2,462 research outputs found
Hole polaron formation and migration in olivine phosphate materials
By combining first principles calculations and experimental XPS measurements,
we investigate the electronic structure of potential Li-ion battery cathode
materials LiMPO4 (M=Mn,Fe,Co,Ni) to uncover the underlying mechanisms that
determine small hole polaron formation and migration. We show that small hole
polaron formation depends on features in the electronic structure near the
valence-band maximum and that, calculationally, these features depend on the
methodology chosen for dealing with the correlated nature of the
transition-metal d-derived states in these systems. Comparison with experiment
reveals that a hybrid functional approach is superior to GGA+U in correctly
reproducing the XPS spectra. Using this approach we find that LiNiPO4 cannot
support small hole polarons, but that the other three compounds can. The
migration barrier is determined mainly by the strong or weak bonding nature of
the states at the top of the valence band, resulting in a substantially higher
barrier for LiMnPO4 than for LiCoPO4 or LiFePO4
Optimizing inhomogeneous spin ensembles for quantum memory
We propose a general method to maximize the fidelity of writing, storage and
reading of quantum information (QI) in a spectrally inhomogeneous spin ensemble
used as quantum memory. The method is based on preselecting the optimal
spectral portion of the ensemble by a judiciously designed pulse. It allows
drastic improvement of quantum memory realized by spin ensembles that store QI
from a resonator or an optical beam.Comment: Corrected m
Therapeutic Efficacy of Sulfadoxine-Pyrimethamine and Prevalence of Resistance Markers in Tanzania Prior to Revision of Malaria Treatment Policy: Plasmodium Falciparum Dihydrofolate Reductase and Dihydropteroate Synthase Mutations in Monitoring in Vivo Resistance.
Prior to the 2001 malarial treatment policy change in Tanzania, we conducted trials to assess the efficacy of sulfadoxine-pyrimethamine (SP) and the usefulness of molecular markers in monitoring resistance. A total of 383 uncomplicated Plasmodium falciparum malaria patients (between 6 and 59 months old) were treated with SP and their responses were assessed. Mutations in the P. falciparum dihydrofolate reductase (pfdhfr) and dihydropteroate synthase (pfdhps) genes in admission day blood samples were analyzed. Results indicated that 85.6% of the patients showed an adequate clinical response, 9.7% an early treatment failure, and 4.7% a late treatment failure. The quintuple mutant genotype (pfdhfr 51 Ile, 59 Arg, and 108 Asn and pfdhps 437 Gly and 540 Glu) showed an association with treatment outcome (odds ratio = 2.1; 95% confidence interval = 0.94-4.48, P = 0.045). The prevalence of the triple pfdhfr mutant genotype (51 Ile, 59 Arg, and 108 Asn) at a site of high SP resistance (23.6%) was four times higher compared with that observed at sites of moderate SP resistance (6.8-14.4%) (P = 0.000001). The genotype failure index calculated by using this marker was invariable (1.96-2.1) at sites with moderate SP resistance, but varied (3.4) at a site of high SP resistance. In conclusion, our clinical and molecular findings suggest that SP may have a short useful therapeutic life in Tanzania; thus, its adoption as an interim first-line antimalarial drug. The findings also point to the potential of the triple pfdhfr mutant genotype as an early warning tool for increasing SP resistance. These data form the baseline SP efficacy and molecular markers profile in Tanzania prior to the policy change
The effect of one additional driver mutation on tumor progression
Tumor growth is caused by the acquisition of driver mutations, which enhance the net reproductive rate of cells. Driver mutations may increase cell division, reduce cell death, or allow cells to overcome density-limiting effects. We study the dynamics of tumor growth as one additional driver mutation is acquired. Our models are based on two-type branching processes that terminate in either tumor disappearance or tumor detection. In our first model, both cell types grow exponentially, with a faster rate for cells carrying the additional driver. We find that the additional driver mutation does not affect the survival probability of the lesion, but can substantially reduce the time to reach the detectable size if the lesion is slow growing. In our second model, cells lacking the additional driver cannot exceed a fixed carrying capacity, due to density limitations. In this case, the time to detection depends strongly on this carrying capacity. Our model provides a quantitative framework for studying tumor dynamics during different stages of progression. We observe that early, small lesions need additional drivers, while late stage metastases are only marginally affected by them. These results help to explain why additional driver mutations are typically not detected in fast-growing metastases
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The effect of one additional driver mutation on tumor progression
Tumor growth is caused by the acquisition of driver mutations, which enhance the net reproductive rate of cells. Driver mutations may increase cell division, reduce cell death, or allow cells to overcome density-limiting effects. We study the dynamics of tumor growth as one additional driver mutation is acquired. Our models are based on two-type branching processes that terminate in either tumor disappearance or tumor detection. In our first model, both cell types grow exponentially, with a faster rate for cells carrying the additional driver. We find that the additional driver mutation does not affect the survival probability of the lesion, but can substantially reduce the time to reach the detectable size if the lesion is slow growing. In our second model, cells lacking the additional driver cannot exceed a fixed carrying capacity, due to density limitations. In this case, the time to detection depends strongly on this carrying capacity. Our model provides a quantitative framework for studying tumor dynamics during different stages of progression. We observe that early, small lesions need additional drivers, while late stage metastases are only marginally affected by them. These results help to explain why additional driver mutations are typically not detected in fast-growing metastases.MathematicsOrganismic and Evolutionary Biolog
Comment on "Measuring the Orbital Angular Momentum of a Single Photon"
Optical modes with different orbital angular momentums (OAMs) per photon may
be sorted by Mach-Zehnder interferometers incorporated with beam rotators,
without resorting to OAM mode converters.Comment: 1 page, 1 figur
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