525 research outputs found
Supporting the planning of a community fisheries monitoring and evaluation database: a collaborative project undertaken by CFDO, FLD, STREAM, VSO and AYAD
Cambodia is one of the poorest countries in the world; much of its population live in rural areas and many live below the local poverty line. The management of common property aquatic resources is of over-riding importance to food security and sustainable rural development in Cambodia. Aquatic resources are utilized principally by subsistence fishers and the landless, for whom aquatic resource use is an important livelihood activity.
Subsistence fishers access mainly the rivers, lakes and inundated forests in Tonle Sap provinces, the lower Mekong and Bassac regions and the upper part of the Mekong.
Freshwater capture fisheries probably contribute more to national food security and the national economy in Cambodia than in any other country in the world. (PDF contains 52 pages
Glioblastoma with primitive neuronal component: A case report and considerations of fluorescence-guided surgery
Background: Glioblastoma with primitive neuronal components (GB/PNC) is an extremely rare type of glioblastoma characterized by presenting histological and cytogenetic features of both entities. The mixed nature of these tumors limits the imaging diagnosis and supposes a therapeutic dilemma.
Case Description: We present the case of a 77-year-old female with a GB/PNC who is treated with surgery and adjuvant radiochemotherapy according to the STUPP protocol, where an abnormal uptake of 5-aminolevulinic acid (5-ALA) is evident during surgery in probable relation to the mixed nature of GB/PNC.
Conclusion: GB/PNC is extremely rare tumors. Given its low prevalence, there are no studies that refer to the macroscopic characteristics of the tumor as well as evidence of the effectiveness of adjuvant treatment. Fluorescence-guided resection with 5-ALA is the surgical treatment of choice in surgery for high-grade gliomas; however, in GB/PNC, it may not be as useful since PNC may have less fluorescent marker uptake and be more dimly visualized when excited by light using the surgical microscope
Chaos and Rotating Black Holes with Halos
The occurrence of chaos for test particles moving around a slowly rotating
black hole with a dipolar halo is studied using Poincar\'e sections. We find a
novel effect, particles with angular momentum opposite to the black hole
rotation have larger chaotic regions in phase space than particles initially
moving in the same direction.Comment: 9 pages, 4 Postscript figures. Phys. Rev. D, in pres
The Villafranca catalog of Galactic OB groups: I. Systems with O2-O3.5 stars
CONTEXT. The GOSSS spectral classifications and Gaia data have significantly
improved our ability to measure distances and determine memberships of stellar
groups with OB stars. AIMS. We have started a program to identify, measure
distances, and determine the membership of Galactic stellar groups with OB
stars. We start with the identification and distance determinations of groups
with O stars. In this paper we concentrate on groups that contain stars with
the earliest spectral subtypes. METHODS. We use GOSSS to select Galactic
stellar groups with O2-O3.5 stars and a method that combines Gaia DR2
photometry, positions, proper motions, and parallaxes to assign robust
memberships and measure distances. We also include the two clusters in that
paper to generate our first list of 16 O-type Galactic stellar groups. RESULTS.
We derive distances, determine the membership, and analyze the structure of
sixteen Galactic stellar groups with O stars, Villafranca O-001 to O-016,
including the 14 groups with the earliest-O-type optically-accessible stars
known in the Milky Way. We compare our distance with previous results and
establish that the best consistency is with VLBI parallaxes and the worst is
with kinematic distances. Our results indicate that massive stars can form in
relatively low-mass clusters or even in near-isolation, as is the case for the
Bajamar star in the North America nebula. This lends support to the
hierarchical scenario of star formation, where some stars are born in
well-defined bound clusters but others are born in associations that are
unbound from the beginning: groups of newborn stars come in many shapes and
sizes. We propose that HD 64 568 and HD 64 315 AB could have been ejected
simultaneously from Villafranca O-012 S. Our results are consistent with a
difference of approx. 20 microas in the Gaia DR2 parallax zero point between
bright and faint stars. (ABRIDGED)Comment: Accepted for publication in A&
The tale of two centres
We study motion in the field of two fixed centres described by a family of
Einstein-dilaton-Maxwell theories. Transitions between regular and chaotic
motion are observed as the dilaton coupling is varied.Comment: 20 pages, RevTeX, 7 figures included, TeX format change
Scaling Relations for Collision-less Dark Matter Turbulence
Many scaling relations are observed for self-gravitating systems in the
universe. We explore the consistent understanding of them from a simple
principle based on the proposal that the collision-less dark matter fluid terns
into a turbulent state, i.e. dark turbulence, after crossing the caustic
surface in the non-linear stage. The dark turbulence will not eddy dominant
reflecting the collision-less property. After deriving Kolmogorov scaling laws
from Navier-Stokes equation by the method similar to the one for Smoluchowski
coagulation equation, we apply this to several observations such as the
scale-dependent velocity dispersion, mass-luminosity ratio, magnetic fields,
and mass-angular momentum relation, power spectrum of density fluctuations.
They all point the concordant value for the constant energy flow per mass: , which may be understood as the speed of the hierarchical
coalescence process in the cosmic structure formation.Comment: 26 pages, 6 figure
Chaos in Static Axisymmetric Spacetimes I : Vacuum Case
We study the motion of test particle in static axisymmetric vacuum spacetimes
and discuss two criteria for strong chaos to occur: (1) a local instability
measured by the Weyl curvature, and (2) a tangle of a homoclinic orbit, which
is closely related to an unstable periodic orbit in general relativity. We
analyze several static axisymmetric spacetimes and find that the first
criterion is a sufficient condition for chaos, at least qualitatively. Although
some test particles which do not satisfy the first criterion show chaotic
behavior in some spacetimes, these can be accounted for the second criterion.Comment: More comments for the quantitative estimation of chaos are added, and
some inappropriate terms are changed. This will appear on Class. Quant. Gra
Chaos in black holes surrounded by gravitational waves
The occurrence of chaos for test particles moving around Schwarzschild black
holes perturbed by a special class of gravitational waves is studied in the
context of the Melnikov method. The explicit integration of the equations of
motion for the homoclinic orbit is used to reduce the application of this
method to the study of simple graphics.Comment: 15 pages, LaTex
Stability analysis and quasinormal modes of Reissner Nordstr{\o}m Space-time via Lyapunov exponent
We explicitly derive the proper time principal Lyapunov exponent
() and coordinate time () principal Lyapunov exponent
() for Reissner Nordstr{\o}m (RN) black hole (BH) . We also
compute their ratio. For RN space-time, it is shown that the ratio is
for
time-like circular geodesics and for Schwarzschild BH it is
. We
further show that their ratio may vary from
orbit to orbit. For instance, Schwarzschild BH at innermost stable circular
orbit(ISCO), the ratio is
and at marginally
bound circular orbit (MBCO) the ratio is calculated to be
. Similarly, for extremal RN
BH the ratio at ISCO is
.
We also further analyse the geodesic stability via this exponent. By evaluating
the Lyapunov exponent, it is shown that in the eikonal limit , the real and
imaginary parts of the quasi-normal modes of RN BH is given by the frequency
and instability time scale of the unstable null circular geodesics.Comment: Accepted in Pramana, 07/09/201
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