83 research outputs found
Lens mounting techniques for precise radial location of fragile lenses in the NGS2 and Veloce instruments
We present novel methods for mounting lenses in a pair of instruments that presented challenging optical and
mechanical requirements. The first instrument is the replacement Natural Guide Star Sensor (NGS2) for CANOPUS
at Gemini South, which incorporates an objective consisting of a stack of six lenses mounted in a common
bore. A compliant radial spacer was used to eliminate lens decentre resulting from the additional radial clearance
required to accommodate differential thermal strains between the low thermal expansion lenses and a common
bore. In the same instrument, tangent contact toroidal spacers were deployed in place of traditional conical spacers
to further reduce contact stresses in fragile calcium fluoride lens elements. The toroidal faces were specified
with a 10µm profile tolerance to avoid possible edge contact between the spacers and lenses. We investigated
milling and turning machining processes for the production of the spacers by comparing their results via Coordinate
Measuring Machine (CMM) measurements. In the second instrument, Veloce, built for the Anglo-Australian
Telescope, a lens decentre requirement of 40µm led us to develop a simple means of in-situ centring adjustment
of the cell mounted lens. Physical testing of the finished instruments verified the performance of each of these
methods. NGS2 produced images at the factory acceptance test in which 94% of encircled energy was captured
by a single 16um detector pixel, surpassing the specification of 80%. Bench testing of Veloce during assembly
showed that the adjustment mechanism allowed centring of the lens over a range of +/- 0.1mm with a precision
of 5µm
AO corrected satellite imaging from Mount Stromlo
The Research School of Astronomy and Astrophysics have been developing adaptive optics systems for space situational awareness. As part of this program we have developed satellite imaging using compact adaptive optics systems for small (1-2 m) telescopes such as those operated by Electro Optic Systems (EOS) from the Mount Stromlo Observatory. We have focused on making compact, simple, and high performance AO systems using modern high stroke high speed deformable mirrors and EMCCD cameras. We are able to track satellites down to magnitude 10 with a Strehl in excess of 20% in median seeing
Pyxis: A ground-based demonstrator for formation-flying optical interferometry
In the past few years, there has been a resurgence in studies towards
space-based optical/infrared interferometry, particularly with the vision to
use the technique to discover and characterise temperate Earth-like exoplanets
around solar analogues. One of the key technological leaps needed to make such
a mission feasible is demonstrating that formation flying precision at the
level needed for interferometry is possible. Here, we present ,
a ground-based demonstrator for a future small satellite mission with the aim
to demonstrate the precision metrology needed for space-based interferometry.
We describe the science potential of such a ground-based instrument, and detail
the various subsystems: three six-axis robots, a multi-stage metrology system,
an integrated optics beam combiner and the control systems required for the
necessary precision and stability. We end by looking towards the next stage of
: a collection of small satellites in Earth orbit.Comment: 27 Pages, 14 Figures, submitted to JATI
Anomalous scattering analysis of Agrobacterium radiobacter phosphotriesterase: the prominent role of iron in the heterobinuclear active site
Bacterial phosphotriesterases are binuclear metalloproteins from which the catalytic
mechanism has been studied with a variety of techniques, principally using active sites
reconstituted in vitro from apo-enzymes. Here, atomic absorption spectroscopy and
anomalous X-ray scattering and have been used to determine the identity of the metals
incorporated into the active site in vivo. We have recombinantly expressed the
phosphotriesterase from Agrobacterium radiobacter (OpdA) in Escherichia coli grown in
medium supplemented with 1 mM CoCl2, and in unsupplemented medium. Anomalous
scattering data, collected from a single crystal at the Fe-K, Co-K and Zn-K edges,
indicate that iron and cobalt are the primary constituents of the two metal binding sites in
the catalytic centre ( and ), in protein expressed in E. coli grown in supplemented
medium. Comparison to OpdA expressed in unsupplemented medium demonstrates that
the cobalt present in the supplemented medium replaced zinc at the -position of the
active site, which results in an increase in the catalytic efficiency of the enzyme. These
results suggest an essential role for iron in the catalytic mechanism of bacterial
phosphotriesterases, and that they are natively heterobinuclear iron-zinc enzymes
Probing the role of the divalent metal ion in uteroferrin using metal ion replacement and a comparison to isostructural biomimetics
Purple acid phosphatases (PAPs) are a group of
heterovalent binuclear metalloenzymes that catalyze the
hydrolysis of phosphomonoesters at acidic to neutral pH.
While the metal ions are essential for catalysis, their precise
roles are not fully understood. Here, the Fe(III)Ni(II)
derivative of pig PAP (uteroferrin) was generated and its
properties were compared with those of the native
Fe(III)Fe(II) enzyme. The kcat of the Fe(III)Ni(II) derivative
(approximately 60 s–1) is approximately 20% of that of
native uteroferrin, and the Ni(II) uptake is considerably
faster than the reconstitution of full enzymatic activity,
suggesting a slow conformational change is required to
attain optimal reactivity. An analysis of the pH dependence
of the catalytic properties of Fe(III)Ni(II) uteroferrin indicates
that the l-hydroxide is the likely nucleophile. Thus,
the Ni(II) derivative employs a mechanism similar to that
proposed for the Ga(III)Zn(II) derivative of uteroferrin, but
different from that of the native enzyme, which uses a
terminal Fe(III)-bound nucleophile to initiate catalysis.
Binuclear Fe(III)Ni(II) biomimetics with coordination
environments similar to the coordination environment of
uteroferrin were generated to provide both experimental
benchmarks (structural and spectroscopic) and further
insight into the catalytic mechanism of hydrolysis. The
data are consistent with a reaction mechanism employing
an Fe(III)-bound terminal hydroxide as a nucleophile,
similar to that proposed for native uteroferrin and various
related isostructural biomimetics. Thus, only in the uteroferrin-
catalyzed reaction are the precise details of the
catalytic mechanism sensitive to the metal ion composition,
illustrating the significance of the dynamic ligand
environment in the protein active site for the optimization
of the catalytic efficiency
A conceptual design study for Subaru ULTIMATE GLAO
We report on the conceptual design study done for the Ground Layer Adaptive Optics system of the ULTIMATE-Subaru project. This is an ambitious instrument project, providing GLAO correction in a square field of view of 14 arcmin on a side, aiming to deliver improved seeing at the near infrared wavelength. Its client instruments are an imager and multi-IFU spectrograph at Cassegrain and a Multi-Object spectrograph at Nasmyth. In this paper, we introduce the ULTIMATE-Subaru project overview and its science case and report the results of the GLAO performance prediction based on the numerical simulation and conceptual design of the wavefront sensor systemThe development of ULTIMATE-Subaru is partly supported by the Japan Society for the Promotion of Science
(Grant-in-Aid for Research #17H06129)
Does owning a pet protect older people against loneliness?
This article has been made available through the Brunel Open Access Publishing Fund.Pet ownership is thought to make a positive contribution to health, health behaviours and the general well-being of older people. More specifically pet ownership is often proposed as a solution to the problem of loneliness in later life and specific 'pet based' interventions have been developed to combat loneliness. However the evidence to support this relationship is slim and it is assumed that pet ownership is a protection against loneliness rather than a response to loneliness. The aim of this paper is to examine the association between pet ownership and loneliness by exploring if pet ownership is a response to, or protection against, loneliness using Waves 0-5 from the English Longitudinal Study of Ageing (ELSA)
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