3,046 research outputs found
PROTECTING SHELL EGGS BETWEEN PACKING PLANT AND SUPERMARKET
Studies the importance of factors affecting eggshell damage such as type of pack, age of laying hen and season of year.Agribusiness,
PREPARING FOR A COMPUTER SYSTEM IN A WHOLESALE FRUIT AND VEGETABLE COMPANY
Agribusiness, Research and Development/Tech Change/Emerging Technologies,
Electronic instabilities of a Hubbard model approached as a large array of coupled chains: competition between d-wave superconductivity and pseudogap phase
We study the electronic instabilities in a 2D Hubbard model where one of the
dimensions has a finite width, so that it can be considered as a large array of
coupled chains. The finite transverse size of the system gives rise to a
discrete string of Fermi points, with respective electron fields that, due to
their mutual interaction, acquire anomalous scaling dimensions depending on the
point of the string. Using bosonization methods, we show that the anomalous
scaling dimensions vanish when the number of coupled chains goes to infinity,
implying the Fermi liquid behavior of a 2D system in that limit. However, when
the Fermi level is at the Van Hove singularity arising from the saddle points
of the 2D dispersion, backscattering and Cooper-pair scattering lead to the
breakdown of the metallic behavior at low energies. These interactions are
taken into account through their renormalization group scaling, studying in
turn their influence on the nonperturbative bosonization of the model. We show
that, at a certain low-energy scale, the anomalous electron dimension diverges
at the Fermi points closer to the saddle points of the 2D dispersion. The
d-wave superconducting correlations become also large at low energies, but
their growth is cut off as the suppression of fermion excitations takes place
first, extending progressively along the Fermi points towards the diagonals of
the 2D Brillouin zone. We stress that this effect arises from the vanishing of
the charge stiffness at the Fermi points, characterizing a critical behavior
that is well captured within our nonperturbative approach.Comment: 13 pages, 7 figure
6-N-Trimethyllysine metabolism and carnitine biosynthesis in N. crassa
6-N-Trimethyllysine metabolism and carnitine biosynthesi
Asymmetric transmission of linearly polarized light at optical metamaterials
We experimentally demonstrate a three-dimensional chiral optical metamaterial
that exhibits an asymmetric transmission for forwardly and backwardly
propagating linearly polarized light. The observation of this novel effect
requires a metamaterial composed of three-dimensional chiral metaatoms without
any rotational symmetry. Our analysis is supported by a systematic
investigation of the transmission matrices for arbitrarily complex, lossy media
that allows deriving a simple criterion for asymmetric transmission in an
arbitrary polarization base. Contrary to physical intuition, in general the
polarization eigenstates in such three-dimensional and low-symmetry
metamaterials do not obey fxed relations and the associated transmission
matrices cannot be symmetrized
Stellar (n,γ) cross sections of ²³Na
The cross section of the ²³Na(n,γ)²⁴Na reaction has been measured via the activation method at the Karlsruhe 3.7 MV Van de Graaff accelerator. NaCl samples were exposed to quasistellar neutron spectra at kT = 5.1 and 25 keV produced via the ¹⁸O(p,n)¹⁸F and ⁷Li(p,n)⁷Be reactions, respectively. The derived capture cross sections (σ)kT=5keV = 9.1 ± 0.3mb and (σ)kT=25keV = 2.03 ± 0.05 mb are significantly lower than reported in literature. These results were used to substantially revise the radiative width of the first ²³Na resonance and to establish an improved set of Maxwellian average cross sections. The implications of the lower capture cross section for current models of s-process nucleosynthesis are discussed
Discrete solitons in coupled active lasing cavities
We examine the existence and stability of discrete spatial solitons in
coupled nonlinear lasing cavities (waveguide resonators), addressing the case
of active defocusing media, where the gain exceeds damping in the low-amplitude
limit. A new family of stable localized structures is found: these are bright
and grey cavity solitons representing the connections between homogeneous and
inhomogeneous states. Solitons of this type can be controlled by the discrete
diffraction and are stable when the bistability of homogenous states is absent.Comment: 3 pages, 3 figures, accepted to Optics Letters (October 2012
Circular Optical Nanoantennas: An Analytical Theory
An entirely analytical theory is provided for describing the resonance
properties of optical nanoantennas made of a stack of homogeneous discs, i.e.
circular patch nanoantennas. It consists in analytically calculating the phase
accumulation of surface plasmon polaritons across the resonator and an
additional contribution from the complex reflection coefficient at the antenna
termination. This makes the theory self-contained with no need for fitting
parameters. The very antenna resonances are then explained by a simple
Fabry-Perot resonator model. Predictions are compared to rigorous simulations
and show excellent agreement. Using this analytical model, circular antennas
can be tuned by varying the composition of the stack
Stellar neutron capture cross sections of ²⁰ ²¹ ²²Ne
The stellar (n,γ) cross sections of the Ne isotopes are important for a number of astrophysical quests, i.e., for the interpretation of abundance patterns in presolar material or with respect to the s-process neutron balance in red giant stars. This paper presents resonance studies of experimental data in the keV range, which had not been fully analyzed before. The analyses were carried out with the R-matrix code sammy. With these results for the resonant part and by adding the components due to direct radiative capture, improved Maxwellian-averaged cross sections (MACS) could be determined. At kT=30keV thermal energy we obtain MACS values of 240±29,1263±160, and 53.2±2.7 μbarn for ²⁰Ne,²¹Ne, and ²²Ne, respectively. In earlier work the stellar rates of ²⁰Ne and ²¹Ne had been grossly overestimated. ²²Ne and ²⁰Ne are significant neutron poisons for the s process in stars because their very small MACS values are compensated by their large abundances
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