First-principles calculation of the thermoelectric figure of merit for [2,2]paracyclophane-based single-molecule junctions

Here we present a theoretical study of the thermoelectric transport through {[}2,2{]}para\-cyclo\-phane-based single-molecule junctions. Combining electronic and vibrational structures, obtained from density functional theory (DFT), with nonequilibrium Green's function techniques, allows us to treat both electronic and phononic transport properties at a first-principles level. For the electronic part, we include an approximate self-energy correction, based on the DFT+$\Sigma$ approach. This enables us to make a reliable prediction of all linear response transport coefficients entering the thermoelectric figure of merit $ZT$. Paracyclophane derivatives offer a great flexibility in tuning their chemical properties by attaching different functional groups. We show that, for the specific molecule, the functional groups mainly influence the thermopower, allowing to tune its sign and absolute value. We predict that the functionalization of the bare paracyclophane leads to a largely enhanced electronic contribution $Z_{\mathrm{el}}T$ to the figure of merit. Nevertheless, the high phononic contribution to the thermal conductance strongly suppresses $ZT$. Our work demonstrates the importance to include the phonon thermal conductance for any realistic estimate of the $ZT$ for off-resonant molecular transport junctions. In addition, it shows the possibility of a chemical tuning of the thermoelectric properties for a series of available molecules, leading to equally performing hole- and electron-conducting junctions based on the same molecular framework.Comment: 8 pages, 7 figure

The effect of growth-promoting methylobacteria on seedling development in Ginkgo biloba L.

Microbes of the genus Methylobacterium are regularly associated with leaves and fruits of plants. In experimental tests, they promote the growth of germ-free liverworts and mosses, which are ancient land plants. In this study we analyzed the effect of M. mesophilicum, a bacterium that has been isolated from the organs of numerous plant species, including gymnosperms and angiosperms, on the development of sterile embryos of Ginkgo biloba L., a unique living fossil among the embryophyta. In addition, germ-free seeds of Pinus sylvestris were inoculated with the same strain of methylobacteria. In G. biloba seedlings that were raised in a 12 h dark/light regime, a promotion of root development was recorded in samples treated with the methylobacteria. A fresh mass increase of + 25 % occurred within 6 weeks of inoculation with bacteria, compared to the aseptic control. In contrast, shoot development of the same plants was not significantly affected by these bacteria. In Pinus seedlings, organ development was unaffected by the presence of methylobacteria. Our results document a differential sensitivity of the root system versus the shoot towards these ubiquitously distributed plant-associated bacteria. The data are discussed with reference to the isolated taxonomic position of Ginkgo biloba, one of the most primitive gymnosperms in the biosphere that is economically important as a medicinal plant

Partial Homology Relations - Satisfiability in terms of Di-Cographs

Directed cographs (di-cographs) play a crucial role in the reconstruction of evolutionary histories of genes based on homology relations which are binary relations between genes. A variety of methods based on pairwise sequence comparisons can be used to infer such homology relations (e.g.\ orthology, paralogy, xenology). They are \emph{satisfiable} if the relations can be explained by an event-labeled gene tree, i.e., they can simultaneously co-exist in an evolutionary history of the underlying genes. Every gene tree is equivalently interpreted as a so-called cotree that entirely encodes the structure of a di-cograph. Thus, satisfiable homology relations must necessarily form a di-cograph. The inferred homology relations might not cover each pair of genes and thus, provide only partial knowledge on the full set of homology relations. Moreover, for particular pairs of genes, it might be known with a high degree of certainty that they are not orthologs (resp.\ paralogs, xenologs) which yields forbidden pairs of genes. Motivated by this observation, we characterize (partial) satisfiable homology relations with or without forbidden gene pairs, provide a quadratic-time algorithm for their recognition and for the computation of a cotree that explains the given relations

On Symbolic Ultrametrics, Cotree Representations, and Cograph Edge Decompositions and Partitions

Symbolic ultrametrics define edge-colored complete graphs K_n and yield a simple tree representation of K_n. We discuss, under which conditions this idea can be generalized to find a symbolic ultrametric that, in addition, distinguishes between edges and non-edges of arbitrary graphs G=(V,E) and thus, yielding a simple tree representation of G. We prove that such a symbolic ultrametric can only be defined for G if and only if G is a so-called cograph. A cograph is uniquely determined by a so-called cotree. As not all graphs are cographs, we ask, furthermore, what is the minimum number of cotrees needed to represent the topology of G. The latter problem is equivalent to find an optimal cograph edge k-decomposition {E_1,...,E_k} of E so that each subgraph (V,E_i) of G is a cograph. An upper bound for the integer k is derived and it is shown that determining whether a graph has a cograph 2-decomposition, resp., 2-partition is NP-complete

The Complement of the Djokovic-Winkler Relation

The Djokovi\'{c}-Winkler relation $\Theta$ is a binary relation defined on the edge set of a given graph that is based on the distances of certain vertices and which plays a prominent role in graph theory. In this paper, we explore the relatively uncharted ``reflexive complement'' $\overline\Theta$ of $\Theta$, where $(e,f)\in \overline\Theta$ if and only if $e=f$ or $(e,f)\notin \Theta$ for edges $e$ and $f$. We establish the relationship between $\overline\Theta$ and the set $\Delta_{ef}$, comprising the distances between the vertices of $e$ and $f$ and shed some light on the intricacies of its transitive closure $\overline\Theta^*$. Notably, we demonstrate that $\overline\Theta^*$ exhibits multiple equivalence classes only within a restricted subclass of complete multipartite graphs. In addition, we characterize non-trivial relations $R$ that coincide with $\overline\Theta$ as those where the graph representation is disconnected, with each connected component being the (join of) Cartesian product of complete graphs. The latter results imply, somewhat surprisingly, that knowledge about the distances between vertices is not required to determine $\overline\Theta^*$. Moreover, $\overline\Theta^*$ has either exactly one or three equivalence classes

A better climate for disaster risk management

Climate-related disasters are by far the most frequent natural disasters, exacting a heavy toll on people and economies. Their frequency and economic losses have steadily increased over the past few decades, stretching the response capacities of governments and humanitarian organizations. One of the many ways this challenge can be addressed is by making more effective use of the increasing wealth of climate information and tailoring it to the needs of those who could use it, to better predict and prepare for such disasters before they occur. Written in partnership with a range of humanitarian organizations, A Better Climate for Disaster Risk Management is the third in the Climate and Society Publication series. This issue highlights recent advances in the use of climate information to manage risks and improve livelihoods, such as new partnerships and user-designed information platforms. It draws together and analyzes experiences from 17 case studies that capture the current state of knowledge. It also highlights research innovations in technical boxes throughout the publication. A problem-solving framework is used to demonstrate the challenges and opportunities facing disaster risk managers in using climate science with a three step approach: identifying the problem, developing tools, and taking action, reflected in the chapter titles. The case studies and experiences presented in this book draw on a wealth of practical experience from within the humanitarian community. They acknowledge the enormous effort and investment by very many national and local governments, international organizations, and an increasing range of other actors in the field of climate information for disaster risk management. This publication adds to the growing body of knowledge, focusing on the experiences of a number of mostly non-governmental actors, especially the International Federation of Red Cross and Red Crescent Societies, and how through partnerships, they have helped to integrate state of the art climate science and information into improved decision-making. Exploring the use of climate information for disaster risk management, it identifies both the achievements and the obstacles associated with this endeavour. From them are distilled the lessons learned, and a series of recommendations. Of these, effective partnership is highlighted as the single most critical ingredient for success. Climate information that can be acted upon is best created in dialogue between the users and providers, and partnerships between climate scientists and disaster risk managers should promote knowledge sharing, trust, and the development of innovative solutions. Efforts to better apply climate information in disaster risk management should first focus on immediate opportunities and potential ‘quick wins’. Practical engagements can be fostered by initially concentrating on countries and regions with relatively good seasonal forecast skills, and where humanitarian decisions can be influenced to provide large and immediate returns on investment. Disaster risk managers must, however, improve their understanding of the potential as well as the limitations of climate information, as the development of realistic expectations is vital to maintaining trust in the information and those who provide it. Cases demonstrate that when climate information can be integrated into existing decision-making support tools or systems, it becomes an important piece of the information that is considered and taken up in the routine activities of disaster risk managers. The relative contribution that seasonal, decadal, and long-term trends make to current and future climate also needs to be better understood. To achieve the goal of providing relevant climate services to support disaster risk management, climate information providers such as national meteorological services must tailor their information to the problem at hand, either by refining products through iterative interaction with partners or by simplifying the presentation. Although there have been many achievements and advances, much potential remains to be realized. Herein lies the opportunity: to build trust and improve the sharing of knowledge between the providers of climate services, and those who can use those services to enhance disaster risk management, jointly reducing human suffering and achieving more sustainable development

Climate risk management in Africa: learning from practice

Assessment, prediction and mitigation of the impact of climate variability and change on many societal sectors such as agriculture, water resources, electricity production and health are broadly being organized under the banner of ‘climate services’. As societal development and sustainability challenges facing many countries continue to mount, there is a growing need for relevant, timely and accurate information on climate processes and improved climate services. The CLIVAR Variability of the American Monsoon Systems (VAMOS) panel seeks to contribute to the development of comprehensive international and domestic climate services by coordinating and conducting foundational climate research on climate processes and their societal impacts. With this goal in mind we are pleased to present this issue of the VAMOS! Newsletter, which contains a series of contributions that relate to current activities in climate research and regional capacity building activities. Five articles are contained herein and discuss a range of activities emerging from the VAMOS community. Douglas et al. provide a comprehensive update on the VAMOS Intra-Americas Study of Climate Processes (IASCLiP) program which has been coordinating a host of modeling, observation network assessment and forecasting activities for the Intra- America Seas region. Next, Taylor et al. describe the evolution of the Caribbean Climate Modeling Initiative which focuses on generating new regional scenarios of climate impacts on Caribbean island nations and on building future modeling capacity in the region. Kirtman et al. then provide a high-level summary of how modeling activities within VAMOS are being coordinated internally and are being connected to extra-VAMOS research efforts. Mechanisms for assessing and prioritizing societal vulnerabilities to climate variability across many time scales is discussed by Baethgen and, lastly, Gochis et al. provide an update on observational infrastructure enhancement in the Caribbean and meso-American regions through the development of an integrated Global Positioning System precipitable water vapor (GPS-PWV) observing network. Combined, we hope these articles stimulate further awareness and progress on meeting the demands of climate services for the American Monsoon region

Preparation And Characterization Of Composite Hollow Fiber Reverse Osmosis Membranes By Plasma Polymerization. 1. Design Of Plasma Reactor And Operational Parameters

Composite hollow fiber reverse osmosis membranes were prepared by depositing a thin layer (10-50 nm) of plasma polymers on hollow fibers with porous walls (made of polysulfone). The coating was carried out in a semicontinuous manner with six strands of substrate fibers. Operational parameters which influence reverse osmosis characteristics of composite membranes were investigated. © 1984, American Chemical Society. All rights reserved

Quadrilateral-octagon coordinates for almost normal surfaces

Normal and almost normal surfaces are essential tools for algorithmic 3-manifold topology, but to use them requires exponentially slow enumeration algorithms in a high-dimensional vector space. The quadrilateral coordinates of Tollefson alleviate this problem considerably for normal surfaces, by reducing the dimension of this vector space from 7n to 3n (where n is the complexity of the underlying triangulation). Here we develop an analogous theory for octagonal almost normal surfaces, using quadrilateral and octagon coordinates to reduce this dimension from 10n to 6n. As an application, we show that quadrilateral-octagon coordinates can be used exclusively in the streamlined 3-sphere recognition algorithm of Jaco, Rubinstein and Thompson, reducing experimental running times by factors of thousands. We also introduce joint coordinates, a system with only 3n dimensions for octagonal almost normal surfaces that has appealing geometric properties.Comment: 34 pages, 20 figures; v2: Simplified the proof of Theorem 4.5 using cohomology, plus other minor changes; v3: Minor housekeepin

Findings of the East Africa Humanitarian Climate Risk Management Workshop

The East African humanitarian community is looking for ways to better respond to the challenges presented by climate risks, including climate change, but is struggling to access appropriate and targeted scientific data that can inform their operations. Recent advances in science and technology have produced a variety of new tools for humanitarian organizations working on climate risk management. Humanitarian actors have an enormous opportunity to utilize these tools to inform risk reduction, preparedness and contingency planning, as well as program implementation. Despite such advances, many challenges remain to the practical application of these tools in the humanitarian context. Often times, climate information is too technical or lacks the context necessary for use in humanitarian planning and operations. Thus, climate information must be tailored to specific needs and presented in formats that are readily accessible to these users. In response, the United Nations Office for the Coordination of Humanitarian Affairs (UNOCHA), in close collaboration with the International Federation of Red Cross/Red Crescent Societies (IFRC), initiated the development of a 2-day Humanitarian Climate Risk Management Workshop on 23- 24 February 2010. Initiatives that enable interaction can help to bridge the divide between humanitarian practitioners and climate experts; feedback provided by end-users can guide research and development of new prediction technologies and tools, as well as more appropriate packaging of current information. At the same time, humanitarian actors need to evaluate how such information can usefully inform their decision-making at various timescales. The challenge of decision-making under uncertainty must be addressed if climate information is to be used effectively within humanitarian planning, preparedness, and response. This workshop aimed to address such barriers to the use of climate information