7,508 research outputs found
The trunk integument of zeuglopteran larvae : one of the most aberrant arthropod cuticles known (Insecta,Lepidoptera (Proceedings of the First International Workshop on Lower Lepidoptera))
The integument of the dorsal/dorsolateral surfaces of micropterigid larvae (Lepidoptera, suborder Zeugloptera) has a strikingly specialized, non-solid, cuticle which seems unparallelled in the phylum Arthropoda. ・・
Bleaching and diffusion dynamics in optofluidic dye lasers
We have investigated the bleaching dynamics that occur in optofluidic dye
lasers where the liquid laser dye in a microfluidic channel is locally bleached
due to optical pumping. We find that for microfluidic devices, the dye
bleaching may be compensated through diffusion of dye molecules alone. By
relying on diffusion rather than convection to generate the necessary dye
replenishment, our observation potentially allows for a significant
simplification of optofluidic dye laser device layouts, omitting the need for
cumbersome and costly external fluidic handling or on-chip microfluidic pumping
devices.Comment: 3 pages including 3 figures. Accepted for AP
Modelling diverse root density dynamics and deep nitrogen uptake — a simple approach
We present a 2-D model for simulation of root density and plant nitrogen (N) uptake for crops grown in agricultural systems, based on a modification of the root density equation originally proposed by Gerwitz and Page in J Appl Ecol 11:773–781, (1974). A root system form parameter was introduced to describe the distribution of root length vertically and horizontally in the soil profile. The form parameter can vary from 0 where root density is evenly distributed through the soil profile, to 8 where practically all roots are found near the surface. The root model has other components describing root features, such as specific root length and plant N uptake kinetics. The same approach is used to distribute root length horizontally, allowing simulation of root growth and plant N uptake in row crops. The rooting depth penetration rate and depth distribution of root density were found to be the most important parameters controlling crop N uptake from deeper soil layers. The validity of the root distribution model was tested with field data for white cabbage, red beet, and leek. The model was able to simulate very different root distributions, but it was not able to simulate increasing root density with depth as seen in the experimental results for white cabbage. The model was able to simulate N depletion in different soil layers in two field studies. One included vegetable crops with very different rooting depths and the other compared effects of spring wheat and winter wheat. In both experiments variation in spring soil N availability and depth distribution was varied by the use of cover crops. This shows the model sensitivity to the form parameter value and the ability of the model to reproduce N depletion in soil layers. This work shows that the relatively simple root model developed, driven by degree days and simulated crop growth, can be used to simulate crop soil N uptake and depletion appropriately in low N input crop production systems, with a requirement of few measured parameters
Electron transport through quantum wires and point contacts
We have studied quantum wires using the Green's function technique and the
density-functional theory, calculating the electronic structure and the
conductance. All the numerics are implemented using the finite-element method
with a high-order polynomial basis. For short wires, i.e. quantum point
contacts, the zero-bias conductance shows, as a function of the gate voltage
and at a finite temperature, a plateau at around 0.7G_0. (G_0 = 2e^2/h is the
quantum conductance). The behavior, which is caused in our mean-field model by
spontaneous spin polarization in the constriction, is reminiscent of the
so-called 0.7-anomaly observed in experiments. In our model the temperature and
the wire length affect the conductance-gate voltage curves in the same way as
in the measured data.Comment: 8 page
Magnetic Moment Formation in Quantum Point Contacts
We study the formation of local magnetic moments in quantum point contacts.
Using a Hubbard-like model to describe point contacts formed in a two
dimensional system, we calculate the magnetic moment using the unrestricted
Hartree approximation. We analyze different type of potentials to define the
point contact, for a simple square potential we calculate a phase diagram in
the parameter space (Coulomb repulsion - gate voltage). We also present an
analytical calculation of the susceptibility to give explicit conditions for
the occurrence of a local moment, we present a simple scaling argument to
analyze how the stability of the magnetic moment depends on the point contact
dimensions.Comment: 7 pages, 2 figure
ALMA CO J=6-5 observations of IRAS16293-2422: Shocks and entrainment
Observations of higher-excited transitions of abundant molecules such as CO
are important for determining where energy in the form of shocks is fed back
into the parental envelope of forming stars. The nearby prototypical and
protobinary low-mass hot core, IRAS16293-2422 (I16293) is ideal for such a
study. The source was targeted with ALMA for science verification purposes in
band 9, which includes CO J=6-5 (E_up/k_B ~ 116 K), at an unprecedented spatial
resolution (~0.2", 25 AU). I16293 itself is composed of two sources, A and B,
with a projected distance of 5". CO J=6-5 emission is detected throughout the
region, particularly in small, arcsecond-sized hotspots, where the outflow
interacts with the envelope. The observations only recover a fraction of the
emission in the line wings when compared to data from single-dish telescopes,
with a higher fraction of emission recovered at higher velocities. The very
high angular resolution of these new data reveal that a bow shock from source A
coincides, in the plane of the sky, with the position of source B. Source B, on
the other hand, does not show current outflow activity. In this region, outflow
entrainment takes place over large spatial scales, >~ 100 AU, and in small
discrete knots. This unique dataset shows that the combination of a
high-temperature tracer (e.g., CO J=6-5) and very high angular resolution
observations is crucial for interpreting the structure of the warm inner
environment of low-mass protostars.Comment: Accepted for publication in A&A Letter
Quantum Interaction : the Construction of Quantum Field defined as a Bilinear Form
We construct the solution of the quantum wave equation
as a bilinear form which can
be expanded over Wick polynomials of the free -field, and where
is defined as the normal ordered product with
respect to the free -field. The constructed solution is correctly defined
as a bilinear form on , where is a
dense linear subspace in the Fock space of the free -field. On
the diagonal Wick symbol of this bilinear form
satisfies the nonlinear classical wave equation.Comment: 32 pages, LaTe
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