462 research outputs found
Chemical characterisation of metakaolin and fly ash based geopolymers during exposure to solvents used in carbon capture
This paper presents an investigation into the chemical resistance of blended alkali activated aluminosilicate materials, specifically under exposure to two solvents used in post-combustion carbon capture, monoethanolamine (MEA) and potassium carbonate, as well as during immersion in distilled water. Geopolymers are formulated based on metakaolin and aon fly ash as aluminosilicate precursors, with the addition of ground granulated blast furnace slag (GGBFS) as a source of Ca. The samples are subjected to mineralogical and chemical characterisation in this paper, with data obtained through leaching analysis and X-ray diffraction, supported by compressive strength data. Exposure to solvents generally results in significant alteration of the geopolymer microstructure. The zeolitic phases formed in undamaged metakaolin-based binders are reduced to undetectable levels after 28 days of solvent exposure, although the hydrosodalite formed in the fly ash binders does persist. Leaching analysis indicates that resistance to structural damage in MEA is quite high, due to the low solubility of Na and hydroxides upon immersion. KCO solutions are aggressive towards geopolymers via alteration of the binder structure and dissolution of network-forming species (Si and Al), leading to the loss of binder strength. This is most marked in the fly ash/GGBFS formulations. Despite the low to intermediate level of Ca present in these geopolymer binders, significant formation of Ca-containing carbonate phases occurs upon exposure to KCO. The limited curing duration of the specimens tested here is certainly contributing to the degradation taking place under KCO exposure, whereas the low water activity in the MEA solutions used means that bond hydrolysis in the aluminosilicate geopolymer framework is restricted, and the materials perform much better than in a more water-rich environment. © 2014 Elsevier Ltd
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Polarized and unpolarized double prommpt photon production in next-to-leading order QCD
We calculate O({alpha}{sub s}) corrections to inclusive and isolated double prompt photon production, both for the unpolarized case, and for longitudinal polarization of the incoming hadrons. The calculation is performed using purely analytical techniques for the inclusive case, and a combination of analytical and Monte Carlo techniques to perform the phase space integration in the isolated case. A brief phenomenological study is made of the process pp {r_arrow} {gamma}{gamma}X at CMS energies appropriate for the RHIC heavy ion collider. 21 refs., 8 figs
Spin Dependent Drell Yan in QCD to (I). (The Non-Singlet Sector)
A study of the order corrections to the Drell Yan (non-singlet)
cross section for incoming states of arbitrary longitudinal helicities is
presented. The study is performed in the case of the transverse momentum
distributions, , of the lepton pair and extends the calculation of Ellis
Martinelli and Petronzio (EMP) to the polarized case. We use the
scheme and the t'Hooft-Veltman regularization for the helicity projectors. From
our results one can obtain the bulk of the totally inclusive NNLO cross section
for the production of a Drell Yan pair in the non-singlet sector by a simple
integration over the heavy photon momentum. We show that in the
helicity is not conserved, unless a finite renormalization is done to reenter
into a physical scheme (). This aspect of the calculation follows
the same trend as in polarized production of single and double photon to
. In the unpolarized limit we reproduce all the results of EMP.Comment: 39 pages, 7 figures (included
Direct photons measured by the PHENIX experiment at RHIC
Results from the PHENIX experiment at RHIC on direct photon production in
p+p, d+Au, and Au+Au collisions at sqrt(s_NN) = 200 GeV are presented. In p+p
collisions, direct photon production at high p_T behaves as expected from
perturbative QCD calculations. The p+p measurement serves as a baseline for
direct photon production in Au+Au collisions. In d+Au collisions, no effects of
cold nuclear matter are found within the large uncertainty of the measurement.
In Au+Au collisions, the production of high p_T direct photons scales as
expected for particle production in hard scatterings. This supports jet
quenching models, which attribute the suppression of high p_T hadrons to the
energy loss of fast partons in the medium produced in the collision. Low p_T
direct photons, measured via e+e- pairs with small invariant mass, are possibly
related to the production of thermal direct photons.Comment: 5 pages, 5 figures, Proceedings of the Hot Quarks 2006 Workshop for
young scientists on the physics of ultra-relativistic nucleus-nucleus
collisions, Villasimius, Sardinia, Italy, May 15--20, 200
Next-to-leading order QCD corrections to one hadron-production in polarized pp collisions at RHIC
We calculate the next-to-leading order QCD corrections to the spin-dependent
cross section for single-inclusive hadron production in hadronic collisions.
This process will be soon studied experimentally at RHIC, providing a tool to
unveil the polarized gluon distribution . We observe a considerably
improvement in the perturbative stability for both unpolarized and polarized
cross sections. The NLO corrections are found to be non-trivial, resulting in a
reduction of the asymmetry.Comment: 8 pages, RevTeX4, 9 figures include
Next-to-leading order QCD corrections to spin-dependent hadron-pair photoproduction
We compute the next-to-leading order QCD corrections to the ``direct'' part
of the spin-dependent cross section for hadron-pair photoproduction. The
calculation is performed using largely analytical methods. We present a brief
phenomenological study of our results focussing on the -factors and scale
dependence of the next-to-leading order cross sections. This process is
relevant for the extraction of the gluon polarization in present and future
spin-dependent lepton-nucleon scattering experiments.Comment: 9 pages, 2 eps figure
Inclusive particle production at HERA: Higher-order QCD corrections to the resolved quasi-real photon contribution
We calculate in next-to-leading order inclusive cross sections of
single-particle production via resolved photons in collisions at HERA.
Transverse-momentum and rapidity distributions are presented and the scale
dependence is studied. The results are compared with first experimental data
from the H1 Collaboration at HERA.Comment: 11 pages with 15 uuencoded PS figures. Preprint DESY 93-03
Structure and Functional Evaluation of Tendon–Skeletal Muscle Constructs Engineered in Vitro
During muscle contraction, the integrity of the myotendinous junction (MTJ) is important for the transmission of force from muscle to tendon. We evaluated the contractile and structural characteristics of 3-dimensional (3-D) skeletal muscle constructs co-cultured with engineered self-organized tendon constructs (n = 4), or segments of adult (n = 4) or fetal (n = 5) rat-tail tendon. We hypothesized that the co-culture of tendon and muscle would produce constructs with viable muscle–tendon interfaces that remain intact during generation of force. Construct diameter (lm) and maximum isometric force (µN) were measured, and specific force (kPa) was determined. After measure of force, constructs were loaded at a constant strain rate until failure and surface strains were recorded optically across the tendon, the muscle and the interface and used to determine the tangent modulus (passive stiffness) of the construct. Frozen samples were used for Trichrome Masson staining and immunofluorescent analysis of the MTJ-specific protein paxillin. No differences were observed between the groups with respect to diameter, maximum force, or specific force. The MTJ was robust and withstood tensile loading beyond the physiological strain range. The majority of the constructs failed in the muscle region. At the MTJ, there is an increase in the expression and localization of paxillin. In conclusion, using 3 sources of tendon tissue, we successfully engineered 3-D muscle–tendon constructs with functionally viable MTJ, characterized by structural features and protein expression patterns resembling neonatal MTJs in vivo.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63387/1/ten.2006.12.3149.pd
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