1,648 research outputs found
Continued Investigation of Leakage and Power Loss Test Results for Competing Turbine Engine Seals
Secondary seal leakage in jet engine applications results in power losses to the engine cycle. Likewise, seal power loss in jet engines not only result in efficiency loss but also increase the heat input into the engine resulting in reduced component lives. Experimental work on labyrinth and annular seals was performed at NASA Glenn Research Center to quantify seal leakage and power loss at various temperatures, seal pressure differentials, and surface speeds. Data from annular and labyrinth seals are compared with previous brush and finger seal test results. Data are also compared to literature. Annular and labyrinth seal leakage rates are 2 to 3 times greater than brush and finger seal rates. Seal leakage decreases with increasing speed but increases with increasing test temperature due to thermal expansion mismatch. Also seal power loss increases with surface speed, seal pressure differential, mass flow rate, and radial clearance. Annular and labyrinth seal power losses were higher than those of brush or finger seal data. The brush seal power loss was 15 to 30 percent lower than annular and labyrinth seal power loss
A Review of Engine Seal Performance and Requirements for Current and Future Army Engine Platforms
Sand ingestion continues to impact combat ground and air vehicles in military operations in the Middle East. The T-700 engine used in Apache and Blackhawk helicopters has been subjected to increased overhauls due to sand and dust ingestion during desert operations. Engine component wear includes compressor and turbine blades/vanes resulting in decreased engine power and efficiency. Engine labyrinth seals have also been subjected to sand and dust erosion resulting in tooth tip wear, increased clearances, and loss in efficiency. For the current investigation, a brief overview is given of the history of the T-700 engine development with respect to sand and dust ingestion requirements. The operational condition of labyrinth seals taken out of service from 4 different locations of the T-700 engine during engine overhauls are examined. Collaborative efforts between the Army and NASA to improve turbine engine seal leakage and life capability are currently focused on noncontacting, low leakage, compliant designs. These new concepts should be evaluated for their tolerance to sand laden air. Future R&D efforts to improve seal erosion resistance and operation in desert environments are recommende
Evaluating A State Opioid Prescribing Limit and Electronic Medical Record Alert
Because long-term opioid use has been linked to the length and strength of an initial prescription, 33 states, Medicare, and some private insurers have set limits on the duration of new opioid prescriptions. In May 2017, New Jersey implemented a statewide 5-day limit on new opioid prescriptions and Penn Medicine implemented an Electronic Medical Record (EMR) alert to notify prescribers when a prescription exceeded the limit and provide compliant prescription orders. This study compared outcomes in Penn Medicine outpatient practices in New Jersey with its practices in Pennsylvania not subject to the law. Outcomes included total opioid dose and number of tablets per prescription as well as rates of prescription refills, health care visits, and telephone calls within 30 days to account for potential unintended consequences
Overview of Turbine Seal Testing at GRC
Objectives: 1) Evaluate feasibility of advanced seal concepts and materials of meeting next generation engine speed and temperature requirements; 2) Provide a state-of-the-art turbomachinery seal test rig capable of testing seals under known and anticipated design conditions; and 3) Work with industry to assess and demonstrate performance of their seals prior to test in engine
Preliminary Test Results of a Non-Contacting Finger Seal on a Herringbone-Grooved Rotor
Low leakage, non-contacting finger seals have potential to reduce gas turbine engine specific fuel consumption by 2 to 3 percent and to reduce direct operating costs by increasing the time between engine overhauls. A non-contacting finger seal with concentric lift-pads operating adjacent to a test rotor with herringbone grooves was statically tested at 300, 533, and 700 K inlet air temperatures at pressure differentials up to 576 kPa. Leakage flow factors were approximately 70 percent less than state-of-the-art labyrinth seals. Leakage rates are compared to first order predictions. Initial spin tests at 5000 rpm, 300 K inlet air temperature and pressure differentials to 241 kPa produced no measurable wear
Overview of NASA Glenn Seal Project
NASA Glenn is currently performing seal research supporting both advanced turbine engine development and advanced space vehicle/propulsion system development. Studies have shown that decreasing parasitic leakage through applying advanced seals will increase turbine engine performance and decrease operating costs. Studies have also shown that higher temperature, long life seals are critical in meeting next generation space vehicle and propulsion system goals in the areas of performance, reusability, safety, and cost. NASA Glenn is developing seal technology and providing technical consultation for the Agency s key aero- and space technology development programs
Estudio jurisprudencial sobre el derecho al trabajo de los vendedores ambulantes en Bogotá
Artículo de ReflexiónEl presente artículo de investigación presenta el resultado de la realización de una revisión jurisprudencial en torno a los pronunciamientos de las Altas Cortes acerca del derecho al trabajo de los vendedores ambulantes, su importancia se enmarca en la vulneración constante que se ha ido presentando frente al derecho de los vendedores ambulantes y en el conflicto que se da entre este derecho y el derecho que tienen los ciudadanos en general a disfrutar del espacio público.INTRODUCCIÓN
1. DESARROLLO JURISPRUDENCIAL
2. CONSIDERACIONES DEL AUTOR
3. CONCLUSIONES
4. REFERENCIASPregradoAbogad
Regionalized differentiation of crh, trh and ghrh peptidergic neurons in the mouse hypothalamus
According to the updated prosomeric model,
the hypothalamus is subdivided rostrocaudally into terminal
and peduncular parts, and dorsoventrally into alar,
basal, and floor longitudinal zones. In this context, we
examined the ontogeny of peptidergic cell populations
expressing Crh, Trh, and Ghrh mRNAs in the mouse
hypothalamus, comparing their distribution relative to the
major progenitor domains characterized by molecular
markers such as Otp, Sim1, Dlx5, Arx, Gsh1, and Nkx2.1.
All three neuronal types originate mainly in the peduncular
paraventricular domain and less importantly at the terminal
paraventricular domain; both are characteristic alar Otp/
Sim1-positive areas. Trh and Ghrh cells appeared specifically
at the ventral subdomain of the cited areas after
E10.5. Additional Ghrh cells emerged separately at the
tuberal arcuate area, characterized by Nkx2.1 expression.
Crh-positive cells emerged instead in the central part of the
peduncular paraventricular domain at E13.5 and remained
there. In contrast, as development progresses (E13.5?
E18.5) many alar Ghrh and Trh cells translocate into the
alar subparaventricular area, and often also into underlying
basal neighborhoods expressing Nkx2.1 and/or Dlx5, such
as the tuberal and retrotuberal areas, becoming partly or
totally depleted at the original birth sites. Our data correlate
a topologic map of molecularly defined hypothalamic
progenitor areas with three types of specific neurons, each
with restricted spatial origins and differential migratory
behavior during prenatal hypothalamic development. The
study may be useful for detailed causal analysis of the
respective differential specification mechanisms. The postulated
migrations also contribute to our understanding of
adult hypothalamic complexity
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