597 research outputs found
Charter-School Management Organizations: Diverse Strategies and Diverse Student Impacts
Examines the growth of charter school management organizations, characteristics of students served, and use of resources; CMO practices; impact on students, including middle school test scores; and structures and practices linked to positive outcomes
Embedded-Cluster Calculations in a Numeric Atomic Orbital Density-Functional Theory Framework
We integrate the all-electron electronic structure code FHI-aims into the
general ChemShell package for solid-state embedding (QM/MM) calculations. A
major undertaking in this integration is the implementation of pseudopotential
functionality into FHI-aims to describe cations at the QM/MM boundary through
effective core potentials and therewith prevent spurious overpolarization of
the electronic density. Based on numeric atomic orbital basis sets, FHI-aims
offers particularly efficient access to exact exchange and second order
perturbation theory, rendering the established QM/MM setup an ideal tool for
hybrid and double-hybrid level DFT calculations of solid systems. We illustrate
this capability by calculating the reduction potential of Fe in the
Fe-substituted ZSM-5 zeolitic framework and the reaction energy profile for
(photo-)catalytic water oxidation at TiO2(110).Comment: 12 pages, 4 figure
Selective Adsorption and Chiral Amplification of Amino Acids in Vermiculite Clay -Implications for the origin of biochirality
Smectite clays are hydrated layer silicates that, like micas, occur naturally
in abundance. Importantly, they have readily modifiable interlayer spaces that
provide excellent sites for nanochemistry. Vermiculite is one such smectite
clay and in the presence of small chain-length alkyl-NH3Cl ions, forms
sensitive, 1-D ordered model clay systems with expandable nano-pore inter-layer
regions. These inter-layers readily adsorb organic molecules. N-propyl NH3Cl
vermiculite clay gels were used to determine the adsorption of alanine, lysine
and histidine by chiral HPLC. The results show that during reaction with fresh
vermiculite interlayers, significant chiral enrichment of either L- and
D-enantiomers occurs depending on the amino acid. Chiral enrichment of the
supernatant solutions is up to about 1% per pass. In contrast, addition to clay
interlayers already reacted with amino acid solutions resulted in little or no
change in D/L ratio during the time of the experiment. Adsorption of small
amounts of amphiphilic organic molecules in clay inter-layers is known to
produce Layer-by-Layer or Langmuir-Blodgett films. Moreover atomistic
simulations show that self-organization of organic species in clay interlayers
is important. These non-centrosymmetric, chirally active nanofilms may cause
clays to act subsequently as chiral amplifiers, concentrating organic material
from dilute solution and having different adsorption energetics for D- and
L-enantiomers. The additional role of clays in RNA oligimerization already
postulated by Ferris and others, together with the need for the organization of
amphiphilic molecules and lipids noted by Szostak and others, suggests that
such chiral separation by clays in lagoonal environments at normal biological
temperatures might also have played a significant role in the origin of
biochirality.Comment: 17 Pages, 2 Figures, 4 Table
Density of mechanisms within the flexibility window of zeolites
By treating idealized zeolite frameworks as periodic mechanical trusses, we
show that the number of flexible folding mechanisms in zeolite frameworks is
strongly peaked at the minimum density end of their flexibility window. 25 of
the 197 known zeolite frameworks exhibit an extensive flexibility, where the
number of unique mechanisms increases linearly with the volume when long
wavelength mechanisms are included. Extensively flexible frameworks therefore
have a maximum in configurational entropy, as large crystals, at their lowest
density. Most real zeolites do not exhibit extensive flexibility, suggesting
that surface and edge mechanisms are important, likely during the nucleation
and growth stage. The prevalence of flexibility in real zeolites suggests that,
in addition to low framework energy, it is an important criterion when
searching large databases of hypothetical zeolites for potentially useful
realizable structures.Comment: 11 pages, 3 figure
On the elastic constants of the zeolite chlorosodalite
The use of force-field based molecular modeling to predict the elastic constants of the zeolite chlorosodalite is described. Theoretical predictions of the on-axis and off-axis elastic constants strongly suggest that an error exists in the published elastic constants of the material. When the previous experimental data are corrected by transposing the published directional ultrasound velocities, excellent agreement is observed between the off-axis plots of sodalite produced by experiment and modeling. Further confirmation of the prediction is supplied by considering the Zener ratios of other inorganic materials that possess cubic symmetry. ©2006 American Institute of Physics
Canterbury game industry action plan 2022
This report reviews the video game and interactive media industry landscape, and is intended for game studios, local and international investors in the games industry, regional policy makers, central government, local government agencies, Christchurch City Council, and sector stakeholders
In vitro assessment of adsorbents aiming to prevent deoxynivalenol and zearalenone mycotoxicoses
The high prevalence of the Fusarium mycotoxins, deoxynivalenol (DON) and zearalenone (ZON) in animal feeds in mild climatic zones of Europe and North America results in considerable economic losses, as these toxins affect health and productivity particularly of pigs from all age groups. The use of mycotoxin adsorbents as feed additives is one of the most prominent approaches to reduce the risk for mycotoxicoses in farm animals, and to minimise carry-over of mycotoxins from contaminated feeds into foods of animal origin. Successful aflatoxin adsorption by means of different substances (phyllosilicate minerals, zeolites, activated charcoal, synthetic resins or yeast cell-wall-derived products) has been demonstrated in vivo and in vitro. However, attempts to adsorb DON and ZON have been less encouraging. Here we describe the adsorption capacity of a variety of potential binders, including compounds that have not been evaluated before, such as humic acids. All compounds were tested at realistic inclusion levels for their capacity to bind ZON and DON, using an in vitro method that resembles the different pH conditions in the gastro-intestinal tract of pigs. Mycotoxin adsorption was assessed by chemical methods and distinct bioassays, using specific markers of toxicity as endpoints of toxicity in cytological assays. Whereas none of the tested substances was able to bind DON in an appreciable percentage, some of the selected smectite clays, humic substances and yeast-wall derived products efficiently adsorbed ZON (>70%). Binding efficiency was indirectly confirmed by the reduction of toxicity in the in vitro bioassays. In conclusion, the presented test protocol allows the rapid screening of potential mycotoxin binders. Like other in vitro assays, the presented protocol combining chemical and biological assays cannot completely simulate the conditions of the gastro-intestinal tract, and hence in vivo experiments remain mandatory to assess the efficacy of mycotoxin binders under practical conditions
Do Leaf Cutting Ants Cut Undetected? Testing the Effect of Ant-Induced Plant Defences on Foraging Decisions in Atta colombica
Leaf-cutting ants (LCAs) are polyphagous, yet highly selective herbivores. The factors that govern their selection of food plants, however, remain poorly understood. We hypothesized that the induction of anti-herbivore defences by attacked food plants, which are toxic to either ants or their mutualistic fungus, should significantly affect the ants' foraging behaviour. To test this “induced defence hypothesis,” we used lima bean (Phaseolus lunatus), a plant that emits many volatile organic compounds (VOCs) upon herbivore attack with known anti-fungal or ant-repellent effects. Our results provide three important insights into the foraging ecology of LCAs. First, leaf-cutting by Atta ants can induce plant defences: Lima bean plants that were repeatedly exposed to foraging workers of Atta colombica over a period of three days emitted significantly more VOCs than undamaged control plants. Second, the level to which a plant has induced its anti-herbivore defences can affect the LCAs' foraging behaviour: In dual choice bioassays, foragers discriminated control plants from plants that have been damaged mechanically or by LCAs 24 h ago. In contrast, strong induction levels of plants after treatment with the plant hormone jasmonic acid or three days of LCA feeding strongly repelled LCA foragers relative to undamaged control plants. Third, the LCA-specific mode of damaging leaves allows them to remove larger quantities of leaf material before being recognized by the plant: While leaf loss of approximately 15% due to a chewing herbivore (coccinelid beetle) was sufficient to significantly increase VOC emission levels after 24 h, the removal of even 20% of a plant's leaf area within 20 min by LCAs did not affect its VOC emission rate after 24 h. Taken together, our results support the “induced defence hypothesis” and provide first empirical evidence that the foraging behaviour of LCAs is affected by the induction of plant defence responses
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