A New Look at Bandwidth Latency Tradeoffs

Concerns about propagation delay have dominated the discussion of latency, bandwidth and their effect on distributed applications. In this paper, we argue that the relevant latency measure for applications is the Application Data Unit (ADU) Latency, defined as the time between the sending of an ADU and its receipt. Since ADUs are often large, ADU latency is influenced by throughput as well as propagation delay. We investigated the effects the effects of ADU latency with an experimental study of several applications. The applications used Distributed Shared Memory as an interprocess communications mechanism, constraining the ADUs to page sized units. The applications were run on an Ethernet, an experimental ATM LAN, and using ATM on an experimental high-speed WAN. The measured results were used to normalize results gathered by inserting an experimental ATM switch output port controller in the network to create tunable delays. The results conclusively demonstrate the effect of ADU latency on distributed application response time. The experiments give a precise characterization of the effect of varying bandwidth and propagation delay on a real system, and suggest promising directions for further improving application performance in future networks

Architecture and Performance of the Mether Network Shared Memory

Mether is a Network Shared Memory (NSM). It allows applications on autonomous computers connected by a network to share a segment of memory. NSMs offer the attraction of a simple abstraction for shared state, i.e., shared memory. NSMs have a potential performance problem in the cost of remote references, which is typically solved by grouping memory into larger units such as pages, and caching pages. While Mether employs grouping and caching to reduce the average memory reference delay, it also removes the need for many remote references (page faults) by providing a facility with relaxed consistency requirements. Applications ported from a multiprocessor supercomputer with shared memory to a 16-workstation Mether configuration showed a cost/performance advantage of over 300 in favor of the Mether system. While Mether is currently implemented for Sun-3 and Sun-4 systems connected via Ethernet, other characteristics (such as a choice of page sizes and a semaphore-like access mode useful for process synchronization) should suit it to a wide variety of networks. A reimplementation for an alternate configuration employing packet-switched networks is in progress

N-of-1 randomized trials for psychological and health behavior outcomes: a systematic review protocol

Background Randomized controlled trials are the sine qua non of causal inference; however, heterogeneity of treatment effects for many chronic conditions and for many symptoms often limits their utility. Single-patient studies in which patients select a treatment after trying a randomized sequence of treatments (i.e., multiple crossover trials) offer an alternative to traditional randomized controlled trials by providing scientifically valid results in a practical manner that can be used by patients and their providers to decide upon their personally optimal treatment. Although N-of-1 trials have been used in the medical literature, their use for interventions that consist of psychological or health behavior outcomes is unknown. This systematic review thus aims to describe the interventions and outcomes and assess the quality of N-of-1 trials for psychological or health behavior outcomes. Methods/Design Electronic databases (Ovid MEDLINE, EMBASE, CINAHL, PsycINFO, and the six databases in the Cochrane Library) will be searched using all relevant subject headings and free-text terms to represent N-of-1 trials and psychological or behavioral interventions. Full text review and bibliography searching will be conducted. Unpublished studies will be sought by searching trial registries and contacting authors of included studies. Eligibility criteria are the following: population, all human participants for whom N-of-1 trials with psychological or health behavior outcomes have been conducted; interventions, all interventions for which N-of-1 trials have been conducted; comparison, placebo or active treatment control; and outcome, psychological and health behavior outcomes including self-perceived disease severity and psychological phenomena such as mood and affect. Studies that do not contain sufficient trial detail, describe only design or statistical analytic issues in N-of-1 trials without presentation of an N-of-1 trial itself, and/or are not written in the English language are ineligible. Screening, data extraction, and quality assessment will be conducted by two independent reviewers with disagreements resolved through discussion. Discussion This systematic review will describe the interventions and outcomes and assess the quality of N-of-1 trials for psychological or health behavior outcomes. The results will clarify the use of this research methodology in the health psychology and behavioral medicine literature and may pave the way for additional N-of-1 trials to be conducted

Gender Differences in Calls to 9-1-1 During an Acute Coronary Syndrome

Calling 911 during acute coronary syndromes (ACS) decreases time to treatment and may improve prognosis. Women may have more atypical ACS symptoms compared to men, but few data are available on differences in gender and ACS symptoms in calling 911. In this study, patient interviews and structured chart reviews were conducted to determine gender differences in calling 911. Calls to 911 were assessed by self-report and validated by medical chart review. Of the 476 patients studied, 292 (61%) were diagnosed with unstable angina and 184 (39%) with myocardial infarctions (MIs). Overall, only 23% of patients called 911. Similar percentages of women and men with unstable angina called 911 (15% and 13%, respectively, p = 0.59). In contrast, women with MIs were significantly more likely to call 911 than men (57% vs 28%, p <0.001). After adjustment for sociodemographic factors, health insurance status, history of MI, the left ventricular ejection fraction, Global Registry of Acute Coronary Events (GRACE) score, and ACS symptoms, women were 1.79 times more likely to call 911 during an MI than men (prevalence ratio 1.79, 95% confidence interval 1.22 to 2.64, p <0.01). In conclusion, the findings of the present study suggest that initiatives to increase calls to 911 are needed for women and men

Neighborhood matters: the impact of Hispanic ethnic density on future depressive symptoms 1-year following an ACS event among Hispanic patients

The Ethnic Density hypothesis posits that living around others from similar ethnic backgrounds reduces the risk of adverse mental health outcomes such as depression. Contrary to this hypothesis, previous work has shown that Hispanic ethnic density is cross-sectionally associated with increased depressive symptom severity among patients hospitalized with an acute coronary syndrome (ACS; myocardial infarction or unstable angina pectoris). To date, no study has examined the prospective association of Hispanic ethnic density on long-term depressive symptom severity following an acute medical event. We prospectively assessed the impact of Hispanic ethnic density on depressive symptoms, 1-year following an ACS event, among Hispanic adult patients. We tested the non-linear association between ethnic density and depressive symptoms to account for inconsistent findings on the ethnic density hypothesis. At the time of an index ACS event (i.e., baseline, N = 326) and 1-year later (N = 252), Hispanic patients from the Prescription Usage, Lifestyle, and Stress Evaluation prospective cohort study completed the Beck Depression Inventory as a measure of depressive symptom severity. Hispanic ethnic density was defined by the percentage of Hispanic residents within each patient’s census tract using data extracted from the American Community Survey Census (2010–2013). Covariates included baseline demographic factors (age, gender, English fluency, education, nativity status), cardiovascular factors (Charlson comorbidity index, left ventricular ejection fraction, Global Registry of Acute Coronary Events 6-month prognostic risk score), and neighborhood factors (residential density, income, and percentage of households receiving public assistance). In an adjusted multivariable linear regression analysis there was a significant curvilinear association between Hispanic ethnic density and depressive symptom severity at 1 year. As Hispanic ethnic density increased from low to moderate density, there was an increase in depressive symptoms, but depressive symptoms slightly declined in census tracts with the highest density of Hispanics. Furthermore, gender significantly moderated the relation between Hispanic ethnic density and 1-year depressive symptom severity, such that Hispanic ethnic density was significantly associated with increased depressive symptom severity for female Hispanic patients with ACS, but not for male Hispanic patients. Previous research suggests that ethnic density may be protective against depression in Hispanic enclaves; however, our findings suggest a non-linear ethnic density effect and an overall more complex association between ethnic density and depression. These data add to a growing body of literature on the effects of sociodemographic and contextual factors on health

Relation of Patients Living Without a Partner or Spouse to Being Physically Active After Acute Coronary Syndromes (from the PULSE Accelerometry Substudy)

Living alone is associated with adverse outcomes after acute coronary syndromes (ACS). One potential mediator of the relation between partner status and outcomes after ACS is physical activity. To evaluate the association of partner status with physical activity after ACS, data from 107 participants enrolled in the Prescription Use, Lifestyle, and Stress Evaluation (PULSE) study, a prospective observational study of post-ACS patients, were analyzed. Accelerometers were used to measure physical activity after hospital discharge. The primary outcome measure was a maximum 10 hours of daytime activity 1 month after discharge. One month after discharge from ACS hospitalizations, participants without a partner or spouse exhibited 24.4% lower daytime activity than those with a partner or spouse (p = 0.003). After controlling for age, gender, body mass index, Charlson co-morbidity index, and traditional psychosocial and clinical cardiovascular correlates of post-ACS physical activity, partner status remained an independent predictor of post-ACS physical activity (20.5% lower daytime activity among those without a partner or spouse, p = 0.008). In conclusion, in this study of accelerometer-measured physical activity after an ACS hospitalization, those without a partner or spouse exhibit significantly less physical activity than those with a partner or spouse 1 month after discharge from the hospital. Low physical activity may be an important mediator of the prognosis associated with partner status after ACS