6,708 research outputs found
Narrowband Photon Pair Source for Quantum Networks
We demonstrate a compact photon pair source based on a periodically poled
lithium niobate nonlinear crystal in a cavity. The cavity parameters are chosen
such that the emitted photon pair modes can be matched in the region of telecom
ultra dense wavelength division multiplexing (U-DWDM) channel spacings. This
approach provides efficient, low-loss, mode selection that is compatible with
standard telecommunication networks. Photons with a coherence time of 8.6 ns
(116 MHz) are produced and their purity is demonstrated. A source brightness of
134 pairs(s.mW.MHz) is reported. The high level of purity and
compatibility with standard telecom networks is of great importance for complex
quantum communication networks
Some boundary effects in quantum field theory
We have constructed a quantum field theory in a finite box, with periodic
boundary conditions, using the hypothesis that particles living in a finite box
are created and/or annihilated by the creation and/or annihilation operators,
respectively, of a quantum harmonic oscillator on a circle. An expression for
the effective coupling constant is obtained showing explicitly its dependence
on the dimension of the box.Comment: 12 pages, Late
Semiclassical description of resonant tunneling
We derive a semiclassical formula for the tunneling current of electrons
trapped in a potential well which can tunnel into and across a wide quantum
well. The calculations idealize an experimental situation where a strong
magnetic field tilted with respect to an electric field is used. The resulting
semiclassical expression is written as the sum over special periodic orbits
which hit both walls of the quantum well and are perpendicular to the first
wall.Comment: LaTeX, 8 page
Effect of glyphosate on the microbial activity of two Brazilian soils.
Glyphosate [N-(phosphonomethyl)-glycine] is a broad-spectrum, non-selective, post-emergence herbicide that is widely used in agricultural. We studied, in vitro, changes in the microbial activity of typical Hapludult and Hapludox Brazilian soils, with and without applied glyphosate. Glyphosate was applied at a rate of 2.16 mg glyphosate kg[-1] of soil and microbial activity was measured by soil respiration (evolution of CO[2]) and fluorescein diacetate (FDA) hydrolysis over a period of 32 days. We found an increase of 10-15% in the CO[2] evolved and a 9-19% increase in FDA hydrolyses in the presence of glyphosate compared with the same type of soil which had never received glyphosate. Soil which had been exposed to glyphosate for several years had the strongest response in microbial activity. Most probable number (MPN) counts showed that after 32 days incubation the number of actinomycetes and fungi had increased while the number of bacteria showed a slight reduction. After the incubation period, high pressure liquid chromatography (HPLC) detected the glyphosate metabolite aminomethyl phosphonic acid (AMPA), indicating glyphosate degradation by soil microorganisms
Poliploidia em seringueira: III - Estudo comparativo entre clones diplóides e novos poliplóides putativos em condições de jardim clonal.
Foram avaliadas a produção de borracha e o vigor das plantas em clones putativos de Hevea brasiliensis (Fx 3864 pl e Fx 985 pl)
Determinação de herbicidas em água por enriquecimento em discos de extração.
Visando à identificação e quantificação de dezenove (19) herbicidas supostamente presentes em águas da bacia do rio CorumbataÃ, estado de São Paulo, Brasil, por causa do uso de agrotóxicos no cultivo predominante da região, cana de açúcar, foi desenvolvido método multiresÃduos para análise desses herbicidas. A detecção e separação dos compostos foi efetuada por cromatografia gasosa com detector especÃfico de nitrogênio e fósforo (NPD) para 8 dos herbicidas, com a utilização de coluna DB-5 30,0m x 0,25mm x 1.0µm, a qual apresentou a melhor resposta dentre as utilizadas. Por cromatografia lÃquida com detector ultravioleta-visÃvel (UV-VIS) os demais herbicidas, foram separados utilizando coluna Lichrosorb RP-18, 5µm x 250mm x 4,6mm. A intenção de estabelecer método único de extração de resÃduos de herbicidas trouxe a vantagem da rapidez no processo e permitiu o uso de volumes adequados de amostras, assim como a utilização de dois sistemas de detecção facilitou a separação dos analitos
Esporulação e eficiência de infecção do mÃldio da videira em cenários de mudanças climáticas.
O objetivo deste trabalho foi avaliar o efeito das mudanças climáticas na favorabilidade à ocorrência de mÃldio (Plasmopara viticola) na região de Bento Gonçalves-RS no perÃodo de 2020 a 2050. Este trabalho teve como base modelos de eficiência de infecção (EI) e esporulação (S) que descrevem esses processos com base em temperatura, duração do molhamento e duração de perÃodos com alta umidade. Para simulações futuras, foram usados os dados de temperatura do modelo climático regional PRECIS nos cenários IPCC A2 e B2 para 2020, 30, 40 e 50. Os resultados indicam pequena diminuição na frequência de dias com EI "alta" (0,7 a 1,0), o que também se reflete em pequena redução nas médias de EI. Por outro lado, ocorre um aumento mais expressivo na S, mais que compensando a perda de EI, resultando em provável maior intensidade da doença no futuro próximo, mantidas as condições de temperatura mais elevada e umidade estável
An instability of higher-dimensional rotating black holes
We present the first example of a linearized gravitational instability of an
asymptotically flat vacuum black hole. We study perturbations of a Myers-Perry
black hole with equal angular momenta in an odd number of dimensions. We find
no evidence of any instability in five or seven dimensions, but in nine
dimensions, for sufficiently rapid rotation, we find perturbations that grow
exponentially in time. The onset of instability is associated with the
appearance of time-independent perturbations which generically break all but
one of the rotational symmetries. This is interpreted as evidence for the
existence of a new 70-parameter family of black hole solutions with only a
single rotational symmetry. We also present results for the Gregory-Laflamme
instability of rotating black strings, demonstrating that rotation makes black
strings more unstable.Comment: 38 pages, 13 figure
Monitoramento da qualidade das misturas de biodiesel/diesel através da técnica fototérmica.
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