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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 91 records · Page 5
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NASA NTRS2002

Evaluation of a Pair-Wise Conflict Detection and Resolution Algorithm in a Multiple Aircraft Scenario

The KB3D algorithm is a pairwise conflict detection and resolution (CD&R) algorithm. It detects and generates trajectory vectoring for an aircraft which has been predicted to be in an airspace minima violation within a given look-ahead time. It has been proven, using mechanized theorem proving techniques, that for a pair of aircraft, KB3D produces at least one vectoring solution and that all solutions produced are correct. Although solutions produced by the algorithm are mathematically correct, they might not be physically executable by an aircraft or might not solve multiple aircraft conflicts. This paper describes a simple solution selection method which assesses all solutions generated by KB3D and determines the solution to be executed. The solution selection method and KB3D are evaluated using a simulation in which N aircraft fly in a free-flight environment and each aircraft in the simulation uses KB3D to maintain separation. Specifically, the solution selection method filters KB3D solutions which are procedurally undesirable or physically not executable and uses a predetermined criteria for selection.

Carreno, Victor A.↗
NASA NTRS2001

A novel bit-wise adaptable entropy coding technique

We present a novel entropy coding technique which is adaptable in that each bit to be encoded may have an associated probability esitmate which depends on previously encoded bits. The technique may have advantages over arithmetic coding. The technique can achieve arbitrarily small redundancy and admits a simple and fast decoder.

data compression entopy coding↗
NASA NTRS2006

WISE 2005: LBNP Exercise and Flywheel Resistive Exercise as an Effective Countermeasure Combination

Long-term exposure to microgravity can cause a severe musculoskeletal loss and cardiovascular deconditioning in astronauts. In this report, the effectiveness of combined supine treadmill exercise in a lower body negative pressure chamber (LBNPex) and flywheel resistive exercise (Rex) countermeasures was determined to prevent bone loss, reduced aerobic upright exercise capacity and reduced muscle strength. We hypothesized that exercise subjects (EX) would show less decrease in bone mineral density (BMD), peak oxygen consumption (VO2pk) and knee extensor strength (KES) than control subjects (CON). Sixteen healthy female subjects (34 plus or minus 4yrs, 164 plus or minus 6.5cm, 58 plus or minus 5kg; mean plus or minus SD) participated in a 60-d 6 degree head-down tilt bed rest (BR) study after providing written informed consent. Subjects were assigned to one of two groups: a non- exercising CON group or an EX group performing LBNPex 2-4 d/wk and Rex every 3rd-d. VO2pk was measured with a maximal, graded, upright treadmill test performed pre-BR and on 3-d after BR. BMD was assessed pre-BR and 3-d after BR by dual energy x-ray absorptiometry total body DEXA scan (DEXA; HOLOGIC QDR 4500 Elite ). A Cybex dynamometer was employed to measure the isokinetic KES before and 5-d after BR. Two-way repeated measures ANOVA were performed with time as the repeated factor. Statistical significance was set at p less than 0.05. CON experienced a significant decrease in BMD in the trochanter (PRE: 0.670 0.045; POST: 0.646 0.352 g(raised dot) per square centimeter) and in the whole hip (PRE: 0.894 0.059; POST: 0.858 0.057 g(raised dot) per square centimeter). BMD also decreased significantly in EX in the trochanter (PRE: 0.753 plus or minus 0.0617; POST: 0.741 plus or minus 0.061 g(raised dot) per square centimeter) and whole hip (PRE: 0.954 plus or minus 0.067; POST: 0.935 plus or minus 0.069 g(raised dot) per square centimeter). BMD losses were significantly less in EX than in CON subjects. VO2pk was significantly decreased in the CON after BR (PRE: 38.0 plus or minus 4.8; POST: 29.9 plus or minus 4.2 ml(raised dot) per kilogram per minute), but not in the EX (PRE: 39.0 plus or minus 2.0; POST: 37.8 plus or minus 1.9 ml(raised dot) per kilogram per minute). KES was significantly reduced by 30% in CON (PRE: 113 plus or minus 12; POST: 78 plus or minus 8 N-m), but was not different in EX (PRE: 126 plus or minus 25; POST: 115 plus or minus 25 N-m). The combination LBNPex and Rex during 60-d BR protects against cardiovascular and musculoskeletal deconditioning and may be an efficacious countermeasure for prolonged space flight.

Meuche, S.↗
NASA NTRS2006

WIse-2005: Combined Aerobic and Resistive Exercise May Help Mitigate Bone Loss During 60-D Simulated Microgravity in Women

Exercise can attenuate bone loss associated with disuse during bed rest (BR), an analog of space flight. Previous studies have examined the efficacy of aerobic or resistive exercise countermeasures, but not in combination. We sought to determine the effect of a combined resistive and aerobic exercise regimen on bone metabolism during BR. After a 20-d ambulatory adaptation to confinement and diet, 16 women participated in a 60-d head-down-tilt BR. Control subjects (CN, n=8) performed no countermeasures. Exercise subjects, (EX, n=8) participated in exercise alternating daily between supine treadmill exercise within lower body negative pressure and resistive fly-wheel exercise (6-d wk(sup -1)). In the last week of BR, bone resorption was greater (p less than 79 plus or minus 44%, mean plus or minus SD) and EX groups (64 50%). N-telopeptide also increased (CN: 51 plus or minus 34%; EX: 43 plus or minus 56%). However, bone-specific alkaline phosphatase, a bone formation marker, tended to be higher in EX (26 plus or minus 18%) than in CN (8 plus or minus 33%) groups. The combination of resistive and aerobic exercise does not prevent bone resorption, but may promote formation, potentially mitigating the net bone loss associated with simulated microgravity. This study was supported by CNES, CSA, ESA, NASA, and NASA grant NNJ04HF71G to ARH. MEDES (French Institute for Space Medicine and Physiology) organized the study.

Smith, Scott M.↗
NASA NTRS2006

WISE-2005 Protective Effect of Exercise within LBNP Countermeasure Detected by Heart Rate Response to Low Levels of LBNP

Sixteen women were studied before, during and after a 60 day, continu ous 6" head-down bed-rest (HDBR). Subjects were randomly assigned to two groups: Control (no countermeasures) and Exercise+LBNP (supine ru nning within an LBNP chamber for 40-min followed by 10-min passive L BNP for 3-4 days/week, plus flywheel resistive training of the legs e very third day). Cardiovascular responses were observed before bed re st, on day 50 of HDBR and R+8 after bed rest. Subjects were supine in the LBNP device with suction applied at 0, -10, -20 and -30 mmHg LBN P for 2-min per stage. In the pre-bed rest testing, there was no diff erence in HR between the groups at rest or at -30 mmHg. On HDBR day 50, HR was elevated at supine rest for the Con not the Ex group, whil e at -30 mmHg HR was elevated above pre-HDBR for both groups, but the magnitude of increase from Pre- to HDBR day 50 was less for the Ex g roup than for the Con group. The change in HR on HDBR day 50 is an im portant indicator as it was less than 24-hours after the Exercise+LBN P countermeasure on day 49. After bed rest, no specific countermeasu res were provided in the first week, so HR responses on day R+8 refle cted the effects of bed rest with or without countermeasure plus any recovery from simply returning to the upright posture. Relative to th e Pre-bed rest responses, HR on day R+8 had recovered in the Ex group but was still elevated in the Con group. These results indicate that the cardiovascular response to LBNP is preserved to a greater degre e during bed rest by the countermeasures, and further that the cardio vascular response returned to pre-bed rest much more rapidly in the E xercise+LBNP group than hi the group that received no cardiovascular countermeasures.

Hughson, R. L.↗
NASA NTRS2006

WISE-2005: LBNP/Treadmill and Resistive Exercise Countermeasures Maintain Aerobic Capacity during a 60-d Bed Rest

We have previously documented that supine treadmill exercise within lower body negative pressure (LBNPex) performed 6 sessions (raised dot) wk(sup -1) during 15- and 30-day bed rests (BR) maintained upright aerobic capacity (VO2pk). In the present study, ure are evaluating whether aerobic capacity is maintained during a 60-d BR when the LBNPex frequency is reduced to 2-4 sessions (raised dot) wk(sup -1) and resistance exercise (REX) is added 2-3 sessions (raised dot) wk(sup -1). Eight healthy women (32 plus or minus 4 yrs; 56.4 plus or minus 3.6 kg; 164 plus or minus 8 cm; mean plus or minus SD) performed maximal-exertion, graded treadmill tests before and 3 days after a 60-d, 6 deg. head-down tilt BR. (Earliest day the medical monitors would permit a maximal exercise test post-BR). During BR, four subjects performed no exercise (CON), while four other subjects (EX) performed LBNPex and REX on separate days. The LBNPex countermeasure employed an intermittent (40-80% pre-BR VO2pk), 40-min protocol against an LBNP pressure (-49 plus or minus 3 mmHg) applied to provide a footward force equivalent to 1.0-1.2 body weight. REX consisted of maximal concentric and eccentric supine leg press and heel raise exercises using a gravity-independent flywheel ergometer. Comparisons were performed using paired (within-group) or non-paired (between-group) t-tests. Three days post-BR, VO2pk of the CON group was reduced significantly from pre-BR (Pre:37.2 plus or minus 1.2, Post: 29.4 plus or minus 2 ml (raised dot) kg(sup -1) (raised dot) min(sup -1), P less than 0.05), while the VO2pk of the EX group was not significantly reduced (Pre: 39.6 plus or minus 1.9, Post: 38.0 plus or minus 0.6 ml (raised dot) kg(sup -1) (raised dot) min(sup -1)). Peak heart rate, ventilation, rating of perceived exertion, and respiratory exchange ratio were not significantly different between the two groups pre- and post-BR. These preliminary results suggest that the combined LBNPex and REX countermeasures may be sufficient to maintain upright aerobic capacity after long-duration space flights.

Schneider, Suzanne M.↗
NASA NTRS2012

High Protein Intake Improves Insulin Sensitivity but Exacerbates Bone Resorption in Immobility (WISE Study)

Inactivity, like bed rest (BR), causes insulin resistance (IR) and bone loss even in healthy subjects. High protein intake seems to mitigate this IR but might exacerbate bone loss. We hypothesized that high protein intake (animal:vegetable protein ratio: 60:40), isocaloric, compared to the control group plus high potassium intake would prevent IR without affecting bone turnover. After a 20-day ambulatory adaptation to controlled confinement and diet, 16 women participated in a 60-day, 6 deg head-down-tilt BR and were assigned randomly to one of the two groups. Control subjects (CON, n=8) received 1g/kg body mass/d dietary protein. Nutrition subjects (NUT, n=8) received 1.45g/kg body mass/d dietary protein plus 7.2g branched chain amino acids per day during BR. All subjects received 1670 kcal/d. Bed rest decreased glucose disposal by 35% (p<0.05) in CON. Isocaloric high protein intake prevented insulin resistance, but exacerbated bed rest induced increase in bone resorption markers C-telopeptide (> 30%) and Ntelopeptide (>20%) (both: p<0.001). Bone formation markers were unaffected by high protein intake. We conclude from these results that high protein intake might positively affect glucose tolerance, but might also foster bone loss. Further long-duration studies are mandatory before high protein intake for diabetic patients, who have an increased fracture risk, might be recommended.

Heer, Martina↗
NASA NTRS2012

Origin of 12 micrometer Emission Across Galaxy Populations from Wise and ADSS Surveys

We cross-matched Wide-field Infrared Survey Explorer sources brighter than 1 mJy at 12 micron with the Sloan Digital Sky Survey galaxy spectroscopic catalog to produce a sample of approx. 10(exp 5) galaxies at z = 0.08, the largest of its kind. This sample is dominated (70%) by star-forming (SF) galaxies from the blue sequence, with total IR luminosities in the range approx 10(exp 8)-10(exp 12) Solar L. We identify which stellar populations are responsible for most of the 12 micron emission. We find that most (approx 80%) of the 12 micron emission in SF galaxies is produced by stellar populations younger than 0.6 Gyr. In contrast, the 12 micron emission in weak active galactic nuclei (AGNs; L [O iii] < 10(exo 7) solar L ) is produced by older stars, with ages of approx 1-3 Gyr. We find that L(sub 12 micron) linearly correlates with stellar mass for SF galaxies. At fixed 12 micron luminosity, weak AGNs deviate toward higher masses since they tend to be hosted by massive, early-type galaxies with older stellar populations. SF galaxies and weak AGNs follow different L(sub 12 micron) - SFR (star formation rate) relations, with weak AGNs showing excess 12 micron emission at low SFR (0.02-1 solar M /yr). This is likely due to dust grains heated by older stars. While the specific star formation rate (SSFR) of SF galaxies is nearly constant, the SSFR of weak AGNs decreases by approx 3 orders of magnitude, reflecting the very different star formation efficiencies between SF galaxies and massive, early-type galaxies. Stronger type II AGNs in our sample (L(sub [O iii]) > 10(exp 7) solar L ), act as an extension of massive SF galaxies, connecting the SF and weak AGN sequences. This suggests a picture where galaxies form stars normally until an AGN (possibly after a starburst episode) starts to gradually quench the SF activity. We also find that 4.6-12 micron color is a useful first-order indicator of SF activity in a galaxy when no other data are available.

Donso, E.↗
NASA NTRS2013

A Step-Wise Approach to Elicit Triangular Distributions

Adapt/combine known methods to demonstrate an expert judgment elicitation process that: 1.Models expert's inputs as a triangular distribution, 2.Incorporates techniques to account for expert bias and 3.Is structured in a way to help justify expert's inputs. This paper will show one way of "extracting" expert opinion for estimating purposes. Nevertheless, as with most subjective methods, there are many ways to do this.

Greenberg, Marc W.↗
NASA NTRS2013

New Brown Dwarf Discs in Upper Scorpius Observed with WISE

We present a census of the disc population for UKIDSS selected brown dwarfs in the 5-10 Myr old Upper Scorpius OB association. For 116 objects originally identified in UKIDSS, the majority of them not studied in previous publications, we obtain photometry from the Wide-Field Infrared Survey Explorer data base. The resulting colour magnitude and colour colour plots clearly show two separate populations of objects, interpreted as brown dwarfs with discs (class II) and without discs (class III). We identify 27 class II brown dwarfs, 14 of them not previously known. This disc fraction (27 out of 116, or 23%) among brown dwarfs was found to be similar to results for K/M stars in Upper Scorpius, suggesting that the lifetimes of discs are independent of the mass of the central object for low-mass stars and brown dwarfs. 5 out of 27 discs (19 per cent) lack excess at 3.4 and 4.6 microns and are potential transition discs (i.e. are in transition from class II to class III). The transition disc fraction is comparable to low-mass stars.We estimate that the time-scale for a typical transition from class II to class III is less than 0.4 Myr for brown dwarfs. These results suggest that the evolution of brown dwarf discs mirrors the behaviour of discs around low-mass stars, with disc lifetimes of the order of 5 10 Myr and a disc clearing time-scale significantly shorter than 1 Myr.

Dawson, P.↗
NASA NTRS2011

Pair-Wise, Deformable Mirror, Image Plane-Based Diversity Electric Field Estimation for High Contrast Coronagraphy

In this paper we describe the complex electric field reconstruction from image plane intensity measurements for high contrast coronagraphic imaging. A deformable mirror (DM) surface is modied with pairs of complementary shapes to create diversity in the image plane of the science camera where the intensity of the light is measured. Along with the Electric Field Conjugation correction algorithm, this estimation method has been used in various high contrast imaging testbeds to achieve the best contrasts to date both in narrow and in broad band light. We present the basic methodology of estimation in easy to follow list of steps, present results from HCIT and raise several open quations we are confronted with using this method.

coronagraphy↗
NASA NTRS2016

Point-Wise Phase Matching for Nonlinear Frequency Generation in Dielectric Resonators

An optical resonator fabricated from a uniaxial birefringent crystal, such as beta barium borate. The crystal is cut with the optical axis not perpendicular to a face of the cut crystal. In some cases the optical axis lies in the plane of the cut crystal face. An incident (input) electromagnetic signal (which can range from the infrared through the visible to the ultraviolet) is applied to the resonator. An output signal is recovered which has a frequency that is an integer multiple of the frequency of the input signal. In some cases a prism is used to evanescently couple the input and the output signals to the resonator.

Yu, Nan↗
NASA NTRS1995

Bit-Wise Arithmetic Coding for Data Compression

Consider the problem of compressing a uniformly quantized source. A traditional approach is to assign variable length codewords to the quantizer output symbols or groups of symbols. Here an alternate solution is proposed: assign a fixed length binary codeword to each output symbol in such a way that a zero is more likely than a one in every codeword bit position. The encoding procedure is described.

Arithmetic↗