15,244 research outputs found
Modelling the spring ozone maximum and the interhemispheric asymmetry in the remote marine boundary layer 1. Comparison with surface and ozonesonde measurements
Here we report a modelling study of the spring ozone maximum and its
interhemispheric asymmetry in the remote marine boundary layer (MBL). The
modelled results are examined at the surface and on a series of time-height
cross sections at several locations spread over the Atlantic, the Indian, and
the Pacific Oceans. Comparison of model with surface measurements at remote MBL
stations indicate a close agreement. The most striking feature of the
hemispheric spring ozone maximum in the MBL can be most easily identified at
the NH sites of Westman Island, Bermuda, and Mauna Loa, and at the SH site of
Samoa. Modelled ozone vertical distributions in the troposphere are compared
with ozone profiles. For the Atlantic and the Indian sites, the model generally
produces a hemispheric spring ozone maximum close to those of the measurements.
The model also produces a spring ozone maximum in the northeastern and tropical
north Pacific close to those measurements, and at sites in the NH high
latitudes. The good agreement between model and measurements indicate that the
model can reproduce the proposed mechanisms responsible for producing the
spring ozone maximum in these regions of the MBL, lending confidence in the use
of the model to investigate MBL ozone chemistry (see part 2 and part 3). The
spring ozone maximum in the tropical central south Pacific and eastern
equatorial Pacific are less well reproduced by the model, indicating that both
the transport of precursors from biomass burning emissions taking place
in southeastern Asia, Australia, Oceania, southern Africa, and South America
are not well represented in the model in these regions. Overall, the model
produces a better simulation at sites where the stratosphere and biomass
burning emissions are the major contributors.Comment: 24 pages, 8 figure
Deep-tissue focal fluorescence imaging with digitally time-reversed ultrasound-encoded light.
Fluorescence imaging is one of the most important research tools in biomedical sciences. However, scattering of light severely impedes imaging of thick biological samples beyond the ballistic regime. Here we directly show focusing and high-resolution fluorescence imaging deep inside biological tissues by digitally time-reversing ultrasound-tagged light with high optical gain (~5Ă—10(5)). We confirm the presence of a time-reversed optical focus along with a diffuse background-a corollary of partial phase conjugation-and develop an approach for dynamic background cancellation. To illustrate the potential of our method, we image complex fluorescent objects and tumour microtissues at an unprecedented depth of 2.5 mm in biological tissues at a lateral resolution of 36 ÎĽmĂ—52 ÎĽm and an axial resolution of 657 ÎĽm. Our results set the stage for a range of deep-tissue imaging applications in biomedical research and medical diagnostics
Using interference for high fidelity quantum state transfer in optomechanics
We revisit the problem of using a mechanical resonator to perform the
transfer of a quantum state between two electromagnetic cavities (e.g. optical
and microwave). We show that this system possesses an effective mechanical dark
state which is immune to mechanical dissipation; utilizing this feature allows
highly efficient transfer of intra-cavity states, as well as of itinerant
photon states. We provide simple analytic expressions for the fidelity of
transferring both Gaussian and non-Gaussian states.Comment: 5 pages, 2 figure
Experimental Validation of the Predicted Binding Site of Escherichia coli K1 Outer Membrane Protein A to Human Brain Microvascular Endothelial Cells: Identification of Critical Mutations That Prevent E. coli Meningitis
Escherichia coli K1, the most common cause of meningitis in neonates, has been shown to interact with GlcNAc1–4GlcNAc epitopes of Ecgp96 on human brain microvascular endothelial cells (HBMECs) via OmpA (outer membrane protein A). However, the precise domains of extracellular loops of OmpA interacting with the chitobiose epitopes have not been elucidated. We report the loop-barrel model of these OmpA interactions with the carbohydrate moieties of Ecgp96 predicted from molecular modeling. To test this model experimentally, we generated E. coli K1 strains expressing OmpA with mutations of residues predicted to be critical for interaction with the HBMEC and tested E. coli invasion efficiency. For these same mutations, we predicted the interaction free energies (including explicit calculation of the entropy) from molecular dynamics (MD), finding excellent correlation (R^2 = 90%) with experimental invasion efficiency. Particularly important is that mutating specific residues in loops 1, 2, and 4 to alanines resulted in significant inhibition of E. coli K1 invasion in HBMECs, which is consistent with the complete lack of binding found in the MD simulations for these two cases. These studies suggest that inhibition of the interactions of these residues of Loop 1, 2, and 4 with Ecgp96 could provide a therapeutic strategy to prevent neonatal meningitis due to E. coli K1
Proper Matter Collineations of Plane Symmetric Spacetimes
We investigate matter collineations of plane symmetric spacetimes when the
energy-momentum tensor is degenerate. There exists three interesting cases
where the group of matter collineations is finite-dimensional. The matter
collineations in these cases are either four, six or ten in which four are
isometries and the rest are proper.Comment: 10 pages, LaTex, accepted for publication in Modern Physics Letters
A New Approach to Modeling Early Warning Systems for Currency Crises : can a machine-learning fuzzy expert system predict the currency crises effectively?
This paper presents a hybrid model for predicting the occurrence of currency crises by using the neuro fuzzy modeling approach. The model integrates the learning ability of neural network with the inference mechanism of fuzzy logic. The empirical results show that the proposed neuro fuzzy model leads to a better prediction of crisis. Significantly, the model can also construct a reliable causal relationship among the variables through the obtained knowledge base. Compared to the traditionally used techniques such as logit, the proposed model can thus lead to a somewhat more prescriptive modeling approach towards finding ways to prevent currency crises.
Unambiguous discrimination among quantum operations
We address the problem of unambiguous discrimination among a given set of
quantum operations. The necessary and sufficient condition for them to be
unambiguously distinguishable is derived in the cases of single use and
multiple uses respectively. For the latter case we explicitly construct the
input states and corresponding measurements that accomplish the task. It is
found that the introduction of entanglement can improve the discrimination.Comment: 5 pages, no figur
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