We establish a tight upper bound for the difference in von Neumann entropies between two quantum states,$\rho _{1}$and$\rho _{2}$. This bound is expressed in terms of the von Neumann entropies of the mutually orthogonal states derived from the Jordan-Hahn decomposition of the difference operator$(\rho _{1} - \rho _{2})$. This yields a novel entropic inequality that implies the well-known Audenaert-Fannes (AF) inequality. In fact, it also leads to a refinement of the AF inequality. We employ this inequality to obtain a uniform continuity bound for the quantum conditional entropy of two states whose marginals on the conditioning system coincide. We additionally use it to derive a continuity bound for the quantum relative entropy in both variables. Interestingly, the fundamental entropic inequality is also valid in infinite dimensions.

A vector clock is a valuable tool for maintaining run time concurrency information in parallel programs. A novel method is presented for modifying vector clocks to make them suitable for programs with nested fork join parallelism (having a variable number of tasks). The resulting kind of clock is called a clock tree, due to its tree structure. The clock tree method compares favorably with other timestamping methods for variable parallelism: task identifier reuse and task recycling. The worst case space requirements of clock trees equals the best case for the latter two methods, and the average size of a clock tree is much smaller than the size of a vector with task recycling. Furthermore, the algorithm for maintaining clock trees does not require a shared data structure and thus avoids the serialization bottleneck that task recycling suffers from.

The authors present a high-resolution sensor composed of three ultrasonic sensors, one transmitter/receiver and two extra receivers, which allows a significant improvement in the information-extraction process. With this sensor the position (distance and bearing) of all isolated objects in an approximately 25 degrees field of view can be determined using information contained in one single snapshot of a moderately complex scene. Within limits, the sensor system can also discriminate between different types of reflectors, in particular, walls and edges, based on their radius of curvature. These results are all based on the determination of the arrival times of the echoes present at the three receivers. A noise model that accounts for the measured variations of the arrival times is used to derive limits on the resolution of the results provided by the sensor. Based on this model it is shown that, to a large extent, the sensor results are impervious to measurement variations common to all three receivers. Results obtained in a realistic environment are compared with those obtained from a conventional time-of-flight sensor.>

The authors propose a measurement setup consisting of a number of ultrasonic sensors used in parallel to perform triangulation measurements. The sensor system is based on two ideas. The first idea was to use signal processing techniques borrowed from existing radar and sonar systems. This allows the accurate determination of the position of multiple objects. Processing data in real time demands a fairly powerful processing system. The second idea was to assign a microprocessor to each transducer. To support the use of multiple sensors in the final measurement setup, transputers were used as processing elements as they offer easy scalability because of their serial links. This sensor measured the distance to multiple objects very accurately and with a resolution of 2 cm. It is shown that these techniques could be implemented in a cost-effective manner.>