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Ubergangsmetallcarbene sind bereits seit 50 Jahren bekannt und haben eine breite Anwendung als Reagentien und Katalysatoren in der organischen Synthese gefunden. Die Carbenchemie der Seltenerdmetalle ist dagegen noch recht wenig untersucht und erst in den letzten Jahren in den Fokus der Forschung geruckt. Vor allem Seltenerdmetallalkylidenverbindungen, insbesondere Methylidenkomplexe, sind eine aufstrebende Verbindungsklasse mit einem hohen Potential fur die Organometallchemie und moglicherweise kunftig fur die organische Synthese.

The treatment of the recently reported potassium salt (S)-N,N'-bis-(1-phenylethyl)benzamidinate ((S)-KPEBA) and its racemic isomer (rac-KPEBA) with anhydrous lanthanide trichlorides (Ln = Sm, Er, Yb, Lu) afforded mostly chiral complexes. The tris(amidinate) complex [{(S)-PEBA}(3)Sm], bis(amidinate) complexes [{Ln(PEBA)(2)(μ-Cl)}(2)] (Ln = Sm, Er, Yb, Lu), and mono(amidinate) compounds [Ln(PEBA)(Cl)(2)(thf)(n)] (Ln = Sm, Yb, Lu) were isolated and structurally characterized. As a result of steric effects, the homoleptic 3:1 complexes of the smaller lanthanide atoms Yb and Lu were not accessible. Furthermore, chiral bis(amidinate)-amido complexes [{(S)-PEBA}(2)Ln{N(SiMe(3))(2)}] (Ln = Y, Lu) were synthesized by an amine-elimination reaction and salt metathesis. All of these chiral bis- and tris(amidinate) complexes had additional axial chirality and they all crystallized as diastereomerically pure compounds. By using rac-PEBA as a ligand, an achiral meso arrangement of the ligands was observed. The catalytic activities and enantioselectivities of [{(S)-PEBA}(2)Ln{N(SiMe(3))(2)}] (Ln = Y, Lu) were investigated in hydroamination/cyclization reactions. A clear dependence of the rate of reaction and enantioselectivity on the ionic radius was observed, which showed higher reaction rates but poorer enantioselectivities for the yttrium compound.

Rosenberg, David E., Kelly Kopp, Heidi A. Kratsch, Larry Rupp, Paul Johnson, and Roger Kjelgren, 2011. Value Landscape Engineering: Identifying Costs, Water Use, Labor, and Impacts to Support Landscape Choice. Journal of the American Water Resources Association (JAWRA) 47(3):635-649. DOI: 10.1111/j.1752-1688.2011.00530.x Abstract: We present a spreadsheet model that identifies the costs, water, labor, fertilizer, pesticides, fuel, energy, carbon emissions, and particulates required of and generated by a user-specified residential or commercial landscape over its economic life. This life includes site preparation, materials purchase, installation, annual maintenance and replacing landscape features that wear out or die. Users provide a variety of site-descriptive information and the model queries an extensive database of landscape data to calculate costs, required inputs, and impacts. We verified model results against observations of water, labor, fertilizer, and fuel use over eight years at three landscapes in the Salt Lake City, Utah metropolitan region. We use the model to show tradeoffs in costs and required inputs for a predominately cool-season turfgrass landscape typical for Salt Lake City and other high desert, intermountain western United States cities and potential modifications to that typical landscape. Results highlight strategies water conservation programs can use to encourage property owners to install and adopt water-conserving landscape features and practices. Residential and commercial landscapers, landscape architects, contractors, and property owners can also model current and proposed landscapes and use results to identify a low-cost, low-input landscape that achieves their client’s or their own goals and values.

Alnus maritima is a shrub that associates with N 2 -fixing Frankia in the wetlands in which it is native. Despite low concentrations in waterlogged soils, O 2 is critical to the maintenance of this symbiosis, and Frankia -infected nodules exist on roots of plants in native stands. The objective of the present study was to determine how root-zone O 2 concentration influences N 2 fixation and the anatomy of nodules on A. maritima . Root zones of plants inoculated with soil from native stands were exposed to eight O 2 concentrations. Nitrogenase activity increased with increasing O 2 concentration. Photosynthetic rate, plant dry mass, leaf N content, and nodule fresh mass were maximal in plants maintained with 15‐25% O 2 in the root zone. Nodule counts were maximal on roots maintained at 10% and above 25% O 2 , and nodules that developed at £ 2% O 2 were < 2 mm in diameter and single-lobed. Mean total area of air spaces within nodules decreased, and mean area per space increased, with increasing O 2 concentration. Seasonal and O 2 -dependent nodule pigmentation was observed. Our data illustrate that O 2 is critical to the development of functional symbioses, and that nodules of this species, which are submersed in nature, possess mechanisms for responding to their low-O 2 environment.

Transition-metal carbene complexes have been known for about 50 years and widely applied as reagents and catalysts in organic transformations. In contrast, the carbene chemistry of the rare-earth metals is much less developed, but has attracted the research interest in the recent years. In this field rare-earth-metal alkylidene, especially methylidene, compounds are an emerging class of compounds with a high synthetic potential for organometallic chemistry and maybe in the future also for organic chemistry.

OBJECTIVE Children with β-thalassaemia major (β-thal) frequently have growth retardation in the presence of low serum IGF-I and a normal GH response to pharmacological stimulation suggesting that they have GH insensitivity (GHIS). This study was carried out to study the cause of their growth retardation. DESIGN We studied IGF-I and IGFBP-3 generation after exogenous GH administration for four days, in 15 prepubertal controls (C) and 41 prepubertal β-thal patients divided into three groups according to their growth status: (Group 1) 15 with normal growth (N-thal) (Group 2) 16 with decelerated growth (D-thal) and (Group 3) 10 with short stature (S-thal), in order to determine whether GHIS is the cause of their growth retardation. MEASUREMENTS IGF-I and IGFBP-3 were measured daily, before and for 4 days after daily administration of 0·1 IU/kg hGH, in 3 groups of prepubertal β-thal patients and normal controls. RESULTS N-thal and C had similar basal serum IGF-I (142 ± 52 and 196 ± 56 ng/ml, respectively) and IGFBP-3 concentrations (2·07 ± 0·49 and 2·66 ± 0·41 mg/l, respectively) as well as a similar percent increase of IGF-I (101 ± 23% and 104 ± 37%, respectively) and IGFBP-3 (52 ± 36%, and 38 ± 14%, respectively) during the generation tests. S-thal and D-thal had significantly lower basal IGF-I and IGFBP-3 concentrations (85 ± 42 and 101 ± 36 ng/ml; and 1·60 ± 0·49 and 1·79 ± 0·52 mg/l, respectively) as compared to N-thal and C (P

Chilling injury to crop plants was first described 70 years ago and has been systematically investigated with electron microscopy since the late 1960s. Chloroplasts are the first and most severely impacted organelle. Thylakoids swell and distort, starch granules disappear, and a peripheral reticulum (vesicles arising from inner membrane of chloroplast envelope) appears. Chloroplast disintegration follows prolonged chilling. Mitochondria, nuclei and other organelles are less susceptible to chilling injury. Organellar development and ontogeny may also be disrupted. The inherent chilling sensitivity of a plant, as well as the ability of some species to acclimate to chilling, influence the timing and appearance of ultrastructural injury with the resulting outcome being mild, moderate, or severe. Other environmental factors that exacerbate injury are irradiance, chilling duration, and water status. The physiological basis for chloroplast swelling may be linked to chilling-stable starch-degrading enzymes that produce soluble sugars thus lowering stromal water potential at a time when chloroplast photosynthate export is reduced. Thylakoid dilation appears to be related to photo-oxidative conditions produced during chilling in the light. The peripheral reticulum is proposed to increase surface area of the transport-limiting membrane (chloroplast inner membrane) in response to the chilling-induced reduction in metabolite transport. Many of the ultrastructural symptoms appearing during moderate stress resemble those seen in programmed cell death. Future research directions are discussed.

Neighborhood-perfect graphs form a subclass of the perfect graphs if the Strong Perfect Graph Conjecture of C. Berge is true. However, they are still not shown to be perfect. Here we propose the characterization of neighborhood-perfect graphs by studying minimal non-neighborhood-perfect graphs (MNNPG). After presenting some properties of MNNPGs, we show that the only MNNPGs with neighborhood independence number one are the 3-sun and K. Also two further classes of neighborhood-perfect graphs are presented: line-graphs of bipartite graphs and a zfree cographs. 0 1996 John Wiley & Sons, Inc.

Standarddiskretisierungsverfahren sind zur Behandlung von konvektionsdominanten Problemen nicht geeignet, da insbesondere die Existenz von Grenzschichten zu Instabilitaten des diskreten Problems fuhrt. Wir suchen nach einem einfachen, gleichmasig stabilen Diskretisierungsverfahren der Ordnung 2 im zweidimensionalen Fall, fur das im globalen Gebiet keine Ordnungsreduktion eintritt, wenn der Storungsparameter gegen Null geht. Es zeigt sich, das es kaum moglich ist, bewahrte Schemata vom eindimensionalen auf den zweidimensionalen Fall zu ubertragen. Fur eine spezielle upwind-Technik jedoch kann die Inversmonotonie des diskreten Problems bewiesen werden. In the standard discretization of convection-dominated problems the existence of boundary layers produces oscillating discrete solutions which are not close to the exact solution. We look for a simple uniformly stable discretization method of order two in the two-dimensional case such that the order of accuracy does not degenerate in the global domain if the perturbation parameters tends do zero. It turns out that it is in general not possible to extend some well known schemes from the 1-D to the 2-D case. In particular we analyze a special upwind technique and prove the inverse-monotonicity of the discrete problem for this discretization technique.

For a graph G, the cochromatic number of G, denoted z(G), is the least m for which there is a partition of the vertex set of G having order m. where each part induces a complete or empty graph. We show that if {Gn} is a family of graphs where Gn has o(n2 log2(n)) edges, then z(Gn) = o(n). We turn our attention to dichromatic numbers. Given a digraph D, the dichromatic number of D is the minimum number of parts the vertex set of D must be partitioned into so that each part induces an acyclic digraph. Given an (undirected) graph G, the dichromatic number of G, denoted d(G), is the maximum dichromatic number of all orientations of G. Let m be an integer; by d(m) we mean the minimum size of all graphs G where d(G) = m. We show that d(m) = θ(m2 ln2(m)).

A novel approach has been employed to suspend highly porous alumina particles within the reticular structure of silicon carbide foam. The particles are slightly smaller than the reticular cells that they occupy, thereby permitting them to “rattle” freely when subjected to a gas stream. Potential applications include low-pressure-drop catalyst supports.

A simple method for dipcoating porous reticular carbon foam with aluminum oxide thin-film coatings is presented. Weight gain versus temperature and number of dipcoatings is presented along with scanning electron micrographs of uniform, adherent alumina thin films. Composite foam structures of up to 57% alumina have been prepared.