Comment on "Classical interventions in quantum systems II. Relativistic invariance"

In a recent paper [Phys. Rev. A 61, 022117 (2000)], quant-ph/9906034, A. Peres argued that quantum mechanics is consistent with special relativity by proposing that the operators that describe time evolution do not need to transform covariantly, although the measurable quantities need to transform covariantly. We discuss the weaknesses of this proposal.Comment: 4 pages, to appear in Phys. Rev.

HST/STIS Imaging of the Host Galaxy of GRB980425/SN1998bw

We present HST/STIS observations of ESO 184-G82, the host galaxy of the gamma-ray burst GRB 980425 associated with the peculiar Type Ic supernova SN1998bw. ESO 184-G82 is found to be an actively star forming SBc sub-luminous galaxy. We detect an object consistent with being a point source within the astrometric uncertainty of 0.018 arcseconds of the position of the supernova. The object is located inside a star-forming region and is at least one magnitude brighter than expected for the supernova based on a simple radioactive decay model. This implies either a significant flattening of the light curve or a contribution from an underlying star cluster.Comment: 12 pages, 2 figures, AASTeX v5.02 accepted for publication in ApJ Letter

Modelling electron distributions within ESA's Gaia satellite CCD pixels to mitigate radiation damage

The Gaia satellite is a high-precision astrometry, photometry and spectroscopic ESA cornerstone mission, currently scheduled for launch in 2012. Its primary science drivers are the composition, formation and evolution of the Galaxy. Gaia will achieve its unprecedented positional accuracy requirements with detailed calibration and correction for radiation damage. At L2, protons cause displacement damage in the silicon of CCDs. The resulting traps capture and emit electrons from passing charge packets in the CCD pixel, distorting the image PSF and biasing its centroid. Microscopic models of Gaia's CCDs are being developed to simulate this effect. The key to calculating the probability of an electron being captured by a trap is the 3D electron density within each CCD pixel. However, this has not been physically modelled for the Gaia CCD pixels. In Seabroke, Holland & Cropper (2008), the first paper of this series, we motivated the need for such specialised 3D device modelling and outlined how its future results will fit into Gaia's overall radiation calibration strategy. In this paper, the second of the series, we present our first results using Silvaco's physics-based, engineering software: the ATLAS device simulation framework. Inputting a doping profile, pixel geometry and materials into ATLAS and comparing the results to other simulations reveals that ATLAS has a free parameter, fixed oxide charge, that needs to be calibrated. ATLAS is successfully benchmarked against other simulations and measurements of a test device, identifying how to use it to model Gaia pixels and highlighting the effect of different doping approximations.Comment: 12 pages, 6 figures, appearing in Proc. of SPIE Optics and Photonics Conference (Focal Plane Arrays for Space telescopes IV), 2-6 August 2009, San Diego, US

Quantum phase transitions in the Fermi-Bose Hubbard model

We propose a multi-band Fermi-Bose Hubbard model with on-site fermion-boson conversion and general filling factor in three dimensions. Such a Hamiltonian models an atomic Fermi gas trapped in a lattice potential and subject to a Feshbach resonance. We solve this model in the two state approximation for paired fermions at zero temperature. The problem then maps onto a coupled Heisenberg spin model. In the limit of large positive and negative detuning, the quantum phase transitions in the Bose Hubbard and Paired-Fermi Hubbard models are correctly reproduced. Near resonance, the Mott states are given by a superposition of the paired-fermion and boson fields and the Mott-superfluid borders go through an avoided crossing in the phase diagram.Comment: 4 pages, 3 figure

The Haptic Bracelets: learning multi-limb rhythm skills from haptic stimuli while reading

The Haptic Bracelets are a system designed to help people learn multi-limbed rhythms (which involve multiple simultaneous rhythmic patterns) while they carry out other tasks. The Haptic Bracelets consist of vibrotactiles attached to each wrist and ankle, together with a computer system to control them. In this chapter, we report on an early empirical test of the capabilities of this system, and consider de-sign implications. In the pre-test phase, participants were asked to play a series of multi-limb rhythms on a drum kit, guided by audio recordings. Participants’ per-formances in this phase provided a base reference for later comparisons. During the following passive learning phase, away from the drum kit, just two rhythms from the set were silently 'played' to each subject via vibrotactiles attached to wrists and ankles, while participants carried out a 30-minute reading comprehen-sion test. Different pairs of rhythms were chosen for different subjects to control for effects of rhythm complexity. In each case, the two rhythms were looped and alternated every few minutes. In the final phase, subjects were asked to play again at the drum kit the complete set of rhythms from the pre-test, including, of course, the two rhythms to which they had been passively exposed. Pending analysis of quantitative data focusing on accuracy, timing, number of attempts and number of errors, in this chapter we present preliminary findings based on participants’ sub-jective evaluations. Most participants thought that the technology helped them to understand rhythms and to play rhythms better, and preferred haptic to audio to find out which limb to play when. Most participants indicated that they would pre-fer using a combination of haptics and audio for learning rhythms to either mo-dality on its own. Replies to open questions were analysed to identify design is-sues, and implications for design improvements were considered

Large classical universes emerging from quantum cosmology

It is generally believed that one cannot obtain a large Universe from quantum cosmological models without an inflationary phase in the classical expanding era because the typical size of the Universe after leaving the quantum regime should be around the Planck length, and the standard decelerated classical expansion after that is not sufficient to enlarge the Universe in the time available. For instance, in many quantum minisuperspace bouncing models studied in the literature, solutions where the Universe leave the quantum regime in the expanding phase with appropriate size have negligible probability amplitude with respect to solutions leaving this regime around the Planck length. In this paper, I present a general class of moving gaussian solutions of the Wheeler-DeWitt equation where the velocity of the wave in minisuperspace along the scale factor axis, which is the new large parameter introduced in order to circumvent the abovementioned problem, induces a large acceleration around the quantum bounce, forcing the Universe to leave the quantum regime sufficiently big to increase afterwards to the present size, without needing any classical inflationary phase in between, and with reasonable relative probability amplitudes with respect to models leaving the quantum regime around the Planck scale. Furthermore, linear perturbations around this background model are free of any transplanckian problem.Comment: 8 pages, 1 figur