9,229 research outputs found
J.J. McNamara from Arthur Roos, September 14, 1911-November 1, 1911
No full textLetters to J.J. McNamara from Arthur Roos dated September 14, 1911 to November 1, 1911
ABSOLUTELY KOSZUL ALGEBRAS AND THE BACKELIN-ROOS PROPERTY
No full textWe study absolutely Koszul algebras, Koszul algebras with the Backelin-Roos
property and their behavior under standard algebraic operations. In particular, we identify
some Veronese subrings of polynomial rings that have the Backelin-Roos property and conjecture
that the list is indeed complete. Among other things, we prove that every universally
Koszul ring defined by monomials has the Backelin-Roos property
Early warning signals in the fully size-structured population model of de Roos and Persson [<b>17</b>].
No full text<p>Independent white noise with σ = 0.002 is added to the death rates of all juvenile consumers. Bifurcation procedure and colors are identical to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062033#pone-0062033-g002" target="_blank">Figure 2</a>, with predator mortality staring at <i>µ<sub>P</sub></i> = 0.01 (note that the original article uses parameter δ instead of <i>µ<sub>P</sub></i>), and incremented with <i>Δµ<sub>P</sub></i> = 0.0002 after each 50,000 time units. The fold catastrophe in this model is located at approximately <i>µ<sub>P</sub></i> = 0.038. Coefficient of variation and lag-1 autocorrelation are computed for each value of <i>µ<sub>P</sub></i> over the last 40,000 time steps. (<b>A</b>) Coefficient of variation, and (<b>B</b>) Autocorrelation. All other parameters have default values as used by de Roos and Persson <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062033#pone.0062033-deRoos1" target="_blank">[17]</a>.</p
Conditional immortalization of human B cells by CD40 ligation
No full textIt is generally assumed that human differentiated cells have a limited life-span and proliferation capacity in vivo, and that genetic modifications are a prerequisite for their immortalization in vitro. Here we readdress this issue, studying the long-term proliferation potential of human B cells. It was shown earlier that human B cells from peripheral blood of healthy donors can be efficiently induced to proliferate for up to ten weeks in vitro by stimulating their receptor CD40 in the presence of interleukin-4. When we applied the same stimuli under conditions of modified cell number and culture size, we were surprised to find that our treatment induced B cells to proliferate throughout an observation period of presently up to 1650 days, representing more than 370 population doublings, which suggested that these B cells were immortalized in vitro. Long-term CD40-stimulated B cell cultures could be established from most healthy adult human donors. These B cells had a constant phenotype, were free from Epstein-Barr virus, and remained dependent on CD40 ligation. They had constitutive telomerase activity and stabilized telomere length. Moreover, they were susceptible to activation by Toll-like receptor 9 ligands, and could be used to expand antigen-specific cytotoxic T cells in vitro. Our results indicate that human somatic cells can evade senescence and be conditionally immortalized by external stimulation only, without a requirement for genetic manipulation or oncoviral infection. Conditionally immortalized human B cells are a new tool for immunotherapy and studies of B cell oncogenesis, activation, and function
A THEORETICAL INVESTIGATION OF VALENCE AND RYDBERG ELECTRONIC STATES OF ACROLEIN,
No full textThe main features of the ultraviolet spectrum of acrolein have been studied by a multireference perturbative treatment and by a time dependent density functional approach. The valence and Rydberg transition energies have been calculated and the assignment of the experimental bands has been clarified. The different relaxation trends of the three lowest singlet and triplet excited states have been analyzed by unconstrained geometry optimizations. This has allowed, in particular, the characterization of a twisted 3(*) state, which is crucial for the interesting photophysics and photochemistry of the acrolein molecule and, more generally, of the ,-enones. Solvatochromic shifts in aqueous solution have been investigated using a combined discrete/continuum approach based on the so called polarizable continuum model. The experimental trends are well reproduced by this approach and a closer degeneracy in the triplet manifold has been detected in solution with respect to gas phase. ©2003 American Institute of Physics
Surface dislocation nucleation controlled deformation of Au nanowires
No full textWe investigate deformation in high quality Au nanowires under both tension and bending using in-situ transmission electron microscopy. Defect evolution is investigated during: (1) tensile deformation of < 110 > oriented, initially defect-free, single crystal nanowires with cross-sectional widths between 30 and 300 nm, (2) bending deformation of the same wires, and (3) tensile deformation of wires containing coherent twin boundaries along their lengths. We observe the formation of twins and stacking faults in the single crystal wires under tension, and storage of full dislocations after bending of single crystal wires and after tension of twinned wires. The stress state dependence of the deformation morphology and the formation of stacking faults and twins are not features of bulk Au, where deformation is controlled by dislocation interactions. Instead, we attribute the deformation morphologies to the surface nucleation of either leading or trailing partial dislocations, depending on the Schmid factors, which move through and exit the wires producing stacking faults or full dislocation slip. The presence of obstacles such as neutral planes or twin boundaries hinder the egress of the freshly nucleated dislocations and allow trailing and leading partial dislocations to combine and to be stored as full dislocations in the wires. We infer that the twins and stacking faults often observed in nanoscale Au specimens are not a direct size effect but the result of a size and obstacle dependent transition from dislocation interaction controlled to dislocation nucleation controlled deformation. (C) 2014 AIP Publishing LLC
Quantum chemical calculations show that the uranium molecule U2 has a quintuple bond
No full textCovalent bonding is commonly described by Lewis's theory(1), with an electron pair shared between two atoms constituting one full bond. Beginning with the valence bond description(2) for the hydrogen molecule, quantum chemists have further explored the fundamental nature of the chemical bond for atoms throughout the periodic table, confirming that most molecules are indeed held together by one electron pair for each bond. But more complex binding may occur when large numbers of atomic orbitals can participate in bond formation. Such behaviour is common with transition metals. When involving heavy actinide elements, metal-metal bonds might prove particularly complicated. To date, evidence for actinide-actinide bonds is restricted to the matrix-isolation(3) of uranium hydrides, including H2U-UH2, and the gas-phase detection(4) and preliminary theoretical study(5) of the uranium molecule, U-2. Here we report quantum chemical calculations on U-2, showing that, although the strength of the U-2 bond is comparable to that of other multiple bonds between transition metals, the bonding pattern is unique. We find that the molecule contains three electron-pair bonds and four one-electron bonds (that is, 10 bonding electrons, corresponding to a quintuple bond), and two ferromagnetically coupled electrons localized on one U atom each-so all known covalent bonding types are contributing
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