Technology development for 4k x 4k, back-illuminated, fully depleted scientific CCD imagers

Journal ArticleWe have developed scientific charge-coupled devices (CCDs) that are fabricated on high-resistivity, n-type silicon substrates, and have demonstrated fully depleted operation for substrate thicknesses of 200-675 μm with formats as large as 2048 × 4096 (15 μm pixels) and 3512 × 3512 (10.5 μm pixels). The main application area for these devices is space and ground-based astronomy, and the CCDs are operated at cryogenic temperatures with slow-scan readout for good performance in terms of dark current and noise. In this work we describe the technology development efforts needed to realize a 4k × 4k (15 μm pixel) CCD with a die area of (64 mm)2. In particular, we describe improved gettering techniques for low dark current and high charge transfer efficiency that have been developed in order to improve fabrication yields for these very large format CCDs

High-voltage-compatible fully depleted CCDs

Journal ArticleWe describe charge-coupled device (CCD) development activities at the Lawrence Berkeley National Laboratory (LBNL). Back-illuminated CCDs fabricated on 200-300 fxm thick, fully depleted, high-resistivity silicon substrates are produced in partnership with a commercial CCD foundry. The CCDs are fully depleted by the application of a substrate bias voltage. Spatial resolution considerations require operation of thick, fully depleted CCDs at high substrate bias voltages. We have developed CCDs that are compatible with substrate bias voltages of at least 200V. This improves spatial resolution for a given thickness, and allows for full depletion of thicker CCDs than previously considered. We have demonstrated full depletion of 650-675 iim thick CCDs, with potential applications in direct x-ray detection. In this work we discuss the issues related to high-voltage operation of fully depleted CCDs, as well as experimental results on high-voltage-compatible CCDs

The effects of charge transfer inefficiency (CTI) on galaxy shape measurements

(Abridged) We examine the effects of charge transfer inefficiency (CTI) during CCD readout on galaxy shape measurements required by studies of weak gravitational lensing. We simulate a CCD readout with CTI such as that caused by charged particle radiation damage. We verify our simulations on data from laboratory-irradiated CCDs. Only charge traps with time constants of the same order as the time between row transfers during readout affect galaxy shape measurements. We characterize the effects of CTI on various galaxy populations. We baseline our study around p-channel CCDs that have been shown to have charge transfer efficiency up to an order of magnitude better than several models of n-channel CCDs designed for space applications. We predict that for galaxies furthest from the readout registers, bias in the measurement of galaxy shapes, Delta(e), will increase at a rate of 2.65 +/- 0.02 x 10^(-4) per year at L2 for accumulated radiation exposure averaged over the solar cycle. If uncorrected, this will consume the entire shape measurement error budget of a dark energy mission within about 4 years. Software mitigation techniques demonstrated elsewhere can reduce this by a factor of ~10, bringing the effect well below mission requirements. CCDs with higher CTI than the ones we studeied may not meet the requirements of future dark energy missions. We discuss ways in which hardware could be designed to further minimize the impact of CTI.Comment: 11 pages, 6 figures, and 2 tables. Accepted for publication in PAS

Radiation Tolerance of Fully-Depleted P-Channel CCDs Designed for the SNAP Satellite

Thick, fully depleted p-channel charge-coupled devices (CCDs) have been developed at the Lawrence Berkeley National Laboratory (LBNL). These CCDs have several advantages over conventional thin, n-channel CCDs, including enhanced quantum efficiency and reduced fringing at near-infrared wavelengths and improved radiation tolerance. Here we report results from the irradiation of CCDs with 12.5 and 55 MeV protons at the LBNL 88-Inch Cyclotron and with 0.1-1 MeV electrons at the LBNL Co60 source. These studies indicate that the LBNL CCDs perform well after irradiation, even in the parameters in which significant degradation is observed in other CCDs: charge transfer efficiency, dark current, and isolated hot pixels. Modeling the radiation exposure over a six-year mission lifetime with no annealing, we expect an increase in dark current of 20 e/pixel/hr, and a degradation of charge transfer efficiency in the parallel direction of 3e-6 and 1e-6 in the serial direction. The dark current is observed to improve with an annealing cycle, while the parallel CTE is relatively unaffected and the serial CTE is somewhat degraded. As expected, the radiation tolerance of the p-channel LBNL CCDs is significantly improved over the conventional n-channel CCDs that are currently employed in space-based telescopes such as the Hubble Space Telescope.Comment: 11 pages, 10 figures, submitted to IEEE Transaction

Using an unmanned aerial vehicle to evaluate nitrogen variability and height effect with an active crop canopy sensor

Ground-based active sensors have been used in the past with success in detecting nitrogen (N) variability within maize production systems. The use of unmanned aerial vehicles (UAVs) presents an opportunity to evaluate N variability with unique advantages compared to ground-based systems. The objectives of this study were to: determine if a UAV was a suitable platform for use with an active crop canopy sensor to monitor in-season N status of maize, if UAV’s were a suitable platform, is the UAV and active sensor platform a suitable substitute for current handheld methods, and is there a height effect that may be confounding measurements of N status over crop canopies? In a 2013 study comparing aerial and ground-based sensor platforms, there was no difference in the ability of aerial and ground-based active sensors to detect N rate effects on a maize crop canopy. In a 2014 study, an active sensor mounted on a UAV was able to detect differences in crop canopy N status similarly to a handheld active sensor. The UAV/active sensor system (AerialActive) platform used in this study detected N rate differences in crop canopy N status within a range of 0.5–1.5 m above a relatively uniform turfgrass canopy. The height effect for an active sensor above a crop canopy is sensor- and crop-specific, which needs to be taken into account when implementing such a system. Unmanned aerial vehicles equipped with active crop canopy sensors provide potential for automated data collection to quantify crop stress in addition to passive sensors currently in use

A predictive analytics model for differentiating between transient ischemic attacks (TIA) and its mimics

Transient ischemic attack (TIA) is a brief episode of neurological dysfunction resulting from cerebral ischemia not associated with permanent cerebral infarction. TIA is associated with high diagnostic errors because of the subjective nature of findings and the lack of clinical and imaging biomarkers. The goal of this study was to design and evaluate a novel multinomial classification model, based on a combination of feature selection mechanisms coupled with logistic regression, to predict the likelihood of TIA, TIA mimics, and minor stroke

Overexpression of Large-Conductance Calcium-Activated Potassium Channels in Human Glioblastoma Stem-Like Cells and Their Role in Cell Migration

Glioblastomas (GBMs) are brain tumors characterized by diffuse invasion of cancer cells into the healthy brain parenchyma, and establishment of secondary foci. GBM cells abundantly express large-conductance, calcium-activated potassium (BK) channels that are thought to promote cell invasion. Recent evidence suggests that the GBM high invasive potential mainly originates from a pool of stem-like cells, but the expression and function of BK channels in this cell subpopulation have not been studied. We investigated the expression of BK channels in GBM stem-like cells using electrophysiological and immunochemical techniques, and assessed their involvement in the migratory process of this important cell subpopulation. In U87-MG cells, BK channel expression and function were markedly upregulated by growth conditions that enriched the culture in GBM stem-like cells (U87-NS). Cytofluorimetric analysis further confirmed the appearance of a cell subpopulation that co-expressed high levels of BK channels and CD133, as well as other stem cell markers. A similar association was also found in cells derived from freshly resected GBM biopsies. Finally, transwell migration tests showed that U87-NS cells migration was much more sensitive to BK channel block than U87-MG cells. Our data show that BK channels are highly expressed in GBM stem-like cells, and participate to their high migratory activity. This article is protected by copyright. All rights reserved

Report of the 2016-2017 Student Affairs Standing Committee

The 2016-2017 AACP Student Affairs Standing Committee addressed charges related to recruitment to the profession of pharmacy and a national awareness campaign for pharmacy careers, as well as promotion of student wellness and stress management. The Committee report provides six recommendations to the American Association of Colleges of Pharmacy (AACP) and one proposed policy statement for the AACP House of Delegates related to recruitment to the pharmacy profession. The Committee report also provides three recommendations to AACP and one proposed policy statement for the AACP House of Delegates related to student wellness and stress management. In addition, this report provides recommendations for future AACP Student Affairs Standing Committee work