4,850 research outputs found
A Molecular Line Survey of the Carbon-Rich Proto-Planetary Nebula AFGL 2688 in the 3mm and 1.3mm Windows
We present a spectral line survey of the proto-planetary nebula AFGL 2688 in
the frequency ranges of 71-111 GHz, 157-160 GHz, and 218-267 GHz using the
Arizona Radio Observatory 12m telescope and the Heinrich Hertz Submillimeter
Telescope. A total of 143 individual spectral features associated with 32
different molecular species and isotopologues were identified. The molecules
C3H, CH3CN, H2CO, H2CS, and HCO+ were detected for the first time in this
object. By comparing the integrated line strengths of different transitions, we
are able to determine the rotation temperatures, column densities, and
fractional abundances of the detected molecules. The C, O, and N isotopic
ratios in AFGL 2688 are compared with those in IRC+10216 and the Sun, and were
found to be consistent with stellar nucleosynthesis theory. Through comparisons
of molecular line strengths in asymptotic giant branch stars, proto-planetary
nebulae, and planetary nebulae, we discuss the evolution in circumstellar
chemistry in the late stages of evolution.Comment: 41 pages, 10 figures. Accepted for publication in Ap
Propagation of highly nonlinear signals in a two dimensional network of granular chains
We report the first experimental observation of highly nonlinear signals propagating in a two dimensional system composed of granular chains. In this system one of the chains contacts two others to allow splitting and redirecting the solitary-like signal formed in the first chain. The system consists of a double Y-shaped guide in which high- and low-modulus chains of spheres are arranged in various geometries. We observed fast splitting of the initial pulse, rapid chaotization of the signal and sharp bending of the propagating acoustic information. Pulse and energy trapping was also observed in composite systems assembled from hard- and soft-particles in the branches
Progress in classically solving ten dimensional supersymmetric reduced Yang-Mills theories
It is shown that there exists an on-shell light cone gauge where half of the
fermionic components of the super vector potential vanish, so that part of the
superspace flatness conditions becomes linear. After reduction to
space-time dimensions, the general solution of this subset of equations is
derived. The remaining non-linear equations are written in a form which is
analogous to Yang equations, albeit with superderivatives involving sixteen
fermionic coordinates. It is shown that this non-linear part may, nevertheless,
be solved by methods similar to powerful technics previously developed for the
(purely bosonic) self-dual Yang Mills equations in four dimensions.Comment: 17 pages Latex non figure
Fungal surface measurements: water contact angles
Non-Peer ReviewedFungal surface properties have been implicated as one of the main factors affecting
fungal colonization and adhesion to plant surfaces. Characterization of fungal surfaces through
hydrophobic measurements is important for understanding its function. Water contact angles are
a direct and simple approach for characterization of fungal surface hydrophobicity. The
objective of this study was to evaluate if utilization of undisturbed fungal cultures coupled with
versatile image analysis allow for more accurate contact angle measurements. Fungal cultures
were grown on agar slide media and contact angles were measured utilizing a modified
microscope and digital camera setup, with Low Bond Axisymmetric Drop Shape Analysis Model
(LB_ADSA) for contact angle determination. Fungal strains were categorized into hydrophobic,
hydrophilic and a newly defined hydroamphiphilic class containing fungi taxa with changing
hydrophobicity
Symmetrization and Entanglement of Arbitrary States of Qubits
Given two arbitrary pure states and of qubits or higher
level states, we provide arguments in favor of states of the form instead of symmetric or
anti-symmetric states, as natural candidates for optimally entangled states
constructed from these states. We show that such states firstly have on the
average a high value of concurrence, secondly can be constructed by a universal
unitary operator independent of the input states. We also show that these
states are the only ones which can be produced with perfect fidelity by any
quantum operation designed for intertwining two pure states with a relative
phase. A probabilistic method is proposed for producing any pre-determined
relative phase into the combination of any two arbitrary states.Comment: 6 pages, 1 figur
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Plastidial carbonic anhydrase in cotton (Gossypium hirsutum L.): characterization, expression, and role in lipid biosynthesis
Recently, plastidial carbonic anhydrase (CA, EC 4.2.1.1) cDNA clones encoding functional CA enzymes were isolated from a nonphotosynthetic cotton tissue. The role of CA in photosynthetic tissues have been well characterized, however there is almost no information for the role of CA in nonphotosynthetic tissues. A survey of relative CA transcript abundance and enzyme activity in different cotton organs revealed that there was substantial CA expression in cotyledons of seedlings and embryos, both nonphotosynthetic tissues. To gain insight into the role(s) of CA, I examined CA expression in cotyledons of seedlings during post-germinative growth at different environmental conditions. CA expression in cotyledons of seedlings increased from 18 h to 72 h after germination in the dark. Seedlings exposed to light had about a 2-fold increase in CA activities when compared with seedlings kept in the dark, whereas relative CA transcript levels were essentially the same. Manipulation of external CO2 environments [zero, ambient (350 ppm), or high (1000 ppm)] modulated coordinately the relative transcript abundance of CA (and rbcS) in cotyledons, but did not affect enzyme activities. On the other hand, regardless of the external CO2 conditions seedlings exposed to light exhibited increase CA activity, concomitant with Rubisco activity and increased chlorophyll content. Our data revealed that steady-state levels of CA and rbcS transcripts are regulated at the transcriptional level in response to external CO2 conditions, while CA and Rubisco activities are modulated at the post-transcriptional level by light. Thus CA expression in cotyledons during post-germinative growth may be to âprimeâ cotyledons for the transition at the subcellular level for the transition from plastids to chloroplasts, where it provides CO2 for Rubisco during photosynthesis. Furthermore, CA expression increased during embryo maturation similar to oil accumulation. Specific sulfonamide inhibitors of CA activity significantly reduced the
rate of [14C]-acetate incorporation into total lipids in cotton embryos and tobacco leaves and cell suspensions in vivo and in vitro. Similar results were obtained in chloroplasts isolated from leaves of transgenic CA antisense-suppressed tobacco plants (5% of wildtype activity). Collectively, these results support the notion that CA plays several physiological roles in nonphotosynthetic tissues
Slider-Block Friction Model for Landslides: Application to Vaiont and La Clapiere Landslides
Accelerating displacements preceding some catastrophic landslides have been
found empirically to follow a time-to-failure power law, corresponding to a
finite-time singularity of the velocity [{\it Voight},
1988]. Here, we provide a physical basis for this phenomenological law based on
a slider-block model using a state and velocity dependent friction law
established in the laboratory and used to model earthquake friction. This
physical model accounts for and generalizes Voight's observation: depending on
the ratio of two parameters of the rate and state friction law and on the
initial frictional state of the sliding surfaces characterized by a reduced
parameter , four possible regimes are found. Two regimes can account for
an acceleration of the displacement. We use the slider-block friction model to
analyze quantitatively the displacement and velocity data preceding two
landslides, Vaiont and La Clapi\`ere. The Vaiont landslide was the catastrophic
culmination of an accelerated slope velocity. La Clapi\`ere landslide was
characterized by a peak of slope acceleration that followed decades of ongoing
accelerating displacements, succeeded by a restabilizing phase. Our inversion
of the slider-block model on these data sets shows good fits and suggest to
classify the Vaiont (respectively La Clapi\`ere) landslide as belonging to the
velocity weakening unstable (respectively strengthening stable) sliding regime.Comment: shortened by focusing of the frictional model, Latex document with
AGU style file of 14 pages + 11 figures (1 jpeg photo of figure 6 given
separately) + 1 tabl
Pd/Cu Site Interchange and Non-Fermi-Liquid Behavior in UCu_4Pd
X-ray-absorption fine-structure measurements of the local structure in
UCu_4Pd are described which indicate a probable lattice-disorder origin for
non-Fermi-liquid behavior in this material. Short Pd-Cu distances are observed,
consistent with 24 +/- 3% of the Pd atoms occupying nominally Cu sites. A
"Kondo disorder" model, based on the effect on the local Kondo temperature T_K
of this interchange and some additional bond-length disorder, agrees
quantitatively with previous experimental susceptibility data, and therefore
also with specific heat and magnetic resonance experiments.Comment: 4 pages, 3 PostScript figures, to be published in PR
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