Measurements of antenna polar diagrams and efficiencies using a phase-switched interferometer

It is desirable to know antenna polar patterns and efficiencies accurately. In the past, calibration measurements have been made using balloons and aircraft and more recently satellites. These techniques are usually very expensive. It is shown that under certain circumstances it is possible to use a simpler and inexpensive technique by connecting together the antenna under test with another antenna to form a phase switched interferometer as first described by Ryle (1952). The technique does require a suitable radio source which gives measurable powers when using small antennas and since dipoles have broad patterns, radio sources with similar right ascensions but different declinations to the primary source can be a problem. These problems can partly be overcome by filtering the interference pattern

An Analytical Model of Packet Collisions in IEEE 802.15.4 Wireless Networks

Numerous studies showed that concurrent transmissions can boost wireless network performance despite collisions. While these works provide empirical evidence that concurrent transmissions may be received reliably, existing signal capture models only partially explain the root causes of this phenomenon. We present a comprehensive mathematical model that reveals the reasons and provides insights on the key parameters affecting the performance of MSK-modulated transmissions. A major contribution is a closed-form derivation of the receiver bit decision variable for arbitrary numbers of colliding signals and constellations of power ratios, timing offsets, and carrier phase offsets. We systematically explore the root causes for successful packet delivery under concurrent transmissions across the whole parameter space of the model. We confirm the capture threshold behavior observed in previous studies but also reveal new insights relevant for the design of optimal protocols: We identify capture zones depending not only on the signal power ratio but also on time and phase offsets.Comment: Accepted for publication in the IEEE Transactions on Wireless Communications under the title "On the Reception of Concurrent Transmissions in Wireless Sensor Networks.

Hole Spin Helix: Anomalous Spin Diffusion in Anisotropic Strained Hole Quantum Wells

We obtain the spin-orbit interaction and spin-charge coupled transport equations of a two-dimensional heavy hole gas under the influence of strain and anisotropy. We show that a simple two-band Hamiltonian can be used to describe the holes. In addition to the well-known cubic hole spin-orbit interaction, anisotropy causes a Dresselhaus-like term, and strain causes a Rashba term. We discover that strain can cause a shifting symmetry of the Fermi surfaces for spin up and down holes. We predict an enhanced spin lifetime associated with a spin helix standing wave similar to the Persistent Spin Helix which exists in the two-dimensional electron gas with equal Rashba and Dresselhaus spin-orbit interactions. These results may be useful both for spin-based experimental determination of the Luttinger parameters of the valence band Hamiltonian and for creating long-lived spin excitations

Hybrid meson masses and the correlated Gaussian basis

We revisited a model for charmonium hybrid meson with a magnetic gluon [Yu. S. Kalashnikova and A. V. Nefediev, Phys. Rev. D {\bf 77}, 054025 (2008)] and improved the numerical calculations. These improvements support the hybrid meson interpretation of X(4260). Within the same model, we computed the hybrid meson mass with an electric gluon which is resolved to be lighter. Relativistic effects and coupling channels decreased also the mass.Comment: 9 pages, 20 figures ; accepted for publication in Phys. Rev.

How long is co-operation in genomics sustainable?

Publications on the 16 yeast chromosome sequences group together over 400 different authors from Europe, Japan, Australia and the USA. When research is not organised in networks, it is carried out in large sequencing centres such as the Sanger Centre in Britain, the Helix Institute in Japan or Saint Louis University in the USA. Both cases illustrate the collective nature of knowledge creation. Other examples of co-operation between numerous researchers in various countries, more closely related to innovation, might also be mentioned, such as the development of software for comparing proteins or DNA sequences. Collective publications reveal the collective nature of research, whether it is carried out by major consortia (the case of yeast) or around large research facilities (such as the synchrotron or major genome sequencing centres). This collective nature stems from two factors: (1) the advantages of co-ordinating efforts on major projects (e.g. economies of scale and of collection) and (2) very strong interdependency in the creation and utilisation of knowledge (related to cumulativeness).

Profile of public laboratories, industrial partnerships and organisation of R & D: the dynamics of industrial relationships in a large research organisation

There is a paucity of papers dealing with the system characteristics of laboratories or, put in another way, the institutional character of research organisations. Neither R & D economics nor the sociology of science, as traditionally conceived, has made much headway in providing insight into sets of R & D laboratories and their evolution. Drawing upon an empirical study in the plant breeding and biochemical industry, this paper presents a typology of public research laboratories which is based on three dimensions: scientific production and visibility, type of funding (public or private) and homogeneity of research themes. Three types of public laboratory emerge: the first, called “research centres for the profession”, is composed essentially of laboratories with close ties with small and medium firms (SMEs) and industry associations. The second, called “designers of generic tools and methods”, is oriented towards basic research and themes of general interest to the industry as a whole. The third type, called “basic and specialised laboratories”, strives to develop its scientific visibility. Contracts between this type of laboratory and industry are mainly bilateral and demonstrate the complementarity between public and private research. Each type of laboratory develops specific types of relationship with private partners. The authors have identified three logics underlying these relationships: proximity, market and club. The main objective of contracts based on a proximity logic is to test a hypothesis, while the knowledge produced is mostly tacit and specific. By contrast, knowledge is entirely coded and specific in the market logic, where the aim of the contract is to implement expertise in order to relieve a scientific bottleneck. In a club logic, the aim of contracts is to produce a technical referent. In each kind of contract, the learning trajectories, modes of co-ordination, role of trust and degree to which contracts are complete or not, are different.

The Cauchy Operator for Basic Hypergeometric Series

We introduce the Cauchy augmentation operator for basic hypergeometric series. Heine's ${}_2\phi_1$ transformation formula and Sears' ${}_3\phi_2$ transformation formula can be easily obtained by the symmetric property of some parameters in operator identities. The Cauchy operator involves two parameters, and it can be considered as a generalization of the operator $T(bD_q)$. Using this operator, we obtain extensions of the Askey-Wilson integral, the Askey-Roy integral, Sears' two-term summation formula, as well as the $q$-analogues of Barnes' lemmas. Finally, we find that the Cauchy operator is also suitable for the study of the bivariate Rogers-Szeg\"o polynomials, or the continuous big $q$-Hermite polynomials.Comment: 21 pages, to appear in Advances in Applied Mathematic