2,047 research outputs found
Classical Robustness of Quantum Unravellings
We introduce three measures which quantify the degree to which quantum
systems possess the robustness exhibited by classical systems when subjected to
continuous observation. Using these we show that for a fixed environmental
interaction the level of robustness depends on the measurement strategy, or
unravelling, and that no single strategy is maximally robust in all ways.Comment: 8 Pages, 2 figures, Version 2. Minor changes to wording for
clarification and some references added. Accepted for publication in
Europhysics Letter
Highly-tunable formation of nitrogen-vacancy centers via ion implantation
We demonstrate highly-tunable formation of nitrogen-vacancy (NV) centers
using 20 keV 15N+ ion implantation through arrays of high-resolution apertures
fabricated with electron beam lithography. By varying the aperture diameters
from 80 to 240 nm, as well as the average ion fluences from 5 x 10^10 to 2 x
10^11 ions/cm^2, we can control the number of ions per aperture. We analyze the
photoluminescence on multiple sites with different implantation parameters and
obtain ion-to-NV conversion yields of 6 to 7%, consistent across all ion
fluences. The implanted NV centers have spin dephasing times T2* ~ 3
microseconds, comparable to naturally occurring NV centers in high purity
diamond with natural abundance 13C. With this technique, we can
deterministically control the population distribution of NV centers in each
aperture, allowing for the study of single or coupled NV centers and their
integration into photonic structures.Comment: Related papers at http://pettagroup.princeton.ed
CFD Assessment of Aerodynamic Degradation of a Subsonic Transport Due to Airframe Damage
A computational study is presented to assess the utility of two NASA unstructured Navier-Stokes flow solvers for capturing the degradation in static stability and aerodynamic performance of a NASA General Transport Model (GTM) due to airframe damage. The approach is to correlate computational results with a substantial subset of experimental data for the GTM undergoing progressive losses to the wing, vertical tail, and horizontal tail components. The ultimate goal is to advance the probability of inserting computational data into the creation of advanced flight simulation models of damaged subsonic aircraft in order to improve pilot training. Results presented in this paper demonstrate good correlations with slope-derived quantities, such as pitch static margin and static directional stability, and incremental rolling moment due to wing damage. This study further demonstrates that high fidelity Navier-Stokes flow solvers could augment flight simulation models with additional aerodynamic data for various airframe damage scenarios
Bosonic Reduction of Susy Generalized Harry Dym Equation
In this paper we construct the two component supersymmetric generalized Harry
Dym equation which is integrable and study various properties of this model in
the bosonic limit. In particular, in the bosonic limit we obtain a new
integrable system which, under a hodograph transformation, reduces to a coupled
three component system. We show how the Hamiltonian structure transforms under
a hodograph transformation and study the properties of the model under a
further reduction to a two component system. We find a third Hamiltonian
structure for this system (which has been shown earlier to be a bi-Hamiltonian
system) making this a genuinely tri-Hamiltonian system. The connection of this
system to the modified dispersive water wave equation is clarified. We also
study various properties in the dispersionless limit of our model.Comment: 21 page
An integrated computational-experimental approach reveals Yersinia pestis genes essential across a narrow or a broad range of environmental conditions
This is the final version. Available from BMC via the DOI in this recordAvailability of data and materials:
The datasets supporting the conclusions of this article are available at the NCBI GEO website https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE100226.BACKGROUND: The World Health Organization has categorized plague as a re-emerging disease and the potential for Yersinia pestis to also be used as a bioweapon makes the identification of new drug targets against this pathogen a priority. Environmental temperature is a key signal which regulates virulence of the bacterium. The bacterium normally grows outside the human host at 28 °C. Therefore, understanding the mechanisms that the bacterium used to adapt to a mammalian host at 37 °C is central to the development of vaccines or drugs for the prevention or treatment of human disease. RESULTS: Using a library of over 1 million Y. pestis CO92 random mutants and transposon-directed insertion site sequencing, we identified 530 essential genes when the bacteria were cultured at 28 °C. When the library of mutants was subsequently cultured at 37 °C we identified 19 genes that were essential at 37 °C but not at 28 °C, including genes which encode proteins that play a role in enabling functioning of the type III secretion and in DNA replication and maintenance. Using genome-scale metabolic network reconstruction we showed that growth conditions profoundly influence the physiology of the bacterium, and by combining computational and experimental approaches we were able to identify 54 genes that are essential under a broad range of conditions. CONCLUSIONS: Using an integrated computational-experimental approach we identify genes which are required for growth at 37 °C and under a broad range of environments may be the best targets for the development of new interventions to prevent or treat plague in humans.This work was funded by the Defence Science and Technology Laboratory, award DSTLX-1000060221 (WP1)
Study of Small-Scale Anisotropy of Ultrahigh Energy Cosmic Rays Observed in Stereo by HiRes
The High Resolution Fly's Eye (HiRes) experiment is an air fluorescence
detector which, operating in stereo mode, has a typical angular resolution of
0.6 degrees and is sensitive to cosmic rays with energies above 10^18 eV. HiRes
is thus an excellent instrument for the study of the arrival directions of
ultrahigh energy cosmic rays. We present the results of a search for
anisotropies in the distribution of arrival directions on small scales (<5
degrees) and at the highest energies (>10^19 eV). The search is based on data
recorded between 1999 December and 2004 January, with a total of 271 events
above 10^19 eV. No small-scale anisotropy is found, and the strongest
clustering found in the HiRes stereo data is consistent at the 52% level with
the null hypothesis of isotropically distributed arrival directions.Comment: 4 pages, 3 figures. Matches accepted ApJL versio
An integrated computational-experimental approach reveals Yersinia pestis genes essential across a narrow or a broad range of environmental conditions
Background
The World Health Organization has categorized plague as a re-emerging disease and the potential for Yersinia pestis to also be used as a bioweapon makes the identification of new drug targets against this pathogen a priority. Environmental temperature is a key signal which regulates virulence of the bacterium. The bacterium normally grows outside the human host at 28 °C. Therefore, understanding the mechanisms that the bacterium used to adapt to a mammalian host at 37 °C is central to the development of vaccines or drugs for the prevention or treatment of human disease.
Results
Using a library of over 1 million Y. pestis CO92 random mutants and transposon-directed insertion site sequencing, we identified 530 essential genes when the bacteria were cultured at 28 °C. When the library of mutants was subsequently cultured at 37 °C we identified 19 genes that were essential at 37 °C but not at 28 °C, including genes which encode proteins that play a role in enabling functioning of the type III secretion and in DNA replication and maintenance. Using genome-scale metabolic network reconstruction we showed that growth conditions profoundly influence the physiology of the bacterium, and by combining computational and experimental approaches we were able to identify 54 genes that are essential under a broad range of conditions.
Conclusions
Using an integrated computational-experimental approach we identify genes which are required for growth at 37 °C and under a broad range of environments may be the best targets for the development of new interventions to prevent or treat plague in humans
Computational Discovery of Hydrogen Bond Design Rules for Electrochemical Ion Separation
Selective ion separation is a major challenge with far-ranging impact from water desalination to product separation in catalysis. Recently introduced ferrocene (Fc)/ferrocenium (Fc⁺) polymer electrode materials have been demonstrated experimentally and theoretically to selectively bind carboxylates over perchlorate through weak C–H···O hydrogen bond (HB) interactions that favor carboxylates, despite the comparable size and charge of the two species. However, practical application of this technology in aqueous environments requires further selectivity enhancement. Using a first-principles discovery approach, we investigate the effect of Fc/Fc⁺ functional groups (FGs) on the selectivity and reversibility of formate–Fc⁺ adsorption with respect to perchlorate in aqueous solution. Our wide design space of 44 FGs enables identification of FGs with higher selectivity and rationalization of trends through electronic energy decomposition analysis or geometric hydrogen bonding analysis. Overall, we observe weaker, longer HBs for perchlorate as compared to formate with Fc⁺. We further identify Fc⁺ functionalizations that simultaneously increase selectivity for formate in aqueous environments but permit rapid release from neutral Fc. We introduce the materiaphore, a 3D abstraction of these design rules, to help guide next-generation material optimization for selective ion sorption. This approach is expected to have broad relevance in computational discovery for molecular recognition, sensing, separations, and catalysis.National Science Foundation (U.S.) (ECCS-1449291
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The Stardust – a successful encounter with the remarkable comet Wild 2
On January 2, 2004 the Stardust spacecraft completed a close flyby of comet Wild2 (P81). Flying at a relative speed of 6.1 km/s within 237km of the 5 km nucleus, the spacecraft took 72 close-in images, measured the flux of impacting particles and did TOF mass spectrometry
Absolutely stable proton and lowering the gauge unification scale
A unified model is constructed, based on flipped SU(5) in which the proton is absolutely stable. The model requires the existence of new leptons with masses of order the weak scale. The possibility that the unification scale could be extremely low is discussed
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