29,642 research outputs found
Characterisation of biodiversity in improved rubber agroforests in West-Kalimantan, Indonesia. Real and Potential uses for spontaneous plants
Since the introduction of rubber at the turn of the 20th century smallholders have developed an original complex agroforestry system called jungle rubber in which non selected young rubber trees (seedlings) are managed extensively alongside secondary forest re-growth. The issue of improving smallholder rubber productivity at affordable capital investments and levels of inputs while maintaining the environmental benefits of jungle rubber has been addressed by the Smallholder Rubber Agroforestry Project (SRAP: a joint project run by ICRAF, GAPKINDO and CIRAD). In 1995-1996, 27 trials (with a total of 100 plots) were set up in three provinces in Indonesia to assess the possibility of associating clonal rubber with agroforestry practices under smallholder conditions (Penot, 1997). Two RAS types were selected for this study: RAS n° 1 and n° 3. RAS n° 1 is basically improved jungle rubber using clonal planting material (see a description of RAS types in annexe 1). The rubber trees are in competition with spontaneous vegetation in the inter-row but results show that there are no negative consequences for rubber growth during the immature period. RAS n° 3 was designed for areas infested by Imperata cylindrica, with the establishment of shrubby leguminous cover crops and fast-growing tree species in the inter-rows with the aim of shading out weeds. The other type, RAS n° 2, is based on intercropping clonal rubber with various annual and perennial crops, including fruit and timber trees (Penot et al, 1994). In all cases, RAS have a planting density of 550 clonal rubber trees/ha and a variable number of associated fruit, timber or fast growing shade trees (from 92 to 256/ha). In addition to the RAS experimental plots, “RAS sendiri” (or “endogenous RAS”) are rubber agroforests improved by farmers without outside assistance. The district of Sanggau in the province of West Kalimantan was identified by SRAP as representative of traditional jungle-rubber-based local farming systems that have developed over the last 90 years. The district of Sanggau is located in the central area of the Kapuas river basin, between 1° N and 0°6' S and 09°8' W and 11°33' E. The district covers 18 302 km2, i.e. 13 % of the province. The trial plots described in this study are located in the villages of Embaong, Engkayu, Kopar, and Trimulia (the last being in the transmigration area). Most soils in the province of West-Kalimantan are acrisoils associated with ferralitic soils. Such soils have relatively good physical characteristics but poor chemical value and become acid. Rubber is widely grown in this area as it can grow in poor soils. The landscape is dominated by logged-over forest, secondary forest and a mosaic of jungle rubber and fallow with secondary forest re-growth. Large scale logging activities took place from 1950s to the 1980s at the expense of primary forest. At present, forested areas are located in hilly or remote areas and are very limited in extent. Oil palm and Acacia mangium plantations developed exponentially in the 1990s increasing the conversion of degraded forest areas into Estates that cultivate perennial crops. The main objective of this study is to assess existing plant biodiversity in RAS systems compared to that of jungle rubber. The second objective is to review the current uses of certain plants and their market potential.
Magnetic frustration in the spinel compounds Ge Co_2 O_4 and Ge Ni_2 O_4
In both spinel compounds GeCoO and GeNiO which order
antiferromagnetically (at and , ) with different Curie Weiss temperatures (=80.5 K and -15 K),
the usual magnetic frustration criterion is not fulfilled.
Using neutron powder diffraction and magnetization measurements up to 55 T,
both compounds are found with a close magnetic ground state at low temperature
and a similar magnetic behavior (but with a different energy scale), even
though spin anisotropy and first neighbor exchange interactions are quite
different. This magnetic behavior can be understood when considering the main
four magnetic exchange interactions. Frustration mechanisms are then
enlightened.Comment: submitted to Phys.Rev.B (2006
Uncertainties in gas kinematics arising from stellar continuum modelling in integral field spectroscopy data: the case of NGC2906 observed with MUSE/VLT
We study how the use of several stellar subtraction methods and line fitting
approaches can affect the derivation of the main kinematic parameters (velocity
and velocity dispersion fields) of the ionized gas component. The target of
this work is the nearby galaxy NGC 2906, observed with the MUSE instrument at
Very Large Telescope. A sample of twelve spectra is selected from the inner
(nucleus) and outer (spiral arms) regions, characterized by different
ionization mechanisms. We compare three different methods to subtract the
stellar continuum (FIT3D, STARLIGHT and pPXF), combined with one of the
following stellar libraries: MILES, STELIB and GRANADA+MILES. The choice of the
stellar subtraction method is the most important ingredient affecting the
derivation of the gas kinematics, followed by the choice of the stellar library
and by the line fitting approach. In our data, typical uncertainties in the
observed wavelength and width of the H\alpha and [NII] lines are of the order
of _rms \sim 0.1\AA\ and _rms \sim 0.2\AA\ (\sim 5
and 10km/s, respectively). The results obtained from the [NII] line seem to be
slightly more robust, as it is less affected by stellar absorption than
H\alpha. All methods considered yield statistically consistent measurements
once a mean systemic contribution
\Delta\bar\lambda=\Delta\bar\sigma=0.2xDelta_{MUSE} is added in quadrature to
the line fitting errors, where \Delta_{MUSE} = 1.1\AA\ \sim 50 km/s denotes the
instrumental resolution of the MUSE spectra. Although the subtraction of the
stellar continuum is critical in order to recover line fluxes, any method
(including none) can be used in order to measure the gas kinematics, as long as
an additional component of 0.2 x Delta_MUSE is added to the error budget.Comment: 20 pages, 14 figure
H^+ -> W^+ l_i^- l_j^+$ decay in the two Higgs doublet model
We study the lepton flavor violating H^+ -> W^+ l_i^- l_j^+ and the lepton
flavor conserving $H^+ -> W^+ l_i^- l_i^+ (l_i=\tau, l_j=\mu) decays in the
general 2HDM, so called model III. We estimate the decay width \Gamma for LFV
(LFC) at the order of the magnitude of (10^{-11}-10^{-5}) GeV
((10^{-9}-10^{-4}) GeV), for 200 GeV\leq m_{H^\pm}\leq 400
GeV, and the intermediate values of the coupling
\bar{\xi}^{E}_{N,\tau \mu}\sim 5 GeV (\bar{\xi}^{E}_{N,\tau
\tau}\sim 30 GeV). We observe that the experimental result of the process
under consideration can give comprehensive information about the physics beyond
the standard model and the existing free parameters.Comment: 8 pages, 7 Figure
Morphological Classification of Local Luminous Infrared Galaxies
We present an analysis of the morphological classification of 89 luminous
infrared galaxies (LIRGs) from the Great Observatories All-sky LIRG Survey
(GOALS) sample using non-parametric coefficients and compare their morphology
as a function of wavelength. We rely on images obtained in the optical (B- and
I-band) as well as in the infrared (H-band and 5.8m). Our classification
is based on the calculation of and the second order of light ()
non-parametric coefficients which we explore as a function of stellar mass
(), infrared luminosity () and star formation rate (SFR). We
investigate the relation between , the specific SFR (sSFR) and the dust
temperature () in our galaxy sample. We find that is a
better morphological tracer than , as it allows to distinguish systems
formed by double systems from isolated and post-merger LIRGs. The
multi-wavelength analysis allows us to identify a region in the -
parameter space where ongoing mergers reside, regardless of the band used to
calculate the coefficients. In particular when measured in the H-band, this
region can be used to identify ongoing mergers, with a minimal contamination
from LIRGs in other stages. We also find that while the sSFR is positively
correlated with when measured in the mid-infrared, i.e. star-bursting
galaxies show more compact emission, it is anti-correlated with the B-band
based . We interpret this as the spatial decoupling between obscured
and un-obscured star formation, whereby the ultraviolet/optical size of a LIRGs
experience an intense dust enshrouded central starburst is larger than in the
one in the mid-infrared since the contrast between the nuclear to the extended
disk emission is smaller in the mid-infrared. This has important implications
for high redshift surveys of dusty sources. [abridged]Comment: ( 18 pages, 12 figures, Accepted for publication in A&A
On the Proof of Dark Matter, the Law of Gravity and the Mass of Neutrinos
We develop a new method to predict the density associated with weak lensing
maps of (un)relaxed clusters in a range of theories interpolating between GR
and MOND (General Relativity and Modified Newtonian Dynamics). We apply it to
fit the lensing map of the bullet merging cluster 1E0657-56, in order to
constrain more robustly the nature and amount of collisionless matter in
clusters {\it beyond} the usual assumption of spherical equilibrium
(Pointecouteau & Silk 2005) and the validity of GR on cluster scales (Clowe et
al. 2006). Strengthening the proposal of previous authors we show that the
bullet cluster is dominated by a collisionless -- most probably non-baryonic --
component in GR as well as in MOND, a result consistent with the dynamics of
many X-ray clusters. Our findings add to the number of known pathologies for a
purely baryonic MOND, including its inability to fit the latest data from the
Wilkinson Microwave Anisotropy Probe. A plausible resolution of all these
issues and standard issues of Cold Dark Matter with galaxy rotation curves is
the "marriage" of MOND with ordinary hot neutrinos of 2eV. This prediction is
just within the GR-independent maximum of neutrino mass from current
-decay experiments, and is falsifiable by the Karlsruhe Tritium Neutrino
(KATRIN) experiment by 2009. Issues of consistency with strong lensing arcs and
the large relative velocity of the two clusters comprising the bullet cluster
are also addressed.Comment: 4 pages, 1 figure, accepted for publication in ApJL. Added a simple
model of the bullet cluster's high velocity in TeVeS, and discussions of
sterile neutrinos and of non-uniqueness of the lensing deprojectio
Solving the two-center nuclear shell-model problem with arbitrarily-orientated deformed potentials
A general new technique to solve the two-center problem with
arbitrarily-orientated deformed realistic potentials is demonstrated, which is
based on the powerful potential separable expansion method. As an example,
molecular single-particle spectra for C + C Mg are
calculated using deformed Woods-Saxon potentials. These clearly show that
non-axial symmetric configurations play a crucial role in molecular resonances
observed in reaction processes for this system at low energy
Ptychographic X-ray computed tomography of extended colloidal networks in food emulsions
As a main structural level in colloidal food materials, extended colloidal
networks are important for texture and rheology. By obtaining the 3D
microstructure of the network, macroscopic mechanical properties of the
material can be inferred. However, this approach is hampered by the lack of
suitable non-destructive 3D imaging techniques with submicron resolution.
We present results of quantitative ptychographic X-ray computed tomography
applied to a palm kernel oil based oil-in-water emulsion. The measurements were
carried out at ambient pressure and temperature. The 3D structure of the
extended colloidal network of fat globules was obtained with a resolution of
around 300 nm. Through image analysis of the network structure, the fat globule
size distribution was computed and compared to previous findings. In further
support, the reconstructed electron density values were within 4% of reference
values.Comment: 19 pages, 4 figures, to be published in Food Structur
The Globular Cluster Systems of Five Nearby Spiral Galaxies: New Insights from Hubble Space Telescope Imaging
We use available multifilter Hubble Space Telescope (HST) WFPC2 imaging of
five (M81, M83, NGC 6946, M101, and M51) low inclination, nearby spiral
galaxies to study ancient star cluster populations. M81 globular clusters (GC)
have an intrinsic color distribution which is very similar to those in the
Milky Way and M31, with ~40% of the clusters having colors expected for a
metal-rich population. On the other hand, the GC system in M51 appears almost
exclusively blue and metal poor. This lack of metal-rich GCs associated with
the M51 bulge indicates that the bulge formation history of this Sbc galaxy may
have differed significantly from that of our own. Ancient clusters in M101, and
possibly in NGC 6946, appear to have luminosity distributions which continue to
rise to our detection limit (M_V ~ -6.0), well beyond the expected turnover
(M_V ~ -7.4) in the luminosity function. This is reminiscent of the situation
in M33, a Local Group galaxy of similar Hubble type. The faint ancient cluster
candidates in M101 and NGC 6946 have colors and radii similar to their more
luminous counterparts, and we suggest that these are either intermediate age
(3-9 Gyr) disk clusters or the low mass end of the original GC population. If
the faint, excess GC candidates are excluded, we find that the specific
frequency (S_N) of ancient clusters formed in later-type spirals is roughly
constant, with S_N=0.5 +- 0.2. By combining the results of this study with
literature values for other systems, we find that the total GC specific
frequencies in spirals appear to correlate best with Hubble type and
bulge/total ratio, rather than with galaxy luminosity or galaxy mass
(abridged).Comment: 31 pages, 11 tables, 10 figure
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