11,371 research outputs found
Valence-bond theory of highly disordered quantum antiferromagnets
We present a large-N variational approach to describe the magnetism of
insulating doped semiconductors based on a disorder-generalization of the
resonating-valence-bond theory for quantum antiferromagnets. This method
captures all the qualitative and even quantitative predictions of the
strong-disorder renormalization group approach over the entire experimentally
relevant temperature range. Finally, by mapping the problem on a hard-sphere
fluid, we could provide an essentially exact analytic solution without any
adjustable parameters.Comment: 5 pages, 3 eps figure
Modeling Neutrino-Induced Scale-Dependent Galaxy Clustering for Photometric Galaxy Surveys
The increasing statistical precision of photometric redshift surveys requires
improved accuracy of theoretical predictions for large-scale structure
observables to obtain unbiased cosmological constraints. In CDM
cosmologies, massive neutrinos stream freely at small cosmological scales,
suppressing the small-scale power spectrum. In massive neutrino cosmologies,
galaxy bias modeling needs to accurately relate the scale-dependent growth of
the underlying matter field to observed galaxy clustering statistics. In this
work, we implement a computationally efficient approximation of the
neutrino-induced scale-dependent bias (NISDB). Through simulated likelihood
analyses of Dark Energy Survey Year 3 (DESY3) and Legacy Survey of Space and
Time Year 1 (LSSTY1) synthetic data that contain an appreciable NISDB, we
examine the impact of linear galaxy bias and neutrino mass modeling choices on
cosmological parameter inference. We find model misspecification of the NISDB
approximation and neutrino mass models to decrease the constraining power of
photometric galaxy surveys and cause parameter biases in the cosmological
interpretation of future surveys. We quantify these biases and devise
mitigation strategies.Comment: 23 pages, 5 figure
Dendroecology of Drimys brasiliensis Miers (Winteraceae) in two Atlantic cloud forests in Paraná State, Southern Brazil.
Ameridendro
Unveiling shocks in planetary nebulae
The propagation of a shock wave into a medium is expected to heat the
material beyond the shock, producing noticeable effects in intensity line
ratios such as [O III]/Halpha. To investigate the occurrence of shocks in
planetary nebulae (PNe), we have used all narrowband [O III] and Halpha images
of PNe available in the HST archive to build their [O III]/Halpha ratio maps
and to search for regions where this ratio is enhanced. Regions with enhanced
[O III]/Halpha emission ratio can be ascribed to two different types of
morphological structures: bow-shock structures produced by fast collimated
outflows and thin skins enveloping expanding nebular shells. Both collimated
outflows and expanding shells are therefore confirmed to generate shocks in
PNe. We also find regions with depressed values of the [O III]/Halpha ratio
which are found mostly around density bounded PNe, where the local contribution
of [N II] emission into the F656N Halpha filter cannot be neglected.Comment: 13 pages, 9 figures, 3 tables; To appear in Astronomy & Astrophysic
Localized charged states and phase separation near second order phase transition
Localized charged states and phase segregation are described in the framework
of the phenomenological Ginzburg-Landau theory of phase transitions. The
Coulomb interactions determines the charge distribution and the characteristic
length of the phase separated states. The phase separation with charge
segregation becomes possible because of the large dielectric constant and the
small density of extra charge in the range of charge localization. The phase
diagram is calculated and the energy gain of the phase separated state is
estimated. The role of the Coulomb interaction is elucidated
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Statistical modelling and forecasting of outstanding liabilities in non-life insurance
Non-life insurance companies need to build reserves to meet their claims liability cash flows. They often work with aggregated data. Recently it has been suggested that better statistical properties can be obtained when more aggregated data is available for the statistical analysis than just the classical aggregated payments. When also the aggregated number of claims is available one can define a full statistical model of the nature of the number of claims, their delay until payment and the nature of these payments. In this paper we provide a new development in this direction by entering yet another set of aggregated data, namely the number of payments and when they occurred. A new element of our statistical analysis is that we are able to incorporate inflationary trends of payments in a direct and explicit way. Our new method is illustrated on a real life data set and the conclusion are informative and useful
Stochastic background of gravitational waves
A continuous stochastic background of gravitational waves (GWs) for burst
sources is produced if the mean time interval between the occurrence of bursts
is smaller than the average time duration of a single burst at the emission,
i.e., the so called duty cycle must be greater than one. To evaluate the
background of GWs produced by an ensemble of sources, during their formation,
for example, one needs to know the average energy flux emitted during the
formation of a single object and the formation rate of such objects as well. In
many cases the energy flux emitted during an event of production of GWs is not
known in detail, only characteristic values for the dimensionless amplitude and
frequencies are known. Here we present a shortcut to calculate stochastic
backgrounds of GWs produced from cosmological sources. For this approach it is
not necessary to know in detail the energy flux emitted at each frequency.
Knowing the characteristic values for the ``lumped'' dimensionless amplitude
and frequency we show that it is possible to calculate the stochastic
background of GWs produced by an ensemble of sources.Comment: 6 pages, 4 eps figures, (Revtex) Latex. Physical Review D (in press
Automated, high accuracy classification of Parkinsonian disorders: a pattern recognition approach
Progressive supranuclear palsy (PSP), multiple system atrophy (MSA) and idiopathic Parkinson’s disease (IPD) can be clinically indistinguishable, especially in the early stages, despite distinct patterns of molecular pathology. Structural neuroimaging holds promise for providing objective biomarkers for discriminating these diseases at the single subject level but all studies to date have reported incomplete separation of disease groups. In this study, we employed multi-class pattern recognition to assess the value of anatomical patterns derived from a widely available structural neuroimaging sequence for automated classification of these disorders. To achieve this, 17 patients with PSP, 14 with IPD and 19 with MSA were scanned using structural MRI along with 19 healthy controls (HCs). An advanced probabilistic pattern recognition approach was employed to evaluate the diagnostic value of several pre-defined anatomical patterns for discriminating the disorders, including: (i) a subcortical motor network; (ii) each of its component regions and (iii) the whole brain. All disease groups could be discriminated simultaneously with high accuracy using the subcortical motor network. The region providing the most accurate predictions overall was the midbrain/brainstem, which discriminated all disease groups from one another and from HCs. The subcortical network also produced more accurate predictions than the whole brain and all of its constituent regions. PSP was accurately predicted from the midbrain/brainstem, cerebellum and all basal ganglia compartments; MSA from the midbrain/brainstem and cerebellum and IPD from the midbrain/brainstem only. This study demonstrates that automated analysis of structural MRI can accurately predict diagnosis in individual patients with Parkinsonian disorders, and identifies distinct patterns of regional atrophy particularly useful for this process
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