1,183 research outputs found
Co-regulation of two tandem genes by one blue-light element in Neurospora crassa
Many genes of Neurospora crassa are regulated by blue light: al-1 (Schmidhauser et al. 1990 Mol. Cell. Biol. 10:5064-5070), al-2 (Lauter, Schmidhauser, Yanofsky, Russo unpublished), al-3 (Nelson et al. 1989 Mol. Cell. Biol. 9:1271-1276), bli-3, bli-4, bli-7, bli-13 (Sommer et al. 1989 NAR 17:5713-5723). For none of these genes are the blue light cis-regulatory sequences (blue-light elements, BE) known. Here we report the presence of such BE in front of bli-4
Superacid resin-based heterogeneous catalysts for the selective acylation of 1,2-methylenedioxybenzene
In this work, we firstly report on the use of highly active and selective Aquivion superacid resins as heterogeneous catalysts for the acylation of 1,2-methylenedioxybenzene (MDB) with propionic anhydride (AP). The reaction was investigated and optimized using solvent-free conditions to selectively produce 3,4-methylenedioxypropiophenone (MDP1P), a key intermediate for the manufacture of active ingredients used in insecticide formulations with a volume of production of roughly 3000 t/y. Interestingly, Aquivion-based catalysts allows to work in mild reaction conditions (i. e. 80 °C), obtaining MDP1P yields as high as 44 % after only 1 h of reaction (selectivity 83 %). A detailed study of the AP reactivity demonstrated its tendency to promote oligomerization reactions that, as confirmed by ex-situ and in-situ FT-ATR analyses, caused the deactivation of the catalyst forming surficial carbonaceous residues. In this context, a fast oxidation of the resin surface organic residues using a diluted HNO3 (or H2O2) solution was proven to be an efficient method to regenerate the catalyst, which can be reused for several reaction cycles. The results obtained in preliminary scale-up tests were basically unaffected by the reaction volume (up to 800 mL), paving the way for possible future applications of the process
Allele Frequency Matching Between SNPs Reveals an Excess of Linkage Disequilibrium in Genic Regions of the Human Genome
Significant interest has emerged in mapping genetic susceptibility for complex traits through whole-genome association studies. These studies rely on the extent of association, i.e., linkage disequilibrium (LD), between single nucleotide polymorphisms (SNPs) across the human genome. LD describes the nonrandom association between SNP pairs and can be used as a metric when designing maximally informative panels of SNPs for association studies in human populations. Using data from the 1.58 million SNPs genotyped by Perlegen, we explored the allele frequency dependence of the LD statistic r (2) both empirically and theoretically. We show that average r (2) values between SNPs unmatched for allele frequency are always limited to much less than 1 (theoretical [Image: see text] approximately 0.46 to 0.57 for this dataset). Frequency matching of SNP pairs provides a more sensitive measure for assessing the average decay of LD and generates average r (2) values across nearly the entire informative range (from 0 to 0.89 through 0.95). Additionally, we analyzed the extent of perfect LD (r (2) = 1.0) using frequency-matched SNPs and found significant differences in the extent of LD in genic regions versus intergenic regions. The SNP pairs exhibiting perfect LD showed a significant bias for derived, nonancestral alleles, providing evidence for positive natural selection in the human genome
Wind on the boundary for the Abelian sandpile model
We continue our investigation of the two-dimensional Abelian sandpile model
in terms of a logarithmic conformal field theory with central charge c=-2, by
introducing two new boundary conditions. These have two unusual features: they
carry an intrinsic orientation, and, more strangely, they cannot be imposed
uniformly on a whole boundary (like the edge of a cylinder). They lead to seven
new boundary condition changing fields, some of them being in highest weight
representations (weights -1/8, 0 and 3/8), some others belonging to
indecomposable representations with rank 2 Jordan cells (lowest weights 0 and
1). Their fusion algebra appears to be in full agreement with the fusion rules
conjectured by Gaberdiel and Kausch.Comment: 26 pages, 4 figure
Pareto Optimization of a Laser Wakefield Accelerator
Optimization of accelerator performance parameters is limited by numerous
trade-offs and finding the appropriate balance between optimization goals for
an unknown system is challenging to achieve. Here we show that multi-objective
Bayesian optimization can map the solution space of a laser wakefield
accelerator in a very sample-efficient way. Using a Gaussian mixture model, we
isolate contributions related to an electron bunch at a certain energy and we
observe that there exists a wide range of Pareto-optimal solutions that trade
beam energy versus charge at similar laser-to-beam efficiency. However, many
applications such as light sources require particle beams at a certain target
energy. Once such a constraint is introduced we observe a direct trade-off
between energy spread and accelerator efficiency. We furthermore demonstrate
how specific solutions can be exploited using \emph{a posteriori} scalarization
of the objectives, thereby efficiently splitting the exploration and
exploitation phases
Acquired demyelination but not genetic developmental defects in myelination leads to brain tissue stiffness changes
Changes in axonal myelination are an important hallmark of aging and a number of neurological diseases. Demyelinated axons are impaired in their function and degenerate over time. Oligodendrocytes, the cells responsible for myelination of axons, are sensitive to mechanical properties of their environment. Growing evidence indicates that mechanical properties of demyelinating lesions are different from the healthy state and thus have the potential to affect myelinating potential of oligodendrocytes. We performed a high-resolution spatial mapping of the mechanical heterogeneity of demyelinating lesions using atomic force microscope-enabled indentation. Our results indicate that the stiffness of specific regions of mouse brain tissue is influenced by age and degree of myelination. Here we specifically demonstrate that acquired acute but not genetic demyelination leads to decreased tissue stiffness, which could influence the remyelination potential of oligodendrocytes. We also demonstrate that specific brain regions have unique ranges of stiffness in white and grey matter. Our ex vivo findings may help the design of future in vitro models to mimic the mechanical environment of the brain in healthy and diseased states. The mechanical properties of demyelinating lesions reported here may facilitate novel approaches in treating demyelinating diseases such as multiple sclerosis
Quantum-sl(2) action on a divided-power quantum plane at even roots of unity
We describe a nonstandard version of the quantum plane, the one in the basis
of divided powers at an even root of unity . It can be regarded
as an extension of the "nearly commutative" algebra with by nilpotents. For this quantum plane, we construct a Wess--Zumino-type de
Rham complex and find its decomposition into representations of the
-dimensional quantum group and its Lusztig extension; the
quantum group action is also defined on the algebra of quantum differential
operators on the quantum plane.Comment: 18 pages, amsart++, xy, times. V2: a reference and related comments
adde
Fusion algebra of critical percolation
We present an explicit conjecture for the chiral fusion algebra of critical
percolation considering Virasoro representations with no enlarged or extended
symmetry algebra. The representations we take to generate fusion are countably
infinite in number. The ensuing fusion rules are quasi-rational in the sense
that the fusion of a finite number of these representations decomposes into a
finite direct sum of these representations. The fusion rules are commutative,
associative and exhibit an sl(2) structure. They involve representations which
we call Kac representations of which some are reducible yet indecomposable
representations of rank 1. In particular, the identity of the fusion algebra is
a reducible yet indecomposable Kac representation of rank 1. We make detailed
comparisons of our fusion rules with the recent results of Eberle-Flohr and
Read-Saleur. Notably, in agreement with Eberle-Flohr, we find the appearance of
indecomposable representations of rank 3. Our fusion rules are supported by
extensive numerical studies of an integrable lattice model of critical
percolation. Details of our lattice findings and numerical results will be
presented elsewhere.Comment: 12 pages, v2: comments and references adde
Upper estimate of martingale dimension for self-similar fractals
We study upper estimates of the martingale dimension of diffusion
processes associated with strong local Dirichlet forms. By applying a general
strategy to self-similar Dirichlet forms on self-similar fractals, we prove
that for natural diffusions on post-critically finite self-similar sets
and that is dominated by the spectral dimension for the Brownian motion
on Sierpinski carpets.Comment: 49 pages, 7 figures; minor revision with adding a referenc
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