1,887 research outputs found
Using N-mixture models to estimate abundance and temporal trends of black rhinoceros (Diceros bicornis L.) populations from aerial counts
Inaccurate estimates of animal populations may lead to flawed management interventions, therefore, it is essential to understand the status and population trend of a species in order to plan its management efficiently. Aerial surveys are considered a useful method for estimating the population size of large conspicuous animals inhabiting large areas, but raw count data from aerial surveys usually underestimate population sizes due to imperfect detection. The use of N-mixture models with aerial count data provides a useful tool to estimate the population sizes while taking detection probability into account. As a study case we used aerial surveys conducted for monitoring black rhinoceros (Diceros bicornis) in Madikwe Game Reserve and Pilanesberg Nature Reserve (South Africa) during 1999–2015, and we analysed data with a dynamic extension of the N-mixture model. We estimated 0.078–0.098 and 0.139–0.142 individuals/km2, respectively, and we found evidence for density dependence in both reserves with a carrying capacity of 0.122 (0.102–0.142) individuals/100 km2. Based on simulations used to assess precision of the estimates, root-mean-square error model (RMSE) estimates was significantly smaller than those for the raw maximum counts. The N-mixture models provide a promising approach to estimate population size, trends and demographic characteristics of large conspicuous mammals such as black rhinoceroses. Such analysis can provide estimates that are more accurate than raw counts. In addition, use of model covariates that affect a species' population parameters can provide useful information for their conservation and management.Jose Jimenez is funded by Plan TIFIES (Spanish Action Plan against illegal trafficking and international poaching of wild species). Ministerio para la Transición Ecológica. Government of Spain.Peer reviewe
Generalized local interactions in 1D: solutions of quantum many-body systems describing distinguishable particles
As is well-known, there exists a four parameter family of local interactions
in 1D. We interpret these parameters as coupling constants of delta-type
interactions which include different kinds of momentum dependent terms, and we
determine all cases leading to many-body systems of distinguishable particles
which are exactly solvable by the coordinate Bethe Ansatz. We find two such
families of systems, one with two independent coupling constants deforming the
well-known delta interaction model to non-identical particles, and the other
with a particular one-parameter combination of the delta- and (so-called)
delta-prime interaction. We also find that the model of non-identical particles
gives rise to a somewhat unusual solution of the Yang-Baxter relations. For the
other model we write down explicit formulas for all eigenfunctions.Comment: 23 pages v2: references adde
Field-induced magnetic transitions in the quasi-two-dimensional heavy-fermion antiferromagnets Ce_{n}RhIn_{3n+2} (n=1 or 2)
We have measured the field-dependent heat capacity in the tetragonal
antiferromagnets CeRhIn and CeRhIn, both of which have an
enhanced value of the electronic specific heat coefficient
mJ/mol-Ce K above . For the specific heat data at zero
applied magnetic field are consistent with the existence of an anisotropic
spin-density wave opening a gap in the Fermi surface for CeRhIn while
CeRhIn shows behavior consistent with a simple antiferromagnetic
magnon. From these results, the magnetic structure, in a manner similar to the
crystal structure, appears more two-dimensional in CeRhIn than in
CeRhIn where only about 12% of the Fermi surface remains ungapped
relative to 92% for CeRhIn. When both compounds behave in a
manner expected for heavy fermion systems as both and the electronic
heat capacity decrease as field is applied. When the field is applied in the
tetragonal basal plane (), CeRhIn and CeRhIn have very
similar phase diagrams which contain both first- and second-order field-induced
magnetic transitions .Comment: 15 pages, 4 figure
Localized f electrons in CexLa1-xRhIn5: dHvA Measurements
Measurements of the de Haas-van Alphen effect in CexLa1-xRhIn5 reveal that
the Ce 4f electrons remain localized for all x, with the mass enhancement and
progressive loss of one spin from the de Haas-van Alphen signal resulting from
spin fluctuation effects. This behavior may be typical of antiferromagnetic
heavy fermion compounds, inspite of the fact that the 4f electron localization
in CeRhIn5 is driven, in part, by a spin-density wave instability.Comment: 4 pages, 4 figures, submitted to PR
Rotational Cooling of Polar Molecules by Stark-tuned Cavity Resonance
A general scheme for rotational cooling of diatomic heteronuclear molecules
is proposed. It uses a superconducting microwave cavity to enhance the
spontaneous decay via Purcell effect. Rotational cooling can be induced by
sequentially tuning each rotational transition to cavity resonance, starting
from the highest transition level to the lowest using an electric field.
Electrostatic multipoles can be used to provide large confinement volume with
essentially homogeneous background electric field.Comment: 10 pages, 6 figure
Heat capacity studies of Ce and Rh site substitution in the heavy fermion antiferromagnet CeRhIn_5;: Short-range magnetic interactions and non-Fermi-liquid behavior
In heavy fermion materials superconductivity tends to appear when long range
magnetic order is suppressed by chemical doping or applying pressure. Here we
report heat capacity measurements on diluted alloyes of the heavy fermion
superconductor CeRhIn_5;. Heat capacity measurements have been performed on
CeRh_{1-y}Ir_{y}In_5; (y <= 0.10) and Ce_{1-x}La_{x}Rh_{1-y}Ir_{y}In_5; (x <=
0.50) in applied fields up to 90 kOe to study the affect of doping and magnetic
field on the magnetic ground state. The magnetic phase diagram of
CeRh_{0.9}Ir_{0.1}In_5; is consistent with the magnetic structure of CeRhIn_5;
being unchanged by Ir doping. Doping of Ir in small concentrations is shown to
slightly increase the antiferromagnetic transition temperature T_{N} (T_{N}=3.8
K in the undoped sample). La doping which causes disorder on the Ce sublattice
is shown to lower T_{N} with no long range order observed above 0.34 K for
Ce_{0.50}La_{0.50}RhIn_5;. Measurements on Ce_{0.50}La_{0.50}RhIn_5; show a
coexistence of short range magnetic order and non-Fermi-liquid behavior. This
dual nature of the Ce 4f-electrons is very similar to the observed results on
CeRhIn_5; when long range magnetic order is suppressed at high pressure.Comment: 8 pages, 9 figure
Unusual giant magnetostriction in the ferrimagnet GdCaMnO
We report an unusual giant linear magnetostrictive effect in the ferrimagnet
GdCaMnO (80 K). Remarkably, the
magnetostriction, negative at high temperature (), becomes
positive below 15 K when the magnetization of the Gd sublattice overcomes the
magnetization of the Mn sublattice. A rather simple model where the magnetic
energy competes against the elastic energy gives a good account of the observed
results and confirms that Gd plays a crucial role in this unusual observation.
Unlike previous works in manganites where only striction associated with 3
Mn orbitals is considered, our results show that the lanthanide 4 orbitals
related striction can be very important too and it cannot be disregarded.Comment: 6 pages, 3 figure
Field dependent effective masses in YbAl
We show for the intermediate valence compound YbAl that the high field
(40 60T) effective masses measured by the de Haas-van
Alphen experiment for field along the direction are smaller by
approximately a factor of two than the low field masses. The field
40T for this reduction is much smaller than the Kondo field ( 670K) but is comparable to the field
where 40K is the temperature for the onset
of Fermi liquid coherence. This suggests that the field scale does not
arise from 4 polarization but is connected with the removal of the anomalies
that are known to occur in the Fermi liquid state of this compound.Comment: 7 pages plus 3 figures Submitted to PRL 9/12/0
Chickadees faced with unpredictable food increase fat reserves but certain components of their immune function decline
In winter, temperate resident birds are often faced with periodic low natural food availability. This reduction or unpredictability in resource availability might then have a negative impact on immune function, given that immune system support is highly resource dependent. We investigated the balance between energetic and immune management in captive black-capped chickadees (Poecile atricapilus) by manipulating the predictability of resources. The control group received food ad lib. every day, while the experimental group received a reduced amount of food on random days and food ad lib. on all other days. We measured two key metrics of energetic management (body and fat mass) as well as a suite of immune system components. Compared with control birds, experimental birds maintained significantly higher total body and fat mass, had lower acute phase protein concentrations, and had decreased body temperature and lost more body mass during the fever response following injection with lipopolysaccharides. Interestingly, birds in both groups had similar levels of complement lysis, delayed-type hypersensitivity response (phytohemagglutinin), and primary antibody production (keyhole limpet hemocyanin). This experiment demonstrates that black-capped chickadees strategically increase their fat mass in response to decreased food availability and that this might allow the birds to maintain most of the immune system unaltered, except some of the most costly immune components
Absence of Hybridization Gap in Heavy Electron Systems and Analysis of YbAl3 in terms of Nearly Free Electron Conduction Band
In the analysis of the heavy electron systems, theoretical models with c-f
hybridization gap are often used. We point out that such a gap does not exist
and the simple picture with the hybridization gap is misleading in the metallic
systems, and present a correct picture by explicitly constructing an effective
band model of YbAl_3. Hamiltonian consists of a nearly free electron model for
conduction bands which hybridize with localized f-electrons, and includes only
a few parameters. Density of states, Sommerfeld coefficient, f-electron number
and optical conductivity are calculated and compared with the band calculations
and the experiments.Comment: 9 pages, 9 figures, submitted to J. Phys. Soc. Jp
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