1,170 research outputs found
Anticancer Drugs
Plant‐derived anticancer drugs play a large role in anticancer pharmaceuticals. Through reviewing the four major types of plant anticancer drugs, namely vinca alkaloids, taxane diterpenoids, podophyllotoxin lignans, and camptothecin quinoline alkaloids, this article illustrates the development process, current status, existing challenges, and future perspective of the plant anticancer drug production. Moreover, this review explains how various biotechnologies, from the mature elicitation strategy to the “omics” techniques that are still undergoing development, can be applied to address the challenges in improving the production of the plant‐sourced anticancer drugs
Multiple planar coincidences with N-fold symmetry
Planar coincidence site lattices and modules with N-fold symmetry are well
understood in a formulation based on cyclotomic fields, in particular for the
class number one case, where they appear as certain principal ideals in the
corresponding ring of integers. We extend this approach to multiple
coincidences, which apply to triple or multiple junctions. In particular, we
give explicit results for spectral, combinatorial and asymptotic properties in
terms of Dirichlet series generating functions.Comment: 13 pages, two figures. For previous related work see math.MG/0511147
and math.CO/0301021. Minor changes and references update
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Carbon flux patterns on U.S. public timberlands under alternative timber harvest policies
This study considers trade-offs between timber harvest and carbon
sequestration on National Forest and other public lands by contemporaneously linking
a model of public harvest and inventory to a carbon accounting system. The public
harvest model treats three harvest scenarios. The first minimizes the cost of meeting
harvest requests that approximate current harvest policy. The second and third models
represent two extremes of harvest policy: maximum strict even-flow scheme and noharvest.
The current harvest scenario results in a maximum average net carbon
sequestration of approximately 35 Teragrams per decade. The maximum strict evenflow
scenario results in a maximum of 19 Teragrams of net carbon sequestration on an
average decadal basis, because of losses to forest product decay and reduced
understory growth. The no harvest scenario results in the highest total carbon
holdings, 164 Pentagrams at the end of the 100 year planning horizon, and has an
average net sequestration rate of 65 Teragrams each decade
Quasar Clustering and the Lifetime of Quasars
Although the population of luminous quasars rises and falls over a period of
10^9 years, the typical lifetime of individual quasars is uncertain by several
orders of magnitude. We show that quasar clustering measurements can
substantially narrow the range of possible lifetimes with the assumption that
luminous quasars reside in the most massive host halos. If quasars are
long-lived, then they are rare phenomena that are highly biased with respect to
the underlying dark matter, while if they are short-lived they reside in more
typical halos that are less strongly clustered. For a given quasar lifetime, we
calculate the minimum host halo mass by matching the observed space density of
quasars, using the Press-Schechter approximation. We use the results of Mo &
White to calculate the clustering of these halos, and hence of the quasars they
contain, as a function of quasar lifetime. A lifetime of t_Q = 4 x 10^7 years,
the e-folding timescale of an Eddington luminosity black hole with accretion
efficiency eps=0.1, corresponds to a quasar correlation length r_0 ~ 10 Mpc/h
in low-density cosmological models at z=2-3; this value is consistent with
current clustering measurements, but these have large uncertainties.
High-precision clustering measurements from the 2dF and Sloan quasar surveys
will test our key assumption of a tight correlation between quasar luminosity
and host halo mass, and if this assumption holds then they should determine t_Q
to a factor of three or better. An accurate determination of the quasar
lifetime will show whether supermassive black holes acquire most of their mass
during high-luminosity accretion, and it will show whether the black holes in
the nuclei of typical nearby galaxies were once the central engines of
high-luminosity quasars.Comment: ApJ Accepted (Feb 2001). 30 pages, 8 embedded ps figures, AASTEX5.
Added discussion of quasar luminosity evolution. Also available at
http://www.ociw.edu/~martini/pubs
Improving Escherichia coli membrane integrity and fatty acid production by expression tuning of FadL and OmpF
Background Construction of microbial biocatalysts for the production of biorenewables at economically viable yields and titers is frequently hampered by product toxicity. Membrane damage is often deemed as the principal mechanism of this toxicity, particularly in regards to decreased membrane integrity. Previous studies have attempted to engineer the membrane with the goal of increasing membrane integrity. However, most of these works focused on engineering of phospholipids and efforts to identify membrane proteins that can be targeted to improve fatty acid production have been unsuccessful. Results Here we show that deletion of outer membrane protein ompF significantly increased membrane integrity, fatty acid tolerance and fatty acid production, possibly due to prevention of re-entry of short chain fatty acids. In contrast, deletion of fadL resulted in significantly decreased membrane integrity and fatty acid production. Consistently, increased expression of fadL remarkably increased membrane integrity and fatty acid tolerance while also increasing the final fatty acid titer. This 34% increase in the final fatty acid titer was possibly due to increased membrane lipid biosynthesis. Tuning of fadL expression showed that there is a positive relationship between fadL abundance and fatty acid production. Combinatorial deletion of ompFand increased expression of fadL were found to have an additive role in increasing membrane integrity, and was associated with a 53% increase the fatty acid titer, to 2.3 g/L. Conclusions These results emphasize the importance of membrane proteins for maintaining membrane integrity and production of biorenewables, such as fatty acids, which expands the targets for membrane engineering
Interacting Boson Theory of the Magnetization Process of the Spin-1/2 Ferromagnetic-Antiferromagnetic Alternating Heisenberg Chain
The low temperature magnetization process of the
ferromagnetic-antiferromagnetic Heisenberg chain is studied using the
interacting boson approximation. In the low field regime and near the
saturation field, the spin wave excitations are approximated by the
function boson gas for which the Bethe ansatz solution is available. The finite
temperature properties are calculated by solving the integral equation
numerically. The comparison is made with Monte Carlo calculation and the limit
of the applicability of the present approximation is discussed.Comment: 4 pages, 7 figure
Semiclassical Quantization by Pade Approximant to Periodic Orbit Sums
Periodic orbit quantization requires an analytic continuation of
non-convergent semiclassical trace formulae. We propose a method for
semiclassical quantization based upon the Pade approximant to the periodic
orbit sums. The Pade approximant allows the re-summation of the typically
exponentially divergent periodic orbit terms. The technique does not depend on
the existence of a symbolic dynamics and can be applied to both bound and open
systems. Numerical results are presented for two different systems with chaotic
and regular classical dynamics, viz. the three-disk scattering system and the
circle billiard.Comment: 7 pages, 3 figures, submitted to Europhys. Let
The groups of automorphisms of the Witt W (n) and Virasoro Lie algebras
Let Ln = K[x1±1,..., xn±1] be a Laurent polynomial algebra over a field K of characteristic zero, Wn:= DerK(Ln) the Lie algebra of K-derivations of the algebra Ln, the so-called Witt Lie algebra, and let Vir be the Virasoro Lie algebra which is a 1-dimensional central extension of the Witt Lie algebra. The Lie algebras Wn and Vir are infinite dimen- sional Lie algebras. We prove that the following isomorphisms of the groups of Lie algebra automorphisms hold: AutLie(Vir
Implicit memory and cognitive aging
It is well documented that explicit (declarative, conscious) memory declines in normal aging. Studies have shown a progressive reduction in this form of memory with age, and healthy older adults (typically aged 65+ years) usually perform worse than younger adults (typically aged 18-30 years) on laboratory tests of explicit memory such as recall and recognition. In contrast, it is less clear whether implicit (procedural, unconscious) memory declines or remains stable in normal aging. Implicit memory is evident when previous experiences affect (e.g., facilitate) performance on tasks that do not require conscious recollection of those experiences. This can manifest in rehearsed motor skills, such as playing a musical instrument, but is typically indexed in the laboratory by the greater ease with which previously studied information is processed relative to non-studied information (e.g., repetition priming). While a vast amount of research has accumulated to suggest that implicit memory remains relatively stable over the adult lifespan, and is similar in samples of young and older adults, other studies have in contrast revealed that implicit memory is subject to age-related decline. Improving methods for determining whether implicit memory declines or remains stable with age is an important goal for future research, as the issue not only has significant implications for an aging society regarding interventions likely to ameliorate the effects of age-related explicit memory decline, but can also inform our theoretical understanding of human memory systems
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