1,485 research outputs found
Regeneración natural y patrones de distribución espacial de la palma chilena Jubaea chilensis (Molina) Baillon en los bosques mediterráneos de Chile central
Jubaea chilensis is an endemic tree of Central Chile (31º15’- 35º22’ S). The current main conservation threats for this species should be associated with different factors which limit its natural regeneration, in particular the intense seeds crop. The analysis of spatial distribution patterns can be an important tool to understand the forest dynamic and the individual interactions. In this study was studied the spatial pattern of species recruitment and identifying the proper conditions for its regeneration. We predicted a clear spatial clumped pattern between regeneration individuals for all distance range studied, and also a clumped distribution associated to adult individuals. Spatial modeling showed that natural regeneration of J. chilensis is significantly related to higher vegetation cover, and especially in those with higher solar radiation. The results suggest that clumped regeneration of J. chilensis could be explained by the associated environmental conditions promoting the establishment of new seedlings, its seed dispersal mechanism, predation avoid, herbivory, and seeds crop. We also found a nurse effect which facilitates the natural regeneration of this species.Jubaea chilensis es un árbol endémico de la zona central de Chile (31º15’- 35º22’ S). Las principales amenazas actuales a su conservación estarían asociadas a diferentes limitantes a su regeneración natural, en especial la intensa cosecha de sus semillas. El análisis de patrones espaciales de distribución puede ser una importante herramienta para entender la dinámica de los bosques y la interacción entre los individuos. En este trabajo se estudió el patrón espacial de reclutamiento de la especie y se identificaron las condiciones favorables para su regeneración. Se estimó una notoria agrupación espacial entre los individuos de regeneración para todos los rangos de distancia analizados, y a su vez una distribución dependiente de los individuos adultos, agrupándose mayormente cercano a ellos. Por otra parte, la modelación espacial reveló que la regeneración natural de J. chilensis se relaciona significativamente con sitios de mayor cobertura vegetacional, y especialmente en sitios con una mayor radiación solar. Los resultados sugieren que la regeneración agrupada de J. chilensis se debería a la asociación de condiciones ambientales propicias para el establecimiento de nuevos individuos, su mecanismo de dispersión de semillas y escape de la depredación, herbivoría y cosecha de sus semillas, lo que estaría determinando la estructura espacial de la población. A su vez, los resultados confirman un efecto nodriza, facilitador de la regeneración natural de la especie
A High Statistics Measurement of the Lambdac+ Lifetime
A high statistics measurement of the Lambdac+ lifetime from the Fermilab
fixed-target FOCUS photoproduction experiment is presented. We describe the
analysis technique with particular attention to the determination of the
systematic uncertainty. The measured value of 204.6 +/- 3.4 (stat.) +/- 2.5
(syst.) fs from 8034 +/- 122 Lambdac -> pKpi decays represents a significant
improvement over the present world average.Comment: Submitted to Physical Review Letter
New FOCUS results on charm mixing and CP violation
We present a summary of recent results on CP violation and mixing in the
charm quark sector based on a high statistics sample collected by
photoproduction experiment FOCUS (E831 at Fermilab). We have measured the
difference in lifetimes for the decays: and . This translates into a measurement of the mixing parameter in
the \d0d0 system, under the assumptions that is an equal mixture of
CP odd and CP even eigenstates, and CP violation is negligible in the neutral
charm meson system. We verified the latter assumption by searching for a CP
violating asymmetry in the Cabibbo suppressed decay modes , and . We show preliminary
results on a measurement of the branching ratio .Comment: 9 pages, 6 figures, requires espcrc2.sty. Presented by S.Bianco at
CPConf2000, September 2000, Ferrara (Italy). In this revision, fixed several
stylistic flaws, add two significant references, fixed a typo in Tab.
A Measurement of the Ds+ Lifetime
A high statistics measurement of the Ds+ lifetime from the Fermilab
fixed-target FOCUS photoproduction experiment is presented. We describe the
analysis of the two decay modes, Ds+ -> phi(1020)pi+ and Ds+ ->
\bar{K}*(892)0K+, used for the measurement. The measured lifetime is 507.4 +/-
5.5 (stat.) +/- 5.1 (syst.) fs using 8961 +/- 105 Ds+ -> phi(1020)pi+ and 4680
+/- 90 Ds+ -> \bar{K}*(892)0K+ decays. This is a significant improvement over
the present world average.Comment: 5 pages, 3 figures, 2 tables, submitted to PR
Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth
The unexpectedly high flux of cosmic ray positrons detected at Earth may
originate from nearby astrophysical sources, dark matter, or unknown processes
of cosmic-ray secondary production. We report the detection, using the
HighAltitude Water Cherenkov Observatory (HAWC), of extended tera-electron volt
gamma-ray emission coincident with the locations of two nearby middle-aged
pulsars (Geminga and PSR B0656+14). The HAWC observations demonstrate that
these pulsars are indeed local sources of accelerated leptons, but the measured
tera-electron volt emission profile constrains the diffusion of particles away
from these sources to be much slower than previously assumed. We demonstrate
that the leptons emitted by these objects are therefore unlikely to be the
origin of the excess positrons, which may have a more exotic origin.Comment: 16 pages (including supplementary material), 5 figure
Search for CP Violation in the decays D+ -> K_S pi+ and D+ -> K_S K+
A high statistics sample of photo-produced charm from the FOCUS(E831)
experiment at Fermilab has been used to search for direct CP violation in the
decays D+->K_S pi+ and D+ -> K_S K+. We have measured the following asymmetry
parameters relative to D+->K-pi+pi+: A_CP(K_S pi+) = (-1.6 +/- 1.5 +/- 0.9)%,
A_CP(K_S K+) = (+6.9 +/- 6.0 +/- 1.5)% and A_CP(K_S K+) = (+7.1 +/- 6.1 +/-
1.2)% relative to D+->K_S pi+. The first errors quoted are statistical and the
second are systematic. We also measure the relative branching ratios:
\Gamma(D+->\bar{K0}pi+)/\Gamma(D+->K-pi+pi+) = (30.60 +/- 0.46 +/- 0.32)%,
\Gamma(D+->\bar{K0}K+)/\Gamma(D+->K-pi+pi+) = (6.04 +/- 0.35 +/- 0.30)% and
\Gamma(D+->\bar{K0}K+)/\Gamma(D+->\bar{K0}pi+) = (19.96 +/- 1.19 +/- 0.96)%.Comment: 4 pages, 3 figure
A measurement of branching ratios of and hadronic decays to four-body final states containing a
We have studied hadronic four-body decays of and mesons with a
in the final state using data recorded during the 1996-1997 fixed-target
run at Fermilab high energy photoproduction experiment FOCUS. We report a new
branching ratio measurement of . We make the first observation
of three new decay modes with branching ratios ,
\Gamma(D^+\to\K_S K^+ K^-\pi^+)/\Gamma(D^+\to K_S
\pi^+\pi^+\pi^-)=0.0077\pm0.0015\pm0.0009, and , where
in each case the first error is statistical and the second error is systematic.Comment: 4 pages, 1 table, 2 figures, submitted to Physical Review Letter
Puerto Rican Karst - A Vital Resource
The limestone region of Puerto Rico covers about 27.5 percent of the island\u27s surface and is subdivided into the northern, southern, and dispersed limestone areas. All limestone areas have karst features. The karst belt is that part of the northern limestone with the most spectacular surficial karst landforms. It covers 142,544 ha or 65 percent of the northern limestone. The karst belt is the focus of this publication, although reference is made to all limestone regions. The northern limestone contains Puerto Rico\u27s most extensive freshwater aquifer, largest continuous expanse of mature forest, and largest coastal wetland, estuary, and underground cave systems. The karst belt is extremely diverse, and its multiple landforms, concentrated in such a small area, make it unique in the world. Puerto Rico\u27s karst forests whether dry, moist, or wet share common physiognomic and structural characteristics. Karst forests contain the largest reported number of tree species per unit area in Puerto Rico. Both fauna and flora are rich in taxa; and many rare, threatened, endangered, and migratory species find refuge in the karst belt. Almost all fossil records of Puerto Rico\u27s extinct flora and fauna come from the karst belt
A Non-parametric Approach to the D+ to K*0bar mu+ nu Form Factors
Using a large sample of D+ -> K- pi+ mu+ nu decays collected by the FOCUS
photoproduction experiment at Fermilab, we present the first measurements of
the helicity basis form factors free from the assumption of spectroscopic pole
dominance. We also present the first information on the form factor that
controls the s-wave interference discussed in a previous paper by the FOCUS
collaboration. We find reasonable agreement with the usual assumption of
spectroscopic pole dominance and measured form factor ratios.Comment: 14 pages, 5 figures, and 2 tables. We updated the previous version by
changing some words, removing one plot, and adding two tables. These changes
are mostly stylisti
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