4,881 research outputs found
Towards Grower-friendly Apple Crop Thinning by Tree Shading
Light management with shading nets, which reduce sunlight by 74%, might be an
alternative to chemicals commonly used for thinning on apple trees. To study the effect of
shading on crop load and fruit quality, trials were conducted in field experiments with the
cultivars Golden Delicious and Elstar in 2006. Trees were either covered 25 days after full
bloom (DAFB) with a net during three days, or until the peak of fruit fall, observed after
seven days shading. Ideal time length for optimal crop yield was seven days shading for
Elstar and three days shading for Golden Delicious. Alternate bearing could be decreased
as flower initiation counts the following year showed. In both experiments, inner quality of
fruit such as sugar and firmness showed good values at optimal shading duration
compared with chemical + hand thinning. In 2007, a second field trial was conducted with
cultivars Golden Delicious and Topaz to study the time period for shading in further detail.
Shading was done for three days at 19, 26 and 33 DAFB using two net types (three- and
two-meter-net width, covering the trees entirely or only down to 50 cm above ground). For
Golden Delicious, shading after 19 and 26 days reduced fruits per 100 flower cluster to the
same extent as with chemical + hand thinning. There was no difference between the two
net types. For Topaz, shading after 19 days showed the best results. Regarding inner
quality of both cultivars, only sugar content for Golden Delicious could be significantly
improved after 19 and 26 days shading. Further analyses are still under way (e.g. for
acidity).
This study is part of an effort for increasing European consumption with fruit from
sustainable production systems, the ISAFRUIT-EU-project
Inferring Chemical Reaction Patterns Using Rule Composition in Graph Grammars
Modeling molecules as undirected graphs and chemical reactions as graph
rewriting operations is a natural and convenient approach tom odeling
chemistry. Graph grammar rules are most naturally employed to model elementary
reactions like merging, splitting, and isomerisation of molecules. It is often
convenient, in particular in the analysis of larger systems, to summarize
several subsequent reactions into a single composite chemical reaction. We use
a generic approach for composing graph grammar rules to define a chemically
useful rule compositions. We iteratively apply these rule compositions to
elementary transformations in order to automatically infer complex
transformation patterns. This is useful for instance to understand the net
effect of complex catalytic cycles such as the Formose reaction. The
automatically inferred graph grammar rule is a generic representative that also
covers the overall reaction pattern of the Formose cycle, namely two carbonyl
groups that can react with a bound glycolaldehyde to a second glycolaldehyde.
Rule composition also can be used to study polymerization reactions as well as
more complicated iterative reaction schemes. Terpenes and the polyketides, for
instance, form two naturally occurring classes of compounds of utmost
pharmaceutical interest that can be understood as "generalized polymers"
consisting of five-carbon (isoprene) and two-carbon units, respectively
Generic Strategies for Chemical Space Exploration
Computational approaches to exploring "chemical universes", i.e., very large
sets, potentially infinite sets of compounds that can be constructed by a
prescribed collection of reaction mechanisms, in practice suffer from a
combinatorial explosion. It quickly becomes impossible to test, for all pairs
of compounds in a rapidly growing network, whether they can react with each
other. More sophisticated and efficient strategies are therefore required to
construct very large chemical reaction networks.
Undirected labeled graphs and graph rewriting are natural models of chemical
compounds and chemical reactions. Borrowing the idea of partial evaluation from
functional programming, we introduce partial applications of rewrite rules.
Binding substrate to rules increases the number of rules but drastically prunes
the substrate sets to which it might match, resulting in dramatically reduced
resource requirements. At the same time, exploration strategies can be guided,
e.g. based on restrictions on the product molecules to avoid the explicit
enumeration of very unlikely compounds. To this end we introduce here a generic
framework for the specification of exploration strategies in graph-rewriting
systems. Using key examples of complex chemical networks from sugar chemistry
and the realm of metabolic networks we demonstrate the feasibility of a
high-level strategy framework.
The ideas presented here can not only be used for a strategy-based chemical
space exploration that has close correspondence of experimental results, but
are much more general. In particular, the framework can be used to emulate
higher-level transformation models such as illustrated in a small puzzle game
Integrated Vertical Bloch Line (VBL) memory
Vertical Bloch Line (VBL) Memory is a recently conceived, integrated, solid state, block access, VLSI memory which offers the potential of 1 Gbit/sq cm areal storage density, data rates of hundreds of megabits/sec, and submillisecond average access time simultaneously at relatively low mass, volume, and power values when compared to alternative technologies. VBLs are micromagnetic structures within magnetic domain walls which can be manipulated using magnetic fields from integrated conductors. The presence or absence of BVL pairs are used to store binary information. At present, efforts are being directed at developing a single chip memory using 25 Mbit/sq cm technology in magnetic garnet material which integrates, at a single operating point, the writing, storage, reading, and amplification functions needed in a memory. The current design architecture, functional elements, and supercomputer simulation results are described which are used to assist the design process
Quantum control of electron--phonon scatterings in artificial atoms
The phonon-induced dephasing dynamics in optically excited semiconductor
quantum dots is studied within the frameworks of the independent Boson model
and optimal control. We show that appropriate tailoring of laser pulses allows
a complete control of the optical excitation despite the phonon dephasing, a
finding in marked contrast to other environment couplings.Comment: to appear in Phys. Rev. Let
Non-volatile, high density, high speed, Micromagnet-Hall effect Random Access Memory (MHRAM)
The micromagnetic Hall effect random access memory (MHRAM) has the potential of replacing ROMs, EPROMs, EEPROMs, and SRAMs because of its ability to achieve non-volatility, radiation hardness, high density, and fast access times, simultaneously. Information is stored magnetically in small magnetic elements (micromagnets), allowing unlimited data retention time, unlimited numbers of rewrite cycles, and inherent radiation hardness and SEU immunity, making the MHRAM suitable for ground based as well as spaceflight applications. The MHRAM device design is not affected by areal property fluctuations in the micromagnet, so high operating margins and high yield can be achieved in large scale integrated circuit (IC) fabrication. The MHRAM has short access times (less than 100 nsec). Write access time is short because on-chip transistors are used to gate current quickly, and magnetization reversal in the micromagnet can occur in a matter of a few nanoseconds. Read access time is short because the high electron mobility sensor (InAs or InSb) produces a large signal voltage in response to the fringing magnetic field from the micromagnet. High storage density is achieved since a unit cell consists only of two transistors and one micromagnet Hall effect element. By comparison, a DRAM unit cell has one transistor and one capacitor, and a SRAM unit cell has six transistors
Saddles and Barrier in Landscapes of Generalized Search Operators
Barrier trees are a convenient way of representing the structure of complex combinatorial landscapes over graphs. Here we generalize the concept of barrier trees to landscapes defined over general multi-parent search operators based on a suitable notion of topological connectedness that depends explicitly on the search operator. We show that in the case of recombination spaces, path-connectedness coincides with connectedness as defined by the mutation operator alone. In contrast, topological connectedness is more general and depends on the details of the recombination operators as well. Barrier trees can be meaningfully defined for both concepts of connectedness
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