6,208 research outputs found
High precision determination of the -evolution of the Bjorken Sum
We present a significantly improved determination of the Bjorken Sum for
0.64.8 GeV using precise new and
data taken with the CLAS detector at Jefferson Lab. A higher-twist analysis of
the -dependence of the Bjorken Sum yields the twist-4 coefficient
. This leads to the color
polarizabilities and
. The strong force coupling is determined to be
\alpha_{s}^{\overline{\mbox{ MS}}}(M_{Z}^{2})=0.1124\pm0.0061, which has an
uncertainty a factor of 1.5 smaller than earlier estimates using polarized DIS
data. This improvement makes the comparison between extracted from
polarized DIS and other techniques a valuable test of QCD.Comment: Published in Phys. Rev. D. V1: 8 pages, 3 figures. V2: Updated
references; Included threshold matching in \alpha_s evolution. Corrected a
typo on the uncertainty for \Lambda_QCD. V3: Published versio
Peptide functionalized superparamagnetic iron oxide nanoparticles as MRI contrast agents
Cataloged from PDF version of article.Magnetic resonance imaging (MRI) attracts great attention in cellular and molecular imaging due to its non-invasive and multidimensional tomographic capabilities. Development of new contrast agents is necessary to enhance the MRI signal in tissues of interest. Superparamagnetic iron oxide nanoparticles (SPIONs) are used as contrast agents for signal enhancement as they have revealed extraordinary magnetic properties at the nanometre size and their toxicity level is very low compared to other commercial contrast agents. In this study, we developed a new method to functionalize the surface of SPIONs. Peptide amphiphile molecules are used to coat SPIONs non-covalently to provide water solubility and to enhance biocompatibility. Superparamagnetic properties of the peptide-SPION complexes and their ability as contrast agents are demonstrated. In vitro cell culture experiments reveal that the peptide-SPION complexes are biocompatible and are localized around the cells due to their peptide coating
Peptide nanofibers for controlled growth factor release
[No abstract available
Measurement of Target and Double-Spin Asymmetries for the ep → eπ+(n) Reaction in the Nucleon Resonance Region at Low Q²
We report measurements of target- and double-spin asymmetries for the exclusive channel →e→p → eπ+(n) in the nucleon resonance region at Jefferson Lab using the CEBAF Large Acceptance Spectrometer (CLAS). These asymmetries were extracted from data obtained using a longitudinally polarized NH3 target and a longitudinally polarized electron beam with energies 1.1, 1.3, 2.0, 2.3, and 3.0 GeV. The new results are consistent with previous CLAS publications but are extended to a low Q2 range from 0.0065 to 0.35(GeV/c)2. The Q2 access was made possible by a custom-built Cherenkov detector that allowed the detection of electrons for scattering angles as low as 6°. These results are compared with the unitary isobar models JANR and MAID, the partial-wave analysis prediction from SAID, and the dynamic model DMT. In many kinematic regions our results, in particular results on the target asymmetry, help to constrain the polarization-dependent components of these models
Amyloid Inspired Self-Assembled Peptide Nanofibers
Cataloged from PDF version of article.Amyloid peptides are important components in many degenerative
diseases as well as in maintaining cellular metabolism. Their unique stable structure
provides new insights in developing new materials. Designing bioinspired selfassembling
peptides is essential to generate new forms of hierarchical nanostructures.
Here we present oppositely charged amyloid inspired peptides (AIPs),
which rapidly self-assemble into nanofibers at pH 7 upon mixing in water caused
by noncovalent interactions. Mechanical properties of the gels formed by selfassembled
AIP nanofibers were analyzed with oscillatory rheology. AIP gels
exhibited strong mechanical characteristics superior to gels formed by self-assembly
of previously reported synthetic short peptides. Rheological studies of gels
composed of oppositely charged mixed AIP molecules (AIP-1 + 2) revealed superior mechanical stability compared to individual
peptide networks (AIP-1 and AIP-2) formed by neutralization of net charges through pH change. Adhesion and elasticity
properties of AIP mixed nanofibers and charge neutralized AIP-1, AIP-2 nanofibers were analyzed by high resolution force−
distance mapping using atomic force microscopy (AFM). Nanomechanical characterization of self-assembled AIP-1 + 2, AIP-1,
and AIP-2 nanofibers also confirmed macroscopic rheology results, and mechanical stability of AIP mixed nanofibers was higher
compared to individual AIP-1 and AIP-2 nanofibers self-assembled at acidic and basic pH, respectively. Experimental results were
supported with molecular dynamics simulations by considering potential noncovalent interactions between the amino acid
residues and possible aggregate forms. In addition, HUVEC cells were cultured on AIP mixed nanofibers at pH 7 and biocompatibility
and collagen mimetic scaffold properties of the nanofibrous system were observed. Encapsulation of a zwitterionic
dye (rhodamine B) within AIP nanofiber network was accomplished at physiological conditions to demonstrate that this network
can be utilized for inclusion of soluble factors as a scaffold for cell culture studies. Copyright © 2012 American Chemical Societ
A Spectroscopic Survey of a Sample of Active M Dwarfs
A moderate resolution spectroscopic survey of Fleming's sample of 54 X-ray
selected M dwarfs with photometric distances less than 25 pc is presented.
Radial and rotation velocities have been measured by fits to the H-alpha
profiles. Radial velocities have been measured by cross correlation. Artificial
broadening of an observed spectrum has produced a relationship between H-alpha
FWHM and rotation speed, which we use to infer rotation speeds for the entire
sample by measurement of the H-alpha emission line. We find 3 ultra-fast
rotators (UFRs, vsini > 100km/s), and 8 stars with 30 < vsini < 100 km/s. The
UFRs have variable emission. Cross-correlation velocities measured for
ultra-fast rotators (UFRs) are shown to depend on rotation speed and the
filtering used. The radial velocity dispersion of the sample is 17 km/s. A new
double emission line spectroscopic binary with a period of 3.55 days has been
discovered, and another known one is in the sample. Three other objects are
suspected spectroscopic binaries, and at least six are visual doubles. The only
star in the sample observed to have significant lithium is a known TW Hya
Association member, TWA 8A. These results show that there are a number of young
(< 10^8 yr) and very young (< 10^7 yr) low mass stars in the immediate solar
neighbourhood. The H-alpha activity strength does not depend on rotation speed.
Our fast rotators are less luminous than similarly fast rotators in the
Pleiades. They are either younger than the Pleiades, or gained angular momentum
in a different way.Comment: 38 pages incl. 14 figures and 4 tables, plus 12 pages of table for
electronic journal only; LaTeX, aastex.cls. Accepted 07/18/02 for publication
in The Astronomical Journa
Neutrino physics at accelerators
Present and future neutrino experiments at accelerators are mainly concerned
with understanding the neutrino oscillation phenomenon and its implications.
Here a brief account of neutrino oscillations is given together with a
description of the supporting data. Some current and planned accelerator
neutrino experiments are also explained.Comment: 23 pages, 24 figures. Talk given at the Corfu Summer Institute on
Elementary Particle Physics 200
Target and Beam-Target Spin Asymmetries in Exclusive Pion Electroproduction for Q² \u3e 1 GeV² . II. ep→ eπºp
Beam-target double-spin asymmetries and target single-spin asymmetries were measured for the exclusive π0 electroproduction reaction γ∗p→pπ0, expanding an analysis of the γ∗p→nπ+ reaction from the same experiment. The results were obtained from scattering of 6-GeV longitudinally polarized electrons off longitudinally polarized protons using the CEBAF Large Acceptance Spectrometer at Jefferson Laboratory. The kinematic ranges covered are 1.1 \u3c W \u3c 3 GeV and 1 \u3c Q2\u3c 6 GeV2 . Results were obtained for about 5700 bins in W, Q2, cos(θ∗) , and ϕ∗. The beam-target asymmetries were found to generally be greater than zero, with relatively modest ϕ∗ dependence. The target asymmetries exhibit very strong ϕ∗ dependence, with a change in sign occurring between results at low W and high W , in contrast to π+ electroproduction. Reasonable agreement is found with phenomenological fits to previous data for W \u3c 1.6 GeV, but significant differences are seen at higher W . When combined with cross-sectional measurements, as well as π+ observables, the present results will provide powerful constraints on nucleon resonance amplitudes at moderate and large values of Q2, for resonances with masses as high as 2.4 GeV
Double Spin Asymmetries A_NN and A_SS at sqrt{s}=200 GeV in Polarized Proton-Proton Elastic Scattering at RHIC
We present the first measurements of the double spin asymmetries A_NN and
A_SS at sqrt{s}=200 GeV, obtained by the pp2pp experiment using polarized
proton beams at the Relativistic Heavy Ion Collider (RHIC). The data were
collected in the four momentum transfer t range 0.01<|t|<0.03 (GeV/c)^2. The
measured asymmetries, which are consistent with zero, allow us to estimate
upper limits on the double helicity-flip amplitudes phi_2 and phi_4 at small t
as well as on the difference Delta(sigma_T) between the total cross sections
for transversely polarized protons with antiparallel or parallel spin
orientations.Comment: 13 pages with 3 figures. Final version accepted by Phys. Lett.
Signaling via interleukin-4, receptor alpha chain is required for successful vaccination against schistosomiasis in BALB/c mice
Radiation-attenuated (RA) schistosome larvae are potent stimulators of innate immune responses at the skin site of exposure (pinna) that are likely to be important factors in the development of Th1-mediated protective immunity. In addition to causing an influx of neutrophils, macrophages, and dendritic cells (DCs) into the dermis, RA larvae induced a cascade of chemokine and cytokine secretion following in vitro culture of pinna biopsy samples. While macrophage inflammatory protein 1 and interleukin-1 (IL-1) were produced transiently within the first few days, the Th1-promoting cytokines IL-12 and IL-18 were secreted at high levels until at least day 14. Assay of C3H/HeJ mice confirmed that IL-12 secretion was not due to lipopolysaccharide contaminants binding Toll-like receptor 4. Significantly, IL-12 p40 secretion was sustained in pinnae from vaccinated mice but not in those from nonprotected infected mice. In contrast, IL-10 was produced from both vaccinated and infected mice. This cytokine regulates IL-12-associated dermal inflammation, since in vaccinated IL-10/ mice, pinna thickness was greatly increased concurrent with elevated levels of IL-12 p40. A significant number of IL-12 p40 cells were detected as emigrants from in vitro-cultured pinnae, and most were within a population of rare large granular cells that were Ia, consistent with their being antigen-presenting cells. Labeling of IL-12 cells for CD11c, CD205, CD8, CD11b, and F4/80 indicated that the majority were myeloid DCs, although a proportion were CD11c F4/80, suggesting that macrophages were an additional source of IL-12 in the skin
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