Superfluid instability of r-modes in "differentially rotating" neutron stars

Superfluid hydrodynamics affects the spin-evolution of mature neutron stars, and may be key to explaining timing irregularities such as pulsar glitches. However, most models for this phenomenon exclude the global instability required to trigger the event. In this paper we discuss a mechanism that may fill this gap. We establish that small scale inertial r-modes become unstable in a superfluid neutron star that exhibits a rotational lag, expected to build up due to vortex pinning as the star spins down. Somewhat counterintuitively, this instability arises due to the (under normal circumstances dissipative) vortex-mediated mutual friction. We explore the nature of the superfluid instability for a simple incompressible model, allowing for entrainment coupling between the two fluid components. Our results recover a previously discussed dynamical instability in systems where the two components are strongly coupled. In addition, we demonstrate for the first time that the system is secularly unstable (with a growth time that scales with the mutual friction) throughout much of parameter space. Interestingly, large scale r-modes are also affected by this new aspect of the instability. We analyse the damping effect of shear viscosity, which should be particularly efficient at small scales, arguing that it will not be sufficient to completely suppress the instability in astrophysical systems.Comment: RevTex, 11 figure

AXA General Insurance Ltd v Lord Advocate : analysis

Discusses the Supreme Court decision in AXA General Insurance Ltd, Petitioners on whether Scottish legislation which reversed a House of Lords ruling concerning the actionability of certain asbestos-related conditions breached insurers' rights

A survey of the properties of early-type galaxies

A compilation of the properties of elliptical and early disk galaxies was completed. In addition to material from the literature, such as Infrared Astronomy Satellite (IRAS) fluxes, the compilation includes recent measurements of HI and CO, as well as a review of the x ray properties by Forman and Jones. The data are used to evaluate the gas content of early systems and to search for correlations with x ray emission. The interstellar medium in early-type galaxies is generally dominated by hot interstellar gas (T approx. 10 to the 7th power K; c.f. the review by Fabbiano 1989 and references therein). In addition, a significant fraction of these galaxies show infrared emission (Knapp, et al., 1989), optical emission lines, and visible dust. Sensitive studies in HI and CO of a number of these galaxies have been completed recently, resulting in several detections, particularly of the later types. Researchers wish to understand the connection among these different forms of the interstellar medium, and to examine the theoretical picture of the fate of the hot gas. To do so, they compiled observations of several forms of interstellar matter for a well-defined sample of early-type galaxies. Here they present a statistical analysis of this data base and discuss the implications of the results

Private Database Queries Using Quantum States with Limited Coherence Times

We describe a method for private database queries using exchange of quantum states with bits encoded in mutually incompatible bases. For technology with limited coherence time, the database vendor can announce the encoding after a suitable delay to allow the user to privately learn one of two items in the database without the ability to also definitely infer the second item. This quantum approach also allows the user to choose to learn other functions of the items, such as the exclusive-or of their bits, but not to gain more information than equivalent to learning one item, on average. This method is especially useful for items consisting of a few bits by avoiding the substantial overhead of conventional cryptographic approaches.Comment: extended to generalized (POVM) measurement

Socially intelligent reasoning for autonomous agents

Socially intelligent agents are autonomous problem solvers that have to achieve their objectives by interacting with other similarly autonomous entities. A major concern, therefore, is with the design of the decision-making mechanism that such agents employ in order to determine which actions to take to achieve their goals. An attractive and much sought after property of this mechanism is that it produces decisions that are rational from the perspective of the individual agent. However, some agents are also inherently social. Moreover, individual and social concerns often conflict, leading to the possibility of inefficient performance of the individual and the system. To address these problems we propose a framework for making socially acceptable decisions, based on social welfare functions, that combines social and individual perspectives in a unified and flexible manner. The framework is realized in an exemplar computational setting and an empirical analysis is made of the relative performance of varying sociable decision-making functions in a range of environments. This analysis is then used to design an agent that adapts its decision-making to reflect the resource constraints that it faces at any given time. A further round of empirical evaluation shows how adding such a metalevel mechanism enhances the performance of the agent by directing reasoning to adopt different strategies in different contexts. Finally, the possibility and efficacy of making the metalevel mechanism adaptive, so that experience of past encounters can be factored into the decision-making, is demonstrated

Study of electro-absorption effects in 1300nm In(Ga)As/GaAs quantum dot materials

No abstract available

GaAs-based Self-Aligned Stripe Superluminescent Diodes Processed Normal to the Cleaved Facet

We demonstrate GaAs-based superluminescent diodes (SLDs) incorporating a window-like back facet in a self-aligned stripe. SLDs are realised with low spectral modulation depth (SMD) at high power spectral density, without application of anti-reflection coatings. Such application of a window-like facet reduces effective facet reflectivity in a broadband manner. We demonstrate 30mW output power in a narrow bandwidth with only 5% SMD, outline the design criteria for high power and low SMD, and describe the deviation from a linear dependence of SMD on output power as a result of Joule heating in SLDs under continuous wave current injection. Furthermore, SLDs processed normal to the facet demonstrate output powers as high as 20mW, offering improvements in beam quality, ease of packaging and use of real estate. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

A Comparison of Candidate Banker Plants for Management of Pests in Lettuce

Agricultural systems are often lacking in resources for natural enemies. Providing alternative prey can help natural enemies persist through periods of low pest abundance, although this approach has been rarely commercially implemented in open field crops. In this study, we tested the potential of eight plant species to provide alternative prey to natural enemies in lettuce fields over a 2-yr period. Results showed that the tested plants would not act as sources of the lettuce aphid Nasonovia ribisnigri Mosley (Hemiptera: Aphididae), the primary lettuce pest. Of the banker plants tested, barley contained high numbers of non-lettuce aphids and appeared to provide reliable habitat for hoverfly larvae. However, lettuce aphids were present on lettuce early in the season, and may have dwarfed any effects of nonlettuce aphids on natural enemy populations. Numbers of hoverfly larvae were also high in lettuce, but did not appear to track numbers of non-lettuce aphids on banker plants. In contrast, numbers of lacewing larvae were highest on plants containing high numbers of non-lettuce aphids, and predatory hemipterans appeared to be associated with numbers of thrips on banker plants. Although barley showed promise as a source of alternative aphids, it did not appear to improve pest control in the adjacent crop

Grounding of Human Environments and Activities for Autonomous Robots

With the recent proliferation of robotic applications in domestic and industrial scenarios, it is vital for robots to continually learn about their environments and about the humans they share their environments with. In this paper, we present a framework for autonomous, unsupervised learning from various sensory sources of useful human ‘concepts’; including colours, people names, usable objects and simple activities. This is achieved by integrating state-of-the-art object segmentation, pose estimation, activity analysis and language grounding into a continual learning framework. Learned concepts are grounded to natural language if commentary is available, allowing the robot to communicate in a human-understandable way. We show, using a challenging, real-world dataset of human activities, that our framework is able to extract useful concepts, ground natural language descriptions to them, and, as a proof-of-concept, to generate simple sentences from templates to describe people and activities