Studies of (GaAI)As injection lasers operating with an optical fiber resonator

The characteristics of an optical fiber external resonator in conjunction with (GaAl)As stripe geometry lasers are described. We have observed a 6–10% reduction in the threshold current and have obtained 150 ps pulses at gigahertz repetition rates. The fiber resonator has also been used to quench self‐pulsations in a (GaAl)As injection laser. In order to explain many of our results we have used a model that uses the conventional semiconductor rate equations modified by the addition of saturable electron traps and the effects of the external cavity. Our results predict many of the self‐locking effects observed in injection lasers operating in an external cavity. Furthermore, the degree of self‐locking will be a strong function of the external cavity length and the density of saturable absorbers

Quantum spatial superresolution by optical centroid measurements

Quantum lithography (QL) has been suggested as a means of achieving enhanced spatial resolution for optical imaging, but its realization has been held back by the low multi-photon detection rates of recording materials. Recently, an optical centroid measurement (OCM) procedure was proposed as a way to obtain spatial resolution enhancement identical to that of QL but with higher detection efficiency (M. Tsang, Phys. Rev. Lett. 102, 253601, 2009). Here we describe a variation of the OCM method with still higher detection efficiency based on the use of photon-number-resolving detection. We also report laboratory results for two-photon interference. We compare these results with those of the standard QL method based on multi-photon detection and show that the new method leads to superresolution but with higher detection efficiency.Comment: 4 pages, 2 figure

Buoyancy Regulation in Phaeocystis globosa Scherffel Colonies

Buoyancy of Phaeocystis globosa Scherffel (Prymnesiophyceae) colonies was investigated by measuring the vertical distribution of colonies in quiescent water where convection had been removed. Over 60% of the colonies exhibited negative buoyancy regardless of light condition or growth phase. Positively and neutrally buoyant colonies lost their buoyancy in the dark, but regained buoyancy upon return to the light. Colonies with closer cell packing; i.e., more cells per unit colonial surface area, had greater capability to remain buoyant. Our results suggest that colony buoyancy was not uniform within a P. globosa population, and that biological regulation of colony buoyancy required light energy

VAR(MA), What is it Good For? More Bad News for Reduced-form Estimation and Inference

It is common practice to use reduced-form vector autoregression (VAR) models, or more generally vector autoregressive moving average (VARMA) models, to characterize the dynamics in observed data and to identify innovations to the macroeconomy in some economically meaningful way. We demonstrate that neither approach|VAR or VARMA|are suitable reduced form guides to \reality", if reality were induced by some underlying structural DSGE model. We conduct such a thought experiment across a wide class of DSGE structures that imply particular VARMA data generating processes (DGPs). We find that with the typical small samples for macroeconomic data, the MA component of the fitted VARMA models is close to being non-identified. This in turn leads to an order reduction when identifying the lag structures of the VARMA models. As a result, VARMA models barely show any advantage over VARs using realistic sample sizes. However, the VAR remains a truly misspecified approximation. The VAR's performance deteriorates, in contrast to the VARMA's, as we enlarge the sample size generated from the true DGPs

Exploring factors associated with participation in citizen science among UK museum visitors aged 40-60: A qualitative study using the theoretical domains framework and the capability opportunity motivation-behaviour model

Citizen science has grown as a form of public engagement in science. Middle-aged citizens who are already consuming scientific information should be a potential outreach group. Behaviour change research in citizen science participation among the demographic is lacking. A total of 47 museum visitors aged 40-60 years took part in qualitative questionnaires and semi-structured interviews. Thematic analysis with the aid of theoretical domains framework and capability opportunity motivation-behaviour model revealed eight themes: (1) limited awareness of citizen science; (2) curiosity, competence and other significant characteristics and skills; (3) important beliefs about one's capability; (4) importance of clear project purpose and impacts; (5) interest, enjoyment and incentives; (6) lasting impacts of family upbringing; (7) project details that make participation easy, better project promotion; and (8) the living environment, availability of free time and money. Addressing a maximum number of these factors with behaviour change techniques can improve the likelihood of citizen science participation

Reversible Metal-Semiconductor Transition of ssDNA-Decorated Single-Walled Carbon Nanotubes

A field effect transistor (FET) measurement of a SWNT shows a transition from a metallic one to a p-type semiconductor after helical wrapping of DNA. Water is found to be critical to activate this metal-semiconductor transition in the SWNT-ssDNA hybrid. Raman spectroscopy confirms the same change in electrical behavior. According to our ab initio calculations, a band gap can open up in a metallic SWNT with wrapped ssDNA in the presence of water molecules due to charge transfer.Comment: 13 pages, 6 figure

The right to spatial development for human flourishing

This paper explores the literature on spatial development for people’s multifaceted well-being and the rights to the city, and argues for people’s right to live with dignity in cities. Nature and people-friendly spatial developments are fundamental to nourishing capabilities of human beings and realising their well-being. However, in reality, spatial developments are determined by legal planning and development regimes and socio-cultural discourses. These allocate different ‘claims, privileges and power rights’ to different stakeholders, and the results may not contribute to human flourishing. This paper attempts to synthesise an evaluation framework to achieve flourishing life with dignity in cities