774 research outputs found
Oxidative biotransformations of phenol substrates catalysed by toluene dioxygenase: a molecular docking study
Red imported fire ant impacts on the endangered Florida grasshopper sparrow
Red imported fire ants (Solenopsis invicta) invaded peninsular Florida more
than 30 years ago. Highlands and Polk counties, Florida, were probably first invaded in
the late 1960s. Since then, fire ants have continued both to spread and to increase in
abundance. Experimental evidence has shown that red imported fire ants may have a
detrimental impact on native species, both invertebrate and vertebrate, and that these
impacts may be both direct and indirect. This segment of research was designed to
determine if fire ants have a negative impact on Florida grasshopper sparrow
(Ammodramus savannarumfloridanus) populations at Avon Park Air Force Bombing
Range, Florida. The sampling reported herein was conducted during June and October,
1997, and all analyses are restricted to data collected during those periods. As assessed
by baits, fire ants were dominant on about half the sites, and absent from others. In
particular, OQ Range sites tended to have fewer fire ants present, while Delta Trail sites
were more heavily infested, although there were exceptions. June fire ant abundance was
strongly negatively correlated with both native ant abundance (r = -0.743, P = 0.006) and
native ant species richness (r = -0.730, P = 0.007). October fire ant abundance was
strongly negatively correlated with both native ant abundance (r = -0.690, P = 0.013) and
native ant species richness (r = -0.736, P = 0.006). The patterns of fire ant abundance as
assessed by pitfalls were very similar to those determined from bait sampling. June fire
ant abundance was negatively correlated (p < 0.05) with native ant richness, but other
June comparisons were not statistically significant (P > 0.05). October fire ant
abundance was negatively correlated (P < 0.05) with native ant richness and abundance,
but other comparisons were not statistically significant (P > 0.05). There was no
significant correlation between overall insect biomass as assessed by light traps and fire
ant abundance as assessed by baits or pitfalls. Total biomass varied considerably among
the two sample periods because of changes in overall insect abundance during different
seasons. There was a negative spatial correspondence between fire ants and native
invertebrates. Over most of the intensive study areas, there was a negative spatial
relationship between fire ants and the abundance of native invertebrates. Over about
50% of the intensive study areas, there was a negative spatial relationship between fire
ants and the abundance of Florida grasshopper sparrows, although the relationship was
not as strong as that between fire ants and native invertebrates. Fire ant and native
invertebrates were negatively correlated at grasshopper sparrow count locations (r =0.347,
P = 0.03). A multiple regression model was fit to the data, using fire ants and
native invertebrates as independent variables, and grasshopper sparrow 100-m population
estimates (n = 39) as the dependent variable. The influence of fire ants on grasshopper
sparrows was negative while the influence of native invertebrates was positive.
However, the overall model, while suggestive, was not significant (r = 0.304, P = 0.17).
Fire ant abundance was a better (negative) predictor of sparrow populations (P = 0.13)
than was invertebrate abundance (P = 0.59). The overall model and influence of fire ants
on sparrow populations was suggestive of a negative influence warranting analyses of
data for 1998 and 1999. (Document has 93 pages
On Aharonov-Casher bound states
In this work bound states for the Aharonov-Casher problem are considered.
According to Hagen's work on the exact equivalence between spin-1/2
Aharonov-Bohm and Aharonov-Casher effects, is known that the
term cannot be neglected in the
Hamiltonian if the spin of particle is considered. This term leads to the
existence of a singular potential at the origin. By modeling the problem by
boundary conditions at the origin which arises by the self-adjoint extension of
the Hamiltonian, we derive for the first time an expression for the bound state
energy of the Aharonov-Casher problem. As an application, we consider the
Aharonov-Casher plus a two-dimensional harmonic oscillator. We derive the
expression for the harmonic oscillator energies and compare it with the
expression obtained in the case without singularity. At the end, an approach
for determination of the self-adjoint extension parameter is given. In our
approach, the parameter is obtained essentially in terms of physics of the
problem.Comment: 11 pages, matches published versio
Rational design of a (S)-selective-transaminase for asymmetric synthesis of (1S)-1-(1,1′-biphenyl-2-yl)ethanamine
Amine transaminases offer an environmentally sustainable synthesis route for the production of pure chiral amines. However, their catalytic efficiency toward bulky ketone substrates is greatly limited by steric hindrance and therefore presents a great challenge for industrial synthetic applications. We hereby report an example of rational transaminase enzyme design to help alleviate these challenges. Starting from the Vibrio fluvialis amine transaminase that has no detectable catalytic activity toward the bulky aromatic ketone 2-acetylbiphenyl, we employed a rational design strategy combining in silico and in vitro studies to engineer the transaminase enzyme with a minimal number of mutations, achieving an high catalytic activity and high enantioselectivity. We found that, by introducing two mutations W57G/R415A, detectable enzyme activity was achieved. The rationally designed variant, W57F/R88H/V153S/K163F/I259M/R415A/V422A, showed an improvement in reaction rate by more than 1716-fold toward the bulky ketone under study, producing the corresponding enantiomeric pure (S)-amine (enantiomeric excess (ee) value of >99%)
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Near-Earth asteroid sample return missions
The rate of discovery of new NEAs and the success of D-S 1 and NEAR-Shoemaker, suggest that sample return from NEAs is now technically feasible. Here we present a summary of a recent workshop on the topic
Asymptotic gluing of asymptotically hyperbolic solutions to the Einstein constraint equations
We show that asymptotically hyperbolic solutions of the Einstein constraint
equations with constant mean curvature can be glued in such a way that their
asymptotic regions are connected.Comment: 37 pages; 2 figure
3α,4α-Epoxy-5α-androstan-17β-yl acetate
The title compound, C21H32O3, results from modifications of the A and D rings of the aromatase substrate androstenedione. Ring A adopts a conformation between 10β-sofa and 1α,10β half-chair. Rings B and C are in slightly flattened chair conformations. Ring D approaches a 13β-envelope conformation, probably due to the acetoxy substituent, and shows a very short Csp
3—Csp
3 bond next to the epoxide ring, which is characteristic of 3–4 epoxides.
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