1/t pressure and fermion behaviour of water in two dimensions

A variety of metal vacuum systems display the celebrated 1/t pressure, namely power-law dependence on time t, with the exponent close to unity, the origin of which has been a long-standing controversy. Here we propose a chemisorption model for water adsorbates, based on the argument for fermion behaviour of water vapour adsorbed on a stainless-steel surface, and obtain analytically the power-law behaviour of pressure, with an exponent of unity. Further, the model predicts that the pressure should depend on the temperature T according to T^(3/2), which is indeed confirmed by our experiment. Our results should help elucidate the unique characteristics of the adsorbed water.Comment: 11 pages, 4 figure

Rapid production of 87^{87}Rb BECs in a combined magnetic and optical potential

We describe an apparatus for quickly and simply producing \Rb87 Bose-Einstein condensates. It is based on a magnetic quadrupole trap and a red detuned optical dipole trap. We collect atoms in a magneto-optical trap (MOT) and then capture the atom in a magnetic quadrupole trap and force rf evaporation. We then transfer the resulting cold, dense cloud into a spatially mode-matched optical dipole trap by lowering the quadrupole field gradient to below gravity. This technique combines the efficient capture of atoms from a MOT into a magnetic trap with the rapid evaporation of optical dipole traps; the approach is insensitive to the peak quadrupole gradient and the precise trapping beam waist. Our system reliably produces a condensate with $N\approx2\times10^6$ atoms every 16\second

Boson stars in massive dilatonic gravity

We study equilibrium configurations of boson stars in the framework of a class scalar-tensor theories of gravity with massive gravitational scalar (dilaton). In particular we investigate the influence of the mass of the dilaton on the boson star structure. We find that the masses of the boson stars in presence of dilaton are close to those in general relativity and they are sensitive to the ratio of the boson mass to the dilaton mass within a typical few percent. It turns out also that the boson star structure is mainly sensitive to the mass term of the dilaton potential rather to the exact form of the potential.Comment: 9 pages, latex, 9 figures, one figure dropped, new comments added, new references added, typos correcte

Thermal gradient-induced forces on geodetic reference masses for LISA

The low frequency sensitivity of space-borne gravitational wave observatories will depend critically on the geodetic purity of the trajectories of orbiting test masses. Fluctuations in the temperature difference across the enclosure surrounding the free-falling test mass can produce noisy forces through several processes, including the radiometric effect, radiation pressure, and outgassing. We present here a detailed experimental investigation of thermal gradient-induced forces for the LISA gravitational wave mission and the LISA Pathfinder, employing high resolution torsion pendulum measurements of the torque on a LISA-like test mass suspended inside a prototype of the LISA gravitational reference sensor that will surround the test mass in orbit. The measurement campaign, accompanied by numerical simulations of the radiometric and radiation pressure effects, allows a more accurate and representative characterization of thermal-gradient forces in the specific geometry and environment relevant to LISA free-fall. The pressure dependence of the measured torques allows clear identification of the radiometric effect, in quantitative agreement with the model developed. In the limit of zero gas pressure, the measurements are most likely dominated by outgassing, but at a low level that does not threaten the LISA sensitivity goals.Comment: 21 pages, 16 figures, submitted to Physical Review

Measuring and reporting the capacity development performance of organizations in water and sanitation

Within the Water, Sanitation and Hygiene (WASH) sector, a range of organizations offer education and training activities. The aim of these activities is to improve access to water and sanitation services through better design and implementation of WASH interventions (Broughton & Hampshire, 1997; Cracknell, 2000). However, it is often not clear how effective education and training activities are at achieving these objectives. A key challenge is lack of clarity on how the results of education and training in WASH should be measured and reported. In order to address this issue, CAWST (The Centre for Affordable Water and Sanitation Technology) and the Centre for Engineering for Sustainable Development at the University of Cambridge conducted a review of measurement and reporting strategies of education and training organizations. Strengths, limitations and best practices were identified and used to develop recommendations for how CAWST, and other education and training organizations in the WASH sector, can improve the way they measure and report their results

Effective decrease of photoelectric emission threshold from gold plated surfaces

Many applications require charge neutralisation of isolated test bodies and this has been successfully done using photoelectric emission from surfaces which are electrically benign(gold) or superconducting (niobium). Gold surfaces nominally have a high work function ($\sim 5.1$\,eV)which should require deep UV photons for photoemission. In practice it has been found that it can be achieved with somewhat lower energy photons with indicative work functions of ($4.1-4.3$\,eV). A detailed working understanding of the process is lacking and this work reports on a study of the photoelectric emission properties of 4.6x4.6 cm^2 gold plated surfaces, representative of those used in typical satellite applications with a film thickness of 800 nm, and measured surface roughnesses between 7 and 340 nm. Various UV sources with photon energies from 4.8 to 6.2 eV and power outputs from 1 nW to 1000 nW, illuminated a ~0.3 cm^2 of the central surface region at angles of incidence from 0 to 60 degrees. Final extrinsic quantum yields in the range 10 ppm to 44 ppm were reliably obtained during 8 campaigns, covering a ~3 year period, but with intermediate long-term variations lasting several weeks and, in some cases, bake-out procedures at up to 200 C. Experimental results were obtained in a vacuum system with a baseline pressure of ~10^{-7} mbar at room temperature. A working model, designed to allow accurate simulation of any experimental configuration, is proposed.Comment: 35 pages, 12 figure

Classical Euclidean wormhole solutions in Palatini f(R~)f(\tilde{R}) cosmology

We study the classical Euclidean wormholes in the context of extended theories of gravity. With no loss of generality, we use the dynamical equivalence between $f(\tilde{R})$ gravity and scalar-tensor theories to construct a point-like Lagrangian in the flat FRW space time. We first show the dynamical equivalence between Palatini $f(\tilde{R})$ gravity and the Brans-Dicke theory with self-interacting potential, and then show the dynamical equivalence between the Brans-Dicke theory with self-interacting potential and the minimally coupled O'Hanlon theory. We show the existence of new Euclidean wormhole solutions for this O'Hanlon theory and, for an special case, find out the corresponding form of $f(\tilde{R})$ having wormhole solution. For small values of the Ricci scalar, this $f(\tilde{R})$ is in agreement with the wormhole solution obtained for higher order gravity theory $\tilde{R}+\epsilon \tilde{R}^2,\epsilon<0$.Comment: 11 page

Laura ++ : a Dalitz plot fitter

The Dalitz plot analysis technique has become an increasingly important method in heavy flavour physics. The Laura fitter has been developed as a flexible tool that can be used for Dalitz plot analyses in different experimental environments. Explicitly designed for three-body decays of heavy-flavoured mesons to spinless final state particles, it is optimised in order to describe all possible resonant or nonresonant contributions, and to accommodate possible violation effects

Frequency Characteristics of Visually Induced Motion Sickness

This article was published in the journal, Human Factors [Sage Publications / © Human Factors and Ergonomics Society.]. The definitive version is available at: http://dx.doi.org/10.1177/0018720812469046Objective: The aim of this study was to explore the frequency response of visually induced motion sickness (VIMS) for oscillating linear motion in the foreand- aft axis. Background: Simulators, virtual environments, and commercially available video games that create an illusion of self-motion are often reported to induce the symptoms seen in response to true motion. Often this human response can be the limiting factor in the acceptability and usability of such systems. Whereas motion sickness in physically moving environments is known to peak at an oscillation frequency around 0.2 Hz, it has recently been suggested that VIMS peaks at around 0.06 Hz following the proposal that the summed response of the visual and vestibular selfmotion systems is maximized at this frequency. Methods: We exposed 24 participants to random dot optical flow patterns simulating oscillating foreand- aft motion within the frequency range of 0.025 to 1.6 Hz. Before and after each 20-min exposure, VIMS was assessed with the Simulator Sickness Questionnaire. Also, a standard motion sickness scale was used to rate symptoms at 1-min intervals during each trial. Results: VIMS peaked between 0.2 and 0.4 Hz with a reducing effect at lower and higher frequencies. Conclusion: The numerical prediction of the “crossover frequency” hypothesis, and the design guidance curve previously proposed, cannot be accepted when the symptoms are purely visually induced. Application: In conditions in which stationary observers are exposed to optical flow that simulates oscillating fore-and-aft motion, frequencies around 0.2 to 0.4 Hz should be avoided

Modified Brans-Dicke theory of gravity from five-dimensional vacuum

We investigate, in the context of five-dimensional (5D) Brans-Dicke theory of gravity, the idea that macroscopic matter configurations can be generated from pure vacuum in five dimensions, an approach first proposed in the framework of general relativity. We show that the 5D Brans-Dicke vacuum equations when reduced to four dimensions lead to a modified version of Brans-Dicke theory in four dimensions (4D). As an application of the formalism, we obtain two five-dimensional extensions of four-dimensional O'Hanlon and Tupper vacuum solution and show that they lead two different cosmological scenarios in 4D.Comment: 9 page