12,772 research outputs found
Corporate Hierarchies and the Size of Nations: Theory and Evidence
Corporate organization varies within a country and across countries with country size. The paper starts by establishing some facts about corporate organization based on unique data of 660 Austrian and German corporations. The larger country (Germany) has larger firms with flatter more decentral corporate hierarchies compared to the smaller country (Austria). Firms in the larger country change their organization less fast than firms in the smaller country. Over time firms have been introducing less hierarchical organizations by delegating power to lower levels of the corporation. We develop a theory which explains these facts and which links these features to the trade environment that countries and firms face. We introduce firms with internal hierarchies in a Krugman (1980) model of trade. We show that international trade and the toughness of competition in international markets induce a power struggle in firms which eventually leads to decentralized corporate hierarchies. We offer econometric evidence which is consistent with the models predictions
Quantum Theory of a Resonant Photonic Crystal
We present a quantum model of two-level atoms localized in a 3D lattice,
based on the Hopfield theory of exciton polaritons. In addition to a
polaritonic gap at the exciton energy, a photonic bandgap opens up at the
Brillouin zone boundary. Upon tuning the lattice period or angle of incidence
to match the photonic gap with the exciton energy, one obtains a combined
polaritonic and photonic gap as a generalization of Rabi splitting. For typical
experimental parameters, the size of the combined gap is on the order of 25
cm^{-1}, up to 10^5 times the detuned gap size. The dispersion curve contains a
branch supporting slow-light modes with vanishing exciton probability density.Comment: 4 pages, 3 figure
Reflection-Free One-Way Edge Modes in a Gyromagnetic Photonic Crystal
We point out that electromagnetic one-way edge modes analogous to quantum
Hall edge states, originally predicted by Raghu and Haldane in 2D gyroelectric
photonic crystals possessing Dirac point-derived bandgaps, can appear in more
general settings. In particular, we show that the TM modes in a gyromagnetic
photonic crystal can be formally mapped to electronic wavefunctions in a
periodic electromagnetic field, so that the only requirement for the existence
of one-way edge modes is that the Chern number for all bands below a gap is
non-zero. In a square-lattice gyromagnetic Yttrium-Iron-Garnet photonic crystal
operating at microwave frequencies, which lacks Dirac points, time-reversal
breaking is strong enough that the effect should be easily observable. For
realistic material parameters, the edge modes occupy a 10% band gap. Numerical
simulations of a one-way waveguide incorporating this crystal show 100%
transmission across strong defects, such as perfect conductors several lattice
constants wide, larger than the width of the waveguide.Comment: 4 pages, 3 figures (Figs. 1 and 2 revised.
Resonant X-ray diffraction studies on the charge ordering in magnetite
Here we show that the low temperature phase of magnetite is associated with
an effective, although fractional, ordering of the charge. Evidence and a
quantitative evaluation of the atomic charges are achieved by using resonant
x-ray diffraction (RXD) experiments whose results are further analyzed with the
help of ab initio calculations of the scattering factors involved. By
confirming the results obtained from X-ray crystallography we have shown that
RXD is able to probe quantitatively the electronic structure in very complex
oxides, whose importance covers a wide domain of applications.Comment: 4 pages 4 figures, accepted for publication in PR
Study of a crankshaft material destruction mechanism of forced diesels
При действии знакопеременных напряжений в материале коленчатого вала возникает усталостная трещина, постепенно проникающая вглубь изделия.
При переменных деформациях края усталостной трещины сближаются, образуя притертую, гладкую зону излома. По мере развития трещины рабочая площадь сечения ослабляется. Что ведет к разрушению элемента коленчатого вала при эксплуатации. Повышение запаса усталостной прочности объясняется двумя основными причинами: благоприятным влиянием сжимающих начальных технологических остаточных напряжений и улучшением механических свойств поверхностного слоя в результате поверхностного пластического деформирования.During sign-variable tension in a material of a cranked shaft there is the fatigue crack can occur, which is gradually getting deep into a product. Variable deformations
produce smooth zone of a break within the material. It leads to destruction of a
cranked shaft while working. Increase of a stock of fatigue durability speaks two main reasons: beneficial effect of compressing initial technological residual tension and improvement of mechanical properties of a blanket as a result of superficial plastic deformation
Optically Thin Metallic Films for High-radiative-efficiency Plasmonics
Plasmonics enables deep-subwavelength concentration of light and has become
important for fundamental studies as well as real-life applications. Two major
existing platforms of plasmonics are metallic nanoparticles and metallic films.
Metallic nanoparticles allow efficient coupling to far field radiation, yet
their synthesis typically leads to poor material quality. Metallic films offer
substantially higher quality materials, but their coupling to radiation is
typically jeopardized due to the large momentum mismatch with free space. Here,
we propose and theoretically investigate optically thin metallic films as an
ideal platform for high-radiative-efficiency plasmonics. For far-field
scattering, adding a thin high-quality metallic substrate enables a higher
quality factor while maintaining the localization and tunability that the
nanoparticle provides. For near-field spontaneous emission, a thin metallic
substrate, of high quality or not, greatly improves the field overlap between
the emitter environment and propagating surface plasmons, enabling high-Purcell
(total enhancement > ), high-quantum-yield (> 50 %) spontaneous emission,
even as the gap size vanishes (35 nm). The enhancement has almost
spatially independent efficiency and does not suffer from quenching effects
that commonly exist in previous structures.Comment: Supporting Information not included but freely available from
DOI:10.1021/acs.nanolett.6b0085
Zoneamento agrícola de riscos climáticos da laranja no Estado de São Paulo.
O presente estudo teve como objetivo realizar um zoneamento climático observando os riscos para o estado de São Paulo no que se refere ao cultivo de laranja. Os resultados foram obtidos através da análise do déficit hídrico médio anual, temperaturas médias anuais e precipitações médias anuais. Essas variáveis foram extraídas do banco de dados da Embrapa Informática Agropecuária. Entretanto, os dados do déficit hídrico foram calculados pelo método de THORNTHWAITE e MATHER (1955), corrigido por CAMARGO et al. (1999). As localidades foram classificadas de acordo com as exigências climáticas de cada cultura, dentro de um ambiente de Sistema de Informação Geográfica (SIG), que produziu mapas de riscos climáticos através de espacialização e interpolação. O zoneamento de riscos mostrou que as regiões do noroeste e litoral do estado de São Paulo possuem alto risco climático para a produção de laranja. Os resultados podem auxiliar em novos estudos desta cultura importante do agronegócio brasileiro.CBA 2009
Zoneamento de riscos climáticos para a dendeicultura no Brasil.
Neste presente trabalho obtiveram-se os resultados do zoneamento de riscos climáticos da cultura do dendê no Brasil. Utilizando os parâmetros climáticos como a temperatura média anual, precipitação média anual e déficit hídrico, puderam-se analisar e espacializar os dados através de um Sistema de Informações Geográficas. Além disso, foi utilizada a máscara do Shutlle Radar Topography Mission (SRTM) para ajustes no relevo. Segundo o método de THORNTHWAITE e MATHER (1955), corrigido por CAMARGO et al. (1999), foram calculados os dados de déficit hídrico. Desta forma, o trabalho teve como principais resultados obtidos, o mapa com a malha municipal de aptidão climática discretizado por classes de riscos. Através desses resultados, observou-se baixo risco climático para estados já produtores como a Bahia, Pará e Amazonas, além de potenciais áreas produtoras como o litoral do nordeste e parte do Rio de Janeiro. Os resultados podem auxiliar no suporte a expansão dessa oleaginosa em território nacional, visto a importância dessa cultura como fonte de biodiesel.CBA 2009
- …