929 research outputs found
Ammonia borane-based nanocomposites as solid state hydrogen stores for portable power applications
Ammonia borane (AB) based nanocomposites have been investigated with the aim of developing a promising solid-state hydrogen store that complies with the requirements of a modular polymer electrolyte membrane fuel cell (PEM FC) in a portable power pack system. AB-carbon nanocomposites (prepared via ball milling or solution-impregnation) demonstrate improved hydrogen release performance compared to AB itself in terms of onset temperature and hydrogen purity, while maintaining a gravimetric density of more than 5 wt. % H2. The most promising of these materials is an AB-AC (activated carbon) composite, synthesised via solution-impregnation with an optimal dehydrogenation temperature of 96 °C. When combined with an external nickel chloride filter downstream, no evolved gaseous by-products can be detected above 100 ppb. The feasibility of an AB-AC storage tank has been further endorsed by simulations in which the reaction rate and the hydrogen flux was found to be almost constant as the temperature front propagated from the bottom to the top of the tank after initiation
Ammonia uptake and release in the MnX<sub>2</sub>–NH<sub>3</sub> (X = Cl, Br) systems and structure of the Mn(NH<sub>3</sub>)nX<sub>2</sub> (n = 6, 2) ammines
Hexa-ammine complexes, Mn(NH<sub>3</sub>)<sub>6</sub>X<sub>2</sub> (X = Cl, Br), have been synthesized by ammoniation of the corresponding transition metal halide and characterized by Powder X-ray diffraction (PXRD) and Raman spectroscopy. The hexa-ammine complexes are isostructural (Cubic,Fm-3m, Z = 4; a = 10.2742(6) Ã… and 10.527(1) Ã… for X = Cl, Br respectively). Temperature programmed desorption (TPD) demonstrated that ammonia release from Mn(NH<sub>3</sub>)<sub>6</sub>X<sub>2</sub> complexes occurred in three stages corresponding to the release of 4, 1 and 1 NH<sub>3</sub> equivalents respectively. The chloride and bromide both exhibit a deammoniation onset temperature below 323 K. The di-ammoniates from the first desorption step were isolated during TPD measurements and their crystal structures determined by Rietveld refinement against PXRD data (X = Cl: orthorhombicCmmm, a = 8.1991(9) Ã…, b = 8.2498(7) Ã…, c = 3.8212(4) Ã…, Z = 2; X = Br: orthorhombic Pbam, a = 6.0109(5) Ã…, b = 12.022(1) Ã…, c = 4.0230(2) Ã…, Z= 2)
Rapid surfactant-free synthesis of Mg(OH)2 nanoplates and pseudomorphic dehydration to MgO
Magnesium hydroxide nanoplates ca. 50 nm in thickness can be prepared over minute timescales via hydrothermal synthesis in a multimode cavity (MMC) microwave reactor. This approach allows ca. 1 g of single-phase Mg(OH)2 to be synthesised in under 3 minutes without the requirement of surfactants or non-aqueous solvents. The hydroxide nanomaterial dehydrates at temperatures >200 K below that of the equivalent bulk material and can be utilised as a precursor for the pseudomorphic synthesis of nanoplates of MgO as investigated by TG-DTA-MS, XRD and SEM measurements. Equally, the pseudomorphic synthesis can be performed by irradiating the Mg(OH)2 nanomaterial with microwaves for 6 minutes to produce single phase MgO
Rapid surfactant-free synthesis of Mg(OH)2 nanoplates and pseudomorphic dehydration to MgO
Magnesium hydroxide nanoplates ca. 50 nm in thickness can be prepared over minute timescales via hydrothermal synthesis in a multimode cavity (MMC) microwave reactor. This approach allows ca. 1 g of single-phase Mg(OH)2 to be synthesised in under 3 minutes without the requirement of surfactants or non-aqueous solvents. The hydroxide nanomaterial dehydrates at temperatures >200 K below that of the equivalent bulk material and can be utilised as a precursor for the pseudomorphic synthesis of nanoplates of MgO as investigated by TG-DTA-MS, XRD and SEM measurements. Equally, the pseudomorphic synthesis can be performed by irradiating the MgIJOH)2 nanomaterial with microwaves for 6 minutes to produce single-phase MgO.JRC.F.2-Energy Conversion and Storage Technologie
Diamond nano-pillar arrays for quantum microscopy of neuronal signals
Modern neuroscience is currently limited in its capacity to perform long
term, wide-field measurements of neuron electromagnetics with nanoscale
resolution. Quantum microscopy using the nitrogen vacancy centre (NV) can
provide a potential solution to this problem with electric and magnetic field
sensing at nano-scale resolution and good biocompatibility. However, the
performance of existing NV sensing technology does not allow for studies of
small mammalian neurons yet. In this paper, we propose a solution to this
problem by engineering NV quantum sensors in diamond nanopillar arrays. The
pillars improve light collection efficiency by guiding excitation/emission
light, which improves sensitivity. More importantly, they also improve the size
of the signal at the NV by removing screening charges as well as coordinating
the neuron growth to the tips of the pillars where the NV is located. Here, we
provide a growth study to demonstrate coordinated neuron growth as well as the
first simulation of nano-scopic neuron electric and magnetic fields to assess
the enhancement provided by the nanopillar geometry.Comment: 18 pages including supplementary and references, 12 figure
The Dark Energy Survey Data Processing and Calibration System
The Dark Energy Survey (DES) is a 5000 deg2 grizY survey reaching
characteristic photometric depths of 24th magnitude (10 sigma) and enabling
accurate photometry and morphology of objects ten times fainter than in SDSS.
Preparations for DES have included building a dedicated 3 deg2 CCD camera
(DECam), upgrading the existing CTIO Blanco 4m telescope and developing a new
high performance computing (HPC) enabled data management system (DESDM).
The DESDM system will be used for processing, calibrating and serving the DES
data. The total data volumes are high (~2PB), and so considerable effort has
gone into designing an automated processing and quality control system. Special
purpose image detrending and photometric calibration codes have been developed
to meet the data quality requirements, while survey astrometric calibration,
coaddition and cataloging rely on new extensions of the AstrOmatic codes which
now include tools for PSF modeling, PSF homogenization, PSF corrected model
fitting cataloging and joint model fitting across multiple input images.
The DESDM system has been deployed on dedicated development clusters and HPC
systems in the US and Germany. An extensive program of testing with small rapid
turn-around and larger campaign simulated datasets has been carried out. The
system has also been tested on large real datasets, including Blanco Cosmology
Survey data from the Mosaic2 camera. In Fall 2012 the DESDM system will be used
for DECam commissioning, and, thereafter, the system will go into full science
operations.Comment: 12 pages, submitted for publication in SPIE Proceeding 8451-1
Panoramic SETI: Program Update and High-Energy Astrophysics Applications
Optical SETI (Search for Extraterrestrial Intelligence) instruments that can
explore the very fast time domain, especially with large sky coverage, offer an
opportunity for new discoveries that can complement multimessenger and time
domain astrophysics. The Panoramic SETI experiment (PANOSETI) aims to observe
optical transients with nanosecond to second duration over a wide field-of-view
(2,500 sq.deg.) by using two assemblies of tens of telescopes to
reject spurious signals by coincidence detection. Three PANOSETI telescopes,
connected to a White Rabbit timing network used to synchronize clocks at the
nanosecond level, have been deployed at Lick Observatory on two sites separated
by a distance of 677 meters to distinguish nearby light sources (such as
Cherenkov light from particle showers in the Earth's atmosphere) from
astrophysical sources at large distances. In parallel to this deployment, we
present results obtained during four nights of simultaneous observations with
the four 12-meter VERITAS gamma-ray telescopes and two PANOSETI telescopes at
the Fred Lawrence Whipple Observatory. We report PANOSETI's first detection of
astrophysical gamma rays, comprising three events with energies in the range
between 15 TeV and 50 TeV. These were emitted by the Crab
Nebula, and identified as gamma rays using joint VERITAS observations.Comment: 9 pages, 5 figures, SPIE Astronomical Telescopes + Instrumentation
conference, 2022, Montr\'eal, Qu\'ebec, Canad
Modified Gravity and Cosmology
In this review we present a thoroughly comprehensive survey of recent work on
modified theories of gravity and their cosmological consequences. Amongst other
things, we cover General Relativity, Scalar-Tensor, Einstein-Aether, and
Bimetric theories, as well as TeVeS, f(R), general higher-order theories,
Horava-Lifschitz gravity, Galileons, Ghost Condensates, and models of extra
dimensions including Kaluza-Klein, Randall-Sundrum, DGP, and higher
co-dimension braneworlds. We also review attempts to construct a Parameterised
Post-Friedmannian formalism, that can be used to constrain deviations from
General Relativity in cosmology, and that is suitable for comparison with data
on the largest scales. These subjects have been intensively studied over the
past decade, largely motivated by rapid progress in the field of observational
cosmology that now allows, for the first time, precision tests of fundamental
physics on the scale of the observable Universe. The purpose of this review is
to provide a reference tool for researchers and students in cosmology and
gravitational physics, as well as a self-contained, comprehensive and
up-to-date introduction to the subject as a whole.Comment: 312 pages, 15 figure
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