Postirradiation behavior of p-channel charge-coupled devices irradiated at 153 K

The displacement damage hardness that can be achieved using p-channel charge-coupled devices (CCD) was originally demonstrated in 1997, and since then a number of other studies have demonstrated an improved tolerance to radiation-induced CTI when compared to n-channel CCDs. A number of recent studies have also shown that the temperature history of the device after the irradiation impacts the performance of the detector, linked to the mobility of defects at different temperatures. This study describes the initial results from an e2v technologies p-channel CCD204 irradiated at 153 K with a 10 MeV equivalent proton fluences of 1.24×109 and 1.24×1011 protons cm-2. The dark current, cosmetic quality and the number of defects identified using trap pumping immediately were monitored after the irradiation for a period of 150 hours with the device held at 153 K and then after different periods of time at room temperature. The device also exhibited a flatband voltage shift of around 30 mV / krad, determined by the reduction in full well capacity

Evolution and impact of defects in a p-channel CCD after cryogenic proton-irradiation

P-channel CCDs have been shown to display improved tolerance to radiation-induced charge transfer inefficiency (CTI) when compared to n-channel CCDs. However, the defect distribution formed during irradiation is expected to be temperature dependent due to the differences in lattice energy caused by a temperature change. This has been tested through defect analysis of two p-channel e2v CCD204 devices, one irradiated at room temperature and one at a cryogenic temperature (153K). Analysis is performed using the method of single trap pumping. The dominant charge trapping defects at these conditions have been identified as the donor level of the silicon divacancy and the carbon interstitial defect. The defect parameters are analysed both immediately post irradiation and following several subsequent room-temperature anneal phases up until a cumulative anneal time of approximately 10 months. We have also simulated charge transfer in an irradiated CCD pixel using the defect distribution from both the room-temperature and cryogenic case, to study how the changes affect imaging performance. The results demonstrate the importance of cryogenic irradiation and annealing studies, with large variations seen in the defect distribution when compared to a device irradiated at room-temperature, which is the current standard procedure for radiation-tolerance testing

hivstigma.com, an innovative web-supported stigma-reduction intervention for gay and bisexual men

An intervention to address stigma directed toward HIV-positive men and to enhance the sexual health of gay and bisexual men was developed through a community-based process involving HIV prevention workers, public health, government, and researchers. The intervention aimed to diminish stigma, create greater support for HIV-positive men, make disclosure safer and easier, discourage reliance on disclosure to prevent transmission, and encourage testing. The question, “If you were rejected every time you disclosed, would you?” was widely disseminated in the gay community and supported by the website, hivstigma.com, to encourage participation in blog-based discussions. Eight bloggers moderated lively discussions over 5 months. There were 20,844 unique visitors to the site averaging more than 5 minutes each; 4,384 visitors returned more than 10 times. 1,942 men answered a pre-test survey on a popular gay dating site and 1,791, a post-test evaluation. Results show a statistically significant shift among those aware of the intervention toward reduced stigma-related attitudes and behaviors, and toward recognition that HIV positive gay men face stigma in the gay community and that stigma reduces the likelihood of HIV disclosure

Comparing simulations and test data of a radiation damaged charge-coupled device for the Euclid mission

The visible imager instrument on board the Euclid mission is a weak-lensing experiment that depends on very precise shape measurements of distant galaxies obtained by a large charge-coupled device (CCD) array. Due to the harsh radiative environment outside the Earth’s atmosphere, it is anticipated that the CCDs over the mission lifetime will be degraded to an extent that these measurements will be possible only through the correction of radiation damage effects. We have therefore created a Monte Carlo model that simulates the physical processes taking place when transferring signals through a radiation-damaged CCD. The software is based on Shockley–Read–Hall theory and is made to mimic the physical properties in the CCD as closely as possible. The code runs on a single electrode level and takes the three-dimensional trap position, potential structure of the pixel, and multilevel clocking into account. A key element of the model is that it also takes device specific simulations of electron density as a direct input, thereby avoiding making any analytical assumptions about the size and density of the charge cloud. This paper illustrates how test data and simulated data can be compared in order to further our understanding of the positions and properties of the individual radiation-induced traps

Determination of <i>in situ</i> trap properties in CCDs using a "single-trap pumping" technique

The science goals of space missions from the Hubble Space Telescope through to Gaia and Euclid require ultraprecise positional, photometric, and shape measurement information. However, in the radiation environment of the space telescopes, damage to the focal plane detectors through high-energy protons leads to the creation of traps, a loss of charge transfer efficiency, and a consequent deterioration in measurement accuracy. An understanding of the traps produced and their properties in the CCD during operation is essential to allow optimization of the devices and suitable modeling to correct the effect of the damage through the postprocessing of images. The technique of “pumping single traps” has allowed the study of individual traps in high detail that cannot be achieved with other techniques, such as deep level transient spectroscopy, whilst also locating each trap to the subpixel level in the device. Outlining the principles used, we have demonstrated the technique for the A-center, the most influential trap in serial readout, giving results consistent with the more general theoretical values, but here showing new results indicating the spread in the emission times achieved and the variation in capture probability of individual traps with increasing signal levels. This technique can now be applied to other time and temperature regimes in the CCD to characterize individual traps in situ under standard operating conditions such that dramatic improvements can be made to optimization processes and modeling techniques

Cost-Effectiveness of Disease-Modifying Therapies in the Management of Multiple Sclerosis for the Medicare Population

AbstractObjectiveTo evaluate the cost-effectiveness of disease-modifying therapies (DMTs) for the management of multiple sclerosis (MS) compared to best supportive care in the United States.MethodsCost-effectiveness analysis was undertaken using a state transition model of disease natural history and the impact of DMTs for the representative Medicare beneficiary with MS. Costs and outcomes were evaluated from the health-care payer perspective using a 50-year time horizon. Natural history data were drawn from a longitudinal cohort study. The effectiveness of the DMTs was evaluated through a systematic review. Utility data were taken from a study of patients with clinically definite MS in Nova Scotia. Resource use and cost data were derived from the Sonya Slifka database and associated literature.ResultsWhen based on placebo-controlled evidence, the marginal cost-effectiveness of interferon beta (IFNβ) and glatiramer acetate compared to best supportive care is expected to be in excess of $100,000 per quality-adjusted life-year gained. When evidence from head-to-head trials is incorporated into the model, the cost-effectiveness of 6 MIU IFNβ-1a is expected to be considerably less favorable. Treatment discontinuation upon progression to Expanded Disability Status Scale 7.0 is expected to improve the cost-effectiveness of all DMTs.ConclusionsFurther research is required to examine the long-term clinical effectiveness and cost-effectiveness of these therapies. There is no definitive guidance in the United States concerning discontinuation of DMTs; this study suggests that the prudent use of a treatment discontinuation rule may considerably improve the cost-effectiveness of DMTs

Assessment of the performance and radiation damage effects under cryogenic temperatures of a P-channel CCD204s

CCDs continue to be the detector of choice for high resolution and high performance space applications. One perceived drawback is their susceptibility to radiation damage, in particular the formation of trap sites leading to a decrease in charge transfer efficiency. To that end, ESA has started a programme to investigate a new generation of devices based upon p-channel technology. The expectation is that once mature, p-channel devices may offer a significant increase in tolerance to proton radiation over traditional n-type buried channel CCDs. Early studies of e2v devices to assess the radiation hardness of p-channel devices were limited by the quality of devices available, however more recently, good quality p-channel CCD204s have been manufactured and studied. A more detailed evaluation of p-channel CCDs is now underway to realise the full potential of the technology for use in future high radiation environment space missions. A key aspect is the development of a cryogenic test rig that will allow for the first time a direct comparison of the radiation damage effects when the irradiation is performed both traditionally unbiased at room temperature and cryogenically with the device operational. Subsequent characterisations will also be performed on the cryogenic device after periods of storage at room temperature to investigate the potential annealing effects upon the lattice damage. Here we describe and present early results from an extensive programme of testing which will address all key performance parameters for p-channel CCDs, such as full electro-optical characterisation, assessment of radiation hardness and investigation of trap species

Diagramming social practice theory:An interdisciplinary experiment exploring practices as networks

Achieving a transition to a low-carbon energy system is now widely recognised as a key challenge facing humanity. To date, the vast majority of research addressing this challenge has been conducted within the disciplines of science, engineering and economics utilising quantitative and modelling techniques. However, there is growing awareness that meeting energy challenges requires fundamentally socio-technical solutions and that the social sciences have an important role to play. This is an interdisciplinary challenge but, to date, there remain very few explorations of, or reflections on, interdisciplinary energy research in practice. This paper seeks to change that by reporting on an interdisciplinary experiment to build new models of energy demand on the basis of cutting-edge social science understandings. The process encouraged the social scientists to communicate their ideas more simply, whilst allowing engineers to think critically about the embedded assumptions in their models in relation to society and social change. To do this, the paper uses a particular set of theoretical approaches to energy use behaviour known collectively as social practice theory (SPT) - and explores the potential of more quantitative forms of network analysis to provide a formal framework by means of which to diagram and visualize practices. The aim of this is to gain insight into the relationships between the elements of a practice, so increasing the ultimate understanding of how practices operate. Graphs of practice networks are populated based on new empirical data drawn from a survey of different types (or variants) of laundry practice. The resulting practice networks are analysed to reveal characteristics of elements and variants of practice, such as which elements could be considered core to the practice, or how elements between variants overlap, or can be shared. This promises insights into energy intensity, flexibility and the rootedness of practices (i.e. how entrenched/ established they are) and so opens up new questions and possibilities for intervention. The novelty of this approach is that it allows practice data to be represented graphically using a quantitative format without being overly reductive. Its usefulness is that it is readily applied to large datasets, provides the capacity to interpret social practices in new ways, and serves to open up potential links with energy modeling. More broadly, a significant dimension of novelty has been the interdisciplinary approach, radically different to that normally seen in energy research. This paper is relevant to a broad audience of social scientists and engineers interested in integrating social practices with energy engineering

Multi-level parallel clocking of CCDs for: improving charge transfer efficiency, clearing persistence, clocked anti-blooming, and generating low-noise backgrounds for pumping

A multi-level clocking scheme has been developed to improve the parallel CTE of four-phase CCDs by suppressing the effects of traps located in the transport channel under barrier phases by inverting one of these phases throughout the transfer sequence. In parallel it was apparent that persistence following optical overload in Euclid VIS detectors would lead to undesirable signal released in subsequent rows and frames and that a suitable scheme for flushing this signal would be required. With care, the negatively biased electrodes during the multi-level transfer sequence can be made to pin the entire surface, row-by-row, and annihilate the problematic charges. This process can also be extended for use during integration to significantly reduce the unusable area of the detector, as per the clocked anti-blooming techniques developed many years ago; however, with the four-phase electrodes architecture of modern CCDs, we can take precautionary measures to avoid the problem of charge pumping and clock induced charge within the science frames. Clock induced charge is not all bad! We also propose the use of on-orbit trap-pumping for Euclid VIS to provide calibration input to ground based correction algorithms and as such a uniform, low noise background is require. Clock induced charge can be manipulated to provide a very suitable, low signal and noise background to the imaging array. Here we describe and present results of multi-level parallel clocking schemes for use in four-phase CCDs that could improve performance of high precision astronomy applications such as Euclid VIS