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)

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.

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.

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.

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.

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.

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 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.

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.

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.

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 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.

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.

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.

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.