9,662 research outputs found
Isotropic photonic band gap and anisotropic structures in transmission spectra of two-dimensional 5-fold and 8-fold symmetric quasiperiodic photonic crystals
We measured and calculated transmission spectra of two-dimensional
quasiperiodic photonic crystals (PCs) based on a 5-fold (Penrose) or 8-fold
(octagonal) symmetric quasiperiodic pattern. The photonic crystal consisted of
dielectric cylindrical rods in air placed normal to the basal plane on vertices
of tiles composing the quasiperiodic pattern. An isotropic photonic band gap
(PBG) appeared in the TM mode, where electric fields were parallel to the rods,
even when the real part of a dielectric constant of the rod was as small as
2.4. An isotropic PBG-like dip was seen in tiny Penrose and octagonal PCs with
only 6 and 9 rods, respectively. These results indicate that local multiple
light scattering within the tiny PC plays an important role in the PBG
formation. Besides the isotropic PBG, we found dips depending on the incident
angle of the light. This is the first report of anisotropic structures clearly
observed in transmission spectra of quasiperiodic PCs. Based on rod-number and
rod-arrangement dependence, it is thought that the shapes and positions of the
anisotropic dips are determined by global multiple light scattering covering
the whole system. In contrast to the isotropic PBG due to local light
scattering, we could not find any PBGs due to global light scattering even
though we studied transmission spectra of a huge Penrose PC with 466 rods.Comment: One tex file for manuscript and 12 PNG files for figures consisting
of Fig.1a-d, 2,3, ...
Currents, Torques, and Polarization Factors in Magnetic Tunnel Junctions
Application of Bardeen's tunneling theory to magnetic tunnel junctions having
a general degree of atomic disorder reveals the close relationship between
magneto-conduction and voltage-driven pseudo-torque, as well as the thickness
dependence of tunnel-polarization factors. Among the results: 1) The torque
generally varies as sin theta at constant applied voltage. 2) Whenever
polarization factors are well defined, the voltage-driven torque on each moment
is uniquely proportional to the polarization factor of the other magnet. 3) At
finite applied voltage, this relation predicts significant voltage-asymmetry in
the torque. For one sign of voltage the torque remains substantial even when
the magnetoconductance is greatly diminished. 4) A broadly defined junction
model, called ideal middle, allows for atomic disorder within the magnets and
F/I interface regions. In this model, the spin dependence of a state-weighting
factor proportional to the sum over general state index of evaluated within the
(e.g. vacuum) barrier generalizes the local state density in previous theories
of the tunnel-polarization factor. 5) For small applied voltage,
tunnel-polarization factors remain legitimate up to first order in the inverse
thickness of the ideal middle. An algebraic formula describes the first-order
corrections to polarization factors in terms of newly defined lateral
auto-correllation scales.Comment: This version no. 3 is thoroughly revised for clarity. Just a few
notations and equations are changed, and references completed. No change in
results. 17 pages including 4 figure
Spin splitting and Kondo effect in quantum dots coupled to noncollinear ferromagnetic leads
We study the Kondo effect in a quantum dot coupled to two noncollinear
ferromagnetic leads. First, we study the spin splitting
of an energy level
in the quantum dot by tunnel couplings to the ferromagnetic leads, using the
Poor man's scaling method. The spin splitting takes place in an intermediate
direction between magnetic moments in the two leads. , where is the spin
polarization in the leads, is the angle between the magnetic moments,
and is an asymmetric factor of tunnel barriers (). Hence the spin
splitting is always maximal in the parallel alignment of two ferromagnets
() and minimal in the antiparallel alignment (). Second,
we calculate the Kondo temperature . The scaling calculation
yields an analytical expression of as a function of
and , , when .
is a decreasing function with respect to
. When is
relevant, we evaluate using the
slave-boson mean-field theory. The Kondo resonance is split into two by finite
, which results in the spin accumulation in the quantum dot and
suppression of the Kondo effect.Comment: 11 pages, 8 figures, revised versio
First-Principles Study of Electronic Structure in -(BEDT-TTF)I at Ambient Pressure and with Uniaxial Strain
Within the framework of the density functional theory, we calculate the
electronic structure of -(BEDT-TTF)I at 8K and room temperature
at ambient pressure and with uniaxial strain along the - and -axes. We
confirm the existence of anisotropic Dirac cone dispersion near the chemical
potential. We also extract the orthogonal tight-binding parameters to analyze
physical properties. An investigation of the electronic structure near the
chemical potential clarifies that effects of uniaxial strain along the a-axis
is different from that along the b-axis. The carrier densities show
dependence at low temperatures, which may explain the experimental findings not
only qualitatively but also quantitatively.Comment: 10 pages, 7 figure
Actividad antifúngica de extractos crudos de bacillus subtilis contra fitopatógenos de soja (Glycine max) y efecto de su coinoculación con bradyrhizobium japonicum
373-383Fungal species Fusarium solani and Pythium sp. are among the microorganisms causing diseases in pre and post harvest crop soybean (Glycine max). Four strains of the genus Bacillus (B. subtilis ATCC6633, B. amylolyticus, B. subtilis var. natto, B. subtilis var. natto domesticated) were tested to evaluate the inhibitory response of them on the phytopathogenic fungi previously mentioned. The inoculation treatments were 1) seeds inoculated with Bradyrhizobium japonicum, and 2) seeds coinoculated with B. japonicum and B. subtilis. Plants were grown in a thermostated culture chamber at 30 more or less 1°C, 60 percent relative humidity and 16/8 light-dark photoperiod for 35 d. Data were analyzed by ANOVA and means were compared by applying the Tukey test (p less or equal to 0.05). The in vitro assays of the strain B. subtilis ATCC6633 reduced the mycelial growth of Fusarium solani (50 percent) and Pythium sp. (47 percent) compared to controls. The coinoculation of B. japonicum and B. subtilis stimulated the growth of the whole plant by 125 percent, 100 percent aerial part, 235 percent root, 20 percent number of leaves, and 88 percent nodule number compared to control. The strain B. subtilis ATCC6633 synthesized metabolites of proteinaceous nature and others with biosurfactant capacity. When the bacteria were grown in minimal saline medium, glycerol 1 percent and concentrations of L-glutamic acid between 40 and 55 mM, the highest concentration of proteinaceous metabolites (35 ug protein mL-1) was obtained and increased biofilm formation. Biofilm formation, the presence of biosurfactants and the release of antifungal metabolites positioned this bacterium in a situation competitively advantageous compared to the rest of the microbiota of the rhizosphere in the soybean plant. Entre los microorganismos causantes de enfermedades pre y post cosecha en los cultivos de soja (Glycine max) están las especies fúngicas Fusarium solani y Pythium sp. Cuatro cepas del género Bacillus (B. subtilis ATCC6633, B. amylolyticus, B. subtilis var. natto, B. subtilis var. natto domesticado) se probaron para evaluar su respuesta inhibitoria en los hongos fitopatógenos mencionados. Los tratamientos de inoculación fueron: 1) semillas inoculadas con Bradyrhizobium japonicum y 2) semillas coinoculadas con B. japonicum y B. subtilis. Las plantas crecieron en cámara de cultivo termostatizada a 30 más o menos 1°C, humedad relativa 60 porciento y fotoperíodo 16/8 luz-oscuridad durante 35 d. Los datos se analizaron mediante ANDEVA y las medias se compararon con la prueba de Tukey (p menor o igual a 0.05). Las pruebas in vitro de la cepa B. subtilis ATCC6633 redujeron el crecimiento micelial de Fusarium solani (50 porciento) y Pythium sp. (47 porciento) respecto a los testigos. La coinoculación de B. japonicum y B. subtilis estimuló el crecimiento de la planta completa en 125 porciento, parte aérea 100 porciento, raíz 235 porciento, número de hojas 20 porciento y número de nódulos 88 porciento respecto al testigo. La cepa de B. subtilis ATCC6633 sintetizó metabolitos de naturaleza proteínica y otros con capacidad biosurfactante. Cuando la bacteria se cultivó en medio mínimo salino, glicerol 1 porciento y concentraciones de ácido L-glutámico entre 40 y 55 mM, se obtuvo la concentración mayor de metabolitos de naturaleza proteínica (35 mg proteína mL-1) y la mayor formación de biopelícula. La formación de la biopelícula, la presencia de biosurfactantes y la liberación de metabolitos antifúngicos, posicionan a esta bacteria en una situación competitivamente ventajosa en relación al resto de la microbiota de la rizósfera en la planta de soja
Actividad antifúngica de extractos crudos de bacillus subtilis contra fitopatógenos de soja (Glycine max) y efecto de su coinoculación con bradyrhizobium japonicum
373-383Fungal species Fusarium solani and Pythium sp. are among the microorganisms causing diseases in pre and post harvest crop soybean (Glycine max). Four strains of the genus Bacillus (B. subtilis ATCC6633, B. amylolyticus, B. subtilis var. natto, B. subtilis var. natto domesticated) were tested to evaluate the inhibitory response of them on the phytopathogenic fungi previously mentioned. The inoculation treatments were 1) seeds inoculated with Bradyrhizobium japonicum, and 2) seeds coinoculated with B. japonicum and B. subtilis. Plants were grown in a thermostated culture chamber at 30 more or less 1°C, 60 percent relative humidity and 16/8 light-dark photoperiod for 35 d. Data were analyzed by ANOVA and means were compared by applying the Tukey test (p less or equal to 0.05). The in vitro assays of the strain B. subtilis ATCC6633 reduced the mycelial growth of Fusarium solani (50 percent) and Pythium sp. (47 percent) compared to controls. The coinoculation of B. japonicum and B. subtilis stimulated the growth of the whole plant by 125 percent, 100 percent aerial part, 235 percent root, 20 percent number of leaves, and 88 percent nodule number compared to control. The strain B. subtilis ATCC6633 synthesized metabolites of proteinaceous nature and others with biosurfactant capacity. When the bacteria were grown in minimal saline medium, glycerol 1 percent and concentrations of L-glutamic acid between 40 and 55 mM, the highest concentration of proteinaceous metabolites (35 ug protein mL-1) was obtained and increased biofilm formation. Biofilm formation, the presence of biosurfactants and the release of antifungal metabolites positioned this bacterium in a situation competitively advantageous compared to the rest of the microbiota of the rhizosphere in the soybean plant. Entre los microorganismos causantes de enfermedades pre y post cosecha en los cultivos de soja (Glycine max) están las especies fúngicas Fusarium solani y Pythium sp. Cuatro cepas del género Bacillus (B. subtilis ATCC6633, B. amylolyticus, B. subtilis var. natto, B. subtilis var. natto domesticado) se probaron para evaluar su respuesta inhibitoria en los hongos fitopatógenos mencionados. Los tratamientos de inoculación fueron: 1) semillas inoculadas con Bradyrhizobium japonicum y 2) semillas coinoculadas con B. japonicum y B. subtilis. Las plantas crecieron en cámara de cultivo termostatizada a 30 más o menos 1°C, humedad relativa 60 porciento y fotoperíodo 16/8 luz-oscuridad durante 35 d. Los datos se analizaron mediante ANDEVA y las medias se compararon con la prueba de Tukey (p menor o igual a 0.05). Las pruebas in vitro de la cepa B. subtilis ATCC6633 redujeron el crecimiento micelial de Fusarium solani (50 porciento) y Pythium sp. (47 porciento) respecto a los testigos. La coinoculación de B. japonicum y B. subtilis estimuló el crecimiento de la planta completa en 125 porciento, parte aérea 100 porciento, raíz 235 porciento, número de hojas 20 porciento y número de nódulos 88 porciento respecto al testigo. La cepa de B. subtilis ATCC6633 sintetizó metabolitos de naturaleza proteínica y otros con capacidad biosurfactante. Cuando la bacteria se cultivó en medio mínimo salino, glicerol 1 porciento y concentraciones de ácido L-glutámico entre 40 y 55 mM, se obtuvo la concentración mayor de metabolitos de naturaleza proteínica (35 mg proteína mL-1) y la mayor formación de biopelícula. La formación de la biopelícula, la presencia de biosurfactantes y la liberación de metabolitos antifúngicos, posicionan a esta bacteria en una situación competitivamente ventajosa en relación al resto de la microbiota de la rizósfera en la planta de soja
Spin-polarized tunneling through randomly transparent magnetic junctions: Reentrant magnetoresistance approaching the Julliere limit
Electron conductance in planar magnetic tunnel junctions with long-range
barrier disorder is studied within Glauber-eikonal approximation enabling exact
disorder ensemble averaging by means of the Holtsmark-Markov method. This
allows us to address a hitherto unexplored regime of the tunneling
magnetoresistance effect characterized by the crossover from
momentum-conserving to random tunneling as a function of the defect
concentration. We demonstrate that such a crossover results in a reentrant
magnetoresistance: It goes through a pronounced minimum before reaching
disorder- and geometry-independent Julliere's value at high defect
concentrations.Comment: 7 pages, 5 figures, derivation of Eq. (39) added, errors in Ref. 7
correcte
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