10,365 research outputs found
The improved phytoextraction of lead (Pb) and the growth of maize (Zeamays L.): the role of plant growth regulators (GA3 and IAA) and EDTA alone and in combinations.
This investigation was made to examine the role of gibberellic acid (GA(3)), indole-3-acetic acid (IAA) and EDTA in improving phytoextraction of the Pb and plant growth on Pb added soil. GA(3), IAA and EDTA were applied separately and in combinations. GA(3) and IAA were applied as foliar spray and seed soaking. EDTA was applied in single and split doses. Analysis of the Pb in different parts of plant was carried out using atomic absorption/flame spectrophotometer. EDTA significantly reduced the plant growth and dry biomass, whereas GA(3) and IAA foliar spray increased it significantly when compared with control (only Pb added soil). In combined treatments of EDTA+GA(3) and EDTA+IAA, the growth and biomass was restored, which shows that GA(3) and IAA did compensate the negative effect of EDTA on plant growth. The separate treatments of EDTA, GA(3) and IAA increased the Pb uptake and translocation significantly moreover in combine treatments, synergistic effect was found and remarkable increase in Pb uptake and translocation into shoot was observed. EDTA increased the Pb uptake but declined the biomass; subsequently the total Pb accumulation was decreased in plant. The maximum total Pb was found in combined treatment of EDTA+GA(3). These findings suggest more investigation to find a combination of GA(3) with a very low concentration of EDTA, as in high concentration it causes soil and ground water pollution
Physical and chemical differentiation of the luminous star-forming region W49A - Results from the JCMT Spectral Legacy Survey
The massive and luminous star-forming region W49A is a well known Galactic
candidate to probe the physical conditions and chemistry similar to those
expected in external starburst galaxies. We aim to probe the physical and
chemical structure of W49A on a spatial scale of ~0.8 pc based on the JCMT
Spectral Legacy Survey, which covers the frequency range between 330 and 373
GHz. The wide 2x2 arcminutes field and the high spectral resolution of the HARP
instrument on JCMT provides information on the spatial structure and kinematics
of the cloud. For species where multiple transitions are available, we estimate
excitation temperatures and column densities. We detected 255 transitions
corresponding to 60 species in the 330-373 GHz range at the center position of
W49A. Excitation conditions can be probed for 16 molecules. The chemical
composition suggests the importance of shock-, PDR-, and hot core chemistry.
Many molecular lines show a significant spatial extent across the maps
including high density tracers (e.g. HCN, HNC, CS, HCO+) and tracers of
UV-irradiation (e.g. CN and C2H). Large variations are seen between the
sub-regions with mostly blue-shifted emission toward the Eastern tail, mostly
red-shifted emission toward the Northern clump, and emission peaking around the
expected source velocity toward the South-west clump. A comparison of column
density ratios of characteristic species observed toward W49A to Galactic PDRs
suggests that while the chemistry toward the W49A center is driven by a
combination of UV-irradiation and shocks, UV-irradiation dominates for the
Northern Clump, Eastern tail, and South-west clump regions. A comparison to a
starburst galaxy and an AGN suggests similar C2H, CN, and H2CO abundances (with
respect to the dense gas tracer 34CS) between the ~0.8 pc scale probed for W49A
and the >1 kpc regions in external galaxies with global star-formation.Comment: Proposed for acceptance in A&A, abstract abridge
Presupernova collapse models with improved weak-interaction rates
Improved values for stellar weak interaction rates have been recently
calculated based upon a large shell model diagonalization. Using these new
rates (for both beta decay and electron capture), we have examined the
presupernova evolution of massive stars in the range 15-40 Msun. Comparing our
new models with a standard set of presupernova models by Woosley and Weaver, we
find significantly larger values for the electron-to-baryon ratio Ye at the
onset of collapse and iron core masses reduced by approximately 0.1 Msun. The
inclusion of beta-decay accounts for roughly half of the revisions, while the
other half is a consequence of the improved nuclear physics. These changes will
have important consequences for nucleosynthesis and the supernova explosion
mechanism.Comment: 4 pages, 2 figure
Crafting a critical technical practice
In recent years, the category of practice-based research has become an essential component of discourse around public funding and evaluation of the arts in British higher education. When included under the umbrella of public policy concerned with the creative industries", technology researchers often find themselves collaborating with artists who consider their own participation to be a form of practice-based research. We are conducting a study under the Creator Digital Economies project asking whether technologists, themselves, should be considered as engaging in practice-based research, whether this occurs in collaborative situations, or even as a component of their own personal research [1]
Comment on "Elasticity Model of a Supercoiled DNA Molecule"
We perform simulations to numerically study the writhe distribution of a
stiff polymer. We compare with analytic results of Bouchiat and Mezard (PRL 80
1556- (1998); cond-mat/9706050).Comment: 1 page, 1 figure revtex
Writhing Photons and Berry Phases in Diffusive Wave Scattering
We study theoretically the polarization state of light in multiple scattering
media in the limit of weak gradients in refractive index. Linearly polarized
photons are randomly rotated due to the Berry phase associated with the
scattering path. For circularly polarized light independent speckle patterns
are found for the two helical states. The statistics of the geometric phase is
related to the writhe distribution of semiflexible polymers such as DNA.Comment: 4 pages, 1 figur
An Iterative and Toolchain-Based Approach to Automate Scanning and Mapping Computer Networks
As today's organizational computer networks are ever evolving and becoming
more and more complex, finding potential vulnerabilities and conducting
security audits has become a crucial element in securing these networks. The
first step in auditing a network is reconnaissance by mapping it to get a
comprehensive overview over its structure. The growing complexity, however,
makes this task increasingly effortful, even more as mapping (instead of plain
scanning), presently, still involves a lot of manual work. Therefore, the
concept proposed in this paper automates the scanning and mapping of unknown
and non-cooperative computer networks in order to find security weaknesses or
verify access controls. It further helps to conduct audits by allowing
comparing documented with actual networks and finding unauthorized network
devices, as well as evaluating access control methods by conducting delta
scans. It uses a novel approach of augmenting data from iteratively chained
existing scanning tools with context, using genuine analytics modules to allow
assessing a network's topology instead of just generating a list of scanned
devices. It further contains a visualization model that provides a clear, lucid
topology map and a special graph for comparative analysis. The goal is to
provide maximum insight with a minimum of a priori knowledge.Comment: 7 pages, 6 figure
Twist and writhe dynamics of stiff filaments
This letter considers the dynamics of a stiff filament, in particular the
coupling of twist and bend via writhe. The time dependence of the writhe of a
filament is for a linear filament and for a curved filament. Simulations are used to study the relative
importance of crankshaft motion and tube like motion in twist dynamics.
Fuller's theorem, and its relation with the Berry phase, is reconsidered for
open filamentsComment: 7 Pages with 2 figure
Electron fraction constraints based on Nuclear Statistical Equilibrium with beta equilibrium
The electron-to-nucleon ratio or electron fraction is a key parameter in many
astrophysical studies. Its value is determined by weak-interaction rates that
are based on theoretical calculations subject to several nuclear physics
uncertainties. Consequently, it is important to have a model independent way of
constraining the electron fraction value in different astrophysical
environments. Here we show that nuclear statistical equilibrium combined with
beta equilibrium can provide such a constraint. We test the validity of this
approximation in presupernova models and give lower limits for the electron
fraction in type Ia supernova and accretion-induced collapse.Comment: 10 pages, 9 figures, Astronomy and Astrophysic
Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN
We present high resolution (0."4) IRAM PdBI and ALMA mm and submm
observations of the (ultra) luminous infrared galaxies ((U)LIRGs)
IRAS17208-0014, Arp220, IC860 and Zw049.057 that reveal intense line emission
from vibrationally excited (=1) J=3-2 and 4-3 HCN. The emission is
emerging from buried, compact (r<17-70 pc) nuclei that have very high implied
mid-infrared surface brightness L kpc.
These nuclei are likely powered by accreting supermassive black holes (SMBHs)
and/or hot (>200 K) extreme starbursts. Vibrational, =1, lines of HCN
are excited by intense 14 micron mid-infrared emission and are excellent probes
of the dynamics, masses, and physical conditions of (U)LIRG nuclei when H
column densities exceed cm. It is clear that these lines open
up a new interesting avenue to gain access to the most obscured AGNs and
starbursts. Vibrationally excited HCN acts as a proxy for the absorbed
mid-infrared emission from the embedded nuclei, which allows for reconstruction
of the intrinsic, hotter dust SED. In contrast, we show strong evidence that
the ground vibrational state (=0), J=3-2 and 4-3 rotational lines of HCN
and HCO fail to probe the highly enshrouded, compact nuclear regions owing
to strong self- and continuum absorption. The HCN and HCO line profiles are
double-peaked because of the absorption and show evidence of non-circular
motions - possibly in the form of in- or outflows. Detections of vibrationally
excited HCN in external galaxies are so far limited to ULIRGs and early-type
spiral LIRGs, and we discuss possible causes for this. We tentatively suggest
that the peak of vibrationally excited HCN emission is connected to a rapid
stage of nuclear growth, before the phase of strong feedback.Comment: 13 pages, 7 figures, accepted for publication in Astronomy and
Astrophysic
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