Determining the Nucleation Rate Curve for Lithium Disilicate Glass by Differential Thermal Analysis

The crystallization of lithium disilicate (Li₂O·2SiO₂) glass nucleated at various temperatures was studied by differential thermal analysis (DTA). A plot of the DTA crystallization peak height versus nucleation temperature closely resembles the classical nucleation rate curve for lithium disilicate glass whose maximum is at 453°C. The glass becomes saturated with internal nuclei when heated at 453°C for 10 h. The DTA technique is a rapid, alternative method for determining the temperature for maximum nucleation. The activation energy for crystallization, E , and the heat of crystallization, H , are independent of the concentration of nuclei and are 249±10 and 67±3 kJ/mol, respectively. The Avrami exponent, n , depends strongly on the concentration of nuclei in the glass.     

A COMPARATIVE ANALYSIS OF URBAN ISSUES: PERCEPTIONS BY MUNICIPAL OFFICIALS IN A SUNBELT AND A FROSTBELT STATE

This comparative study of Texas and Pennsylvania municipal officials seeks to determine on what urban issues there is the greatest divergence and convergence. Based on states representative of the Sunbelt and the Frostbelt, the study demonstrates that Pennsylvania officials view urban problems as much more critical than their Texas counterparts, and these different perspectives may well translate into political action at the national level.     

Harderian gland pheromone in the Mongolian gerbilMeriones unguiculatus

The Mongolian gerbil (Meriones unguiculatus) secretes an attractant pheromone from the Harderian gland during a facial groom. The material exits at the external nares and is spread over select areas of the face. Its presence stimulates investigation by conspecifics, as seen by video observations. The half-life of the fluorescence of the material on the face following a groom parallels the half-life of attraction. Shock-avoidance and taste-aversion conditioning indicate that animals can both smell and taste a chloroform extract of Harderian glands. They will also seek out and investigate the extract when presented alone. It is suggested that thermoregulatory grooming, social needs, and chemosignaling are intimately linked.This research was supported by grant No. MH 14076-08 awarded to Dr. D. D. Thiessen.     

Ecological consequences of chemically mediated prey perception

To locate food, mobile consumers in aquatic habitats perceive and move towards sources of attractive chemicals. There has been much progress in understanding how consumers use chemicals to identify and locate prey despite the elusive identity of odor signals and the complex effects of turbulence on chemical dispersion. This review highlights how integrative studies on behavior, fluid physics, and chemical isolation can be fundamental in elucidating mechanisms that regulate species composition and distribution. We suggest three areas where further research may yield important ecological insights. First, although basic aspects of stimulatory molecules are known, our understanding of how consumers identify prey from a distance remains poor, and the lack of studies examining the influence of distance perception on food preference may result in inaccurate estimation of foraging behavior in the field. Second, the ability of many animals to find prey is greatest in unidirectional, low turbulence flow environments, although recent evidence indicates a trade-off in movement speed versus tracking ability in turbulent conditions. This suggests that predator foraging mode may affect competitive interactions among consumers, and that turbulence provides a hydrodynamic refuge in space or time, leading to particular associations between predator success, prey distributions, and flow. Third, studies have been biased towards examining predator tracking. Current data suggest a variety of mechanisms prey may use to disguise their presence and avoid predation; these mechanisms also may produce associations between prey and flow environments. These examples of how chemical attraction may mediate interactions between consumers and their resources suggest that the ecology of chemically mediated prey perception may be as fundamental to the organization of aquatic communities as the ecology of chemical deterrence.     

PbO-B2O3玻璃在不同重力条件下相组成和成分均匀性的研究

以3.5PbO·96.5B2O3(mol%)玻璃作为研究对象,着重研究其在不同重力条件下的分相现象.该部分讨论了2个落塔实验试样发生分相的重力条件,同时分析了试样的相组成和试样成分的不均匀性.结果发现,该成分玻璃发生分相后形成的富硼相和富铅相都是玻璃相.分相在高重力阶段发生的试样其成分均匀性最差,原因在于富硼相和富铅相间存在较大的密度差.     

Melting and phase-separation of lead borate glasses in low gravity drop shaft

A drop shaft experiment was conducted to melt and solidify a glass of 3.5PbO–96.5B₂O₃ (mol%) composition adhered to a small platinum heating coil (2–3 mm i.d., 5–6 mm long) at the Japan Microgravity Center (JAMIC). The temperature of glass melt recorded during the drop experiment indicates that the phase-separation of this glass mainly happened during the high gravity period of the experiment. A similar experiment was conducted on the ground to explore the effect of gravity level on the melting and phase-separation of lead borate glass. The homogeneity of different samples was compared through EDS analysis and the microstructure of the samples were observed by SEM. The lead borate glasses separated into two different glass phases, the separated phase (Pb-rich phase) and the continuous phase (B-rich phase), regardless of the gravity level the phase-separation happened. The size of separated Pb-rich phase in the top of sample from drop shaft experiment is much smaller than that in the bottom of sample, while the sizes of separated Pb-rich phase are almost the same in different locations in the ground sample. The homogeneity of the drop shaft sample is much worse than that of ground sample.     

Na2O·8TeO2晶相的转变分解机理探索

以Na2O-TeO2玻璃系统中发现的一个新晶相Na2O·8TeO2(NT8)为研究对象,通过热分析和X-射线衍射等分析手段,着重探讨了该晶相的形成条件和分解条件,分析了该晶相发生转变的过程和机理.结果发现该晶相在330℃下能够稳定存在,而在330～340 ℃之间则会分解成Na2O·4TeO2(NT4)和TeO2两种晶体.在由NT8向NT4和TeO2的转变过程中出现了两个热效应,先是一个吸热反应,然后是一个放热反应,这说明在NT8向NT4和TeO2的转变过程中,出现了一个中间相,该中间相为一种非晶相.作者认为,NT8向NT4和TeO2的转变分为两个步骤,第一步是由NT8向中间非晶相的转变,第二步是中间非晶相向NT4和TeO2的转变,而且由NT8向中间相转变的过程与由中间相向NT4和TeO2转变的过程是同时进行的.     

Na2O·8TeO2晶相的转变分解机理探索

以Na2O—TeO2玻璃系统中发现的一个新晶相Na2O8·TeO2（NT8）为研究对象，通过热分析和X-射线衍射等分析手段，着重探讨了该晶相的形成条件和分解条件，分析了该晶相发生转变的过程和机理。结果发现该晶相在330℃下能够稳定存在，而在330-340℃之间则会分解成Na2O·4TeO2（NT4）和TeO2两种晶体。在由NT8向NT4和TeO2的转变过程中出现了两个热效应，先是一个吸热反应，然后是一个放热反应，这说明在NT8向NT4和TeO2的转变过程中，出现了一个中间相，该中间相为一种非晶相。作者认为，NT8向NT4和TeO2的转变分为两个步骤，第一步是由NT8向中间非晶相的转变，第二步是中间非晶相向NT4和TeO2的转变，而且由NT8向中间相转变的过程与由中间相向NT4和TeO2转变的过程是同时进行的。     

Hollow hydroxyapatite microspheres as a device for controlled delivery of proteins

Hollow hydroxyapatite (HA) microspheres were prepared by reacting solid microspheres of Li₂O–CaO–B₂O₃ glass (106–150 μm) in K₂HPO₄ solution, and evaluated as a controlled delivery device for a model protein, bovine serum albumin (BSA). Reaction of the glass microspheres for 2 days in 0.02 M K₂HPO₄ solution (pH = 9) at 37°C resulted in the formation of biocompatible HA microspheres with a hollow core diameter equal to 0.6 the external diameter, high surface area (~100 m²/g), and a mesoporous shell wall (pore size ≈13 nm). After loading with a solution of BSA in phosphate-buffered saline (PBS) (5 mg BSA/ml), the release kinetics of BSA from the HA microspheres into a PBS medium were measured using a micro bicinchoninic acid (BCA) protein assay. Release of BSA initially increased linearly with time, but almost ceased after 24–48 h. Modification of the BSA release kinetics was achieved by modifying the microstructure of the as-prepared HA microspheres using a controlled heat treatment (1–24 h at 600–900°C). Sustained release of BSA was achieved over 7–14 days from HA microspheres heated for 5 h at 600°C. The amount of BSA released at a given time was dependent on the concentration of BSA initially loaded into the HA microspheres. These hollow HA microspheres could provide a novel inorganic device for controlled local delivery of proteins and drugs.     

Corrosion behavior of Inconel 690 and 693 in an iron phosphate melt

The corrosion resistance of Inconel 690 and 693 coupons submerged in an iron phosphate melt has been investigated. After 155 days in an iron phosphate melt at 1050 °C, which contained 30 wt% of a simulated low activity waste (LAW at Hanford), the weight loss of Inconel 690 and 693 was 14% and 8%, respectively. The overall corrosion rate, calculated from the initial and final dimensions of each coupon, was 1.3 and 0.7 μm/day for the Inconel 690 and 693, respectively. Scanning electron microscopy and X-ray diffraction of the submerged Inconel coupons after 155 days in the iron phosphate melt showed that an altered surface layer had formed which was depleted in nickel and consisted of a (Fe, Cr)₂O₃ solid solution. This altered layer appears to be chemically protective as indicated by the gradual reduction in weight loss which occurred with time in the iron phosphate melt. Inconel 693 appears to be a better candidate to use as an electrode in iron phosphate melts since its corrosion rate and weight loss was only about one half that of Inconel 690.