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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS2022

An ALMA Study of the Massive Molecular Clump N159W-North in the Large Magellanic Cloud: A Possible Gas Flow Penetrating One of the Most Massive Protocluster Systems in the Local Group

Massive dense clumps in the Large Magellanic Cloud can be an important laboratory to explore the formation ofpopulous clusters. We report multiscale ALMA observations of the N159W-North clump, which is the most CO-intense region in the galaxy. High-resolution CO isotope and 1.3 mm continuum observations with an angularresolution of∼025(∼0.07 pc)revealed more thanfive protostellar sources with CO outflows within the mainridge clump. One of the thermal continuum sources, MMS-2, shows an especially massive/dense nature whosetotal H2mass and peak column density are∼104Meand∼1024cm−2, respectively, and harbors massive(∼100Me)starless core candidates identified as its internal substructures. The main ridge containing this sourcecan be categorized as one of the most massive protocluster systems in the Local Group. The CO high-resolutionobservations found several distinctfilamentary clouds extending southward from the star-forming spots. The CO(1–0)data set with a largerfield of view reveals a conical,∼30 pc long complex extending toward the northerndirection. These features indicate that a large-scale gas compression event may have produced the massive star-forming complex. Based on the striking similarity between the N159W-North complex and the other twopreviously reported high-mass star-forming clouds in the nearby regions, we propose a“teardrops inflow model”that explains the synchronized, extreme star formation across>50 pc, including one of the most massiveprotocluster clumps in the Local Group.

Kazuki Tokuda↗
NASA NTRS2011

Sample Acquisition and Handling System from a Remote Platform

A system has been developed to acquire and handle samples from a suspended remote platform. The system includes a penetrator, a penetrator deployment mechanism, and a sample handler. A gravity-driven harpoon sampler was used for the system, but other solutions can be used to supply the penetration energy, such as pyrotechnic, pressurized gas, or springs. The deployment mechanism includes a line that is attached to the penetrator, a spool for reeling in the line, and a line engagement control mechanism. The penetrator has removable tips that can collect liquid, ice, or solid samples. The handling mechanism consists of a carousel that can store a series of identical or different tips, assist in penetrator reconfiguration for multiple sample acquisition, and deliver the sample to a series of instruments for analysis. The carousel sample handling system was combined with a brassboard reeling mechanism and a penetrator with removable tips. It can attach the removable tip to the penetrator, release and retrieve the penetrator, remove the tip, and present it to multiple instrument stations. The penetrator can be remotely deployed from an aerobot, penetrate and collect the sample, and be retrieved with the sample to the aerobot. The penetrator with removable tips includes sample interrogation windows and a sample retainment spring for unconsolidated samples. The line engagement motor can be used to control the penetrator release and reeling engagement, and to evenly distribute the line on the spool by rocking between left and right ends of the spool. When the arm with the guiding ring is aligned with the spool axis, the line is free to unwind from the spool without rotating the spool. When the arm is perpendicular to the spool axis, the line can move only if the spool rotates.

Badescu, Mircea↗
NASA NTRS1997

Ground-Support Algorithms for Simulation, Processing, and Calibration of Barnes Static Earth Sensor Measurements: Applications to Tropical Rainfall Measuring Mission Observatory

New algorithms are described covering the simulation, processing, and calibration of penetration angles of the Barnes static Earth sensor assembly (SESA) as implemented in the Goddard Space Flight Center Flight Dynamics Division ground support system for the Tropical Rainfall Measuring Mission (TRMM) Observatory. The new treatment involves a detailed analysis of the measurements by individual quadrants. It is shown that, to a good approximation, individual quadrant misalignments can be treated simply as penetration angle biases. Simple formulas suitable for real-time applications are introduced for computing quadrant-dependent effects. The simulator generates penetration angles by solving a quadratic equation with coefficients uniquely determined by the spacecraft's position and the quadrant's orientation in GeoCentric Inertial (GCI) coordinates. Measurement processing for attitude determination is based on linearized equations obtained by expanding the coefficients of the aforementioned quadratic equation as a Taylor series in both the Earth oblateness coefficient (alpha approx. 1/150) and the angle between the pointing axis and the geodetic nadir vector. A simple formula relating a measured value of the penetration angle to the deviation of the Earth-pointed axis from the geodetic nadir vector is derived. It is shown that even near the very edge of the quadrant's Field Of View (FOV), attitude errors resulting from quadratic effects are a few hundredths of a degree, which is small compared to the attitude determination accuracy requirement (0.18 degree, 3 sigma) of TRMM. Calibration of SESA measurements is complicated by a first-order filtering used in the TRMM onboard algorithm to compute penetration angles from raw voltages. A simple calibration scheme is introduced where these complications are avoided by treating penetration angles as the primary raw measurements, which are adjusted using biases and scale factors. In addition to three misalignment parameters, the calibration state vector contains only two average penetration angle biases (one per each pair of opposite quadrants) since, because of the very narrow sensor FOV (+/- 2.6 degrees), differences between biases of the penetration angles measured by opposite quadrants cannot be distinguished from roll and pitch sensor misalignments. After calibration, the estimated misalignments and average penetration angle biases are converted to the four penetration angle biases and to the yaw misalignment angle. The resultant biases and the estimated scale factors are finally used to update the coefficients necessary for onboard computations of penetration angles from measured voltages.

Natanson, G. A.↗
NASA NTRS1997

Planetary and Primitive Object Strength Measurements and Sampling Apparatus

We present experimental data and a model for the low-velocity (subsonic, 0 - 1000 m/s) penetration of brittle materials by both solid and hollow (i.e., coring) penetrators. The experiments show that penetration is proportional to momentum/frontal area of the penetrator. Because of the buildup of a cap in front of blunt penetrators, the presence or absence of a streamlined or sharp front end usually has a negligible effect for impact into targets with strength. The model accurately predicts the dependence of penetration depth on the various parameters of the target-penetrator system, as well as the qualitative condition of the target material ingested by a corer. In particular, penetration depth is approximately inversely proportional to the static bearing strength of the target. The bulk density of the target material has only a small effect on penetration, whereas friction can be significant, especially at higher impact velocities, for consolidated materials. This trend is reversed for impacts into unconsolidated materials. The present results suggest that the depth of penetration is a good measure of the strength, but not the density, of a consolidated target. Both experiments and model results show that, if passage through the mouth of a coring penetrator requires initially porous target material to be compressed to less than 26% porosity, the sample collected by the corer will be highly fragmented. If the final porosity remains above 26%, then most materials, except cohesionless materials, such as dry sand, will be collected as a compressed slug of material.

Ahrens, Thomas J.↗
NASA NTRS2005

Controlling Force and Depth in Friction Stir Welding

Feedback control of the penetration force applied to a pin tool in friction stir welding has been found to be a robust and reliable means for controlling the depth of penetration of the tool. This discovery has made it possible to simplify depth control and to weld with greater repeatability, even on workpieces with long weld joints. Prior to this discovery, depths of penetration in friction stir welding were controlled by hard-tooled roller assemblies or by depth actuators controlled by feedback from such external sensors as linear variable-differential transformers or laser-based devices. These means of control are limited: A hard-tooled roller assembly confines a pin tool to a preset depth that cannot be changed easily during the welding process. A measurement by an external sensor is only an indirect indicative of the depth of penetration, and computations to correlate such a measurement with a depth of penetration are vulnerable to error. The present force-feedback approach exploits the proportionality between the depth and the force of penetration Unlike a depth measurement taken by an external sensor, a force measurement can be direct because it can be taken by a sensor coupled directly to the pin tool. The reading can be processed through a modern electronic servo control system to control an actuator to keep the applied penetration force at the desired level. In comparison with the older depth-control methods described above, this method offers greater sensitivity to plasticizing of the workpiece metal and is less sensitive to process noise, resulting in a more consistent process. In an experiment, a tapered panel was friction stir welded while controlling the force of penetration according to this method. The figure is a plot of measurements taken during the experiment, showing that force was controlled with a variation of 200 lb (890 N), resulting in control of the depth of penetration with a variation of 0.004 in. (0.1 mm).

Adams, Glynn↗
NASA NTRS2015

Numerical Experiments of Counterflowiing Jet Effects on Supersonic Slender-Body Configurations

Previous studies have demonstrated that the use of counterflowing jets can greatly reduce the drag and heat loads on blunt-body geometries, especially when the long penetration mode jet condition can be established. Previously, the authors had done some preliminary numerical studies to determine the ability to establish long penetration mode jets on a typical Mach 1.6 slender configuration, and study its impact on the boom signature. The results indicated that a jet with a longer penetration length was required to achieve any impact on the boom signature of a typical Mach 1.6 slender configuration. This paper focuses on an in-depth parametric study, done using the space-time conservation element solution element Navier-Stokes flow solver, for investigating the effect of various counterflowing jet conditions/configurations on two supersonic slender-body models (cone-cylinder and quartic body of revolution). The study is aimed at gaining a better understanding of the relationship between the shock penetration length and reduction of drag and boom signature for these two supersonic slender-body configurations. Different jet flow rates, Mach numbers, nozzle jet exit diameters and jet-to-base diameter ratios were examined. The results show the characteristics of a short-to-long-to-short penetration-mode pattern with the increase of jet mass flow rates, observed across various counterflowing jet nozzle configurations. Though the optimal shock penetration length for potential boom-signature mitigation is tied to the long penetration mode, it often results in a very unsteady flow and leads to large oscillations of surface pressure and drag. Furthermore, depending on the geometry of the slender body, longer jet penetration did not always result in maximum drag reduction. For the quartic geometry, the maximum drag reduction corresponds well to the longest shock penetration length, while this was not the case for the cone-cylinder-as the geometry was already optimized for drag. Numerical results and assessments obtained from this parametric study along with the recommendation for future implementation of counterflowing jets as a means for drag and noise reduction are detailed in this paper.

Venkatachari, Balaji Shankar↗
NASA NTRS1975

Differential permeation of artemia cysts and cucumber seeds by alcohols

The rate of penetration of the simpler alcohols into brine shrimp cysts and cucumber seeds was studied. In solutions below 70% the rate of penetration is related to lipid solvent capacity of the alcohol. In concentrations above 70%, particularly in absolute alcohols, methanol penetrates brine shrimp rapidly and ethanol penetrates slowly. All the other alcohols tested did not penetrate the dormant structures. Ethionine and deuteroxy-methanol did not affect the rate of penetration of methanol. It is suggested that in dehydrated membranes the lipid moiety is protected by a continuous sheet of protein. Methanol, which is fairly similar to water, is probably able to penetrate the membrane by initiating a conformation change in the protein, exposing the lipid which subsequently dissolves in the methanol thus destroying the membrane.

Smith, C. W.↗
NASA NTRS1980

Results of Pioneer 10 and 11 meteoroid experiments - Interplanetary and near-Saturn

The meteoroid penetration detectors on Pioneer 10 (channel 0) recorded 95 penetrations through the 25-micron stainless steel test material while the spacecraft was between 1 and 18 AU. The spatial density of 10 to the -9 g meteoroids is found to be essentially constant between 1 and 18 AU. The meteoroid penetration detectors on Pioneer 11 recorded 87 penetrations (55 on channel 0 and 32 on channel 1) through the 50-micron stainless steel test material while the spacecraft was between 1 and 9 AU. It is found that the meteoroids between 4 and 5 AU are not in direct circular or near-circular orbits near the ecliptic plane. The Pioneer 11 data obtained between 4 and 5 AU are best explained by the meteoroids being in randomly inclined orbits of high eccentricity. If meteoroids are in these cometlike orbits, the great increase in penetration flux previously measured near Jupiter with the Pioneer 10 experiment cannot be attributed to gravitational focusing unless the size distribution of meteoroids changes substantially between 1 and 5 AU. At Saturn encounter, the penetration flux increased by about three orders of magnitude, probably as the result of impacts from ring particles. Saturn's ring E is estimated to be 1800 km thick with an optical thickness greater than 10 to the -8.

Humes, D. H.↗
NASA NTRS1993

NDE of PWA 1480 single crystal turbine blade material

Cantilever bending fatigue specimens were examined by fluorescent liquid penetrant and radioactive gas penetrant (Krypton) non-destructive evaluation (NDE) methods and tested. Specimens with cast, ground, or polished surface were evaluated to study the effect of surface condition on NDE and fatigue crack initiation. Fractographic and metallurgical analyses were performed to determine the nature of crack precursors. Preliminary results show that fatigue strength was lower for specimens with cast surfaces than for specimens with machined surfaces. The liquid penetrant and gas penetrant techniques both provided indications of a large population of defects on the cast surfaces. On ground or polished specimen surfaces, the gas penetrant appeared to estimate the actual number of voids more accurately than the liquid penetrant.

Klima, Stanley J.↗
NASA NTRS1993

NDE of PWA 1480 single crystal turbine blade material

Cantilever bending fatigue specimens were examined by fluorescent liquid penetrant and radioactive gas penetrant (Krypton) Nondestructive Evaluation (NDE) methods and tested. Specimens with cast, ground, or polished surfaces were evaluated to study the effect of surface condition on NDE and fatigue crack initiation. Fractographic and metallurgical analyses were performed to determine the nature of crack precursors. Preliminary results show that fatigue strength was lower for specimens with cast surfaces than for specimens with machined surfaces. The liquid penetrant and gas penetrant techniques both provided indications of a large population of defects on the cast surfaces. On ground or polished specimen surfaces, the gas penetrant appeared to estimate the actual number of voids more accurately than the liquid penetrant.

Klima, Stanley J.↗