3,862 research outputs found
Apollo experience report: Food systems
Development, delivery, and use of food systems in support of the Apollo 7 to 14 missions are discussed. Changes in design criteria for this unique program as mission requirements varied are traced from the baseline system that was established before the completion of the Gemini Program. Problems and progress in subsystem management, material selection, food packaging, development of new food items, menu design, and food-consumption methods under zero-gravity conditions are described. The effectiveness of various approaches in meeting food system objectives of providing flight crews with safe, nutritious, easy to prepare, and highly acceptable foods is considered. Nutritional quality and adequacy in maintaining crew health are discussed in relation to the establishment of nutritional criteria for future missions. Technological advances that have resulted from the design of separate food systems for the command module, the lunar module, The Mobile Quarantine Facility, and the Lunar Receiving Laboratory are presented for application to future manned spacecraft and to unique populations in earthbound situations
Light echoes reveal an unexpectedly cool Eta Carinae during its 19th-century Great Eruption
Eta Carinae (Eta Car) is one of the most massive binary stars in the Milky
Way. It became the second-brightest star in the sky during its mid-19th century
"Great Eruption," but then faded from view (with only naked-eye estimates of
brightness). Its eruption is unique among known astronomical transients in that
it exceeded the Eddington luminosity limit for 10 years. Because it is only 2.3
kpc away, spatially resolved studies of the nebula have constrained the ejected
mass and velocity, indicating that in its 19th century eruption, Eta Car
ejected more than 10 M_solar in an event that had 10% of the energy of a
typical core-collapse supernova without destroying the star. Here we report the
discovery of light echoes of Eta Carinae which appear to be from the 1838-1858
Great Eruption. Spectra of these light echoes show only absorption lines, which
are blueshifted by -210 km/s, in good agreement with predicted expansion
speeds. The light-echo spectra correlate best with those of G2-G5 supergiant
spectra, which have effective temperatures of ~5000 K. In contrast to the class
of extragalactic outbursts assumed to be analogs of Eta Car's Great Eruption,
the effective temperature of its outburst is significantly cooler than allowed
by standard opaque wind models. This indicates that other physical mechanisms
like an energetic blast wave may have triggered and influenced the eruption.Comment: Accepted for publication by Nature; 4 pages, 4 figures, SI: 6 pages,
3 figures, 5 table
Analysis of Multiple Plasmodium falciparum Infections in Tanzanian Children during the Phase III Trial of the Malaria Vaccine SPf66
In the first phase III efficacy trial of the malaria vaccine SPf66 in Africa, MOIs in SPf66- and placebo-vaccinated children were analyzed by polymerase chain reaction-restriction fragment length polymorphism of the Plasmodium falciparum merozoite surface antigen 2 (MSA2). MOIs were significantly reduced in asymptomatic vaccine recipients compared with those in asymptomatic placebo recipients; however, no differences were observed among symptomatic children in the vaccine and control groups. These results show that immunization with SPf66 modulates the course of naturally occurring infections, as reflected by reduced MOIs. In placebo recipients, however, there was a significant negative correlation between numbers of infecting genotypes, as identified by MSA2, and morbidity. Asymptomatic placebo recipients had an average of 5 concurrent infections, whereas children with clinical cases had an average of 3.4 infections. These data provide further evidence that premunition from concurrent infections is important in immunity against clinical malaria. No such effect of multiple infections was found in the vaccinated grou
Investigation of the neurovascular coupling in positive and negative BOLD responses in human brain at 7T
Decreases in stimulus-dependent blood oxygenation level dependent (BOLD) signal and their underlying neurovascular origins have recently gained considerable interest. In this study a multi-echo, BOLD-corrected vascular space occupancy (VASO) functional magnetic resonance imaging (fMRI) technique was used to investigate neurovascular responses during stimuli that elicit positive and negative BOLD responses in human brain at 7 T. Stimulus-induced BOLD, cerebral blood volume (CBV), and cerebral blood flow (CBF) changes were measured and analyzed in ‘arterial’ and ‘venous’ blood compartments in macro- and microvasculature. We found that the overall interplay of mean CBV, CBF and BOLD responses is similar for tasks inducing positive and negative BOLD responses. Some aspects of the neurovascular coupling however, such as the temporal response, cortical depth dependence, and the weighting between ‘arterial’ and ‘venous’ contributions, are significantly different for the different task conditions. Namely, while for excitatory tasks the BOLD response peaks at the cortical surface, and the CBV change is similar in cortex and pial vasculature, inhibitory tasks are associated with a maximum negative BOLD response in deeper layers, with CBV showing strong constriction of surface arteries and a faster return to baseline. The different interplays of CBV, CBF and BOLD during excitatory and inhibitory responses suggests different underlying hemodynamic mechanisms
Direct Confirmation of the Asymmetry of the Cas A Supernova with Light Echoes
We report the first detection of asymmetry in a supernova (SN) photosphere
based on SN light echo (LE) spectra of Cas A from the different perspectives of
dust concentrations on its LE ellipsoid. New LEs are reported based on
difference images, and optical spectra of these LEs are analyzed and compared.
After properly accounting for the effects of finite dust-filament extent and
inclination, we find one field where the He I and H alpha features are
blueshifted by an additional ~4000 km/s relative to other spectra and to the
spectra of the Type IIb SN 1993J. That same direction does not show any shift
relative to other Cas A LE spectra in the Ca II near-infrared triplet feature.
We compare the perspectives of the Cas A LE dust concentrations with recent
three-dimensional modeling of the SN remnant (SNR) and note that the location
having the blueshifted He I and H alpha features is roughly in the direction of
an Fe-rich outflow and in the opposite direction of the motion of the compact
object at the center of the SNR. We conclude that Cas A was an intrinsically
asymmetric SN. Future LE spectroscopy of this object, and of other historical
SNe, will provide additional insight into the connection of explosion mechanism
to SN to SNR, as well as give crucial observational evidence regarding how
stars explode.Comment: 13 pages, 7 figures, accepted for publication in Ap
GALEX Detection of Shock Breakout in Type II-P Supernova PS1-13arp: Implications for the Progenitor Star Wind
We present the GALEX detection of a UV burst at the time of explosion of an
optically normal Type II-P supernova (PS1-13arp) from the Pan-STARRS1 survey at
z=0.1665. The temperature and luminosity of the UV burst match the theoretical
predictions for shock breakout in a red supergiant, but with a duration a
factor of ~50 longer than expected. We compare the light curve of
PS1-13arp to previous GALEX detections of Type IIP SNe, and find clear
distinctions that indicate that the UV emission is powered by shock breakout,
and not by the subsequent cooling envelope emission previously detected in
these systems. We interpret the ~ 1 d duration of the UV signal with a shock
breakout in the wind of a red supergiant with a pre-explosion mass-loss rate of
~ 10^-3 Msun yr^-1. This mass-loss rate is enough to prolong the duration of
the shock breakout signal, but not enough to produce an excess in the optical
plateau light curve or narrow emission lines powered by circumstellar
interaction. This detection of non-standard, potentially episodic high
mass-loss in a RSG SN progenitor has favorable consequences for the prospects
of future wide-field UV surveys to detect shock breakout directly in these
systems, and provide a sensitive probe of the pre-explosion conditions of SN
progenitors.Comment: Accepted for Publication in Ap
Optically trapped bacteria pairs reveal discrete motile response to control aggregation upon cell–cell approach
Aggregation of bacteria plays a key role in the formation of many biofilms. The critical first step is cell–cell approach, and yet the ability of bacteria to control the likelihood of aggregation during this primary phase is unknown. Here, we use optical tweezers to measure the force between isolated Bacillus subtilis cells during approach. As we move the bacteria towards each other, cell motility (bacterial swimming) initiates the generation of repulsive forces at bacterial separations of ~3 μm. Moreover, the motile response displays spatial sensitivity with greater cell–cell repulsion evident as inter-bacterial distances decrease. To examine the environmental influence on the inter-bacterial forces, we perform the experiment with bacteria suspended in Tryptic Soy Broth, NaCl solution and deionised water. Our experiments demonstrate that repulsive forces are strongest in systems that inhibit biofilm formation (Tryptic Soy Broth), while attractive forces are weak and rare, even in systems where biofilms develop (NaCl solution). These results reveal that bacteria are able to control the likelihood of aggregation during the approach phase through a discretely modulated motile response. Clearly, the force-generating motility we observe during approach promotes biofilm prevention, rather than biofilm formation
Ultra-Luminous Supernovae as a New Probe of the Interstellar Medium in Distant Galaxies
We present the Pan-STARRS1 discovery and light curves, and follow-up MMT and
Gemini spectroscopy of an ultra-luminous supernova (ULSN; dubbed PS1-11bam) at
a redshift of z=1.566 with a peak brightness of M_UV=-22.3 mag. PS1-11bam is
one of the highest redshift spectroscopically-confirmed SNe known to date. The
spectrum is characterized by broad absorption features typical of previous
ULSNe (e.g., CII, SiIII), and by strong and narrow MgII and FeII absorption
lines from the interstellar medium (ISM) of the host galaxy, confirmed by an
[OII]3727 emission line at the same redshift. The equivalent widths of the
FeII2600 and MgII2803 lines are in the top quartile of the quasar intervening
absorption system distribution, but are weaker than those of gamma-ray burst
intrinsic absorbers (i.e., GRB host galaxies). We also detect the host galaxy
in pre-explosion Pan-STARRS1 data and find that its UV spectral energy
distribution is best fit with a young stellar population age of tau~15-45 Myr
and a stellar mass of M \sim (1.1-2.6)x10^9 M_sun (for Z=0.05-1 Z_sun). The
star formation rate inferred from the UV continuum and [OII]3727 emission line
is ~10 M_sun/yr, higher than in any previous ULSN host. PS1-11bam provides the
first direct demonstration that ULSNe can serve as probes of the interstellar
medium in distant galaxies. At the present, the depth and red sensitivity of
PS1 are uniquely suited to finding such events at cosmologically interesting
redshifts (z~1-2); the future combination of LSST and 30-m class telescopes
promises to extend this technique to z~4.Comment: Submitted to ApJL; 9 pages; 4 figures; 1 tabl
Hydrogen-Poor Superluminous Supernovae and Long-Duration Gamma-Ray Bursts Have Similar Host Galaxies
We present optical spectroscopy and optical/near-IR photometry of 31 host
galaxies of hydrogen-poor superluminous supernovae (SLSNe), including 15 events
from the Pan-STARRS1 Medium Deep Survey. Our sample spans the redshift range
0.1 < z < 1.6 and is the first comprehensive host galaxy study of this specific
subclass of cosmic explosions. Combining the multi-band photometry and
emission-line measurements, we determine the luminosities, stellar masses, star
formation rates and metallicities. We find that as a whole, the hosts of SLSNe
are a low-luminosity ( ~ -17.3 mag), low stellar mass ( ~ 2 x 10^8
M_sun) population, with a high median specific star formation rate ( ~ 2
Gyr^-1). The median metallicity of our spectroscopic sample is low, 12 +
log(O/H}) ~ 8.35 ~ 0.45 Z_sun, although at least one host galaxy has solar
metallicity. The host galaxies of H-poor SLSNe are statistically distinct from
the hosts of GOODS core-collapse SNe (which cover a similar redshift range),
but resemble the host galaxies of long-duration gamma-ray bursts (LGRBs) in
terms of stellar mass, SFR, sSFR and metallicity. This result indicates that
the environmental causes leading to massive stars forming either SLSNe or LGRBs
are similar, and in particular that SLSNe are more effectively formed in low
metallicity environments. We speculate that the key ingredient is large core
angular momentum, leading to a rapidly-spinning magnetar in SLSNe and an
accreting black hole in LGRBs.Comment: ApJ in press; updated to match accepted version. Some additional data
added, discussion of selection effects expanded; conclusions unchanged. 22
pages in emulateapj forma
Spectral Identification of an Ancient Supernova using Light Echoes in the LMC
We report the successful identification of the type of the supernova
responsible for the supernova remnant SNR 0509-675 in the Large Magellanic
Cloud (LMC) using Gemini spectra of surrounding light echoes. The ability to
classify outbursts associated with centuries-old remnants provides a new window
into several aspects of supernova research and is likely to be successful in
providing new constraints on additional LMC supernovae as well as their
historical counterparts in the Milky Way Galaxy (MWG). The combined spectrum of
echo light from SNR 0509-675 shows broad emission and absorption lines
consistent with a supernova (SN) spectrum. We create a spectral library
consisting of 26 SNe Ia and 6 SN Ib/c that are time-integrated, dust-scattered
by LMC dust, and reddened by the LMC and MWG. We fit these SN templates to the
observed light echo spectrum using minimization as well as correlation
techniques, and we find that overluminous 91T-like SNe Ia with \dm15<0.9
match the observed spectrum best.Comment: 12 pages, 18 Figures, to be published in Ap
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