1,209 research outputs found
Evaluation of a chiral cubane-based Schiff base ligand in asymmetric catalysis reactions
Recently, a novel chiral cubane-based Schiff base ligand was reported to yield modest enantioselectivity in the Henry reaction. To further explore the utility of this ligand in other asymmetric organic transformations, we evaluated its stereoselectivity in cyclopropanation and Michael addition reactions. Although there was no increase in stereocontrol, upon computational evaluation using both M06L and B3LYP calculations, it was revealed that a pseudo six-membered ring exists, through H-bonding of a cubyl hydrogen to the copper core. This decreases the steric bulk above the copper center and limits the asymmetric control with this ligand.The authors thank the Niagara University Academic Center for Integrated Science and the Rochester Academy of Science for their financial support. MLI would like to thank the Barbara S. Zimmer Memorial Research Award for financial aid. MLC gratefully acknowledges generous allocations of supercomputing time from the Australian National Computational Infrastructure, support from the Australian Research Council under its Centers of Excellence program, and an ARC Future Fellowship. RP would also like to thank Western New England University, College of Pharmacy for generous financial support
Preference Transitivity and Symbolic Representation in Capuchin Monkeys (Cebus apella)
BACKGROUND: Can non-human animals comprehend and employ symbols? The most convincing empirical evidence comes from language-trained apes, but little is known about this ability in monkeys. Tokens can be regarded as symbols since they are inherently non-valuable objects that acquire an arbitrarily assigned value upon exchange with an experimenter. Recent evidence suggested that capuchin monkeys, which diverged from the human lineage 35 million years ago, can estimate, represent and combine token quantities. A fundamental and open question is whether monkeys can reason about symbols in ways similar to how they reason about real objects. METHODOLOGY/PRINCIPAL FINDINGS: Here we examined this broad question in the context of economic choice behavior. Specifically, we assessed whether, in a symbolic context, capuchins' preferences satisfy transitivity--a fundamental trait of rational decision-making. Given three options A, B and C, transitivity holds true if A > or = B, B > or = C and A > or = C (where > or = indicates preference). In this study, we trained monkeys to exchange three types of tokens for three different foods. We then compared choices monkeys made between different types of tokens with choices monkeys made between the foods. Qualitatively, capuchins' preferences revealed by the way of tokens were similar to those measured with the actual foods. In particular, when choosing between tokens, monkeys displayed strict economic preferences and their choices satisfied transitivity. Quantitatively, however, values measured by the way of tokens differed systematically from those measured with the actual foods. In particular, for any pair of foods, the relative value of the preferred food increased when monkeys chose between the corresponding tokens. CONCLUSIONS/SIGNIFICANCE: These results indicate that indeed capuchins are capable of treating tokens as symbols. However, as they do so, capuchins experience the cognitive burdens imposed by symbolic representation
Light dark matter in the NMSSM: upper bounds on direct detection cross sections
In the Next-to-Minimal Supersymmetric Standard Model, a bino-like LSP can be
as light as a few GeV and satisfy WMAP constraints on the dark matter relic
density in the presence of a light CP-odd Higgs scalar. We study upper bounds
on the direct detection cross sections for such a light LSP in the mass range
2-20 GeV in the NMSSM, respecting all constraints from B-physics and LEP. The
OPAL constraints on e^+ e^- -> \chi^0_1 \chi^0_i (i > 1) play an important role
and are discussed in some detail. The resulting upper bounds on the
spin-independent and spin-dependent nucleon cross sections are ~ 10^{-42}
cm^{-2} and ~ 4\times 10^{-40} cm^{-2}, respectively. Hence the upper bound on
the spin-independent cross section is below the DAMA and CoGeNT regions, but
could be compatible with the two events observed by CDMS-II.Comment: 17 pages, 3 figure
Abatacept treatment for rheumatoid arthritis
Significant advances in our understanding of RA and its management have been made in the past decade, resulting in earlier intervention with biologic DMARDs, particularly in patients with evidence of aggressive, erosive disease. Here, one such biologic therapy, the T-cell co-stimulation modulator abatacept, is discussed, exploring clinical evidence published to date on its use in patients with very early arthritis/early RA who are MTX naïve, and in patients with established RA and an inadequate response to MTX or TNF antagonists. Data from relevant clinical trials are overviewed, discussing the clinical efficacy of abatacept in early disease, the clinical outcomes over long-term treatment in different patient populations and the effects of abatacept on structural damage. Findings from integrated safety analyses of abatacept clinical trial data, representing 10 366 patient-years of exposure are described, and clinically important safety events, including serious infections, malignancies and autoimmune events, are highlighted. It is concluded that abatacept represents an effective treatment option with an established safety profile across different patient populations, including patients with both early and erosive RA and those with established disease. Furthermore, efficacy data from studies in patients with early disease suggest that the risk–benefit profile of abatacept may be more favourable when introduced earlier in the treatment paradigm
Discretionary power of project managers in knowledge intensive firms and gender issues
The scarcity of women among the highly qualified professionals in business-to-business information and communication technologies (ICT), either in Europe andor in North America, has been noted as recently as the late 1990’s (Panteli, Stack, Atkinson, & Ramsay, 1999). The organization and management of work in such organizations firms is typically project-based. This has many consequences, including: long working hours with fierce resistance to shorter hoursany reduction, unpaid overtime, high management expectations of employee flexibility to meet unanticipated client demands, and the need for employees to negotiate flexible work arrangements on a case-by-cases basis with a project manager who often has much discretion on whether to accommodate such requests. We found that women are particularly disadvantaged in such a system, which could partly explain their under-representation in such jobs
Search for Neutral Higgs Bosons in Events with Multiple Bottom Quarks at the Tevatron
The combination of searches performed by the CDF and D0 collaborations at the
Fermilab Tevatron Collider for neutral Higgs bosons produced in association
with b quarks is reported. The data, corresponding to 2.6 fb-1 of integrated
luminosity at CDF and 5.2 fb-1 at D0, have been collected in final states
containing three or more b jets. Upper limits are set on the cross section
multiplied by the branching ratio varying between 44 pb and 0.7 pb in the Higgs
boson mass range 90 to 300 GeV, assuming production of a narrow scalar boson.
Significant enhancements to the production of Higgs bosons can be found in
theories beyond the standard model, for example in supersymmetry. The results
are interpreted as upper limits in the parameter space of the minimal
supersymmetric standard model in a benchmark scenario favoring this decay mode.Comment: 10 pages, 2 figure
Observation of the Baryonic Flavor-Changing Neutral Current Decay Lambda_b -> Lambda mu+ mu-
We report the first observation of the baryonic flavor-changing neutral
current decay Lambda_b -> Lambda mu+ mu- with 24 signal events and a
statistical significance of 5.8 Gaussian standard deviations. This measurement
uses ppbar collisions data sample corresponding to 6.8fb-1 at sqrt{s}=1.96TeV
collected by the CDF II detector at the Tevatron collider. The total and
differential branching ratios for Lambda_b -> Lambda mu+ mu- are measured. We
find B(Lambda_b -> Lambda mu+ mu-) = [1.73+-0.42(stat)+-0.55(syst)] x 10^{-6}.
We also report the first measurement of the differential branching ratio of B_s
-> phi mu+ mu- using 49 signal events. In addition, we report branching ratios
for B+ -> K+ mu+ mu-, B0 -> K0 mu+ mu-, and B -> K*(892) mu+ mu- decays.Comment: 8 pages, 2 figures, 4 tables. Submitted to Phys. Rev. Let
Spherical perspective
We survey the present state of spherical perspective, regarding both mathematical structure and drawing practice, with a view to applications in the visual arts. We define a spherical perspective as the entailment of a conical anamorphosis with a compact flattening of the visual sphere. We examine a general framework for solving spherical perspectives, exemplified with the azimuthal equidistant (“fisheye”) and equirectangular cases. We consider the relation between spherical and curvilinear perspectives. We briefly discuss computer renderings but focus on methods adapted to freehand sketching or technical drawing with simple instruments such as ruler and compass. We discuss how handmade spherical perspective drawings can generate immersive anamorphoses, which can be rendered as virtual reality panoramas, leading to hybrid visual creations that bridge the gap between traditional drawing and digital environments.info:eu-repo/semantics/publishedVersio
Search for the standard model Higgs boson decaying to a pair in events with no charged leptons and large missing transverse energy using the full CDF data set
We report on a search for the standard model Higgs boson produced in
association with a vector boson in the full data set of proton-antiproton
collisions at TeV recorded by the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45 fb. We
consider events having no identified charged lepton, a transverse energy
imbalance, and two or three jets, of which at least one is consistent with
originating from the decay of a quark. We place 95% credibility level upper
limits on the production cross section times standard model branching fraction
for several mass hypotheses between 90 and . For a Higgs
boson mass of , the observed (expected) limit is 6.7
(3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let
Search for the standard model Higgs boson decaying to a bb pair in events with one charged lepton and large missing transverse energy using the full CDF data set
We present a search for the standard model Higgs boson produced in
association with a W boson in sqrt(s) = 1.96 TeV p-pbar collision data
collected with the CDF II detector at the Tevatron corresponding to an
integrated luminosity of 9.45 fb-1. In events consistent with the decay of the
Higgs boson to a bottom-quark pair and the W boson to an electron or muon and a
neutrino, we set 95% credibility level upper limits on the WH production cross
section times the H->bb branching ratio as a function of Higgs boson mass. At a
Higgs boson mass of 125 GeV/c2 we observe (expect) a limit of 4.9 (2.8) times
the standard model value.Comment: Submitted to Phys. Rev. Lett (v2 contains clarifications suggested by
PRL
- …