Bosonic Memory Channels

We discuss a Bosonic channel model with memory effects. It relies on a multi-mode squeezed (entangled) environment's state. The case of lossy Bosonic channels is analyzed in detail. We show that in the absence of input energy constraints the memory channels are equivalent to their memoryless counterparts. In the case of input energy constraint we provide lower and upper bounds for the memory channel capacity.Comment: 6 pages, 2 figure

Topology design and performance analysis of an integrated communication network

A research study on the topology design and performance analysis for the Space Station Information System (SSIS) network is conducted. It is begun with a survey of existing research efforts in network topology design. Then a new approach for topology design is presented. It uses an efficient algorithm to generate candidate network designs (consisting of subsets of the set of all network components) in increasing order of their total costs, and checks each design to see if it forms an acceptable network. This technique gives the true cost-optimal network, and is particularly useful when the network has many constraints and not too many components. The algorithm for generating subsets is described in detail, and various aspects of the overall design procedure are discussed. Two more efficient versions of this algorithm (applicable in specific situations) are also given. Next, two important aspects of network performance analysis: network reliability and message delays are discussed. A new model is introduced to study the reliability of a network with dependent failures. For message delays, a collection of formulas from existing research results is given to compute or estimate the delays of messages in a communication network without making the independence assumption. The design algorithm coded in PASCAL is included as an appendix

Changes in Polarization Position Angle across the Eclipse in the Double Pulsar System

We investigate the changes in polarization position angle in radiation from pulsar A around the eclipse in the Double Pulsar system PSR J0737-3039A/B at the 20 cm and 50 cm wavelengths using the Parkes 64-m telescope. The changes are ~2\sigma\ during and shortly after the eclipse at 20 cm but less significant at 50 cm. We show that the changes in position angle during the eclipse can be modelled by differential synchrotron absorption in the eclipse regions. Position angle changes after the eclipse are interpreted as Faraday rotation in the magnetotail of pulsar B. Implied charge densities are consistent with the Goldreich-Julian density, suggesting that the particle energies in the magnetotail are mildly relativistic.Comment: Accepted for publication in The Astrophysical Journal Letter

Two-mode heterodyne phase detection

We present an experimental scheme that achieves ideal phase detection on a two-mode field. The two modes $a$ and $b$ are the signal and image band modes of an heterodyne detector, with the field approaching an eigenstate of the photocurrent $\hat{Z}=a+b^{\dag}$. The field is obtained by means of a high-gain phase-insensitive amplifier followed by a high-transmissivity beam-splitter with a strong local oscillator at the frequency of one of the two modes.Comment: 3 pages, 1 figur

Laparoscopic incisional hernioplasty utilising on-lay expanded polytetrafluoroethylene DualMesh: Prospective study

Objective. To evaluate the early outcomes of laparoscopic incisional hernioplasties using on-lay GORE-TEX DualMesh. Design. Prospective study. Setting. Medical centre of a regional hospital, Hong Kong. Subjects and methods. Between June 2000 and October 2001, 11 consecutive patients underwent attempted laparoscopic incisional hernioplasties at the University of Hong Kong Medical Centre. A prospective collection of perioperative data and assessment of postoperative outcomes was performed. Results. Laparoscopic incisional hernioplasty was successfully performed for 10 (91%) patients. One patient was converted to open repair because of extensive adhesions within the peritoneal cavity. The overall mean operative time was 107 minutes. Five (45%) patients were found to have more than one hernial defect after reduction of the hernial contents. Eight (73%) patients were discharged within 2 days after operation. Postoperative morbidities included wound bruising (n=4), seroma (n=2), and prolonged suture site pain (n=l). All postoperative morbidities resolved spontaneously without intervention. With a mean follow-up of 3 months, no early recurrence was detected. Conclusion. Early outcomes of laparoscopic incisional hernioplasty utilising GORE-TEX DualMesh were promising. This technique confers the advantages of minimal access surgery and allows clear identification of multiple hernial defects. Extensive adhesion, which does not allow the establishment of pneumoperitoneum, is a condition that precludes the safe performance of laparoscopic repair.published_or_final_versio

Scheme for teleportation of quantum states onto a mechanical resonator

We propose an experimentally feasible scheme to teleport an unkown quantum state onto the vibrational degree of freedom of a macroscopic mirror. The quantum channel between the two parties is established by exploiting radiation pressure effects.Comment: 5 pages, 2 figures, in press on PR

Continuous variable cloning via network of parametric gates

We propose an experimental scheme for the cloning machine of continuous quantum variables through a network of parametric amplifiers working as input-output four-port gates.Comment: 4 pages, 2 figures. To appear on Phys. Rev. Let

Outpatient laparoscopic cholecystectomy in Hong Kong Chinese - An outcome analysis

BACKGROUND: Laparoscopic cholecystectomy (LC) is now the procedure of choice for symptomatic gallbladder disease. Although many recent studies, mostly from abroad, report that it can be performed safely in the outpatient setting, the experience of outpatient LC in Hong Kong is still limited. This retrospective study evaluated the feasibility, safety and patient acceptance of outpatient LC in Hong Kong Chinese patients. PATIENTS AND METHODS: The data of 73 consecutive patients who had undergone outpatient LC between February 2000 and October 2002 in the Day Surgery Centre of Tung Wah Hospital were prospectively collected and reviewed. The selection criteria for patients undergoing outpatient LC included American Society of Anesthesiologists risk classification I or II, age less than 70 years, and the availability of a competent adult to accompany the patient home and look after them for 24 hours. No effort was made to exclude complicated cases. After assessment by the operating surgeon, patients were discharged from the Day Surgery Centre in the afternoon when their clinical condition satisfied pre-defined discharge criteria. All patients were followed up in the Day Surgery Centre in the first and fourth postoperative weeks. RESULTS: The same-day discharge rate was 88% and the conversion rate was 4%. Six patients (8.2%) with uneventful LC required hospitalization after the procedure. There was no major complication and no unplanned admission. Two patients had port site wound infection requiring hospital admission at the first follow-up. Patient satisfaction was high, pain acceptance was good, and analgesic consumption was minimal. Mild fat intolerance was common in patients postoperatively (> 50%), but this had almost all resolved by postoperative week four. All patients were able to resume their usual daily activities within 2 weeks after surgery. CONCLUSIONS: LC is a safe and feasible outpatient procedure in Hong Kong, with high levels of patient satisfaction. A prospective study with a larger patient population is warranted to verify whether it should be recommended as treatment for gallstone disease in selected patients in future.postprin