On hydrogen bond correlations at high pressures

In situ high pressure neutron diffraction measured lengths of O H and H O pairs in hydrogen bonds in substances are shown to follow the correlation between them established from 0.1 MPa data on different chemical compounds. In particular, the conclusion by Nelmes et al that their high pressure data on ice VIII differ from it is not supported. For compounds in which the O H stretching frequencies red shift under pressure, it is shown that wherever structural data is available, they follow the stretching frequency versus H O (or O O) distance correlation. For compounds displaying blue shifts with pressure an analogy appears to exist with improper hydrogen bonds.Comment: 12 pages,4 figure

Digital Health Intervention Design and Deployment for Engaging Demographic Groups Likely to Be Affected by the Digital Divide: Protocol for a Systematic Scoping Review

Background: Digital health interventions (DHIs) refer to interventions designed to support health-related knowledge transfer and delivered via digital technologies, such as mobile applications (apps). DHIs are a double-edged sword: they have the potential to reduce health inequalities, for example by making treatments available remotely to rural populations underserved by healthcare facilities or by helping to overcome language barriers via in-app translation services. However, if not designed and deployed with care, DHIs also have the potential to increase health inequalities and exacerbate effects of the digital divide. / Objective: The objective of this study was to review ways to mitigate the digital divide through DHI design, deployment and engagement mechanisms sensitive to the needs of digitally-excluded populations. / Methods: This protocol outlines the procedure for a systematic scoping review focussing on features of DHI design and deployment that enable or hinder access to and engagement with DHIs by people from demographic groups likely to be affected by the digital divide. / Results: The review is underway and is anticipated to be completed by the end of September 2021. / Conclusions: The results will have wider implications for researchers and policy makers using DHIs for health improvement peri-pandemic and post-pandemic and will inform best practices in the design and delivery of DHIs. Clinical Trial: A summary of the protocol and any supplementary material will be registered with the Open Science Framework (OSF) and assigned a Digital Object Identifier (DOI) for long-term retrieval

A visualisation tool to analyse usage of web-based interventions: The example of Positive Online Weight Reduction (POWeR)

Background: Attrition is a significant problem in web-based interventions. Consequently, research aims to identify the relation between web usage and benefit from such interventions. We have developed a visualisation tool that enables researchers to more easily examine large data sets on intervention usage that can be difficult to make sense of using traditional descriptive or statistical techniques alone. Objectives: This paper demonstrates how the visualisation tool was used to explore patterns in participants’ use of a web-based weight management intervention (POWeR: Positive Online Weight Reduction). We also demonstrate how the visualisation tool can be used to inform subsequent statistical analyses of the association between usage patterns, participant characteristics, and intervention outcome. Methods: The visualisation tool was used to analyse data from 132 participants who had accessed at least one session of the POWeR intervention. Results: There was a drop in usage of optional sessions after participants had accessed the initial, core POWeR sessions, but many users nevertheless continued to complete goal and weight review. POWeR tools relating to the food diary and steps diary were re-used most often. Differences in participant characteristics and usage of other intervention components were identified between participants who did and did not choose to access optional POWeR sessions (in addition to the initial core sessions) or re-use the food and steps diary. Re-use of the steps diary and the getting support tools was associated with greater weight loss. Conclusions: The visualisation tool provided a quick and efficient method for exploring patterns of web usage, which enabled further analyses of whether different usage patterns were associated with participant characteristics or differences in intervention outcome. Further usage of visualisation techniques is recommended in order to 1) make sense of large data sets more quickly and efficiently, 2) determine the likely active ingredients in web-based interventions, and thereby enhance the benefit they may provide and 3) inform (re-)design of future interventions to promote greater use and engagement by enabling users to easily access valued intervention content/tools

Observations of TeV gamma rays from Markarian 501 at large zenith angles

TeV gamma rays from the blazar Markarian 501 have been detected with the University of Durham Mark 6 atmospheric Cerenkov telescope using the imaging technique at large zenith angles. Observations were made at zenith angles in the range 70 - 73 deg during 1997 July and August when Markarian 501 was undergoing a prolonged and strong flare.Comment: 7 pages, 2 figures, accepted for publication in J. Phys. G.: Nucl. Part. Phy

Evidence for Intergalactic Absorption in the TeV Gamma-Ray Spectrum of Mkn 501

The recent HEGRA observations of the blazar Mkn 501 show strong curvature in the very high energy gamma-ray spectrum. Applying the gamma-ray opacity derived from an empirically based model of the intergalactic infrared background radiation field (IIRF), to these observations, we find that the intrinsic spectrum of this source is consistent with a power-law: dN/dE~ E^-alpha with alpha=2.00 +/- 0.03 over the range 500 GeV - 20 TeV. Within current synchrotron self-Compton scenarios, the fact that the TeV spectral energy distribution of Mkn 501 does not vary with luminosity, combined with the correlated, spectrally variable emission in X-rays, as observed by the BeppoSAX and RXTE instruments, also independently implies that the intrinsic spectrum must be close to alpha=2. Thus, the observed curvature in the spectrum is most easily understood as resulting from intergalactic absorption.Comment: 7 pages, 1 figure, accepted in ApJ Letters 1999 April

Multiwavelength Observations of a Flare from Markarian 501

We present multiwavelength observations of the BL Lacertae object Markarian 501 (Mrk 501) in 1997 between April 8 and April 19. Evidence of correlated variability is seen in very high energy (VHE, E > 350 GeV) gamma-ray observations taken with the Whipple Observatory gamma-ray telescope, data from the Oriented Scintillation Spectrometer Experiment of the Compton Gamma-Ray Observatory, and quicklook results from the All-Sky Monitor of the Rossi X-ray Timing Explorer while the Energetic Gamma-Ray Experiment Telescope did not detect Mrk 501. Short term optical correlations are not conclusive but the U-band flux observed with the 1.2m telescope of the Whipple Observatory was 10% higher than in March. The average energy output of Mrk 501 appears to peak in the 2 keV to 100 keV range suggesting an extension of the synchrotron emission to at least 100 keV, the highest observed in a blazar and ~100 times higher than that seen in the other TeV-emitting BL Lac object, Mrk 421. The VHE gamma-ray flux observed during this period is the highest ever detected from this object. The VHE gamma-ray energy output is somewhat lower than the 2-100 keV range but the variability amplitude is larger. The correlations seen here do not require relativistic beaming of the emission unless the VHE spectrum extends to >5 TeV.Comment: 10 pages, 2 figures, accepted for publication in ApJ Letter

High Energy Neutrinos from Astrophysical Sources: An Upper Bound

We show that cosmic-ray observations set a model-independent upper bound to the flux of high-energy, > 10^14 eV, neutrinos produced by photo-meson (or p-p) interactions in sources of size not much larger than the proton photo-meson (or pp) mean-free-path. The bound applies, in particular, to neutrino production by either AGN jets or GRBs. This upper limit is two orders of magnitude below the flux predicted in some popular AGN jet models, but is consistent with our predictions from GRB models. We discuss the implications of these results for future km^2 high-energy neutrino detectors.Comment: Added discussion showing bound cannot be evaded by invoking magnetic fields. Accepted Phys Rev

Muddled Boundaries of Digital Shrines

International audienceBased on an online ethnography study of 274 YouTube videos posted during the Virginia Tech or the Newtown massacres, this article discusses how users resort to participatory media during such mediatized events to create a digital spontaneous shrine. The assemblage of this sanctuary on a website hosting billions of user-generated contents is made possible by means of folksonomy and website architecture, and a two-fold social dynamic based on participatory commitment and the institutionalization of a collective entity. Unlike “physical” spontaneous shrines erected in public spaces, these digital shrines connect the bereaved with provocative or outrageous contributions, notably tributes from school shooting fans using participatory media to commemorate the killer’s memory. This side effect, generated by the technical properties of the platform, compromises the tranquility of the memorial and muddles the boundaries and the contents of such sanctuaries

VSOP and Ground-based VLBI Imaging of the TeV Blazar Markarian 421 at Multiple Epochs

We present thirty VLBI images of the TeV blazar Markarian 421 (1101+384) at fifteen epochs spanning the time range from 1994 to 1997, and at six different frequencies from 2.3 to 43 GHz. The imaged observations include a high-resolution 5 GHz VLBI Space Observatory Programme (VSOP) observation with the HALCA satellite on 1997 November 14; full-track VLBA observations from 1994 April, 1996 November, and 1997 May at frequencies between 5 and 43 GHz; six epochs of VLBA snapshot observations at frequencies between 2 and 15 GHz from Radio Reference Frame studies; and five geodetic VLBI observations at 2 and 8 GHz from the archive of the Washington VLBI Correlator Facility located at the U.S. Naval Observatory. The dense time coverage of the images allows us to unambiguously track components in the parsec-scale jet over the observed time range. We measure the speeds of three inner jet components located between 0.5 and 5 mas from the core (0.3 to 3 pc projected linear distance) to be 0.19 +/- 0.27, 0.30 +/- 0.07, and -0.07 +/- 0.07 c (H_{0}=65 km s^{-1} Mpc^{-1}). If the sole 43 GHz image is excluded, all measured speeds are consistent with no motion. These speeds differ from tentative superluminal speeds measured by Zhang & B\aa\aa th from three epochs of data from the early 1980's. Possible interpretations of these subluminal speeds in terms of the high Doppler factor demanded by the TeV variability of this source are discussed.Comment: 18 pages, including 7 figures, emulateapj.sty, accepted by The Astrophysical Journal; modified text describing Radio Reference Frame observation