Friends, Neighbours and Distant Partners: Extending or Decentring Family Relationships?

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HST/NICMOS Observations of Fast Infrared Flickering in the Microquasar GRS 1915+105

We report infrared observations of the microquasar GRS 1915+105 using the NICMOS instrument of the Hubble Space Telescope during 9 visits in April-June 2003. During epochs of high X-ray/radio activity near the beginning and end of this period, we find that the $1.87$\um infrared flux is generally low ($\sim 2$ mJy) and relatively steady. However, during the X-ray/radio ``plateau'' state between these epochs, we find that the infrared flux is significantly higher ($\sim 4-6$ mJy), and strongly variable. In particular, we find events with amplitudes $\sim 20-30$% occurring on timescales of $\sim 10-20$s (e-folding timescales of $\sim 30$s). These flickering timescales are several times faster than any previously-observed infrared variability in GRS 1915+105 and the IR variations exceed corresponding X-ray variations at the same ($\sim 8s$) timescale. These results suggest an entirely new type of infrared variability from this object. Based on the properties of this flickering, we conclude that it arises in the plateau-state jet outflow itself, at a distance $<2.5$ AU from the accretion disk. We discuss the implications of this work and the potential of further flickering observations for understanding jet formation around black holes.Comment: 19 pages, incl. 4 figures; accepted for publication in Ap

Superconducting Diamond on Silicon Nitride for Device Applications

Chemical vapour deposition (CVD) grown nanocrystalline diamond is an attractive material for the fabrication of devices. For some device architectures, optimisation of its growth on silicon nitride is essential. Here, the effects of three pre-growth surface treatments, often employed as cleaning methods of silicon nitride, were investigated. Such treatments provide control over the surface charge of the substrate through modification of the surface functionality, allowing for the optimisation of electrostatic diamond seeding densities. Zeta potential measurements and X-ray photoelectron spectroscopy (XPS) were used to analyse the silicon nitride surface following each treatment. Exposing silicon nitride to an oxygen plasma offered optimal surface conditions for the electrostatic self-assembly of a hydrogen-terminated diamond nanoparticle monolayer. The subsequent growth of boron-doped nanocrystalline diamond thin films on modified silicon nitride substrates under CVD conditions produced coalesced films for oxygen plasma and solvent treatments, whilst pin-holing of the diamond film was observed following RCA-1 treatment. The sharpest superconducting transition was observed for diamond grown on oxygen plasma treated silicon nitride, demonstrating it to be of the least structural disorder. Modifications to the substrate surface optimise the seeding and growth processes for the fabrication of diamond on silicon nitride devices

Testing a MultiTEP-based combination vaccine to reduce Aβ and tau pathology in Tau22/5xFAD bigenic mice.

BackgroundAlzheimer disease (AD) is characterized by the accumulation of beta-amyloid (Aβ) plaques and neurofibrillary tangles composed of hyperphosphorylated tau, which together lead to neurodegeneration and cognitive decline. Current therapeutic approaches have primarily aimed to reduce pathological aggregates of either Aβ or tau, yet phase 3 clinical trials of these approaches have thus far failed to delay disease progression in humans. Strong preclinical evidence indicates that these two abnormally aggregated proteins interact synergistically to drive downstream neurodegeneration. Therefore, combinatorial therapies that concurrently target both Aβ and tau might be needed for effective disease modification.MethodsA combinatorial vaccination approach was designed to concurrently target both Aβ and tau pathologies. Tau22/5xFAD (T5x) bigenic mice that develop both pathological Aβ and tau aggregates were injected intramuscularly with a mixture of two MultiTEP epitope vaccines: AV-1959R and AV-1980R, targeting Aβ and tau, respectively, and formulated in AdvaxCpG, a potent polysaccharide adjuvant. Antibody responses of vaccinated animals were measured by ELISA, and neuropathological changes were determined in brain homogenates of vaccinated and control mice using ELISA and Meso Scale Discovery (MSD) multiplex assays.ResultsT5x mice immunized with a mixture of Aβ- and tau-targeting vaccines generated high Aβ- and tau-specific antibody titers that recognized senile plaques and neurofibrillary tangles/neuropil threads in human AD brain sections. Production of these antibodies in turn led to significant reductions in the levels of soluble and insoluble total tau, and hyperphosphorylated tau as well as insoluble Aβ42, within the brains of bigenic T5x mice.ConclusionsAV-1959R and AV-1980R formulated with AdvaxCpG adjuvant are immunogenic and therapeutically potent vaccines that in combination can effectively reduce both of the hallmark pathologies of AD in bigenic mice. Taken together, these findings warrant further development of this vaccine technology for ultimate testing in human AD

Using conceptual metaphor and functional grammar to explore how language used in physics affects student learning

This paper introduces a theory about the role of language in learning physics. The theory is developed in the context of physics students' and physicists' talking and writing about the subject of quantum mechanics. We found that physicists' language encodes different varieties of analogical models through the use of grammar and conceptual metaphor. We hypothesize that students categorize concepts into ontological categories based on the grammatical structure of physicists' language. We also hypothesize that students over-extend and misapply conceptual metaphors in physicists' speech and writing. Using our theory, we will show how, in some cases, we can explain student difficulties in quantum mechanics as difficulties with language.Comment: Accepted for publication in Phys. Rev. ST:PE

Process evaluation of a school-based high-intensity interval training program for older adolescents : the Burn 2 Learn cluster randomised controlled trial

Process evaluations can help to optimise the implementation of school-based physical activity interventions. The purpose of this paper is to describe the process evaluation of a school-based high-intensity interval training (HIIT) program for older adolescent students, known as Burn 2 Learn (B2L). B2L was evaluated via a cluster randomised controlled trial in 20 secondary schools (10 intervention, 10 control) in New South Wales, Australia. Teachers (n = 22 (55% female)) from the 10 intervention schools, delivered the program over three phases (Phases 1 and 2, 6 months; Phase 3, 6 months) to older adolescent students (n = 337 (50% female); mean ± standard deviation (SD) age = 16.0 ± 0.4 years). Process evaluation data were collected across the 12-month study period. Teachers delivered 2.0 ± 0.8 and 1.7 ± 0.6 sessions/week in Phases 1 and 2 respectively (mean total 25.9 ± 5.2), but only 0.6 ± 0.7 sessions/week in Phase 3. Observational data showed that session quality was high, however heart rate (HR) data indicated that only half of the students reached the prescribed threshold of ≥85% predicted HRmax during sessions. Over 80% of teachers reported they intended to deliver the B2L program to future student cohorts. Almost 70% of students indicated they intended to participate in HIIT in the future. Teachers considered the program to be adaptable, and both students and teachers were satisfied with the intervention. B2L was implemented with moderate-to-high fidelity in Phases 1 and 2, but low in Phase 3. Our findings add to the relatively scant process evaluation literature focused on the delivery of school-based physical activity programs

Mapping the Magnetic Field of Flare Coronal Loops

Here we report on the unique observation of flaring coronal loops at the solar limb using high resolution imaging spectropolarimetry from the Swedish 1-meter Solar Telescope. The vantage position, orientation and nature of the chromospheric material that filled the flare loops allowed us to determine their magnetic field with unprecedented accuracy using the weak-field approximation method. Our analysis reveals coronal magnetic field strengths as high as 350 Gauss at heights up to 25 Mm above the solar limb. These measurements are substantially higher than a number of previous estimates and may have considerable implications for our current understanding of the extended solar atmosphere.Comment: 12 pages, 14 figures, accepted in Ap

The Spectra of T Dwarfs I: Near-Infrared Data and Spectral Classification

We present near-infrared spectra for a sample of T dwarfs, including eleven new discoveries made using the Two Micron All Sky Survey. These objects are distinguished from warmer (L-type) brown dwarfs by the presence of methane absorption bands in the 1--2.5 \micron spectral region. A first attempt at a near-infrared classification scheme for T dwarfs is made, based on the strengths of CH$_4$ and H$_2$O bands and the shapes of the 1.25, 1.6, and 2.1 \micron flux peaks. Subtypes T1 V through T8 V are defined, and spectral indices useful for classification are presented. The subclasses appear to follow a decreasing T$_{eff}$ scale, based on the evolution of CH$_4$ and H$_2$O bands and the properties of L and T dwarfs with known distances. However, we speculate that this scale is not linear with spectral type for cool dwarfs, due to the settling of dust layers below the photosphere and subsequent rapid evolution of spectral morphology around T$_{eff}$ $\sim$ 1300--1500 K. Similarities in near-infrared colors and continuity of spectral features suggest that the gap between the latest L dwarfs and earliest T dwarfs has been nearly bridged. This argument is strengthened by the possible role of CH$_4$ as a minor absorber shaping the K-band spectra of the latest L dwarfs. Finally, we discuss one peculiar T dwarf, 2MASS 0937+2931, which has very blue near-infrared colors (J-K$_s$ = $-0.89\pm$0.24) due to suppression of the 2.1 \micron peak. The feature is likely caused by enhanced collision-induced H$_2$ absorption in a high pressure or low metallicity photosphere.Comment: 74 pages including 26 figures, accepted by ApJ v563 December 2001; full paper including all of Table 3 may be downloaded from http://www.gps.caltech.edu/~pa/adam/classification ;also see submission 010844

Rationalization of the X-ray photoelectron spectroscopy of aluminium phosphates synthesized from different precursors

The aim of this paper is to clarify the assignments of X-ray photoelectron spectra of aluminium phosphate materials prepared from the reaction of phosphoric acid with three different aluminium precursors [Al(OH)3, Al(NO3)3 and AlCl3] at different annealing temperatures. The materials prepared have been studied by X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (XRD), infrared spectroscopy and high-resolution solid-state 31P NMR spectroscopy. A progressive polymerization from orthophosphate to metaphosphates is observed by XRD, ATR-FTIR and solid state 31P NMR, and on this basis the oxygen states observed in the XP spectra at 532.3 eV and 533.7 eV are assigned to P–O–Al and P–O–P environments, respectively. The presence of cyclic polyphosphates at the surface of the samples is also evident