20 results
Robust reference group normative data for neuropsychological tests accounting for primary language use in Asian American older adults
- Arunima Kapoor, Jean K. Ho, Jung Yun Jang, Daniel A. Nation
-
- Journal:
- Journal of the International Neuropsychological Society / Volume 30 / Issue 4 / May 2024
- Published online by Cambridge University Press:
- 01 March 2024, pp. 402-409
-
- Article
-
- You have access Access
- Open access
- HTML
- Export citation
-
Objective:
The present study aimed to develop neuropsychological norms for older Asian Americans with English as a primary or secondary language, using data from the National Alzheimer’s Coordinating Center (NACC).
Method:A normative sample of Asian American participants was derived from the NACC database using robust criteria: participants were cognitively unimpaired at baseline (i.e., no MCI or dementia) and remained cognitively unimpaired at 1-year follow-up. Clinical and demographic characteristics were compared between Primary and Secondary English speakers using analyses of variance for continuous measures and chi-square tests for categorical variables. Linear regression models compared neuropsychological performance between the groups, adjusting for demographics (age, sex, and education). Regression models were developed for clinical application to compute demographically adjusted z-scores.
Results:Secondary English speakers were younger than Primary English speakers (p < .001). There were significant differences between the groups on measures of mental status (Mini-Mental State Examination, p = .002), attention (Trail Making Test A, Digit Span Forward Total Score, p <.001), language (Boston Naming Test, Animal Fluency, Vegetable Fluency, p < .001), and executive function (Trail Making Test B, p = .02).
Conclusions:Separate normative data are needed for Primary vs. Secondary English speakers from Asian American backgrounds. We provide normative data on older Asian Americans to enable clinicians to account for English use in the interpretation of neuropsychological assessment scores.
32 Elevated Plasma pTau-181 is Associated with Lower Global Cognition and Executive Function in Older Adults
- Arunima Kapoor, Jean K Ho, Shubir Dutt, Yanrong Li, John P Alitin, Jung Yun Jang, Aimee Gaubert, Amy Nguyen, Belinda Yew, Anna E Blanken, Isabel J Sible, Anisa Marshall, Fatemah Shenasa, Alessandra Martini, Kathleen E Rodgers, Elizabeth Head, Daniel A Nation
-
- Journal:
- Journal of the International Neuropsychological Society / Volume 29 / Issue s1 / November 2023
- Published online by Cambridge University Press:
- 21 December 2023, pp. 907-908
-
- Article
-
- You have access Access
- Export citation
-
Objective:
Aggregation of phosphorylated tau (pTau) is a hallmark feature of Alzheimer’s disease (AD). Novel assays now allow pTau to be measured in plasma. Elevated plasma pTau predicts subsequent development of AD, cortical atrophy and AD-related pathologies in the brain. We aimed to determine whether elevated pTau is associated with cognitive functioning in older adults prior to the development of dementia.
Participants and Methods:Independently living older adults (N = 48, mean age = 70.0 years; SD = 7.7; age range 55-88 years; 35.4% male) free of dementia or clinical stroke were recruited from the community and underwent blood draw and neuropsychological assessment. Plasma was assayed using the Quanterix Simoa® pTau-181 V2 Advantage Kit to quantify pTau-181 levels and APOE genotyping was conducted on the blood cell pellet fraction obtained from plasma separation. Global cognition was assessed using the Dementia Rating Scale-2 (DRS-2) and executive function was assessed using the Stroop, D-KEFS-2 Fluency, and Trails Making Test. Diagnosis of mild cognitive impairment (MCI) was determined based on overall neuropsychological performance. Participants were diagnosed as MCI if they scored >1 SD below norm-referenced values on 2 or more tests within a domain (language, executive, memory) or on 3 tests across domains.
Results:Multiple linear regression analysis revealed a significant negative association between plasma pTau-181 levels and DRS-2 (B = -2.57, 95% CI (-3.68, -1.47), p <.001), Stroop Color-Word score (B = -2.64, 95% CI (-4.56, - 0.71), p = .009) and Fruits and Vegetables Fluency (B = -1.67, 95% CI (-2.84, -0.49), p = .007), adjusting for age, sex, education and APOE4 status. MCI diagnosis was determined for 43 participants, of which 8 (18.6%) met criteria. Logistic regression analysis revealed that pTau-181 levels are associated with increased odds of MCI diagnosis (OR = 2.18, 95% CI (1.01, 4.68), p = .046), after accounting for age, sex, education and APOE4 status.
Conclusions:Elevated plasma pTau-181 is associated with worse cognition, particularly executive function, and predicts MCI diagnosis in older adults. Higher plasma pTau-181 was associated with increased odds of MCI diagnosis. Detection of pTau-181 in plasma allows a novel, non-invasive method to detect burden of one form of AD pathology. These findings lend support to the use of plasma pTau-181 as a valuable marker in detecting even early cognitive changes prior to the development of AD. Additional longitudinal studies are warranted to explore the prognostic value of plasma pTau-181 over time.
5 Associations Between Regional Perfusion and Locus Coeruleus MRI Contrast are Moderated by Plasma Alzheimer’s Disease Biomarkers in Older Adults
- Shubir Dutt, Shelby L Bachman, Yanrong Li, Belinda Yew, Jung Y Jang, Jean K Ho, Kaoru Nashiro, Jungwon Min, Hyun Joo Yoo, Aimee Gaubert, Amy Nguyen, Isabel J Sible, Anna E Blanken, Anisa J Marshall, Arunima Kapoor, John P Alitin, Kim Hoang, Alessandra C Martini, Elizabeth Head, Xingfeng Shao, Danny J J Wang, Mara Mather, Daniel A Nation
-
- Journal:
- Journal of the International Neuropsychological Society / Volume 29 / Issue s1 / November 2023
- Published online by Cambridge University Press:
- 21 December 2023, pp. 610-611
-
- Article
-
- You have access Access
- Export citation
-
Objective:
The locus coeruleus (LC) innervates the cerebrovasculature and plays a crucial role in optimal regulation of cerebral blood flow. However, no human studies to date have examined links between these systems with widely available neuroimaging methods. We quantified associations between LC structural integrity and regional cortical perfusion and probed whether varying levels of plasma Alzheimer’s disease (AD) biomarkers (Aß42/40 ratio and ptau181) moderated these relationships.
Participants and Methods:64 dementia-free community-dwelling older adults (ages 55-87) recruited across two studies underwent structural and functional neuroimaging on the same MRI scanner. 3D-pCASL MRI measured regional cerebral blood flow in limbic and frontal cortical regions, while T1-FSE MRI quantified rostral LC-MRI contrast, a well-established proxy measure of LC structural integrity. A subset of participants underwent fasting blood draw to measure plasma AD biomarker concentrations (Aß42/40 ratio and ptau181). Multiple linear regression models examined associations between perfusion and LC integrity, with rostral LC-MRI contrast as predictor, regional CBF as outcome, and age and study as covariates. Moderation analyses included additional terms for plasma AD biomarker concentration and plasma x LC interaction.
Results:Greater rostral LC-MRI contrast was linked to lower regional perfusion in limbic regions, such as the amygdala (ß = -0.25, p = 0.049) and entorhinal cortex (ß = -0.20, p = 0.042), but was linked to higher regional perfusion in frontal cortical regions, such as the lateral (ß = 0.28, p = 0.003) and medial (ß = 0.24, p = 0.05) orbitofrontal (OFC) cortices. Plasma amyloid levels moderated the relationship between rostral LC and amygdala CBF (Aß42/40 ratio x rostral LC interaction term ß = -0.31, p = 0.021), such that as plasma Aß42/40 ratio decreased (i.e., greater pathology), the strength of the negative relationship between rostral LC integrity and amygdala perfusion decreased. Plasma ptau181levels moderated the relationship between rostral LC and entorhinal CBF (ptau181 x rostral LC interaction term ß = 0.64, p = 0.001), such that as ptau181 increased (i.e., greater pathology), the strength of the negative relationship between rostral LC integrity and entorhinal perfusion decreased. For frontal cortical regions, ptau181 levels moderated the relationship between rostral LC and lateral OFC perfusion (ptau181 x rostral LC interaction term ß = -0.54, p = .004), as well as between rostral LC and medial OFC perfusion (ptau181 x rostral LC interaction term ß = -0.53, p = .005), such that as ptau181 increased (i.e., greater pathology), the strength of the positive relationship between rostral LC integrity and frontal perfusion decreased.
Conclusions:LC integrity is linked to regional cortical perfusion in non-demented older adults, and these relationships are moderated by plasma AD biomarker concentrations. Variable directionality of the associations between the LC and frontal versus limbic perfusion, as well as the differential moderating effects of plasma AD biomarkers, may signify a compensatory mechanism and a shifting pattern of hyperemia in the presence of aggregating AD pathology. Linking LC integrity and cerebrovascular regulation may represent an important understudied pathway of dementia risk and may help to bridge competing theories of dementia progression in preclinical AD studies.
96 Short-Term Blood Pressure Variability and Cerebrovascular Health in OlderaAdults
- Isabel J Sible, Belinda Yew, Arunima Kapoor, Jung Y Jang, John Paul M Alitin, Shubir Dutt, Yanrong Li, Anna E Blanken, Jean K Ho, Anisa J Marshall, Fatemah Shenasa, Aimee Gaubert, Amy Nguyen, Kathleen E Rodgers, Virginia E Sturm, Daniel A Nation
-
- Journal:
- Journal of the International Neuropsychological Society / Volume 29 / Issue s1 / November 2023
- Published online by Cambridge University Press:
- 21 December 2023, pp. 195-196
-
- Article
-
- You have access Access
- Export citation
-
Objective:
Blood pressure variability (BPV), independent of traditionally targeted average blood pressure levels, is an emerging vascular risk factor for stroke, cerebrovascular disease, and dementia, possibly through links with vascular-endothelial injury. Recent evidence suggests visit-to-visit (e.g., over months, years) BPV is associated with cerebrovascular disease severity, but less is known about relationships with short-term (e.g., < 24 hours) fluctuations in blood pressure. Additionally, it is unclear how BPV may be related to angiogenic growth factors that play a role in cerebral arterial health.
Participants and Methods:We investigated relationships between short-term BPV, white matter hyperintensities on MRI, and levels of plasma vascular endothelial growth factor (VEGF) in a sample of community-dwelling older adults (n = 57, ages 55-88) without history of dementia or stroke. Blood pressure was collected continuously during a 5-minute resting period. BPV was calculated as variability independent of mean, a commonly used index of BPV uncorrelated with average blood pressure levels. Participants underwent T2-FLAIR MRI to determine severity of white matter lesion burden. Severity of lesions was classified as Fazekas scores (0-3). Participants also underwent venipuncture to determine levels of plasma VEGF. Ordinal logistic regression examined the association between BPV and Fazekas scores. Multiple linear regression explored relationships between BPV and VEGF. Models controlled for age, sex, and average blood pressure.
Results:Elevated BPV was related to greater white matter lesion burden (i.e., Fazekas score) (systolic: OR = 1.17 [95% CI 1.01, 1.37]; p = .04; diastolic: OR = 2.47 [95% CI 1.09, 5.90]; p = .03) and increased levels of plasma VEGF (systolic: ß = .39 [95% CI .11, .67]; adjusted R2 = .16; p = .007; diastolic: ß = .48 [95% CI .18, .78]; adjusted R2 = .18; p = .003).
Conclusions:Findings suggest short-term BPV may be related to cerebrovascular disease burden and angiogenic growth factors relevant to cerebral arterial health, independent of average blood pressure. Understanding the role of BPV in cerebrovascular disease and vascular-endothelial health may help elucidate the increased risk for stroke and dementia associated with elevated BPV.
Neuropsychological Profiles and Trajectories in Preclinical Alzheimer’s Disease
- Jean K. Ho, Daniel A. Nation, for the Alzheimer’s Disease Neuroimaging Initiative
-
- Journal:
- Journal of the International Neuropsychological Society / Volume 24 / Issue 7 / August 2018
- Published online by Cambridge University Press:
- 30 April 2018, pp. 693-702
-
- Article
-
- You have access Access
- HTML
- Export citation
-
Objectives: The present study investigated the independent and synergistic effects of amyloid beta (Aβ1-42) and phosphorylated tau (Ptau) pathologies on neuropsychological profiles and trajectories in cognitively normal older adults. Methods: Alzheimer’s Disease Neuroimaging Initiative participants identified as cognitively normal at baseline underwent longitudinal assessment (N=518; 0, 12, 24, 36 months), baseline lumbar puncture and follow-up cognitive exams. Cerebral spinal fluid (CSF) biomarker profiles (Aβ-Ptau-, Aβ+Ptau-, Aβ-Ptau+, Aβ+Ptau+) were compared on baseline profiles and trajectories for memory (Rey Auditory Verbal Learning Test), attention/executive function (Trail Making Test, A and B), language (Animal Fluency, Vegetable Fluency, Boston Naming Test) and processing speed (Digit Symbol) using multilevel models. Results: The Aβ+Ptau+ group exhibited significantly worse baseline performance on tests of memory and executive function relative to the Aβ-Ptau+ and Aβ-Ptau- groups. The Aβ+Ptau- group fell between the Aβ+Ptau+ participants and the Aβ-Ptau- and Aβ-Ptau+ groups on all three cognitive domains and exhibited worse baseline executive function. The Aβ-Ptau+ group performed worse than Aβ-Ptau- participants on processing speed. Over 36-month follow-up, the Aβ+Ptau+ group exhibited the greatest declines in memory and semantic fluency compared to all other groups. Conclusions: Cognitively normal older adults with both Aβ and Ptau pathology exhibited the weakest profile, marked by the worst memory decline compared to the other groups. Other subtle changes in this group included declines in executive function and semantic fluency. Those with Ptau pathology alone showed slowed processing speed, and those with Aβ pathology alone showed worse attention and executive function compared to biomarker negative participants. (JINS, 2018, 24, 1–10)
Contributors
-
- By Rose Teteki Abbey, K. C. Abraham, David Tuesday Adamo, LeRoy H. Aden, Efrain Agosto, Victor Aguilan, Gillian T. W. Ahlgren, Charanjit Kaur AjitSingh, Dorothy B E A Akoto, Giuseppe Alberigo, Daniel E. Albrecht, Ruth Albrecht, Daniel O. Aleshire, Urs Altermatt, Anand Amaladass, Michael Amaladoss, James N. Amanze, Lesley G. Anderson, Thomas C. Anderson, Victor Anderson, Hope S. Antone, María Pilar Aquino, Paula Arai, Victorio Araya Guillén, S. Wesley Ariarajah, Ellen T. Armour, Brett Gregory Armstrong, Atsuhiro Asano, Naim Stifan Ateek, Mahmoud Ayoub, John Alembillah Azumah, Mercedes L. García Bachmann, Irena Backus, J. Wayne Baker, Mieke Bal, Lewis V. Baldwin, William Barbieri, António Barbosa da Silva, David Basinger, Bolaji Olukemi Bateye, Oswald Bayer, Daniel H. Bays, Rosalie Beck, Nancy Elizabeth Bedford, Guy-Thomas Bedouelle, Chorbishop Seely Beggiani, Wolfgang Behringer, Christopher M. Bellitto, Byard Bennett, Harold V. Bennett, Teresa Berger, Miguel A. Bernad, Henley Bernard, Alan E. Bernstein, Jon L. Berquist, Johannes Beutler, Ana María Bidegain, Matthew P. Binkewicz, Jennifer Bird, Joseph Blenkinsopp, Dmytro Bondarenko, Paulo Bonfatti, Riet en Pim Bons-Storm, Jessica A. Boon, Marcus J. Borg, Mark Bosco, Peter C. Bouteneff, François Bovon, William D. Bowman, Paul S. Boyer, David Brakke, Richard E. Brantley, Marcus Braybrooke, Ian Breward, Ênio José da Costa Brito, Jewel Spears Brooker, Johannes Brosseder, Nicholas Canfield Read Brown, Robert F. Brown, Pamela K. Brubaker, Walter Brueggemann, Bishop Colin O. Buchanan, Stanley M. Burgess, Amy Nelson Burnett, J. Patout Burns, David B. Burrell, David Buttrick, James P. Byrd, Lavinia Byrne, Gerado Caetano, Marcos Caldas, Alkiviadis Calivas, William J. Callahan, Salvatore Calomino, Euan K. Cameron, William S. Campbell, Marcelo Ayres Camurça, Daniel F. Caner, Paul E. Capetz, Carlos F. Cardoza-Orlandi, Patrick W. Carey, Barbara Carvill, Hal Cauthron, Subhadra Mitra Channa, Mark D. Chapman, James H. Charlesworth, Kenneth R. Chase, Chen Zemin, Luciano Chianeque, Philip Chia Phin Yin, Francisca H. Chimhanda, Daniel Chiquete, John T. Chirban, Soobin Choi, Robert Choquette, Mita Choudhury, Gerald Christianson, John Chryssavgis, Sejong Chun, Esther Chung-Kim, Charles M. A. Clark, Elizabeth A. Clark, Sathianathan Clarke, Fred Cloud, John B. Cobb, W. Owen Cole, John A Coleman, John J. Collins, Sylvia Collins-Mayo, Paul K. Conkin, Beth A. Conklin, Sean Connolly, Demetrios J. Constantelos, Michael A. Conway, Paula M. Cooey, Austin Cooper, Michael L. Cooper-White, Pamela Cooper-White, L. William Countryman, Sérgio Coutinho, Pamela Couture, Shannon Craigo-Snell, James L. Crenshaw, David Crowner, Humberto Horacio Cucchetti, Lawrence S. Cunningham, Elizabeth Mason Currier, Emmanuel Cutrone, Mary L. Daniel, David D. Daniels, Robert Darden, Rolf Darge, Isaiah Dau, Jeffry C. Davis, Jane Dawson, Valentin Dedji, John W. de Gruchy, Paul DeHart, Wendy J. Deichmann Edwards, Miguel A. De La Torre, George E. Demacopoulos, Thomas de Mayo, Leah DeVun, Beatriz de Vasconcellos Dias, Dennis C. Dickerson, John M. Dillon, Luis Miguel Donatello, Igor Dorfmann-Lazarev, Susanna Drake, Jonathan A. Draper, N. Dreher Martin, Otto Dreydoppel, Angelyn Dries, A. J. Droge, Francis X. D'Sa, Marilyn Dunn, Nicole Wilkinson Duran, Rifaat Ebied, Mark J. Edwards, William H. Edwards, Leonard H. Ehrlich, Nancy L. Eiesland, Martin Elbel, J. Harold Ellens, Stephen Ellingson, Marvin M. Ellison, Robert Ellsberg, Jean Bethke Elshtain, Eldon Jay Epp, Peter C. Erb, Tassilo Erhardt, Maria Erling, Noel Leo Erskine, Gillian R. Evans, Virginia Fabella, Michael A. Fahey, Edward Farley, Margaret A. Farley, Wendy Farley, Robert Fastiggi, Seena Fazel, Duncan S. Ferguson, Helwar Figueroa, Paul Corby Finney, Kyriaki Karidoyanes FitzGerald, Thomas E. FitzGerald, John R. Fitzmier, Marie Therese Flanagan, Sabina Flanagan, Claude Flipo, Ronald B. Flowers, Carole Fontaine, David Ford, Mary Ford, Stephanie A. Ford, Jim Forest, William Franke, Robert M. Franklin, Ruth Franzén, Edward H. Friedman, Samuel Frouisou, Lorelei F. Fuchs, Jojo M. Fung, Inger Furseth, Richard R. Gaillardetz, Brandon Gallaher, China Galland, Mark Galli, Ismael García, Tharscisse Gatwa, Jean-Marie Gaudeul, Luis María Gavilanes del Castillo, Pavel L. Gavrilyuk, Volney P. Gay, Metropolitan Athanasios Geevargis, Kondothra M. George, Mary Gerhart, Simon Gikandi, Maurice Gilbert, Michael J. Gillgannon, Verónica Giménez Beliveau, Terryl Givens, Beth Glazier-McDonald, Philip Gleason, Menghun Goh, Brian Golding, Bishop Hilario M. Gomez, Michelle A. Gonzalez, Donald K. Gorrell, Roy Gottfried, Tamara Grdzelidze, Joel B. Green, Niels Henrik Gregersen, Cristina Grenholm, Herbert Griffiths, Eric W. Gritsch, Erich S. Gruen, Christoffer H. Grundmann, Paul H. Gundani, Jon P. Gunnemann, Petre Guran, Vidar L. Haanes, Jeremiah M. Hackett, Getatchew Haile, Douglas John Hall, Nicholas Hammond, Daphne Hampson, Jehu J. Hanciles, Barry Hankins, Jennifer Haraguchi, Stanley S. Harakas, Anthony John Harding, Conrad L. Harkins, J. William Harmless, Marjory Harper, Amir Harrak, Joel F. Harrington, Mark W. Harris, Susan Ashbrook Harvey, Van A. Harvey, R. Chris Hassel, Jione Havea, Daniel Hawk, Diana L. Hayes, Leslie Hayes, Priscilla Hayner, S. Mark Heim, Simo Heininen, Richard P. Heitzenrater, Eila Helander, David Hempton, Scott H. Hendrix, Jan-Olav Henriksen, Gina Hens-Piazza, Carter Heyward, Nicholas J. Higham, David Hilliard, Norman A. Hjelm, Peter C. Hodgson, Arthur Holder, M. Jan Holton, Dwight N. Hopkins, Ronnie Po-chia Hsia, Po-Ho Huang, James Hudnut-Beumler, Jennifer S. Hughes, Leonard M. Hummel, Mary E. Hunt, Laennec Hurbon, Mark Hutchinson, Susan E. Hylen, Mary Beth Ingham, H. Larry Ingle, Dale T. Irvin, Jon Isaak, Paul John Isaak, Ada María Isasi-Díaz, Hans Raun Iversen, Margaret C. Jacob, Arthur James, Maria Jansdotter-Samuelsson, David Jasper, Werner G. Jeanrond, Renée Jeffery, David Lyle Jeffrey, Theodore W. Jennings, David H. Jensen, Robin Margaret Jensen, David Jobling, Dale A. Johnson, Elizabeth A. Johnson, Maxwell E. Johnson, Sarah Johnson, Mark D. Johnston, F. Stanley Jones, James William Jones, John R. Jones, Alissa Jones Nelson, Inge Jonsson, Jan Joosten, Elizabeth Judd, Mulambya Peggy Kabonde, Robert Kaggwa, Sylvester Kahakwa, Isaac Kalimi, Ogbu U. Kalu, Eunice Kamaara, Wayne C. Kannaday, Musimbi Kanyoro, Veli-Matti Kärkkäinen, Frank Kaufmann, Léon Nguapitshi Kayongo, Richard Kearney, Alice A. Keefe, Ralph Keen, Catherine Keller, Anthony J. Kelly, Karen Kennelly, Kathi Lynn Kern, Fergus Kerr, Edward Kessler, George Kilcourse, Heup Young Kim, Kim Sung-Hae, Kim Yong-Bock, Kim Yung Suk, Richard King, Thomas M. King, Robert M. Kingdon, Ross Kinsler, Hans G. Kippenberg, Cheryl A. Kirk-Duggan, Clifton Kirkpatrick, Leonid Kishkovsky, Nadieszda Kizenko, Jeffrey Klaiber, Hans-Josef Klauck, Sidney Knight, Samuel Kobia, Robert Kolb, Karla Ann Koll, Heikki Kotila, Donald Kraybill, Philip D. W. Krey, Yves Krumenacker, Jeffrey Kah-Jin Kuan, Simanga R. Kumalo, Peter Kuzmic, Simon Shui-Man Kwan, Kwok Pui-lan, André LaCocque, Stephen E. Lahey, John Tsz Pang Lai, Emiel Lamberts, Armando Lampe, Craig Lampe, Beverly J. Lanzetta, Eve LaPlante, Lizette Larson-Miller, Ariel Bybee Laughton, Leonard Lawlor, Bentley Layton, Robin A. Leaver, Karen Lebacqz, Archie Chi Chung Lee, Marilyn J. Legge, Hervé LeGrand, D. L. LeMahieu, Raymond Lemieux, Bill J. Leonard, Ellen M. Leonard, Outi Leppä, Jean Lesaulnier, Nantawan Boonprasat Lewis, Henrietta Leyser, Alexei Lidov, Bernard Lightman, Paul Chang-Ha Lim, Carter Lindberg, Mark R. Lindsay, James R. Linville, James C. Livingston, Ann Loades, David Loades, Jean-Claude Loba-Mkole, Lo Lung Kwong, Wati Longchar, Eleazar López, David W. Lotz, Andrew Louth, Robin W. Lovin, William Luis, Frank D. Macchia, Diarmaid N. J. MacCulloch, Kirk R. MacGregor, Marjory A. MacLean, Donald MacLeod, Tomas S. Maddela, Inge Mager, Laurenti Magesa, David G. Maillu, Fortunato Mallimaci, Philip Mamalakis, Kä Mana, Ukachukwu Chris Manus, Herbert Robinson Marbury, Reuel Norman Marigza, Jacqueline Mariña, Antti Marjanen, Luiz C. L. Marques, Madipoane Masenya (ngwan'a Mphahlele), Caleb J. D. Maskell, Steve Mason, Thomas Massaro, Fernando Matamoros Ponce, András Máté-Tóth, Odair Pedroso Mateus, Dinis Matsolo, Fumitaka Matsuoka, John D'Arcy May, Yelena Mazour-Matusevich, Theodore Mbazumutima, John S. McClure, Christian McConnell, Lee Martin McDonald, Gary B. McGee, Thomas McGowan, Alister E. McGrath, Richard J. McGregor, John A. McGuckin, Maud Burnett McInerney, Elsie Anne McKee, Mary B. McKinley, James F. McMillan, Ernan McMullin, Kathleen E. McVey, M. Douglas Meeks, Monica Jyotsna Melanchthon, Ilie Melniciuc-Puica, Everett Mendoza, Raymond A. Mentzer, William W. Menzies, Ina Merdjanova, Franziska Metzger, Constant J. Mews, Marvin Meyer, Carol Meyers, Vasile Mihoc, Gunner Bjerg Mikkelsen, Maria Inêz de Castro Millen, Clyde Lee Miller, Bonnie J. Miller-McLemore, Alexander Mirkovic, Paul Misner, Nozomu Miyahira, R. W. L. Moberly, Gerald Moede, Aloo Osotsi Mojola, Sunanda Mongia, Rebeca Montemayor, James Moore, Roger E. Moore, Craig E. Morrison O.Carm, Jeffry H. Morrison, Keith Morrison, Wilson J. Moses, Tefetso Henry Mothibe, Mokgethi Motlhabi, Fulata Moyo, Henry Mugabe, Jesse Ndwiga Kanyua Mugambi, Peggy Mulambya-Kabonde, Robert Bruce Mullin, Pamela Mullins Reaves, Saskia Murk Jansen, Heleen L. Murre-Van den Berg, Augustine Musopole, Isaac M. T. Mwase, Philomena Mwaura, Cecilia Nahnfeldt, Anne Nasimiyu Wasike, Carmiña Navia Velasco, Thulani Ndlazi, Alexander Negrov, James B. Nelson, David G. Newcombe, Carol Newsom, Helen J. Nicholson, George W. E. Nickelsburg, Tatyana Nikolskaya, Damayanthi M. A. Niles, Bertil Nilsson, Nyambura Njoroge, Fidelis Nkomazana, Mary Beth Norton, Christian Nottmeier, Sonene Nyawo, Anthère Nzabatsinda, Edward T. Oakes, Gerald O'Collins, Daniel O'Connell, David W. Odell-Scott, Mercy Amba Oduyoye, Kathleen O'Grady, Oyeronke Olajubu, Thomas O'Loughlin, Dennis T. Olson, J. Steven O'Malley, Cephas N. Omenyo, Muriel Orevillo-Montenegro, César Augusto Ornellas Ramos, Agbonkhianmeghe E. Orobator, Kenan B. Osborne, Carolyn Osiek, Javier Otaola Montagne, Douglas F. Ottati, Anna May Say Pa, Irina Paert, Jerry G. Pankhurst, Aristotle Papanikolaou, Samuele F. Pardini, Stefano Parenti, Peter Paris, Sung Bae Park, Cristián G. Parker, Raquel Pastor, Joseph Pathrapankal, Daniel Patte, W. Brown Patterson, Clive Pearson, Keith F. Pecklers, Nancy Cardoso Pereira, David Horace Perkins, Pheme Perkins, Edward N. Peters, Rebecca Todd Peters, Bishop Yeznik Petrossian, Raymond Pfister, Peter C. Phan, Isabel Apawo Phiri, William S. F. Pickering, Derrick G. Pitard, William Elvis Plata, Zlatko Plese, John Plummer, James Newton Poling, Ronald Popivchak, Andrew Porter, Ute Possekel, James M. Powell, Enos Das Pradhan, Devadasan Premnath, Jaime Adrían Prieto Valladares, Anne Primavesi, Randall Prior, María Alicia Puente Lutteroth, Eduardo Guzmão Quadros, Albert Rabil, Laurent William Ramambason, Apolonio M. Ranche, Vololona Randriamanantena Andriamitandrina, Lawrence R. Rast, Paul L. Redditt, Adele Reinhartz, Rolf Rendtorff, Pål Repstad, James N. Rhodes, John K. Riches, Joerg Rieger, Sharon H. Ringe, Sandra Rios, Tyler Roberts, David M. Robinson, James M. Robinson, Joanne Maguire Robinson, Richard A. H. Robinson, Roy R. Robson, Jack B. Rogers, Maria Roginska, Sidney Rooy, Rev. Garnett Roper, Maria José Fontelas Rosado-Nunes, Andrew C. Ross, Stefan Rossbach, François Rossier, John D. Roth, John K. Roth, Phillip Rothwell, Richard E. Rubenstein, Rosemary Radford Ruether, Markku Ruotsila, John E. Rybolt, Risto Saarinen, John Saillant, Juan Sanchez, Wagner Lopes Sanchez, Hugo N. Santos, Gerhard Sauter, Gloria L. Schaab, Sandra M. Schneiders, Quentin J. Schultze, Fernando F. Segovia, Turid Karlsen Seim, Carsten Selch Jensen, Alan P. F. Sell, Frank C. Senn, Kent Davis Sensenig, Damían Setton, Bal Krishna Sharma, Carolyn J. Sharp, Thomas Sheehan, N. Gerald Shenk, Christian Sheppard, Charles Sherlock, Tabona Shoko, Walter B. Shurden, Marguerite Shuster, B. Mark Sietsema, Batara Sihombing, Neil Silberman, Clodomiro Siller, Samuel Silva-Gotay, Heikki Silvet, John K. Simmons, Hagith Sivan, James C. Skedros, Abraham Smith, Ashley A. Smith, Ted A. Smith, Daud Soesilo, Pia Søltoft, Choan-Seng (C. S.) Song, Kathryn Spink, Bryan Spinks, Eric O. Springsted, Nicolas Standaert, Brian Stanley, Glen H. Stassen, Karel Steenbrink, Stephen J. Stein, Andrea Sterk, Gregory E. Sterling, Columba Stewart, Jacques Stewart, Robert B. Stewart, Cynthia Stokes Brown, Ken Stone, Anne Stott, Elizabeth Stuart, Monya Stubbs, Marjorie Hewitt Suchocki, David Kwang-sun Suh, Scott W. Sunquist, Keith Suter, Douglas Sweeney, Charles H. Talbert, Shawqi N. Talia, Elsa Tamez, Joseph B. Tamney, Jonathan Y. Tan, Yak-Hwee Tan, Kathryn Tanner, Feiya Tao, Elizabeth S. Tapia, Aquiline Tarimo, Claire Taylor, Mark Lewis Taylor, Bishop Abba Samuel Wolde Tekestebirhan, Eugene TeSelle, M. Thomas Thangaraj, David R. Thomas, Andrew Thornley, Scott Thumma, Marcelo Timotheo da Costa, George E. “Tink” Tinker, Ola Tjørhom, Karen Jo Torjesen, Iain R. Torrance, Fernando Torres-Londoño, Archbishop Demetrios [Trakatellis], Marit Trelstad, Christine Trevett, Phyllis Trible, Johannes Tromp, Paul Turner, Robert G. Tuttle, Archbishop Desmond Tutu, Peter Tyler, Anders Tyrberg, Justin Ukpong, Javier Ulloa, Camillus Umoh, Kristi Upson-Saia, Martina Urban, Monica Uribe, Elochukwu Eugene Uzukwu, Richard Vaggione, Gabriel Vahanian, Paul Valliere, T. J. Van Bavel, Steven Vanderputten, Peter Van der Veer, Huub Van de Sandt, Louis Van Tongeren, Luke A. Veronis, Noel Villalba, Ramón Vinke, Tim Vivian, David Voas, Elena Volkova, Katharina von Kellenbach, Elina Vuola, Timothy Wadkins, Elaine M. Wainwright, Randi Jones Walker, Dewey D. Wallace, Jerry Walls, Michael J. Walsh, Philip Walters, Janet Walton, Jonathan L. Walton, Wang Xiaochao, Patricia A. Ward, David Harrington Watt, Herold D. Weiss, Laurence L. Welborn, Sharon D. Welch, Timothy Wengert, Traci C. West, Merold Westphal, David Wetherell, Barbara Wheeler, Carolinne White, Jean-Paul Wiest, Frans Wijsen, Terry L. Wilder, Felix Wilfred, Rebecca Wilkin, Daniel H. Williams, D. Newell Williams, Michael A. Williams, Vincent L. Wimbush, Gabriele Winkler, Anders Winroth, Lauri Emílio Wirth, James A. Wiseman, Ebba Witt-Brattström, Teofil Wojciechowski, John Wolffe, Kenman L. Wong, Wong Wai Ching, Linda Woodhead, Wendy M. Wright, Rose Wu, Keith E. Yandell, Gale A. Yee, Viktor Yelensky, Yeo Khiok-Khng, Gustav K. K. Yeung, Angela Yiu, Amos Yong, Yong Ting Jin, You Bin, Youhanna Nessim Youssef, Eliana Yunes, Robert Michael Zaller, Valarie H. Ziegler, Barbara Brown Zikmund, Joyce Ann Zimmerman, Aurora Zlotnik, Zhuo Xinping
- Edited by Daniel Patte, Vanderbilt University, Tennessee
-
- Book:
- The Cambridge Dictionary of Christianity
- Published online:
- 05 August 2012
- Print publication:
- 20 September 2010, pp xi-xliv
-
- Chapter
- Export citation
Calcium absorption in postmenopausal Chinese women: a randomized crossover intervention study
- Yu-ming Chen, Birgit Teucher, Xin-yi Tang, Jack R. Dainty, Kenneth K. C. Lee, Jean L. F. Woo, Suzanne C. Ho
-
- Journal:
- British Journal of Nutrition / Volume 97 / Issue 1 / January 2007
- Published online by Cambridge University Press:
- 01 January 2007, pp. 160-166
- Print publication:
- January 2007
-
- Article
-
- You have access Access
- HTML
- Export citation
-
The Ca intake and food sources of Chinese postmenopausal women are quite different from those of their Western counterparts. But, little information on Ca metabolism is available in Chinese populations. We determined true fractional calcium absorption (TFCA), true Ca absorption ( = TFCA × Ca intake, Va), urinary Ca excretion (Vu) and the difference between Va and Vu (Va − u), in response to three dietary Ca intake levels. Twenty-one healthy postmenopausal Chinese women aged 49–64 years were recruited for this randomized crossover trial from a general community, Guangzhou, China. Subjects were randomly assigned to receive 0, 500 and 1000 mg Ca/d for 5 weeks separated by 2-week washout periods. TFCA using Ca stable isotopes, total urinary Ca excretion and Ca intake were determined after 4 weeks of adaptation. Mean values for total Ca intake (Vi) of the three phases were 391 (sd 197), 880 (sd 130) and 1382 (sd 160) mg/d. On usual diet, TFCA, Vu, Va and Va − u were 0·57 (sd 0·12), 175 (sd 59) mg/d, 216 (sd 98) mg/d and 41 (sd 99) mg/d, respectively. With the supplementations of 500 and 1000 mg Ca/d, TFCA significantly decreased to 0·52 (sd 0·12) and 0·43 (sd 0·13) (P < 0·001); whereas urinary Ca (P = 0·003), Va and Va − u increased significantly (P < 0·001). Using a mixed-effects nonlinear regression model, it was estimated that Va − u was approaching a plateau when mean Ca intake reached 1300 mg/d. In conclusion, the present findings suggest postmenopausal Chinese women have high Ca absorption efficiency and a mean Ca intake of about 1300 mg/d is required to maximize the Va − u.
Principles of the development of a silica dielectric for microelectronics packaging
- Tapan K. Gupta, Jau-Ho Jean
-
- Journal:
- Journal of Materials Research / Volume 11 / Issue 1 / January 1996
- Published online by Cambridge University Press:
- 31 January 2011, pp. 243-263
- Print publication:
- January 1996
-
- Article
- Export citation
-
Recognizing that speed, size, reliability, and cost are the principal driving forces for advanced electronic packages, this review article describes the much needed development of a new, phase transformation-free, single-phase silica dielectric with a dielectric constant (k) of about 4, the lowest among the inorganic oxides, and a coefficient of thermal expansion (CTE) of about 3 ppm/°C, similar to that of Si. This dielectric, consisting largely of SiO2, represents a gain in media speed by about 50% over alumina dielectric, combined with an improvement in reliability of the package by a factor of about 1000. The feature size and system cost can also be drastically reduced by using this dielectric. It is made from a mixture of binary borosilicate glasses that normally exhibit an undesirable characteristic of precipitating cristobalite during sintering that severely weakens the structure. The most important aspect of this article is the design and development of a strategy that prevents the cristobalite growth by incorporating a crystal growth inhibitor in the binary mixture of glasses. Since kinetics, not thermodynamics, are shown to be the key to success of this strategy, the roles of rate-controlling parameters are deliberately emphasized. A working model is delineated to identify compositions that yield a cristobalite-free silica dielectric with values of CTE that match those of Si and GaAs. Critical issues of co-firing between metals and this dielectric are addressed within the context of multilayer packaging fabrication. Finally, a list of measured properties is presented that clearly shows new opportunities for this silica dielectric.
Devitrification inhibitors in borosilicate glass and binary borosilicate glass composite
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 10 / Issue 5 / May 1995
- Published online by Cambridge University Press:
- 03 March 2011, pp. 1312-1320
- Print publication:
- May 1995
-
- Article
- Export citation
-
Cristobalite is known to precipitate out of borosilicate glass (Corning 7740) and a binary glass mixture of borosilicate glass and high silica glass when these glasses are heated to elevated temperatures. To prevent cristobalite from forming in these glass systems, a devitrification inhibitor needs to be found. Among oxides selected for testing, both Al2O3 and Ga2O3 are found to prevent cristobalite from forming in these glass systems.
Effect of alumina on densification of binary borosilicate glass composite
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 9 / Issue 8 / August 1994
- Published online by Cambridge University Press:
- 03 March 2011, pp. 1990-1996
- Print publication:
- August 1994
-
- Article
- Export citation
-
The effect of alumina on densification of the binary borosilicate glass composite, containing low-softening borosilicate glass (BSG) and high-softening high silica (HSG) glass, has been investigated. It is found that with a small amount of alumina, 2-10 vol. %, present as a dopant in the binary glass mixture of BSG and HSG, both densification and densification rate are significantly reduced, but the activation energy of densification at a given densification is dramatically increased. However, no significant change in densification behavior with increasing alumina content from 2 to 10 vol. % is observed. These results are attributed to a chemical reaction taking place at the interface of alumina/BSG, forming a reaction layer adjacent to alumina. Since the composition of the reaction layer is known to be rich in aluminum and alkali ions and poor in silicon, the alkali ions content in BSG is continuously decreased during sintering. Accordingly, the resultant loss of alkali ions from BSG causes a rise in viscosity of BSG, thus slowing down the densification kinetics and increasing the activation energy of densification.
Origin of cristobalite formation during sintering of a binary mixture of borosilicate glass and high silica glass
- Tapan K. Gupta, Jau-Ho Jean
-
- Journal:
- Journal of Materials Research / Volume 9 / Issue 4 / April 1994
- Published online by Cambridge University Press:
- 03 March 2011, pp. 999-1005
- Print publication:
- April 1994
-
- Article
- Export citation
-
It was shown previously1 that cristobalite precipitates out of a mixture of borosilicate glass (BSG) and high silica glass (HSG) when sintered at temperatures ranging from 800 to 1200 °C. In this paper, both direct and indirect evidences are presented to conclude that the formation of cristobalite originates in HSG. It is proposed that the cristobalite is formed as a result of dissolution of HSG in BSG and precipitation at heterogeneously nucleated sites. The process of dissolution and precipitation continues until the whole HSG particle is consumed.
Densification kinetics and modeling of glass-filled alumina composite
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 9 / Issue 3 / March 1994
- Published online by Cambridge University Press:
- 03 March 2011, pp. 771-780
- Print publication:
- March 1994
-
- Article
- Export citation
-
Kinetics and mechanism of sintering in a model borosilicate glass (BSG) + alumina composite system have been investigated isothermally at 600 to 1000 °C. A faster and greater densification is observed with higher sintering temperature, greater BSG content, and larger alumina particle size. Using measurable densification kinetics, it is found that the activation energy of densification (Q) increases continuously with increasing BSG content, from predominant <110 kJ/mol for BSG < 40 vol.% to 245 kJ/mol for BSG ≥ 90 vol.%. The rate-limiting step during densification is identified to be diffusion of alkali ions in BSG when BSG < 40 vol.% (Q = 110–170 kJ/mol), diffusion of both alkali and aluminum ions when BSG = 40–60 vol.% (Q = 110–170 kJ/mol), diffusion of aluminum ion in BSG when BSG = 60–80 vol.% (Q = 170 kJ/mol), and viscous flow of BSG when BSG ≥ 90 vol.% (Q = 245 kJ/mol). These observations are attributed to a chemical reaction taking place at the interface of alumina/BSG, resulting in a reaction layer adjacent to alumina. Since the composition of the reaction layer is known to be rich in aluminum and alkali ions and poor in silicon, the alkali ions content in BSG is continuously decreased during sintering. Accordingly, when the BSG content in the mixture is low, the resultant loss of alkali ions from BSG causes a rise in viscosity of BSG, thus slowing down the densification kinetics and changing the densification mechanism. As the amount of BSG is increased to ≥90 vol.% at the expense of alumina, the reaction as described above becomes less dominant and the sintering proceeds by viscous flow of glass.
Densification kinetics of binary borosilicate glass composite
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 9 / Issue 2 / February 1994
- Published online by Cambridge University Press:
- 03 March 2011, pp. 486-492
- Print publication:
- February 1994
-
- Article
- Export citation
-
Densification kinetics and mechanism of a binary borosilicate glass composite, containing low-softening borosilicate (BSG) and high-softening high silica (HSG) glasses, have been studied. Apparent activation energy of densification varies from 200 to 400 kJ/mol, and decreases with increasing BSG content at a given densification factor. At a given BSG content, the activation energy of densification initially remains relatively unchanged with increasing densification factor (DF), but increases with densification when DF reaches a critical value (DF∗). Moreover, the value of DF∗ increases with increasing BSG content. From the activation energy estimates of densification, it is concluded that the predominant densification mechanism for BSG ≥ 30 vol. % with DF < DF∗ is viscous flow of low-softening BSG. For BSG ≥ 30 vol. % with DF < DF∗ and BSG ⋚ 20 vol. % with all DF investigated, the activation energies are within the range governed by viscous flow of both BSG and HSG, indicating that the densification is controlled by viscous flow of a new glass with a composition between BSG and HSG. The latter evidence stems from the microstructural observation that as sintering proceeds, the HSG particle undergoes an extensive dissolution process.
Effect of gallium oxide in preventing cristobalite formation in binary borosilicate glass composite
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 8 / Issue 9 / September 1993
- Published online by Cambridge University Press:
- 03 March 2011, pp. 2393-2399
- Print publication:
- September 1993
-
- Article
- Export citation
-
When an appropriate mixture of low-softening borosilicate (BSG) and high-softening high silica (HSG) glasses is sintered at temperatures ranging from 800 to 1000 °C, a crystalline phase, identified as cristobalite by XRD, is known to precipitate out of the initial amorphous binary mixture of glasses as the sintering continues. The precipitation of cristobalite is found to originate in HSG and is controlled by the transport of alkali ions (e.g., K, Na, and Li) from BSG to HSG.1 In this paper we report that when a small amount of gallium oxide is present as a dopant in the above binary mixture of BSG and HSG, the cristobalite formation is completely prevented at the sintering temperatures investigated. The above result is attributed to a strong affinity between Ga+3 from gallium oxide particle and alkali ions from BSG, which diverts the diffusion of alkali ions from HSG to gallium oxide, thus forming a K+ and Ga+3-rich reaction layer adjacent to gallium oxide particles far too rapidly compared with that of cristobalite formation.
Cristobalite growth inhibitor in Pyrex borosilicate glass—gallium oxide
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 8 / Issue 8 / August 1993
- Published online by Cambridge University Press:
- 31 January 2011, pp. 1767-1769
- Print publication:
- August 1993
-
- Article
- Export citation
-
The effect of gallium oxide on cristobalite formation in Pyrex borosilicate glass has been studied. XRD results show that with 20 vol.% gallium oxide, the precipitation of cristobalite at 800 °C is completely prevented. This result is further evidenced by the linear thermal expansion measurement, in which, in contrast to the system without a sufficient amount of gallium oxide (0–10 vol.%), the thermal expansion coefficient of the composite with 20 vol.% gallium oxide remains unchanged with sintering time at the temperature investigated and, moreover, is very close to the theoretically calculated value.
Devitrification inhibitor in binary borosilicate glass composite
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 8 / Issue 2 / February 1993
- Published online by Cambridge University Press:
- 31 January 2011, pp. 356-363
- Print publication:
- February 1993
-
- Article
- Export citation
-
When an appropriate mixture of a low-softening borosilicate glass (BSG) and a high-softening high silica glass (HSG) is sintered at temperatures ranging from 800 to 1000 °C, a crystalline phase, identified as cristobalite by XRD, is known to precipitate out of the initial amorphous binary mixture of glasses as the sintering continues. The precipitation of cristobalite is found to originate in HSG, and is controlled by the transport of alkali ions (e.g., K+, Na+, and Li+) from BSG to HSG.1 In this paper, we report that when a small amount of alumina is present as a dopant in the above binary mixture of BSG and HSG, the cristobalite formation is completely prevented at the sintering temperatures investigated. The above result is attributed to a strong affinity between Al+3 from alumina and alkali ions from BSG, which diverts the diffusion of alkali ions from HSG to alumina, thus forming a K+ and Al+3-rich reaction layer adjacent to the alumina particles far too rapidly compared to that of cristobalite formation.
Isothermal and nonisothermal sintering kinetics of glass-filled ceramics
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 7 / Issue 12 / December 1992
- Published online by Cambridge University Press:
- 31 January 2011, pp. 3342-3347
- Print publication:
- December 1992
-
- Article
- Export citation
-
Isothermal and nonisothermal sintering behaviors of glass-filled ceramics are compared in this paper. Equations developed to describe the kinetics of shrinkage for both techniques can be readily used to interpret the experimental data. It is shown that the kinetics of linear shrinkage of powder compacts during isothermal and nonisothermal constant rate of heating are consistent and can be described by the viscous flow of glass.
Crystallization kinetics of binary borosilicate glass composite
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 7 / Issue 11 / November 1992
- Published online by Cambridge University Press:
- 31 January 2011, pp. 3103-3111
- Print publication:
- November 1992
-
- Article
- Export citation
-
Kinetics of cristobalite precipitation in a binary glass composite, containing a low-softening borosilicate (BSG) and a high-softening high silica (HSG) glass, have been investigated. XRD results show that the pure glasses do not crystallize under the sintering conditions used, but when mixed in appropriate proportions the cristobalite gradually precipitates out of the initial amorphous binary glass mixture as the sintering continues at temperatures ranging from 800 to 1000 °C. Average linear thermal expansion coefficient (TCE) results show that the TCE increases significantly with increasing precipitation of cristobalite as a function of sintering time. Comparing the experimental TCE results with those theoretically calculated, it is concluded that the precipitation originates most likely in the HSG rather than in the BSG. The precipitation kinetics follow the Avrami equation, and the results show an apparent activation energy of 82 kJ/mol which is close to those for the diffusion of alkali ions in silicate glasses, suggesting mass-transport controlled kinetics. The values of the Avrami exponent are 1.7–1.8, which could be interpreted as a 3-dimension diffusional growth at zero nucleation rate. The linear growth rates of cristobalite, calculated from the precipitation curve, are in the range of 4–8 × 10−5 μm/min, and show slight temperature dependence from 800 to 1000 °C. The linear growth rates of cristobalite are also calculated theoretically using the equation derived by Turnbull et al.,2 and the data are 0–3 orders of magnitude smaller than those observed experimentally. This disparity is attributed to the catalytic effect of the OH and O in air and in the glass network, as well as the diffusion of alkali ions from BSG to HSG.
Kinetics of interfacial reaction between borosilicate glass and sapphire substrate
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- Journal of Materials Research / Volume 7 / Issue 9 / September 1992
- Published online by Cambridge University Press:
- 31 January 2011, pp. 2514-2520
- Print publication:
- September 1992
-
- Article
- Export citation
-
Reaction kinetics between borosilicate glass (BSG) and sapphire has been studied at temperatures from 850 °C to 950 °C. Microstructural and chemical analyses show that the nonporous interdiffusion layer is formed with Al+3 ion dissolving from sapphire and K+ diffusing from BSG onto the interface of sapphire/BSG, and that both ions are always coupled together in the reaction layer. The interdiffusion layer moves toward BSG with time and the reaction starts immediately at temperatures investigated without incubation period. The growth kinetics for the interdiffusion layer follows a parabolic rate law in the temperature range investigated, and shows an apparent activation energy in the range of 176 k–/mol. The diffusion coefficient of aluminum ion is determined from EDX analysis, and the values range from 0.7–1.4 × 10−12 at 850 °C to 3.0–6.0 × 10−12 cm2/s at 950 °C. The above results also show an activation energy close to that determined from the parabolic growth rate constants, suggesting that the mass-transport kinetics of aluminum ion from sapphire into the interdiffusion layer controls the formation process.
Liquid Phase Sintering in the Glass-Cordierite System - Effect of Melt Infiltration Distance
- Jau-Ho Jean, Tapan K. Gupta
-
- Journal:
- MRS Online Proceedings Library Archive / Volume 249 / 1991
- Published online by Cambridge University Press:
- 25 February 2011, 419
- Print publication:
- 1991
-
- Article
- Export citation
-
Effect of glass infiltration distance, controlled by particle sizes of glass and ceramic filler, and green density, on densification kinetics of glass-filled ceramics has been studied using borosilicate glass-cordierite as the model system. Within the particle size range investigated, the densification is found to be significantly enhanced by increasing cordierite size, reducing glass size and increasing green density. The above results are attributed to both increased driving force of densification by reducing glass particle size, and decreased glass redistribution distance by either increasing green density of compacts or increasing the particle size ratio between cordierite and glass powders.