U-duality Covariant M-theory Cosmology

A manifestly U-duality covariant approach to M-theory cosmology is developed and applied to cosmologies in dimensions D=4,5. Cosmological properties such as expansion powers and Hubble parameters turn out to be U-duality invariant in certain asymptotic regions. U-duality transformations acting on cosmological solutions, on the other hand, shift the transition time between two asymptotic regions and determine the details of the transition. Moreover, in D=5, we show that U-duality can map expanding negative and positive branch solutions into each other.Comment: 18 pages, LATEX, 1 Postscript figure include

SGN Database: From QTLs to Genomes

Quantitative trait loci (QTL) analysis is used to dissect the genetic basis underlying polygenic traits. Several public databases have been storing and making QTL data available to research communities. To our knowledge, current QTL databases rely on manual curation where curators read literature and extract relevant QTL information to store in databases. Evidently, this approach is expensive in terms of expert manpower and time use and limits the type of data that can be curated. At the Solanaceae Genomics Network (SGN) ("http://sgn.cornell.edu":http://sgn.cornell.edu), we have developed a database to store raw phenotype and genotype data from QTL studies, perform, on the fly, QTL analysis using R/QTL statistical software ("http://www.rqtl.org":http://www.rqtl.org) and visualize QTLs on a genetic map. Users can identify peak, and flanking markers for QTLs of traits of interest. The QTL database is integrated with other SGN databases (eg. Marker, BACs, and Unigenes), and analysis tools such as the Comparative Map Viewer. Using the comparative map viewer, users can compare chromosome with QTL regions to genetic maps of interest from the same or different Solanaceae species. As the tomato genome sequencing advances, users can also identify corresponding BAC sequences or locations on the tomato physical map, which can be suggestive of candidate genes for a trait of interest.

Furthermore at SGN, images, quantitative phenotype and genotype data, publications, genetic maps generated by QTL studies are displayed and available for download. Currently, data from three F2 and two backcross population QTL studies on fruit morphology traits (18 – 46 traits per population) is available at the SGN website for viewing at population, accession, and trait levels. Traits are described using ontology terms. Phenotype data is presented in tabular and graphical formats such as frequency distributions with basic descriptive statistics. Mapping data showing location of parental alleles on individual accession genetic maps is also available.

SGN is a public database hosted at Boyce Thomson Institute, Cornell University, and funded by USDA CSREES and NSF

Estimating Crypto-Related Risk: Market-Based Evidence from FTX’s Failure and Its Contagion on U.S. Banks

We use historical covariance between stock returns of U.S. banks and bitcoin returns to estimate a sensitivity measure that captures crypto-related risk in financial institutions. The measure effectively explains cross-sectional stock returns of 219 U.S. based financial institutions in response to the failure of FTX on November 11, 2022. Overall we document negative contagion effects on the market valuation of U.S. banks. We further show that this risk measure is unrelated to variables that have been used to explain operational risk in previous literature, i.e., corporate governance and business complexity. However, we document a significant relation with bank liquidity as measured by the Tier 1 capital adequacy ratio. We conclude that, on average, it is the banks with sufficient liquidity reserves that venture into the crypto sphere. Our approach offers individual investors and customers the opportunity to leverage market efficiency to evaluate the idiosyncratic level of crypto-related risk in a financial institution

Optical imaging of strain in two-dimensional crystals

Strain engineering is widely used in material science to tune the (opto-)electronic properties of materials and enhance the performance of devices. Two-dimensional atomic crystals are a versatile playground to study the influence of strain, as they can sustain very large deformations without breaking. Various optical techniques have been employed to probe strain in two-dimensional materials, including micro-Raman and photoluminescence spectroscopy. Here we demonstrate that optical second harmonic generation constitutes an even more powerful technique, as it allows to extract the full strain tensor with a spatial resolution below the optical diffraction limit. Our method is based on the strain-induced modification of the nonlinear susceptibility tensor due to a photoelastic effect. Using a two-point bending technique, we determine the photoelastic tensor elements of molybdenum disulfide. Once identified, these parameters allow us to spatially image the two-dimensional strain field in an inhomogeneously strained sample.Comment: 13 pages, 4 figure

A river's connective tissue: Lab observations of particle pathways and riffle formation during floods

In rivers it is difficult to quantify bedform dynamics during storm events. Direct observation of sediment pathways would provide insight into the mechanisms that underly bedform formation and destruction. In the current study, our objective was to visualize these processes in a meandering pool riffle system with partial bed cover. Observing erosive and depositional patterns, as well as the locations of active sediment transport, provides insight into the validity of various pool-riffle maintenance theories. We used a physical 1:40 scaled model of Toronto’s Wilket Creek to simulate storm events during which riffles formed as connective bedforms between alternate point bars. Exported sediment was weighed and sieved to measure the grain size distribution, while the bed’s pre- and post- storm topography was quantified using Structure-from-Motion techniques. Sediment pathways were observed using a novel technique, where regions of interest were filmed at 60 frames per second under ultra violet light, illuminating painted tracers. Three paint colors were used for different size tracers, which allowed us to apply image segmentation and create separate videos for three size fractions of the sediment. Pathways were then extracted using Lagrangian tracking software. Results show that the area of active transport is limited to a narrow portion of the channel width that increases with flood stage. At low flow, transport is routed along the toe of point bars, while no particles travel into the region of the pool, where the bed is uncovered. Riffles are rarely observed at these stages. As the flow increases, the lateral extent of active transport expands to include the higher parts of the bars, while connective riffles grow in areal extent and height. Erosion and deposition was found to occur more readily along the active sediment transport zones. Pathways varied by particle size so that smaller particles traveled higher over the point bar and large particles tended to collect in the riffle. These results indicate that sediment-routing is a dominant mechanism behind the formation and maintenance of riffles in meandering rivers. Future work to quantify these processes will increase the effectiveness and longevity of river remediation design through targeted sediment augmentation instead of bedform reconstruction

Controlled generation of a pn-junction in a waveguide integrated graphene photodetector

With its electrically tunable light absorption and ultrafast photoresponse, graphene is a promising candidate for high-speed chip-integrated photonics. The generation mechanisms of photosignals in graphene photodetectors have been studied extensively in the past years. However, the knowledge about efficient light conversion at graphene pn-junctions has not yet been translated into high-performance devices. Here, we present a graphene photodetector integrated on a silicon slot-waveguide, acting as a dual-gate to create a pn-junction in the optical absorption region of the device. While at zero bias the photo-thermoelectric effect is the dominant conversion process, an additional photoconductive contribution is identified in a biased configuration. Extrinsic responsivities of 35 mA/W, or 3.5 V/W, at zero bias and 76 mA/W at 300 mV bias voltage are achieved. The device exhibits a 3 dB-bandwidth of 65 GHz, which is the highest value reported for a graphene-based photodetector.Comment: 19 pages, 16 figure

The SOL Genomics Network Model: Making Community Annotation Work

The concept of community annotation is a growing discipline for achieving participation of the research community in depositing up‐to‐date knowledge in biological databases.
The Solanaceae Genomics Network ("SGN":http://sgn.cornell.edu/) is a clade‐oriented database (COD) focusing on plants of the nightshade family, including tomato, potato, pepper, eggplant, and tobacco, and is one of the bioinformatics nodes of the international tomato genome sequencing project. One of our major efforts is linking Solanaceae phenotype information with the underlying genes, and subsequently the genome. As part of this goal, SGN has introduced a database for locus names and descriptors, and a database for phenotypes of natural and induced variation. These two databases have web interfaces that allow cross references, associations with tomato gene models, and in‐house curated information of sequences, literature, ontologies, gene networks, and the Solanaceae biochemical pathways database ("SolCyc":http://solcyc.sgn.cornell.edu). All of our curator tools are open for online community annotation, through specially assigned “submitter” accounts. 

Currently the community database consists of 5,548 phenotyped accessions, and 5,739 curated loci, out of which more than 300 loci where contributed or annotated by 66 active submitters, creating a database that is truly community driven.
This framework is easily adaptable for other projects working on other taxa (for example see "http://chlamybase.org":http://chlamybase.org), greatly expanding the application of this user‐friendly online annotation system. Community participation is fostered by an active outreach program that includes contacting potential submitters via emails, at meetings and conferences, and by promoting featured user submitted annotations on the SGN homepage. The source code and database schema for all SGN functionalities are freely available. Please contact SGN at "sgn‐feedback[at]sgn.cornell.edu":mailto:[email protected] for more information