1,280 research outputs found
Histochemical assessment of tissue viability and herbicide damage in woody stems of Lonicera maackii
Spectral properties of the three-dimensional Hubbard model
We present momentum resolved single-particle spectra for the
three-dimensional Hubbard model for the paramagnetic and antiferromagnetically
ordered phase obtained within the dynamical cluster approximation. The
effective cluster problem is solved by continuous-time Quantum Monte Carlo
simulations. The absence of a time discretization error and the ability to
perform Monte Carlo measurements directly in Matsubara frequencies enable us to
analytically continue the self-energies by maximum entropy, which is essential
to obtain momentum resolved spectral functions for the N'eel state. We
investigate the dependence on temperature and interaction strength and the
effect of magnetic frustration introduced by a next-nearest neighbor hopping.
One particular question we address here is the influence of the frustrating
interaction on the metal insulator transition of the three-dimensional Hubbard
model.Comment: 16 pages, 14 figure
Casimir Invariants for Systems Undergoing Collective Motion
Dicke states are states of a collection of particles which have been under
active investigation for several reasons. One reason is that the decay rates of
these states can be quite different from a set of independently evolving
particles. Another reason is that a particular class of these states are
decoherence-free or noiseless with respect to a set of errors. These noiseless
states, or more generally subsystems, can avoid certain types of errors in
quantum information processing devices. Here we provide a method for
calculating invariants of systems of particles undergoing collective motions.
These invariants can be used to determine a complete set of commuting
observables for a class of Dicke states as well as identify possible logical
operations for decoherence-free/noiseless subsystems. Our method is quite
general and provides results for cases where the constituent particles have
more than two internal states.Comment: 5 page
Gene expression in bryozoan larvae suggest a fundamental importance of pre-patterned blastemic cells in the bryozoan life-cycle
<p>Abstract</p> <p>Background</p> <p>Bryozoa is a clade of aquatic protostomes. The bryozoan life cycle typically comprises a larval stage, which metamorphoses into a sessile adult that proliferates by asexual budding to form colonies. The homology of bryozoan larvae with other protostome larvae is enigmatic. Bryozoan larvae exhibit blastemic tissues that contribute to build the adult during morphogenesis. However, it remains unclear if the cells of these tissues are pre-determined according to their future fate or if the cells are undifferentiated, pluripotent stem cells. Gene expression studies can help to identify molecular patterning of larval and adult tissues and enlighten the evolution of bryozoan life cycle stages.</p> <p>Results</p> <p>We investigated the spatial expression of 13 developmental genes in the larval stage of the gymnolaemate bryozoan <it>Bugula neritina</it>. We found most genes expressed in discrete regions in larval blastemic tissues that form definitive components of the adult body plan. Only two of the 13 genes, <it>BnTropomyosin </it>and <it>BnFoxAB</it>, were exclusively expressed in larval tissues that are discarded during metamorphosis.</p> <p>Conclusions</p> <p>Our results suggest that the larval blastemas in <it>Bugula </it>are pre-patterned according to their future fate in the adult. The gene expression patterns indicate that some of the bryozoan blastemas can be interpreted to correspond to homologous adult tissues of other animals. This study challenges an earlier proposed view that metazoan larvae share homologous undifferentiated "set-aside cells", and instead points to an independent origin of the bryozoan larval stage with respect to other lophotrochozoans.</p
A generic physical vulnerability model for floods: review and concept for data-scarce regions
The use of different methods for physical flood vulnerability assessment has evolved over time, from traditional single-parameter stage–damage curves to multi-parameter approaches such as multivariate or indicator-based models. However, despite the extensive implementation of these models in flood risk assessment globally, a considerable gap remains in their applicability to data-scarce regions. Considering that these regions are mostly areas with a limited capacity to cope with disasters, there is an essential need for assessing the physical vulnerability of the built environment and contributing to an improvement of flood risk reduction. To close this gap, we propose linking approaches with reduced data requirements, such as vulnerability indicators (integrating major damage drivers) and damage grades (integrating frequently observed damage patterns). First, we present a review of current studies of physical vulnerability indicators and flood damage models comprised of stage–damage curves and the multivariate methods that have been applied to predict damage grades. Second, we propose a new conceptual framework for assessing the physical vulnerability of buildings exposed to flood hazards that has been specifically tailored for use in data-scarce regions. This framework is operationalized in three steps: (i) developing a vulnerability index, (ii) identifying regional damage grades, and (iii) linking resulting index classes with damage patterns, utilizing a synthetic “what-if” analysis. The new framework is a first step for enhancing flood damage prediction to support risk reduction in data-scarce regions. It addresses selected gaps in the literature by extending the application of the vulnerability index for damage grade prediction through the use of a synthetic multi-parameter approach. The framework can be adapted to different data-scarce regions and allows for integrating possible modifications to damage drivers and damage grades
Analytic Continuation of Quantum Monte Carlo Data by Stochastic Analytical Inference
We present an algorithm for the analytic continuation of imaginary-time
quantum Monte Carlo data which is strictly based on principles of Bayesian
statistical inference. Within this framework we are able to obtain an explicit
expression for the calculation of a weighted average over possible energy
spectra, which can be evaluated by standard Monte Carlo simulations, yielding
as by-product also the distribution function as function of the regularization
parameter. Our algorithm thus avoids the usual ad-hoc assumptions introduced in
similar algortihms to fix the regularization parameter. We apply the algorithm
to imaginary-time quantum Monte Carlo data and compare the resulting energy
spectra with those from a standard maximum entropy calculation
Studies on the double alkylation of 2,2-disubstituted-1,3-dithiacycloalkane-S-oxides: synthesis of tertiary thiol derivatives
Di-alkylation of 2,2-dimethyl-1,3-dithiacycloalkane-S-oxides has been achieved allowing the synthesis of
two tertiary thiol centres. The diastereoisomers of the mono-alkylated products have been shown to
react at different rates. The X-ray crystal structures of three substituted dithiane-S-oxides have been
determined, and the conversion of the dialkylated products into cyclic disulfide derivatives of tertiary
thiols (1,2-dithiolanes) has been achieved by treatment with acid
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