254 research outputs found
Gaussian Process Modeling of In-Season Physiological Parameters of Spring Wheat Based on Airborne Imagery from Two Hyperspectral Cameras and Apparent Soil Electrical Conductivity
The remote sensing of the biophysical and biochemical parameters of crops facilitates the preparation of application maps for variable-rate nitrogen fertilization. According to comparative studies of machine learning algorithms, Gaussian process regression (GPR) can outperform more popular methods in the prediction of crop status from hyperspectral data. The present study evaluates GPR model accuracy in the context of spring wheat dry matter, nitrogen content, and nitrogen uptake estimation. Models with the squared exponential covariance function were trained on images from two hyperspectral cameras (a frenchFabry–Pérot interferometer camera and a push-broom scanner). The most accurate predictions were obtained for nitrogen uptake (R2=0.75–0.85, RPDP=2.0–2.6). Modifications of the basic workflow were then evaluated: the removal of soil pixels from the images prior to the training, data fusion with apparent soil electrical conductivity measurements, and replacing the Euclidean distance in the GPR covariance function with the spectral angle distance. Of these, the data fusion improved the performance while predicting nitrogen uptake and nitrogen content. The estimation accuracy of the latter parameter varied considerably across the two hyperspectral cameras. Satisfactory nitrogen content predictions (R2>0.8, RPDP>2.4) were obtained only in the data-fusion scenario, and only with a high spectral resolution push-broom device capable of capturing longer wavelengths, up to 1000 nm, while the full-frame camera spectral limit was 790 nm. The prediction performance and uncertainty metrics indicated the suitability of the models for precision agriculture applications. Moreover, the spatial patterns that emerged in the generated crop parameter maps accurately reflected the fertilization levels applied across the experimental area as well as the background variation of the abiotic growth conditions, further corroborating this conclusion.publishedVersio
Hearing sensitivity: An underlying mechanism for niche differentiation in gleaning bats
Tropical ecosystems are known for high species diversity. Adaptations permitting niche differentiation enable species to coexist. Historically, research focused primarily on morphological and behavioral adaptations for foraging, roosting, and other basic ecological factors. Another important factor, however, is differences in sensory capabilities. So far, studies mainly have focused on the output of behavioral strategies of predators and their prey preference. Understanding the coexistence of different foraging strategies, however, requires understanding underlying cognitive and neural mechanisms. In this study, we investigate hearing in bats and how it shapes bat species coexistence. We present the hearing thresholds and echolocation calls of 12 different gleaning bats from the ecologically diverse Phyllostomid family. We measured their auditory brainstem responses to assess their hearing sensitivity. The audiograms of these species had similar overall shapes but differed substantially for frequencies below 9 kHz and in the frequency range of their echolocation calls. Our results suggest that differences among bats in hearing abilities contribute to the diversity in foraging strategies of gleaning bats. We argue that differences in auditory sensitivity could be important mechanisms shaping diversity in sensory niches and coexistence of species
Heterogeneity shapes groups growth in social online communities
Many complex systems are characterized by broad distributions capturing, for
example, the size of firms, the population of cities or the degree distribution
of complex networks. Typically this feature is explained by means of a
preferential growth mechanism. Although heterogeneity is expected to play a
role in the evolution it is usually not considered in the modeling probably due
to a lack of empirical evidence on how it is distributed. We characterize the
intrinsic heterogeneity of groups in an online community and then show that
together with a simple linear growth and an inhomogeneous birth rate it
explains the broad distribution of group members.Comment: 5 pages, 3 figure panel
Reactivity of the Halogen in the Isomeric 4- and 4\u27-Chloroazoxybenzenes
The relative ease of displacement of a halogen in the benzene ring by anionic reagents is markedly influenced by the character of other substituents in the ring. A thorough survey of the literature on these aromatic nucleophilic substitution reactions has been given by Bunnett and Zahler (1). These authors discuss the influences exerted by various groups in the ortho, meta and para positions, the effects of different electron donor reagents and variations in experimental conditions. Since no data are available concerning the effect of the azoxy group, it was desirable to synthesize some chloro-substituted aromatic azoxy compounds and compare them with chloro-nitro-compounds and chloro-azo-compounds. The azo-grouping has only a slight activating effect (2) being reported by Badger, Cook and Vidal (3) to be about one-sixth as effective as a nitro group
Age-Related Differences in Moral Judgment: The Role of Probability Judgments
This is the final version. Available on open access from Wiley via the DOI in this recordData availability: The data and Supplementary Material are available on the Open Science Framework, see https://osf.io/8hac5/Research suggests that moral evaluations change during adulthood. Older adults (75+) tend to judge accidentally harmful acts more severely than younger adults do, and this age-related difference is in part due to the greater negligence older adults attribute to the accidental harmdoers. Across two studies (N = 254), we find support for this claim and report the novel discovery that older adults' increased attribution of negligence, in turn, is associated with a higher perceived likelihood that the accident would occur. We propose that, because older adults perceive accidents as more likely than younger adults do, they condemn the agents and their actions more and even infer that the agents' omission to exercise due care is intentional. These findings refine our understanding of the cognitive processes underpinning moral judgment in older adulthood and highlight the role of subjective probability judgments in negligence attribution
Anomalous low doping phase of the Hubbard model
We present results of a systematic Quantum-Monte-Carlo study for the
single-band Hubbard model. Thereby we evaluated single-particle spectra (PES &
IPES), two-particle spectra (spin & density correlation functions), and the
dynamical correlation function of suitably defined diagnostic operators, all as
a function of temperature and hole doping. The results allow to identify
different physical regimes. Near half-filling we find an anomalous `Hubbard-I
phase', where the band structure is, up to some minor modifications, consistent
with the Hubbard-I predictions. At lower temperatures, where the spin response
becomes sharp, additional dispersionless `bands' emerge due to the dressing of
electrons/holes with spin excitatons. We present a simple phenomenological fit
which reproduces the band structure of the insulator quantitatively. The Fermi
surface volume in the low doping phase, as derived from the single-particle
spectral function, is not consistent with the Luttinger theorem, but
qualitatively in agreement with the predictions of the Hubbard-I approximation.
The anomalous phase extends up to a hole concentration of 15%, i.e. the
underdoped region in the phase diagram of high-T_c superconductors. We also
investigate the nature of the magnetic ordering transition in the single
particle spectra. We show that the transition to an SDW-like band structure is
not accomplished by the formation of any resolvable `precursor bands', but
rather by a (spectroscopically invisible) band of spin 3/2 quasiparticles. We
discuss implications for the `remnant Fermi surface' in insulating cuprate
compounds and the shadow bands in the doped materials.Comment: RevTex-file, 20 PRB pages, 16 figures included partially as gif. A
full ps-version including ps-figures can be found at
http://theorie.physik.uni-wuerzburg.de/~eder/condmat.ps.gz Hardcopies of
figures (or the entire manuscript) can also be obtained by e-mail request to:
[email protected]
Superconductivity in the two dimensional Hubbard Model.
Quasiparticle bands of the two-dimensional Hubbard model are calculated using
the Roth two-pole approximation to the one particle Green's function. Excellent
agreement is obtained with recent Monte Carlo calculations, including an
anomalous volume of the Fermi surface near half-filling, which can possibly be
explained in terms of a breakdown of Fermi liquid theory. The calculated bands
are very flat around the (pi,0) points of the Brillouin zone in agreement with
photoemission measurements of cuprate superconductors. With doping there is a
shift in spectral weight from the upper band to the lower band. The Roth method
is extended to deal with superconductivity within a four-pole approximation
allowing electron-hole mixing. It is shown that triplet p-wave pairing never
occurs. Singlet d_{x^2-y^2}-wave pairing is strongly favoured and optimal
doping occurs when the van Hove singularity, corresponding to the flat band
part, lies at the Fermi level. Nearest neighbour antiferromagnetic correlations
play an important role in flattening the bands near the Fermi level and in
favouring superconductivity. However the mechanism for superconductivity is a
local one, in contrast to spin fluctuation exchange models. For reasonable
values of the hopping parameter the transition temperature T_c is in the range
10-100K. The optimum doping delta_c lies between 0.14 and 0.25, depending on
the ratio U/t. The gap equation has a BCS-like form and (2*Delta_{max})/(kT_c)
~ 4.Comment: REVTeX, 35 pages, including 19 PostScript figures numbered 1a to 11.
Uses epsf.sty (included). Everything in uuencoded gz-compressed .tar file,
(self-unpacking, see header). Submitted to Phys. Rev. B (24-2-95
Interpolating self-energy of the infinite-dimensional Hubbard model: Modifying the iterative perturbation theory
We develop an analytical expression for the self-energy of the
infinite-dimensional Hubbard model that is correct in a number of different
limits. The approach represents a generalization of the iterative perturbation
theory to arbitrary fillings. In the weak-coupling regime perturbation theory
to second order in the interaction U is recovered. The theory is exact in the
atomic limit. The high-energy behavior of the self-energy up to order (1/E)**2
and thereby the first four moments of the spectral density are reproduced
correctly. Referring to a standard strong-coupling moment method, we analyze
the limit of strong U. Different modifications of the approach are discussed
and tested by comparing with the results of an exact diagonalization study.Comment: LaTeX, 14 pages, 5 ps figures included, title changed, references
updated, minor change
Effects of place attachment on home return travel: a spatial perspective
Recent studies on place-mobility relationships suggest an increasing possibility that people can have multiple place attachments at varied spatial scales. Yet our understanding of how place attachment in different spatial scales affects mobility remains limited. This study investigates home return visits by Chinese diaspora tourists from North America who have made multiple trips to China. A total of 27 in-depth interviews with repeat home return travellers was conducted. Four different types of return movements were identified: local; dispersed; local & dispersed; and second-migration locale focused. A relationship was found between the participants’ sense of place, place identity and home return travel. The findings suggest that home return travel is more complex than previously thought. More focused sense of place and strong personal connection to ancestral homes may lead to more localized return, while a more generic sense of place (i.e. to ‘China’) and collective personal identity would result in a more dispersed travel pattern. Family migration history and strong attachment to family’s first migration destination also leads to focused return to the place. The study highlights the fact that place and place attachment are deeply personal and can evolve over time and space
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