Explosion models for thermonuclear supernovae resulting from different ignition conditions

We have explored in three dimensions the fate of a massive white dwarf as a function of different initial locations of carbon ignition, with the aid of a SPH code. The calculated models cover a variety of possibilities ranging from the simultaneous ignition of the central volume of the star to the off-center ignition in multiple scattered spots. In the former case, there are discussed the possibility of a transition to a detonation when the mean density of the nuclear flame decreases below 2x10**7 g cm**-3, and its consequences. In the last case, the dependence of the results on the number of initial igniting spots and the chance of some of these models to evolve to the pulsating delayed detonation scenario are also outlined.Comment: 5 pages, 1 figure, proceedings of IAU Colloquium 192, 'Supernovae (10 years of SN1993J)', 22-26 April 2003, Valencia, Spai

Functional genomic and transformation resources for commercially important red macroalgae (Rhodophyta)

Red macroalgae underpin many commercially important food, pharmaceutical and other important industries. To date, research into these species has generally focused on improving seaweed cultivation, developing new methods to extract useful compounds, or identify novel applications. Due to their economic importance, there is a requirement to develop a more complete understanding of the genome and metabolic pathways in these key seaweed species. This review describes progress in genomics, transcriptomics, protoplast isolation, and transformation approaches. It also explores the potential of genome editing using the CRISPR/Cas system to further our understanding of gene function related to different metabolic pathways and resolving unexplored aspects of macroalgal physiology traits linked to crop improvement. The application of functional genomics is essential to gain a complete understanding of both physiological and metabolomic processes, that will ultimately enhance the commercial resilience of macroalgae related industries that are subject to numerous pressures, including climate change. Although the use of genetic manipulation to alter growth characteristics or composition in seaweed will not readily apply to the macroalgae industry in the short term, it is likely to be critical for sustaining future commercial growth. The functional characterisation of macroalgal genes through the CRISPR/ Cas approach promises to open new avenues for translational research on utilising macroalgal resources for the sustainable development of these aquaculture systems

The X-ray nebula around the Seyfert 2 galaxy NGC4388

We report on X-ray emission from the Seyfert 2 galaxy NGC4388 observed with the Chandra X-ray Observatory. A hard X-ray peak is found at the position of the active nucleus suggested by optical and radio observations. Extended soft X-ray emission correlates well with the ionization cone found in optical line emission. A large soft X-ray extension is found up to 16 kpc to the north of the galaxy. Photoionized gas with low ionization parameters (xi<3) appears to be the likely explanation of this emission. The same ionized gas clouds could be responsible for the optical [OIII] emission. Fe K line emission from cold material is found to be extended by a few kpc.Comment: 12 pages, one colour figure included, MNRAS in pres

Phase Coherence and Control of Stored Photonic Information

We report the demonstration of phase coherence and control for the recently developed "light storage" technique. Specifically, we use a pulsed magnetic field to vary the phase of atomic spin excitations which result from the deceleration and storing of a light pulse in warm Rb vapor. We then convert the spin excitations back into light and detect the resultant phase shift in an optical interferometric measurement. The coherent storage of photon states in matter is essential for the practical realization of many basic concepts in quantum information processing.Comment: 5 pages, 3 figures. Submitted to Phys. Rev. Let

Supernovae as a probe of particle physics and cosmology

It has very recently been demonstrated by Csaki, Kaloper and Terning (CKT) that the faintness of supernovae at high redshift can be accommodated by mixing of a light axion with the photon in the presence of an intergalactic magnetic field, as opposed to the usual explanation of an accelerating universe by a dark energy component. In this paper we analyze further aspects of the CKT mechanism and its generalizations. The CKT mechanism also passes various cosmological constraints from the fluctuations of the CMB and the formation of structure at large scales, without requiring an accelerating phase in the expansion of the Universe. We investigate the statistical significance of current supernova data for pinning down the different components of the cosmological energy-momentum tensor and for probing physics beyond the standard models.Comment: 17 pages, LaTeX, 4 figures; v2: typos corrected, minor changes, references added; v3: updated figures, details regarding fits include

A Comment on the Topological Phase for Anti-Particles in a Lorentz-violating environment

Recently, a scheme to analyse topological phases in Quantum Mechanics by means of the non-relativistic limit of fermions non-minimally coupled to a Lorentz-breaking background has been proposed. In this letter, we show that the fixed background, responsible for the Lorentz-symmetry violation, may induce opposite Aharonov-Casher phases for a particle and its corresponding antiparticle. We then argue that such a difference may be used to investigate the asymmetry for particle/anti-particle as well as to propose bounds on the associated Lorentz-symmetry violating parameters.Comment: 4 pages - A published versio

Nonlinear optics via double dark resonances

Double dark resonances originate from a coherent perturbation of a system displaying electromagnetically induced transparency. We experimentally show and theoretically confirm that this leads to the possibility of extremely sharp resonances prevailing even in the presence of considerable Doppler broadening. A gas of 87Rb atoms is subjected to a strong drive laser and a weak probe laser and a radio frequency field, where the magnetic coupling between the Zeeman levels leads to nonlinear generation of a comb of sidebands.Comment: 6 pages, 9 figure

From Storage and Retrieval of Pulses to Adiabatons

We investigate whether it is possible to store and retrieve the intense probe pulse from a $\Lambda$-type homogeneous medium of cold atoms. Through numerical simulations we show that it is possible to store and retrieve the probe pulse which are not necessarily weak. As the intensity of the probe pulse increases, the retrieved pulse remains a replica of the original pulse, however there is overall broadening and loss of the intensity. These effects can be understood in terms of the dependence of absorption on the intensity of the probe. We include the dynamics of the control field, which becomes especially important as the intensity of the probe pulse increases. We use the theory of adiabatons [Grobe {\it et al.} Phys. Rev. Lett. {\bf 73}, 3183 (1994)] to understand the storage and retrieval of light pulses at moderate powers.Comment: 15 pages, 7 figures, typed in RevTe