Large Observational Database Research Articles

Hydrodynamics and membrane seal capacity

AbstractThe impact of hydrodynamic groundwater movement on the capacity of seals is currently in debate. There is an extensive record of publication on seals analysis and a similar history on petroleum hydrodynamics yet little work addresses the links between the two. Understanding and quantifying the effects of hydrodynamic flow has important implications for calibrating commonly used seal capacity estimation techniques. These are often based on measurements such as shale gouge, clay smear or mercury porosimitry where membrane sealing is thought to occur. For standard membrane seal analysis, seal capacity is estimated by quantifying capillary pressure‐related measurements and calibrating them with a large observational database of hydrocarbon column heights and measured buoyancy pressures. The seal capacity estimation process has historically been adjusted to account for a number of different generic trapping geometries. We define the characteristics of these geometries from a hydrodynamics viewpoint in order to fine‐tune the seal capacity calibration process. From theoretical analyses of several simplified trapping geometries, it can be concluded that generally, the high pressure side of the seal should be used as the water pressure gradient with which to calculate buoyancy pressure. Secondly, trap geometries where hydrocarbon is reservoired on both sides of a fault are not useful for estimating across fault seal capacity.

Do Atypical Antipsychotics Cause Stroke?

Post hoc analyses of pooled results from 11 randomised controlled trials of risperidone and olanzapine in elderly dementia subjects revealed an increased incidence of cerebrovascular adverse events compared with placebo. Reanalysis of the risperidone trials suggests that some of the increased incidence may be accounted for by nonspecific events that were not strokes. Large observational administrative health database studies appear to confirm that risperidone and olanzapine are not associated with an increased risk of stroke in elderly patients compared with typical antipsychotics or untreated dementia patients. A larger number of subjects with vascular and mixed dementias were included in the risperidone studies compared with the olanzapine studies, which likely accounts for the increased incidence of cerebrovascular adverse events in the risperidone trials compared with the olanzapine studies. Potential mechanisms proposed to explain an association between atypical antipsychotics and cerebrovascular adverse events include thromboembolic effects, cardiovascular effects (e.g. orthostatic hypotension, arrhythmias), excessive sedation resulting in dehydration and haemoconcentration, and hyperprolactinaemia. However, there is little evidence to support these hypothesised mechanisms at present. The association between atypical antipsychotics and cerebrovascular adverse events requires further clarification. At the present time, this association is another factor that clinicians should consider when weighing the risks and benefits of treating behavioural and psychological disturbances in elderly dementia patients.

Time-dependent, coupled, Ekman boundary layer solutions incorporating Stokes drift

Recent technological advances in current measuring devices has resulted in a large observational database related to wind-driven motions in the upper ocean mixed layer. This has served to highlight the fact that transient motions make up a substantial contribution of the resulting Ekman currents. At the same time, certain discrepancies have emerged between the observed angular deflections of the steady-state currents from the surface wind stress, both at the surface and at sub-surface depths, which cannot be reconciled using the classical Ekman model. This paper seeks to tackle these two issues. First a general analytical method is presented for solving the time dependent horizontal momentum Ekman equations. Analysis of the unsteady terms that arise from simple special cases shows how the evolution proceeds through three stages. At early times, the Coriolis acceleration is insignificant, and the current is unidirectional and deepens through downward diffusion of momentum. Later Coriolis acceleration deflects the current vectors in the upper layers, whilst downward diffusion of momentum continues to deepen the layer. Finally, once diffusion has penetrated down to the depth of the steady-state current, then the transients decay on the inertial or diffusive timescale, depending upon the boundary conditions of the particular problem. In the second half of the paper, a new steady-state model is developed that includes the effects of wind-generated waves, through the action of their Stokes drift on the planetary vorticity. Comparisons between observations and the theoretical predictions, demonstrate that inclusion of the Stokes drift is the key to reconciling the discrepancies in the angular deflections of the steady-state currents. This leads to the conclusion that Ekman layer currents are significantly influenced by the surface waves.

Global metallicity of globular cluster stars from colour-magnitude diagrams

We have developed an homogeneous evolutionary scenario for H- and He-burning low-mass stars by computing updated stellar models for a wide metallicity and age range (0.0002$\le Z \le$0.004 and 9$\le t(Gyr) \le$15, respectively) suitable to study globular clusters. This theoretical scenario allows us to provide self-consistent predictions about the dependence of selected observational features of the colour-magnitude diagram, such as the brightness of the Turn Off (TO), Zero Age Horizontal Branch (ZAHB) and Red Giant Branch bump (BUMP), on the cluster metallicity and age. Taking into account these predictions, we introduce a new observable based on the visual magnitude difference between the TO and the ZAHB, and the TO and the RGB-bump, given by $A=\Delta M_V$(TO-BUMP)$-0.566\Delta M_V$(TO-ZAHB). We show that the parameter $A$ does not depend at all on the cluster age, whereas it does strongly depend on the cluster global metallicity. The calibration of the parameter $A$ as a function of $Z$ is then provided, as based on our evolutionary models. We tested the reliability of this result by also considering stellar models computed by other authors,employing different input physics. Eventually, we present clear evidence that the variation of $\Delta M_V$(TO-BUMP) with $\Delta M_V$(TO-ZAHB) does supply a powerful probe of the global metal abundance, at least when homogeneous theoretical frameworks are adopted. We provide an estimate of the global metallicity of 36 globular clusters in the Milky Way, based on our {\it A-Z} calibration, and a large observational database of Galactic GCs. By considering the empirical [Fe/H] scales by both Zinn & West (1984) and Carretta & Gratton (1997), we are also able to provide an estimate of the GC $\alpha-$element enhancement.

Using observational data to estimate prognosis: an example using a coronary artery disease registry

With the proliferation of clinical data registries and the rising expense of clinical trials, observational data sources are increasingly providing evidence for clinical decision making. These data are viewed as complementary to randomized clinical trials (RCT). While not as rigorous a methodological design, observational studies yield important information about effectiveness of treatment, as compared with the efficacy results of RCTs. In addition, these studies often have the advantage of providing longer-term follow-up, beyond that of clinical trials. Hence, they are useful for assessing and comparing patients' long-term prognosis under different treatment strategies. For patients with coronary artery disease, many observational comparisons have focused on medical therapy versus interventional procedures. In addition to the well-studied problem of treatment selection bias (which is not the focus of the present study), three significant methodological problems must be addressed in the analysis of these data: (i) designation of the therapeutic arms in the presence of early deaths, withdrawals, and treatment cross-overs; (ii) identification of an equitable starting point for attributing survival time; (iii) site to site variability in short-term mortality. This paper discusses these issues and suggests strategies to deal with them. A proposed methodology is developed, applied and evaluated on a large observational database that has long-term follow-up on nearly 10 000 patients. Copyright © 2001 John Wiley & Sons, Ltd.

Using observational data to estimate prognosis: an example using a coronary artery disease registry.

With the proliferation of clinical data registries and the rising expense of clinical trials, observational data sources are increasingly providing evidence for clinical decision making. These data are viewed as complementary to randomized clinical trials (RCT). While not as rigorous a methodological design, observational studies yield important information about effectiveness of treatment, as compared with the efficacy results of RCTs. In addition, these studies often have the advantage of providing longer-term follow-up, beyond that of clinical trials. Hence, they are useful for assessing and comparing patients' long-term prognosis under different treatment strategies. For patients with coronary artery disease, many observational comparisons have focused on medical therapy versus interventional procedures. In addition to the well-studied problem of treatment selection bias (which is not the focus of the present study), three significant methodological problems must be addressed in the analysis of these data: (i) designation of the therapeutic arms in the presence of early deaths, withdrawals, and treatment cross-overs; (ii) identification of an equitable starting point for attributing survival time; (iii) site to site variability in short-term mortality. This paper discusses these issues and suggests strategies to deal with them. A proposed methodology is developed, applied and evaluated on a large observational database that has long-term follow-up on nearly 10 000 patients.

What determines the magnitude of forbush decreases?

Abstract Cosmic ray Forbush effects (FEs) have been studied for more than 60 years, but even today this phenomenon has no universally accepted definition, which leads to misunderstanding among researchers. There are no complete and convincing answers to the following questions: What are the distinctive features of FEs? What determines the magnitude of FEs and their variety? How are FEs associated with disturbances of the interplanetary medium, coronal mass ejections and high speed flows of the solar wind? What relation exists between FEs and geomagnetic storms? In order to answer these and other questions a data base of transient effects in cosmic rays and in the interplanetary medium is constructed and is being upgraded continuously. It combines variations in cosmic ray densities and anisotropies obtained from data of the world-wide neutron monitor (NM) network, characteristics of solar wind disturbances, solar and geomagnetic data. This data base presently contains more than 1400 events, observed during 1978–1996. The preliminary analysis allowed us to get the main characteristics of FEs, to determine what distinguishes this phenomenon among other cosmic ray variations, and propose a definition of the Forbush effect. In addition, an interplanetary disturbance parameter was derived, which is most closely associated with the magnitude of a FE. Using this large observational database, a relation between FEs and geomagnetic activity was analyzed statistically as a dependence of the FE magnitude on the maximum Kp-index measured during the associated magnetic storm.

Lack of benefit for intravenous thrombolysis in patients with myocardial infarction who are older than 75 years.

The benefit of intravenous thrombolytic therapy in elderly patients with myocardial infarction is uncertain. There are no randomized trials of thrombolytic efficacy or observational studies of clinical effectiveness that focus specifically on the elderly. To determine whether thrombolytic therapy for elderly patients is associated with a survival advantage in a large observational database, we conducted a retrospective cohort study of 7864 Medicare fee-for-service patients aged 65 to 86 years with the primary discharge diagnosis of acute myocardial infarction who were admitted with clinical and ECG indications for thrombolytic therapy and no absolute contraindications. The study included all US acute care nongovernment hospitals without on-site angioplasty capability. Using proportional-hazards methods, we found that in a comprehensive multivariate model, there was a significant interaction (P<0.001) between age and the effect of thrombolytic therapy on 30-day mortality rates. For patients 65 to 75 years old, thrombolytic therapy was associated with a survival benefit, consistent with randomized trials. Among patients aged 76 to 86 years, thrombolytic therapy was associated with a survival disadvantage, with a 30-day mortality hazard ratio of 1.38 (95% CI 1. 12 to 1.71, P=0.003). For these patients, there was no benefit from thrombolytic therapy in any clinical subgroup. In nationwide clinical practice, thrombolytic therapy for patients >75 years old is unlikely to confer survival benefit and may have a significant survival disadvantage. Reperfusion research that is focused on elderly patients is urgently needed.

The Effect of Adjunctive Corticosteroids for the Treatment of Pneumocystis carinii Pneumonia on Mortality and Subsequent Complications

To assess the long-term safety of adjunctive corticosteroids in the treatment of Pneumocystis carinii pneumonia (PCP). Analysis of data from a large prospective observational database. HIV clinic at a large urban teaching hospital. One hundred seventy-four patients who developed PCP after being enrolled in the database. Fifty-three patients (30%) received adjunctive corticosteroids and 121 (70%) did not. Survival did not differ between groups after adjusting for CD4 count (relative risk for adjunctive corticosteroids = 0.74, p = 0.13). There were no differences in the incidence of cytomegalovirus disease (adjunctive corticosteroids: 18.5 cases per 100 person-years vs no adjunctive corticosteroids: 15.7, p = 0.22), Mycobacterium avium complex (23.4 vs 27.0, p = 0.73), cryptococcal meningitis (1.8 vs 4.1, p = 0.58), toxoplasmosis (3.6 vs 11.0, p = 0.28), Kaposi's sarcoma (1.8 vs 2.2, p = 0.92), herpes simplex (27.1 vs 42.7, p = 0.66), herpes zoster (3.8 vs 6.9, p = 0.71), oropharyngeal candidiasis (18.9 vs 10.9, p = 0.09), or non-Hodgkin's lymphoma (3.5 vs 4.2, p = 0.92). Esophageal candidiasis was more common among adjunctive corticosteroid recipients (45.1 vs 26.6, p = 0.01). Results were similar for time to development of opportunistic conditions. Adjunctive corticosteroids do not increase mortality or the risk of most common HIV-associated complications.

An Attempt to Characterize Traffic in Metropolitan Areas

An attempt has been made to explore the differences and the similarities in traffic characteristics among various metropolitan areas using a large observational data base. The results show that speed distribution functions, including the percent of time stopped and average speed are traffic attributes that are useful in characterizing traffic on various roadways. In terms of the average speed and the percent of time stopped the character of the traffic in several metropolitan areas has been compared and found to be different, although the levels of acceleration used by drivers are similar. Relations appear to exist between the average speed and a number of other traffic variables, such as acceleration noise, coefficient of variation of speed, and stop time which are independent of the area studied. Therefore, among all the mentioned variables average speed is particularly useful in measuring the “quality” of traffic in different areas on various roadway types. Based on information on average speeds, the extent to which “traffic quality” might affect fuel consumption in different metropolitan areas has been estimated.