The effect of grasses grown for seed in mixture with legumes on the incidence of weeds and soil nitrogen content

This report was presented at the UK Organic Research 2002 Conference on behalf of the Colloquium of Organic Researchers (COR). The incidence of weeds and the content of soil nitrogen were investigated in the first year of a field trial with organic grass seed production in which the grasses were grown with companion legumes. Two grass species, timothy (Phleum pratense L.) cv. Sobol and perennial ryegrass (Lolium perenne L.) cv. Baca, were tested together with three legumes: red clover (Trifolium pratense L.) cv. Start, white clover (Trifolium repens L.) cv. Vysocan and black medick (Medicago lupulina L.) cv. Ekola. The N-nutrition and control of weeds were provided by three “ecological” methods and a conventional one (bacterial nodules of legumes, mulch, organic manure and mineral fertilizer). Plots with red clover had the lowest number of weeds, those with black medick the highest. Perennial ryegrass was more competitive than timothy against weeds and the companion legume. Soil nitrogen was highest in plots with white clover and red clover. During the vegetative period the level of soil nitrogen increased in the combinations with red clover, stayed the same in combinations with white clover, but decreased in those with black medick and in control plots

Planar Resonators for Metamaterials

This paper presents the results of an investigation into a combination of electric and magnetic planar resonators in order to design the building element of a volumetric metamaterial showing simultaneously negative electric and magnetic polarizabilities under irradiation by an electromagnetic wave. Two combinations of particular planar resonators are taken into consideration. These planar resonators are an electric dipole, a split ring resonator and a double H-shaped resonator. The response of the single resonant particle composed of a resonator with an electric response and a resonator with a magnetic response is strongly anisotropic. Proper spatial arrangement of these particles can make the response isotropic. This is obtained by proper placement of six planar resonators on the surface of a cube that now represents a metamaterial unit cell. The cells are distributed in space with 3D periodicity

Universal Generator of Ultra-Wideband Pulses

An Ultra-Wideband (UWB) subnanosecond pulse generator is described in this paper. High amplitude Gaussian pulses are generated by a Step Recovery Diode (SRD) included in a novel pulse forming circuit. The pro-posed circuit solution utilizes the performance of the SRD effectively, without excessive requirements regarding the driver section of the generator. Monocycle pulses are then generated by an additional pulse forming network. A sim-ple transistor driver is also described, which transforms a TTL trigger signal to a driving pulse with the timing and amplitude parameters required by the SRD. Measurement results are presented, which show the proposed generator operating with stable output pulse parameters at arbitrary pulse repetition frequency up to 20 MHz. The generated monocycle pulses are 25 V in amplitude and approximately 500 ps in width

New Planar and Volume Versions of a Metamaterial

Some characteristics of materials with negative permittivity and permeability, i.e., with a negative refrative index, known as metamaterials, are presented in this paper. Dispersion characteristics of left-handed parallel strips calculated by different methods are compared with each other. The calculated and measured dispersion and transmission characteristics of a newly proposed left-handed coplanar waveguide and of a novel volume metmaterial are shown. Simple equivalent circuits of both structures are presented together with elements values. The structures exhibit a negative refractive index in a wide frequency band

Ni and Ni Silicides Ohmic Contacts on N-type 6H-SiC with Medium and Low Doping Level

Ni silicides contacts, which are expected to be advantageous contact materials on SiC, were tested in this work. Prepared contact structures were ohmic with low contact resistivity approximately 8×10-4 Ω cm2 after annealing at 960°C as far as the SiC substrate with a medium doping level was concerned, no matter whether Ni or Ni silicides were used. At lower annealing temperatures, only Schottky behavior was observed by means of I-V characteristics measurements. In the case of SiC substrate with a low doping level, the behavior differed. It was necessary to anneal the structures at 1070°C to see ohmic behavior appearing with resistivities reaching 8×10-3 Ω cm2 and this was valid only for Ni and Ni2Si. Raman spectroscopy measurements confirmed formation of single Ni silicides as expected. It was found that Ni silicides can keep as good resistivity as Ni contacts while they interact with SiC in limited way and their undesirable drop-like morphology is expected to be overcome for example with a covering layer

Isotropic Single Negative Metamaterials

This paper presents the application of simple, and therefore cheap, planar resonators for building 3D isotropic metamaterials. These resonators are: a broadside-coupled split ring resonator with a magnetic response providing negative permeability; an electric dipole terminated by a loop inductor together with a double H-shaped resonator with an electric response providing negative permittivity. Two kinds of 3D isotropic single negative metamaterials are reported. The first material consists of unit cells in the form of a cube bearing on its faces six equal planar resonators with tetrahedral symmetry. In the second material, the planar resonators boxed into spherical plastic shells and randomly distributed in a hosting material compose a real 3D volumetric metamaterial with an isotropic response. In both cases the metamaterial shows negative permittivity or permeability, according to the type of resonators that are used. The experiments prove the isotropic behavior of the cells and of the metamaterial specimens

Генезис либерализма и прагматизма в современном образовании

В статье представлен анализ возможности комплементарного сочетания двух базовых образовательных стратегий в системе высшего образования. Актуальность исследования обусловлена коренными изменениями, происходящими в мировом образовательном пространстве. В современном обществе ключевую роль играет уже не знание как абсолютная истина, которым с необходимостью должен овладеть человек в процессе обучения, а, скорее, информация, в которой нам необходимо научиться ориентироваться. Это, в свою очередь, приводит к изменениям в понимании задачи образования. В частности, становится необходимым сделать акцент не только на раз- витии профессиональных, компетентностных, но и социокультурных навыков студентов. На данный момент достаточно сложно выделить в образовательном процессе какую- либо ключевую, системообразующую и оригинальную идею, которая была бы понята и принята как в современной Европе, так и в России. Цель работы: проанализировать генезис и специфику либерального и прагматического подходов в современных образовательных системах, выявить общее и отличное, а также показать возможность и перспективы их гармоничного сочетания в современном университете. Методы исследования: основу работы составляет междисциплинарный метод, который формируется посредством синтеза методологических принципов: философского анализа, социологических методов, принципа историзма. Результаты: обосновано, что одним из важнейших условий продуктивного развития современного университета является сочетание либеральной и прагматической стратегий образовательного процесса. Первая связана с социокультурной миссией университета, последняя - с потребностями современного общества. The paper shows the analysis of the possibilities of complemental unity of two basic educational strategies in higher education system. We argue that leading modern universities are educational and training ones. The global changes in higher education have happened. In the modern society, knowledge plays a key role but not as the absolute truth, which people must obtain in the learning process, rather the information that we need to learn to navigate. This leads to the change in the understanding of the problem of education. In today's world the emphasis should be put not only on the development of professional competency, but also on socio-cultural skills of students. At the moment, it is quite difficult to point out a key, system and original idea in the educational process that would be understood and accepted both in modern Europe and Russia. The main aim of the study is to reveal the specifics of liberal and pragmatic approaches in the modern education systems, to identify something common and different, as well as to demonstrate the possibility of their harmonious combination at a modern university. Methods. The authors have applied interdisciplinary principle, which is formed by the synthesis of the methodological principles: philosophical analysis, sociological methods, principle of historicism. Results. The authors acknowledged that there are several trends in higher education today: multilevel system; modern information technologies; distant educational system and development; university complexes; new educational standards; new educational technologies and management structures, etc. We at the same time argue that there are at least two systems (tendencies) in the theory of university development: liberal and pragmatic. The former is connected with educational university's mission; the later is related with the needs of the modern society

Geographical range in liverworts: does sex really matter?

AimWhy some species exhibit larger geographical ranges than others remains a fundamental, but largely unanswered, question in ecology and biogeography. In plants, a relationship between range size and mating system was proposed over a century ago and subsequently formalized in Baker's Law. Here, we take advantage of the extensive variation in sexual systems of liverworts to test the hypothesis that dioecious species compensate for limited fertilization by producing vegetative propagules more commonly than monoecious species. As spores are assumed to contribute to random long-distance dispersal, whereas vegetative propagules contribute to colony maintenance and frequent short-distance dispersal, we further test the hypothesis that monoecious species exhibit larger geographical ranges than dioecious ones.LocationWorldwide.MethodsWe used comparative phylogenetic methods to assess the correlation between range size and life history traits related to dispersal, including mating systems, spore size and production of specialized vegetative propagules.ResultsNo significant correlation was found between dioecy and production of vegetative propagules. However, production of vegetative propagules is correlated with the size of geographical ranges across the liverwort tree of life, whereas sexuality and spores size are not. Moreover, variation in sexual systems did not have an influence on the correlation between geographical range and production of asexual propagules.Main conclusionsOur results challenge the long-held notion that spores, and not vegetative propagules, are involved in long-distance dispersal. Asexual reproduction seems to play a major role in shaping the global distribution patterns of liverworts, so that monoecious species do not tend to display, on average, broader distribution ranges than dioecious ones. Our results call for further investigation on the spatial genetic structure of bryophyte populations at different geographical scales depending on their mating systems to assess the dispersal capacities of spores and asexual propagules and determine their contribution in shaping species distribution ranges

Synthesis of Graphene on Metal/SiC Structure

The chapter deals with the synthesis of graphene on metal/SiC substrates. The graphene synthesis is pursued at a relatively low temperature. The method can be used for the graphene transfer from SiC to dielectric materials. Annealing of the structure results in a chemical reaction of a metal with SiC forming silicides and carbon-rich products at the boundary between metal and silicon carbide. Carbon atoms segregate at the top of metal/metal silicide layer during the cooling period of the process. The chapter is divided into the following sections: Introduction, Structure preparation, Graphene preparation from the structure Ni/SiC, Graphene preparation from the structure Co/SiC, Application of other metals, Influence of additive materials, and Conclusion

An FET-Based Unit Cell for an Active Magnetic Metamaterial

A particle that can be used to create an active magnetic metamaterial has been designed using an FET transistor loaded in its gate by a conducting ring and in its source by a parallel resonance circuit. The design procedure is discussed and the working principle is experimentally demonstrated in the RF range.Comment: 4 pages, 6 figure