Externally Dispersed Interferometry for Precision Radial Velocimetry

Externally Dispersed Interferometry (EDI) is the series combination of a fixed-delay field-widened Michelson interferometer with a dispersive spectrograph. This combination boosts the spectrograph performance for both Doppler velocimetry and high resolution spectroscopy. The interferometer creates a periodic spectral comb that multiplies against the input spectrum to create moire fringes, which are recorded in combination with the regular spectrum. The moire pattern shifts in phase in response to a Doppler shift. Moire patterns are broader than the underlying spectral features and more easily survive spectrograph blurring and common distortions. Thus, the EDI technique allows lower resolution spectrographs having relaxed optical tolerances (and therefore higher throughput) to return high precision velocity measurements, which otherwise would be imprecise for the spectrograph alone.Comment: 7 Pages, White paper submitted to the AAAC Exoplanet Task Forc

Experiences of learning through collaborative evaluation from a masters programme in professional education

This paper presents findings from a collaborative evaluation project within a masters programme in professional education. The project aimed to increase knowledge of research methodologies and methods through authentic learning where participants worked in partnership with the tutor to evaluate the module which they were studying. The project processes, areas of the course evaluated and the data collection methods are outlined. The findings focus on key themes from evaluating the effectiveness of using a collaborative evaluation approach, including: enhanced student engagement; creativity of the collaborative evaluation approach; equality between the tutor and students; and enhanced research skills. Discussion focuses on the outcomes and effectiveness of the project and tutor reflections on adopting a collaborative approach. This paper highlights lessons from the project relevant to those interested in staff-student partnership approaches and those facilitating postgraduate learning and teaching programmes and educational research courses

PEPSI: The high-resolution echelle spectrograph and polarimeter for the Large Binocular Telescope

PEPSI is the bench-mounted, two-arm, fibre-fed and stabilized Potsdam Echelle Polarimetric and Spectroscopic Instrument for the 2x8.4 m Large Binocular Telescope (LBT). Three spectral resolutions of either 43 000, 120 000 or 270 000 can cover the entire optical/red wavelength range from 383 to 907 nm in three exposures. Two 10.3kx10.3k CCDs with 9-{\mu}m pixels and peak quantum efficiencies of 96 % record a total of 92 echelle orders. We introduce a new variant of a wave-guide image slicer with 3, 5, and 7 slices and peak efficiencies between 96 %. A total of six cross dispersers cover the six wavelength settings of the spectrograph, two of them always simultaneously. These are made of a VPH-grating sandwiched by two prisms. The peak efficiency of the system, including the telescope, is 15% at 650 nm, and still 11% and 10% at 390 nm and 900 nm, respectively. In combination with the 110 m2 light-collecting capability of the LBT, we expect a limiting magnitude of 20th mag in V in the low-resolution mode. The R=120 000 mode can also be used with two, dual-beam Stokes IQUV polarimeters. The 270 000-mode is made possible with the 7-slice image slicer and a 100- {\mu}m fibre through a projected sky aperture of 0.74", comparable to the median seeing of the LBT site. The 43000-mode with 12-pixel sampling per resolution element is our bad seeing or faint-object mode. Any of the three resolution modes can either be used with sky fibers for simultaneous sky exposures or with light from a stabilized Fabry-Perot etalon for ultra-precise radial velocities. CCD-image processing is performed with the dedicated data-reduction and analysis package PEPSI-S4S. A solar feed makes use of PEPSI during day time and a 500-m feed from the 1.8 m VATT can be used when the LBT is busy otherwise. In this paper, we present the basic instrument design, its realization, and its characteristics

Mass dependence of spectral and angular distributions of Cherenkov radiation from relativistic isotopes in solid radiators and its possible application as mass selector

The first proof of principle experiment with a prototype of a Time-of-Flight (TOF) - Cherenkov detector of relativistic heavy ions (RHI) exploiting a liquid Iodine Naphthalene radiator has been performed at Cave C at GSI (Darmstadt, Germany). A conceptual design for a liquid Cherenkov detector was proposed as a prototype for the future TOF measurements at the SuperFRS by detection of total number of Cherenkov photons. The ionization energy loss of RHI in a liquid radiator decreases only slightly this number, while in a solid radiator changes sufficiently not the total number of ChR photons, but ChR angular and spectral distributions. By means of computer simulations, we showed that these distributions are very sensitive to the isotope mass, due to different stopping powers of isotopes with initial equal relativistic factors. The results of simulations for light (Li, Be) and heavy (Xe) isotopes at 500-1000 MeV/u are presented indicating the possibility to use the isotopic effect in ChR of RHI as the mass selector

Collinear helium under periodic driving: stabilization of the asymmetric stretch orbit

The collinear eZe configuration of helium, with the electrons on opposite sides of the nucleus, is studied in the presence of an external electromagnetic (laser or microwave) field. We show that the classically unstable "asymmetric stretch" orbit, on which doubly excited intrashell states of helium with maximum interelectronic angle are anchored, can be stabilized by means of a resonant driving where the frequency of the electromagnetic field equals the frequency of Kepler-like oscillations along the orbit. A static magnetic field, oriented parallel to the oscillating electric field of the driving, can be used to enforce the stability of the configuration with respect to deviations from collinearity. Quantum Floquet calculations within a collinear model of the driven two-electron atom reveal the existence of nondispersive wave packets localized on the stabilized asymmetric stretch orbit, for double excitations corresponding to principal quantum numbers of the order of N > 10.Comment: 13 pages, 12 figure

Coordinated generation of multiple ocular-like cell lineages and fabrication of functional corneal epithelial cell sheets from human iPS cells

We describe a protocol for the generation of a functional and transplantable corneal epithelium derived from human induced pluripotent stem (iPS) cells. When this protocol is followed, a proportion of iPS cells spontaneously form circular colonies, each of which is composed of four concentric zones. Cells in these zones have different morphologies and immunostaining characteristics, resembling neuroectoderm, neural crest, ocular-surface ectoderm, or surface ectoderm. We have named this 2D colony a 'SEAM' (self-formed ectodermal autonomous multizone), and previously demonstrated that cells within the SEAM have the potential to give rise to anlages of different ocular lineages, including retinal cells, lens cells, and ocular-surface ectoderm. To investigate the translational potential of the SEAM, cells within it that resemble ocular-surface epithelia can be isolated by pipetting and FACS sorting into a population of corneal epithelial-like progenitor cells. These can be expanded and differentiated to form an epithelial layer expressing K12 and PAX6, and able to recover function in an animal model of corneal epithelial dysfunction after surgical transplantation. The whole protocol, encompassing human iPS cell preparation, autonomous differentiation, purification, and subsequent differentiation, takes between 100 and 120 d, and is of potential use to researchers with an interest in eye development and/or ocular-surface regeneration. Experience with human iPS cell culture and sorting via FACS will be of benefit for researchers performing this protocol

Cancer Survivors’ Social Context in the Return to Work Process:Narrative Accounts of Social Support and Social Comparison Information

Purpose: Returning to work is a process that is intertwined with the social aspects of one’s life, which can influence the way in which that person manages their return to work and also determines the support available to them. This study aimed to explore cancer patients’ perceptions of the role of their social context in relation to returning to work following treatment. Methods: Twenty-three patients who had received a diagnosis of either urological, breast, gynaecological, or bowel cancer participated in semi-structured interviews examining general perceptions of cancer, work values and perceptions of the potential impact of their cancer diagnosis and treatment on work. Interviews were analysed using the iterative process of Framework Analysis. Results: Two superordinate themes emerged as influential in the return to work process: Social support as a facilitator of return to work (e.g. co-workers’ support and support outside of the workplace) and Social comparison as an appraisal of readiness to return to work (e.g. comparisons with other cancer patients, colleagues, and employees in other organisations or professions). Conclusions: Two functions of the social context of returning to work after cancer were apparent in the participants’ narrative: the importance of social support as a facilitator of returning to work and the utilisation of social comparison information in order to appraise one’s readiness to return to work. The role of social context in returning to work has largely been absent from the research literature to date. The findings of this study suggest that social support and social comparison mechanisms may have a significant impact on an individual’s successful return to the workplace

Adsorption of mono- and multivalent cat- and anions on DNA molecules

Adsorption of monovalent and multivalent cat- and anions on a deoxyribose nucleic acid (DNA) molecule from a salt solution is investigated by computer simulation. The ions are modelled as charged hard spheres, the DNA molecule as a point charge pattern following the double-helical phosphate strands. The geometrical shape of the DNA molecules is modelled on different levels ranging from a simple cylindrical shape to structured models which include the major and minor grooves between the phosphate strands. The densities of the ions adsorbed on the phosphate strands, in the major and in the minor grooves are calculated. First, we find that the adsorption pattern on the DNA surface depends strongly on its geometrical shape: counterions adsorb preferentially along the phosphate strands for a cylindrical model shape, but in the minor groove for a geometrically structured model. Second, we find that an addition of monovalent salt ions results in an increase of the charge density in the minor groove while the total charge density of ions adsorbed in the major groove stays unchanged. The adsorbed ion densities are highly structured along the minor groove while they are almost smeared along the major groove. Furthermore, for a fixed amount of added salt, the major groove cationic charge is independent on the counterion valency. For increasing salt concentration the major groove is neutralized while the total charge adsorbed in the minor groove is constant. DNA overcharging is detected for multivalent salt. Simulations for a larger ion radii, which mimic the effect of the ion hydration, indicate an increased adsorbtion of cations in the major groove.Comment: 34 pages with 14 figure

Numerical Investigation into the Effect of Splats and Pores on the Thermal Fracture of Air Plasma-Sprayed Thermal Barrier Coatings

The effect of splat interfaces on the fracture behavior of air plasma-sprayed thermal barrier coatings (APS-TBC) is analyzed using finite element modeling involving cohesive elements. A multiscale approach is adopted in which the explicitly resolved top coat microstructural features are embedded in a larger domain. Within the computational cell, splat interfaces are modeled as being located on a sinusoidal interface in combination with a random distribution of pores. Parametric studies are conducted for different splat interface waviness, spacing, pore volume fraction and fracture properties of the splat interface. The results are quantified in terms of crack nucleation temperature and total microcrack length. It is found that the amount of cracking in TBCs actually decreases with increased porosity up to a critical volume fraction. In contrast, the presence of splats is always detrimental to the TBC performance. This detrimental effect is reduced for the splat interfaces with high waviness and spacing compared to those with low waviness and spacing. The crack initiation temperature was found to be linearly dependent on the normal fracture properties of the splat interface. Insights derived from the numerical results aid in engineering the microstructure of practical TBC systems for improved resistance against thermal fracture

Quasi-Optical Mode Generator for Excitation of Very High-Order Modes up to 240 GHz

A new quasi-optical mode generator setup has been designed to excite the TE48,26 mode operating at 238 GHz. It will be the mode with the highest eigenvalue , = 146.80) ever measured in cold tests and therefore the successor of the TE40,23 mode operating at 204 GHz. In this paper, the design of the new coaxial cavity for the mode generator setup is presented, which is based on the cavity design of the corresponding gyrotron. Simulations using a scattering matrix code show a mode purity of 99.5 % at the output of the cavity at an operating frequency of 238.101 GHz. Recently, the main components are under manufacturing. After delivery mid-2024, first experiments will be performed