431 research outputs found
Growers’ risk perception and trust in control options for huanglongbing citrus-disease in Florida and California
Citrus huanglongbing disease is an acute bacterial disease that threatens the sustainability of citrus production across the world. In the USA, the Asian Citrus Psyllid (ACP) is responsible for spreading the disease. Successful suppression of HLB requires action against ACP at large spatial scales, i.e. growers must cooperate. In Florida and California, the regions in which citrus is grown have been split into management areas and growers are encouraged to coordinate spraying of insecticide across these (area-wide control). We surveyed growers from Florida and California to assess the consensus of opinions concerning issues that influence HLB management. Our results show that risk perception and trust in control options are central to the decision by growers on whether to join an area-wide control program. Growers’ perceptions on risk and control efficacy are influenced by information networks and observations about the state of the epidemic and psyllid populations. Researchers and extension agents were reported to have the largest influence on these perceptions. Differences in opinion between California and Florida growers as to the efficacy of treatments were largely a function of experience. A large proportion of growers identified failure of participation as a reason why participation in area-wide control might not occur
An evaporation-based model of thermal neutron induced ternary fission of plutonium
Ternary fission probabilities for thermal neutron induced fission of
plutonium are analyzed within the framework of an evaporation-based model where
the complexity of time-varying potentials, associated with the neck collapse,
are included in a simplistic fashion. If the nuclear temperature at scission
and the fission-neck-collapse time are assumed to be ~1.2 MeV and ~10^-22 s,
respectively, then calculated relative probabilities of ternary-fission
light-charged-particle emission follow the trends seen in the experimental
data. The ability of this model to reproduce ternary fission probabilities
spanning seven orders of magnitude for a wide range of light-particle charges
and masses implies that ternary fission is caused by the coupling of an
evaporation-like process with the rapid re-arrangement of the nuclear fluid
following scission.Comment: 25 pages, 12 figures, accepted for publication in IJMP
Selfie-Objectification:Self-Objectification and Positive Feedback (“Likes”) are Associated with Frequency of Posting Sexually Objectifying Self-Images on Social Media
The present study is the first to examine the extent to which young adult women post objectifying self-images on social media, and whether the frequency of posting such content can be predicted by self-objectification and positive feedback (likes). Eighty-six young adult women from the UK (Age M = 19.88; SD = 1.34, Range = 18-24) completed self-report measures of self-objectification and social media use. The 20 most recent images they had posted on their personal Instagram accounts were downloaded (Image N = 1720) and content analysed for self-objectifying content. The analysis found that 29.77% of participants’ Instagram images were objectified, though there were individual differences. Higher frequency of posting objectified self-images was associated with trait self-objectification and receiving more likes on this type of self-image, relative to non-objectified self-images. The implications of the novel findings for objectification theory are discussed within
Prospects for the discovery of the next new element: Influence of projectiles with Z > 20
The possibility of forming new superheavy elements with projectiles having Z
> 20 is discussed. Current research has focused on the fusion of 48Ca with
actinides targets, but these reactions cannot be used for new element
discoveries in the future due to a lack of available target material. The
influence on reaction cross sections of projectiles with Z > 20 have been
studied in so-called analog reactions, which utilize lanthanide targets
carefully chosen to create compound nuclei with energetics similar to those
found in superheavy element production. The reactions 48Ca, 45Sc, 50Ti, 54Cr +
159Tb, 162Dy have been studied at the Cyclotron Institute at Texas A&M
University using the Momentum Achromat Recoil Spectrometer. The results of
these experimental studies are discussed in terms of the influence of
collective enhancements to level density for compound nuclei near closed
shells, and the implications for the production of superheavy elements. We have
observed no evidence to contradict theoretical predictions that the maximum
cross section for the 249Cf(50Ti, 4n)295120 and 248Cm(54Cr, 4n)298120 reactions
should be in the range of 10-100 fb.Comment: An invited talk given by Charles M. Folden III at the 11th
International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio,
Texas, USA, May 27-June 1, 2012. Also contains information presented by
Dmitriy A. Mayorov and Tyler A. Werke in separate contributions to the
conference. This contribution will appear in the NN2012 Proceedings in
Journal of Physics: Conference Series (JPCS
Decay modes of 250No
The Fragment Mass Analyzer at the ATLAS facility has been used to
unambiguously identify the mass number associated with different decay modes of
the nobelium isotopes produced via 204Pb(48Ca,xn)(252-x)No reactions.
Isotopically pure (>99.7%) 204Pb targets were used to reduce background from
more favored reactions on heavier lead isotopes. Two spontaneous fission
half-lives (t_1/2 = 3.7+1.1-0.8 us and 43+22-15 us) were deduced from a total
of 158 fission events. Both decays originate from 250No rather than from
neighboring isotopes as previously suggested. The longer activity most likely
corresponds to a K-isomer in this nucleus. No conclusive evidence for an alpha
branch was observed, resulting in upper limits of 2.1% for the shorter lifetime
and 3.4% for the longer activity.Comment: RevTex4, 10 pages, 5 figures, submitted to PR
Relations between fusion cross sections and average angular momenta
We study the relations between moments of fusion cross sections and averages
of angular momentum. The role of the centrifugal barrier and the target
deformation in determining the effective barrier radius are clarified. A simple
method for extracting average angular momentum from fusion cross sections is
demonstrated using numerical examples as well as actual data.Comment: 16 REVTeX pages plus 8 included Postscript figures (uses the epsf
macro); submitted to Phys. Rev. C; also available at
http://nucth.physics.wisc.edu/preprint
An Improved Quantum Molecular Dynamics Model and its Applications to Fusion Reaction near Barrier
An improved Quantum Molecular Dynamics model is proposed. By using this
model, the properties of ground state of nuclei from Li to Pb can
be described very well with one set of parameters. The fusion reactions for
Ca+Zr, Ca+Zr and Ca+Zr at energy near
barrier are studied by this model. The experimental data of the fusion cross
sections for Ca+Zr at the energy near barrier can be
reproduced remarkably well without introducing any new parameters. The
mechanism for the enhancement of fusion probability for fusion reactions with
neutron-rich projectile or target is analyzed.Comment: 20 pages, 12 figures, 3 table
Population of isomers in decay of the giant dipole resonance
The value of an isomeric ratio (IR) in N=81 isotones (Ba, Ce,
Nd and Sm) is studied by means of the ( reaction.
This quantity measures a probability to populate the isomeric state in respect
to the ground state population. In ( reactions, the giant dipole
resonance (GDR) is excited and after its decay by a neutron emission, the
nucleus has an excitation energy of a few MeV. The forthcoming decay
by direct or cascade transitions deexcites the nucleus into an isomeric or
ground state. It has been observed experimentally that the IR for Ba
and Ce equals about 0.13 while in two heavier isotones it is even less
than half the size. To explain this effect, the structure of the excited states
in the energy region up to 6.5 MeV has been calculated within the Quasiparticle
Phonon Model. Many states are found connected to the ground and isomeric states
by , and transitions. The single-particle component of the wave
function is responsible for the large values of the transitions. The calculated
value of the isomeric ratio is in very good agreement with the experimental
data for all isotones. A slightly different value of maximum energy with which
the nuclei rest after neutron decay of the GDR is responsible for the reported
effect of the A-dependence of the IR.Comment: 16 pages, 4 Fig
Quasi-fission reactions as a probe of nuclear viscosity
Fission fragment mass and angular distributions were measured from the
^{64}Ni+^{197}Au reaction at 418 MeV and 383 MeV incident energy. A detailed
data analysis was performed, using the one-body dissipation theory implemented
in the code HICOL. The effect of the window and the wall friction on the
experimental observables was investigated. Friction stronger than one-body was
also considered. The mass and angular distributions were consistent with
one-body dissipation. An evaporation code DIFHEAT coupled to HICOL was
developed in order to predict reaction time scales required to describe
available data on pre-scission neutron multiplicities. The multiplicity data
were again consistent with one-body dissipation. The cross-sections for touch,
capture and quasi-fission were also obtained.Comment: 25 pages REVTeX, 3 tables, 13 figures, submitted to Phys. Rev
Systematics of Fission Barriers in Superheavy Elements
We investigate the systematics of fission barriers in superheavy elements in
the range Z = 108-120 and N = 166-182. Results from two self-consistent models
for nuclear structure, the relativistic mean-field (RMF) model as well as the
non-relativistic Skyrme-Hartree-Fock approach are compared and discussed. We
restrict ourselves to axially symmetric shapes, which provides an upper bound
on static fission barriers. We benchmark the predictive power of the models
examining the barriers and fission isomers of selected heavy actinide nuclei
for which data are available. For both actinides and superheavy nuclei, the RMF
model systematically predicts lower barriers than most Skyrme interactions. In
particular the fission isomers are predicted too low by the RMF, which casts
some doubt on recent predictions about superdeformed ground states of some
superheavy nuclei. For the superheavy nuclei under investigation, fission
barriers drop to small values around Z = 110, N = 180 and increase again for
heavier systems. For most of the forces, there is no fission isomer for
superheavy nuclei, as superdeformed states are in most cases found to be
unstable with respect to octupole distortions.Comment: 17 pages REVTEX, 12 embedded eps figures. corrected abstrac
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