1,572 research outputs found
Surface protection of graphite fabric/PMR-15 composites subjected to thermal oxidation
Graphite fabric/PMR-15 laminates develop matrix cracks during long-term exposure in air at temperatures in the range of 500 to 600 F. This study was performed to demonstrate the effectiveness of incorporating graphite mat surface plies as a means of reducing the developing of matrix cracks. Celion 3000 graphite fabric/PMR-15 laminates were fabricated with graphite or graphite mat/325-mesh boron powder surface plies. Laminates without mat surface plies were also fabricated for control purposes. Composite flexural strength, flexural modulus, and interlaminar shear strength were determined at 288 C before and after long-term exposure (up to 1500 hr) in air at 316 C. The results of this study showed that the incorporation of graphite mat surface plies reduces matrix cracking and improves the elevated temperature mechanical property retention characteristics of the composites
Equations to assess the impact resistance of fiber composites
Numerical analysis of impact resistance of composite materials containing fibers is discussed. Mathematical model of longitudinal impact resistance is presented. Potential impact resistance of various fiber composites as obtained by numerical analysis is presented as plotted curve
Bonding of strain gages to fiber reinforced composite plastic materials
Strain gage is installed during molding of composite and utilizes the adhesive properties of the matrix resin in the composite to bond the strain gage in place. Gages thus embedded provide data at all temperatures that the matrix can withstand
Criteria for selecting resin matrices for improved composite strength
Area under matrix of typical stress-strain diagram bounded by one percent strain is good index for priority assessment of matrix contribution to composite strength. Initial tangent modulus to stress-strain curve is useful parameter in translating matrix properties to composite properties
Observation of a Spinning Top in a Bose-Einstein Condensate
Boundaries strongly affect the behavior of quantized vortices in
Bose-Einstein condensates, a phenomenon particularly evident in elongated
cigar-shaped traps where vortices tend to orient along a short direction to
minimize energy. Remarkably, contributions to the angular momentum of these
vortices are tightly confined to the region surrounding the core, in stark
contrast to untrapped condensates where all atoms contribute . We
develop a theoretical model and use this, in combination with numerical
simulations, to show that such localized vortices precess in an analogous
manner to that of a classical spinning top. We experimentally verify this
spinning-top behavior with our real-time imaging technique that allows for the
tracking of position and orientation of vortices as they dynamically evolve.
Finally, we perform an in-depth numerical investigation of our real-time
expansion and imaging method, with the aim of guiding future experimental
implementation, as well as outlining directions for its improvement.Comment: 10 pages, 7 figure
Manipulating the quantum information of the radial modes of trapped ions: Linear phononics, entanglement generation, quantum state transmission and non-locality tests
We present a detailed study on the possibility of manipulating quantum
information encoded in the "radial" modes of arrays of trapped ions (i.e., in
the ions' oscillations orthogonal to the trap's main axis). In such systems,
because of the tightness of transverse confinement, the radial modes pertaining
to different ions can be addressed individually. In the first part of the paper
we show that, if local control of the radial trapping frequencies is available,
any linear optical and squeezing operation on the locally defined modes - on
single as well as on many modes - can be reproduced by manipulating the
frequencies. Then, we proceed to describe schemes apt to generate unprecedented
degrees of bipartite and multipartite continuous variable entanglement under
realistic noisy working conditions, and even restricting only to a global
control of the trapping frequencies. Furthermore, we consider the transmission
of the quantum information encoded in the radial modes along the array of ions,
and show it to be possible to a remarkable degree of accuracy, for both
finite-dimensional and continuous variable quantum states. Finally, as an
application, we show that the states which can be generated in this setting
allow for the violation of multipartite non-locality tests, by feasible
displaced parity measurements. Such a demonstration would be a first test of
quantum non-locality for "massive" degrees of freedom (i.e., for degrees of
freedom describing the motion of massive particles).Comment: 21 pages; this paper, presenting a far more extensive and detailed
analysis, completely supersedes arXiv:0708.085
Quantifying decoherence in continuous variable systems
We present a detailed report on the decoherence of quantum states of
continuous variable systems under the action of a quantum optical master
equation resulting from the interaction with general Gaussian uncorrelated
environments. The rate of decoherence is quantified by relating it to the decay
rates of various, complementary measures of the quantum nature of a state, such
as the purity, some nonclassicality indicators in phase space and, for two-mode
states, entanglement measures and total correlations between the modes.
Different sets of physically relevant initial configurations are considered,
including one- and two-mode Gaussian states, number states, and coherent
superpositions. Our analysis shows that, generally, the use of initially
squeezed configurations does not help to preserve the coherence of Gaussian
states, whereas it can be effective in protecting coherent superpositions of
both number states and Gaussian wave packets.Comment: Review article; 36 pages, 19 figures; typos corrected, references
adde
Design considerations for table-top, laser-based VUV and X-ray free electron lasers
A recent breakthrough in laser-plasma accelerators, based upon ultrashort
high-intensity lasers, demonstrated the generation of quasi-monoenergetic
GeV-electrons. With future Petawatt lasers ultra-high beam currents of ~100 kA
in ~10 fs can be expected, allowing for drastic reduction in the undulator
length of free-electron-lasers (FELs). We present a discussion of the key
aspects of a table-top FEL design, including energy loss and chirps induced by
space-charge and wakefields. These effects become important for an optimized
table-top FEL operation. A first proof-of-principle VUV case is considered as
well as a table-top X-ray-FEL which may open a brilliant light source also for
new ways in clinical diagnostics.Comment: 6 pages, 4 figures; accepted for publication in Appl. Phys.
Encouraging impact following 2.5 years of reinforced malaria control interventions in a hyperendemic region of the Republic of Guinea.
Malaria is one of the principal causes of morbidity and mortality in the Republic of Guinea, particularly in the highly endemic regions. To assist in malaria control efforts, a multi-component malaria control intervention was implemented in the hyperendemic region of Guéckédou Prefecture. The coverage of the intervention and its impact on malaria parasite prevalence were assessed.
Five cross-sectional surveys using cluster-based sampling and stratified by area were conducted from 2011 to 2013 in three sous-préfectures of Guéckédou Préfecture that received the intervention: Guéckédou City, Tékoulo and Guendembou in addition to one comparison sous-préfecture that did not receive the intervention, Koundou. Surveys were repeated every 6 months, corresponding with the dry and rainy seasons. Rapid diagnostic tests (RDT) were used to diagnose malaria infection. In each selected household, bed net use and ownership were assessed.
A total of 35,123 individuals participated in the surveys. Malaria parasite prevalence declined in all intervention sous-préfectures from 2011 to 2013 (56.4-45.9 % in Guéckédou City, 64.9-54.1 % in Tékoulo and 69.4-56.9 % in Guendembou) while increasing in the comparison sous-préfecture (64.5-69 %). It was consistently higher in children 5-14 years of age followed by those 1-59 months and ≥15 years. Indicators of intervention coverage, the proportion of households reporting ownership of at least one bed net and the proportion of survey participants with fever who received treatment from a health facility or community health worker also increased significantly in the intervention areas.
Implementation of the multi-component malaria control intervention significantly reduced the prevalence of malaria in the sous-préfectures of intervention while also increasing the coverage of bed nets. However, malaria prevalence remains unacceptably high and disproportionately affects children <15 years of age. In such situations additional vector control interventions and age specific interventions should be considered
- …