131 research outputs found
The Relative Role of Land in Climate Policy
Replaced with revised version of paper 06/26/09.Climate policy, land use related emissions, carbon forest sequestration, CGE, Environmental Economics and Policy,
Hard Rescattering in QCD and High Energy Two-Body Photodisintegration of the Deuteron
Photon absorption by a quark in one nucleon followed by its high momentum
transfer interaction with a quark in the other may produce two nucleons with
high relative momentum. We sum the relevant quark rescattering diagrams, to
show that the scattering amplitude depends on a convolution between the large
angle scattering amplitude, the hard photon-quark interaction vertex and
the low-momentum deuteron wave function. The computed cross sections are in
reasonable agreement with the data.Comment: Four pages Latex, uses espcrc1.sty. Presented at 15th International
Conference on Particle and Nuclei (PANIC 99), Uppsala, Sweden, 10-16 Jun 199
Quantifying the Effects of Hyperthermal Atomic Oxygen and Thermal Fatigue Environments on Carbon Nanotube Sheets for Space-Based Applications
The effects of atomic oxygen and thermal fatigue on two different types of carbon nanotube sheets were studied. One set was treated with nitric acid, while the other set was left untreated. Monotonic tensile tests were performed before and after exposure to determine the effects of either exposure type on the sheets’ mechanical properties. Electrical conductivity and electromagnetic interference measurements were recorded to determine the effects of AO-exposure and thermal cycling on the sheets’ electrical properties. Neither exposure type affected the sheets’ specific strengths. Both exposure types increased the sheets’ specific stiffnesses and decreased the sheets’ strains at failure. The electrical conductivity of both sheets decreased due to the different exposure types, while the EMI shielding effectiveness was unaffected. Scanning electron microscopy was used to observe any changes in the sheets’ surface morphologies, while energy-dispersive X-ray spectroscopy was used to determine the effects of AO on the sheets’ chemical makeup
Hard Break-Up of Two-Nucleons from the 3He Nucleus
We investigate a large angle photodisintegration of two nucleons from the
He nucleus within the framework of the hard rescattering model (HRM). In
the HRM a quark of one nucleon knocked out by an incoming photon rescatters
with a quark of the other nucleon leading to the production of two nucleons
with large relative momentum. Assuming the dominance of the quark-interchange
mechanism in a hard NN scattering, the HRM allows to express the amplitude of a
two-nucleon break-up reaction through the convolution of photon-quark
scattering, hard scattering amplitude and nuclear spectral function. The
photon-quark scattering amplitude can be explicitly calculated in the high
energy regime, whereas for scattering one uses the fit of the available
experimental data. The HRM predicts several specific features for the hard
breakup reaction. First, the cross section will approximately scale as
. Secondly, the weighted cross section will have the shape of
energy dependence similar to that of weighted elastic scattering
cross section. Also one predicts an enhancement of the breakup relative to
the breakup cross section as compared to the results from low energy
kinematics. Another result is the prediction of different spectator momentum
dependencies of and breakup cross sections. This is due to the fact
that same-helicity -component is strongly suppressed in the ground state
wave function of He. Because of this suppression the HRM predicts
significantly different asymmetries for the cross section of polarization
transfer breakup reactions for circularly polarized photons. For the
breakup this asymmetry is predicted to be zero while for the it is close
to .Comment: 33 pages and 8 figures, version published in Physical Review
Spectrally-resolved Imaging of the Transverse Modes in Multimode VCSELs
Vertical-cavity surface-emitting lasers (VCSELs) enable a range of applications such as data transmission, trace sensing, atomic clocks, and optical mice. For many of these applications, the output power and beam quality are both critical (i.e. high output power with good beam quality is desired). Multi-mode VCSELs offer much higher power than single-mode devices, but this comes at the expense of lower beam quality. Directly observing the resolved mode structure of multi-mode VCSELs would enable engineers to better understand the underlying physics and help them to develop multi-mode devices with improved beam quality. In this work, a low-cost, high-resolution (\u3c3 \u3epm) Echelle grating spectrometer system is used to map the two-dimensional VCSEL near-field emission profile. The system spectrally disperses the VCSEL beam and images it with high magnification onto a CMOS camera. The narrow spectral content of each LP mode allows direct observation of the modal content of the VCSEL
Male Partners Involvement in Spousal Contraceptive Use: A Perspective of a Contemporary African Setting
Background: Contraceptive use by women is one of the tools used for promoting family health and slowing population growth. Evidence has suggested that contraceptive use in Nigeria is below acceptable levels in spite of the fact that family planning services are readily available, accessible and affordable. The involvement and participation of males in spousal contraceptive use is seen as the driver to achieving better reproductive outcomes. Hence, this study aimed to determine the level of male involvement in spousal contraceptive use so as to provide evidence based and people oriented information on the available male partner support system for contraceptive use and factors influence it.Methodology: This was a cross sectional study conducted among 80 male partners between April and May, 2017 using quantitative method of data collection and SPSS version 20 was used for data analysis.nbsp Crude and adjusted odds ratios as well asnbsp 95% confidence interval were used in this study with a p-value of le 0.05 considered statistically significant.Results: The mean age of the respondents in the study was 40.0 plusmn 10 years with only 13 (16.3%) of the respondents adjudged as being involved in their spousal contraceptive use. Currently use of male contraceptive method was found to significantly influence involvement in spousal contraceptive use (AOR = 7.1 95% CI = 2.1092 ndash 10.5818 P = 0.015). Conclusion: This study has demonstrated a low level of male involvement in spousal contraceptive use hence, relevant male educational intervention on contraception is required
QCD Rescattering and High Energy Two-Body Photodisintegration of the Deuteron
Photon absorption by a quark in one nucleon followed by its high momentum
transfer interaction with a quark in the other may produce two final-state
nucleons with high relative momentum. We sum the relevant quark rescattering
diagrams, to show that the scattering amplitude depends on a convolution
between the large angle scattering amplitude, the hard photon-quark
interaction vertex and the low-momentum deuteron wave function. The computed
absolute values of the cross section are in reasonable agreement with the data.Comment: 4 pages, revised version to be published in Phys. Rev. Let
Recent observation of short range nucleon correlations in nuclei and their implications for the structure of nuclei and neutron stars
Novel processes probing the decay of nucleus after removal of a nucleon with
momentum larger than Fermi momentum by hard probes finally proved unambiguously
the evidence for long sought presence of short-range correlations (SRCs) in
nuclei. In combination with the analysis of large , A(e,e')X processes at
they allow us to conclude that (i) practically all nucleons with momenta
300 MeV/c belong to SRCs, consisting mostly of two nucleons, ii)
probability of such SRCs in medium and heavy nuclei is , iii) a fast
removal of such nucleon practically always leads to emission of correlated
nucleon with approximately opposite momentum, iv) proton removal from
two-nucleon SRCs in 90% of cases is accompanied by a removal of a neutron and
only in 10% by a removal of another proton. We explain that observed absolute
probabilities and the isospin structure of two nucleon SRCs confirm the
important role that tensor forces play in internucleon interactions. We find
also that the presence of SRCs requires modifications of the Landau Fermi
liquid approach to highly asymmetric nuclear matter and leads to a
significantly faster cooling of cold neutron stars with neutrino cooling
operational even for . The effect is even stronger for the
hyperon stars. Theoretical challenges raised by the discovered dominance of
nucleon degrees of freedom in SRCs and important role of the spontaneously
broken chiral symmetry in quantum chromodynamics (QCD) in resolving them are
considered. We also outline directions for future theoretical and experimental
studies of the physics relevant for SRCs.Comment: 74 pages. Review article, updated version to be published in
International Journal of Modern Physics
Selected Topics in High Energy Semi-Exclusive Electro-Nuclear Reactions
We review the present status of the theory of high energy reactions with
semi-exclusive nucleon electro-production from nuclear targets. We demonstrate
how the increase of transferred energies in these reactions opens a complete
new window in studying the microscopic nuclear structure at small distances.
The simplifications in theoretical descriptions associated with the increase of
the energies are discussed. The theoretical framework for calculation of high
energy nuclear reactions based on the effective Feynman diagram rules is
described in details. The result of this approach is the generalized eikonal
approximation (GEA), which is reduced to Glauber approximation when nucleon
recoil is neglected. The method of GEA is demonstrated in the calculation of
high energy electro-disintegration of the deuteron and A=3 targets.
Subsequently we generalize the obtained formulae for A>3 nuclei. The relation
of GEA to the Glauber theory is analyzed. Then based on the GEA framework we
discuss some of the phenomena which can be studied in exclusive reactions,
these are: nuclear transparency and short-range correlations in nuclei. We
illustrate how light-cone dynamics of high-energy scattering emerge naturally
in high energy electro-nuclear reactions.Comment: LaTex file with 51 pages and 23 eps figure
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