Gigahertz quantized charge pumping in graphene quantum dots.

Single-electron pumps are set to revolutionize electrical metrology by enabling the ampere to be redefined in terms of the elementary charge of an electron. Pumps based on lithographically fixed tunnel barriers in mesoscopic metallic systems and normal/superconducting hybrid turnstiles can reach very small error rates, but only at megahertz pumping speeds that correspond to small currents of the order of picoamperes. Tunable barrier pumps in semiconductor structures are operated at gigahertz frequencies, but the theoretical treatment of the error rate is more complex and only approximate predictions are available. Here, we present a monolithic, fixed-barrier single-electron pump made entirely from graphene that performs at frequencies up to several gigahertz. Combined with the record-high accuracy of the quantum Hall effect and proximity-induced Josephson junctions, quantized-current generation brings an all-graphene closure of the quantum metrological triangle within reach. Envisaged applications for graphene charge pumps outside quantum metrology include single-photon generation via electron-hole recombination in electrostatically doped bilayer graphene reservoirs, single Dirac fermion emission in relativistic electron quantum optics and read-out of spin-based graphene qubits in quantum information processing.

Clinical characteristics and outcomes of patients with obstructive sleep apnoea requiring intensive care.

We reviewed the clinical characteristics, required intervention and short- and long-term outcomes in obstructive sleep apnoea (OSA) patients requiring intensive care. A retrospective, single-centre, observational cohort study was undertaken in a multidisciplinary teaching medical and surgical intensive care unit. Adult patients with OSA (apnoea-hypopnoea index of 5 or higher) requiring intensive care from January 2000 to January 2005 were included. Thirty-seven OSA patients (age: 58 +/- 14 years, male:female 27:10) were admitted due to respiratory (n=12, 32%), cerebrovascular (n=8, 22%), cardiovascular (n=16, 43%) and infectious events (n=1, 2.7%). Comparing the clinical features, polysomnographic data and outcome among these groups, we found that OSA patients admitted due to respiratory events had significantly higher Acute Physiology and Chronic Health Evaluation II scores, lower arterial blood gas pH, higher PaCO2, a higher incidence of respiratory failure (92%) and required non-invasive ventilation after extubation (73%), and higher intensive care unit readmission rates than patients admitted due to cerebrovascular events and cardiovascular events (P < 0.05). No difference was found in the in-hospital and long-term mortality rate. The most common reason for intensive care unit admission in critically ill OSA patients was a cardiovascular event, followed by respiratory and cerebrovascular events. The baseline polysomnographic data of the OSA patients were not correlated with their clinical features and outcomes in the intensive care unit. A more complicated clinical course and higher intensive care unit readmission rate were encountered in OSA patients admitted due to respiratory events. Further studies would be required to evaluate the efficacy of non-invasive ventilation for facilitation of extubation in OSA patients presenting with hypercapnic respiratory failure.

Computer-aided diagnosis in two-phase 201Tl-SPECT of thoracic lesions.

AIM: The retention index, a traditionally quantitative analysis of two-phase (201)Tl single photon emission computed tomography (SPECT) of the chest, is manually calculated by experienced physicians from comparable 2-D ROI. However, a 3-D ROI would provide more information than a 2-D ROI extracted from a single frame of SPECT. We propose a new diagnostic system, computer-aided diagnosis (CAD), to automatically detect suspicious lesions as 3-D objects on chest (201)Tl-SPECT, and assist the physician in interpreting these images. PATIENTS, METHODS: Seventy patients with thoracic lesions and confirmed diagnoses were enrolled to test this automatic CAD system. The reliability of the CAD system in detecting lesions as 3-D objects was compared to the 2-D ROI of (201)Tl-SPECT found by the manually visualized method. Furthermore, we also proposed a novel index, the retention index using the heart (RIH), to differentiate high retention (slow clearance, increasing target to heart ratio) as a criterion for a malignant lesion, from low retention (faster clearance, small or no increase of the target to heart ratio) for benign lesions. RESULTS: The CAD system can achieve a detection rate of 100% in automatically searching for thoracic lesions in (201)Tl-SPECT. In diagnostic performance, the CAD system with the RIH of comparable 3-D objects has an area under the ROC curve of 0.86, higher than the 0.78 of the traditional RI method (p=0.198). CONCLUSION: The CAD system of two-phase (201)Tl-SPECT is a promising tool for detecting and diagnosing thoracic lesions with a diagnostic accuracy of 0.81.