2,132 research outputs found
Biophilic Design at Pomona College: An Analysis of the New Sontag and Pomona Residence Halls
The Leadership in Energy and Environmental Design for New Construction (or LEED-NC) has become one of the most commonly used green building standards during the turn of the 21st century. While many champion LEED-NC, certain architects and academics believe that its low-environmental impact design approach toward green building isolates people from nature and thus cannot achieve sustainable development over the long-term. Pomona College’s green buildings, including its newest LEED Platinum certified Sontag and Pomona Residence Halls, exemplify this fact, as their designs fail to communicate their sustainable goals or inspire sustainable behavior. By examining the LEED-NC standards, the history of environmental conservation, Modern architecture, biophilia, and the Living Building Challenge, this thesis seeks to provide recommendations for how Pomona College can alter its existing green buildings as well as improve its green building policies for future projects so that its built environment better fosters positive human-nature interactions
Energy dependence of nucleus-nucleus potential close to the Coulomb barrier
The nucleus-nucleus interaction potentials in heavy-ion fusion reactions are
extracted from the microscopic time-dependent Hartree-Fock theory for mass
symmetric reactions OO, CaCa,
CaCa and mass asymmetric reactions OCa,
CaCa, O+Pb, Ca+Zr. When the
center-of-mass energy is much higher than the Coulomb barrier energy,
potentials deduced with the microscopic theory identify with the frozen density
approximation. As the center-of-mass energy decreases and approaches the
Coulomb barrier, potentials become energy dependent. This dependence signs
dynamical reorganization of internal degrees of freedom and leads to a
reduction of the "apparent" barrier felt by the two nuclei during fusion of the
order of compared to the frozen density case. Several examples
illustrate that the potential landscape changes rapidly when the center-of-mass
energy is in the vicinity of the Coulomb barrier energy. The energy dependence
is expected to have a significant role on fusion around the Coulomb barrier.Comment: 11 pages, 13 figures, 1 table, discussion of effects of
coordinate-dependent mass added, accepted for publication in Phys. Rev.
From finite nuclei to the nuclear liquid drop: leptodermous expansion based on the self-consistent mean-field theory
The parameters of the nuclear liquid drop model, such as the volume, surface,
symmetry, and curvature constants, as well as bulk radii, are extracted from
the non-relativistic and relativistic energy density functionals used in
microscopic calculations for finite nuclei. The microscopic liquid drop energy,
obtained self-consistently for a large sample of finite, spherical nuclei, has
been expanded in terms of powers of A^{-1/3} (or inverse nuclear radius) and
the isospin excess (or neutron-to-proton asymmetry). In order to perform a
reliable extrapolation in the inverse radius, the calculations have been
carried out for nuclei with huge numbers of nucleons, of the order of 10^6. The
Coulomb interaction has been ignored to be able to approach nuclei of arbitrary
sizes and to avoid radial instabilities characteristic of systems with very
large atomic numbers. The main contribution to the fluctuating part of the
binding energy has been removed using the Green's function method to calculate
the shell correction. The limitations of applying the leptodermous expansion to
actual nuclei are discussed. While the leading terms in the macroscopic energy
expansion can be extracted very precisely, the higher-order, isospin-dependent
terms are prone to large uncertainties due to finite-size effects.Comment: 13 pages revtex4, 7 eps figures, submitted to Phys. Rev.
Stochastic Semi-Classical Description of Fusion at Near-Barrier Energies
Fusion reactions of heavy ions are investigated by employing a simple
stochastic semi-classical model which includes the coupling between relative
motion and low frequency collective surface modes of colliding ions similarly
to the quantal coupled-channels description. The quantal effect enters into the
calculation through the initial zero-point fluctuations of the surface
vibrations. Good agreement with the result of coupled-channels calculations as
well as data is obtained for the fusion cross sections of nickel isotopes. The
internal excitations in non-fusing events as well as the fusion time are
investigated.Comment: 8 pages, 8 figures, Published in Phys. Rev.
Origin of the neutron skin thickness of 208Pb in nuclear mean-field models
We study whether the neutron skin thickness (NST) of 208Pb originates from
the bulk or from the surface of the nucleon density distributions, according to
the mean-field models of nuclear structure, and find that it depends on the
stiffness of the nuclear symmetry energy. The bulk contribution to NST arises
from an extended sharp radius of neutrons, whereas the surface contribution
arises from different widths of the neutron and proton surfaces. Nuclear models
where the symmetry energy is stiff, as typical relativistic models, predict a
bulk contribution in NST of 208Pb about twice as large as the surface
contribution. In contrast, models with a soft symmetry energy like common
nonrelativistic models predict that NST of 208Pb is divided similarly into bulk
and surface parts. Indeed, if the symmetry energy is supersoft, the surface
contribution becomes dominant. We note that the linear correlation of NST of
208Pb with the density derivative of the nuclear symmetry energy arises from
the bulk part of NST. We also note that most models predict a mixed-type
(between halo and skin) neutron distribution for 208Pb. Although the halo-type
limit is actually found in the models with a supersoft symmetry energy, the
skin-type limit is not supported by any mean-field model. Finally, we compute
parity-violating electron scattering in the conditions of the 208Pb parity
radius experiment (PREX) and obtain a pocket formula for the parity-violating
asymmetry in terms of the parameters that characterize the shape of the 208Pb
nucleon densities.Comment: 11 pages, 4 figures; minor stylistic changes in text, new Ref. [56]
added (new measurement of the neutron skin thickness of 208Pb
Cluster formations in deformed states for Si and S
We study cluster formation in strongly deformed states for Si and
S using a macroscopic-microscopic model. The study is based on
calculated total-energy surfaces, which are the sums of deformation-dependent
macroscopic-microscopic potential-energy surfaces and rotational-energy
contributions. We analyze the angular-momentum-dependent total-energy surfaces
and identify the normal- and super-deformed states in Si and S,
respectively. We show that at sufficiently high angular momenta strongly
deformed minima appear. The corresponding microscopic density distributions
show cluster structure that closely resemble the O+C and
O+O configurations. At still higher deformations, beyond the
minima, valleys develop in the calculated surfaces. These valleys lead to mass
divisions that correspond to the target-projectile configurations for which
molecular resonance states have been observed. We discuss the relation between
the one-body deformed minima and the two-body molecular-resonance states.Comment: 6 pages, 7 figure
Analysis of bulk and surface contributions in the neutron skin of nuclei
The neutron skin thickness of nuclei is a sensitive probe of the nuclear
symmetry energy having multiple implications for nuclear and astrophysical
studies. However, precision measurements of this observable are difficult. The
analysis of the experimental data may imply some assumptions about the bulk or
surface nature of the formation of the neutron skin. Here, we study the bulk or
surface character of neutron skins of nuclei following from calculations with
Gogny, Skyrme, and covariant nuclear mean-field interactions. These
interactions are successful in describing nuclear charge radii and binding
energies but predict different values for neutron skins. We perform the study
by fitting two-parameter Fermi distributions to the calculated self-consistent
neutron and proton densities. We note that the equivalent sharp radius is a
more suitable reference quantity than the half-density radius parameter of the
Fermi distributions to discern between the bulk and surface contributions in
neutron skins. We present calculations for nuclei in the stability valley and
for the isotopic chains of Sn and Pb.Comment: 13 pages, 9 figure
Analysis of bulk and surface contributions in the neutron skin of nuclei
The neutron skin thickness of nuclei is a sensitive probe of the nuclear
symmetry energy having multiple implications for nuclear and astrophysical
studies. However, precision measurements of this observable are difficult. The
analysis of the experimental data may imply some assumptions about the bulk or
surface nature of the formation of the neutron skin. Here, we study the bulk or
surface character of neutron skins of nuclei following from calculations with
Gogny, Skyrme, and covariant nuclear mean-field interactions. These
interactions are successful in describing nuclear charge radii and binding
energies but predict different values for neutron skins. We perform the study
by fitting two-parameter Fermi distributions to the calculated self-consistent
neutron and proton densities. We note that the equivalent sharp radius is a
more suitable reference quantity than the half-density radius parameter of the
Fermi distributions to discern between the bulk and surface contributions in
neutron skins. We present calculations for nuclei in the stability valley and
for the isotopic chains of Sn and Pb.Comment: 13 pages, 9 figure
Observation of Three-dimensional Long-range Order in Smaller Ion Coulomb Crystals in an rf Trap
Three-dimensional long-range ordered structures in smaller and
near-spherically symmetric Coulomb crystals of ^{40}Ca^+ ions confined in a
linear rf Paul trap have been observed when the number of ions exceeds ~1000
ions. This result is unexpected from ground state molecular dynamics (MD)
simulations, but found to be in agreement with MD simulations of metastable ion
configurations. Previously, three-dimensional long-range ordered structures
have only been reported in Penning traps in systems of ~50,000 ions or more.Comment: 5 pages; 4 figures; to appear in Phys. Rev. Lett.; changed content
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