1,112 research outputs found
Shot noise in carbon nanotube based Fabry-Perot interferometers
We report on shot noise measurements in carbon nanotube based Fabry-Perot
electronic interferometers. As a consequence of quantum interferences, the
noise power spectral density oscillates as a function of the voltage applied to
the gate electrode. The quantum shot noise theory accounts for the data
quantitatively. It allows to confirm the existence of two nearly degenerate
orbitals. At resonance, the transmission of the nanotube approaches unity, and
the nanotube becomes noiseless, as observed in quantum point contacts. In this
weak backscattering regime, the dependence of the noise on the backscattering
current is found weaker than expected, pointing either to electron-electron
interactions or to weak decoherence
Conserved spin and orbital phase along carbon nanotubes connected with multiple ferromagnetic contacts
We report on spin dependent transport measurements in carbon nanotubes based
multi-terminal circuits. We observe a gate-controlled spin signal in non-local
voltages and an anomalous conductance spin signal, which reveal that both the
spin and the orbital phase can be conserved along carbon nanotubes with
multiple ferromagnetic contacts. This paves the way for spintronics devices
exploiting both these quantum mechanical degrees of freedom on the same
footing.Comment: 8 pages - minor differences with published versio
Causes of prehospital misinterpretations of ST elevation myocardial infarction
Objectives: To determine the causes of software misinterpretation of ST elevation myocardial infarction (STEMI) compared to clinically identified STEMI to identify opportunities to improve prehospital STEMI identification. Methods: We compared ECGs acquired from July 2011 through June 2012 using the LIFEPAK 15 on adult patients transported by the Los Angeles Fire Department. Cases included patients ≥18 years who received a prehospital ECG. Software interpretation of the ECG (STEMI or not) was compared with data in the regional EMS registry to classify the interpretation as true positive (TP), true negative (TN), false positive (FP), or false negative (FN). For cases where classification was not possible using registry data, 3 blinded cardiologists interpreted the ECG. Each discordance was subsequently reviewed to determine the likely cause of misclassification. The cardiologists independently reviewed a sample of these discordant ECGs and the causes of misclassification were updated in an iterative fashion. Results: Of 44,611 cases, 50% were male (median age 65; inter-quartile range 52–80). Cases were classified as 482 (1.1%) TP, 711 (1.6%) FP, 43371 (97.2%) TN, and 47 (0.11%) FN. Of the 711 classified as FP, 126 (18%) were considered appropriate for, though did not undergo, emergent coronary angiography, because the ECG showed definite (52 cases) or borderline (65 cases) ischemic ST elevation, a STEMI equivalent (5 cases) or ST-elevation due to vasospasm (4 cases). The sensitivity was 92.8% [95% CI 90.6, 94.7%] and the specificity 98.7% [95% CI 98.6, 98.8%]. The leading causes of FP were ECG artifact (20%), early repolarization (16%), probable pericarditis/myocarditis (13%), indeterminate (12%), left ventricular hypertrophy (8%), and right bundle branch block (5%). There were 18 additional reasons for FP interpretation (<4% each). The leading causes of FN were borderline ST-segment elevations less than the algorithm threshold (40%) and tall T waves reducing the ST/T ratio below threshold (15%). There were 11 additional reasons for FN interpretation occurring ≤3 times each. Conclusion: The leading causes of FP automated interpretation of STEMI were ECG artifact and non-ischemic causes of ST-segment elevation. FN were rare and were related to ST-segment elevation or ST/T ratio that did not meet the software algorithm threshold
Active Control of Fan Noise: Feasibility Study
An extension of a prior study has been completed to examine the potential reduction of aircraft flyover noise by the method of active noise control (ANC). It is assumed that the ANC system will be designed such that it cancels discrete tones radiating from the engine fan inlet or fan exhaust duct, at least to the extent that they no longer protrude above the surrounding broadband noise levels. Thus, without considering the engineering details of the ANC system design, tone levels am arbitrarily removed from the engine component noise spectrum and the flyover noise EPNL levels are compared with and without the presence of tones. The study was conducted for a range of engine cycles, corresponding to fan pressure ratios of 1.3, 1.45, 1.6, and 1.75. This report is an extension of an effort reported previously. The major conclusions drawn from the prior study, which was restricted to fan pressure ratios of 1.45 and 1.75, are that, for a fan pressure ratio of 1.75, ANC of tones gives about the same suppression as acoustic treatment without ANC. For a fan pressure ratio of 1.45, ANC appears to offer less effectiveness from passive treatment. In the present study, the other two fan pressure ratios are included in a more detailed examination of the benefits of the ANC suppression levels. The key results of this extended study are the following observations: (1) The maximum overall benefit obtained from suppression of BPF alone was 2.5 EPNdB at high fan speeds. The suppression benefit increases with increase in fan pressure ratio (FPR), (2) The maximum overall benefit obtained from suppression of the first three harmonics was 3 EPNdB at high speeds. Suppression benefit increases with increase in FPR, (3) At low FPR, only about 1.0 EPNdB maximum reduction was obtained. Suppression is primarily from reduction of BPF at high FPR values and from the combination of tones at low FPR, (4) The benefit from ANC is about the same as the benefit from passive treatment at fan pressure ratios of 1.75 and 1.60. At the two lower fan pressure ratios, the effectivness of treatment is much greater than that of ANC, and (5) No significant difference in ANC suppression behavior was found from the QCSEE engine database analysis compared to that of the E3 engine database, for the FPR = 1.3 engine cycle. The effects of ANC on EPNL noise reduction are difficult to generalize. It was found that the reduction obtained in any particular case depended upon the frequency of the tones and their shift with rpm, the amount of ANC suppression received by each tone (which depended on its protrusion from the background), and the NOY-value of the tone relative to the NOY-value of other tones and the peak broadband levels, because PNL is determined from the sum of the NOY-values
Active Control of Fan Noise-Feasibility Study
A study has been completed to examine the potential reduction of aircraft flyover noise by the method of active noise control (ANC). It is assumed that the ANC system will be designed such that it cancels discrete tones radiating from the engine fan inlet or fan exhaust duct. Thus, without considering the engineering details of the ANC system design, tone levels are arbitrarily removed from the engine component noise spectrum and the flyover noise EPNL levels are compared with and without the presence of tones. The study was conducted for a range of engine cycles, corresponding to fan pressure ratios from 1.3 to 1.75. The major conclusions that can be drawn are that, for a fan pressure ratio of 1.75, ANC of tones gives about the same suppression as acoustic treatment without ANC, and for a fan pressure ratio of 1.45, ANC appears to offer less effectiveness than passive treatment. Additionally, ANC appears to be more effective at sideline and cutback conditions than at approach. Overall EPNL suppressions due to tone removal range from about 1 to 3 dB at takeoff engine speeds and from 1 to 5 db at approach speeds. Studies of economic impact of the installation of an ANC system for the four engine cases indicate increases of DOC ranging from 1 to 2 percent, favoring the lower fan pressure ratio engines. Further study is needed to confirm the results by examining additional engine data, particularly at low fan pressure ratios, and studying the details of the current results to obtain a more complete understanding. Further studies should also include determining the effects of combining passive and active treatment
Ground state and bias current induced rearrangement of semifluxons in 0-pi long Josephson junctions
We investigate numerically a long Josephson junction with several phase
pi-discontinuity points. Such junctions are usually fabricated as a ramp
between an anisotropic cuprate superconductor like YBCO and an isotropic metal
superconductor like Nb. From the top, they look like zigzags with pi-jumps of
the Josephson phase at the corners. These pi-jumps, at certain conditions, lead
to the formation of half-integer flux quanta, which we call semifluxons (SF),
pinned at the corners. We show (a) that the spontaneous formation of SFs
depends on the junction length, (b) that the ground state without SFs can be
converted to a state with SFs by applying a bias current, (c) that the SF
configuration can be rearranged by the bias current. All these effects can be
observed using a SQUID microscope.Comment: ~8 pages, 6 figures, submitted to PR
Superconducting crossed correlations in ferromagnets: implications for thermodynamics and quantum transport
It is demonstrated that non local Cooper pairs can propagate in ferromagnetic
electrodes having an opposite spin orientation. In the presence of such crossed
correlations, the superconducting gap is found to depend explicitly on the
relative orientation of the ferromagnetic electrodes. Non local Cooper pairs
can in principle be probed with dc-transport. With two ferromagnetic
electrodes, we propose a ``quantum switch'' that can be used to detect
correlated pairs of electrons. With three or more ferromagnetic electrodes, the
Cooper pair-like state is a linear superposition of Cooper pairs which could be
detected in dc-transport. The effect also induces an enhancement of the
ferromagnetic proximity effect on the basis of crossed superconducting
correlations propagating along domain walls.Comment: 4 pages, RevTe
Nanospintronics with carbon nanotubes
One of the actual challenges of spintronics is the realization of a
spin-transistor allowing to control spin transport through an electrostatic
gate. In this review, we report on different experiments which demonstrate a
gate control of spin transport in a carbon nanotube connected to ferromagnetic
leads. We also discuss some theoretical approaches which can be used to analyze
spin transport in these systems. We emphasize the roles of the gate-tunable
quasi-bound states inside the nanotube and the coherent spin-dependent
scattering at the interfaces between the nanotube and its ferromagnetic
contacts.Comment: 35 pages, 15 figures, some figures in gi
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