467 research outputs found
Search for Dust Emission from (24) Themis Using the Gemini-North Telescope
We report the results of a search for a dust trail aligned with the orbit
plane of the large main-belt asteroid (24) Themis, which has been reported to
have water ice frost on its surface. Observations were obtained with the GMOS
instrument on the Gemini-North Observatory in imaging mode, where we used a
chip gap to block much of the light from the asteroid, allowing us to take long
exposures while avoiding saturation by the object. No dust trail is detected
within 2' of Themis to a 3-sigma limiting surface brightness magnitude of 29.7
mag/arcsec^2, as measured along the expected direction of the dust trail.
Detailed consideration of dust ejection physics indicates that particles large
enough to form a detectable dust trail were unlikely to be ejected as a result
of sublimation from an object as large as Themis. We nonetheless demonstrate
that our observations would have been capable of detecting faint dust emission
as close as 20" from the object, even in a crowded star field. This approach
could be used to conduct future searches for sublimation-generated dust
emission from Themis or other large asteroids closer to perihelion than was
done in this work. It would also be useful for deep imaging of collisionally
generated dust emission from large asteroids at times when the visibility of
dust features are expected to be maximized, such as during orbit plane
crossings, during close approaches to the Earth, or following detected impact
events.Comment: 11 pages, 4 figures, accepted for publication in PAS
Vertical axis wind turbine
Includes bibliographical references.The objective of this project was to design and simulate a turbine capable of effectively harnessing wind energy into a viable and practical source of consumer electric energy. This was done by the optimization of three different portions of the design. First, restraint of the column that transferred the physical energy to the generator was optimized. This took into consideration the weight of the turbine portion of the structure, the torque seen due to the rotation of the blades, and the bending caused by the wind and other transverse loads upon the column. Second, the propeller design was optimized. This was done by designing and testing blades that had a low coefficient of drag on one side and a very high coefficient on the opposite side. Finally, the generator was optimized for the maximal electric output due to our expected revolutions per minute of the transfer column. The optimizations of the column portion of the project were done by an initial analysis of the structure by methods of strength of materials. Once broad dimensions were decided, they were further narrowed down by the help of analytical computer software, in this case, the Mechanica add-on for Pro/Engineer. The expected RPMs of the blade portion were determined by methods of fluid mechanics and also by simulation in Fluent, a fluid flow simulation software package. The generator was then optimized in the ELE lab for maximum electrical output from the resulting RPMs we expected the generator to see. What this project resulted in was a fully functional design of a vertical axis wind turbine that is capable of producing a significant amount of electrical energy.B.S. (Bachelor of Science
Development of a Cross-border Business-to-Business-to-Consumer (B2B2C) System to Enhance Enterprise Performance: A Case Study of Legend Harvest Group
This research focused on the efforts of Legend Harvest Group (LHG), a California startup, to realise its cross-border business-to-business-to-consumer (B2B2C) e-commerce business opportunities. The issues identified during the research demonstrated that an operational B2B2C system is more complicated than a manually operated business-to-business (B2B) trade. The complexities of cross-border e-commerce platforms include insufficient data transparency, logistical obstacles, and Customs hurdles. LHG encountered difficulties in understanding and dealing with these obstacles. My research focused on analysing the technological, operational and organisational requirements and finding the critical elements and leverage points of adopting a new B2B2C system. I developed a platform–system–technology–human (PSTH) conceptual framework based on my literature review that served as the theoretical blueprint of this action research. I adopted a participatory action research (PAR) method and a purposeful sampling strategy to conduct an action research study. The sampling population comprised LHG’s executives, as well as board members, officers, employees, and consultants associated with the company. I applied a qualitative approach as the most suitable choice in action research study, using interviews, semi-structured discussions, and observations to collect data. This research was based on three action cycles. Each action cycle consisted of four phases: reflect, plan, act and observe. The first action cycle (AC1) focused on scanning the environment to identify the barriers preventing LHG from adopting a B2B2C system. The second action cycle (AC2) addressed the technological, operational and organisational requirements, and collaborated with a Software-as-a-Service (SaaS) provider to implement a trial run and collect actual data. The third action cycle (AC3) involved an in-depth thematic analysis to evaluate the trial-run results and proposed an integrators network for LHG’s future B2B2C system development. Research accomplishments include initial identification of sixty-one emergent codes as barriers to LHG’s supply chain automation quest, categorisation of these codes into fifteen actionable themes, and, finally, selection of five actionable themes as critical elements to follow in adopting a B2B2C system, namely, process automation (A), SaaS adoption (S), supply chain integration (I), collaboration (C) and trust (T). From post-trial-run analysis, I recognised these five themes as the key integrators and proposed a B2B2C supply chain model to cope with the cross-border e-commerce platforms. The interdependent nature of these five integrators led to the conceptualisation of an “ASICT” network that can be used to tackle the platforms’ demands. Based on the research findings, I learned that a sustainable B2B2C system will depend not only on technology implementation such as SaaS adoption, supply chain integration and process automation, but also on human interaction such as collaboration and trust. This research concluded that these five “ASICT” integrators are critical elements, and that trust and collaboration are the key leverage points in the company’s efforts to develop a cross-border B2B2C system. The benefits projected by adopting the B2B2C system included not only reducing LHG’s transactional costs but also enhancing its enterprise performance by automating and integrating the supply chain, allowing the management to map operational efficiency with financial outcome and to transform the e-commerce supply chain into a value chain
Observational and Dynamical Characterization of Main-Belt Comet P/2010 R2 (La Sagra)
We present observations of comet-like main-belt object P/2010 R2 (La Sagra)
obtained by Pan-STARRS 1 and the Faulkes Telescope-North on Haleakala in
Hawaii, the University of Hawaii 2.2 m, Gemini-North, and Keck I telescopes on
Mauna Kea, the Danish 1.54 m telescope at La Silla, and the Isaac Newton
Telescope on La Palma. An antisolar dust tail is observed from August 2010
through February 2011, while a dust trail aligned with the object's orbit plane
is also observed from December 2010 through August 2011. Assuming typical phase
darkening behavior, P/La Sagra is seen to increase in brightness by >1 mag
between August 2010 and December 2010, suggesting that dust production is
ongoing over this period. These results strongly suggest that the observed
activity is cometary in nature (i.e., driven by the sublimation of volatile
material), and that P/La Sagra is therefore the most recent main-belt comet to
be discovered. We find an approximate absolute magnitude for the nucleus of
H_R=17.9+/-0.2 mag, corresponding to a nucleus radius of ~0.7 km, assuming an
albedo of p=0.05. Using optical spectroscopy, we find no evidence of
sublimation products (i.e., gas emission), finding an upper limit CN production
rate of Q_CN<6x10^23 mol/s, from which we infer an H2O production rate of
Q_H2O<10^26 mol/s. Numerical simulations indicate that P/La Sagra is
dynamically stable for >100 Myr, suggesting that it is likely native to its
current location and that its composition is likely representative of other
objects in the same region of the main belt, though the relatively close
proximity of the 13:6 mean-motion resonance with Jupiter and the (3,-2,-1)
three-body mean-motion resonance with Jupiter and Saturn mean that dynamical
instability on larger timescales cannot be ruled out.Comment: 23 pages, 13 figures, accepted for publication in A
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α-Lactosylceramide Protects Against iNKT-Mediated Murine Airway Hyperreactivity and Liver Injury Through Competitive Inhibition of Cd1d Binding.
Invariant natural killer T (iNKT) cells, which are activated by T cell receptor (TCR)-dependent recognition of lipid-based antigens presented by the CD1d molecule, have been shown to participate in the pathogenesis of many diseases, including asthma and liver injury. Previous studies have shown the inhibition of iNKT cell activation using lipid antagonists can attenuate iNKT cell-induced disease pathogenesis. Hence, the development of iNKT cell-targeted glycolipids can facilitate the discovery of new therapeutics. In this study, we synthesized and evaluated α-lactosylceramide (α-LacCer), an α-galactosylceramide (α-GalCer) analog with lactose substitution for the galactose head and a shortened acyl chain in the ceramide tail, toward iNKT cell activation. We demonstrated that α-LacCer was a weak inducer for both mouse and human iNKT cell activation and cytokine production, and the iNKT induction by α-LacCer was CD1d-dependent. However, when co-administered with α-GalCer, α-LacCer inhibited α-GalCer-induced IL-4 and IFN-γ production from iNKT cells. Consequently, α-LacCer also ameliorated both α-GalCer and GSL-1-induced airway hyperreactivity and α-GalCer-induced neutrophilia when co-administered in vivo. Furthermore, we were able to inhibit the increases of ConA-induced AST, ALT and IFN-γ serum levels through α-LacCer pre-treatment, suggesting α-LacCer could protect against ConA-induced liver injury. Mechanistically, we discerned that α-LacCer suppressed α-GalCer-stimulated cytokine production through competing for CD1d binding. Since iNKT cells play a critical role in the development of AHR and liver injury, the inhibition of iNKT cell activation by α-LacCer present a possible new approach in treating iNKT cell-mediated diseases
The Transient Jupiter Trojan-Like Orbit of P/2019 LD2 (ATLAS)
Comet P/2019 LD2 has orbital elements currently resembling those of a Jupiter
Trojan, and therefore superficially appears to represent a unique opportunity
to study the volatile content and active behavior of a member of this
population for the first time. However, numerical integrations show that it was
previously a Centaur before reaching its current Jupiter Trojan-like orbit in
2018 July, and is expected to return to being a Centaur in 2028 February,
before eventually becoming a Jupiter-family comet in 2063 February. The case of
P/2019 LD2 highlights the need for mechanisms to quickly and reliably
dynamically classify small solar system bodies discovered in current and
upcoming wide-field surveys.Comment: 7 pages, 3 figures. Accepted for publication in Icaru
The proposed Caroline ESA M3 mission to a Main Belt Comet
We describe Caroline, a mission proposal submitted to the European Space Agency in 2010 in response to the Cosmic Visions M3 call for medium-sized missions. Caroline would have travelled to a Main Belt Comet (MBC), characterizing the object during a flyby, and capturing dust from its tenuous coma for return to Earth. MBCs are suspected to be transition objects straddling the traditional boundary between volatile–poor rocky asteroids and volatile–rich comets. The weak cometary activity exhibited by these objects indicates the presence of water ice, and may represent the primary type of object that delivered water to the early Earth. The Caroline mission would have employed aerogel as a medium for the capture of dust grains, as successfully used by the NASA Stardust mission to Comet 81P/Wild 2. We describe the proposed mission design, primary elements of the spacecraft, and provide an overview of the science instruments and their measurement goals. Caroline was ultimately not selected by the European Space Agency during the M3 call; we briefly reflect on the pros and cons of the mission as proposed, and how current and future mission MBC mission proposals such as Castalia could best be approached
SuperWASP Observations of the 2007 Outburst of Comet 17P/Holmes
We present wide-field imaging of the 2007 outburst of Comet 17P/Holmes
obtained serendipitously by SuperWASP-North on 17 nights over a 42-night period
beginning on the night (2007 October 22-23) immediately prior to the outburst.
Photometry of 17P's unresolved coma in SuperWASP data taken on the first night
of the outburst is consistent with exponential brightening, suggesting that the
rapid increase in the scattering cross-section of the coma could be largely due
to the progressive fragmentation of ejected material produced on a very short
timescale at the time of the initial outburst, with fragmentation timescales
decreasing from t(frag)~2x10^3 s to t(frag)~1x10^3 s over our observing period.
Analysis of the expansion of 17P's coma reveals a velocity gradient suggesting
that the outer coma was dominated by material ejected in an instantaneous,
explosive manner. We find an expansion velocity at the edge of the dust coma of
v(exp) = 0.55+/-0.02 km/s and a likely outburst date of t_0=2007 October
23.3+/-0.3, consistent with our finding that the comet remained below
SuperWASP's detection limit of m(V)~15 mag until at least 2007 October 23.3.
Modelling of 17P's gas coma indicates that its outer edge, which was observed
to extend past the outer dust coma, is best explained with a single pulse of
gas production, consistent with our conclusions concerning the production of
the outer dust coma.Comment: 36 pages, 8 figures, accepted for publication in MNRA
Observational Constraints on the Catastrophic Disruption Rate of Small Main Belt Asteroids
We have calculated 90% confidence limits on the steady-state rate of
catastrophic disruptions of main belt asteroids in terms of the absolute
magnitude at which one catastrophic disruption occurs per year (HCL) as a
function of the post-disruption increase in brightness (delta m) and subsequent
brightness decay rate (tau). The confidence limits were calculated using the
brightest unknown main belt asteroid (V = 18.5) detected with the Pan-STARRS1
(Pan-STARRS1) telescope. We measured the Pan-STARRS1's catastrophic disruption
detection efficiency over a 453-day interval using the Pan-STARRS moving object
processing system (MOPS) and a simple model for the catastrophic disruption
event's photometric behavior in a small aperture centered on the catastrophic
disruption event. Our simplistic catastrophic disruption model suggests that
delta m = 20 mag and 0.01 mag d-1 < tau < 0.1 mag d-1 which would imply that H0
= 28 -- strongly inconsistent with H0,B2005 = 23.26 +/- 0.02 predicted by
Bottke et al. (2005) using purely collisional models. We postulate that the
solution to the discrepancy is that > 99% of main belt catastrophic disruptions
in the size range to which this study was sensitive (100 m) are not
impact-generated, but are instead due to fainter rotational breakups, of which
the recent discoveries of disrupted asteroids P/2013 P5 and P/2013 R3 are
probable examples. We estimate that current and upcoming asteroid surveys may
discover up to 10 catastrophic disruptions/year brighter than V = 18.5.Comment: 61 Pages, 10 Figures, 3 Table
On-chip two-octave supercontinuum generation by enhancing self-steepening of optical pulses
Dramatic advances in supercontinuum generation have been made recently using
photonic crystal fibers, but it is quite challenging to obtain an
octave-spanning supercontinuum on a chip, partially because of strong
dispersion in high-index-contrast nonlinear integrated waveguides. We show by
simulation that extremely flat and low dispersion can be achieved in silicon
nitride slot waveguides over a wavelength band of 500 nm. Different from
previously reported supercontinua that were generated either by higher-order
soliton fission in anomalous dispersion regime or by self phase modulation in
normal dispersion regime, a two-octave supercontinuum from 630 to 2650 nm (360
THz in total) can be generated by greatly enhancing self-steepening in
nonlinear pulse propagation in almost zero dispersion regime, when an optical
shock as short as 3 fs is formed, which enables on-chip ultra-wide-band
applications
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