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Effect of Build Parameters and Build Geometries on Residual Microstructures and Mechanical Properties of Ti-6Al-4V Components Built by Electron Beam Melting (EBM)
In this study, involving additive manufacturing (AM) using electron beam melting (EBM), we
have examined build defects which result from beam tripping, porosities (including unmelted or
unsintered zones) due to excursions from optimal build parameters (especially variations in melt
scan beam current and scan speed), and gas bubbles trapped in atomized Ti-6Al-4V starting
powder as well as recycled powder, and retained in the build. At optimized build conditions we
have also examined microstructure-mechanical property (hardness, tensile strength, and
elongation) variations for multiple rake building and multiple melt scans using optical
metallography and scanning and transmission electron microscopy (SEM and TEM). These
build variances cause cooling rate variances which promote α-phase growth and variations in
dislocation density, as well as α-to-α' (martensite) phase changes, all of which produce some
degree of mechanical property variations. These features (especially α-to-α' phase changes) are
notable on comparing solid builds in comparison with a variety of mesh arrays where strut
dimension and build-element complexities alter the cooling rates in a significant way. We
illustrate these microstructure variations with corresponding variations in microindentation
hardness measurements made directly on fine mesh (strut) structures. Finally, we have examined
Ti-6Al-4V powder chemistries and solid build chemistries which for single-pass melt scans at
optimized build conditions are shown to be relatively constant up to 40 cycles of powder reuse
with the exception of Al content which was reduced by 10 to 15% in solid builds at optimized
conditions. However, Al loss in solid builds approached 25% for multiple (2 and 3) melt scans,
while no changes in Ar gas-bubble density were observed with changes in α-phase (grain) width
which increased from 3 µm for a single melt scan to 4.5 and 6 µm for 2 and 3 melt scans,
respectively. Corresponding Rockwell C-scale (HRC) hardness varied from 37, 36, and 35,
respectively; with ultimate tensile strengths exceeding 1.2 GPa at elongations of 12% or higher
for this melt scan sequence.Mechanical Engineerin
kt Effects in Direct-Photon Production
We discuss the phenomenology of initial-state parton-kt broadening in
direct-photon production and related processes in hadron collisions. After a
brief summary of the theoretical basis for a Gaussian-smearing approach, we
present a systematic study of recent results on fixed-target and collider
direct-photon production, using complementary data on diphoton and pion
production to provide empirical guidance on the required amount of kt
broadening. This approach provides a consistent description of the observed
pattern of deviation of next-to-leading order QCD calculations relative to the
direct-photon data, and accounts for the shape and normalization difference
between fixed-order perturbative calculations and the data. We also discuss the
uncertainties in this phenomenological approach, the implications of these
results on the extraction of the gluon distribution of the nucleon, and the
comparison of our findings to recent related work.Comment: LaTeX, uses revtex and epsf, 37 pages, 15 figure
Towards a global analysis of polarized parton distributions
We present a technique for implementing in a fast way, and without any
approximations, higher-order calculations of partonic cross sections into
global analyses of parton distribution functions. The approach, which is set up
in Mellin-moment space, is particularly suited for analyses of future data from
polarized proton-proton collisions, but not limited to this case. The
usefulness and practicability of this method is demonstrated for the
semi-inclusive production of hadrons in deep-inelastic scattering and the
transverse momentum distribution of ``prompt'' photons in pp collisions, and a
case study for a future global analysis of polarized parton densities is
presented.Comment: 20 pages, LaTeX, 6 eps figures, final version to appear in PRD (minor
changes
Factorization Breaking in Dijet Photoproduction with a Leading Neutron
The production of dijets with a leading neutron in ep-interactions at HERA is
calculated in leading order and next-to-leading order of perturbative QCD using
a pion-exchange model. Differential cross sections for deep-inelastic
scattering (DIS) and photoproduction are presented as a function of several
kinematic variables. By comparing the theoretical predictions for DIS dijets to
recent H1 data, the pion flux factor together with the parton distribution
functions of the pion is determined. The dijet cross sections in
photoproduction show factorization breaking if compared to the H1
photoproduction data. The suppression factor is S = 0.48 (0.64) for resolved
(global) suppression.Comment: 16 pages, 5 figure
Influencia del agua en la esterificación enzimática de ketoprofeno racémico con etanol sin co-solvente agregado
Las lipasas son las enzimas más comúnmente usadas para producir dexketoprofeno mediante resolución cinética. Este isómero es farmacológicamente activo, por lo que su obtención de forma pura disminuiría los efectos adversos del AINE
Single-Inclusive Jet Production in Polarized pp Collisions at O(alpha_s^3)
We present a next-to-leading order QCD calculation for single-inclusive
high-p_T jet production in longitudinally polarized pp collisions within the
``small-cone'' approximation. The fully analytical expressions obtained for the
underlying partonic hard-scattering cross sections greatly facilitate the
analysis of upcoming BNL-RHIC data on the double-spin asymmetry A_{LL}^{jet}
for this process in terms of the unknown polarization of gluons in the nucleon.
We simultaneously rederive the corresponding QCD corrections to unpolarized
scattering and confirm the results existing in the literature. We also
numerically compare to results obtained with Monte-Carlo methods and assess the
range of validity of the ``small-cone'' approximation for the kinematics
relevant at BNL-RHIC.Comment: 23 pages, 8 eps-figure
Next-to-leading order QCD corrections to A_TT for prompt photon production
We present a next-to-leading order QCD calculation of the cross section for
isolated large-p_T prompt photon production in collisions of transversely
polarized protons. We devise a simple method of dealing with the phase space
integrals in dimensional regularization in the presence of the cos(2 phi)
azimuthal-angular dependence occurring for transverse polarization. Our results
allow to calculate the double-spin asymmetry A_TT for this process at
next-to-leading order accuracy, which may be used at BNL-RHIC to measure the
transversity parton distributions of the proton.Comment: 19 pages, LaTeX, 2 figures as eps file
Maladaptive avoidance patterns in Parkinson's disease are exacerbated by symptoms of depression
Available online 11 January 2020Parkinson’s disease (PD) is a chronic, progressive neurodegenerative disorder, characterized by a loss of dopaminergic neurons in the substantia nigra pars compacta. Given that dopamine is critically involved in learning and other cognitive processes, such as working memory, dopamine loss in PD has been linked both to learning abnormalities and to cognitive dysfunction more generally in the disease. It is unclear, however, whether avoidance behavior is impacted in PD. This is significant, as this type of instrumental behavior plays an important role in both decision-making and emotional (dys) function. Consequently, the aim of the present study was to examine avoidance learning and operant extinction in PD using a computer-based task. On this task, participants control a spaceship and attempt to shoot an enemy spaceship to gain points. They also learn to hide in safe areas to protect from (i.e., avoid) aversive events (on-screen explosions and point loss). The results showed that patients with PD (N = 25) acquired an avoidance response during aversive periods to the same extent as healthy age-matched controls (N = 19); however, patients demonstrated greater hiding during safe periods not associated with aversive events, which could represent maladaptive generalization of the avoidance response. Furthermore, this impairment was more pronounced during the extinction phase, and in patients who reported higher levels of depression. These results demonstrate for the first time that PD is associated with maladaptive avoidance patterns, which could possibly contribute to the emergence of depression in the disease.Jony Sheynin, Irina Baetu, Lyndsey E. Collins-Praino, Catherine E. Myers, Robyn Winwood-Smith, Ahmed A. Moustaf
Multiparton Interactions in Photoproduction at HERA
The high energy photoproduction of jets is being observed at the ep collider,
HERA. It may be that the HERA centre-of-mass energy is sufficiently large that
the production of more than one pair of jets per ep collision becomes possible,
owing to the large number density of the probed gluons. We construct a Monte
Carlo model of such multiparton interactions and study their effects on a wide
range of physical observables. The conclusion is that multiple interactions
could have very significant effects upon the photoproduction final state and
that this would for example make extractions of the gluon density in the photon
rather difficult. Total rates for the production of many (i.e. > 2) jets could
provide direct evidence for the presence of multiple interactions, although
parton showering and hadronization significantly affect low transverse energy
jets.Comment: 21 pages, 8 figures include
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