Florida Space Grant Consortium

We report the results of the first sensitive L-band (3.5 micron) survey of the intermediate age (2.5 - 30 Myr) clusters NGC 2264, NGC 2362 and NGC 1960. We use JHKL colors to obtain a census of the circumstellar disk fractions in each cluster. We find disk fractions of 52% +/- 10%, 12% +/- 4% and 3% +/- 3% for the three clusters respectively. Together with our previously published JHKL investigations of the younger NGC 2024, Trapezium and IC 348 clusters, we have completed the first systematic and homogenous survey for circumstellar disks in a sample of young clusters that both span a significant range in age (0.3 - 30 Myr) and contain statistically significant numbers of stars whose masses span nearly the entire stellar mass spectrum. Analysis of the combined survey indicates that the cluster disk fraction is initially very high (> 80%) and rapidly decreases with increasing cluster age, such that half the stars within the clusters lose their disks in < ~3 Myr. Moreover, these observations yield an overall disk lifetime of ~ 6 Myr in the surveyed cluster sample. This is the timescale for essentially all the stars in a cluster to lose their disks. This should set a meaningful constraint for the planet building timescale in stellar clusters. The implications of these results for current theories of planet formation are briefly discussed.

We report the results of the first sensitive L-band (3.5 micron) survey of the intermediate age (2.5 - 30 Myr) clusters NGC 2264, NGC 2362 and NGC 1960. We use JHKL colors to obtain a census of the circumstellar disk fractions in each cluster. We find disk fractions of 52% +/- 10%, 12% +/- 4% and 3% +/- 3% for the three clusters respectively. Together with our previously published JHKL investigations of the younger NGC 2024, Trapezium and IC 348 clusters, we have completed the first systematic and homogenous survey for circumstellar disks in a sample of young clusters that both span a significant range in age (0.3 - 30 Myr) and contain statistically significant numbers of stars whose masses span nearly the entire stellar mass spectrum. Analysis of the combined survey indicates that the cluster disk fraction is initially very high (&gt; 80%) and rapidly decreases with increasing cluster age, such that half the stars within the clusters lose their disks in &lt; ~3 Myr. Moreover, these observations yield an overall disk lifetime of ~ 6 Myr in the surveyed cluster sample. This is the timescale for essentially all the stars in a cluster to lose their disks. This should set a meaningful constraint for the planet building timescale in stellar clusters. The implications of these results for current theories of planet formation are briefly discussed.

We report the results of the first sensitive L-band (3.4 micron) imaging survey of the young IC 348 cluster in Perseus. In conjunction with previously acquired JHK (1.25, 1.65, 2.2 micron) observations, we use L-band data to obtain a census of the circumstellar disk population to m_K=m_L<=12.0 in the central 110 square arcmin region of the cluster. An analysis of the JHKL colors of 107 sources indicates that 65% +/- 8% of the cluster membership possesses (inner) disks. This fraction is lower than those (86% +/- 8% and 80% +/- 7%) obtained from similar JHKL surveys of the younger NGC 2024 and Trapezium clusters, suggesting that the disk fraction in clusters decreases with cluster age. Sources with circumstellar disks in IC 348 have a median age of 0.9 Myr, while the diskless sources have a median age of 1.4 Myr, for a cluster distance of 320 pc. Although the difference in the median ages between the two populations is only marginally significant, our results suggest that over a timescale of 2 - 3 Myr, more than a third of the disks in the IC 348 cluster disappear. Moreover, we find that at a very high confidence level, the disk fraction is a function of spectral type. All stars earlier than G appear diskless, while stars with spectral types G and later have a disk fraction ranging between 50% - 67%, with the latest type stars having the higher disk fraction. This suggests that the disks around stars with spectral types G and earlier have evolved more rapidly than those with later spectral types. The L-band disk fraction for sources with similar ages in both IC 348 and Taurus is the same, within the errors, suggesting that, at least in clusters with no O stars, the disk lifetime is independent of environment.

We present the results of the first sensitive L band (3.4 micron) imaging study of the nearby young embedded cluster NGC 2024. Two separate surveys of the cluster were acquired in order to obtain a census of the circumstellar disk fraction in the cluster. From an analysis of the JHKL colors of all sources in our largest area, we find an infrared excess fraction of > 86%. The JHKL colors suggest that the infrared excesses arise in circumstellar disks, indicating that the majority of the sources which formed in the NGC 2024 cluster are currently surrounded by, and likely formed with circumstellar disks. The excess fractions remain very high, within the errors, even at the faintest L magnitudes from our deeper surveys suggesting that disks form around the majority of the stars in very young clusters such as NGC 2024 independent of mass. From comparison with published JHKL observations of Taurus, we find the K - L excess fraction in NGC 2024 to be consistent with a high initial incidence of circumstellar disks in both NGC 2024 and Taurus. Because NGC 2024 represents a region of much higher stellar density than Taurus, this suggests that disks may form around most of the YSOs in star forming regions independent of environment. We find a relatively constant JHKL excess fraction with increasing cluster radius, indicating that the disk fraction is independent of location in the cluster. In contrast, the JHK excess fraction increases rapidly toward the central region of the cluster, and is most likely due to contamination of the K band measurements by bright nebulosity in the central regions of the cluster. We identify 45 candidate protostellar sources in the central regions of the NGC 2024 cluster, and find a lower limit on the protostellar phase of early stellar evolution of 0.4 - 1.4 X 10^5 yr, similar to that in Taurus.

We present the results of the rst broadband N (10.8 km) survey of the NGC 2024 cluster.The midinfrared data were combined with our previously published JHKL photometry to construct spectral energy distributions for all detected sources.The main scientic goals were to investigate the nature of the young stellar objects (YSOs) in the cluster and to examine the efficiency of detecting circumstellar disk sources from near-infrared JHKL color-color diagrams.Out of 59 sources surveyed having K-band (2.2 km) magnitudes we detected 35 (D59%) at 10 km.Combining these detections and upper m K 10.5, limits for the nondetections with existing JHKL data, we identify one Class I, six at-spectrum, 28 Class II, and ve Class III sources.We nd a circumstellar disk fraction for NGC 2024 of D85% ^15%, which conrms earlier published suggestions that the majority, if not all, of the stars in the NGC 2024 cluster formed with disks, and these disks still exist at the present time.In addition, all but one of the disk sources identied in our survey lie in the infrared-excess region of the JHKL color-color diagram for the NGC 2024 cluster.This demonstrates that JHKL color-color diagrams are extremely efficient in identifying YSOs with circumstellar disks.Of the 14 sources in our survey with K[L colors suggestive of protostellar objects, D29% are protostellar in nature, while D7% are true Class I sources.This may be due to extinction producing very red K[L colors in Class II YSOs, thus making them appear similar in color to protostars.This suggests that caution must be applied when estimating the sizes and lifetimes of protostellar populations within star-forming regions based on K[L colors alone.A comparison of the ratio of the number of Class I and at-spectrum sources to the number of Class II and III sources in NGC 2024, o Oph, and Taurus-Auriga indicates that NGC 2024 and o Oph have similar ages, while Taurus-Auriga is an older region of star formation, consistent with published T Tauri star ages in each region.Finally, we calculate the luminosities of the Class II sources in NGC 2024, o Oph, and Taurus and discuss the results.

Abstract A set of high‐fidelity simulated asteroid materials, or simulants, was developed based on the mineralogy of carbonaceous chondrite meteorites. Three varieties of simulant were developed based on CI 1 chondrites (typified by Orgueil), CM 2 chondrites (typified by Murchison), and CR 2/3 chondrites (multiple samples). The simulants were designed to replicate the mineralogy and physical properties of the corresponding meteorites and anticipated asteroid surface materials as closely as is reasonably possible for bulk amounts. The simulants can be made in different physical forms ranging from larger cobbles to fine‐grained regolith. We analyzed simulant prototypes using scanning electron microscopy, X‐ray fluorescence, reflectance spectroscopy at ambient conditions and in vacuum, thermal emission spectroscopy in a simulated asteroid environment chamber, and combined thermogravimetry and evolved gas analysis. Most measured properties compare favorably to the reference meteorites and therefore to predicted volatile‐rich asteroid surface materials, including boulders, cobbles, and fine‐grained soils. However, there were also discrepancies, and mistakes were made in the original mineral formulations that will be updated in the future. The asteroid simulants are available to the community from the nonprofit Exolith Lab at UCF , and the mineral recipes are freely published for other groups to reproduce and modify as they see fit.

We fit elliptical isophotes to the Hubble Deep Field-North WFPC-2 and NICMOS data to study the rest-frame UV_{218}-U_{300} color profiles and rest-frame B surface brightness profiles of 33 intermediate redshift galaxies (0.5 <= z <= 1.2) with I_{814} < 25 and 50 high redshift galaxies (2.0 <= z <= 3.5) with H_{160}< 27. From the weighted least-squares fit to the color profiles we find that, at intermediate redshifts, the galaxies possess negative color gradients indicating a reddening towards the center of the profile similar to local samples whereas, at high redshifts, the galaxies possess positive color gradients. This indicates that star formation is more centrally concentrated in the distant galaxy sample which differs from the prevalent mode of extended disk star formation that we observe in the local universe. Additionally, we find that it is critical to correct for PSF effects when evaluating the surface brightness profiles since at small scale lengths and faint magnitudes, an r^{1/4} profile can be smoothed out substantially to become consistent with an exponential profile. After correcting for PSF effects, we find that at higher look-back time, the fraction of galaxies possessing exponential profiles have slightly decreased while the fraction of galaxies possessing r^{1/4} profiles have slightly increased. Our results also suggest a statistically insignificant increase in the fraction of peculiar/irregular type galaxies. We compare our results with recent semi-analytical models which treat galaxy formation and evolution following the cold dark matter hierarchical framework.

We fit elliptical isophotes to the Hubble Deep Field-North WFPC-2 and NICMOS data to study the rest-frame UV_{218}-U_{300} color profiles and rest-frame B surface brightness profiles of 33 intermediate redshift galaxies (0.5 &lt;= z &lt;= 1.2) with I_{814} &lt; 25 and 50 high redshift galaxies (2.0 &lt;= z &lt;= 3.5) with H_{160}&lt; 27. From the weighted least-squares fit to the color profiles we find that, at intermediate redshifts, the galaxies possess negative color gradients indicating a reddening towards the center of the profile similar to local samples whereas, at high redshifts, the galaxies possess positive color gradients. This indicates that star formation is more centrally concentrated in the distant galaxy sample which differs from the prevalent mode of extended disk star formation that we observe in the local universe. Additionally, we find that it is critical to correct for PSF effects when evaluating the surface brightness profiles since at small scale lengths and faint magnitudes, an r^{1/4} profile can be smoothed out substantially to become consistent with an exponential profile. After correcting for PSF effects, we find that at higher look-back time, the fraction of galaxies possessing exponential profiles have slightly decreased while the fraction of galaxies possessing r^{1/4} profiles have slightly increased. Our results also suggest a statistically insignificant increase in the fraction of peculiar/irregular type galaxies. We compare our results with recent semi-analytical models which treat galaxy formation and evolution following the cold dark matter hierarchical framework.

Abstract As space travel matures and extended duration voyages become increasingly common, it will be necessary to include arrays of early fire detection systems aboard spacefaring vessels, space habitats, and in spacesuits. As gasses that are relevant to combustion and pyrolysis have absorption features in the mid-infrared range, it is possible to utilize absorption spectroscopy as a means of detecting and quantifying the concentration of these hazardous compounds. Within this work, a sensor for detecting carbon dioxide has been designed and tested autonomously on a high-altitude balloon flight. The sensor utilizes a 4.2- μ m light-emitting diode source, amplitude modulation to characterize species concentrations, and frequency modulation to characterize ambient temperature. Future work will include expanding the sensor design to detect other gases, and demonstrating suborbital flight capability.

There is conflicting evidence regarding the prevalence and magnitude of exercise-induced muscle damage (EIMD) following low-load resistance exercise with blood flow restriction (LL + BFR) that may be related to exercise protocols. The purpose of this investigation was to examine the effects of 75-repetition (BFR-75) (1 × 30, 3 × 15) and 4 sets to failure (BFR-4x) protocols on indices of EIMD among untrained women. Thirteen women completed this investigation. One leg was randomly assigned to BFR-75 and the other to BFR-4x. Each leg performed isokinetic, unilateral, concentric-eccentric, leg extension muscle actions at 30% of maximal strength. Indices of EIMD (muscle soreness, range of motion [ROM], limb circumference, pain pressure threshold [PPT], and maximal voluntary isometric contraction [MVIC]) were recorded before exercise, 0-, 24-, 48-, 72-, and 96-hours post-exercise. There were no changes for ROM, circumference, or PPT. Muscle soreness increased similarly in both conditions 0-, 24-, and 48-hours post-exercise and MVIC increased 24-, 48-, 72-, and 96-hours post-exercise. These findings suggested BFR-75 and BFR-4x were not associated with EIMD and elicited similar physiological responses. The increases in muscle soreness may be due to metabolic stress associated with LL + BFR protocols apart from EIMD.

We present observations from the gas regolith interaction testbed (GRIT), which is a plume surface interaction (PSI) drop tower experiment conducted at the Center for Microgravity Research. We conducted experiments with four different media: steel beads, quartz sand, glass beads, and high-fidelity asteroid regolith simulant. Particle sizes ranged from hundreds of microns up to centimeter scale. By varying the jetting pulse time, we observe behaviors ranging from slight perturbation of the granular media all the way to lofting the entire simulant mass. Phenomena are much more pronounced in microgravity when compared to control experiments conducted at Earth gravity. Differences in particle size and nozzle distance produce varied PSI phenomena. These bear some resemblance to solid impactor experiments, but we observe flow-driven behaviors unique to gas-granular interactions.

Surface electromyography (EMG) and mean force can be used to identify motor unit excitation and fatigue. Low-load resistance training with blood flow restriction (LL+BFR) may result in earlier fatigue and maximal muscle fibre recruitment compared to low-load resistance training (LL). The purpose of this investigation was to examine EMG and force responses during LL versus LL+BFR. Thirteen males (mean ± standard deviation = 24±4 years) completed a bout (1×30) of leg extension muscle actions at 30% of their 1 repetition maximum LL and LL+BFR while force, EMG amplitude, and EMG mean power frequency (EMG MPF) were recorded. EMG amplitude increased (74.2%) and EMG MPF decreased (22.6%) similarly during both conditions. There was no significant difference in mean force during the first 3 repetitions between LL+BFR (477.3±132.3 N) and LL (524.3±235.1 N) conditions, but mean force was lower during the last 3 repetitions for LL+BFR (459.7±179.3 N) compared to LL (605.4±276.4 N). The results of the present study indicated that a fatiguing bout of leg extension muscle actions performed LL and LL+BFR elicited similar neuromuscular responses. There was a significant difference in mean force during the last 3 repetitions (LL&gt;LL+BFR) that may have been due to differences in the time spent near peak force.

To further extended deep space exploration missions, both through commercial space endeavors and through government-funded opportunities, the hazard of toxic gas accumulation onboard space vehicles must be quickly resolved to ensure mission success. Such events can occur due to fire events or fuel/oxidizer leaks. Several hazardous gases that are present in a space environment have absorption features in the mid-infrared range and thus can be detected and quantified via absorption spectroscopy. This work presents a benchtop sensor that utilizes a 4.2 μm light-emitting diode and a rotating diffraction grating to detect both carbon dioxide and nitrous oxide. Subsequent works will focus on adding further species of interest and post benchtop testing.

Reaction in powdered energetics involves a multitude of timescales born out of combustion physics. With high self-illumination, an external source of illumination is generally not used in bulk combustion of powder or pelletized energetics. Melt phase visualization is useful for understanding multiphase reaction dynamics but is inaccessible in common imaging setups for studying solid reactive material. The imaging setup in this study is based on concepts from Fourier optics, utilizing standard imaging optical components. The technique uses jetted particles as fast-radiating sources to illuminate adjoining slower melt dynamics, providing a unique solution to multiphase visualization in a multiscale solid-state reactive system. Only a narrow bandwidth of the emitted thermal light is used for imaging. In the Fourier filtering scheme, using a combination of intensity and spatial filtering of the reference beam, the contrast of a multiphase body is enhanced in the scene. Qualitative imaging results from the setup show features of shadowgraphy as the dominant pathway for contrast development. Direction asymmetry in the transfer function and cutoff with angular frequencies or blurring indicates a scope of improvement with the usage of thin lenses, instead of stock components. This work demonstrates that phase contrast imaging in combustion studies of powdered energetics provides a viable method for visualizing melt phase dynamics.

PURPOSE: The application of blood flow restriction (BFR) with resistance training has been applied to various exercise modalities, but no previous investigations have examined isotonic BFR vs isokinetic BFR. Therefore, the purpose of this study was to examine the neuromuscular, swelling, and rating of perceived exertion (RPE) responses following isotonic and isokinetic BFR exercise. METHODS: Fifteen (22 ± 2 years) women randomly performed (on separate days) 75 (1x30, 3x15) submaximal (30% of one repetition maximum [isotonic] or 30% maximal voluntary isometric contraction (MVIC) [isokinetic]) unilateral leg extensions with BFR (60% of total arterial occlusion pressure). Before and immediately after each exercise, subjects performed MVICs while electromyography (EMG) was simultaneously recorded from the vastus lateralis (VL) muscle. Ultrasound muscle thickness (MT) was assessed from the VL prior to and after the MVICs. RPE was recorded during all 4 sets. Separate 2 (Condition [Isotonic, Isokinetic]) × 2 (Time [pretest, posttest]) repeated measures ANOVAs were used to examine the EMG and MT responses. A separate 2 (Condition [Isotonic, Isokinetic]) × 4 (Time [set 1, set 2, set 3, set 4]) repeated measures ANOVAs was used to assess RPE. Paired samples t-tests were used to analyze percent change in MVIC torque. RESULTS: There was no significant (p = 0.294-0.823) interaction or main effect for normalized EMG amplitude. For EMG frequency and MT there were significant interactions (p = 0.008) that indicated greater decreases in EMG frequency following isotonic (13%) than isokinetic (6%) but similar increases in MT (22%). For RPE, there was no significant (p = 0.368) interaction, but there were significant (p = 0.004) main effects for Time (set 4 > set 3 > set 2 > set 1) and Condition (isotonic > isokinetic) (p = 0.018). Additionally, there was a greater (34.9%) decrease in MVIC following the isotonic than isokinetic (15.2%) condition. CONCLUSIONS: Isotonic BFR exercise elicited greater fatigue-induced changes in EMG frequency, MVIC, and perceived effort than isokinetic condition. Therefore, relative to isokinetic, isotonic BFR exercise may provide a more potent acute exercise response and discomfort, but this may not translate to chronic adaptations as there were similar EMG amplitude responses between conditions.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Roelof L. Schuiling, Edward A. O'Connor; Development of a quick-reaction commercial launch site at the Cape Canaveral Air Station. AIP Conf. Proc. 15 January 1998; 420 (1): 899–904. https://doi.org/10.1063/1.54949 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search