327 research outputs found
Comparison of optical model results from a microscopic Schr\"odinger approach to nucleon-nucleus elastic scattering with those from a global Dirac phenomenology
Comparisons are made between results of calculations for intermediate energy
nucleon-nucleus scattering for 12C, 16O, 40Ca, 90Zr, and 208Pb, using optical
potentials obtained from global Dirac phenomenology and from a microscopic
Schr\"odinger model. Differential cross sections and spin observables for
scattering from the set of five nuclei at 65 MeV and 200 MeV have been studied
to assess the relative merits of each approach. Total reaction cross sections
from proton-nucleus and total cross sections from neutron-nucleus scattering
have been evaluated and compared with data for those five targets in the energy
range 20 MeV to 800 MeV. The methods of analyses give results that compare well
with experimental data in those energy regimes for which the procedures are
suited.Comment: 22 pages, 12 figure
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In vitro model suggests oxidative stress involved in keratoconus disease
Keratoconus (KC) affects 1:2000 people and is a disorder where cornea thins and assumes a conical shape. Advanced KC requires surgery to maintain vision. The role of oxidative stress in KC remains unclear. We aimed to identify oxidative stress levels between human corneal keratocytes (HCKs), fibroblasts (HCFs) and keratoconus cells (HKCs). Cells were cultured in 2D and 3D systems. Vitamin C (VitC) and TGF-β3 (T3) were used for 4 weeks to stimulate self-assembled extracellular matrix (ECM). No T3 used as controls. Samples were analyzed using qRT-PCR and metabolomics. qRT-PCR data showed low levels of collagen I and V, as well as keratocan for HKCs, indicating differentiation to a myofibroblast phenotype. Collagen type III, a marker for fibrosis, was up regulated in HKCs. We robustly detected more than 150 metabolites of the targeted 250 by LC-MS/MS per condition and among those metabolites several were related to oxidative stress. Lactate levels, lactate/malate and lactate/pyruvate ratios were elevated in HKCs, while arginine and glutathione/oxidized glutathione ratio were reduced. Similar patterns found in both 2D and 3D. Our data shows that fibroblasts exhibit enhanced oxidative stress compared to keratocytes. Furthermore the HKC cells exhibit the greatest level suggesting they may have a myofibroblast phenotype
Probing Correlated Ground States with Microscopic Optical Model for Nucleon Scattering off Doubly-Closed-Shell Nuclei
The RPA long range correlations are known to play a significant role in
understanding the depletion of single particle-hole states observed in (e, e')
and (e, e'p) measurements. Here the Random Phase Approximation (RPA) theory,
implemented using the D1S force is considered for the specific purpose of
building correlated ground states and related one-body density matrix elements.
These may be implemented and tested in a fully microscopic optical model for NA
scattering off doubly-closed-shell nuclei. A method is presented to correct for
the correlations overcounting inherent to the RPA formalism. One-body density
matrix elements in the uncorrelated (i.e. Hartree-Fock) and correlated (i.e.
RPA) ground states are then challenged in proton scattering studies based on
the Melbourne microscopic optical model to highlight the role played by the RPA
correlations. Effects of such correlations which deplete the nuclear matter at
small radial distance (r 2 fm) and enhance its surface region, are getting
more and more sizeable as the incident energy increases. Illustrations are
given for proton scattering observables measured up to 201 MeV for the
O, Ca, Ca and Pb target nuclei. Handling the RPA
correlations systematically improves the agreement between scattering
predictions and data for energies higher than 150 MeV.Comment: 20 pages, 7 figure
Evolution of oxygen isotopic composition in the inner solar nebula
Changes in the chemical and isotopic composition of the solar nebula with
time are reflected in the properties of different constituents that are
preserved in chondritic meteorites. CR carbonaceous chondrites are among the
most primitive of all chondrite types and must have preserved solar nebula
records largely unchanged. We have analyzed the oxygen and magnesium isotopes
in a range of the CR constituents of different formation temperatures and ages,
including refractory inclusions and chondrules of various types. The results
provide new constraints on the time variation of the oxygen isotopic
composition of the inner (<5 AU) solar nebula - the region where refractory
inclusions and chondrules most likely formed. A chronology based on the decay
of short-lived 26Al (t1/2 ~ 0.73 Ma) indicates that the inner solar nebula gas
was 16O-rich when refractory inclusions formed, but less than 0.8 Ma later, gas
in the inner solar nebula became 16O-poor and this state persisted at least
until CR chondrules formed ~1-2 Myr later. We suggest that the inner solar
nebula became 16O-poor because meter-size icy bodies, which were enriched in
17,18O due to isotopic self-shielding during the ultraviolet photo dissociation
of CO in the protosolar molecular cloud or protoplanetary disk, agglomerated
outside the snowline, drifted rapidly towards the Sun, and evaporated at the
snowline. This led to significant enrichment in 16O-depleted water, which then
spread through the inner solar system. Astronomical studies of the spatial
and/or temporal variations of water abundance in protoplanetary disks may
clarify these processes.Comment: 27 pages, 5 figure
A Zero-Gravity Instrument to Study Low Velocity Collisions of Fragile Particles at Low Temperatures
We discuss the design, operation, and performance of a vacuum setup
constructed for use in zero (or reduced) gravity conditions to initiate
collisions of fragile millimeter-sized particles at low velocity and
temperature. Such particles are typically found in many astronomical settings
and in regions of planet formation. The instrument has participated in four
parabolic flight campaigns to date, operating for a total of 2.4 hours in
reduced gravity conditions and successfully recording over 300 separate
collisions of loosely packed dust aggregates and ice samples. The imparted
particle velocities achieved range from 0.03-0.28 m s^-1 and a high-speed,
high-resolution camera captures the events at 107 frames per second from two
viewing angles separated by either 48.8 or 60.0 degrees. The particles can be
stored inside the experiment vacuum chamber at temperatures of 80-300 K for
several uninterrupted hours using a built-in thermal accumulation system. The
copper structure allows cooling down to cryogenic temperatures before
commencement of the experiments. Throughout the parabolic flight campaigns,
add-ons and modifications have been made, illustrating the instrument
flexibility in the study of small particle collisions.Comment: D. M. Salter, D. Hei{\ss}elmann, G. Chaparro, G. van der Wolk, P.
Rei{\ss}aus, A. G. Borst, R. W. Dawson, E. de Kuyper, G. Drinkwater, K.
Gebauer, M. Hutcheon, H. Linnartz, F. J. Molster, B. Stoll, P. C. van der
Tuijn, H. J. Fraser, and J. Blu
Sensitivity of nucleon-nucleus scattering to the off-shell behavior of on-shell equivalent NN potentials
The sensitivity of nucleon-nucleus elastic scattering to the off-shell
behavior of realistic nucleon-nucleon interactions is investigated when
on-shell equivalent nucleon-nucleon potentials are used. The study is based on
applications of the full-folding optical model potential for an explicit
treatment of the off-shell behavior of the nucleon-nucleon effective
interaction. Applications were made at beam energies between 40 and 500 MeV for
proton scattering from 40Ca and 208Pb. We use the momentum-dependent Paris
potential and its local on-shell equivalent as obtained with the
Gelfand-Levitan and Marchenko inversion formalism for the two nucleon
Schroedinger equation. Full-folding calculations for nucleon-nucleus scattering
show small fluctuations in the corresponding observables. This implies that
off-shell features of the NN interaction cannot be unambiguously identified
with these processes. Inversion potentials were also constructed directly from
NN phase-shift data (SM94) in the 0-1.3 GeV energy range. Their use in
proton-nucleus scattering above 200 MeV provide a superior description of the
observables relative to those obtained from current realistic NN potentials.
Limitations and scope of our findings are presented and discussed.Comment: 17 pages tightened REVTeX, 8 .ps figures, submitted to Phys. Rev.
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PDGFRα Is a Key Regulator of T1 and T3's Differential Effect on SMA Expression in Human Corneal Fibroblasts
Purpose The goal of this study was to examine the mechanism behind the unique differential action of transforming growth factor β3 (TGF-β3) and TGF-β1 on SMA expression. It was our hypothesis that platelet-derived growth factor receptor α (PDGFRα) played a key role in determining TGF-β3's response to wounding. Methods: A stable cell line, human corneal fibroblast (HCF)-P, was created from HCFs by knocking down PDGFRα expression using a lentivirus-delivered shRNA sequence. A three-dimensional (3D) in vitro model was constructed by culturing HCF or HCF-P on poly-transwell membranes for 4 weeks in the presence and absence of 0.1 ng/mL TGF-β1 or -β3. At the end of 4 weeks, the constructs were processed for immunofluorescence and reverse transcription–quantitative polymerase chain reaction (RT-qPCR). In addition, HCF and HCF-P cell migration was evaluated. Results: In HCF, TGF-β3 treatment resulted in significantly lower α-smooth muscle actin (SMA) mRNA expression and immunolocalization when compared to TGF-β1, while in HCF-P, both TGF-β1 and -β3 treatment increased the SMA mRNA expression and immunolocalization compared to both the untreated HCF-P control and TGF-β3-treated HCF. Human corneal fibroblast-P also had a lower migration rate and construct thickness when compared to HCF. Conclusions: These results show that TGF-β3 decreases SMA in HCF, while remarkably increasing SMA in HCF-P, thus indicating that the presence or absence of PDGFRα elicits contrasting responses to the same TGF-β3 treatment. Understanding the role of PDGFRα in TGF-β3's ability to stimulate SMA may potentially help in understanding the differential functions of TGF-β1 and TGF-β3 in corneal wound healing
Full-Folding Optical Potentials for Elastic Nucleon-Nucleus Scattering based on Realistic Densities
Optical model potentials for elastic nucleon nucleus scattering are
calculated for a number of target nuclides from a full-folding integral of two
different realistic target density matrices together with full off-shell
nucleon-nucleon t-matrices derived from two different Bonn meson exchange
models. Elastic proton and neutron scattering observables calculated from these
full-folding optical potentials are compared to those obtained from `optimum
factorized' approximations in the energy regime between 65 and 400 MeV
projectile energy. The optimum factorized form is found to provide a good
approximation to elastic scattering observables obtained from the full-folding
optical potentials, although the potentials differ somewhat in the structure of
their nonlocality.Comment: 21 pages, LaTeX, 17 postscript figure
The pd <--> pi+ t reaction around the Delta resonance
The pd pi+ t process has been calculated in the energy region around the
Delta-resonance with elementary production/absorption mechanisms involving one
and two nucleons. The isobar degrees of freedom have been explicitly included
in the two-nucleon mechanism via pi-- and rho-exchange diagrams. No free
parameters have been employed in the analysis since all the parameters have
been fixed in previous studies on the simpler pp pi+ d process. The
treatment of the few-nucleon dynamics entailed a Faddeev-based calculation of
the reaction, with continuum calculations for the initial p-d state and
accurate solutions of the three-nucleon bound-state equation. The integral
cross-section was found to be quite sensitive to the NN interaction employed
while the angular dependence showed less sensitivity. Approximately a 4% effect
was found for the one-body mechanism, for the three-nucleon dynamics in the p-d
channel, and for the inclusion of a large, possibly converged, number of
three-body partial states, indicating that these different aspects are of
comparable importance in the calculation of the spin-averaged observables.Comment: 40 Pages, RevTex, plus 5 PostScript figure
Research On The Legal Issues Of Domestic Enterprises For Overseas Stock Market Listing ——From The Perspective Of VIE Agreements
2011年发生的“支付宝股权转移事件”引发了各界对我国境内公司以协议控制模式在境外上市法律问题的广泛关注。协议控制模式最初是为规避外商投资产业准入政策而设计,其合法性至今还存有很大的争议。本文从相关概念的界定入手,介绍了境内企业以协议控制模式在境外上市的操作方式,分析了导致协议控制模式存在和发展的法律动因及其存在的问题,在此基础上,对如何解决其存在的问题提出了几点建议。 本文分为引言、正文、结论三部分。其中正文共分为四章: 第一章从相关概念的界定入手,对协议控制上市模式进行分析。 第二章分析了境内企业以协议控制模式境外上市的法律动因主要是:规避外资行业准入政策;规避商务部关联并购的审批程...The Alipay’s transfer of ownership in 2011 draws public attention to legal defects of domestic enterprises for overseas stock market listing by VIE agreements . VIE agreements aims to avoid industry access policy to foreign merchants at first, which arouse controversy about its legitimacy until now. This paper begins to illustrates the conception of VIE agreements, followed by the operating ways a...学位:法律硕士院系专业:法学院法律系_法律硕士(JM)学号:1302009115033
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