DEM Simulation of Concrete Fracture Phenomena

Concrete fracture phenomena are investigated in this work. It is the fracture processes and failure mechanisms which are specifically investigated rather than the reaching of a certain maximum load or the investigation of the concrete’s behaviour within a range of safe working loads. The following questions are addressed. How do the crack positions vary from one test to another? Is it possible to identify in advance where for example micro-cracks will emerge to a global macro-crack later on? In order to investigate this matter, a two-dimensional numerical simulation based on the Discrete Element Method (DEM) is used for the analysis of concrete behaviour under compression load. Frictional behaviour, crack initiation and damage evolution are analysed. Regarding the concrete body, convex and concave geometries can be treated. The cracks are discrete just as in real laboratory experiments. The cracks arise due to the interaction of the concrete particle elements and without the predefinition of any crack zones or crack elements. The simulation results are compared to the ones of laboratory experiments. The ratio of longitudinal strain to lateral strain is obtained as a result of the simulation and compared to experimental results. The qualitative evolution of postprocessing entities such as stresses and strains is analysed

Contacting single bundles of carbon nanotubes with alternating electric fields

Single bundles of carbon nanotubes have been selectively deposited from suspensions onto sub-micron electrodes with alternating electric fields. We explore the resulting contacts using several solvents and delineate the differences between Au and Ag as electrode materials. Alignment of the bundles between electrodes occurs at frequencies above 1 kHz. Control over the number of trapped bundles is achieved by choosing an electrode material which interacts strongly with the chemical functional groups of the carbon nanotubes, with superior contacts being formed with Ag electrodes.Comment: 4 pages, RevTe

Determination of Abundant Metabolite Matrix Adducts Illuminates the Dark Metabolome of MALDI-Mass Spectrometry Imaging Datasets

: Spatial metabolomics using mass spectrometry imaging (MSI) is a powerful tool to map hundreds to thousands of metabolites in biological systems. One major challenge in MSI is the annotation of m/z values, which is substantially complicated by background ions introduced throughout the chemicals and equipment used during experimental procedures. Among many factors, the formation of adducts with sodium or potassium ions, or in case of matrix-assisted laser desorption ionization (MALDI)- MSI, the presence of abundant matrix clusters strongly increases total m/z peak counts. Currently, there is a limitation to identify the chemistry of the many unknown peaks to interpret their biological function. We took advantage of the co-localization of adducts with their parent ions and the accuracy of high mass resolution to estimate adduct abundance in 20 datasets from different vendors of mass spectrometers. Metabolites ranging from lipids to amines and amino acids form matrix adducts with the commonly used 2,5-dihydroxybenzoic acid (DHB) matrix like [M + (DHB-H2O) + H]+ and [M + DHB + Na]+ . Current data analyses neglect those matrix adducts and overestimate total metabolite numbers, thereby expanding the number of unidentified peaks. Our study demonstrates that MALDI-MSI data are strongly influenced by adduct formation across different sample types and vendor platforms and reveals a major influence of so far unrecognized metabolite−matrix adducts on total peak counts (up to one third). We developed a software package, mass2adduct, for the community for an automated putative assignment and quantification of metabolite−matrix adducts enabling users to ultimately focus on the biologically relevant portion of the MSI data

Methyl and T-Butyl Group Reorientation in Planar Aromatic Solids: Low-Frequency Nuclear Magnetic Resonance Relaxometry and X-Ray Diffraction

We have synthesized 3-t-butylchrysene and measured the Larmor frequency omega/2pi (= 8.50, 22.5, and 53.0 MHz) and temperature T (110-310 K) dependence of the proton spin-lattice relaxation rate R in the polycrystalline solid [low-frequency solid state nuclear magnetic resonance (NMR) relaxometry]. We have also determined the molecular and crystal structure in a single crystal of 3-t-butylchrysene using x-ray diffraction, which indicates the presence of a unique t-butyl group environment. The spin-1/2 protons relax as a result of the spin-spin dipolar interactions being modulated by the superimposed reorientation of the t-butyl groups and their constituent methyl groups. The reorientation is successfully modeled by the simplest motion; that of random hopping describable by Poisson statistics. The x-ray data indicate near mirror-plane symmetry that places one methyl group nearly in the aromatic plane and the other two almost equally above and below the plane. The NMR relaxometry data indicate that the nearly in-plane methyl group and the entire t-butyl group reorient with a barrier of 24.2 +/- 0.9 kJ mol(-1), and the two out-of-plane methyl groups reorient with a barrier of 14.2 +/- 0.6 kJ mol(-1). Following a brief review of methyl group rotation in simple ethyl-, and isopropyl-substituted one- and two-ring aromatic van der Waals molecular solids, the barriers for the out-of-plane methyl groups and the t-butyl group in 3-t-butylchrysene are compared with those barriers in three related molecular solids whose crystal structure is known: 4-methyl-2,6-di-t-butylphenol, 1,4-di-t-butylbenzene, and polymorph A of 2,6-di-t-butyl- naphthalene. A trend is observed in the reorientational barriers for the t-butyl and the out-of-plane methyl groups across this series of four compounds: as the t-butyl barriers decrease, the out-of-plane methyl barriers increase

Driving current through single organic molecules

We investigate electronic transport through two types of conjugated molecules. Mechanically controlled break-junctions are used to couple thiol endgroups of single molecules to two gold electrodes. Current-voltage characteristics (IVs) of the metal-molecule-metal system are observed. These IVs reproduce the spatial symmetry of the molecules with respect to the direction of current flow. We hereby unambigously detect an intrinsic property of the molecule, and are able to distinguish the influence of both the molecule and the contact to the metal electrodes on the transport properties of the compound system.Comment: 4 pages, 5 figure

Whirlpool: Improving Dynamic Cache Management with Static Data Classification

Cache hierarchies are increasingly non-uniform and difficult to manage. Several techniques, such as scratchpads or reuse hints, use static information about how programs access data to manage the memory hierarchy. Static techniques are effective on regular programs, but because they set fixed policies, they are vulnerable to changes in program behavior or available cache space. Instead, most systems rely on dynamic caching policies that adapt to observed program behavior. Unfortunately, dynamic policies spend significant resources trying to learn how programs use memory, and yet they often perform worse than a static policy. We present Whirlpool, a novel approach that combines static information with dynamic policies to reap the benefits of each. Whirlpool statically classifies data into pools based on how the program uses memory. Whirlpool then uses dynamic policies to tune the cache to each pool. Hence, rather than setting policies statically, Whirlpool uses static analysis to guide dynamic policies. We present both an API that lets programmers specify pools manually and a profiling tool that discovers pools automatically in unmodified binaries. We evaluate Whirlpool on a state-of-the-art NUCA cache. Whirlpool significantly outperforms prior approaches: on sequential programs, Whirlpool improves performance by up to 38% and reduces data movement energy by up to 53%; on parallel programs, Whirlpool improves performance by up to 67% and reduces data movement energy by up to 2.6x.National Science Foundation (U.S.) (grant CCF-1318384)National Science Foundation (U.S.) (CAREER-1452994)Samsung (Firm) (GRO award

An integrated gene annotation and transcriptional profiling approach towards the full gene content of the Drosophila genome

BACKGROUND: While the genome sequences for a variety of organisms are now available, the precise number of the genes encoded is still a matter of debate. For the human genome several stringent annotation approaches have resulted in the same number of potential genes, but a careful comparison revealed only limited overlap. This indicates that only the combination of different computational prediction methods and experimental evaluation of such in silico data will provide more complete genome annotations. In order to get a more complete gene content of the Drosophila melanogaster genome, we based our new D. melanogaster whole-transcriptome microarray, the Heidelberg FlyArray, on the combination of the Berkeley Drosophila Genome Project (BDGP) annotation and a novel ab initio gene prediction of lower stringency using the Fgenesh software. RESULTS: Here we provide evidence for the transcription of approximately 2,600 additional genes predicted by Fgenesh. Validation of the developmental profiling data by RT-PCR and in situ hybridization indicates a lower limit of 2,000 novel annotations, thus substantially raising the number of genes that make a fly. CONCLUSIONS: The successful design and application of this novel Drosophila microarray on the basis of our integrated in silico/wet biology approach confirms our expectation that in silico approaches alone will always tend to be incomplete. The identification of at least 2,000 novel genes highlights the importance of gathering experimental evidence to discover all genes within a genome. Moreover, as such an approach is independent of homology criteria, it will allow the discovery of novel genes unrelated to known protein families or those that have not been strictly conserved between species

Origin of the giant magnetic moments of Fe impurities on and in Cs films

To explore the origin of the observed giant magnetic moments ($\sim 7 \mu_B$) of Fe impurities on the surface and in the bulk of Cs films, we have performed the relativistic LSDA + U calculations using the linearized muffin-tin orbital (LMTO) band method. We have found that Fe impurities in Cs behave differently from those in noble metals or in Pd. Whereas the induced spin polarization of Cs atoms is negligible, the Fe ion itself is found to be the source of the giant magnetic moment. The 3d electrons of Fe in Cs are localized as the 4f electrons in rare-earth ions so that the orbital magnetic moment becomes as large as the spin magnetic moment. The calculated total magnetic moment of $M = 6.43 \mu_B$, which comes mainly from Fe ion, is close to the experimentally observed value.Comment: 4 pages including 3 figures and 1 table. Submitted to PR