662 research outputs found
The Influence of Galactic Cosmic Rays on Ion-Neutral Hydrocarbon Chemistry in the Upper Atmospheres of Free-Floating Exoplanets
Cosmic rays may be linked to the formation of volatiles necessary for
prebiotic chemistry. We explore the effect of cosmic rays in a
hydrogen-dominated atmosphere, as a proof-of-concept that ion-neutral chemistry
may be important for modelling hydrogen-dominated atmospheres. In order to
accomplish this, we utilize Monte Carlo cosmic ray transport models with
particle energies of eV eV in order to investigate the
cosmic ray enhancement of free electrons in substellar atmospheres. Ion-neutral
chemistry is then applied to a Drift-Phoenix model of a free-floating giant gas
planet. Our results suggest that the activation of ion-neutral chemistry in the
upper atmosphere significantly enhances formation rates for various species,
and we find that CH, CH, NH, CH and possibly
CH are enhanced in the upper atmospheres because of cosmic rays. Our
results suggest a potential connection between cosmic ray chemistry and the
hazes observed in the upper atmospheres of various extrasolar planets.
Chemi-ionization reactions are briefly discussed, as they may enhance the
degree of ionization in the cloud layer.Comment: 22 pages, 4 figures. Accepted to the International Journal of
Astrobiolog
Search for Narrow NNpi Resonances in Exclusive p p -> p p pi+ pi- Measurements
Narrow structures in the range of a few MeV have been searched for in p p pi+
and p p pi- invariant mass spectra obtained from exclusive measurements of the
p p -> p p pi+ pi- reaction at Tp = 725, 750 and 775 MeV using the PROMICE/WASA
detector at CELSIUS. The selected reaction is particularily well suited for the
search for NN and / or N Delta decoupled dibaryon resonances. Except for a
possible fluctuation at 2087 MeV/c^2 in Mpppi- no narrow structures could be
identified neither in Mpppi+ nor in Mpppi- on the 3 sigma level of statistical
significance, giving an upper limit (95% C.L.) for dibaryon production in this
reaction of sigma < 20 nb for 2020 MeV/c^2 < m(dibaryon) < 2085 MeV/c^2Comment: 3 pages, 4 figure
Induction of Lambing at Weekly Intervals
Lambing season is the time in the sheep production year which demands the largest input of labor. Due to problems associated with the birth process, it is also one of the most critical times. By controlling the time of parturition, producers are better able to schedule labor and facilities more effectively. Ewes induced to lamb on specified days allow for more uniform groups of lambs for management practices. Flumethasone, a glucocorticoid, will induce parturition in ewes when administered late in gestation. The objective of this study was to determine the optimum range of days for once per week treatment for practical application of a grouped lambing program
``Superfast'' Reaction in Turbulent Flow with Potential Disorder
We explore the regime of ``superfast'' reactivity that has been predicted to
occur in turbulent flow in the presence of potential disorder. Computer
simulation studies confirm qualitative features of the previous renormalization
group predictions, which were based on a static model of turbulence. New
renormalization group calculations for a more realistic, dynamic model of
turbulence show that the superfast regime persists. This regime, with
concentration decay exponents greater than that for a well-mixed reaction,
appears to be a general result of the interplay among non-linear reaction
kinetics, turbulent transport, and local trapping by potential disorder.Comment: 14 pages. 4 figures. Uses IOP styles. To appear in J. Phys. A: Math.
Ge
Search for Low Mass Exotic mesonic structures. Part I: experimental results
Recently, several papers discussed on the existence of a low mass new
structure at a mass close to M=214.3 MeV. It was suggested that the
disintegration: pP, P
proceeds through an intermediate particle P having such mass. The present
work intends to look at other new or available data, in order to observe the
eventual existence of small narrow peaks or shoulders in very low mesonic
masses. Indeed narrow structures were already extracted from various data in
dibaryons, baryons and mesons (at larger masses that those studied here).Comment: 7 pages 11 figure
Resonant behaviour in double charge exchange reaction of \pi^+ mesons on the nuclear photoemulsion
The invariant mass spectra of the and systems produced in the
double charge exchange (DCX) of positively charged pions on photoemulsion are
analysed. A pronounced peak is observed in the invariant mass
spectrum, while the spectrum exhibits a strong Migdal-Watson effect of
the proton-proton final state interaction. These findings are in favor of the
-decoupled pseudoscalar resonance with T=0 called .Comment: 13 pages, 5 figures, revised versio
Possible Dibaryons with Strangeness s=-5
In the framework of , the binding energy of the six quark system with
strangeness s=-5 is systematically investigated under the SU(3) chiral
constituent quark model. The single channel calculation with
spins S=0 and 3 and the coupled and channel
calculation with spins S=1 and 2 are considered, respectively. The results show
following observations: In the spin=0 case, is a bound dibaryon
with the binding energy being . In the S=1 case,
is also a bound dibaryon. Its binding energy is ranged from to . In the S=2 and S=3 cases, no evidence of bound dibaryons
are found. The phase shifts and scattering lengths in the S=0 and S=1 cases are
also given.Comment: 10 pages, late
The d' dibaryon in the quark-delocalization, color-screening model
We study the questions of the existence and mass of the proposed dibaryon in the quark-delocalization, color-screening model
(QDCSM). The transformation between physical and symmetry bases has been
extended to the cases beyond the SU(2) orbital symmetry. Using parameters fixed
by baryon properties and scattering, we find a mild attraction in the
channel, but it is not strong enough to form a deeply bound state
as proposed for the state. Nor does the (isospin) I=2 N
configuration have a deeply bound state. These results show that if a narrow
dibaryon state does exist, it must have a more complicated structure.Comment: 12 pp. latex, no figs., 2 tables, additional refs., Report-no was
adde
Possible dibaryons in the quark cluster model
In the framework of RGM, the binding energy of one channel
() and are studied in the
chiral SU(3) quark cluster model. It is shown that the binding energies of the
systems are a few tens of MeV. The behavior of the chiral field is also
investigated by comparing the results with those in the SU(2) and the extended
SU(2) chiral quark models. It is found that the symmetry property of the
system makes the contribution of the relative kinetic energy
operator between two clusters attractive. This is very beneficial for forming
the bound dibaryon. Meanwhile the chiral-quark field coupling also plays a very
important role on binding. The S-wave phase shifts and the corresponding
scattering lengths of the systems are also given.Comment: LeTex with 2 ps figure
Search for the Hypothetical pi -> mu x Decay
The KARMEN collaboration has reported the possible observation of a hitherto
unknown neutral and weakly interacting particle x, which is produced in the
decay pi -> mu + x with a mass m(x) = 33.9 MeV. We have searched for this
hypothetical decay branch by studying muons from pion decay in flight with the
LEPS spectrometer at the piE3 channel at PSI and find branching ratios BR(pi-
to mu- anti-x) < 4e-7 and BR(pi+ to mu+ x) < 7e-8 (95\% C.L.). Together with
the limit BR > 2e-8 derived in a recent theoretical paper our result would
leave only a narrow region for the existence of x if it is a heavy neutrino.Comment: 10 pages, TeX (uses epsf), 3 Postscript figures uu-encode
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