1,053 research outputs found
Entanglement between charge qubits induced by a common dissipative environment
We study entanglement generation between two charge qubits due to the strong
coupling with a common bosonic environment (Ohmic bath). The coupling to the
boson bath is a source of both quantum noise (leading to decoherence) and an
indirect interaction between qubits. As a result, two effects compete as a
function of the coupling strength with the bath: entanglement generation and
charge localization induced by the bath. These two competing effects lead to a
non-monotonic behavior of the concurrence as a function of the coupling
strength with the bath. As an application, we present results for charge qubits
based on double quantum dots.Comment: 9 pages, 7 figure
Virtual reality training for endoscopic surgery: voluntary or obligatory?
INTRODUCTION: Virtual reality (VR) simulators have been developed to train basic endoscopic surgical skills outside of the operating room. An important issue is how to create optimal conditions for integration of these types of simulators into the surgical training curriculum. The willingness of surgical residents to train these skills on a voluntary basis was surveyed. METHODS: Twenty-one surgical residents were given unrestricted access to a VR simulator for a period of four months. After this period, a competitive element was introduced to enhance individual training time spent on the simulator. The overall end-scores for individual residents were announced periodically to the full surgical department, and the winner was awarded a prize. RESULTS: In the first four months of study, only two of the 21 residents (10%) trained on the simulator, for a total time span of 163 minutes. After introducing the competitive element the number of trainees increased to seven residents (33%). The amount of training time spent on the simulator increased to 738 minutes. CONCLUSIONS: Free unlimited access to a VR simulator for training basic endoscopic skills, without any form of obligation or assessment, did not motivate surgical residents to use the simulator. Introducing a competitive element for enhancing training time had only a marginal effect. The acquisition of expensive devices to train basic psychomotor skills for endoscopic surgery is probably only effective when it is an integrated and mandatory part of the surgical curriculu
Aperture array development for future large radio telescopes
We present the design of a phased array system for future radio telescopes. This includes a system overview and recent results of the designed and implemented system, the Electronic Multi-Beam Radio Astronomy Concept (EMBRACE). Furthermore, simulations with a full-EM antenna simulator, combined with measurements on actual hardware, will provide information for the next design step, the Aperture Array Verification System (AAVS). With AAVS, we will prove design readiness of this novel array technology
Highly abundant HCN in the inner hot envelope of GL 2591: probing the birth of a hot core?
We present observations of the v2=0 and vibrationally excited v2=1 J=9-8
rotational lines of HCN at 797 GHz toward the deeply embedded massive young
stellar object GL 2591, which provide the missing link between the extended
envelope traced by lower-J line emission and the small region of hot (T_ex >=
300 K), abundant HCN seen in 14 micron absorption with the Infrared Space
Observatory (ISO). The line ratio yields T_ex=720^+135_-100 K and the line
profiles reveal that the hot gas seen with ISO is at the velocity of the
protostar, arguing against a location in the outflow or in shocks. Radiative
transfer calculations using a depth-dependent density and temperature structure
show that the data rule out a constant abundance throughout the envelope, but
that a model with a jump of the abundance in the inner part by two orders of
magnitude matches the observations. Such a jump is consistent with the sharp
increase in HCN abundance at temperatures >~230 K predicted by recent chemical
models in which atomic oxygen is driven into water at these temperatures.
Together with the evidence for ice evaporation in this source, this result
suggests that we may be witnessing the birth of a hot core. Thus, GL 2591 may
represent a rare class of objects at an evolutionary stage just preceding the
`hot core' stage of massive star formation.Comment: Accepted by ApJ Letters, 11 pages including 3 figures, uses AASTe
Interference effects in isolated Josephson junction arrays with geometric symmetries
As the size of a Josephson junction is reduced, charging effects become
important and the superconducting phase across the link turns into a periodic
quantum variable. Isolated Josephson junction arrays are described in terms of
such periodic quantum variables and thus exhibit pronounced quantum
interference effects arising from paths with different winding numbers
(Aharonov-Casher effects). These interference effects have strong implications
for the excitation spectrum of the array which are relevant in applications of
superconducting junction arrays for quantum computing. The interference effects
are most pronounced in arrays composed of identical junctions and possessing
geometric symmetries; they may be controlled by either external gate potentials
or by adding/removing charge to/from the array. Here we consider a loop of N
identical junctions encircling one half superconducting quantum of magnetic
flux. In this system, the ground state is found to be non-degenerate if the
total number of Cooper pairs on the array is divisible by N, and doubly
degenerate otherwise (after the stray charges are compensated by the gate
voltages).Comment: 9 pages, 6 figure
An Easy-to-Use Prognostic Model for Survival Estimation for Patients with Symptomatic Long Bone Metastases
BACKGROUND: A survival estimation for patients with symptomatic long bone metastases (LBM) is crucial to prevent overtreatment and undertreatment. This study analyzed prognostic factors for overall survival and developed a simple, easy-to-use prognostic model. METHODS: A multicenter retrospective study of 1,520 patients treated for symptomatic LBM between 2000 and 2013 at the radiation therapy and/or orthopaedic departments was performed. Primary tumors were categorized into 3 clinical profiles (favorable, moderate, or unfavorable) according to an existing classification system. Associations between prognostic variables and overall survival were investigated using the Kaplan-Meier method and multivariate Cox regression models. The discriminatory ability of the developed model was assessed with the Harrell C-statistic. The observed and expected survival for each survival category were compared on the basis of an external cohort. RESULTS: Median overall survival was 7.4 months (95% confidence interval [CI], 6.7 to 8.1 months). On the basis of the independent prognostic factors, namely the clinical profile, Karnofsky Performance Score, and presence of visceral and/or brain metastases, 12 prognostic categories were created. The Harrell C-statistic was 0.70. A flowchart was developed to easily stratify patients. Using cutoff points for clinical decision-making, the 12 categories were narrowed down to 4 categories with clinical consequences. Median survival was 21.9 months (95% CI, 18.7 to 25.1 months), 10.5 months (95% CI, 7.9 to 13.1 months), 4.6 months (95% CI, 3.9 to 5.3 months), and 2.2 months (95% CI, 1.8 to 2.6 months) for the 4 categories. CONCLUSIONS: This study presents a model to easily stratify patients with symptomatic LBM according to their expected survival. The simplicity and clarity of the model facilitate and encourage its use in the routine care of patients with LBM, to provide the most appropriate treatment for each individual patient. LEVEL OF EVIDENCE: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence
- …