Coulomb Blockade in a Nonthermalized Quantum Dot.

We investigate nonequilibrium transport properties of a quantum dot in the Coulomb blockade regime under the condition of negligible inelastic scattering during the dwelling time of the electrons in the dot. Using the quantum kinetic equation we show that the absence of thermalization leads to a double step in the distribution function of electrons on the dot, provided that it is symmetrically coupled to the leads. This drastically changes nonlinear transport through the dot resulting in an additional (compared to the thermalized case) jump in the conductance at voltages close to the charging energy, which could serve as an experimental manifestation of the absence of thermalization.

Coulomb staircase in an asymmetrically coupled quantum dot.

We investigate the Coulomb blockade in quantum dots asymmetrically coupled to the leads for an arbitrary voltage bias focusing on the regime where electrons do not thermalise during their dwell time in the dot. By solving the quantum kinetic equation, we show that the current-voltage characteristics are crucially dependent on the ratio of the Fermi energy to charging energy on the dot. In the standard regime when the Fermi energy is large, there is a Coulomb staircase which is practically the same as in the thermalised regime. In the opposite case of the large charging energy, we identify a new regime in which only one step is left in the staircase, and we anticipate experimental confirmation of this finding.

A field programmable gate array unit for the diagnosis and control of neoclassical tearing modes on MAST.

A real-time system has been developed to trigger both the MAST Thomson scattering (TS) system and the plasma control system on the phase and amplitude of neoclassical tearing modes (NTMs), extending the capabilities of the original system. This triggering system determines the phase and amplitude of a given NTM using magnetic coils at different toroidal locations. Real-time processing of the raw magnetic data occurs on a low cost field programmable gate array (FPGA) based unit which permits triggering of the TS lasers on specific amplitudes and phases of NTM evolution. The MAST plasma control system can receive a separate trigger from the FPGA unit that initiates a vertical shift of the MAST magnetic axis. Such shifts have fully removed m∕n = 2∕1 NTMs instabilities on a number of MAST discharges.

Optical boundary reconstruction of tokamak plasmas for feedback control of plasma position and shape.

A new diagnostic is developed to reconstruct the plasma boundary using visible wavelength images. Exploiting the plasma's edge localized and toroidally symmetric emission profile, a new coordinate transform is presented to reconstruct the plasma boundary from a poloidal view image. The plasma boundary reconstruction is implemented in MATLAB and applied to camera images of Mega-Ampere Spherical Tokamak discharges. The optically reconstructed plasma boundaries are compared to magnetic reconstructions from the offline reconstruction code EFIT, showing very good qualitative and quantitative agreement. Average errors are within 2 cm and correlation is high. In the current software implementation, plasma boundary reconstruction from a single image takes 3 ms. The applicability and system requirements of the new optical boundary reconstruction, called OFIT, for use in both feedback control of plasma position and shape and in offline reconstruction tools are discussed.

Design of a new Nd:YAG Thomson scattering system for MAST.

A new infrared Thomson scattering system has been designed for the MAST tokamak. The system will measure at 120 spatial points with approximately 10 mm resolution across the plasma. Eight 30 Hz 1.6 J Nd:YAG lasers will be combined to produce a sampling rate of 240 Hz. The lasers will follow separate parallel beam paths to the MAST vessel. Scattered light will be collected at approximately f/6 over scattering angles ranging from 80 degrees to 120 degrees. The laser energy and lens size, relative to an existing 1.2 J f/12 system, greatly increases the number of scattered photons collected per unit length of laser beam. This is the third generation of this polychromator to be built and a number of modifications have been made to facilitate mass production and to improve performance. Detected scattered signals will be digitized at a rate of 1 GS/s by 8 bit analog to digital converters (ADCs.) Data may be read out from the ADCs between laser pulses to allow for real-time analysis.

Positive fluid balance is associated with complications after elective open infrarenal abdominal aortic aneurysm repair.

BACKGROUND: Open abdominal aortic aneurysm (AAA) repair is associated with cardiac and respiratory complications and an overall mortality rate of 2 to 8%. We hypothesised that excessive fluid administration during the perioperative period contributes to complications and poor outcome after AAA repair. METHODS: This was a retrospective cohort study. Medical records were analysed for fluid balance and complications in 100 consecutive patients treated by open AAA repair at a single centre between 2002-2005. Mortality and all major adverse events (MAE) such as myocardial infarction (MI), cardiac arrhythmia (Arr), pulmonary oedema (PO), pulmonary infection (PI), and acute renal failure (ARF) were included in the analysis. Level of care and hospital stay, were also recorded. RESULTS: There were no in-hospital deaths. MAE occurred in 40/100 (40%): MI (6%); Arr (14%); PO (14%); PI (25%); ARF (8%). Complications were not predicted by preoperative cardiovascular risk factors, operative and clamp time, or blood loss. Patients with complications had significantly greater cumulative positive fluid balance on postoperative day 0 (p<0.01), day 1 (p<0.05), day 2 (p<0.03) and day 3 (p<0.04). This relationship also existed for individual complications such as MI, and pulmonary oedema. These patients had significantly longer ICU/HDU (p<0.002) and hospital stay (p<0.0001). CONCLUSIONS: Serious complications are common after elective open AAA repair, and we have shown that positive fluid balance is predictive of major adverse events increased HDU/ICU and overall hospital stay.

Is inguinal hernia a defect in human evolution and would this insight improve concepts for methods of surgical repair?

In Homo sapiens sapiens and many mammalian quadrupeds, there is an absence of the posterior rectus sheath below the arcuate line (of Douglas) and an insubstantial transversalis fascia in the groin. This anatomical arrangement presents no particular functional anatomic difficulty for quadrupeds as their inguinal canal is directed "uphill" during ambulation and therefore is not subjected to significant gravitational stress. In humans, however, gravitational stress necessitated by erect posture, including bearing the weight of the intra-abdominal organs directed toward the lower abdomen, considerably amplifies this intrinsic anatomic weakness. It allows a significant number of pathologic inguinal hernias, both direct and indirect, to become clinically manifest and associated with a coincident increase in morbidity and mortality, especially in patients with strangulated hernias and/or delayed treatment. The morbidity is associated with a significant national economic loss secondary to work hour loss from pain, discomfort, surgical treatment, and rehabilitation following therapy. The mortality is usually associated with strangulation, especially in those in patients with delayed treatment. The lack of the evolutionary development of a strong posterior rectus sheath and transversalis fascia in the lower abdomen is thought to represent a significant specific anatomic defect in the evolution of humankind. If so, then perhaps methods for surgical repair will be directed toward correction of this defect and avoid, not encourage, such methods as the utilization of the weak or absent transversalis "fascia," which are doomed to a high recurrence rate, or other methods that are unnecessarily complicated, such as certain laparoscopic repairs of inguinal hernia.

Capitated contracting in radiology: negotiating techniques, financial calculations, and utilization management.

The authors describe how to develop and manage a capitated outpatient radiology contract. Aspects of a capitated fee structure and the need to apportion fees between a hospital and its radiology group are discussed. During negotiations with a managed care organization (MCO), certain information and commitments should be obtained. Utilization data should also be obtained from the MCO, but if they are not available (or are thought to be unreliable), certain norms can be used. Once a utilization projection is arrived at, reimbursement calculations can be made and compared with assumed reimbursements under a known fee schedule, such as that of Medicare. This procedure allows one to estimate whether a capitated proposal is financially feasible. Once a contractual agreement is instituted, the radiology group must then track and manage utilization. An understanding of these principles should enable radiologists to deal effectively with both practice and fiscal concerns presented by managed care.

Cost containment in the use of low-osmolar contrast agents: effect of guidelines, monitoring, and feedback mechanisms.

PURPOSE: To describe a program for controlling intravenous use of low-osmolar contrast agents (LOCAs). MATERIALS AND METHODS: The department of radiology at the authors' institution adopted a policy of selective use of intravenously administered LOCAs. Clinical indications for LOCA use were specified after consultation with the administration, risk managers, legal department, and ethics committee of the hospital. The guidelines were then publicized throughout the department and hospital, and a contrast agent data form was developed to collect data on all cases. Monitoring mechanisms were instituted. RESULTS: Over the next 23 months, 11,373 patients received intravenous iodinated contrast agents, of whom 28.1% were deemed to be at high risk and were given LOCAs. Monthly tracking showed no evidence of a trend toward increasing use of LOCAs. CONCLUSION: Clear definition of use guidelines, close monitoring, and feedback can stabilize LOCA use at acceptably low levels.

Adverse reactions to intravenous anaesthetics.

One hundred consecutive reports of reactions to intravenous anaesthetics Althesin, thiopentone and Epontol are reviewed and analysed. Ten reactions are attributed to causes other than the anaesthetic drug, and four are believed to have been caused by the muscle relaxant employed. The remaining 86 reactions were grouped according to their clinical presentation: histaminoid reactions ( 19), histaminoid with bronchospasm (33), bronchospasm (12), cardiovascular collapse (uu), delayed histaminoid reactions (6), and clonic contractions (5). None of the first four reaction types was associated with only one anaesthetic. A knowledge of the sales of Althesin has allowed the incidence of reactions to be estimated as between one in 11,000 and one in 19,000.

Laser modification to an x-ray collimator: an aid in positioning patients for neurosurgical and radiographic procedures.

In high-ambient-light levels such as are found in operating rooms, and at long target-to-patient distances, the cross lines and light field projected from conventional x-ray collimators are not easily visible and proper patient positioning is difficult. The collimators on two mutually perpendicular x-ray units have been modified by replacing the incandescent bulbs with lasers and adjusting the lasers to be coaxial with the x-ray beams. These modifications have been coupled with a third wall-mounted laser to facilitate patient positioning for stereotaxic thermal hypophysectomy. The use of the laser-modified collimators has resulted in considerable saving of time for the operating team and has markedly reduced patient anesthesia time. The laser-modified collimator has also been found useful in positioning patients for other radiographic procedures in the operating room and has virtually eliminated retakes due to malpositioning.