310 research outputs found
An infrared measurement of chemical desorption from interstellar ice analogues
In molecular clouds at temperatures as low as 10 K, all species except
hydrogen and helium should be locked in the heterogeneous ice on dust grain
surfaces. Nevertheless, astronomical observations have detected over 150
different species in the gas phase in these clouds. The mechanism by which
molecules are released from the dust surface below thermal desorption
temperatures to be detectable in the gas phase is crucial for understanding the
chemical evolution in such cold clouds. Chemical desorption, caused by the
excess energy of an exothermic reaction, was first proposed as a key molecular
release mechanism almost 50 years ago. Chemical desorption can, in principle,
take place at any temperature, even below the thermal desorption temperature.
Therefore, astrochemical net- work models commonly include this process.
Although there have been a few previous experimental efforts, no infrared
measurement of the surface (which has a strong advantage to quantify chemical
desorption) has been performed. Here, we report the first infrared in situ
measurement of chemical desorption during the reactions H + H2S -> HS + H2
(reaction 1) and HS + H -> H2S (reaction 2), which are key to interstellar
sulphur chemistry. The present study clearly demonstrates that chemical
desorption is a more efficient process for releasing H2S into the gas phase
than was previously believed. The obtained effective cross-section for chemical
desorption indicates that the chemical desorption rate exceeds the
photodesorption rate in typical interstellar environments
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
Spatial water surface variations in open channel flows downstream of side disturbances
River hydrodynamicsInteraction with structure
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
Comparison of allometric equations to estimate the above-ground biomass of Populus alba species (Case study; poplar plantations in Chaharmahal and Bakhtiari province, Iran)
Carbon sequestration into plants biomass, especially in fast growing trees is an easier and economically way for
dropping off Co2 from atmosphere. This study was carried out in order to investigate above-ground biomass of
white poplar (Populous alba, L.) plantations that was planted in four different plant spacing (0.5 × 0.5, 1 × 1, 2 × 2
and 4 × 4 m) in Chaharmahal and Bakhtiari province in west of Iran. Selecting the trees was according to diameter
classes. After inventory, 10 trees were selected from each density at one hectare area. The tree’s characteristics
including diameter at breast height (DBH), total height, and crown diameter measured. Then measured trees felled
down in order to measure the wet and dry weight of different organs including (whole tree, trunk, main branches,
twigs and leaf).The regression analysis was applied to find out a relationship between mass production and poplar
characteristics and to develop different allometry models between different organs and their carbon sequestration
ability. The results showed that the independent DBH factor in P. alba, demonstrated high correlation against all
the dependent variables. Height of trees also creates the allometric equations with average accuracy (0.30 - 0.81)
against all the dependent variables. The crown diameter in dependent variable almost creates weakest equations.
The result also indicated that there is no significant difference among equations of different planting spaces
Formation of hydrogen peroxide and water from the reaction of cold hydrogen atoms with solid oxygen at 10K
The reactions of cold H atoms with solid O2 molecules were investigated at 10
K. The formation of H2O2 and H2O has been confirmed by in-situ infrared
spectroscopy. We found that the reaction proceeds very efficiently and obtained
the effective reaction rates. This is the first clear experimental evidence of
the formation of water molecules under conditions mimicking those found in cold
interstellar molecular clouds. Based on the experimental results, we discuss
the reaction mechanism and astrophysical implications.Comment: 12 pages, 3 Postscript figures, use package amsmath, amssymb,
graphic
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
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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