Optical and X-ray Variability in The Least Luminous AGN, NGC4395

We report the detection of optical and X-ray variability in the least luminous known Seyfert galaxy, NGC4395. The featureless continuum changed by a factor of 2 in 6 months, which is typical of more luminous AGN. The largest variation was seen at shorter wavelengths, so that the spectrum becomes `harder' during higher activity states. In a one week optical broad band monitoring program, a 20% change was seen between successive nights. In a 1 month period the spectral shape changed from a power law with spectral index alpha ~0 (characteristic of quasars) to a spectral index alpha ~2 (as observed in other dwarf AGN). ROSAT HRI and PSPC archive data show a variable X-ray source coincident with the galactic nucleus. A change in X-ray flux by a factor \~2 in 15 days has been observed. When compared with more luminous AGN, NGC4395 appears to be very X-ray quiet. The hardness ratio obtained from the PSPC data suggests that the spectrum could be absorbed. We also report the discovery of weak CaIIK absorption, suggesting the presence of a young stellar cluster providing of the order of 10% of the blue light. Using HST UV archive data, together with the optical and X-ray observations, we examine the spectral energy distribution for NGC4395 and discuss the physical conditions implied by the nuclear activity under the standard AGN model. The observations can be explained by either an accreting massive black hole emitting at about 10^(-3) L_(Edd) or by a single old compact SNR with an age of 50 to 500 yr generated by a small nuclear starburst.Comment: 19 pages, 9 figures, to appear in MNRA

A Universal Point Set for 2-Outerplanar Graphs

A point set $S \subseteq \mathbb{R}^2$ is universal for a class $\cal G$ if every graph of ${\cal G}$ has a planar straight-line embedding on $S$. It is well-known that the integer grid is a quadratic-size universal point set for planar graphs, while the existence of a sub-quadratic universal point set for them is one of the most fascinating open problems in Graph Drawing. Motivated by the fact that outerplanarity is a key property for the existence of small universal point sets, we study 2-outerplanar graphs and provide for them a universal point set of size $O(n \log n)$.Comment: 23 pages, 11 figures, conference version at GD 201

Copyrighting the Past? Emerging Intellectual Property Rights Issues in Archaeology1

Rights to intellectual property have become a major issue in eth- nobotany and many other realms of research involving Indige- nous communities. This paper examines intellectual-property- rights-related issues in archaeology, including the relevance of such rights within the discipline, the forms these rights take, and the impacts of applying intellectual property protection in archaeology. It identifies the “products” of archaeological re- search and what they represent in a contemporary sociocultural context, examines ownership issues, assesses the level of protec- tion of these products provided by existing legislation, and dis- cusses the potential of current intellectual property protection mechanisms to augment cultural heritage protection for Indige- nous communities

Ensemble prediction for nowcasting with a convection-permitting model - II: forecast error statistics

A 24-member ensemble of 1-h high-resolution forecasts over the Southern United Kingdom is used to study short-range forecast error statistics. The initial conditions are found from perturbations from an ensemble transform Kalman filter. Forecasts from this system are assumed to lie within the bounds of forecast error of an operational forecast system. Although noisy, this system is capable of producing physically reasonable statistics which are analysed and compared to statistics implied from a variational assimilation system. The variances for temperature errors for instance show structures that reflect convective activity. Some variables, notably potential temperature and specific humidity perturbations, have autocorrelation functions that deviate from 3-D isotropy at the convective-scale (horizontal scales less than 10 km). Other variables, notably the velocity potential for horizontal divergence perturbations, maintain 3-D isotropy at all scales. Geostrophic and hydrostatic balances are studied by examining correlations between terms in the divergence and vertical momentum equations respectively. Both balances are found to decay as the horizontal scale decreases. It is estimated that geostrophic balance becomes less important at scales smaller than 75 km, and hydrostatic balance becomes less important at scales smaller than 35 km, although more work is required to validate these findings. The implications of these results for high-resolution data assimilation are discussed

Oxygen Isotopes of Al-Rich Chondrules from Unequilibrated Ordinary Chondrites

Al-rich chondrules (ARCs) are a rare constituent of chondrites. They have relatively high bulk Al_2O_3 content (> 10 wt%), which is due to the presence of Al-rich phases, such as plagioclase, spinel, Al-rich glass etc. [1]. ARCs share some chemical and petrologic characteristics with Ca, Al-rich inclusions (CAis), and may represent a genetic link between ferromagnesian chondrules and CAis

Dialysis residential care : a future dialysis service model

People with chronic kidney disease are ageing and have increasing co-morbidities. The current delivery of renal replacement therapy, dialysis and transplantation, needs to adjust to changing patient needs. This paper proposes a potential future service delivery model featuring a dialysis residential care facility and a care coordination focus. The residential care facility would be composed of four levels of care; high, hostel, independent and outpatient. The paper argues that this model may result in decreased morbidity, improved patient quality of life and may prove cost effective. Patients\u27 nutritional status, medication adherence and transport efficiency may be improved. We propose this model to stimulate further debate in order to meet the needs of current and future chronic kidney disease patients.<br /

Acoustic scattering by impedance screens/cracks with fractal boundary: well-posedness analysis and boundary element approximation

We study time-harmonic scattering in $\mathbb{R}^n$ ($n=2,3$) by a planar screen (a "crack" in the context of linear elasticity), assumed to be a non-empty bounded relatively open subset $\Gamma$ of the hyperplane $\mathbb{R}^{n-1}\times \{0\}$, on which impedance (Robin) boundary conditions are imposed. In contrast to previous studies, $\Gamma$ can have arbitrarily rough (possibly fractal) boundary. To obtain well-posedness for such $\Gamma$ we show how the standard impedance boundary value problem and its associated system of boundary integral equations must be supplemented with additional solution regularity conditions, which hold automatically when $\partial\Gamma$ is smooth. We show that the associated system of boundary integral operators is compactly perturbed coercive in an appropriate function space setting, strengthening previous results. This permits the use of Mosco convergence to prove convergence of boundary element approximations on smoother "prefractal" screens to the limiting solution on a fractal screen. We present accompanying numerical results, validating our theoretical convergence results, for three-dimensional scattering by a Koch snowflake and a square snowflake