464 research outputs found
A Search for N2+ in Spectra of Comet C/2002C1 (Ikeya-Zhang)
We report low- and high-resolution spectra of comet C/2002 C1 (Ikeya-Zhang)
from McDonald Observatory. The comet had a well-developed ion tail including
CO+, CO2+, CH+, and H2O+. We used our high-resolution spectra to search for
N2+. None was detected and we placed upper limits on N2+/CO+ of 5.4 times
10^{-4}. N2+ was detected in the low-resolution spectra but we show that this
emission was probably telluric in origin (if cometary, we derive N2+/CO+ = 5.5
times 10^{-3}, still very low). We discuss the implications for the conditions
in the early solar nebula of the non-detection of N2+. These depend on whether
the H2O ice was deposited in the amorphous or crystalline form. If H2O was
deposited in its crystalline form, the detection of CO+ but not N2+ has
implications for H2O/H2 in the early solar nebula.Comment: Accepted for publication in ApJ (Letters) - 10 Sept 200
A new measurement of thermal conductivity of amorphous ice and its implications for the thermal evolution of comets
Very slowly deposited amorphous ice has a thermal conductivity about four orders of magnitude or more smaller than hitherto estimated. Using the exceedingly low value of the thermal conductivity of comets deduced from the properties of amorphous ice leads to the expectation that internal heating of comets is negligible below the outer several tens of centimeters
Additive Manufacturing for the Rapid Prototyping of Economical Biosensors
Current methods of developing wearable electronics through reductive manufacturing pose a substantial ecological footprint. To address this issue, it is imperative to investigate alternative additive manufacturing techniques. Aerosol jet printing (AJP) is a promising approach that relies on the optimization of gas flow rates and ink rheology to produce high-resolution printed structures. Implementing a low-intensity layered delamination approach to synthesize titanium carbide MXene, and further produce MXene ink, reduces environmental impact while enhancing the device performance. MXene ink yields desirable rheology, including viscosity, surface tension, density, and contact angles compatible with AJP technique. In terms of cost, ecological effect, time, and process development, traditional manufacturing exacerbates the level of e-waste produced. However, this additive manufacturing technique offers a unique solution for rapidly prototyping and manufacturing economical biosensors while minimizing resource consumption, reducing environmental impact, and addressing the growing issue of e-waste
Dynamics of orbital degrees of freedom probed via isotope Sb nuclear quadrupole moments in Sb-substituted iron-pnictide superconductors
Isotope Sb nuclei with large electric quadrupole moments are
applied to investigate the dynamics of orbital degrees of freedom in
Sb-substituted iron(Fe)-based compounds. In the parent compound
LaFe(AsSb)O, the nuclear spin relaxation rate
at Sb sites was enhanced at structural
transition temperature ( 135 K), which is higher than N\'eel
temperature (125 K). The isotope ratio
indicates that the electric quadrupole
relaxation due to the dynamical electric field gradient at Sb site increases
significantly toward . It is attributed to the critically enhanced
nematic fluctuations of stripe-type arrangement of Fe- (or )
orbitals. In the lightly electron-doped superconducting (SC) compound
LaFe(AsSb)(OF), the nematic fluctuations are
largely suppressed in comparison with the case of the parent compound, however,
it remains a small enhancement below 80 K down to the ( 20 K). The
results indicate that the fluctuations from both the spin and orbital degrees
of freedom on the (or ) orbitals can be seen in lightly
electron-doped SC state of LaFeAsO-based compounds. We emphasize that isotope
Sb quadrupole moments are sensitive local probe to identify the
dynamics of orbital degrees of freedom in Fe-pnictides, which provides with a
new opportunity to discuss the microscopic correlation between the
superconductivity and both nematic and spin fluctuations simultaneously even in
the polycrystalline samples.Comment: 7 pages, 4 figures and 1 supplemental fil
H-D Substitution in Interstellar Solid Methanol: A Key Route for D Enrichment
Deuterium enrichment of interstellar methanol is reproduced experimentally
for the first time via grain-surface H-D substitution in solid methanol at an
atomic D/H ratio of 0.1. Although previous gas-grain models successfully
reproduce the deuterium enrichments observed in interstellar methanol molecules
(D/H of up to 0.4, compared to the cosmic ratio of , the models
exclusively focus on deuterium fractionation resulting from the successive
addition of atomic hydrogen/deuterium on CO. The mechanism proposed here
represents a key route for deuterium enrichment that reproduces the high
observed abundances of deuterated methanol, including multiple deuterations.Comment: 4 pages, 4 figures, Accepted to the ApJ
A Hot Gap Around Jupiter's Orbit in the Solar Nebula
The Sun was an order of magnitude more luminous during the first few hundred
thousand years of its existence, due in part to the gravitational energy
released by material accreting from the Solar nebula. If Jupiter was already
near its present mass, the planet's tides opened an optically-thin gap in the
nebula. We show using Monte Carlo radiative transfer calculations that sunlight
absorbed by the nebula and re-radiated into the gap raised temperatures well
above the sublimation threshold for water ice, with potentially drastic
consequences for the icy bodies in Jupiter's feeding zone. Bodies up to a meter
in size were vaporized within a single orbit if the planet was near its present
location during this early epoch. Dust particles lost their ice mantles, and
planetesimals were partially to fully devolatilized, depending on their size.
Scenarios in which Jupiter formed promptly, such as those involving a
gravitational instability of the massive early nebula, must cope with the high
temperatures. Enriching Jupiter in the noble gases through delivery trapped in
clathrate hydrates will be more difficult, but might be achieved by either
forming the planet much further from the star, or capturing planetesimals at
later epochs. The hot gap resulting from an early origin for Jupiter also would
affect the surface compositions of any primordial Trojan asteroids.Comment: 25 pages, 10 figures. ApJ in press. Discussion of Jupiter's volatile
enrichment revised in sec. 4.
How Many Peas in a Pod? Legume Genes Responsible for Mutualistic Symbioses Underground
The nitrogen-fixing symbiosis between legume plants and Rhizobium bacteria is the most prominent plant–microbe endosymbiotic system and, together with mycorrhizal fungi, has critical importance in agriculture. The introduction of two model legume species, Lotus japonicus and Medicago truncatula, has enabled us to identify a number of host legume genes required for symbiosis. A total of 26 genes have so far been cloned from various symbiotic mutants of these model legumes, which are involved in recognition of rhizobial nodulation signals, early symbiotic signaling cascades, infection and nodulation processes, and regulation of nitrogen fixation. These accomplishments during the past decade provide important clues to understanding not only the molecular mechanisms underlying plant–microbe endosymbiotic associations but also the evolutionary aspects of nitrogen-fixing symbiosis between legume plants and Rhizobium bacteria. In this review we survey recent progress in molecular genetic studies using these model legumes
Large-Eddy / Reynolds-Averaged Navier-Stokes Simulations of a Dual-Mode Scramjet Combustor
Numerical simulations of reacting and non-reacting flows within a scramjet combustor configuration experimentally mapped at the University of Virginia s Scramjet Combustion Facility (operating with Configuration A ) are described in this paper. Reynolds-Averaged Navier-Stokes (RANS) and hybrid Large Eddy Simulation / Reynolds-Averaged Navier-Stokes (LES / RANS) methods are utilized, with the intent of comparing essentially blind predictions with results from non-intrusive flow-field measurement methods including coherent anti-Stokes Raman spectroscopy (CARS), hydroxyl radical planar laser-induced fluorescence (OH-PLIF), stereoscopic particle image velocimetry (SPIV), wavelength modulation spectroscopy (WMS), and focusing Schlieren. NC State's REACTMB solver was used both for RANS and LES / RANS, along with a 9-species, 19- reaction H2-air kinetics mechanism by Jachimowski. Inviscid fluxes were evaluated using Edwards LDFSS flux-splitting scheme, and the Menter BSL turbulence model was utilized in both full-domain RANS simulations and as the unsteady RANS portion of the LES / RANS closure. Simulations were executed and compared with experiment at two equivalence ratios, PHI = 0.17 and PHI = 0.34. Results show that the PHI = 0.17 flame is hotter near the injector while the PHI = 0.34 flame is displaced further downstream in the combustor, though it is still anchored to the injector. Reactant mixing was predicted to be much better at the lower equivalence ratio. The LES / RANS model appears to predict lower overall heat release compared to RANS (at least for PHI = 0.17), and its capability to capture the direct effects of larger turbulent eddies leads to much better predictions of reactant mixing and combustion in the flame stabilization region downstream of the fuel injector. Numerical results from the LES/RANS model also show very good agreement with OH-PLIF and SPIV measurements. An un-damped long-wave oscillation of the pre-combustion shock train, which caused convergence problems in some RANS simulations, was also captured in LES / RANS simulations, which were able to accommodate its effects accurately
Upregulation of casein kinase 1ε in dorsal root ganglia and spinal cord after mouse spinal nerve injury contributes to neuropathic pain
<p>Abstract</p> <p>Background</p> <p>Neuropathic pain is a complex chronic pain generated by damage to, or pathological changes in the somatosensory nervous system. Characteristic features of neuropathic pain are allodynia, hyperalgesia and spontaneous pain. Such abnormalities associated with neuropathic pain state remain to be a significant clinical problem. However, the neuronal mechanisms underlying the pathogenesis of neuropathic pain are complex and still poorly understood. Casein kinase 1 is a serine/threonine protein kinase and has been implicated in a wide range of signaling activities such as cell differentiation, proliferation, apoptosis, circadian rhythms and membrane transport. In mammals, the CK1 family consists of seven members (α, β, γ1, γ2, γ3, δ, and ε) with a highly conserved kinase domain and divergent amino- and carboxy-termini.</p> <p>Results</p> <p>Preliminary cDNA microarray analysis revealed that the expression of the <it>casein kinase 1 epsilon </it>(<it>CK1ε</it>) mRNA in the spinal cord of the neuropathic pain-resistant N- type Ca<sup>2+ </sup>channel deficient (<it>Ca</it><sub><it>v</it></sub><it>2.2</it><sup>-/-</sup>) mice was decreased by the spinal nerve injury. The same injury exerted no effects on the expression of <it>CK1ε </it>mRNA in the wild-type mice. Western blot analysis of the spinal cord identified the downregulation of CK1ε protein in the injured <it>Ca</it><sub><it>v</it></sub><it>2.2</it><sup>-/- </sup>mice, which is consistent with the data of microarray analysis. However, the expression of CK1ε protein was found to be up-regulated in the spinal cord of injured wild-type mice. Immunocytochemical analysis revealed that the spinal nerve injury changed the expression profiles of CK1ε protein in the dorsal root ganglion (DRG) and the spinal cord neurons. Both the percentage of CK1ε-positive neurons and the expression level of CK1ε protein were increased in DRG and the spinal cord of the neuropathic mice. These changes were reversed in the spinal cord of the injured <it>Ca</it><sub><it>v</it></sub><it>2.2</it><sup>-/- </sup>mice. Furthermore, intrathecal administration of a CK1 inhibitor IC261 produced marked anti-allodynic and anti-hyperalgesic effects on the neuropathic mice. In addition, primary afferent fiber-evoked spinal excitatory responses in the neuropathic mice were reduced by IC261.</p> <p>Conclusions</p> <p>These results suggest that CK1ε plays important physiological roles in neuropathic pain signaling. Therefore CK1ε is a useful target for analgesic drug development.</p
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