ABSTRACT
A theory is developed for the emission noise at frequency ν in a quantum dot in the presence of Coulomb interactions and asymmetric couplings to the reservoirs. We give an analytical expression for the noise in terms of the various transmission amplitudes. Including the inelastic scattering contribution, it can be seen as the analog of the Meir-Wingreen formula for the current. A physical interpretation is given on the basis of the transmission of one electron-hole pair to the concerned reservoir where it emits an energy after recombination. We then treat the interactions by solving the self-consistent equations of motion for the Green functions. The results for the noise derivative versus eV show a zero value until eV=hν, followed by a Kondo peak in the Kondo regime, in good agreement with recent measurements in carbon nanotube quantum dots.
ABSTRACT
We consider the measurement of higher current moments with a dissipative resonant circuit, which is coupled inductively to a mesoscopic device in the coherent regime. Information about the higher current moments is coded in the histograms of the charge on the capacitor plates of the resonant circuit. The role of dissipation is shown to be essential for the measured noise to remain finite. We also identify which combination of current correlators enters the measurement of the third moment. The results are illustrated for a quantum point contact.
ABSTRACT
The transport properties of a simple model for a finite level structure (a molecule or a dot) connected to metal electrodes in an alternating current scanning tunneling microscope (ac-STM) configuration is studied. The finite level structure is assumed to have strong binding properties with the metallic substrate, and the bias between the STM tip and the hybrid metal-molecule interface has both an ac and a dc component. The finite frequency current response and the zero-frequency photoassisted shot noise are computed using the Keldysh technique, and examples for a single-site molecule (a quantum dot) and for a two-site molecule are examined. The model may be useful for the interpretation of recent experiments using an ac-STM for the study of both conducting and insulating surfaces, where the third harmonic component of the current is measured. The zero-frequency photoassisted shot noise serves as a useful diagnosis for analyzing the energy level structure of the molecule. The present work motivates the need for further analysis of current fluctuations in electronic molecular transport.
ABSTRACT
In a series of 300 cases whose atrial septal defects were closed (268 with ostium secundum, 27 with ostium primum, and 5 cases with both), arrhythmias were found in 60%. These were usually slow supraventricular arrhythmias caused by substitution (51%), and less commonly rapid supraventricular arrhythmias (27%), extra-systoles (16%), disorders of atrio-ventricular conduction of second and third degree and disorders of the auricle (6%). Conduction disorders were significantly more common (p less than 0.001) after closure of ostium primum (37%) than after closure of an ostium secundum (4.5%). Arrhythmias are most common during the first week (56%), and are usually of the slow type, and during the three succeeding weeks are markedly less frequent (31%) with a higher proportion (p less than 0.001) of the rapid type. No one anatomical type of ASD was complicated with arrhythmia more than the others. The slow type of arrhythmias occurred in the high ASDs, and the fast type especially amongst elderly patients. Longterm follow-up showed arrhythmias in 28% of patients with an ostium secundum defect. The factors influencing arrhythmias were age, cardiac enlargement, and the mean pulmonary arterial pressure. Arrhythmias were just as common in cases with a small shunt.
