Spacecraft formation flying using bifurcating potential fields

The distributed control of spacecraft flying in formation has been shown to have advantages over conventional single spacecraft systems. These include scalability, flexibility and robustness to failures. This paper considers the real problem of actuator saturation and shows how bound control laws can be developed that allow pattern formation and reconfigurability in a formation of spacecraft using bifurcating potential fields. In addition the stability of the system is ensured mathematically through dynamical systems theory

Three-dimensional formation flying using bifurcating potential fields

This paper describes the design of a three-dimensional formation flying guidance and control algorithm for a swarm of autonomous Unmanned Aerial Vehicles (UAVs), using the new approach of bifurcating artificial potential fields. We consider a decentralized control methodology that can create verifiable swarming patterns, which guarantee obstacle and vehicle collision avoidance. Based on a steering and repulsive potential field the algorithm supports flight that can transition between different formation patterns by way of a simple parameter change. The algorithm is applied to linear longitudinal and lateral models of a UAV. An experimental system to demonstrate formation flying is also developed to verify the validity of the proposed control system

Entanglement via Barut-Girardello coherent state for suq(1,1)su_{q}(1, 1) quantum algebra: bipartite composite system

Using noncocommutative coproduct properties of the quantum algebras, we introduce and obtain, in a bipartite composite system, the Barut-Girardello coherent state for the q-deformed $su_{q}(1,1)$ algebra. The quantum coproduct structure ensures this normalizable coherent state to be entangled. The entanglement disappears in the classical $q \to 1$ limit, giving rise to a factorizable state.Comment: 12 page

A deterministic cavity-QED source of polarization entangled photon pairs

We present two cavity quantum electrodynamics proposals that, sharing the same basic elements, allow for the deterministic generation of entangled photons pairs by means of a three-level atom successively coupled to two single longitudinal mode high-Q optical resonators presenting polarization degeneracy. In the faster proposal, the three-level atom yields a polarization entangled photon pair via two truncated Rabi oscillations, whereas in the adiabatic proposal a counterintuitive Stimulated Raman Adiabatic Passage process is considered. Although slower than the former process, this second method is very efficient and robust under fluctuations of the experimental parameters and, particularly interesting, almost completely insensitive to atomic decay.Comment: 5 pages, 5 figure

Quantum error-correcting codes associated with graphs

We present a construction scheme for quantum error correcting codes. The basic ingredients are a graph and a finite abelian group, from which the code can explicitly be obtained. We prove necessary and sufficient conditions for the graph such that the resulting code corrects a certain number of errors. This allows a simple verification of the 1-error correcting property of fivefold codes in any dimension. As new examples we construct a large class of codes saturating the singleton bound, as well as a tenfold code detecting 3 errors.Comment: 8 pages revtex, 5 figure

Quantum correlations from local amplitudes and the resolution of the Einstein-Podolsky-Rosen nonlocality puzzle

The Einstein-Podolsky-Rosen nonlocality puzzle has been recognized as one of the most important unresolved issues in the foundational aspects of quantum mechanics. We show that the problem is resolved if the quantum correlations are calculated directly from local quantities which preserve the phase information in the quantum system. We assume strict locality for the probability amplitudes instead of local realism for the outcomes, and calculate an amplitude correlation function.Then the experimentally observed correlation of outcomes is calculated from the square of the amplitude correlation function. Locality of amplitudes implies that the measurement on one particle does not collapse the companion particle to a definite state. Apart from resolving the EPR puzzle, this approach shows that the physical interpretation of apparently `nonlocal' effects like quantum teleportation and entanglement swapping are different from what is usually assumed. Bell type measurements do not change distant states. Yet the correlations are correctly reproduced, when measured, if complex probability amplitudes are treated as the basic local quantities. As examples we discuss the quantum correlations of two-particle maximally entangled states and the three-particle GHZ entangled state.Comment: Std. Latex, 11 pages, 1 table. Prepared for presentation at the International Conference on Quantum Optics, ICQO'2000, Minsk, Belaru

Using of small-scale quantum computers in cryptography with many-qubit entangled states

We propose a new cryptographic protocol. It is suggested to encode information in ordinary binary form into many-qubit entangled states with the help of a quantum computer. A state of qubits (realized, e.g., with photons) is transmitted through a quantum channel to the addressee, who applies a quantum computer tuned to realize the inverse unitary transformation decoding of the message. Different ways of eavesdropping are considered, and an estimate of the time needed for determining the secret unitary transformation is given. It is shown that using even small quantum computers can serve as a basis for very efficient cryptographic protocols. For a suggested cryptographic protocol, the time scale on which communication can be considered secure is exponential in the number of qubits in the entangled states and in the number of gates used to construct the quantum network

The Present status of our knowledge on the lesser sardines of Indian waters

The results of research carried out at Waltair, Mandapam. Tuticorin and Vizhinjam and another centres on the lesser sardines over the past up till 1978 are reviewed in detail. In the twentyyear period from 1958 to 1978 there was an increasing trend of production of these fishes along the different coasts of India, the average annual landings nearly doubling from 36,000 t in 1958-67 to 70,000 t in 1968-78. The bulk of the catches came from Tamil Nadu, including Pondicherry, (32.6%), Kerala (32.2%) and Andhra Pradesh (26.5%)- Fishing was mostly by the labour-intensive traditional methods in close-shore waters, better catches coming from 30-55 m depths. Shore seines, boat seines and gill nets were the principal gears employed in the fishery though gill nets were the most effective

Understanding the link between trafficking in persons and HIV and AIDS risk in Tanzania

The magnitude of trafficking in persons in Tanzania is unknown. Consequently, available information on health risks of persons trafficked for different forms of exploitation is extremely scanty. We conducted a baseline study in eight administrative regions of Tanzania using both qualitative and quantitative methods to generate data on the health conditions of trafficked persons to inform trafficking in persons control measures through HIV and AIDS interventions. Study participants included the national, regional and district community development officers, district medical officers, local government leaders, managers or representatives of non-governmental organizations involved in anti-trafficking in persons activities, members of the community and victims. Findings indicated that common forms of labour into which persons are trafficked include domestic services, agriculture (farming), construction, mining/quarrying, fishing, lumbering and manufacturing. Trafficked persons are reported to be exposed to risks like overcrowding, long working hours, psychological problems, physical injuries, impotence, breathing problems and sexually transmitted infections including HIV. It is concluded that the reported occupational hazards in industries where trafficked persons are forced into are not specific to trafficked persons as they affect all labourers. However, the underground nature of the trafficking in persons process increases health problems and risks, including the vulnerability to HIV infection. More tailored research is needed, especially to find means of how to reach out and provide services to this particular vulnerable population, validate labour forms of exploitation into which persons are trafficked to enable the integration or mainstreaming of HIV and AIDS and trafficking in persons at the policy and programmatic levels. In addition, findings would facilitate the understanding of the link between increased risk of HIV and trafficking in persons