4,914 research outputs found
Characterization of aerosol hygroscopicity over the Northeast Pacific Ocean: Impacts on prediction of CCN and stratocumulus cloud droplet number concentrations
During the Marine Aerosol Cloud and Wildfire Study (MACAWS) in June and July of 2018, aerosol composition and cloud condensation nuclei (CCN) properties were measured over the N.E. Pacific to characterize the influence of aerosol hygroscopicity on predictions of ambient CCN and stratocumulus cloud droplet number concentrations (CDNC). Three vertical regions were characterized, corresponding to the marine boundary layer (MBL), an aboveâcloud organic aerosol layer (ACâOAL), and the free troposphere (FT) above the ACâOAL. The aerosol hygroscopicity parameter (Îș) was calculated from CCN measurements (Îș_(CCN)) and bulk aerosol mass spectrometer (AMS) measurements (Îș_(AMS)). Within the MBL, measured hygroscopicities varied between values typical of both continental environments (~0.2) and remote marine locations (~0.7). For most flights, CCN closure was achieved within 20% in the MBL. For five of the seven flights, assuming a constant aerosol size distribution produced similar or better CCN closure than assuming a constant âmarineâ hygroscopicity (Îș = 0.72). An aerosolâcloud parcel model was used to characterize the sensitivity of predicted stratocumulus CDNC to aerosol hygroscopicity, size distribution properties, and updraft velocity. Average CDNC sensitivity to accumulation mode aerosol hygroscopicity is 39% as large as the sensitivity to the geometric median diameter in this environment. Simulations suggest CDNC sensitivity to hygroscopicity is largest in marine stratocumulus with low updraft velocities (0.6 m sâ»Âč), where hygroscopic properties of the Aitken mode dominate hygroscopicity sensitivity
Characterization of aerosol hygroscopicity over the Northeast Pacific Ocean: Impacts on prediction of CCN and stratocumulus cloud droplet number concentrations
During the Marine Aerosol Cloud and Wildfire Study (MACAWS) in June and July of 2018, aerosol composition and cloud condensation nuclei (CCN) properties were measured over the N.E. Pacific to characterize the influence of aerosol hygroscopicity on predictions of ambient CCN and stratocumulus cloud droplet number concentrations (CDNC). Three vertical regions were characterized, corresponding to the marine boundary layer (MBL), an aboveâcloud organic aerosol layer (ACâOAL), and the free troposphere (FT) above the ACâOAL. The aerosol hygroscopicity parameter (Îș) was calculated from CCN measurements (Îș_(CCN)) and bulk aerosol mass spectrometer (AMS) measurements (Îș_(AMS)). Within the MBL, measured hygroscopicities varied between values typical of both continental environments (~0.2) and remote marine locations (~0.7). For most flights, CCN closure was achieved within 20% in the MBL. For five of the seven flights, assuming a constant aerosol size distribution produced similar or better CCN closure than assuming a constant âmarineâ hygroscopicity (Îș = 0.72). An aerosolâcloud parcel model was used to characterize the sensitivity of predicted stratocumulus CDNC to aerosol hygroscopicity, size distribution properties, and updraft velocity. Average CDNC sensitivity to accumulation mode aerosol hygroscopicity is 39% as large as the sensitivity to the geometric median diameter in this environment. Simulations suggest CDNC sensitivity to hygroscopicity is largest in marine stratocumulus with low updraft velocities (0.6 m sâ»Âč), where hygroscopic properties of the Aitken mode dominate hygroscopicity sensitivity
Inclusive Scattering of Polarized Electrons on Polarized 3He Effects of Final State Interaction and the Magnetic Form Factor of the Neutron
Effects of final state interaction on asymmetries in inclusive scattering of
polarized electrons on polarized 3He are investigated using consistent 3He
bound state wave function and 3N continuum scattering states. Significant
effects are found, which influence the extraction of the magnetic neutron form
factor from A_T'. The enhancement found experimentally for A_TL' near the 3N
breakup threshold, which could not be explained in calculations carried through
in plane wave impulse approximation up to now, occurs now also in theory if the
full final state interaction is included.Comment: 29 pages, 5 figure
Inorganic Approach to Stabilizing Nanoscale Toroidicity in a Tetraicosanuclear FeDy Single Molecule Magnet
Cyclic coordination clusters (CCCs) are proving to provide an extra dimension in terms of exotic magnetic behavior as a result of their finite but cyclized chain structures. The FeDy CCC is a Single Molecule Magnet with the highest nuclearity among Ln containing clusters. The three isostructural compounds [FeLn(Ό-OH)(ampd)(Hampd)(PhCO)](NO)·38MeCN for Ln = Dy (1), Lu (2), or Y (3), where Hampd = 2-amino-2-methyl-1,3-propanediol, are reported. These can be described in terms of the cyclization of six {FeLn(ΌOH)(ampd)(Hampd)(PhCO)} units with six nitrate counterions to give the neutral cluster. The overall structure consists of two giant Dy triangles sandwiching a strongly antiferromagnetically coupled Fe ring, leading to a toroidal arrangement of the anisotropy axis of the Dy ions, making this the biggest toroidal arrangement on a molecular level known so far
Angle-resolved photoemission and first-principles electronic structure of single-crystalline -uranium (001)
Continuing the photoemission study begun with the work of Opeil et al. [Phys.
Rev. B \textbf{73}, 165109 (2006)], in this paper we report results of an
angle-resolved photoemission spectroscopy (ARPES) study performed on a
high-quality single-crystal -uranium at 173 K. The absence of
surface-reconstruction effects is verified using X-ray Laue and low-energy
electron diffraction (LEED) patterns. We compare the ARPES intensity map with
first-principles band structure calculations using a generalized gradient
approximation (GGA) and we find good correlations with the calculated
dispersion of the electronic bands
Nucleon-Nucleon Phase Shifts and Pairing in Neutron Matter and Nuclear Matter
We consider 1S0 pairing in infinite neutron matter and nuclear matter and
show that in the lowest order approximation, where the pairing interaction is
taken to be the bare nucleon-nucleon (NN) interaction in the 1S0 channel, the
pairing interaction and the energy gap can be determined directly from the 1S0
phase shifts. This is due to the almost separable character of the NN
interaction in this partial wave. Since the most recent NN interactions are
charge-dependent, we have to solve coupled gap equations for proton-proton,
neutron-neutron, and neutron-proton pairing in nuclear matter. The results,
however, are found to be close to those obtained with charge-independent
potentials.Comment: 5 pages, 3 figures, RevTe
Hybrid stars with the color dielectric and the MIT bag models
We study the hadron-quark phase transition in the interior of neutron stars
(NS). For the hadronic sector, we use a microscopic equation of state (EOS)
involving nucleons and hyperons derived within the Brueckner-Bethe-Goldstone
many-body theory, with realistic two-body and three-body forces. For the
description of quark matter, we employ both the MIT bag model with a density
dependent bag constant, and the color dielectric model. We calculate the
structure of NS interiors with the EOS comprising both phases, and we find that
the NS maximum masses are never larger than 1.7 solar masses, no matter the
model chosen for describing the pure quark phase.Comment: 11 pages, 5 figures, submitted to Phys. Rev.
Anderson-localization versus delocalization of interacting fermions in one dimension
Using the density matrix renormalization group algorithm, we investigate the
lattice model for spinless fermions in one dimension in the presence of a
strong interaction and disorder. The phase sensitivity of the ground state
energy is determined with high accuracy for systems up to a size of 60 lattice
constants. This quantity is found to be log-normally distributed. The
fluctuations grow algebraically with system size with a universal exponent of
~2/3 in the localized region of the phase diagram. Surprizingly, we find, for
an attractive interaction, a delocalized phase of finite extension. The
boundary of this delocalized phase is determined.Comment: 5 pages, 6 figures, revte
Phases of asymmetric nuclear matter with broken space symmetries
Isoscalar Cooper pairing in isospin asymmetric nuclear matter occurs between
states populating two distinct Fermi surfaces, each for neutrons and protons.
The transition from a BCS-like to the normal (unpaired) state, as the isospin
asymmetry is increased, is intervened by superconducting phases which
spontaneously break translational and rotational symmetries. One possibility is
the formation of a condensate with a periodic crystallinelike structure where
Cooper pairs carry net momentum (the nuclear
Larkin-Ovchinnikov-Fulde-Ferrell-phase). Alternatively, perturbations of the
Fermi surfaces away from spherical symmetry allow for minima in the condensate
free energy which correspond to a states with quadrupole deformations of Fermi
surfaces and zero momentum of the Cooper pairs. In a combined treatment of
these phases we show that, although the Cooper pairing with finite momentum
might arise as a local minimum, the lowest energy state features are deformed
Fermi surfaces and Cooper pairs with vanishing total momentum.Comment: 22 pages, 6 figures, RevTex; v2: matches published version; v3:
changes in the frontmatter, content unchange
- âŠ