Experimental and numerical investigations of an oxygen single-bubble shrinkage in a borosilicate glass-forming liquid doped with cerium oxide

The shrinkage of an oxygen single-bubble is investigated in a cerium-doped borosilicate glass melt at 1150°C. Nine glass samples are synthesized and investigated, utilizing three different amounts of Ce₂O₃ and three different redox ratios (Ce-(III)/Ce_total). Employing in-situ observation, the single-bubble behavior is recorded with a camera. For each glass melt, five experiments are performed with different initial bubble radii. The shrinkage rate () depends strongly on the cerium content as well as the redox ratio. Numerical calculations are also conducted to support the understanding of the bubble shrinkage mechanism in the given cases. The model adequately estimates the experimental data for several cases, and an explanation is proposed for the cases, in which it does not. Moreover, we demonstrate, physically and mathematically, the influence of the initial radius of the bubble on the mass transfer between the rising bubble and the melt. We confirm the utilization of the “modified Péclet number,” which is a dimensionless number that takes into consideration the influence of multivalent elements on mass transfer. Finally, we master the bubble shrinkage behavior by normalizing the experimental data employing a characteristic time for the mass transfer (τ).     

Kinetic study of the retrogradation of gelatinised starch

A method was developed for the study of starch retrogradation by differential thermal analysis. The kinetics of the crystallisation process were studied using the expression θ8 = exp (-ktⁿ), where θ = the fraction of crystallisable starch remaining uncrystallised at time t. The values for the Avrami exponent (n) and the rate constant (k) were found to coincide with values previously obtained for the staling of bread, as followed by measurement of crumb elastic modulus. No difference between the time constants of gels cooled slowly and rapidly after gelatinisation was found, indicating that the nucleation process in starch crystallisation is instantaneous in the systems studied. The fact that the Avrami exponent is unity also suggests that the nucleation process is instantaneous, and that it is followed by rod-like growth of crystals.     

Iron and arsenic cycling in intertidal surface sediments during wetland remediation

The accumulation and behavior of arsenic at the redox interface of Fe-rich sediments is strongly influenced by Fe(III) precipitate mineralogy, As speciation, and pH. In this study, we examined the behavior of Fe and As during aeration of natural groundwater from the intertidal fringe of a wetland being remediated by tidal inundation. The groundwater was initially rich in Fe(2+) (32 mmol L(-1)) and As (1.81 μmol L(-1)) with a circum-neutral pH (6.05). We explore changes in the solid/solution partitioning, speciation and mineralogy of Fe and As during long-term continuous groundwater aeration using a combination of chemical extractions, SEM, XRD, and synchrotron XAS. Initial rapid Fe(2+) oxidation led to the formation of As(III)-bearing ferrihydrite and sorption of >95% of the As(aq) within the first 4 h of aeration. Ferrihydrite transformed to schwertmannite within 23 days, although sorbed/coprecipitated As(III) remained unoxidized during this period. Schwertmannite subsequently transformed to jarosite at low pH (2-3), accompanied by oxidation of remaining Fe(2+). This coincided with a repartitioning of some sorbed As back into the aqueous phase as well as oxidation of sorbed/coprecipitated As(III) to As(V). Fe(III) precipitates formed via groundwater aeration were highly prone to reductive dissolution, thereby posing a high risk of mobilizing sorbed/coprecipitated As during any future upward migration of redox boundaries. Longer-term investigations are warranted to examine the potential pathways and magnitude of arsenic mobilization into surface waters in tidally reflooded wetlands.     

Motion trapping structures in the three-dimensional water-wave problem

Trapped modes in the linearized water-wave problem are free oscillations of finite energy in an unbounded fluid with a free surface. It has been known for some time that such modes are supported by certain structures when held fixed, but recently it has been demonstrated that in two dimensions trapped modes are also possible for freely floating structures that are able to respond to the hydrodynamic forces acting upon them. For a freely floating structure such a mode is a coupled oscillation of the fluid and the structure that, in the absence of viscosity, persists for all time. Here previous work on the two-dimensional problem is extended to give motion trapping structures in the three-dimensional water-wave problem that have a vertical axis of symmetry. Nick Newman has made many important contributions to the theory of the interaction between water waves and structures, and his panel code WAMIT has been adopted as one of the industry standards for the calculation of wave loading on offshore structures. It gives us great pleasure to celebrate Nick’s achievements through the presentation of this work on a new type of structure that both draws on his theoretical work and uses WAMIT to perform relevant computations.     

Design and synthesis of conformationally-constrained MMP inhibitors

A novel series of conformationally constrained matrix metalloprotease inhibitors was identified. The potencies observed for these inhibitors were highly dependent upon the substitution pattern on the caprolactam ring as well as the succinate moiety.     

Evaluation and management of amenorrhea

All women who enter menopause experience amenorrhea unless they receive hormone replacement therapy. In younger women, amenorrhea unrelated to pregnancy and lactation can be a distressing symptom. In addition to its psychologic morbidity, amenorrhea may be the manifesting feature of a wide array of anatomic and endocrine abnormalities. Amenorrhea results in impaired fertility. When estrogen levels are low, changes in mineral, glucose, and fat metabolism accompany amenorrhea. These metabolic changes affect bone and cardiovascular health, increasing the risk of osteoporosis and coronary heart disease in later life. Amenorrhea with hyperandrogenism, most commonly caused by the polycystic ovarian syndrome, may cause endometrial hyperplasia and increases the risk of endometrial adenocarcinoma. Because of the broad differential diagnosis of amenorrhea, establishing an accurate diagnosis can prove challenging. In this article, we outline one approach to the assessment of patients with amenorrhea and to the management of its common causes and consequences.     

Subjective qualities of memories associated with the picture superiority effect in schizophrenia.

Patients with schizophrenia (n=24) matched with 24 normal subjects were presented with both words and pictures. On a recognition memory task, they were asked to give remember, know, or guess responses to items that were recognized on the basis of conscious recollection, familiarity, or guessing, respectively. Compared with normal subjects, patients exhibited a lower picture superiority effect selectively related to remember responses. Unlike normal subjects, they did not exhibit any word superiority effect in relation to guess responses; this explains why the overall picture superiority effect appeared to be intact. These results emphasize the need to take into account the subjective states of awareness when analyzing memory impairments in schizophrenia. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Design of a Soft-Switched 6-kW Battery Charger for Traction Applications

Auxiliary power converters for traction rolling stock applications have to operate under difficult conditions, including high-input voltages which are subject to wide fluctuations, high temperatures, and harsh environmental constraints. Additionally there is often a need for silent operation, which implies switching frequencies above 20 kHz. Increasingly, high-frequency DC-DC converters are being used for these applications, with their advantages of reduced size and weight. However, the requirement to accommodate high-input voltages and switch at high frequencies is challenging for a conventional hard-switched converter based on IGBTs, which makes soft-switching topologies an attractive alternative. This paper presents the design strategy for a zero-voltage switched (ZVS) 6-kW battery charger switching at 20 kHz using IGBTs. This paper illustrates how the design is a tradeoff between managing the hard-switch turn-on losses at light load, minimizing the duty cycle loss caused by soft-switching delays, and minimizing the effects of tail current-switching losses. These tradeoffs affect the selection of the ZVS capacitors, the determination of the series inductance value, the transformer turns ratio, and the selection of the IGBTs to be used. Design details, theoretical predictions, and experimental results are presented in this paper for the conversion system that was developed.     

Estimating pixel-scale land cover classification confidence usingnonparametric machine learning methods

Conventional approaches to accuracy assessment for land cover maps produced from remote sensing use either confusion matrices or the Kappa statistic to quantify map quality. These approaches yield global or class-specific measures of map quality by comparing classification results with independent ground-truth data. In most maps, considerable spatial variation is present in the accuracy of land cover labels that is not captured by these statistics. To date, this issue has rarely been addressed in the land cover remote sensing literature. The authors present a method to estimate pixel-scale land cover classification confidence using nonparametric machine learning methods. The method is based on recent theoretical developments from the domains of statistics and machine learning that explain the machine learning technique known as “boosting” as being equivalent to additive logistic regression. As a result, results from classification algorithms that use boosting can be assigned classification confidences based on probability estimates assigned to them using this theory. they test this approach using three different data sets. Their results demonstrate that classification errors tend to have low classification confidence while correctly classified pixels tend to have higher confidence. Thus, the method described in this paper may be used as a basis for providing spatially explicit maps of classification quality. This type of information will provide substantial additional information regarding map quality relative to more conventional quality measures and should be useful to end-users of map products derived from remote sensing