The Doppler Spectra of Medium Grazing Angle Sea Clutter; Part 1: Characterisation

This paper is concerned with the characterisation of Doppler spectra from high range resolution X-band radar sea clutter observed from an airborne platform over the range of grazing angles, 15° to 45°. It is observed that when looking up or down wind there is a strong correlation between mean Doppler shift and local spectrum intensity. When combined with random fluctuations of spectrum width, these characteristics give the spectra a temporal and spatial variability. This behaviour has previously been observed in low grazing angle data and these results confirm the wider applicability of the models developed using that data. The modelling method is also extended here to capture the bimodal behaviour observed with high intensity returns from breaking waves looking up or down-wind

Non-Poissonian statistics from Poissonian light sources with application to passive decoy state quantum key distribution

We propose a method to prepare different non-Poissonian signal pulses from sources of Poissonian photon number distribution using only linear optical elements and threshold photon detectors. This method allows a simple passive preparation of decoy states for quantum key distribution. We show that the resulting key rates are comparable to the performance of active choices of intensities of Poissonian signals.Comment: 7 pages, 3 figures, accepted for publication in Opt. Let

Unified Supersymmetric Model of Naturally Small Dirac Neutrino Masses and the Axionic Solution of the Strong CP Problem

Using the particle content of the fundamental {27} supermultiplet of E_6, naturally small Dirac neutrino masses are obtained in the context of SU(3)_C times SU(2)_L times U(1)_Y times U(1)_{chi}, where U(1)_{chi} comes from the decomposition E_6 to SO(10) times U(1)_{psi}, then SO(10) to SU(5) times U(1)_{chi}. New observable consequences are predicted at the TeV scale. An axionic solution of the strong CP problem may be included at no extra cost.Comment: 10 pages, no figure, Eqs.(16)-(20) are correcte

Anti-jamming techniques for multichannel SAR imaging

© The Institution of Engineering and Technology 2006 IEE Proceedings online no. 20045090An airborne broadband jammer present in the mainbeam of a synthetic aperture radar (SAR) can potentially destroy a large region of the SAR image. In addition to this, multipath reflections from the ground, known as hot-clutter or terrain scattered interference will add a non-stationary interference component to the image. The goal of interference suppression for SAR is to successfully suppress these interferences while not significantly effecting the image quality by blurring, reducing the resolution or raising the sidelobe level. The paper provides an analysis of the degradation from hot-clutter, the limited restoration that multichannel imaging and slow-time space time adaptive processing (STAP) can provide and how fast-time STAP can improve the final image quality.L. Rosenberg and D. Gra

Levinson's theorem for the Schr\"{o}dinger equation in two dimensions

Levinson's theorem for the Schr\"{o}dinger equation with a cylindrically symmetric potential in two dimensions is re-established by the Sturm-Liouville theorem. The critical case, where the Schr\"{o}dinger equation has a finite zero-energy solution, is analyzed in detail. It is shown that, in comparison with Levinson's theorem in non-critical case, the half bound state for $P$ wave, in which the wave function for the zero-energy solution does not decay fast enough at infinity to be square integrable, will cause the phase shift of $P$ wave at zero energy to increase an additional $\pi$.Comment: Latex 11 pages, no figure and accepted by P.R.A (in August); Email: [email protected], [email protected]

The Doppler Spectra of Medium Grazing Angle Sea Clutter; Part 2: Model Assessment and Simulation

This paper is concerned with the assessment of models of Doppler spectra, derived from high range resolution X-band radar sea clutter observed from an airborne platform over the range of grazing angles, 15 to 45. When looking up or downwind these models represent the strong correlation between mean Doppler shift and local spectrum intensity. When combined with random fluctuations of spectrum width, these characteristics give the spectra a temporal and spatial variability. The models are used to predict clutter spectrum statistics as a function of Doppler frequency and these are compared with statistics derived from the original data. It is also shown how realistic range-varying coherent clutter returns can be simulated using the models

Making Neutrinos Massive with an Axion in Supersymmetry

The minimal supersymmetric standard model (MSSM) of particle interactions is extended to include three singlet (right-handed) neutrino superfields together with three other singlet superfields. The resulting theory is assumed to be invariant under an anomalous global U(1) (Peccei-Quinn) symmetry with one fundamental mass $m_2$. The soft breaking of supersymmetry at the TeV scale is shown to generate an axion scale $f_a$ of order $m_2$. Neutrino masses are generated by $f_a$ according to the usual seesaw mechanism.Comment: 11 pages, substantially revised with important change

BSAVA Formulary: Your questions answered

A new edition of the BSAVA Small Animal Formulary has been published. Ian Ramsey explains what is in and what is out of this new version

Long-distance practical quantum key distribution by entanglement swapping

We develop a model for practical, entanglement-based long-distance quantum key distribution employing entanglement swapping as a key building block. Relying only on existing off-the-shelf technology, we show how to optimize resources so as to maximize secret key distribution rates. The tools comprise lossy transmission links, such as telecom optical fibers or free space, parametric down-conversion sources of entangled photon pairs, and threshold detectors that are inefficient and have dark counts. Our analysis provides the optimal trade-off between detector efficiency and dark counts, which are usually competing, as well as the optimal source brightness that maximizes the secret key rate for specified distances (i.e. loss) between sender and receiver.Comment: 14 pages, 9 figures; published in Optics Expres