The aerodynamic challenges of SRB recovery

Recovery and reuse of the Space Shuttle solid rocket boosters was baselined to support the primary goal to develop a low cost space transportation system. The recovery system required for the 170,000-lb boosters was for the largest and heaviest object yet to be retrieved from exoatmospheric conditions. State-of-the-art design procedures were ground-ruled and development testing minimized to produce both a reliable and cost effective system. The ability to utilize the inherent drag of the boosters during the initial phase of reentry was a key factor in minimizing the parachute loads, size and weight. A wind tunnel test program was devised to enable the accurate prediction of booster aerodynamic characteristics. Concurrently, wind tunnel, rocket sled and air drop tests were performed to develop and verify the performance of the parachute decelerator subsystem. Aerodynamic problems encountered during the overall recovery system development and the respective solutions are emphasized

IMPACTS ON FAST-START PERFORMANCE: HOW DO GROUP SIZE AND HABITAT DEGRADATION ALTER THE ESCAPE BEHAVIOR OF A SCHOOLING CORAL REEF FISH?

Escaping predation is essential for species survival, but prey must effectively match their response to the perceived threat imposed by a predator. Fish evaluate their surroundings using several sensory stimuli, including olfactory, visual, auditory, and mechanical cues. A range of taxa use the fast-start response to evade predators, including fishes, sharks, and larval amphibians. While the fast-start response (rapid bursts of swimming) is extensively studied in solitary fishes, the factors that mediate the collective escape response in schools of fish have historically been investigated far less. To address this knowledge gap, the collective escape behavior and individual escape performance of schools of the tropical damselfish species Chromis viridis, a common gregarious and coral-associated coral reef fish species found throughout the Indo-Pacific, were investigated. The first data chapter explored the theory of optimal group size, comparing various sized groups of fish. Fish strategically adjusted their escape response in coordination with other group mates, validating the connectivity within conspecific schools. The second data chapter investigated how degrading coral health influences antipredator behavior in fish schools. Habitat degradation was revealed to have a negative effect on schooling, and the combination of a chemical alarm cue intensified this impact. While the singular effect of a chemical alarm acted as a prewarning to strengthen the fast-start

Cold Flow Determination of the Internal Flow Environment Around the Submerged TVC Nozzle for the Space Shuttle SRM

A series of subscale cold flow tests was performed to quantify the gas flow characteristics at the aft end of the Space Shuttle Solid Rocket Motor. This information was used to support the analyses of the redesigned nozzle/case joint. A portion of the thermal loads at the joint are due to the circumferential velocities and pressure gradients caused primarily by the gimbaling of the submerged nose TVC nozzle. When the nozzle centerline is vectored with respect to the motor centerline, asymmetries are set up in the flow field under the submerged nozzle and immediately adjacent to the nozzle/case joint. Specific program objectives included: determination of the effects of nozzle gimbal angle and propellant geometry on the circumferential flow field; measurement of the static pressure and gas velocities in the vicinity of the nozzle/case joint; use of scaling laws to apply the subscale cold flow data to the full scale SRM; and generation of data for use in validation of 3-D computational fluid dynamic, CFD, models of the SRM flow field. These tests were conducted in the NASA Marshall Space Flight Center Airflow Facility with a 7.5 percent scale model of the aft segment of the SRM. Static and dynamic pressures were measured in the model to quantify the flow field. Oil flow data was also acquired to obtain qualitative visual descriptions of the flow field. Nozzle gimbal angles of 0, 3.5, and 7 deg were used with propellant grain configurations corresponding to motor burn times of 0, 9, 19, and 114 seconds. This experimental program was successful in generating velocity and pressure gradient data for the flow field around the submerged nose nozzle of the Space Shuttle SRM at various burn times and gimbal angles. The nature of the flow field adjacent to the nozzle/case joint was determined with oil droplet streaks, and the velocity and pressure gradients were quantified with pitot probes and wall static pressure measurements. The data was applied to the full scale SRM thru a scaling analysis and the results compared well with the 3-D computational fluid dynamics computer model

The role of the agent's outside options in principal-agent relationships

We consider a principal-agent model of adverse selection where, in order to trade with the principal, the agent must undertake a relationship-specific investment which affects his outside option to trade, i.e. the payoff that he can obtain by trading with an alternative principal. This creates a distinction between the agent’s ex ante (before investment) and ex post (after investment) outside options to trade. We investigate the consequences of this distinction, and show that whenever an agent’s ex ante and ex post outside options differ, this may equip the principal with an additional tool for screening among different agent types, by randomizing over the probability with which trade occurs once the agent has undertaken the investment. In turn, this may enhance the efficiency of the optimal second-best contract

"It's made me reassess what I think and believe." An Exploratory Study of Therapists' Experiences with Their Clients' Deathbed Visions, Deathbed Coincidences, and After-Death Communication

Research literature has highlighted the occurrence of deathbed vision (DBV), deathbed coincidence (DBC), and after-death communication (ADC) phenomena. To better inform the mental health profession about how psychotherapists respond to and are affected by working with these client experiences, we interviewed four therapists in private practice in the United Kingdom who reported having worked with clients who disclosed one or more of the phenomena. Using interpretative phenomenological analysis (IPA), we identified three main themes from their accounts: (a) making sense of inexplicable transpersonal experiences on a professional and personal level, (b) experiencing personal transformation, and (c) perceiving clients’ therapeutic benefits from addressing DBV, DBC, and ADC experiences. We discuss these findings in the context of the existing literature along with implications for clinical practice and possible future research directions

Potassium-uracil/thymine ring cleavage enhancement as studied in electron transfer experiments and theoretical calculations

We report experimental and theoretical studies on ring cleavage enhancement in collisions of potassium atoms with uracil/thymine in order to further increase the understanding of the complex mechanisms yielding such fragmentation pathways. In these electron transfer processes time-of-flight (TOF) negative ion mass spectra were obtained in the collision energy range 13.5 – 23.0 eV. We note that CNO– is the major ring breaking anion formed and its threshold formation is discussed within the collision energy range studied. Such decomposition process is supported by the first theoretical calculations in order to clarify how DNA/RNA pyrimidine bases fragmentation is enhanced in electron transfer processes yielding ion-pair formation

Regulation of the Phonotactic Threshold of the Female Cricket, Acheta domesticus: Juvenile Hormone III, Allatectomy, L1 Auditory Neuron Thresholds and Environmental Factors

Juvenile hormone III (JHIII), when applied to the abdomen of 1-day-old female Acheta domesticus (in quantities that would create JHIII titers in the hemolymph that were within the range measured in females of this species) caused a significant decrease in phonotactic thresholds (Fig. 1). Removal of the corpora allata from 5-day-old females with low phonotactic thresholds caused significantly increased phonotactic thresholds 2-5 days later. After a temporary increase (24 h) of, on average, about 25 dB, the phonotactic thresholds drop to about 10 dB above preallatectomy levels (Fig. 2), but remain significantly higher than controls. Application of JHIII to allatectomized females, with a mean increase in thresholds of 20 dB, results in significantly decreased thresholds (mean of about 20 dB) over the next 6 h (Fig. 3). Exposure to males 1 week before the imaginal molt causes the phonotactic thresholds of postimaginal females to drop 1-2 days significantly earlier than controls (Fig. 4). One- and 3-day-old females, phonotactically tested only once, exhibit lower thresholds in the early morning than they do in the late afternoon (Fig. 5). Five-day-old females do not exhibit such a diurnal rhythm. Phonotactically testing females more than once a day significantly influences their phonotactic thresholds (Figs. 6, 7). In 1-day-old females, with high (above 70 dB) phonotactic thresholds, the threshold of their L1 auditory interneurons can be 30 dB or more below their phonotactic threshold (Fig. 8). In females with phonotactic thresholds of 70 dB or lower, the L1 threshold is within 10 dB of their phonotactic threshold. Both JHIII and allatectomy influence phonotactic and L1 thresholds in a similar manner

OperA/ALIVE/OperettA

Comprehensive models for organizations must, on the one hand, be able to specify global goals and requirements but, on the other hand, cannot assume that particular actors will always act according to the needs and expectations of the system design. Concepts as organizational rules (Zambonelli 2002), norms and institutions (Dignum and Dignum 2001; Esteva et al. 2002), and social structures (Parunak and Odell 2002) arise from the idea that the effective engineering of organizations needs high-level, actor-independent concepts and abstractions that explicitly define the organization in which agents live (Zambonelli 2002).Peer ReviewedPostprint (author's final draft