Quantum symmetrically-private information retrieval

Private information retrieval systems (PIRs) allow a user to extract an item from a database that is replicated over k?1 servers, while satisfying various privacy constraints. We exhibit quantum k-server symmetrically-private information retrieval systems (QSPIRs) that use sublinear communication, do not use shared randomness among the servers, and preserve privacy against honest users and dishonest servers. Classically, SPIRs without shared randomness do not exist at all.     

Fast neighbor positioning and medium access in wireless networks with directional antennas

We study the problem of fast neighbor positioning and medium access in wireless networks with directional antennas. In this problem, the cross-layer dimension inherently comes into stage through the impact of PHY-layer antenna directionality on medium access. Fast neighbor positioning reduces the network initialization overhead and leaves more time for executing other protocols. Fast medium access leads to larger volume of transmitted data per unit of time. The two problems are studied in a unified manner in a system with one Access Point (AP) and multiple users around it. The AP sequentially scans the space by forming directional beams and applies contention-free or contention-based user polling within each beam. In the former method, polling messages are addressed to a specific user. In the latter, users in a beam contend to have their message received by the AP.We explore the impact of the contention resolution protocol and the directional beam width on user positioning and medium access delay. A large beam width incurs large expected delay for contention resolution due to the larger expected amount of contention in the beam, but on the other hand, it implies that fewer beams, and hence smaller delay is needed to scan the entire space. We obtain analytic expressions for the total average user positioning and the medium access delay, and we present an optimization method for minimizing it by appropriately selecting the beam width and the persistence probability of the collision resolution protocol. Our method uses accumulated knowledge from previous scans to estimate the anticipated amount of contention in upcoming scans and to adjust the beam width and persistence probability accordingly. Our numerical results demonstrate the efficiency of our techniques in terms of fast neighbor positioning.     

Work environment and computer systems development

Work environment and occupational health problems of different nature are constantly increasing in computer supported work. Most efforts to improve the work environment are focused primarily on physical aspects, and to some extent on psychosocial aspects. Mental workload and cognitive problems are of a more complex nature, more difficult to measure and provide efficient solutions to, and are more seldom studied or solved. Solutions to work environment problems are usually applied to already existing work situations through improved equipment and work place design, health programmes, education, reorganizations, etc. The problems are seldom prevented by means of applying relevant methods early in the systems development process, before the artefacts have been designed and implemented. This paper, and the following papers of this special issue, will focus on the need to integrate different interdisciplinary methods at different phases in the development process of computerized support systems, with the ultimate goal to prevent work environment problems and decrease the health risks to the users.     

A structured autopsy-based audit of 370 firearm fatalities: Contribution to inform policy decisions and the probability of the injured arriving alive at a hospital and receiving definitive care

The objectives of this autopsy-based audit of firearm-related fatalities were to acquire data to inform policy decisions and to assess the probability of the injured arriving alive at a hospital and receiving definitive care.