239 research outputs found
Atomically-precise lanthanide-iron-oxo clusters featuring the ε-Keggin ion.
Atomically precise molecular metal-oxo clusters provide ideal models to understand metal oxide surfaces, self-assembly, and form-function relationships. Devising strategies for synthesis and isolation of these molecular forms remains a challenge. Here, we report the synthesis of four Ln-Fe oxo clusters that feature the ε -{Fe 13 } Keggin cluster in its core. The {Fe 13 } metal-oxo cluster motif is the building block of two important iron oxyhydroxyide phases in nature and technology, ferrihydrite (as the δ -isomer) and magnetite (the ε -isomer). The reported ε -{Fe 13 } Keggin isomer as an isolated molecule provides opportunity to study the formation of ferrihydrite and magnetite from this building unit. The next metal layer surrounding the ε -{Fe 13 } core within these clusters exhibit a similar arrangement as the magnetite lattice, and Fe and Ln can occupy the same positions. This provides opportunity to construct a family of compounds and optimize magnetic exchange in these molecules via composition tuning. Small angle X-ray scattering (SAXS) and high-resolution electrospray ionization mass spectrometry (HRESI-MS) show these clusters are stable upon dissolution in both water and organic solvents, as a first step to perform further chemistry towards building magnetic arrays or invetigating ferrihydrite and magnetite assembly from pre-nucleation clusters
Limits on WWZ and WW\gamma couplings from p\bar{p}\to e\nu jj X events at \sqrt{s} = 1.8 TeV
We present limits on anomalous WWZ and WW-gamma couplings from a search for
WW and WZ production in p-bar p collisions at sqrt(s)=1.8 TeV. We use p-bar p
-> e-nu jjX events recorded with the D0 detector at the Fermilab Tevatron
Collider during the 1992-1995 run. The data sample corresponds to an integrated
luminosity of 96.0+-5.1 pb^(-1). Assuming identical WWZ and WW-gamma coupling
parameters, the 95% CL limits on the CP-conserving couplings are
-0.33<lambda<0.36 (Delta-kappa=0) and -0.43<Delta-kappa<0.59 (lambda=0), for a
form factor scale Lambda = 2.0 TeV. Limits based on other assumptions are also
presented.Comment: 11 pages, 2 figures, 2 table
Search for Top Squark Pair Production in the Dielectron Channel
This report describes the first search for top squark pair production in the
channel stop_1 stopbar_1 -> b bbar chargino_1 chargino_1 -> ee+jets+MEt using
74.9 +- 8.9 pb^-1 of data collected using the D0 detector. A 95% confidence
level upper limit on sigma*B is presented. The limit is above the theoretical
expectation for sigma*B for this process, but does show the sensitivity of the
current D0 data set to a particular topology for new physics.Comment: Five pages, including three figures, submitted to PRD Brief Report
Search for a Fourth Generation Charge -1/3 Quark via Flavor Changing Neutral Current Decay
We report on a search for pair production of a fourth generation charge -1/3
quark (b') in pbar p collisions at sqrt(s) = 1.8 TeV at the Fermilab Tevatron
using an integrated luminosity of 93 pb^-1. Both quarks are assumed to decay
via flavor changing neutral currents (FCNC). The search uses the signatures
gamma + 3 jets + mu-tag and 2 gamma + 2 jets. We see no significant excess of
events over the expected background. We place an upper limit on the production
cross section times branching fraction that is well below theoretical
expectations for a b' quark decaying exclusively via FCNC for b' quark masses
up to m(Z) + m(b).Comment: Eleven pages, two postscript figures, submitted to Physical Review
Letter
Measurement of Dijet Angular Distributions and Search for Quark Compositeness
We have measured the dijet angular distribution in =1.8 TeV
collisions using the D0 detector. Order QCD
predictions are in good agreement with the data. At 95% confidence the data
exclude models of quark compositeness in which the contact interaction scale is
below 2 TeV.Comment: 11 pages, Latex, 3 postscript figure
Measurement of the Top Quark Mass Using Dilepton Events
The D0 collaboration has performed a measurement of the top quark mass based
on six candidate events for the process t tbar -> b W+ bbar W-, where the W
bosons decay to e nu or mu nu. This sample was collected during an exposure of
the D0 detector to an integrated luminosity of 125 pb^-1 of sqrt(s)=1.8 TeV
p-pbar collisions. We obtain mt = 168.4 +- 12.3 (stat) +- 3.7 (sys) GeV/c^2,
consistent with the measurement obtained using single-lepton events.
Combination of the single-lepton and dilepton results yields mt = 172.0 +- 7.5
GeV/c^2.Comment: 12 pages, 3 figure
Measurement of the Top Quark Pair Production Cross Section in pbarp Collisions
We present a measurement of the ttbar production cross section in ppbar
collisions at root(s) = 1.8TeV by the D0 experiment at the Fermilab Tevatron.
The measurement is based on data from an integrated luminosity of approximately
125 pb^-1 accumulated during the 1992-1996 collider run. We observe 39 ttbar
candidate events in the dilepton and lepton+jets decay channels with an
expected background of 13.7+-2.2 events. For a top quark mass of 173.3GeV/c^2,
we measure the ttbar production cross section to be 5.5+-1.8 pb.Comment: 11 pages with 3 encapsulated PostScript figures and 2 PostScript
table included in the body of the articl
Zgamma Production in pbarp Collisions at sqrt(s)=1.8 TeV and Limits on Anomalous ZZgamma and Zgammagamma Couplings
We present a study of Z +gamma + X production in p-bar p collisions at
sqrt{S}=1.8 TeV from 97 (87) pb^{-1} of data collected in the eegamma
(mumugamma) decay channel with the D0 detector at Fermilab. The event yield and
kinematic characteristics are consistent with the Standard Model predictions.
We obtain limits on anomalous ZZgamma and Zgammagamma couplings for form factor
scales Lambda = 500 GeV and Lambda = 750 GeV. Combining this analysis with our
previous results yields 95% CL limits |h{Z}_{30}| < 0.36, |h{Z}_{40}| < 0.05,
|h{gamma}_{30}| < 0.37, and |h{gamma}_{40}| < 0.05 for a form factor scale
Lambda=750 GeV.Comment: 17 Pages including 2 Figures. Submitted to PR
Direct Measurement of the Top Quark Mass
We measure the top quark mass m_t using t tbar pairs produced in the D0
detector by root(s) = 1.8 TeV p pbar collisions in a 125 pb^-1 exposure at the
Fermilab Tevatron. We make a two constraint fit to m_t in t tbar --> b W^+ bbar
W^- final states with one W decaying to q qbar and the other to e nu or mu nu.
Events are binned in fit mass versus a measure of probability for events to be
signal rather than background. Likelihood fits to the data yield m_t = 173.3 +-
5.6 (stat) +- 6.2 (syst) GeV/c^2.Comment: 11 pages with 3 encapsulated PostScript figures and 1 encapsulated
PostScript table included in the body of the articl
Polyenylpyrrole Derivatives Inhibit NLRP3 Inflammasome Activation and Inflammatory Mediator Expression by Reducing Reactive Oxygen Species Production and Mitogen-Activated Protein Kinase Activation
10.1371/journal.pone.0076754PLoS ONE810-POLN
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