Complex multicolor tilings and critical phenomena in tetraphilic liquid crystals     

Zeng X  Kieffer R  Glettner B  Nürnberger C  Liu F  Pelz K  Prehm M  Baumeister U  Hahn H  Lang H  Gehring GA  Weber CH  Hobbs JK  Tschierske C  Ungar G 《Science (New York, N.Y.)》2011,331(6022):1302-1306

T-shaped molecules with a rod-like aromatic core and a flexible side chain form liquid crystal honeycombs with aromatic cell walls and a cell interior filled with the side chains. Here, we show how the addition of a second chain, incompatible with the first (X-shaped molecules), can form honeycombs with highly complex tiling patterns, with cells of up to five different compositions ("colors") and polygonal shapes. The complexity is caused by the inability of the side chains to separate cleanly because of geometric frustration. Furthermore, a thermoreversible transition was observed between a multicolor (phase-separated) and a single-color (mixed) honeycomb phase. This is analogous to the Curie transition in simple and frustrated ferro- and antiferromagnets; here spin flips are replaced by 180° reorientations of the molecules.  相似文献   

Impact of land-use type and harvesting on population structure of a non-timber forest product-providing tree in a semi-arid savanna, West Africa     

Katharina Schumann  Rüdiger Wittig  Adjima Thiombiano  Ute Becker  Karen Hahn 《Biological conservation》2011,144(9):2369-2376

Non-timber forest products (NTFPs) strongly contribute to livelihood security in the semi-arid tropics. Main factors determining the populations of NTFP-providing species are human activities. This study examined the impact of land-use, combined with rates and patterns of debarking and chopping on a NTFP-providing tree (Anogeissus leiocarpa) in Burkina Faso. We compared stands in a protected area (W National Park) with those of its surrounding communal area (fallows, croplands) in order to (i) obtain an indication on the status of the population, (ii) assess its harvesting tolerance, (iii) estimate the sustainability of present management, and (iv) derive which additional management strategies may foster its conservation. Our results reveal that the stands of A. leiocarpa are in healthy states in fallows and in the park. In croplands, the absence of saplings gives evidence of a declining population. Nearly all individuals of A. leiocarpa were harvested in croplands and fallows, while the number of harvested individuals in the park was negligible. Intensity of debarking and chopping was tree size-specific. The sprouting ability significantly increased with higher chopping intensity. We conclude that despite the land-use impact and the intense harvesting, stands of A. leiocarpa are still well preserved due to the species life history (fast growing and high sprouting) and due to indirect positive influences of human activities by providing better environmental conditions for its recruitment. Thus, the population of A. leiocarpa is not at risk to over-harvesting and land-use even though it is not protected.  相似文献   

Carbon and nitrogen degradation on molecular scale of grass-derived pyrogenic organic material during 28 months of incubation in soil     

André Hilscher  Heike Knicker 《Soil biology & biochemistry》2011,43(2):261-270

The present study focuses on the microbial recalcitrance of pyrogenic organic material (PyOM) on a molecular scale. We performed microcosm incubation experiments using ¹³C- and ¹⁵N-enriched grass-derived PyOM mixed with a sub soil material taken from a Haplic Cambisol. Solid-state ¹³C and ¹⁵N NMR studies were conducted to elucidate the humification processes at different stages of PyOM degradation. The chemical structure of the remaining PyOM after incubation was clearly different from the initial pyrogenic material. The proportion of O-containing functional groups was increased, whereas that of aryl C and of N-containing heterocyclic structures had decreased, probably due to mineralisation and conversion to other C and N groups. After 20 months of incubation the aryl C loss reached up to 40% of the initial amount and up to 29% of the remaining PyOM C was assigned to carboxyl/carbonyl C and O-aryl C. These reactions alter the chemical and physical properties of the char residue and make it more available for further microbial attack but also for adsorption processes. Our study presents direct evidence for the degradation of N-heterocyclic domains in charred plant remains adding new aspects to the understanding of the N cycling in fire-affected ecosystems.  相似文献   

A rapid and simple method for determining fungicide resistance in Botrytis     

Weber  Roland W. S.  Hahn  Matthias 《植物病害和植物保护杂志》2011,118(1):17-25

A simple test based on the germination of conidia of Botrytis on agar media augmented with various fungicides has been developed. Average concentrations causing a 50% reduction of germ-tube growth (EC₅₀) of highly sensitive isolates were determined on 1% malt extract agar (thiophanate-methyl 0.090 ppm; iprodione 0.566 ppm; fludioxonil 0.026 ppm; fenhexamid 0.144 ppm), 1% malt extract agar with 100 ppm salicyl hydroxamic acid (QoI fungicides, viz. trifloxystrobin 0.009 ppm; pyraclostrobin 0.013 ppm; azoxystrobin 0.087 ppm), 0.5% yeast extract agar (boscalid 0.069 ppm) and 0.5% sucrose agar (cyprodinil 0.053 ppm). In order to detect different levels of resistance against these various fungicides, two discriminatory concentrations were identified for each compound. A routine assay method was developed in which drops of a conidial suspension harvested directly from diseased plant material or sporulating cultures were incubated on each of 20 different agar media. Because of a very short time-span of 24–48 h between sample collection and evaluation of results, field-specific information on the occurrence, frequency and types of resistance of Botrytis against common botryticides in soft-fruit production may be generated prior to the main fungicide spray season at blossom time.

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Variability of the quality and quantity of organic matter in soil affected by multiple wildfires     

María López-Martín  Marta Velasco-Molina  Heike Knicker 《Journal of Soils and Sediments》2016,16(2):360-370

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Der Einfluß künstlicher vertikaler Grobporen in einer verdichteten Bodenmatrix auf das Wachstum von Winterweizen II. Wachstum von Winterweizen auf einem primären Pseudogley     

Heike Bohne 《植物养料与土壤学杂志》1991,154(1):63-67

The influence of artificial vertical macropores in a compacted soil on the growth of winterwheat. II. Growth of winterwheat on a pseudogley In a pseudogley the effect of artificial vertical macropores in a compacted structure was compared to a compacted structure without artificial vertical macropores and to a loosened structure. Only in a very wet year (830 mm precipitation), water extraction and yield were positively influenced by the artificial vertical macropores in the compacted structure. Compared to the compacted structure without artificial macropores, where most of the water was extracted from the upper 25 cm of the soil, with vertical macropores most water was extracted from the depth 25–50 cm. In a dry year (700 mm precipitation), the difference in water extraction between the compacted structures with and without vertical macropores was only small. Most water was extracted from the loosened structure, but yield was reduced compared to both compacted structures. However, in the dry year, water extraction from the compacted structure without artificial macropores was uniform for the depth 0–50 cm, whereas for the structure with artificial macropores and for the loosened structure most water was extracted from the depth 0-25 cm. Neither in the wet nor in the dry year, vertical root extension was increased by the vertical macropores, but in the wet year root mass was positively influenced by the vertical macropores.  相似文献   

Fate of Protozoa transiting the digestive tract of the earthworm Lumbricus terrestris L.     

Houjian CaiBoris Zarda  Geoffrey R. Mattison  Frank SchönholzerDittmar Hahn 《Pedobiologia》2002,46(2):161-175

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Vincristine sulfate as single-agent chemotherapy in a dog and a cat with malignant neoplasms     

K A Hahn 《Journal of the American Veterinary Medical Association》1990,197(4):504-506

A 12-year-old 4-kg spayed domestic shorthair cat with a poorly differentiated fibrosarcoma of the rostral aspect of the mandible and an 11-year-old 13-kg castrated dog of mixed breeding with pulmonary metastatic hemangiosarcoma were treated with 0.5 mg of vincristine sulfate/m2 of body surface, IV, weekly. Three months after beginning treatment, both animals had complete clinical remission. The role of this vinca alkaloid as a single agent for malignant neoplasms has seldom been discussed in the veterinary scientific literature. The results of these two cases indicate that single-agent vincristine sulfate chemotherapy is effective in the treatment of feline fibrosarcoma and canine hemangiosarcoma.  相似文献   

Attempts at sex determination on 6- and 7- day old cattle embyros     

L A Moustafa  J Hahn  R Roselius 《Berliner und Münchener tier?rztliche Wochenschrift》1978,91(12):236-238

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Cultural demonstration of Campylobacter fetus subspecies fetus in preputial rinsing samples from insemination and breeding bulls     

H Stadtfeld  E Nitzschke  W Hahn  A Konz 《Berliner und Münchener tier?rztliche Wochenschrift》1982,95(20):393-397

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