1,091 research outputs found
Transmission electron microscopy characterization of fluorescently labelled amyloid β 1-40 and α-synuclein aggregates
<p>Abstract</p> <p>Background</p> <p>Fluorescent tags, including small organic molecules and fluorescent proteins, enable the localization of protein molecules in biomedical research experiments. However, the use of these labels may interfere with the formation of larger-scale protein structures such as amyloid aggregates. Therefore, we investigate the effects of some commonly used fluorescent tags on the morphologies of fibrils grown from the Alzheimer's disease-associated peptide Amyloid β 1-40 (Aβ40) and the Parkinson's disease-associated protein α-synuclein (αS).</p> <p>Results</p> <p>Using transmission electron microscopy (TEM), we verify that N-terminal labeling of Aβ40 with AMCA, TAMRA, and Hilyte-Fluor 488 tags does not prevent the formation of protofibrils and amyloid fibrils of various widths. We also measure the two-photon action cross-section of Aβ40 labelled with Hilyte Fluor 488 and demonstrate that this tag is suitable for use with two-photon fluorescence techniques. Similarly, we find that Alexa Fluor 488 labelling of αS variant proteins near either the N or C terminus (position 9 or 130) does not interfere with the formation of amyloid and other types of αS fibrils. We also present TEM images of fibrils grown from αS C-terminally labelled with enhanced green fluorescent protein (EGFP). Near neutral pH, two types of αS-EGFP fibrils are observed via TEM, while denaturation of the EGFP tag leads to the formation of additional species.</p> <p>Conclusions</p> <p>We demonstrate that several small extrinsic fluorescent tags are compatible with studies of amyloid protein aggregation. However, although fibrils can be grown from αS labelled with EGFP, the conformation of the fluorescent protein tag affects the observed aggregate morphologies. Thus, our results should assist researchers with label selection and optimization of solution conditions for aggregation studies involving fluorescence techniques.</p
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A Search for Dark Higgs Bosons
Recent astrophysical and terrestrial experiments have motivated the proposal
of a dark sector with GeV-scale gauge boson force carriers and new Higgs
bosons. We present a search for a dark Higgs boson using 516 fb-1 of data
collected with the BABAR detector. We do not observe a significant signal and
we set 90% confidence level upper limits on the product of the Standard
Model-dark sector mixing angle and the dark sector coupling constant.Comment: 7 pages, 5 postscript figures, published version with improved plots
for b/w printin
Search for Kaluza-Klein Graviton Emission in Collisions at TeV using the Missing Energy Signature
We report on a search for direct Kaluza-Klein graviton production in a data
sample of 84 of \ppb collisions at = 1.8 TeV, recorded
by the Collider Detector at Fermilab. We investigate the final state of large
missing transverse energy and one or two high energy jets. We compare the data
with the predictions from a -dimensional Kaluza-Klein scenario in which
gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for
=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71
TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure
Measurement of B(t->Wb)/B(t->Wq) at the Collider Detector at Fermilab
We present a measurement of the ratio of top-quark branching fractions R= B(t
-> Wb)/B(t -> Wq), where q can be a b, s or a d quark, using lepton-plus-jets
and dilepton data sets with integrated luminosity of ~162 pb^{-1} collected
with the Collider Detector at Fermilab during Run II of the Tevatron. The
measurement is derived from the relative numbers of t-tbar events with
different multiplicity of identified secondary vertices. We set a lower limit
of R > 0.61 at 95% confidence level.Comment: 7 pages, 2 figures, published in Physical Review Letters; changes
made to be consistent with published versio
Measurement of the average time-integrated mixing probability of b-flavored hadrons produced at the Tevatron
We have measured the number of like-sign (LS) and opposite-sign (OS) lepton
pairs arising from double semileptonic decays of and -hadrons,
pair-produced at the Fermilab Tevatron collider. The data samples were
collected with the Collider Detector at Fermilab (CDF) during the 1992-1995
collider run by triggering on the existence of and candidates
in an event. The observed ratio of LS to OS dileptons leads to a measurement of
the average time-integrated mixing probability of all produced -flavored
hadrons which decay weakly, (stat.)
(syst.), that is significantly larger than the world average .Comment: 47 pages, 10 figures, 15 tables Submitted to Phys. Rev.
Search for ZZ and ZW Production in ppbar Collisions at sqrt(s) = 1.96 TeV
We present a search for ZZ and ZW vector boson pair production in ppbar
collisions at sqrt(s) = 1.96 TeV using the leptonic decay channels ZZ --> ll nu
nu, ZZ --> l l l' l' and ZW --> l l l' nu. In a data sample corresponding to an
integrated luminosity of 194 pb-1 collected with the Collider Detector at
Fermilab, 3 candidate events are found with an expected background of 1.0 +/-
0.2 events. We set a 95% confidence level upper limit of 15.2 pb on the cross
section for ZZ plus ZW production, compared to the standard model prediction of
5.0 +/- 0.4 pb.Comment: 7 pages, 2 figures. This version is accepted for publication by Phys.
Rev. D Rapid Communication
Measurement of the Cross Section for Prompt Diphoton Production in p-pbar Collisions at sqrt(s) = 1.96 TeV
We report a measurement of the rate of prompt diphoton production in
collisions at using a data sample of 207
pb collected with the upgraded Collider Detector at Fermilab (CDF II).
The background from non-prompt sources is determined using a statistical method
based on differences in the electromagnetic showers. The cross section is
measured as a function of the diphoton mass, the transverse momentum of the
diphoton system, and the azimuthal angle between the two photons and is found
to be consistent with perturbative QCD predictions.Comment: 7 pages, 3 figures,revtex4. Version accepted by PRL, but with cross
section tables i
Measurement of the Dipion Mass Spectrum in X(3872) -> J/Psi Pi+ Pi- Decays
We measure the dipion mass spectrum in X(3872)--> J/Psi Pi+ Pi- decays using
360 pb-1 of pbar-p collisions at 1.96 TeV collected with the CDF II detector.
The spectrum is fit with predictions for odd C-parity (3S1, 1P1, and 3DJ)
charmonia decaying to J/Psi Pi+ Pi-, as well as even C-parity states in which
the pions are from Rho0 decay. The latter case also encompasses exotic
interpretations, such as a D0-D*0Bar molecule. Only the 3S1 and J/Psi Rho
hypotheses are compatible with our data. Since 3S1 is untenable on other
grounds, decay via J/Psi Rho is favored, which implies C=+1 for the X(3872).
Models for different J/Psi-Rho angular momenta L are considered. Flexibility in
the models, especially the introduction of Rho-Omega interference, enable good
descriptions of our data for both L=0 and 1.Comment: 7 pages, 4 figures -- Submitted to Phys. Rev. Let
Search for New Physics in Lepton + Photon + X Events with L=305 pb-1 of ppbar Collisions at roots=1.96 TeV
We present results of a search for anomalous production of events containing
a charged lepton (either electron or muon) and a photon, both with high
transverse momentum, accompanied by additional signatures, X, including missing
transverse energy (MET) and additional leptons and photons. We use the same
kinematic selection criteria as in a previous CDF search, but with a
substantially larger data set, 305 pb-1, a ppbar collision energy of 1.96 TeV,
and the upgraded CDF II detector. We find 42 Lepton+Photon+MET events versus a
standard model expectation of 37.3 +- 5.4 events. The level of excess observed
in Run I, 16 events with an expectation of 7.6 +- 0.7 events (corresponding to
a 2.7 sigma effect), is not supported by the new data. In the signature of
Multi-Lepton+Photon+X we observe 31 events versus an expectation of 23.0 +- 2.7
events. In this sample we find no events with an extra photon or MET and so
find no events like the one ee+gg+MET event observed in Run I.Comment: 7 pages, 3 figures, 1 table. Accepted to PR
Search for Pair Production of Scalar Top Quarks Decaying to a tau Lepton and a b Quark in ppbar Collisions at sqrt{s}=1.96 TeV
We search for pair production of supersymmetric top quarks (~t_1), followed
by R-parity violating decay ~t_1 -> tau b with a branching ratio beta, using
322 pb^-1 of ppbar collisions at sqrt{s}=1.96 TeV collected by the CDF II
detector at Fermilab. Two candidate events pass our final selection criteria,
consistent with the standard model expectation. We set upper limits on the
cross section sigma(~t_1 ~tbar_1)*beta^2 as a function of the stop mass
m(~t_1). Assuming beta=1, we set a 95% confidence level limit m(~t_1)>153
GeV/c^2. The limits are also applicable to the case of a third generation
scalar leptoquark (LQ_3) decaying LQ_3 -> tau b.Comment: 7 pages, 2 eps figure
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