21,056 research outputs found
Linear response separation of a solid into atomic constituents: Li, Al, and their evolution under pressure
We present the first realization of the generalized pseudoatom concept
introduced by Ball, and adopt the name enatom to minimize confusion. This
enatom, which consists of a unique decomposition of the total charge density
(or potential) of any solid into a sum of overlapping atomiclike contributions
that move rigidly with the nuclei to first order, is calculated using
(numerical) linear response methods, and is analyzed for both fcc Li and Al at
pressures of 0, 35, and 50 GPa. These two simple fcc metals (Li is fcc and a
good superconductor in the 20-40 GPa range) show different physical behaviors
under pressure, which reflects the increasing covalency in Li and the lack of
it in Al. The nonrigid (deformation) parts of the enatom charge and potential
have opposite signs in Li and Al; they become larger under pressure only in Li.
These results establish a method of construction of the enatom, whose potential
can be used to obtain a real-space understanding of the vibrational properties
and electron-phonon interaction in solids.Comment: 13 pages, 9 figures, 1 table, V2: fixed problem with Fig. 7, V3:
minor correction
Interplay of individual interactions and turbidity affects the functional response of three-spined sticklebacks \u3ci\u3eGasterosteus aculeatus\u3c/i\u3e
The effects of turbidity, size and the presence of conspecifics on the functional response, feeding latency and activity in the three-spined stickleback Gasterosteus aculeatus were examined. A significant interaction between standard length and presence of conspecifics demonstrated an increase in attack rates of larger individuals in the presence of conspecifics. Attack rate was also higher in turbid water. Feeding latency decreased with prey concentration and presence of conspecifics, but was not affected by turbidity. Activity level did not change with prey levels, but increased with turbidity. These results can help to better understand how individual flexibility in the functional response can affect prey mortality according to environmental perturbation and social interaction at the level of the predator
Interplay of individual interactions and turbidity affects the functional response of three-spined sticklebacks \u3ci\u3eGasterosteus aculeatus\u3c/i\u3e
The effects of turbidity, size and the presence of conspecifics on the functional response, feeding latency and activity in the three-spined stickleback Gasterosteus aculeatus were examined. A significant interaction between standard length and presence of conspecifics demonstrated an increase in attack rates of larger individuals in the presence of conspecifics. Attack rate was also higher in turbid water. Feeding latency decreased with prey concentration and presence of conspecifics, but was not affected by turbidity. Activity level did not change with prey levels, but increased with turbidity. These results can help to better understand how individual flexibility in the functional response can affect prey mortality according to environmental perturbation and social interaction at the level of the predator
Regression of binary network data with exchangeable latent errors
Undirected, binary network data consist of indicators of symmetric relations
between pairs of actors. Regression models of such data allow for the
estimation of effects of exogenous covariates on the network and for prediction
of unobserved data. Ideally, estimators of the regression parameters should
account for the inherent dependencies among relations in the network that
involve the same actor. To account for such dependencies, researchers have
developed a host of latent variable network models, however, estimation of many
latent variable network models is computationally onerous and which model is
best to base inference upon may not be clear. We propose the Probit
Exchangeable (PX) Model for undirected binary network data that is based on an
assumption of exchangeability, which is common to many of the latent variable
network models in the literature. The PX model can represent the second moments
of any exchangeable network model, yet specifies no particular parametric
model. We present an algorithm for obtaining the maximum likelihood estimator
of the PX model, as well as a modified version of the algorithm that is
extremely computationally efficient and provides an approximate estimator.
Using simulation studies, we demonstrate the improvement in estimation of
regression coefficients of the proposed model over existing latent variable
network models. In an analysis of purchases of politically-aligned books, we
demonstrate political polarization in purchase behavior and show that the
proposed estimator significantly reduces runtime relative to estimators of
latent variable network models while maintaining predictive performance
Intrasexual aggression reduces mating success in field crickets
This work was supported by the UK Natural Environment Research Council (NE/L011255/1 and NE/T000619/1).Aggressive behaviour is thought to have significant consequences for fitness, sexual selection and the evolution of social interactions, but studies measuring its expression across successive encounters?both intra- and intersexual?are limited. We used the field cricket Teleogryllus oceanicus to evaluate factors affecting repeatability of male aggression and its association with mating success. We quantified focal male aggression expressed towards partners and received from partners in three successive, paired trials, each involving a different male partner. We then measured a proxy of focal male fitness in mating trials with females. The likelihood and extent of aggressive behaviour varied across trials, but repeatability was negligible, and we found no evidence that patterns of focal aggression resulted from interacting partner identity or prior experience. Males who consistently experienced aggression in previous trials showed decreased male mating ?efficiency??determined by the number of females a male encountered before successfully mating, but the effect was weak and we found no other evidence that intrasexual aggression was associated with later mating success. During mating trials, however, we observed unexpected male aggression towards females, and this was associated with markedly decreased male mating efficiency and success. Our findings suggest that nonadaptive aggressive spillover in intersexual mating contexts could be an important but underappreciated factor influencing the evolution of intrasexual aggression.Publisher PDFPeer reviewe
Calf health and performance during receiving is not changed by fence-line preconditioning on flint hills range vs. drylot preconditioning
Ranch-of-origin preconditioning can improve the welfare and performance of beef
calves by decreasing the stress associated with weaning, transport, diet change, and
commingling with other calves. Preconditioning methods that involve pasture weaning
coupled with maternal contact (i.e., fence-line weaning) have been promoted as possible
best management practices for minimizing stress. Prior studies focused on performance
and behavior during preconditioning on the ranch of origin. Little information has
been published relating to carryover effects of fence-line preconditioning compared
with conventional drylot preconditioning on performance and behavior during feedlot
receiving.
Our objectives were to measure growth and health during a 28-day ranch-of-origin
preconditioning phase and during a 60-day feedlot receiving phase among beef calves
subjected to 1 of 3 ranch-of-origin preconditioning programs: (1) drylot preconditioning
+ dam separation, (2) pasture preconditioning + fence-line contact with dams, and
(3) pasture preconditioning + fence-line contact with dams + supplemental feed delivered
in a bunk. In addition, we recorded incidences of behavioral distress among these
treatments during first 7 days of feedlot receiving
Spin pumping damping and magnetic proximity effect in Pd and Pt spin-sink layers
We investigated the spin pumping damping contributed by paramagnetic layers
(Pd, Pt) in both direct and indirect contact with ferromagnetic
NiFe films. We find a nearly linear dependence of the
interface-related Gilbert damping enhancement on the heavy-metal
spin-sink layer thicknesses t in direct-contact
NiFe/(Pd, Pt) junctions, whereas an exponential dependence is
observed when NiFe and (Pd, Pt) are separated by \unit[3]{nm} Cu.
We attribute the quasi-linear thickness dependence to the presence of induced
moments in Pt, Pd near the interface with NiFe, quantified using
X-ray magnetic circular dichroism (XMCD) measurements. Our results show that
the scattering of pure spin current is configuration-dependent in these systems
and cannot be described by a single characteristic length
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