1,444 research outputs found
Effects of distance dependence of exciton hopping on the Davydov soliton
The Davydov model of energy transfer in molecular chains is reconsidered
assuming the distance dependence of the exciton hopping term. New equations of
motion for phonons and excitons are derived within the coherent state
approximation. Solving these nonlinear equations result in the existence of
Davydov-like solitons. In the case of a dilatational soliton, the amplitude and
width is decreased as a results of the mechanism introduced here and above a
critical coupling strength our equations do not allow for localized solutions.
For compressional solitons, stability is increased.Comment: RevTeX 13 pages, 3 Postscript figure
A model for the fate of carbon dioxide from a simulated carbon storage seep
Offshore geological carbon storage (GCS) is a rapidly developing technology essential for meeting international climate goals. While the likelihood of leakage from a properly planned geological sequestration site is low, assurance that CO stays contained will require robust monitoring programs. While seismic imaging methods are used to monitor the geological reservoir, the ideal method for monitoring the water column above the reservoir depends on the fate and transport of CO. Whether CO is likely to be present as a rising seep of bubbles or dissolved in the water column near the seafloor will determine the appropriate monitoring technology and lead to a better understanding of the environmental impact of a potential leak. In this study, high definition video of a laboratory release of a carbon dioxide bubble seep recorded the size distribution of bubbles as a function of flow rate and orifice diameter. The transport of CO from different bubble size distributions was then modeled using the Texas A&M Oil Spill Calculator modeling suite. Model results show that the most important factor determining the rise height and transport of CO from the simulated leak was the maximum initial bubble size. For a maximum bubble radius of 5 mm, 95% of CO in the simulated seep reached a height of 17.1 m above the seafloor. When the maximum bubble radius was limited to 3 mm, 95% of CO dissolved by 7.8 m above the seafloor. The modeled results were verified during a controlled release of CO in Oslo Fjord.publishedVersio
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The visibility of environmental rights in the EU legal order: eurolegalism in action?
The current article responds to a key puzzle and a question. First, why, given the potential for ‘rights talk’ that has been seen in other countries and other policy areas, have environmental rights in the EU legal order been relatively invisible until recently? And second, with Daniel Kelemen’s influential work on Eurolegalism arguing that the EU has become much more reliant on US-style adversarial legalism, including a shift towards rights-based litigation, do EU environmental rights fit the picture Kelemen has painted, or are they an exception? The article explores the visibility of EU environmental rights at EU level and then seeks to explain the possible reasons for visibility/invisibility
Cysteine String Protein Regulates G Protein Modulation of N-Type Calcium Channels
AbstractCysteine string proteins (CSPs) are secretory vesicle proteins bearing a “J domain” and a palmitoylated cysteine-rich “string” region that are critical for neurotransmitter release. The precise role of CSP in neurotransmission is controversial. Here, we demonstrate a novel interaction between CSP, receptor-coupled trimeric GTP binding proteins (G proteins), and N-type Ca2+ channels. Gα subunits interact with the J domain of CSP in an ATP-dependent manner; in contrast, Gβγ subunits interact with the C terminus of CSP in both the presence and absence of ATP. The interaction of CSP with both G proteins and N-type Ca2+ channels results in a tonic G protein inhibition of the channels. In view of the crucial importance of N-type Ca2+ channels in presynaptic vesicle release, our data attribute a key role to CSP in the fine tuning of neurotransmission
A first-principles study of oxygen vacancy pinning of domain walls in PbTiO3
We have investigated the interaction of oxygen vacancies and 180-degree
domain walls in tetragonal PbTiO3 using density-functional theory. Our
calculations indicate that the vacancies do have a lower formation energy in
the domain wall than in the bulk, thereby confirming the tendency of these
defects to migrate to, and pin, the domain walls. The pinning energies are
reported for each of the three possible orientations of the original Ti-O-Ti
bonds, and attempts to model the results with simple continuum models are
discussed.Comment: 8 pages, with 3 postscript figures embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/lh_dw/index.htm
The Abundance of New Kind of Dark Matter Structures
A new kind of dark matter structures, ultracompact minihalos (UCMHs) was
proposed recently. They would be formed during the radiation dominated epoch if
the large density perturbations are existent. Moreover, if the dark matter is
made up of weakly interacting massive particles, the UCMHs can have effect on
cosmological evolution because of the high density and dark matter annihilation
within them. In this paper, one new parameter is introduced to consider the
contributions of UCMHs due to the dark matter annihilation to the evolution of
cosmology, and we use the current and future CMB observations to obtain the
constraint on the new parameter and then the abundance of UCMHs. The final
results are applicable for a wider range of dark matter parametersComment: 4 pages, 1 tabl
Direct Constraints on Minimal Supersymmetry from Fermi-LAT Observations of the Dwarf Galaxy Segue 1
The dwarf galaxy Segue 1 is one of the most promising targets for the
indirect detection of dark matter. Here we examine what constraints 9 months of
Fermi-LAT gamma-ray observations of Segue 1 place upon the Constrained Minimal
Supersymmetric Standard Model (CMSSM), with the lightest neutralino as the dark
matter particle. We use nested sampling to explore the CMSSM parameter space,
simultaneously fitting other relevant constraints from accelerator bounds, the
relic density, electroweak precision observables, the anomalous magnetic moment
of the muon and B-physics. We include spectral and spatial fits to the Fermi
observations, a full treatment of the instrumental response and its related
uncertainty, and detailed background models. We also perform an extrapolation
to 5 years of observations, assuming no signal is observed from Segue 1 in that
time. Results marginally disfavour models with low neutralino masses and high
annihilation cross-sections. Virtually all of these models are however already
disfavoured by existing experimental or relic density constraints.Comment: 22 pages, 5 figures; added extra scans with extreme halo parameters,
expanded introduction and discussion in response to referee's comment
Stochastic volatility and leverage effect
We prove that a wide class of correlated stochastic volatility models exactly
measure an empirical fact in which past returns are anticorrelated with future
volatilities: the so-called ``leverage effect''. This quantitative measure
allows us to fully estimate all parameters involved and it will entail a deeper
study on correlated stochastic volatility models with practical applications on
option pricing and risk management.Comment: 4 pages, 2 figure
Conservative Constraints on Dark Matter from the Fermi-LAT Isotropic Diffuse Gamma-Ray Background Spectrum
We examine the constraints on final state radiation from Weakly Interacting
Massive Particle (WIMP) dark matter candidates annihilating into various
standard model final states, as imposed by the measurement of the isotropic
diffuse gamma-ray background by the Large Area Telescope aboard the Fermi
Gamma-Ray Space Telescope. The expected isotropic diffuse signal from dark
matter annihilation has contributions from the local Milky Way (MW) as well as
from extragalactic dark matter. The signal from the MW is very insensitive to
the adopted dark matter profile of the halos, and dominates the signal from
extragalactic halos, which is sensitive to the low mass cut-off of the halo
mass function. We adopt a conservative model for both the low halo mass
survival cut-off and the substructure boost factor of the Galactic and
extragalactic components, and only consider the primary final state radiation.
This provides robust constraints which reach the thermal production
cross-section for low mass WIMPs annihilating into hadronic modes. We also
reanalyze limits from HESS observations of the Galactic Ridge region using a
conservative model for the dark matter halo profile. When combined with the
HESS constraint, the isotropic diffuse spectrum rules out all interpretations
of the PAMELA positron excess based on dark matter annihilation into two lepton
final states. Annihilation into four leptons through new intermediate states,
although constrained by the data, is not excluded.Comment: 11 pages, 5 figures. v3: minor revisions, matches version to appear
in JCA
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