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Chapter 4 - Contribution of RADx® Tech to the Rapid Development of COVID-19 Diagnostic Tests
- Edited by Steven C. Schachter, Harvard Medical School, Wade E. Bolton, VentureWell/Rapid Acceleration of Diagnostics (RADx)
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- Accelerating Diagnostics in a Time of Crisis
- Published online:
- 06 January 2024
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- 07 March 2024, pp 74-87
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Summary
Rapid Acceleration of Diagnostics (RADx®) Tech was the key diagnostics component of a three-pronged national strategy, including vaccines and therapeutics, to respond to the COVID-19 pandemic. Unprecedented in the scale of its mission, its budget, its accelerated time frame, the extent of cross-government agency collaboration and information exchange, and the blending of business, academic, and investment best practices, RAD Tech successfully launched dozens of US Food and Drug Administration Emergency Use Authorization diagnostic tests, established a new model for rapidly translating diagnostic tests from the laboratory to the marketplace, and accelerated public acceptance of home-based diagnostic tests. This chapter provides an overview of the processes utilized by RADx Tech during the COVID-19 pandemic to improve clinical laboratory tests and identify, evaluate, support, validate, and commercialize innovative point-of-care and home-based tests that directly detected the presence of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus.
Chapter 23 - Neurotransmitter Disorders: Disorders of GABA Metabolism and Movement Disorders
- from Section II - A Metabolism-Based Approach to Movement Disorders and Inherited Metabolic Disorders
- Edited by Darius Ebrahimi-Fakhari, Phillip L. Pearl
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- Movement Disorders and Inherited Metabolic Disorders
- Published online:
- 24 September 2020
- Print publication:
- 01 October 2020, pp 296-306
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Summary
Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain. The primary precursor of GABA is glutamate, the major excitatory neurotransmitter in the brain. Glutamate is converted into GABA via glutamate decarboxylase (GAD). GABA-transaminase (GABA-T) metabolizes GABA to succinic semialdehyde, which is rapidly metabolized to succinic acid by succinic semialdehyde dehydrogenase (SSADH) and then enters the tricarboxylic acid (TCA) cycle (Figure 23.1).
Diagnostic stewardship of C. difficile testing: a quasi-experimental antimicrobial stewardship study
- Alyssa B. Christensen, Viktorija O. Barr, David W. Martin, Morgan M. Anderson, Amanda K. Gibson, Brian M. Hoff, Sarah H. Sutton, Valerie Widmaier, Asra A. Salim, Christina Silkaitis, Chao Qi, Teresa R. Zembower, Michael J. Postelnick, Nathaniel J. Rhodes
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- Journal:
- Infection Control & Hospital Epidemiology / Volume 40 / Issue 3 / March 2019
- Published online by Cambridge University Press:
- 21 February 2019, pp. 269-275
- Print publication:
- March 2019
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Objective:
We evaluated whether a diagnostic stewardship initiative consisting of ASP preauthorization paired with education could reduce false-positive hospital-onset (HO) Clostridioides difficile infection (CDI).
Design:Single center, quasi-experimental study.
Setting:Tertiary academic medical center in Chicago, Illinois.
Patients:Adult inpatients were included in the intervention if they were admitted between October 1, 2016, and April 30, 2018, and were eligible for C. difficile preauthorization review. Patients admitted to the stem cell transplant (SCT) unit were not included in the intervention and were therefore considered a contemporaneous noninterventional control group.
Intervention:The intervention consisted of requiring prescriber attestation that diarrhea has met CDI clinical criteria, ASP preauthorization, and verbal clinician feedback. Data were compared 33 months before and 19 months after implementation. Facility-wide HO-CDI incidence rates (IR) per 10,000 patient days (PD) and standardized infection ratios (SIR) were extracted from hospital infection prevention reports.
Results:During the entire 52 month period, the mean facility-wide HO-CDI-IR was 7.8 per 10,000 PD and the SIR was 0.9 overall. The mean ± SD HO-CDI-IR (8.5 ± 2.0 vs 6.5 ± 2.3; P < .001) and SIR (0.97 ± 0.23 vs 0.78 ± 0.26; P = .015) decreased from baseline during the intervention. Segmented regression models identified significant decreases in HO-CDI-IR (Pstep = .06; Ptrend = .008) and SIR (Pstep = .1; Ptrend = .017) trends concurrent with decreases in oral vancomycin (Pstep < .001; Ptrend < .001). HO-CDI-IR within a noninterventional control unit did not change (Pstep = .125; Ptrend = .115).
Conclusions:A multidisciplinary, multifaceted intervention leveraging clinician education and feedback reduced the HO-CDI-IR and the SIR in select populations. Institutions may consider interventions like ours to reduce false-positive C. difficile NAAT tests.
Contributors
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- By Mitchell Aboulafia, Frederick Adams, Marilyn McCord Adams, Robert M. Adams, Laird Addis, James W. Allard, David Allison, William P. Alston, Karl Ameriks, C. Anthony Anderson, David Leech Anderson, Lanier Anderson, Roger Ariew, David Armstrong, Denis G. Arnold, E. J. Ashworth, Margaret Atherton, Robin Attfield, Bruce Aune, Edward Wilson Averill, Jody Azzouni, Kent Bach, Andrew Bailey, Lynne Rudder Baker, Thomas R. Baldwin, Jon Barwise, George Bealer, William Bechtel, Lawrence C. Becker, Mark A. Bedau, Ernst Behler, José A. Benardete, Ermanno Bencivenga, Jan Berg, Michael Bergmann, Robert L. Bernasconi, Sven Bernecker, Bernard Berofsky, Rod Bertolet, Charles J. Beyer, Christian Beyer, Joseph Bien, Joseph Bien, Peg Birmingham, Ivan Boh, James Bohman, Daniel Bonevac, Laurence BonJour, William J. Bouwsma, Raymond D. Bradley, Myles Brand, Richard B. Brandt, Michael E. Bratman, Stephen E. Braude, Daniel Breazeale, Angela Breitenbach, Jason Bridges, David O. Brink, Gordon G. Brittan, Justin Broackes, Dan W. Brock, Aaron Bronfman, Jeffrey E. Brower, Bartosz Brozek, Anthony Brueckner, Jeffrey Bub, Lara Buchak, Otavio Bueno, Ann E. Bumpus, Robert W. Burch, John Burgess, Arthur W. Burks, Panayot Butchvarov, Robert E. Butts, Marina Bykova, Patrick Byrne, David Carr, Noël Carroll, Edward S. Casey, Victor Caston, Victor Caston, Albert Casullo, Robert L. Causey, Alan K. L. Chan, Ruth Chang, Deen K. Chatterjee, Andrew Chignell, Roderick M. Chisholm, Kelly J. Clark, E. J. Coffman, Robin Collins, Brian P. Copenhaver, John Corcoran, John Cottingham, Roger Crisp, Frederick J. Crosson, Antonio S. Cua, Phillip D. Cummins, Martin Curd, Adam Cureton, Andrew Cutrofello, Stephen Darwall, Paul Sheldon Davies, Wayne A. Davis, Timothy Joseph Day, Claudio de Almeida, Mario De Caro, Mario De Caro, John Deigh, C. F. Delaney, Daniel C. Dennett, Michael R. DePaul, Michael Detlefsen, Daniel Trent Devereux, Philip E. Devine, John M. Dillon, Martin C. Dillon, Robert DiSalle, Mary Domski, Alan Donagan, Paul Draper, Fred Dretske, Mircea Dumitru, Wilhelm Dupré, Gerald Dworkin, John Earman, Ellery Eells, Catherine Z. Elgin, Berent Enç, Ronald P. Endicott, Edward Erwin, John Etchemendy, C. Stephen Evans, Susan L. Feagin, Solomon Feferman, Richard Feldman, Arthur Fine, Maurice A. Finocchiaro, William FitzPatrick, Richard E. Flathman, Gvozden Flego, Richard Foley, Graeme Forbes, Rainer Forst, Malcolm R. Forster, Daniel Fouke, Patrick Francken, Samuel Freeman, Elizabeth Fricker, Miranda Fricker, Michael Friedman, Michael Fuerstein, Richard A. Fumerton, Alan Gabbey, Pieranna Garavaso, Daniel Garber, Jorge L. A. Garcia, Robert K. Garcia, Don Garrett, Philip Gasper, Gerald Gaus, Berys Gaut, Bernard Gert, Roger F. Gibson, Cody Gilmore, Carl Ginet, Alan H. Goldman, Alvin I. Goldman, Alfonso Gömez-Lobo, Lenn E. Goodman, Robert M. Gordon, Stefan Gosepath, Jorge J. E. Gracia, Daniel W. Graham, George A. Graham, Peter J. Graham, Richard E. Grandy, I. Grattan-Guinness, John Greco, Philip T. Grier, Nicholas Griffin, Nicholas Griffin, David A. Griffiths, Paul J. Griffiths, Stephen R. Grimm, Charles L. Griswold, Charles B. Guignon, Pete A. Y. Gunter, Dimitri Gutas, Gary Gutting, Paul Guyer, Kwame Gyekye, Oscar A. Haac, Raul Hakli, Raul Hakli, Michael Hallett, Edward C. Halper, Jean Hampton, R. James Hankinson, K. R. Hanley, Russell Hardin, Robert M. Harnish, William Harper, David Harrah, Kevin Hart, Ali Hasan, William Hasker, John Haugeland, Roger Hausheer, William Heald, Peter Heath, Richard Heck, John F. Heil, Vincent F. Hendricks, Stephen Hetherington, Francis Heylighen, Kathleen Marie Higgins, Risto Hilpinen, Harold T. Hodes, Joshua Hoffman, Alan Holland, Robert L. Holmes, Richard Holton, Brad W. Hooker, Terence E. Horgan, Tamara Horowitz, Paul Horwich, Vittorio Hösle, Paul Hoβfeld, Daniel Howard-Snyder, Frances Howard-Snyder, Anne Hudson, Deal W. Hudson, Carl A. Huffman, David L. Hull, Patricia Huntington, Thomas Hurka, Paul Hurley, Rosalind Hursthouse, Guillermo Hurtado, Ronald E. Hustwit, Sarah Hutton, Jonathan Jenkins Ichikawa, Harry A. Ide, David Ingram, Philip J. Ivanhoe, Alfred L. Ivry, Frank Jackson, Dale Jacquette, Joseph Jedwab, Richard Jeffrey, David Alan Johnson, Edward Johnson, Mark D. Jordan, Richard Joyce, Hwa Yol Jung, Robert Hillary Kane, Tomis Kapitan, Jacquelyn Ann K. Kegley, James A. Keller, Ralph Kennedy, Sergei Khoruzhii, Jaegwon Kim, Yersu Kim, Nathan L. King, Patricia Kitcher, Peter D. Klein, E. D. Klemke, Virginia Klenk, George L. Kline, Christian Klotz, Simo Knuuttila, Joseph J. Kockelmans, Konstantin Kolenda, Sebastian Tomasz Kołodziejczyk, Isaac Kramnick, Richard Kraut, Fred Kroon, Manfred Kuehn, Steven T. Kuhn, Henry E. Kyburg, John Lachs, Jennifer Lackey, Stephen E. Lahey, Andrea Lavazza, Thomas H. Leahey, Joo Heung Lee, Keith Lehrer, Dorothy Leland, Noah M. Lemos, Ernest LePore, Sarah-Jane Leslie, Isaac Levi, Andrew Levine, Alan E. Lewis, Daniel E. Little, Shu-hsien Liu, Shu-hsien Liu, Alan K. L. Chan, Brian Loar, Lawrence B. Lombard, John Longeway, Dominic McIver Lopes, Michael J. Loux, E. J. Lowe, Steven Luper, Eugene C. Luschei, William G. Lycan, David Lyons, David Macarthur, Danielle Macbeth, Scott MacDonald, Jacob L. Mackey, Louis H. Mackey, Penelope Mackie, Edward H. Madden, Penelope Maddy, G. B. Madison, Bernd Magnus, Pekka Mäkelä, Rudolf A. Makkreel, David Manley, William E. Mann (W.E.M.), Vladimir Marchenkov, Peter Markie, Jean-Pierre Marquis, Ausonio Marras, Mike W. Martin, A. P. Martinich, William L. McBride, David McCabe, Storrs McCall, Hugh J. McCann, Robert N. McCauley, John J. McDermott, Sarah McGrath, Ralph McInerny, Daniel J. McKaughan, Thomas McKay, Michael McKinsey, Brian P. McLaughlin, Ernan McMullin, Anthonie Meijers, Jack W. Meiland, William Jason Melanson, Alfred R. Mele, Joseph R. Mendola, Christopher Menzel, Michael J. Meyer, Christian B. Miller, David W. Miller, Peter Millican, Robert N. Minor, Phillip Mitsis, James A. Montmarquet, Michael S. Moore, Tim Moore, Benjamin Morison, Donald R. Morrison, Stephen J. Morse, Paul K. Moser, Alexander P. D. Mourelatos, Ian Mueller, James Bernard Murphy, Mark C. Murphy, Steven Nadler, Jan Narveson, Alan Nelson, Jerome Neu, Samuel Newlands, Kai Nielsen, Ilkka Niiniluoto, Carlos G. Noreña, Calvin G. Normore, David Fate Norton, Nikolaj Nottelmann, Donald Nute, David S. Oderberg, Steve Odin, Michael O’Rourke, Willard G. Oxtoby, Heinz Paetzold, George S. Pappas, Anthony J. Parel, Lydia Patton, R. P. Peerenboom, Francis Jeffry Pelletier, Adriaan T. Peperzak, Derk Pereboom, Jaroslav Peregrin, Glen Pettigrove, Philip Pettit, Edmund L. Pincoffs, Andrew Pinsent, Robert B. Pippin, Alvin Plantinga, Louis P. Pojman, Richard H. Popkin, John F. Post, Carl J. Posy, William J. Prior, Richard Purtill, Michael Quante, Philip L. Quinn, Philip L. Quinn, Elizabeth S. Radcliffe, Diana Raffman, Gerard Raulet, Stephen L. Read, Andrews Reath, Andrew Reisner, Nicholas Rescher, Henry S. Richardson, Robert C. Richardson, Thomas Ricketts, Wayne D. Riggs, Mark Roberts, Robert C. Roberts, Luke Robinson, Alexander Rosenberg, Gary Rosenkranz, Bernice Glatzer Rosenthal, Adina L. Roskies, William L. Rowe, T. M. Rudavsky, Michael Ruse, Bruce Russell, Lilly-Marlene Russow, Dan Ryder, R. M. Sainsbury, Joseph Salerno, Nathan Salmon, Wesley C. Salmon, Constantine Sandis, David H. Sanford, Marco Santambrogio, David Sapire, Ruth A. Saunders, Geoffrey Sayre-McCord, Charles Sayward, James P. Scanlan, Richard Schacht, Tamar Schapiro, Frederick F. Schmitt, Jerome B. Schneewind, Calvin O. Schrag, Alan D. Schrift, George F. Schumm, Jean-Loup Seban, David N. Sedley, Kenneth Seeskin, Krister Segerberg, Charlene Haddock Seigfried, Dennis M. Senchuk, James F. Sennett, William Lad Sessions, Stewart Shapiro, Tommie Shelby, Donald W. Sherburne, Christopher Shields, Roger A. Shiner, Sydney Shoemaker, Robert K. Shope, Kwong-loi Shun, Wilfried Sieg, A. John Simmons, Robert L. Simon, Marcus G. Singer, Georgette Sinkler, Walter Sinnott-Armstrong, Matti T. Sintonen, Lawrence Sklar, Brian Skyrms, Robert C. Sleigh, Michael Anthony Slote, Hans Sluga, Barry Smith, Michael Smith, Robin Smith, Robert Sokolowski, Robert C. Solomon, Marta Soniewicka, Philip Soper, Ernest Sosa, Nicholas Southwood, Paul Vincent Spade, T. L. S. Sprigge, Eric O. Springsted, George J. Stack, Rebecca Stangl, Jason Stanley, Florian Steinberger, Sören Stenlund, Christopher Stephens, James P. Sterba, Josef Stern, Matthias Steup, M. A. Stewart, Leopold Stubenberg, Edith Dudley Sulla, Frederick Suppe, Jere Paul Surber, David George Sussman, Sigrún Svavarsdóttir, Zeno G. Swijtink, Richard Swinburne, Charles C. Taliaferro, Robert B. Talisse, John Tasioulas, Paul Teller, Larry S. Temkin, Mark Textor, H. S. Thayer, Peter Thielke, Alan Thomas, Amie L. Thomasson, Katherine Thomson-Jones, Joshua C. Thurow, Vzalerie Tiberius, Terrence N. Tice, Paul Tidman, Mark C. Timmons, William Tolhurst, James E. Tomberlin, Rosemarie Tong, Lawrence Torcello, Kelly Trogdon, J. D. Trout, Robert E. Tully, Raimo Tuomela, John Turri, Martin M. Tweedale, Thomas Uebel, Jennifer Uleman, James Van Cleve, Harry van der Linden, Peter van Inwagen, Bryan W. Van Norden, René van Woudenberg, Donald Phillip Verene, Samantha Vice, Thomas Vinci, Donald Wayne Viney, Barbara Von Eckardt, Peter B. M. Vranas, Steven J. Wagner, William J. Wainwright, Paul E. Walker, Robert E. Wall, Craig Walton, Douglas Walton, Eric Watkins, Richard A. Watson, Michael V. Wedin, Rudolph H. Weingartner, Paul Weirich, Paul J. Weithman, Carl Wellman, Howard Wettstein, Samuel C. Wheeler, Stephen A. White, Jennifer Whiting, Edward R. Wierenga, Michael Williams, Fred Wilson, W. Kent Wilson, Kenneth P. Winkler, John F. Wippel, Jan Woleński, Allan B. Wolter, Nicholas P. Wolterstorff, Rega Wood, W. Jay Wood, Paul Woodruff, Alison Wylie, Gideon Yaffe, Takashi Yagisawa, Yutaka Yamamoto, Keith E. Yandell, Xiaomei Yang, Dean Zimmerman, Günter Zoller, Catherine Zuckert, Michael Zuckert, Jack A. Zupko (J.A.Z.)
- Edited by Robert Audi, University of Notre Dame, Indiana
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- The Cambridge Dictionary of Philosophy
- Published online:
- 05 August 2015
- Print publication:
- 27 April 2015, pp ix-xxx
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Neuropsychiatric Morbidity in Adolescent and Adult Succinic Semialdehyde Dehydrogenase Deficiency Patients
- Ina Knerr, K. Michael Gibson, Cornelis Jakobs, Phillip L. Pearl
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- CNS Spectrums / Volume 13 / Issue 7 / July 2008
- Published online by Cambridge University Press:
- 07 November 2014, pp. 598-605
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Introduction:
Succinic semialdehyde dehydrogenase (SSADH) deficiency (γ-hydroxybutyric aciduria) is a rare neurometabolic disorder of γ-aminobutyric acid degradation. While neurological manifestations, such as developmental delay, are typical during infancy, limited data are available on adolescent and adult symptomatology.
Methods:We overview the phenotype of 33 adolescents and adults (10.1–39.5 years of age, mean: 17.1 years, 48% females) with SSADH deficiency. For this purpose, we applied a database with systematic questionnaire-based follow-up data.
Results:Sixty-six percent of patients (n=21) presented by 6 months of age, 14% from 6–12 months of age, 5% from 1–2 years of age, and 14% from 2–4 years of age, mean age at first symptoms was 11±12 months. However, mean age at diagnosis was 6.6±6.4 years of age. Presenting symptoms encompassed motor delay, hypotonia, speech delay, autistic features, seizures, and ataxia. Eighty-two percent demonstrated behavioral problems, such as attention deficit, hyperactivity, anxiety, or aggression, and 33% had ≥3 behavior problems. Electroencephalograms showed background slowing or epileptiform discharges in 40% of patients. Treatment approaches are then summarized.
Conclusion:The variable phenotype in SSADH deficiency suggests the likelihood that this disease may be under-diagnosed. Families of patients with SSADH deficiency should be counseled and supported regarding the anticipated persistence of various neuropsychiatric symptoms into adulthood.
Galaxy Groups: Proceedings from a Swinburne University Workshop
- Virginia A. Kilborn, Kenji Bekki, Sarah Brough, Marianne T. Doyle, Ekaterina A. Evstigneeva, Duncan A. Forbes, Bärbel S. Koribalski, Matthew S. Owers, Chris Power, Michael J. Drinkwater, David J. Rohde, Christopher A. Blake, Warrick J. Couch, Michael B. Pracy, Brad K. Gibson
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- Journal:
- Publications of the Astronomical Society of Australia / Volume 22 / Issue 4 / 2005
- Published online by Cambridge University Press:
- 05 March 2013, pp. 326-334
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We present the proceedings from a two-day workshop held at Swinburne University on 2005 May 24–25. The workshop participants highlighted current Australian research on both theoretical and observational aspects of galaxy groups. These proceedings include short one-page summaries of a number of the talks presented at the workshop. The talks presented ranged from reconciling N-body simulations with observations, to the Hı content of galaxies in groups and the existence of ‘dark galaxies’. The formation and existence of ultra-compact dwarfs in groups, and a new supergroup in Eridanus were also discussed.
AAT/WFI Observations of the Extragalactic HI Cloud HIPASS J1712-64
- Geraint F. Lewis, Michael J. Irwin, Rodrigo A. Ibata, Brad K. Gibson
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- Journal:
- Publications of the Astronomical Society of Australia / Volume 19 / Issue 2 / 2002
- Published online by Cambridge University Press:
- 05 March 2013, pp. 257-259
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AAT/WFI optical images of a candidate extragalactic HI cloud, HIPASS J1712–64, are presented. The g and r band CCD mosaic camera frames were processed using a new data pipeline recently installed at the AAO. The resultant stacked images reach significantly deeper levels than those of previous published optical imaging of this candidate, providing a detection limit Mg ˜ −7 at a distance of 3 Mpc, the inferred distance to HIPASS J1712–64. However, detailed analysis of the images fails to uncover any stellar population associated with the HI emission. If this system is a member of the Local Group then it is pathologically different to other members. Hence, our observations reinforce earlier suggestions that this HI cloud is most likely Galactic in origin and not a Local Volume dwarf galaxy.
Inadequate intakes of dietary zinc among pregnant women from subsistence households in Sidama, Southern Ethiopia
- Yewelsew Abebe, Alemtsehay Bogale, K Michael Hambidge, Barbara J Stoecker, Isabel Arbide, Akilu Teshome, Nancy F Krebs, Jamie E Westcott, Karl B Bailey, Rosalind S Gibson
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- Journal:
- Public Health Nutrition / Volume 11 / Issue 4 / April 2008
- Published online by Cambridge University Press:
- 01 April 2008, pp. 379-386
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Objective
To assess the prevalence of zinc inadequacy based on dietary intakes and plasma zinc concentrations and, simultaneously, the prevalence of inadequate intakes of energy, protein, calcium and iron.
DesignA cross-sectional study of a convenience sample of subsistence farming households in Sidama, Southern Ethiopia.
SubjectsDietary intakes were calculated from 1-day weighed food records and 40 repeats from 99 pregnant women in the third trimester using analysed values of major staple foods for zinc, iron, calcium and phytate. The distribution of observed intakes was adjusted for usual intakes and the prevalence of inadequacy estimated using the estimated average requirement (EAR) cutpoint method. Prevalence of inadequacy for zinc, protein and iron intakes were compared with those based on biochemical measures.
ResultsPrevalence of zinc inadequacy was very high: 99% for US FNB EAR and 100% for IZiNCG EAR compared to 72% based on low plasma zinc concentrations. Corresponding prevalence estimates for iron were much lower: 4% for inadequate intakes based on US FNB EAR vs. 8.7% for iron deficiency anaemia (haemoglobin < 110 g l−1; ferritin < 12 μg l−1) and 32.3% for low storage iron. Prevalence of inadequacy for protein was 100% for adjusted intakes and 91% for serum albumin < 32 g l−1. For calcium, 74% were at risk for inadequate intakes.
ConclusionThe high prevalence of inadequate intakes of zinc and protein was reasonably consistent with those based on biochemical measures. Such dietary deficits could be overcome by regular consumption of cellular animal protein. In contrast, both dietary and biochemical measures of iron inadequacy were low.
MO-CVD GaAs Grown by Direct Deposition on Si
- S. M. Vernon, S. J. Pearton, J. M. Gibson, R. Caruso, C. R. Abernathy, K. T. Short, Michael Stavola, V. E. Haven, D. C. Jacobson
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- Journal:
- MRS Online Proceedings Library Archive / Volume 91 / 1987
- Published online by Cambridge University Press:
- 28 February 2011, 187
- Print publication:
- 1987
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GaAs layers were grown directly on misoriented (2° off (100)→[011]) Si substrates by Metalorganic Chemical Vapor Deposition. The threading dislocation density at the surface of 4 μm thick layers was typically 108cm−2, as determined by both preferential etching and transmission electron microscopy. Rapid thermal annealing (900°C, 10s) improved the crystalline quality of the GaAs near the heterointerface while allowing no detectable Si diffusion into this layer. Two deep electron traps were observed in the undoped GaAs, but were present at a low concentration (∼ 1013 cm−3 ). The (400) x-ray diffraction peak width from the GaAs was significantly reduced with increasing GaAs layer thickness, indicating improved material quality. This is supported by Si implant activation data, which shows higher net donor activity in thicker layers.