The microdetermination of cadmium and zinc by photometric titration

M.S.H. A. Flaschk

Spatiotemporal Dynamics of Neural Activity During Human Episodic Memory Encoding and Retrieval

Throughout literary history, the ability to travel in time has been a source of wonder and amusement. Why this fascination with moving through time? One reason may be that people are especially attuned to the concept of time travel because we each possess our own personal mental time machine: episodic memory. Through episodic memory, we transport ourselves back in time to re-live experiences from our past. This allows us to reflect on our own self-knowledge, effectively placing ourselves in context of our lives. This dissertation investigates how our brains accomplish this highly sophisticated cognitive operation. Using a laboratory model of episodic memory (free recall) and a particularly powerful neuroimaging tool (intracranial EEG), I document the changes that occur in the brain as episodic memories are first formed and then later retrieved. I find that the episodic memory system is best conceptualized as stage-wise process consisting of distinct brain regions that activate at highly conserved times relative to memory formation/retrieval. These discrete activations are used to construct a novel neurological model of episodic memory, the Neurological Stages of Episodic Retrieval and Formation (N-SERF) model. Future work should be aimed at verifying the hypotheses put forward by the N-SERF model, we well as relating the N-SERF model to prominent computational models of episodic memory

Assessment of kinetic modeling for lean H 2 /CH 4 /O 2 /diluent flames at high pressures

Abstract Experimental measurements of burning rates, analysis of key reactions and kinetic pathways, and modeling studies were performed for H 2 /CH 4 /O 2 /diluent flames spanning a wide range of fuel-lean conditions: equivalence ratios from 0.30 to 1.0, flame temperatures from 1400 to 1800 K, pressures from 1 to 25 atm, CH 4 fuel fractions from 0 to 0.1. The experimental data show negative pressure dependence of burning rate at high-pressure, low-flame-temperature conditions for all equivalence ratios and with CH 4 addition. Substantial differences are observed between literature model predictions and the experimental data as well as among model predictions themselves -up to a factor of four at high pressures. Similar to our previous work that demonstrated that none of the recent kinetic models reproduced the measured pressure dependence of the mass burning rate for all diluent concentrations and medium to high equivalence ratios, here it is demonstrated that none reproduce the measured pressure dependence for very low equivalence ratios. The effect of pressure on the kinetics of lean flames is largely driven by competition of both H + O 2 (+M) = HO 2 (+M) and HO 2 + O/OH/HO 2 with the main branching reactions, in contrast to rich mixtures that are largely driven by competition of both H + O 2 (+M) = HO 2 (+M) and HO 2 + H with the main branching reactions. Methane addition is shown to influence the pressure dependence mainly through reactions of CH 3 with H and HO 2 . Given the nature of the modeling problem for high-pressure flames, it appears that a rigorous solution to improving predictive capabilities will require both empirical adjustments of multiple rate constant parameters as well as improved characterization of the functional temperature and pressure dependence of certain highly sensitive reactions. Furthermore, many of the reactions responsible for uncertainties in the pressure dependence of H 2 /O 2 flames at high pressures are shown to contribute significantly to uncertainties in the pressure dependence of flames of hydrocarbon fuels

Protein sequestration generates a flexible ultrasensitive response in a genetic network

Ultrasensitive responses are crucial for cellular regulation. Protein sequestration, where an active protein is bound in an inactive complex by an inhibitor, can potentially generate ultrasensitivity. Here, in a synthetic genetic circuit in budding yeast, we show that sequestration of a basic leucine zipper transcription factor by a dominant-negative inhibitor converts a graded transcriptional response into a sharply ultrasensitive response, with apparent Hill coefficients up to 12. A simple quantitative model for this genetic network shows that both the threshold and the degree of ultrasensitivity depend upon the abundance of the inhibitor, exactly as we observed experimentally. The abundance of the inhibitor can be altered by simple mutation; thus, ultrasensitive responses mediated by protein sequestration are easily tuneable. Gene duplication of regulatory homodimers and loss-of-function mutations can create dominant negatives that sequester and inactivate the original regulator. The generation of flexible ultrasensitive responses is an unappreciated adaptive advantage that could explain the frequent evolutionary emergence of dominant negatives

Multidetector Computed Tomography Findings of a Papillary Fibroelastoma of the Aortic Valve: A Case Report

Papillary fibroelastoma is a rare benign cardiac tumor that represents 10% of all primary cardiac tumors. Diagnosis is accomplished incidentally by echocardiography that is usually performed for another purpose. Most papillary fibroelastomas are asymptomatic, but the lesions are recognized as a cause of embolisms. To the best of our knowledge, there has been no case report of computed tomography findings of a papillary fibroelastoma. We report a case of a papillary fibroelastoma in a 78-yr-old woman who had dyspnea and chest tightness. Echocardiography revealed a small lobulated mobile echogenic mass attached to the aortic valve, and CT demonstrated a lobulated soft tissue density mass with a thin stalk at the sinotubular junction of the aortic valve

Reefs at Risk: A Map-Based Indicator of Threats to the Worlds Coral Reefs

This report presents the first-ever detailed, map-based assessment of potential threats to coral reef ecosystems around the world. "Reefs at Risk" draws on 14 data sets (including maps of land cover, ports, settle-ments, and shipping lanes), information on 800 sites known to be degraded by people, and scientific expertise to model areas where reef degradation is predicted to occur, given existing human pressures on these areas. Results are an indicator of potential threat (risk), not a measure of actual condition. In some places, particularly where good management is practiced, reefs may be at risk but remain relatively healthy. In others, this indicator underestimates the degree to which reefs are threatened and degraded.Our results indicate that:Fifty-eight percent of the world's reefs are poten-tially threatened by human activity -- ranging from coastal development and destructive fishing practices to overexploitation of resources, marine pollution, and runoff from inland deforestation and farming.Coral reefs of Asia (Southeastern); the most species-rich on earth, are the most threatened of any region. More than 80 percent are at risk (undermedium and high potential threat), and over half are at high risk, primarily from coastal development and fishing-related pressures.Overexploitation and coastal development pose the greatest potential threat of the four risk categories considered in this study. Each, individually, affects a third of all reefs.The Pacific, which houses more reef area than any other region, is also the least threatened. About 60 percent of reefs here are at low risk.Outside of the Pacific, 70 percent of all reefs are at risk.At least 11 percent of the world's coral reefs contain high levels of reef fish biodiversity and are under high threat from human activities. These "hot spot" areas include almost all Philippine reefs, and coral communities off the coasts of Asia, the Comoros, and the Lesser Antilles in the Caribbean.Almost half a billion people -- 8 percent of the total global population -- live within 100 kilometers of a coral reef.Globally, more than 400 marine parks, sanctuaries, and reserves (marine protected areas) contain coral reefs. Most of these sites are very small -- more than 150 are under one square kilometer in size. At least 40 countries lack any marine protected areas for conserving their coral reef systems

Does the Tripartite Influence Model of Body Image and Eating Pathology Function Similarly Across Racial/Ethnic Groups of White, Black, Latina, and Asian Women?

The tripartite influence model suggests that appearance pressures from family, peers, and the media contribute to thin-ideal internalization, which leads to increased body dissatisfaction and subsequent eating disorder pathology. The tripartite influence model was initially developed and tested among primarily White samples, and emerging research suggests racial/ethnic differences in mean levels of particular model constructs. Consequently, the model\u27s appropriateness for understanding eating disorder risk in racial/ethnic minorities warrants investigation to determine its usefulness in explicating eating disorder risk in diverse populations. Participants in the current study were White (n = 1167), Black (n = 212), Latina (n = 203), and Asian (n = 176) women from five geographically disparate college campuses in the United States. Participants completed the Sociocultural Attitudes Towards Appearance Questionnaire-4, the Multidimensional Body-Self Relations Questionnaire - Appearance Evaluation Subscale, and the Eating Disorder Examination-Questionnaire. Analysis of variance was used to compare mean levels of each construct across racial/ethnic groups. Multigroup structural equation modeling was used to assess the appropriateness of the tripartite influence model for each racial/ethnic group, and to examine differences in the strength of the model pathways across groups. There were significant mean level differences across groups for most model constructs. However, results indicated similar model fit across racial/ethnic groups, with few differences in the strength of model pathways. Findings suggest that although some groups report lower levels of proposed risk factors, the sociocultural risk processes for eating pathology identified through the tripartite influence model are similar across racial/ethnic groups of young adult women. Such information can be used to inform culturally-sensitive interventions