684,985 research outputs found
Fragmentation Functions approach in pQCD fragmentation phenomena
Next-to-leading order parton fragmentation functions into light mesons are
presented. They have been extracted from real and simulated data and
used to predict inclusive single particle distributions at different machines.Comment: proceeding of the XXXI Rencontres de Morion
Chameleon Fragmentation
A scalar field dark energy candidate could couple to ordinary matter and
photons, enabling its detection in laboratory experiments. Here we study the
quantum properties of the chameleon field, one such dark energy candidate, in
an "afterglow" experiment designed to produce, trap, and detect chameleon
particles. In particular, we investigate the possible fragmentation of a beam
of chameleon particles into multiple particle states due to the highly
non-linear interaction terms in the chameleon Lagrangian. Fragmentation could
weaken the constraints of an afterglow experiment by reducing the energy of the
regenerated photons, but this energy reduction also provides a unique signature
which could be detected by a properly-designed experiment. We show that
constraints from the CHASE experiment are essentially unaffected by
fragmentation for and potentials, but are weakened for
steeper potentials, and we discuss possible future afterglow experiments.Comment: 27 pages, 7 figure
The minimum mass for star formation, and the origin of binary brown dwarfs
Our first aim is to calculate the minimum mass for Primary Fragmentation in a
variety of potential star-formation scenarios, i.e. (i) hierarchical
fragmentation of a 3-D medium; (ii) one-shot, 2-D fragmentation of a
shock-compressed layer; (iii) fragmentation of a circumstellar disc. Our second
aim is to evaluate the role of H2 dissociation in facilitating Secondary
Fragmentation and thereby producing close, low-mass binaries. Results: (i)For
contemporary, local star formation, the minimum mass for Primary Fragmentation
is in the range 0.001-0.004Msun, irrespective of the scenario considered.
(ii)Circumstellar discs are only able to radiate fast enough to undergo Primary
Fragmentation in their cool outer parts (R>100AU). Therefore brown dwarfs (BDs)
should have difficulty forming by Primary Fragmentation at R<30AU, explaining
the Brown Dwarf Desert.Conversely, Primary Fragmentation at R>100AU could be
the source of brown dwarfs in wide orbits, and could explain why massive discs
with Rd>100AU are rarely seen.(iii)H2 dissociation can lead to collapse and
Secondary Fragmentation, thereby converting primary fragments into close,
low-mass binaries, with semi-major axes a~5AU(Msystem/0.1Msun), in good
agreement with observation; in this case, the minimum mass for Primary
Fragmentation becomes a minimum system mass, rather than a minimum stellar
mass.(iv)Any primary fragment can undergo Secondary Fragmentation, producing a
close low-mass binary, provided only that the fragment is spinning. Secondary
Fragmentation is therefore most likely in fragments formed in the outer parts
of discs, and this could explain why a BD in a wide orbit about a Sun-like star
has a greater likelihood of having a BD companion than a BD in the field -as
seems to be observed.Comment: 15 pages, A&A accepte
On the Application of Gluon to Heavy Quarkonium Fragmentation Functions
We analyze the uncertainties induced by different definitions of the momentum
fraction in the application of gluon to heavy quarkonium fragmentation
function. We numerically calculate the initial fragmentation
functions by using the non-covariant definitions of with finite gluon
momentum and find that these fragmentation functions have strong dependence on
the gluon momentum . As , these fragmentation
functions approach to the fragmentation function in the light-cone definition.
Our numerical results show that large uncertainties remains while the
non-covariant definitions of are employed in the application of the
fragmentation functions. We present for the first time the polarized gluon to
fragmentation functions, which are fitted by the scheme exploited in
this work.Comment: 11 pages, 7 figures;added reference for sec.
Fragmentation of compositions and intervals
The fragmentation processes of exchangeable partitions have already been
studied by several authors. In this paper, we examine rather fragmentation of
exchangeable compositions, that means partitions of where the
order of the blocks counts. We will prove that such a fragmentation is
bijectively associated to an interval fragmentation. Using this correspondence,
we then calculate the Hausdorff dimension of certain random closed set that
arise in interval fragmentations and we study Ruelle's interval fragmentation
QCD evolution of naive-time-reversal-odd fragmentation functions
We study QCD evolution equations of the first transverse-momentum-moment of
the naive-time-reversal-odd fragmentation functions - the Collins function and
the polarizing fragmentation function. We find for the Collins function case
that the evolution kernel has a diagonal piece same as that for the
transversity fragmentation function, while for the polarizing fragmentation
function case this piece is the same as that for the unpolarized fragmentation
function. Our results might have important implications in the current global
analysis of spin asymmetries.Comment: 8 pages,4 figure
Quantification of habitat fragmentation reveals extinction risk in terrestrial mammals
Although habitat fragmentation is often assumed to be a primary driver of extinction, global patterns of fragmentation and its relationship to extinction risk have not been consistently quantified for any major animal taxon. We developed high-resolution habitat fragmentation models and used phylogenetic comparative methods to quantify the effects of habitat fragmentation on the world's terrestrial mammals, including 4,018 species across 26 taxonomic Orders. Results demonstrate that species with more fragmentation are at greater risk of extinction, even after accounting for the effects of key macroecological predictors, such as body size and geographic range size. Species with higher fragmentation had smaller ranges and a lower proportion of high-suitability habitat within their range, andmost high-suitability habitat occurred outside of protected areas, further elevating extinction risk. Our models provide a quantitative evaluation of extinction risk assessments for species, allow for identification of emerging threats in species not classified as threatened, and provide maps of global hotspots of fragmentation for the world's terrestrial mammals. Quantification of habitat fragmentation will help guide threat assessment and strategic priorities for global mammal conservation
Weak solutions to the continuous coagulation equation with multiple fragmentation
The existence of weak solutions to the continuous coagulation equation with
multiple fragmentation is shown for a class of unbounded coagulation and
fragmentation kernels, the fragmentation kernel having possibly a singularity
at the origin. This result extends previous ones where either boundedness of
the coagulation kernel or no singularity at the origin for the fragmentation
kernel were assumed
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