2,154 research outputs found
Bistable hysteresis and resistance switching in hydrogen gold junctions
Current-voltage characteristics of H2-Au molecular junctions exhibit
intriguing steps around a characteristic voltage of 40 mV. Surprisingly, we
find that a hysteresis is connected to these steps with a typical time scale >
10 ms. This time constant scales linearly with the power dissipated in the
junction beyond an ofset power P_s = IV_s. We propose that the hysteresis is
related to vibrational heating of both the molecule in the junction and a set
of surrounding hydrogen molecules. Remarkably, we can engineer our junctions
such that the hysteresis' characteristic time becomes >days. We demonstrate
that reliable switchable devices can be built from such junctions.Comment: Submitted to Phys. Rev. Let
Localized states influence spin transport in epitaxial graphene
We developed a spin transport model for a diffusive channel with coupled
localized states that result in an effective increase of spin precession
frequencies and a reduction of spin relaxation times in the system. We apply
this model to Hanle spin precession measurements obtained on monolayer
epitaxial graphene on SiC(0001) (MLEG). Combined with newly performed
measurements on quasi-free-standing monolayer epitaxial graphene on SiC(0001)
our analysis shows that the different values for the diffusion coefficient
measured in charge and spin transport measurements in MLEG and the high values
for the spin relaxation time can be explained by the influence of localized
states arising from the buffer layer at the interface between the graphene and
the SiC surface.Comment: 6 pages, 3 figures, including supplementary materia
Spin Relaxation in Graphene with self-assembled Cobalt Porphyrin Molecules
In graphene spintronics, interaction of localized magnetic moments with the
electron spins paves a new way to explore the underlying spin relaxation
mechanism. A self-assembled layer of organic cobalt-porphyrin (CoPP) molecules
on graphene provides a desired platform for such studies via the magnetic
moments of porphyrin-bound cobalt atoms. In this work a study of spin transport
properties of graphene spin-valve devices functionalized with such CoPP
molecules as a function of temperature via non-local spin-valve and Hanle spin
precession measurements is reported. For the functionalized (molecular)
devices, we observe a slight decrease in the spin relaxation time ({\tau}s),
which could be an indication of enhanced spin-flip scattering of the electron
spins in graphene in the presence of the molecular magnetic moments. The effect
of the molecular layer is masked for low quality samples (low mobility),
possibly due to dominance of Elliot-Yafet (EY) type spin relaxation mechanisms
Results of the Anaconda endovascular graft in abdominal aortic aneurysm with a severe angulated infrarenal neck
Objective: Proximal neck anatomy of an abdominal aortic aneurysm (AAA), especially a severe angulated neck of more than 60 degrees, predicts adverse outcome in endovascular aneurysm repair. In the present study, we evaluate the feasibility of the use of the Anaconda endovascular graft (Vascutec, Terumo, Inchinnan, Scotland) for treating infrarenal AAA with a severe angulated neck (>60 degrees) and report the midterm outcomes. Methods: In total, nine Dutch hospitals participated in this prospective cohort study. From December 2005 to January 2011, a total of 36 AAA patients, 30 men and six women, were included. Mean and median follow-up were both 40 months. Results: Mean infrarenal neck angulation was 82 degrees. Successful deployment was reached in 34 of 36 patients. Primary technical success was achieved in 30 of 36 patients (83%). There was no aneurysm-related death. Four-year primary clinical success was 69%. In the first year, eight clinical failures were reported including four leg occlusions which could be solved using standard procedures. After the first year, three patients with additional failures occurred; two of them were leg occlusions. Four patients needed conversion to open AAA exclusion. In six of 36 patients, one or more reinterventions were necessary. Three of them were performed for occlusion of one Anaconda leg and two were for occlusion of the body. Conclusions: The use of the Anaconda endovascular graft in AAA with a severe angulated infrarenal neck is feasible but has its side effects. Most clinical failures occur in the first year. Thereafter, few problems occur, and midterm results are acceptable. Summarizing the present experiences, we conclude that open AAA repair is still a preferable option in patients with challenging aortic neck anatomy and fit for open surgery
Twenty-Four Hour Tonometry in Patients Suspected of Chronic Gastrointestinal Ischemia
Background and aims: Gastrointestinal tonometry is currently the only clinical diagnostic test that enables identification of symptomatic chronic gastrointestinal ischemia. Gastric exercise tonometry has proven its value for detection of ischemia in this patients group, but has its disadvantages. Earlier studies with postprandial tonometry gave unreliable results. In this study we challenged (again) the use of postprandial tonometry in patients suspected of gastrointestinal ischemia. Methods: Patients suspected for chronic gastrointestinal ischemia had standard diagnostic work up, including gastric exercise tonometry and 24-h tonometry using standard meals. Results: Thirty-three patients were enrolled in the study. Chronic gastrointestinal ischemia was diagnosed in 17 (52%) patients. The 24-h tonometry correctly predicted the presence of ischemia in 13/17 patients, and absence of ischemia in 15/16 patients. Conclusions: The use of 24-h tonometry after meals in patients suspected of gastrointestinal ischemia seems feasible, with promising accuracy for the detection of ischemia
Controlling the quality factor of a tuning-fork resonance between 9 K and 300 K for scanning-probe microscopy
We study the dynamic response of a mechanical quartz tuning fork in the
temperature range from 9 K to 300 K. Since the quality factor Q of the
resonance strongly depends on temperature, we implement a procedure to control
the quality factor of the resonance. We show that we are able to dynamically
change the quality factor and keep it constant over the whole temperature
range. This procedure is suitable for applications in scanning probe
microscopy.Comment: 5 pages, 6 figure
Phenotypic plasticity of carbon fixation stimulates cyanobacterial blooms at elevated CO2
Although phenotypic plasticity is a widespread phenomenon, its implications for species responses to climate change are not well understood. For example, toxic cyanobacteria can form dense surface blooms threatening water quality in many eutrophic lakes, yet a theoretical framework to predict how phenotypic plasticity affects bloom development at elevated pCO2 is still lacking. We measured phenotypic plasticity of the carbon fixation rates of the common bloom-forming cyanobacterium Microcystis. Our results revealed a 1.8- to 5-fold increase in the maximum CO2 uptake rate of Microcystis at elevated pCO2, which exceeds CO2 responses reported for other phytoplankton species. The observed plasticity was incorporated into a mathematical model to predict dynamic changes in cyanobacterial abundance. The model was successfully validated by laboratory experiments and predicts that acclimation to high pCO2 will intensify Microcystis blooms in eutrophic lakes. These results indicate that this harmful cyanobacterium is likely to benefit strongly from rising atmospheric pCO2
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