439 research outputs found
Submodular memetic approximation for multiobjective parallel test paper generation
Parallel test paper generation is a biobjective distributed resource optimization problem, which aims to generate multiple similarly optimal test papers automatically according to multiple user-specified assessment criteria. Generating high-quality parallel test papers is challenging due to its NP-hardness in both of the collective objective functions. In this paper, we propose a submodular memetic approximation algorithm for solving this problem. The proposed algorithm is an adaptive memetic algorithm (MA), which exploits the submodular property of the collective objective functions to design greedy-based approximation algorithms for enhancing steps of the multiobjective MA. Synergizing the intensification of submodular local search mechanism with the diversification of the population-based submodular crossover operator, our algorithm can jointly optimize the total quality maximization objective and the fairness quality maximization objective. Our MA can achieve provable near-optimal solutions in a huge search space of large datasets in efficient polynomial runtime. Performance results on various datasets have shown that our algorithm has drastically outperformed the current techniques in terms of paper quality and runtime efficiency
Measuring the 3D Clustering of Undetected Galaxies Through Cross Correlation of their Cumulative Flux Fluctuations from Multiple Spectral Lines
We discuss a method for detecting the emission from high redshift galaxies by
cross correlating flux fluctuations from multiple spectral lines. If one can
fit and subtract away the continuum emission with a smooth function of
frequency, the remaining signal contains fluctuations of flux with frequency
and angle from line emitting galaxies. Over a particular small range of
observed frequencies, these fluctuations will originate from sources
corresponding to a series of different redshifts, one for each emission line.
It is possible to statistically isolate the fluctuations at a particular
redshift by cross correlating emission originating from the same redshift, but
in different emission lines. This technique will allow detection of clustering
fluctuations from the faintest galaxies which individually cannot be detected,
but which contribute substantially to the total signal due to their large
numbers. We describe these fluctuations quantitatively through the line cross
power spectrum. As an example of a particular application of this technique, we
calculate the signal-to-noise ratio for a measurement of the cross power
spectrum of the OI(63 micron) and OIII(52 micron) fine structure lines with the
proposed Space Infrared Telescope for Cosmology and Astrophysics. We find that
the cross power spectrum can be measured beyond a redshift of z=8. Such
observations could constrain the evolution of the metallicity, bias, and duty
cycle of faint galaxies at high redshifts and may also be sensitive to the
reionization history through its effect on the minimum mass of galaxies. As
another example, we consider the cross power spectrum of CO line emission
measured with a large ground based telescope like CCAT and 21-cm radiation
originating from hydrogen in galaxies after reionization with an interferometer
similar in scale to MWA, but optimized for post-reionization redshifts.Comment: 21 pages, 6 figures; Replaced with version accepted by JCAP; Added an
example of cross correlating CO line emission and 21cm line emission from
galaxies after reionizatio
VFISV: Very Fast Inversion of the Stokes Vector for the Helioseismic and Magnetic Imager
In this paper we describe in detail the implementation and main properties of
a new inversion code for the polarized radiative transfer equation (VFISV: Very
Fast inversion of the Stokes vector). VFISV will routinely analyze pipeline
data from the Helioseismic and Magnetic Imager (HMI) on-board of the Solar
Dynamics Observatory (SDO). It will provide full-disk maps (40964096
pixels) of the magnetic field vector on the Solar Photosphere every 10 minutes.
For this reason VFISV is optimized to achieve an inversion speed that will
allow it to invert 16 million pixels every 10 minutes with a modest number
(approx. 50) of CPUs. Here we focus on describing a number of important
details, simplifications and tweaks that have allowed us to significantly speed
up the inversion process. We also give details on tests performed with data
from the spectropolarimeter on-board of the Hinode spacecraft.Comment: 23 pages, 9 figures (2 color). Submitted for publication to Solar
Physic
Interplay of quantum magnetic and potential scattering around Zn or Ni impurity ions in superconducting cuprates
To describe the scattering of superconducting quasiparticles from
non-magnetic (Zn) or magnetic (Ni) impurities in optimally doped high T
cuprates, we propose an effective Anderson model Hamiltonian of a localized
electron hybridizing with -wave BCS type superconducting
quasiparticles with an attractive scalar potential at the impurity site. Due to
the strong local antiferromagnetic couplings between the original Cu ions and
their nearest neighbors, the localized electron in the Ni-doped materials is
assumed to be on the impurity sites, while in the Zn-doped materials the
localized electron is distributed over the four nearest neighbor sites of the
impurities with a dominant symmetric form of the wave function.
With Ni impurities, two resonant states are formed above the Fermi level in the
local density of states at the impurity site, while for Zn impurities a sharp
resonant peak below the Fermi level dominates in the local density of states at
the Zn site, accompanied by a small and broad resonant state above the Fermi
level mainly induced by the potential scattering. In both cases, there are no
Kondo screening effects. The local density of states and their spatial
distribution at the dominant resonant energy around the substituted impurities
are calculated for both cases, and they are in good agreement with the
experimental results of scanning tunneling microscopy in
BiSrCaCuO with Zn or Ni impurities, respectively.Comment: 24 pages, Revtex, 8 figures, submitted to Physical Review B for
publication. Sub-ject Class: Superconductivity; Strongly Correlated Electron
Inflationary signatures of single-field models beyond slow-roll
If the expansion of the early Universe was not close to de Sitter, the
statistical imprints of the primordial density perturbation on the cosmic
microwave background can be quite different from those derived in slow-roll
inflation. In this paper we study the inflationary signatures of all
single-field models which are free of ghost-like instabilities. We allow for a
rapid change of the Hubble parameter and the speed of sound of scalar
fluctuations, in a way that is compatible with a nearly scale-invariant
spectrum of perturbations, as supported by current cosmological observations.
Our results rely on the scale-invariant approximation, which is different from
the standard slow-roll approximation. We obtain the propagator of scalar
fluctuations and compute the bispectrum, keeping next-order corrections
proportional to the deviation of the spectral index from unity. These theories
offer an explicit example where the shape and scale-dependences of the
bispectrum are highly non-trivial whenever slow-roll is not a good
approximation.Comment: v1: 36 pages, including tables, appendices and references. v2:
abstract improved, references added, minor clarifications throughout the
text; matches version published in JCA
Viral Loads in Clinical Specimens and SARS Manifestations
The number of anatomical sites with detectable viral loads by RT-qPCR appeared to correlate with death risk
The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets
This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics
Latitudinal gradient of nestedness and its potential drivers in stream detritivores
Understanding what mechanisms shape the diversity and composition of biological assemblages across broad-scale gradients is central to ecology. Litter-consuming detritivorous invertebrates in streams show an unusual diversity gradient, with α-diversity increasing towards high latitudes but no trend in γ -diversity. We hypothesized this pattern to be related
to shifts in nestedness and several ecological processes shaping their assemblages (dispersal, environmental filtering and competition). We tested this hypothesis, using a global dataset, by examining latitudinal trends in nestedness and several indicators of the above processes along the latitudinal gradient. Our results suggest that strong environmental filtering and low dispersal in the tropics lead to often species-poor local detritivore assemblages, nested in richer regional assemblages. At higher latitudes, dispersal becomes stronger, disrupting the nested assemblage structure and resulting in local assemblages that are generally more species-rich and non-nested subsets of the regional species pools. Our results provide
evidence that mechanisms underlying assemblage composition and diversity of stream litter-consuming detritivores shift
across latitudes, and provide an explanation for their unusual pattern of increasing α-diversity with latitude. When we repeated these analyses for whole invertebrate assemblages of leaf litter and for abundant taxa showing reverse or no diversity gradients we found no latitudinal patterns, suggesting that function-based rather than taxon-based analyses of assemblages may help elucidate the mechanisms behind diversity gradients
The Epigenetic Evolution of Glioma Is Determined by the IDH1 Mutation Status and Treatment Regimen
Tumor adaptation or selection is thought to underlie therapy resistance in glioma. To investigate longitudinal epigenetic evolution of gliomas in response to therapeutic pressure, we performed an epigenomic analysis of 132 matched initial and recurrent tumors from patients with IDH-wildtype (IDHwt) and IDH-mutant (IDHmut) glioma. IDHwt gliomas showed a stable epigenome over time with relatively low levels of global methylation. The epigenome of IDHmut gliomas showed initial high levels of genome-wide DNA methylation that was progressively reduced to levels similar to those of IDHwt tumors. Integration of epigenomics, gene expression, and functional genomics identified HOXD13 as a master regulator of IDHmut astrocytoma evolution. Furthermore, relapse of IDHmut tumors was accompanied by histologic progression that was associated with survival, as validated in an independent cohort. Finally, the initial cell composition of the tumor microenvironment varied between IDHwt and IDHmut tumors and changed differentially following treatment, suggesting increased neoangiogenesis and T-cell infiltration upon treatment of IDHmut gliomas. This study provides one of the largest cohorts of paired longitudinal glioma samples with epigenomic, transcriptomic, and genomic profiling and suggests that treatment of IDHmut glioma is associated with epigenomic evolution toward an IDHwt-like phenotype.</p
Milagro limits and HAWC sensitivity for the rate-density of evaporating Primordial Black Holes
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