributions from the Aitken and coarse mode aerosol, respectively. The distal ash mass flux on 2 May was of the order of 500 (240-1600) kgs -1. The volcano induced about 10 (2.5-50) Tg of distal ash mass and about 3 (0.6-23) Tg of SO2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of volcanic ash.Peer reviewe
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