1,565 research outputs found
Accurately monitoring the Florida Current with motionally induced voltages
A new experimental technique for appraising how accurately submarine-cable (subcable) voltages monitor oceanic volume transport is presented and then used to study voltages induced by the northern Florida Current. Until recently, subcable voltages have been largely dismissed as an oceanographic tool because their interpretation can be ambiguous. They depend upon the transport field, the electrical conductance of the environment, and the mutual spatial distribution of these two quantities. To examine how these three factors affect subcable voltages at a particular site, we combine data from two different velocity profilers: XCP and PEGASUS. These instruments provide vertical profiles of velocity, temperature, and motion ally induced voltage at several sites across a transect. From this information, we determine if and why subcable voltages track volume transport. We conclude that subcable voltages measured in the northern Florida Straits accurately monitor the Florida Current transport because they are insensitive to the spatial distribution of the flow—a result that stems from a large and rather uniform seabed conductance. Subcable voltages should be reconsidered for oceanic monitoring elsewhere because the validity of their interpretation can now be assessed
Supersonic aeroelastic instability results for a NASP-like wing model
An experimental study and an analytical study have been conducted to examine static divergence for hypersonic-vehicle wing models at supersonic conditions. A supersonic test in the Langley Unitary Plan Wind Tunnel facility was conducted for two wind-tunnel models. These models were nearly identical with the exception of airfoil shape. One model had a four-percent maximum thickness airfoil and the other model had an eight-percent maximum thickness airfoil. The wing models had low-aspect ratios and highly swept leading edges. The all-movable wing models were supported by a single-pivot mechanism along the wing root. For both of the wind-tunnel models, configuration changes could be made in the wing-pivot location along the wing root and in the wing-pivot pitch stiffness. Three divergence conditions were measured for the four-percent thick airfoil model in the Mach number range of 2.6 to 3.6 and one divergence condition was measured for the eight-percent thick airfoil model at a Mach number of 2.9. Analytical divergence calculations were made for comparison with experimental results and to evaluate the parametric effects of wing-pivot stiffness, wing-pivot location, and airfoil thickness variations. These analyses showed that decreasing airfoil thickness, moving the wing-pivot location upstream, or increasing the pitch-pivot stiffness have the beneficial effect of increasing the divergence dynamic pressures. The calculations predicted the trend of experimental divergence dynamic pressure with Mach number accurately; however, the calculations were approximately 25 percent conservative with respect to dynamic pressure
Trials and evaluation of an RD Instruments Acoustic Correlation Current Profiler in the Agulhas Current on RRS "Discovery" Cruise 214
High Sensitivity DNA Detection Using Gold Nanoparticle Functionalised Polyaniline Nanofibres
Polyaniline (PANI) nanofibres (PANI-NF) have been modified with chemically grown gold nanoparticles to give a nanocomposite material (PANI-NF–AuNP) and deposited on gold electrodes. Single stranded capture DNA was then bound to the gold nanoparticles and the underlying gold electrode and allowed to hybridise with a complementary target strand that is uniquely associated with the pathogen, Staphylococcus aureus (S. aureus), that causes mastitis. Significantly, cyclic voltammetry demonstrates that deposition of the gold nanoparticles increases the area available for DNA immobilisation by a factor of approximately 4. EPR reveals that the addition of the Au nanoparticles efficiently decreases the interactions between adjacent PANI chains and/or motional broadening. Finally, a second horseradish peroxidase (HRP) labelled DNA strand hybridises with the target allowing the concentration of the target DNA to be detected by monitoring the reduction of a hydroquinone mediator in solution. The sensors have a wide dynamic range, excellent ability to discriminate DNA mismatches and a high sensitivity. Semi-log plots of the pathogen DNA concentration vs. faradaic current were linear from 150 × 10−12 to 1 × 10−6 mol L−1 and pM concentrations could be detected without the need for molecular, e.g., PCR or NASBA, amplification
Finite temperature bosonization
Finite temperature properties of a non-Fermi liquid system is one of the most
challenging probelms in current understanding of strongly correlated electron
systems. The paradigmatic arena for studying non-Fermi liquids is in one
dimension, where the concept of a Luttinger liquid has arisen. The existence of
a critical point at zero temperature in one dimensional systems, and the fact
that experiments are all undertaken at finite temperature, implies a need for
these one dimensional systems to be examined at finite temperature.
Accordingly, we extended the well-known bosonization method of one dimensional
electron systems to finite temperatures. We have used this new bosonization
method to calculate finite temperature asymptotic correlation functions for
linear fermions, the Tomonaga-Luttinger model, and the Hubbard model.Comment: REVTex, 48 page
EVALUATION OF RELATIONSHIPS BETWEEN REPORTED RESILIENCE AND SOLDIER OUTCOMES, Report #2: Positive Performance Outcomes in Officers (Promotions, Selections, & Professions)
This technical report presents an analysis of reported resilience and psychological health among the U.S. Army’s Officer Corps. The focus of the current report is on linking resilience and psychological health (hereafter referred to as R/PH) to objective outcomes associated with high job performance.
Specifically, this report examines the statistical relationships between officer R/PH - as measured by the Army’s Global Assessment Tool (GAT) - and promotions to Brigadier General, early (below zone) Field Grade Officer promotions, selections for command / key billet assignments, and officers who serve in career fields that require terminal professional degrees (e.g., medical doctors, dentists, lawyers, etc).
Results show that officers who have been promoted to Brigadier General are more emotionally and socially fit than their peers who have not received a promotion to Brigadier General. These officers are more engaged with their work, have higher levels of organizational trust and friendship, report lower levels of loneliness, are more optimistic, and report higher levels of positive affect and lower levels of negative affect. Each of these findings is in line with our expectations regarding R/PH and job performance, and the findings comport with a substantial body of work in the academic literature.
Additionally, analysis of R/PH for officers promoted early resulted in findings similar to above. In particular, those who have been promoted below zone report higher levels of work engagement, friendship, organizational trust, optimism, and coping abilities. In short, these officers score higher on the GAT dimensions of Emotional and Social Fitness than their peers who were not promoted early (“due course” officers). Similar results were found for officers selected for command for key billet assignments. They are also more emotionally and socially fit than their peers who were not selected for command (more engaged with their work, have higher levels of organizational trust and friendship, are less lonely, are more optimistic, and report higher levels of positive affect and lower levels of negative affect).
There are no practical differences in R/PH between officers serving in career fields that require terminal professional degrees and other officers serving in “line” career fields (rank-matched analysis, Captain - Colonel). In light of academic literature on the subject, this finding is somewhat surprising as it suggests that advanced professional education / training alone may not influence (or be influenced by) R/PH.
When taken together, the findings above strongly suggest there is a relationship between reported resilience and psychological health and outcomes associated with high job performance, but we are currently unable to determine causality. Stated differently, we do not know if the reported R/PH contributed to the performance outcomes, or if the high job performance outcomes contributed to the reported R/PH. Further data collection and analysis over the next 12-24 months will broaden our understanding of the relationships
Insights into the internal structures of nanogels using a versatile asymmetric-flow field-flow fractionation method
Poly(N-isopropylacrylamide) (pNIPAM) nanogels are a highly researched type of colloidal material. In this work, we establish a versatile asymmetric-flow field-flow fractionation (AF4) method that can provide high resolution particle sizing and also structural information on nanogel samples from 65–310 nm in hydrodynamic diameter and so different chemical compositions. To achieve this online multi-angle light scattering and dynamic light scattering detectors were used to provide measurement of the radius of gyration (Rg) and hydrodynamic radius (Rh) respectively. Two different eluents and a range of cross-flows were evaluated in order to provide effective fractionation and high recovery for the different nanogel samples. We found that using 0.1 M NaNO3 as the eluent and an initial cross-flow of 1 mL min−1 provided optimal separation conditions for all samples tested. Using this method, we analysed two types of samples, pNIPAM nanogels prepared by free radical dispersion polymerisation with increasing diameters and analysed poly(acrylic acid)-b-pNIPAM crosslinked nanogels prepared by reversible addition–fragmentation chain transfer dispersion polymerisation. We could determine that the differently sized free radical nanogels possessed differing internal structures; shape factors (Rg/Rh) ranged from 0.58–0.73 and revealed that the smallest nanogel had a homogeneous internal crosslinking density, while the larger nanogels had a more densely crosslinked core compared to the shell. The poly(acrylic acid)-b-pNIPAM crosslinked nanogels displayed clear core–shell structures due to all the crosslinking being contained in the core of the nanogel
Screening and interlayer coupling in multilayer graphene field-effect transistors
With the motivation of improving the performance and reliability of
aggressively scaled nano-patterned graphene field-effect transistors, we
present the first systematic experimental study on charge and current
distribution in multilayer graphene field-effect transistors. We find a very
particular thickness dependence for Ion, Ioff, and the Ion/Ioff ratio, and
propose a resistor network model including screening and interlayer coupling to
explain the experimental findings. In particular, our model does not invoke
modification of the linear energy-band structure of graphene for the multilayer
case. Noise reduction in nano-scale few-layer graphene transistors is
experimentally demonstrated and can be understood within this model as well.Comment: 13 pages, 4 figures, 20 reference
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