262 research outputs found
CP,T and/or CPT Violations in the K0-K0bar System --Implications of the KTeV,NA48 and CPLEAR Results
Possible violation of CP, T and/or CPT symmetries in the \ko-\kob system
is studied from a phenomenological point of view. For this purpose, we first
introduce parameters which represent violation of these symmetries in mixing
parameters and decay amplitudes in a convenient and well-defined way and,
treating these parameters as small, derive formulas which relate them to the
experimentally measured quantities. We then perform numerical analyses, with
the aid of the Bell-Steinberger relation, to derive constraints to these
symmetry-violating parameters, firstly paying particular attention to the
results reported by KTeV Collaboration and NA48 Collaboration, and then with
the results reported by CPLEAR Collaboration as well taken into account. A case
study, in which either CPT symmetry or T symmetry is assumed, is also carried
out. It is demonstrated that CP and T symmetries are violated definitively at
the level of 10^{-4} in decays and presumably at the level of 10^{-3} in
the \ko-\kob mixing, and that the Bell-Steinberger relation helps us to
establish CP and T violations being definitively present in the \ko-\kob
mixing and to test CPT symmetry to a level of 10^{-4} ~ 10^{-5}.Comment: 21 pages, 1 figure
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
Spatial water surface variations in open channel flows downstream of side disturbances
River hydrodynamicsInteraction with structure
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
Direct CP, T and/or CPT violations in the K^0-\bar{K^0} system - Implications of the recent KTeV results on decays -
The recent results on the CP violating parameters Re(e'/e) and \Delta\phi =
\phi_{00}-\phi_{+-} reported by the KTeV Collaboration are analyzed with a view
to constrain CP, T and CPT violations in a decay process. Combining with some
relevant data compiled by the Particle Data Group, we find Re(e_2-e_0) = (0.85
+- 3.11)*10^{-4} and Im(e_2-e_0) = (3.2 +- 0.7)*10^{-4}, where Re(e_I) and
Im(e_I) represent respectively CP/CPT and CP/T violations in decay of K^0 and
\bar{K^0} into a 2\pi state with isospin I.Comment: 7 pages, No figure
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
Spatially Resolved 3 micron Spectroscopy of Elias 1: Origin of Diamonds in Protoplanetary Disks
We present spatially resolved 3 um spectra of Elias 1 obtained with an
adaptive optics system. The central part of the disk is almost devoid of PAH
emission at 3.3 um; it shows up only at 30 AU and beyond. The PAH emission
extends up to 100 AU, at least to the outer boundary of our observation. The
diamond emission, in contrast, is more centrally concentrated, with the column
density peaked around 30 AU from the star. There are only three Herbig Ae/Be
stars known to date that show diamond emission at 3.53 um. Two of them have
low-mass companions likely responsible for the large X-ray flares observed
toward the Herbig Ae/Be stars. We speculate on the origin of diamonds in
circumstellar disks in terms of the graphitic material being transformed into
diamond under the irradiation of highly energetic particles.Comment: 7 pages, 4 figures, Accepted for publication in the Astrophysical
Journ
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