Venus steep-sided domes: Relationships between geological associations and possible petrogenetic models

Venus domes are characterized by steep sides, a circular shape, and a relatively flat summit area. In addition, they are orders of magnitude larger in volume and have a lower height/diameter ratio than terrestrial silicic lava domes. The morphology of the domes is consistent with formation by lava with a high apparent viscosity. Twenty percent of the domes are located in or near tessera (highly deformed highlands), while most other (62 percent) are located in and near coronae (circular deformational features thought to represent local mantle upwelling). These geological associations provide evidence for mechanisms of petrogenesis and several of these models are found to be plausible: remelting of basaltic or evolved crust, differentiation of basaltic melts, and volatile enhancement and eruption of basaltic foams. Hess and Head have shown that the full range of magma compositions existing on the Earth is plausible under various environmental conditions on Venus. Most of the Venera and Vego lander compostional data are consistent with tholeiitic basalt; however, evidence for evolved magmas was provided by Venera 8 data consistent with a quartz monzonite composition. Pieters et al. have examined the color of the Venus surface from Venera lander images and interpret the surface there to be oxidized. Preliminary modeling of dome growth has provided some interpretations of lava rheology. Viscosity values obtained from these models range from 10(exp 14) - 10(exp 17) pa*s, and the yield strength has been calculated to be between 10(exp 4) and 10(exp 6) Pa, consistent with terrestrial silicic rocks. The apparent high viscosity of the dome lavas suggests that the domes have a silicic composition or must augment their viscosity with increased visicularity or crystal content. Sixty-two percent of the Venus domes are associated with coronae, circular features that have been proposed as sites of mantle upwelling, and 20 percent of the domes are located near tessera, relatively high areas of complex deformed terrain. We have investigated several models that are consistent with these geologic associations. The first case involves the differentiation of basalt in a magma reservoir in the crust, perhaps produced by partial melting within a mantle plume. The second case is melting at the base of thickened basaltic crust, and the final case is volatile exsolution and enhancement within a basaltic magma reservoir. The association of domes with tessera might be explained by crustal remelting, while the association with coronae may be consistent with chemical differentiation of a magma reservoir or the exsolution and concentration of volatiles in the reservoir before eruption

An Empirical Study Of The Factors Contributing To Microcomputer Usage

Information technology--computers, communication networks and the like--has assumed a role of growing importance in both private and public sector organizations during the 1980\u27s. This technology is no longer the private preserve of small groups of computer specialists; rather, the office automation and end user computing movements are placing information technology into the hands of workers at all levels, and in all areas. The emergence of the business microcomputer has played a central role in this trend.;The rapid growth of microcomputers in the workplace, however, has not been without problems. In some offices, even where having a microcomputer is viewed as a status symbol, the systems themselves are highly used.;Because information technology, and in particular the microcomputer, has come to play such an important role in modern organizations, it is crucial that we develop a better understanding of the various factors that affect managers\u27 decisions whether to adopt this technology. The purpose of this research is to develop and test a model of the relationships between a variety of external variables, and the managers\u27 usage of computers.;Fishbein\u27s \u27theory of reasoned action,\u27 a widely accepted model of human behaviour, lies at the core of this study. Fishbein\u27s model posits that one\u27s intention to act a certain way (e.g., begin to use a microcomputer) is derived from two general classes of factors: attitudes, and subjective norms. Furthermore, intention leads to action (barring the presence of external variables, e.g., unavailability of a microcomputer).;Data was collected from a cross-sectional survey of 519 managers, drawn from managers of 54 corporations in Ontario. The results provided support for 11 of the 16 propositions in the model. Using LISREL as the data analysis technique, it was found that positive attitudes towards computer usage, and subjective norms that supported usage led to higher levels of usage. In turn, attitudes were affected by computer anxiety, computer skills, the quality of the system and management support. Subjective norms were affected by management support, and usage by upper level managers and peer managers in the organization

Evaluation of Ventricular Repolarization in Patients Undergoing Cardiac Resynchronization Therapy (CRT) Using Two Modalities: Conventional Biventricular Pacing vs. His-Bundle Pacing

Introduction: Permanent His-bundle pacing (HBP) is being used as an alternative to biventricular pacing (BiVP) for CRT. HBP preserves the physiologic pattern of ventricular activation and markedly reduces ventricular dyssynchrony. While ventricular depolarization with HBP vs. BiVP has been studied, the effects of the 2 modalities on repolarization have not been compared. The purpose of this study was to compare ventricular repolarization in patients with HBP and BiVP. We hypothesize that HBP provides more physiologic repolarization as compared to BiVP. Methods: ECG repolarization parameters were analyzed in patients who underwent HBP and BiVP using the first available ECG post implant. Parameters included: 1) T Peak – T End (Tp-TeApical): Tp-Te in lead V5, and if not measurable, then in V4/V6 2) Tp-TeTotal: Earliest T peak to the latest T end across all precordial leads 3) T Peak Dispersion: Absolute difference between the earliest and latest T peaks across all precordial leads. Data was compared using a two-tailed unequal variance Student’s t-test. Results: Data from 23 HBP patients and 23 BiVP patients was analyzed. The average HBP Tp-TeApical of 74 ± 7ms was less than the BiVP Tp-TeApical of 112 ± 15ms (p\u3c0.01). Similarly, average HBP Tp-TeTotal of 106 ± 11ms was smaller than the BiVP Tp-TeTotal of 145 ± 17ms (p\u3c0.01). The difference between Tpeak dispersion between the two groups was not significant. Conclusion: Tp-Te interval, a known measure of dispersion of repolarization and marker of arrhythmic risk, is more physiologic (lower) with HBP as compared to BiVP. These data suggest that in addition to physiologic depolarization, HBP also provides physiologic repolarization and potentially lower arrhythmic risk compared to BiVP

Land Use and Socioeconomic Influences on a Vulnerable Freshwater Resource in Northern New England, United States

Land use and cover conversions as well as climatic factors drive current and future threats to freshwater systems. Research from the United States and across the globe has focused on already threatened and degraded freshwater systems, whose recovery requires significant investments. Attention must also be directed to monitoring freshwater systems that may appear robust, yet are likely to face enhanced vulnerabilities in the future due to climate and land use and cover changes. Such proactive monitoring can help identify problems early and provide potential solutions. In this study, we consider the case of Sebago Lake and its watershed in southern Maine; a region that has experienced significant population growth and development activity. Land use, socioeconomic change and water quality trends are monitored over a 20-year period using Landsat imagery, census, water quality and precipitation data. Our results indicate that Developed Land within the watershed has increased from 5.4 % of the total land area in 1987 to 8.9 % in 2009 with associated increases in population and housing activity. Sebago Lake’s water quality indicators from 1990 to 2010 show a directional trend concomitant with this change. The increase in Developed Land is likely to place additional pressures on water quality in the future. The analysis also indicates that precipitation trends play an important role in water quality variability for Sebago Lake. Predicted changes to climatic factors including enhanced spring time precipitation or earlier ice-out conditions combined with further land use change may play an influential role in determining water quality. The analysis highlights emerging areas of concern and reiterates the essential role of proactively monitoring vulnerable systems to help mitigate future threats

Validation of a Novel, Non-Invasive System for Autonomic Profiling in Healthy Volunteers

Noninvasive profiling of the autonomic nervous system has been shown to have prognostic value in patients with myocardial infarction, CHF and diabetes. The ANSAR system (ANX 3.0, Philadelphia, PA) is a new commercially available system that utilizes respiratory rate, HR and BP to assess on-going sympathovagal modulation during various maneuvers known to evoke autonomic perturbations. Instead of using conventional Fast Fourier Transform for frequency domain analysis, a Continuous Wavelet Transform (CWT) is used to generate numerical and graphical data. The system calculates Low Frequency Area (LFA, analogous to LF Power) and Respiratory Frequency Area (RFA, analogous to High Frequency Power.) A time domain index (pNN50 is also calculated

Improving Evaluation and Follow-up of Patients Diagnosed with Left Bundle Branch Block

Left bundle branch block (LBBB) is a pathologic finding on electrocardiogram (ECG). Most commonly present in patients with antecedent hypertension, cardiac enlargement, coronary artery disease or a combination of these Class 1B recommendation: Those with findings of LBBB on ECG should undergo transthoracic echocardiography for evaluation of underlying heart disease LBBB is prevalent (33%) in patients with heart failure Cardiac resynchronization therapy can improve left ventricular mechanical function in patients with LBBB (QRS \u3e150 msec) This study aims to understand how effectively we are evaluating and following up these patients at Thomas Jefferson University Hospital

Cryo vs RF p-wave Characteristics Comparative Analysis

Introduction: Atrial fibrillation is one of the leading causes of heart failure and stroke in the US, meaning that optimizing treatment is essential. There are two catheter based PVI techniques used to treat drug-refractory AF patients: radiofrequency and cryo-balloon ablation. The goal of this study is to determine if there is a difference in efficacy between these two procedures. Methods: The study consisted of a retrospective chart review and ECG analysis of approximately 130 patients. The criteria for involvement is patients diagnosed with drug-refractory paroxysmal AF and who have undergone an ablation procedure in the past two years. Baseline characteristics were measured from EPIC and p-wave parameters were measured on ECG’s using MUSE. Statistical analysis was done to determine if there is any significant difference in p wave parameters between the two groups of patients. Results: At this point in time, there remains data to be collected, but we are able to share preliminary results. The only significant finding was when we looked at p-wave duration, specifically the change in V1 duration, which showed that patients were less likely to have an AF recurrence if their p-wave duration lengthened after the procedure. Discussion: These results are important, as the change of lead V1 duration could be used as a predictor of AF recurrence. However, at this point we are unable to find a difference in efficacy between cryo-ablation and RF ablation and so our main objective is incomplete. the hope is upon completing data collection, we will be able to answer our research question