387 research outputs found
Ice Dragon: A Mission to Address Science and Human Exploration Objectives on Mars
We present a mission concept where a SpaceX Dragon capsule lands a payload on Mars that samples ground ice to search for evidence of life, assess hazards to future human missions, and demonstrate use of Martian resources
Resource Prospector: Mission Goals, Relevance and Site Selection
Over the last two decades a wealth of new observations of the moon have demonstrated a lunar water system dramatically more complex and rich than was deduced following the Apollo era. Observation from the Lunar Prospector Neutron Spectrometer (LPNS) revealed enhancements of hydrogen near the lunar poles. This observation has since been confirmed by the Lunar Reconnaissance Orbiter (LRO) Lunar Exploration Neutron Detector (LEND) instrument. The Lunar Crater Observation and Sensing Satellite (LCROSS) mission targeted a permanently shadowed, enhanced hydrogen location within the crater Cabeus. The LCROSS impact showed that at least some of the hydrogen enhancement is in the form of water ice and molecular hydrogen (H2). Other volatiles were also observed in the LCROSS impact cloud, including CO2, CO, an H2S. These volatiles, and in particular water, have the potential to be a valuable or enabling resource for future exploration. In large part due to these new findings, the NASA Human Exploration and Operations Mission Directorate (HEOMD) have selected a lunar volatiles prospecting mission for a concept study and potential flight in CY2020. The mission includes a rover-borne payload that (1) can locate surface and near-subsurface volatiles, (2) excavate and analyze samples of the volatile-bearing regolith (up to 1 meter), and (3) demonstrate the form, extractability and usefulness of the materials
Water induced sediment levitation enhances downslope transport on Mars
On Mars, locally warm surface temperatures (~293 K) occur, leading to the possibility of (transient) liquid water on the surface. However, water exposed to the martian atmosphere will boil, and the sediment transport capacity of such unstable water is not well understood. Here, we present laboratory studies of a newly recognized transport mechanism: “levitation” of saturated sediment bodies on a cushion of vapor released by boiling. Sediment transport where this mechanism is active is about nine times greater than without this effect, reducing the amount of water required to transport comparable sediment volumes by nearly an order of magnitude. Our calculations show that the effect of levitation could persist up to ~48 times longer under reduced martian gravity. Sediment levitation must therefore be considered when evaluating the formation of recent and present-day martian mass wasting features, as much less water may be required to form such features than previously thought
Gravitino Dark Matter Scenarios with Massive Metastable Charged Sparticles at the LHC
We investigate the measurement of supersymmetric particle masses at the LHC
in gravitino dark matter (GDM) scenarios where the next-to-lightest
supersymmetric partner (NLSP) is the lighter scalar tau, or stau, and is stable
on the scale of a detector. Such a massive metastable charged sparticle would
have distinctive Time-of-Flight (ToF) and energy-loss () signatures. We
summarise the documented accuracies expected to be achievable with the ATLAS
detector in measurements of the stau mass and its momentum at the LHC. We then
use a fast simulation of an LHC detector to demonstrate techniques for
reconstructing the cascade decays of supersymmetric particles in GDM scenarios,
using a parameterisation of the detector response to staus, taus and jets based
on full simulation results. Supersymmetric pair-production events are selected
with high redundancy and efficiency, and many valuable measurements can be made
starting from stau tracks in the detector. We recalibrate the momenta of taus
using transverse-momentum balance, and use kinematic cuts to select
combinations of staus, taus, jets and leptons that exhibit peaks in invariant
masses that correspond to various heavier sparticle species, with errors often
comparable with the jet energy scale uncertainty.Comment: 23 pages, 10 figures, updated to version published in JHE
Neutron Spectrometer Prospecting in the Mojave Volatiles Project Analog Field Test
We know that volatiles are sequestered at the poles of the Moon. While we have evidence of water ice and a number of other compounds based on remote sensing, the detailed distribution, and physical and chemical form are largely unknown. Additional orbital studies of lunar polar volatiles may yield further insights, but the most important next step is to use landed assets to fully characterize the volatile composition and distribution at scales of tens to hundreds of meters. To achieve this range of scales, mobility is needed. Because of the proximity of the Moon, near real-time operation of the surface assets is possible, with an associated reduction in risk and cost. This concept of operations is very different from that of rovers on Mars, and new operational approaches are required to carry out such real-time robotic exploration. The Mojave Volatiles Project (MVP) was a Moon-Mars Analog Mission Activities (MMAMA) program project aimed at (1) determining effective approaches to operating a real-time but short-duration lunar surface robotic mission, and (2) performing prospecting science in a natural setting, as a test of these approaches. Here we describe some results from the first such test, carried out in the Mojave Desert between 16 and 24 October, 2014. The test site was an alluvial fan just E of the Soda Mountains, SW of Baker, California. This site contains desert pavements, ranging from the late Pleistocene to early-Holocene in age. These pavements are undergoing dissection by the ongoing development of washes. A principal objective was to determine the hydration state of different types of desert pavement and bare ground features. The mobility element of the test was provided by the KREX-2 rover, designed and operated by the Intelligent Robotics Group at NASA Ames Research Center. The rover-borne neutron spectrometer measured the neutron albedo at both thermal and epithermal energies. Assuming uniform geochemistry and material bulk density, hydrogen as either hydroxyl/water in mineral assemblages or as moisture will significantly enhance the return of thermalized neutrons. However, in the Mojave test setting there is little uniformity, especially in bulk material density. We find that lighter toned materials (immature pavements, bar and swale, and wash materials) have lower thermal neutron flux, while mature, darker pavements with the greatest desert varnish development have higher neutron fluxes. Preliminary analysis of samples from the various terrain types in the test area indicates a prevailing moisture content of 2-3 wt% H2O. However, soil mineralogy suggests that the welldeveloped Av1 soil horizon beneath the topmost dark pavement clast layer contains the highest clay content. Structural water (including hydroxyl) in these clays may explain the enhanced neutron albedo over dark pavements. On the other hand, surface and subsurface bulk density can also play a role in neutron albedo - lower density of materials found in washes, for example, can result in a reduction in neutron flux. Analysis is ongoing
Overview of NASA FINESSE (Field Investigations to Enable Solar System Science and Exploration) Science and Exploration Results
NASA's FINESSE (Field Investigations to Enable Solar System Science and Exploration) project is focused on a science and exploration field-based research program to generate strategic knowledge in preparation for human and robotic exploration of other planetary bodies including our moon, Mars' moons Phobos and Deimos, and near-Earth asteroids. Scientific study focuses on planetary volcanism (e.g., the formation of volcanoes, evolution of magma chambers and the formation of multiple lava flow types, as well as the evolution and entrapment of volatile chemicals) and impact cratering (impact rock modification, cratering mechanics, and the chronologic record). FINESSE conducts multiple terrestrial field campaigns (Craters of the Moon National Monument and Preserve in Idaho for volcanics, and West Clearwater Impact Structure in Canada for impact studies) to study such features as analogs relevant to our moon, Phobos, Deimos, and asteroids. Here we present the science and exploration results from two deployments to Idaho (2014, 2015) and our first deployment to Canada (2014). FINESSE was selected as a research team by NASA's Solar System Exploration Research Virtual Institute (SSERVI). SSERVI is a joint effort by NASA's Science Mission Directorate (SMD) and Human Exploration and Operations Mission Directorate (HEOMD)
From oil field to geothermal reservoir: assessment for geothermal utilization of two regionally extensive Devonian carbonate aquifers in Alberta, Canada
The Canadian province of
Alberta has one of the highest per capita CO2-equivalent emissions
in Canada, predominantly due to the industrial burning of coal for the
generation of electricity and mining operations in the oil sands deposits.
Alberta's geothermal potential could reduce CO2 emissions by
substituting at least some fossil fuels with geothermal energy.The Upper Devonian carbonate aquifer systems within the Alberta Basin are
promising target formations for geothermal energy. To assess their
geothermal reservoir potential, detailed knowledge of the thermophysical and
petrophysical rock properties is needed. An analogue study was conducted on
two regionally extensive Devonian carbonate aquifers, the Southesk-Cairn
Carbonate Complex and the Rimbey-Meadowbrook Reef Trend, to furnish a
preliminary assessment of the potential for geothermal utilization. Samples
taken from outcrops were used as analogues to equivalent formations in the
reservoir and correlated with core samples of the reservoir. Analogue
studies enable the determination and correlation of facies-related rock
properties to identify sedimentary, diagenetic, and structural variations,
allowing for more reliable reservoir property prediction.Rock samples were taken from several outcrops of Upper Devonian carbonates
in the Rocky Mountain Front Ranges and from four drill cores from the
stratigraphically equivalent Leduc Formation and three drill cores of the slightly
younger Nisku Formation in the subsurface of the Alberta Basin. The samples
were analyzed for several thermophysical and petrophysical properties, i.e.,
thermal conductivity, thermal diffusivity, and heat capacity, as well as
density, porosity, and permeability. Furthermore, open-file petrophysical
core data retrieved from the AccuMap database were used for correlation.The results from both carbonate complexes indicate good reservoir conditions
regarding geothermal utilization with an average reservoir porosity of about
8 %, average reservoir permeability between 10−12 and
10−15 m2, and relatively high thermal conductivities
ranging from 3 to 5 W m−1 K−1. The most promising target
reservoirs for hydrothermal utilisation are the completely dolomitized reef
sections. The measured rock properties of the Leduc Formation in the
subsurface show no significant differences between the Rimbey-Meadowbrook
Reef Trend and the Southesk-Cairn Carbonate Complex. Differences between the
dolomitized reef sections of the examined Leduc and Nisku Formation are also
minor to insignificant, whereas the deeper basinal facies of the Nisku
Formation differs significantly.In contrast, the outcrop analogue samples have lower porosity and
permeability, likely caused by low-grade metamorphism and deformation during
the Laramide orogeny that formed the Rocky Mountains. As such, the outcrop
analogues are not valid proxies for the buried reservoirs in the Alberta
Basin.Taken together, all available data suggest that dolomitization enhanced the
geothermal properties, but depositional patterns and other diagenetic
events, e.g., fracturing, also played an important role.</p
Probing for Invisible Higgs Decays with Global Fits
We demonstrate by performing a global fit on Higgs signal strength data that
large invisible branching ratios Br_{inv} for a Standard Model (SM) Higgs
particle are currently consistent with the experimental hints of a scalar
resonance at the mass scale m_h ~ 124 GeV. For this mass scale, we find
Br_{inv} < 0.64 (95 % CL) from a global fit to individual channel signal
strengths supplied by ATLAS, CMS and the Tevatron collaborations. Novel tests
that can be used to improve the prospects of experimentally discovering the
existence of a Br_{inv} with future data are proposed. These tests are based on
the combination of all visible channel Higgs signal strengths, and allow us to
examine the required reduction in experimental and theoretical errors in this
data that would allow a more significantly bounded invisible branching ratio to
be experimentally supported. We examine in some detail how our conclusions and
method are affected when a scalar resonance at this mass scale has couplings
deviating from the SM ones.Comment: 32pp, 15 figures v2: JHEP version, ref added & comment added after
Eq.
Long-term efficiency of infliximab in patients with ankylosing spondylitis : real life data confirm the potential for dose reduction
Objective: To analyse the treatment outcome of patients with ankylosing spondylitis (AS) in the European AS infliximab cohort (EASIC) study after a total period of 8 years with specific focus on dosage and the duration of intervals between infliximab infusions.
Methods: EASIC included patients with AS who had received infliximab for 2 years as part of the ASSERT trial. After that period, rheumatologists were free to change the dose or the intervals of infliximab. Clinical data were status at baseline, end of ASSERT and for a total of 8 years of follow-up.
Results: Of the initially 71 patients with AS from EASIC, 55 patients (77.5%) had completed the 8th year of anti-tumour necrosis factor (TNF) treatment. Of those, 48 patients (87.3%) still continued on infliximab. The mean infusion interval increased slightly from 6 to 7.1 +/- 1.5 weeks, while 45.8% patients had increased the intervals up to a maximum of 12 weeks. The mean infliximab dose remained stable over time, with a minimum of 3.1 mg/kg and a maximum of 6.4 mg/kg. In patients receiving <5 mg/kg infliximab, the mean infusion interval increased to 7.0 +/- 1.2 weeks. In total, the mean cumulative dose per patient and per year decreased from 3566.30 to 2973.60 mg.
Conclusions: We could observe that over a follow-up of 8 years of treatment with infliximab, >85% patients still remained on the same treatment, without any major safety events. Furthermore, both the infusion intervals and also the mean infliximab dose were modestly reduced in >= 70% of the patients without the loss of clinical efficiency
Searching for WR stars in I Zw 18 -- The origin of HeII emission
I Zw 18 is the most metal poor star-forming galaxy known and is an ideal
laboratory to probe stellar evolution theory at low metallicities. Using
archival HST WFPC2 imaging and FOS spectroscopy we were able to improve
previous studies. We constructed a continuum free HeII map, which was used to
identify Wolf-Rayet (WR) stars recently found by ground-based spectroscopy and
to locate diffuse nebular emission. Most of the HeII emission is associated
with the NW stellar cluster, clearly displaced from the surrounding shell-like
[OIII] and Halpha emission. We found evidence for HeII sources, compatible with
5--9 WNL stars and/or compact nebular HeII emission, as well as residual
diffuse emission. Only one of them is outside the NW cluster. We have
calculated evolutionary tracks for massive stars and synthesis models at the
appropriate metallicity (Z ~ 0.02 Zsun). These single star models predict a
mass limit M_WR ~ 90 Msun for WR stars to become WN and WC/WO. For an
instantaneous burst model with a Salpeter IMF extending up to M_up ~ 120-150
Msun our model predictions are in reasonable agreement with the observed
equivalent widths. Our model is also able to fully reproduce the observed
equivalent widths of nebular HeII emission due to the presence of WC/WO stars.
This quantitative agreement and the spatial correlation of nebular HeII with
the stellar cluster and the position of WR stars shown from the ground-based
spectra further supports the hypothesis that WR stars are responsible for
nebular HeII emission in extra-galactic HII regions. (Abridged abstract)Comment: Accepted by ApJ. LaTeX using aas2pp4, psfigs macros. 23 pages
including 6 figures. Paper and figures also separately available at
http://www.obs-mip.fr/omp/astro/people/schaerer
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