1,777 research outputs found
Molecular Valves for Controlling Gas Phase Transport Made from Discrete Angstrom-Sized Pores in Graphene
An ability to precisely regulate the quantity and location of molecular flux
is of value in applications such as nanoscale 3D printing, catalysis, and
sensor design. Barrier materials containing pores with molecular dimensions
have previously been used to manipulate molecular compositions in the gas
phase, but have so far been unable to offer controlled gas transport through
individual pores. Here, we show that gas flux through discrete angstrom-sized
pores in monolayer graphene can be detected and then controlled using
nanometer-sized gold clusters, which are formed on the surface of the graphene
and can migrate and partially block a pore. In samples without gold clusters,
we observe stochastic switching of the magnitude of the gas permeance, which we
attribute to molecular rearrangements of the pore. Our molecular valves could
be used, for example, to develop unique approaches to molecular synthesis that
are based on the controllable switching of a molecular gas flux, reminiscent of
ion channels in biological cell membranes and solid state nanopores.Comment: to appear in Nature Nanotechnolog
Measurement of inclusive D*+- and associated dijet cross sections in photoproduction at HERA
Inclusive photoproduction of D*+- mesons has been measured for photon-proton
centre-of-mass energies in the range 130 < W < 280 GeV and a photon virtuality
Q^2 < 1 GeV^2. The data sample used corresponds to an integrated luminosity of
37 pb^-1. Total and differential cross sections as functions of the D*
transverse momentum and pseudorapidity are presented in restricted kinematical
regions and the data are compared with next-to-leading order (NLO) perturbative
QCD calculations using the "massive charm" and "massless charm" schemes. The
measured cross sections are generally above the NLO calculations, in particular
in the forward (proton) direction. The large data sample also allows the study
of dijet production associated with charm. A significant resolved as well as a
direct photon component contribute to the cross section. Leading order QCD
Monte Carlo calculations indicate that the resolved contribution arises from a
significant charm component in the photon. A massive charm NLO parton level
calculation yields lower cross sections compared to the measured results in a
kinematic region where the resolved photon contribution is significant.Comment: 32 pages including 6 figure
Measurement of Jet Shapes in Photoproduction at HERA
The shape of jets produced in quasi-real photon-proton collisions at
centre-of-mass energies in the range GeV has been measured using the
hadronic energy flow. The measurement was done with the ZEUS detector at HERA.
Jets are identified using a cone algorithm in the plane with a
cone radius of one unit. Measured jet shapes both in inclusive jet and dijet
production with transverse energies GeV are presented. The jet
shape broadens as the jet pseudorapidity () increases and narrows
as increases. In dijet photoproduction, the jet shapes have been
measured separately for samples dominated by resolved and by direct processes.
Leading-logarithm parton-shower Monte Carlo calculations of resolved and direct
processes describe well the measured jet shapes except for the inclusive
production of jets with high and low . The observed
broadening of the jet shape as increases is consistent with the
predicted increase in the fraction of final state gluon jets.Comment: 29 pages including 9 figure
Selective Molecular Sieving through Porous Graphene
Membranes act as selective barriers and play an important role in processes
such as cellular compartmentalization and industrial-scale chemical and gas
purification. The ideal membrane should be as thin as possible to maximize
flux, mechanically robust to prevent fracture, and have well-defined pore sizes
to increase selectivity. Graphene is an excellent starting point for developing
size selective membranes because of its atomic thickness, high mechanical
strength, relative inertness, and impermeability to all standard gases.
However, pores that can exclude larger molecules, but allow smaller molecules
to pass through have to be introduced into the material. Here we show
UV-induced oxidative etching can create pores in micrometre-sized graphene
membranes and the resulting membranes used as molecular sieves. A pressurized
blister test and mechanical resonance is used to measure the transport of a
variety of gases (H2, CO2, Ar, N2, CH4, and SF6) through the pores. The
experimentally measured leak rates, separation factors, and Raman spectrum
agree well with models based on effusion through a small number of
angstrom-sized pores.Comment: to appear in Nature Nanotechnolog
Measurement of event shapes in deep inelastic scattering at HERA
Inclusive event-shape variables have been measured in the current region of
the Breit frame for neutral current deep inelastic ep scattering using an
integrated luminosity of 45.0 pb^-1 collected with the ZEUS detector at HERA.
The variables studied included thrust, jet broadening and invariant jet mass.
The kinematic range covered was 10 < Q^2 < 20,480 GeV^2 and 6.10^-4 < x < 0.6,
where Q^2 is the virtuality of the exchanged boson and x is the Bjorken
variable. The Q dependence of the shape variables has been used in conjunction
with NLO perturbative calculations and the Dokshitzer-Webber non-perturbative
corrections (`power corrections') to investigate the validity of this approach.Comment: 7+25 pages, 6 figure
High-E_T dijet photoproduction at HERA
The cross section for high-E_T dijet production in photoproduction has been
measured with the ZEUS detector at HERA using an integrated luminosity of 81.8
pb-1. The events were required to have a virtuality of the incoming photon,
Q^2, of less than 1 GeV^2 and a photon-proton centre-of-mass energy in the
range 142 < W < 293 GeV. Events were selected if at least two jets satisfied
the transverse-energy requirements of E_T(jet1) > 20 GeV and E_T(jet2) > 15 GeV
and pseudorapidity requirements of -1 < eta(jet1,2) < 3, with at least one of
the jets satisfying -1 < eta(jet) < 2.5. The measurements show sensitivity to
the parton distributions in the photon and proton and effects beyond
next-to-leading order in QCD. Hence these data can be used to constrain further
the parton densities in the proton and photon.Comment: 36 pages, 13 figures, 20 tables, including minor revisions from
referees. Accepted by Phys. Rev.
Co-administration With the Pharmacological Chaperone AT1001 Increases Recombinant Human α-Galactosidase A Tissue Uptake and Improves Substrate Reduction in Fabry Mice
Fabry disease is an X-linked lysosomal storage disorder (LSD) caused by mutations in the gene (GLA) that encodes the lysosomal hydrolase α-galactosidase A (α-Gal A), and is characterized by pathological accumulation of the substrate, globotriaosylceramide (GL-3). Regular infusion of recombinant human α-Gal A (rhα-Gal A), termed enzyme replacement therapy (ERT), is the primary treatment for Fabry disease. However, rhα-Gal A has low physical stability, a short circulating half-life, and variable uptake into different disease-relevant tissues. We hypothesized that coadministration of the orally available, small molecule pharmacological chaperone AT1001 (GR181413A, 1-deoxygalactonojirimycin, migalastat hydrochloride) may improve the pharmacological properties of rhα-Gal A via binding and stabilization. AT1001 prevented rhα-Gal A denaturation and activity loss in vitro at neutral pH and 37 °C. Coincubation of Fabry fibroblasts with rhα-Gal A and AT1001 resulted in up to fourfold higher cellular α-Gal A and ~30% greater GL-3 reduction compared to rhα-Gal A alone. Furthermore, coadministration of AT1001 to rats increased the circulating half-life of rhα-Gal A by >2.5-fold, and in GLA knockout mice resulted in up to fivefold higher α-Gal A levels and fourfold greater GL-3 reduction than rhα-Gal A alone. Collectively, these data highlight the potentially beneficial effects of AT1001 on rhα-Gal A, thus warranting clinical investigation
Angular and Current-Target Correlations in Deep Inelastic Scattering at HERA
Correlations between charged particles in deep inelastic ep scattering have
been studied in the Breit frame with the ZEUS detector at HERA using an
integrated luminosity of 6.4 pb-1. Short-range correlations are analysed in
terms of the angular separation between current-region particles within a cone
centred around the virtual photon axis. Long-range correlations between the
current and target regions have also been measured. The data support
predictions for the scaling behaviour of the angular correlations at high Q2
and for anti-correlations between the current and target regions over a large
range in Q2 and in the Bjorken scaling variable x. Analytic QCD calculations
and Monte Carlo models correctly describe the trends of the data at high Q2,
but show quantitative discrepancies. The data show differences between the
correlations in deep inelastic scattering and e+e- annihilation.Comment: 26 pages including 10 figures (submitted to Eur. J. Phys. C
Measurement of (anti)deuteron and (anti)proton production in DIS at HERA
The first observation of (anti)deuterons in deep inelastic scattering at HERA
has been made with the ZEUS detector at a centre-of-mass energy of 300--318 GeV
using an integrated luminosity of 120 pb-1. The measurement was performed in
the central rapidity region for transverse momentum per unit of mass in the
range 0.3<p_T/M<0.7. The particle rates have been extracted and interpreted in
terms of the coalescence model. The (anti)deuteron production yield is smaller
than the (anti)proton yield by approximately three orders of magnitude,
consistent with the world measurements.Comment: 26 pages, 9 figures, 5 tables, submitted to Nucl. Phys.
Measurement of the open-charm contribution to the diffractive proton structure function
Production of D*+/-(2010) mesons in diffractive deep inelastic scattering has
been measured with the ZEUS detector at HERA using an integrated luminosity of
82 pb^{-1}. Diffractive events were identified by the presence of a large
rapidity gap in the final state. Differential cross sections have been measured
in the kinematic region 1.5 < Q^2 < 200 GeV^2, 0.02 < y < 0.7, x_{IP} < 0.035,
beta 1.5 GeV and |\eta(D*+/-)| < 1.5. The measured cross
sections are compared to theoretical predictions. The results are presented in
terms of the open-charm contribution to the diffractive proton structure
function. The data demonstrate a strong sensitivity to the diffractive parton
densities.Comment: 35 pages, 11 figures, 6 table
- …