Space station stabilization and control study Final engineering report

Simulation of stabilization and control for spinning, manned space station to provide artificial gravity station environmen

State-recycling and time-resolved imaging in topological photonic lattices

Photonic lattices - arrays of optical waveguides - are powerful platforms for simulating a range of phenomena, including topological phases. While probing dynamics is possible in these systems, by reinterpreting the propagation direction as "time," accessing long timescales constitutes a severe experimental challenge. Here, we overcome this limitation by placing the photonic lattice in a cavity, which allows the optical state to evolve through the lattice multiple times. The accompanying detection method, which exploits a multi-pixel single-photon detector array, offers quasi-real time-resolved measurements after each round trip. We apply the state-recycling scheme to intriguing photonic lattices emulating Dirac fermions and Floquet topological phases. In this new platform, we also realise a synthetic pulsed electric field, which can be used to drive transport within photonic lattices. This work opens a new route towards the detection of long timescale effects in engineered photonic lattices and the realization of hybrid analogue-digital simulators.Comment: Comments are welcom

Calculation of Elastic Green's Functions for Lattices with Cavities

In this Brief Report, we present an algorithm for calculating the elastic Lattice Greens Function of a regular lattice, in which defects are created by removing lattice points. The method is computationally efficient, since the required matrix operations are on matrices that scale with the size of the defect subspace, and not with the size of the full lattice. This method allows the treatment of force fields with multi-atom interactions.Comment: 3 pages. RevTeX, using epsfig.sty. One figur

Conceptual design of an airborne laser Doppler velocimeter system for studying wind fields associated with severe local storms

An airborne laser Doppler velocimeter was evaluated for diagnostics of the wind field associated with an isolated severe thunderstorm. Two scanning configurations were identified, one a long-range (out to 10-20 km) roughly horizontal plane mode intended to allow probing of the velocity field around the storm at the higher altitudes (4-10 km). The other is a shorter range (out to 1-3 km) mode in which a vertical or horizontal plane is scanned for velocity (and possibly turbulence), and is intended for diagnostics of the lower altitude region below the storm and in the out-flow region. It was concluded that aircraft flight velocities are high enough and severe storm lifetimes are long enough that a single airborne Doppler system, operating at a range of less than about 20 km, can view the storm area from two or more different aspects before the storm characteristics change appreciably

Velocity, energy and helicity of vortex knots and unknots

In this paper we determine the velocity, the energy and estimate writhe and twist helicity contributions of vortex filaments in the shape of torus knots and unknots (toroidal and poloidal coils) in a perfect fluid. Calculations are performed by numerical integration of the Biot-Savart law. Vortex complexity is parametrized by the winding number $w$, given by the ratio of the number of meridian wraps to that of the longitudinal wraps. We find that for $w<1$ vortex knots and toroidal coils move faster and carry more energy than a reference vortex ring of same size and circulation, whereas for $w>1$ knots and poloidal coils have approximately same speed and energy of the reference vortex ring. Helicity is dominated by the writhe contribution. Finally, we confirm the stabilizing effect of the Biot-Savart law for all knots and unknots tested, that are found to be structurally stable over a distance of several diameters. Our results also apply to quantized vortices in superfluid $^4$He.Comment: 17 pages, 8 figures, 2 table

Digital Intimacies and LGBT+ Youth: Celebration, Equity and Safety

“Digital Intimacies and LGBT+ youth” was commissioned by Brook, the wellbeing and sexual health charity for under-25s. It builds on the insights of its earlier report Digital Romance (McGeeney and Hanson 2017) which researched young people’s digital intimacy practices. For this report, we revisited survey and focus group data specifically from LGBT+ participants in that research. Additionally, we reviewed academic literature and gathered new data from LGBT+ youth groups, youth work practitioners and teachers, and parents / carers. Our research took place during the period of lockdowns due to Covid-19. These induced rapid shifts in perceptions of the online and in youth work practices, which have shaped our analysis here. The report summarises its findings under the headings of: // Celebration: We acknowledge the positive experiences that LGBT+ youth have online. We recognise LGBT+ youth as engaged creatively in diverse practices of community-building across many digital and offline spaces. Although there may be some (real and imagined) generational gaps in appreciating the value of digital cultures, we describe how youth work professionals rapidly and flexibly adapted their work with young people to online spaces under lockdown. Evidence that youth work practices were in turn able to positively impact some young people’s online relationship-building shows the value and vitality of cross-generational work and spaces. // Equity: We acknowledge the particular challenges faced by LGBT+ youth in a heteronormative world, which require specific resources to ameliorate. Some of these resources – especially for LGBT+ friendly youth services and other provision – are inadequate and / or under threat. Young people in our research looked particularly to schools to create safe and inclusive spaces including through relationships and sexuality education. We also draw attention to the responsibilities of platform providers, since many features of internet architecture prioritise commercial imperatives above privacy, preventing online harassment, or access to information. // Safety: We acknowledge the particular issues faced by LGBT+ youth in forging relationships and identities and their need for support. These intersect with many different aspects of identity. However we argue that an overemphasis on risk can be alienating and counterproductive, especially if it comes at the expense of more positive representations. Risk-taking is a necessary part of growing and learning. Managing risk should be seen as a lifelong project for all of us, constantly revisited, rather than something that can be avoided entirely or achieved at a single point in time. We conclude by offering a set of recommendations for practice relevant to funding bodies, campaigners, youth work professionals, schools, families and carers. These relate to: • Inclusive Relationships and Sex(uality) Education • Inclusive online safety • Resourcing anti-harassment strategies • Demanding more from digital media providers • Actively supporting parents and carers • Creating and networking safe spaces • Supporting youth community spaces • Supporting creativity/world-making • Outreach and exchang