Bostonia. Volume 14

Founded in 1900, Bostonia magazine is Boston University's main alumni publication, which covers alumni and student life, as well as university activities, events, and programs

Delay and Disruption Tolerant Networking MACHETE Model

To verify satisfaction of communication requirements imposed by unique missions, as early as 2000, the Communications Networking Group at the Jet Propulsion Laboratory (JPL) saw the need for an environment to support interplanetary communication protocol design, validation, and characterization. JPL's Multi-mission Advanced Communications Hybrid Environment for Test and Evaluation (MACHETE), described in Simulator of Space Communication Networks (NPO-41373) NASA Tech Briefs, Vol. 29, No. 8 (August 2005), p. 44, combines various commercial, non-commercial, and in-house custom tools for simulation and performance analysis of space networks. The MACHETE environment supports orbital analysis, link budget analysis, communications network simulations, and hardware-in-the-loop testing. As NASA is expanding its Space Communications and Navigation (SCaN) capabilities to support planned and future missions, building infrastructure to maintain services and developing enabling technologies, an important and broader role is seen for MACHETE in design-phase evaluation of future SCaN architectures. To support evaluation of the developing Delay Tolerant Networking (DTN) field and its applicability for space networks, JPL developed MACHETE models for DTN Bundle Protocol (BP) and Licklider/Long-haul Transmission Protocol (LTP). DTN is an Internet Research Task Force (IRTF) architecture providing communication in and/or through highly stressed networking environments such as space exploration and battlefield networks. Stressed networking environments include those with intermittent (predictable and unknown) connectivity, large and/or variable delays, and high bit error rates. To provide its services over existing domain specific protocols, the DTN protocols reside at the application layer of the TCP/IP stack, forming a store-and-forward overlay network. The key capabilities of the Bundle Protocol include custody-based reliability, the ability to cope with intermittent connectivity, the ability to take advantage of scheduled and opportunistic connectivity, and late binding of names to addresses

Targeted Reflection-Waveform Inversion of Experimental Ground-Penetrating Radar Data for Quantification of Oil Spills Under Sea Ice

Rapid spill detection and mapping are needed with increasing levels of oil exploration and production in the Arctic. Previous work has found that ground-penetrating radar (GPR) is effective for qualitative identification of oil spills under, and encapsulated within, sea ice. Quantifying the spill distribution will aid effective spill response. To this end, we have developed a targeted GPR reflection-waveform inversion algorithm to quantify the geometry of oil spills under and within sea ice. With known electric properties of the ice and oil, we have inverted for oil thickness and variations in ice thickness. We have tested the algorithm with data collected during a controlled spill experiment using 500-MHz radar reflection data. The algorithm simultaneously recovered the thickness of a 5-cm-thick oil layer at the base of the ice to within 8% of the control value, estimated the thickness of a 1-cm-thick oil layer encapsulated within the ice to within 30% of the control value, and accurately mapped centimeter-scale variations in ice thickness

Modeling Excitable Systems: Reentrant Tachycardia

Excitable membranes are an important type of nonlinear dynamical system and their study can be used to provide a connection between physical and biological circuits. We discuss two models of excitable membranes important in cardiac and neural tissues. One model is based on the Fitzhugh-Nagumo equations and the other is based on a three-transistor excitable circuit. We construct a circuit that simulates reentrant tachycardia and its treatment by surgical ablation. This project is appropriate for advanced undergraduates as a laboratory capstone project, or as a senior thesis or honors project, and can also be a collaborative project, with one student responsible for the computational predictions and another for the circuit construction and measurements.Comment: 9 pages, twocolumn, revised and published in American Journal of Physic

Once Nocturia, Always Nocturia? Natural History of Nocturia in Older Men Based on Frequency-Volume Charts:The Krimpen Study

Purpose: Nocturia is a highly prevalent and bothersome symptom that might (spontaneously) resolve. However, longitudinal data are not available on the incidence and resolution of nocturia assessed with frequency-volume charts. In this study we determined the prevalence, incidence and resolution rates of nocturia assessed by frequency-volume charts, and compared nocturnal voiding frequency over time as assessed by frequency-volume charts and questionnaires. Materials and Methods: A longitudinal, population based study was conducted among 1,688 men 50 to 78 years old with followup rounds at 2.1, 4.2 and 6.5 years. Nocturnal voiding frequency was determined with frequency-volume charts and, for comparison purposes, with a question from the International Prostate Symptom Score. Nocturia was defined as nocturnal voiding frequency 2 or greater. Prevalence, incidence and resolution rates were also determined. Results: At the 2.1-year followup the incidence rate was 23.9% and the resolution rate was 36.7%. The incidence rate was highest in the oldest group (70 to 78 years) and lowest in the youngest (50 to 54 years), whereas the resolution rate was highest in the group 55 to 59 years old and lowest in the oldest group. Because of the high resolution rate, no reliable incidence rates can be calculated. Despite fluctuation, the prevalence of nocturia increased with age and over time (from 34.4% to 44.7% for the total group, p <0.05). Men who had a frequency-volume chart-nocturnal voiding frequency less than International Prostate Symptom Score-nocturnal voiding frequency (6% of the population) more often had this later on. Conclusions: In this population frequency-volume chart assessed nocturia shows considerable fluctuation. Nevertheless, prevalence increases over time and with increasing age. Men who once had frequency-volume chart-nocturnal voiding frequency less than International Prostate Symptom Score-nocturnal voiding frequency are more likely to have this again. Therefore, frequency-volume charts as well as the International Prostate Symptom Score should be used when evaluating nocturia

Coping Strategies of Family Members of Hospitalized Psychiatric Patients

This exploratory research paper investigated the coping strategies of families of hospitalized psychiatric patients and identified their positive and negative coping strategies. In this paper, the coping strategies of 45 family members were examined using a descriptive, correlational, mixed method research approach. Guided by the Neuman Systems Model and using the Family Crisis Oriented Personal Evaluation Scales and semistructured interviews, this paper found that these family members used more emotion-focused coping strategies than problem-focused coping strategies. The common coping strategies used by family members were communicating with immediate family, acceptance of their situation, passive appraisal, avoidance, and spirituality. The family members also utilized resources and support systems, such as their immediate families, mental health care professionals, and their churches

Flecainide Paradoxically Activates Cardiac Ryanodine Receptor Channels under Low Activity Conditions: A Potential Pro-Arrhythmic Action.

Cardiac ryanodine receptor (RyR2) mutations are implicated in the potentially fatal catecholaminergic polymorphic ventricular tachycardia (CPVT) and in atrial fibrillation. CPVT has been successfully treated with flecainide monotherapy, with occasional notable exceptions. Reported actions of flecainide on cardiac sodium currents from mice carrying the pro-arrhythmic homozygotic RyR2-P2328S mutation prompted our explorations of the effects of flecainide on their RyR2 channels. Lipid bilayer electrophysiology techniques demonstrated a novel, paradoxical increase in RyR2 activity. Preceding flecainide exposure, channels were mildly activated by 1 mM luminal Ca2+ and 1 µM cytoplasmic Ca2+, with open probabilities (Po) of 0.03 ± 0.01 (wild type, WT) or 0.096 ± 0.024 (P2328S). Open probability (Po) increased within 0.5 to 3 min of exposure to 0.5 to 5.0 µM cytoplasmic flecainide, then declined with higher concentrations of flecainide. There were no such increases in a subset of high Po channels with Po ≥ 0.08, although Po then declined with ≥5 µM (WT) or ≥50 µM flecainide (P2328S). On average, channels with Po < 0.08 were significantly activated by 0.5 to 10 µM of flecainide (WT) or 0.5 to 50 µM of flecainide (P2328S). These results suggest that flecainide can bind to separate activation and inhibition sites on RyR2, with activation dominating in lower activity channels and inhibition dominating in more active channels