30,985 research outputs found
A Criterion for Comparing Measurement Results and Determining Conformity with Specifications
In this paper a new criterion for comparing measurement results and determining conformity with specifications is proposed, which essentially is a strategy of estimating the empirical relationships of objects. Comparing with traditional methods given in GUM: 2008 and ISO 14253-1, this criterion improves the resolution of comparison by reducing the sizes of the coverage intervals to be compared. Interval order (a binary relation) is used for comparing the coverage intervals of the measurand and represents the empirical relations. The systematic effects of measurement are classified into two types: monotonic and non-monotonic effects, so that, without correcting the monotonic effects, a biased measurand can be specified to represent the empirical relations. Thereby the uncertainty components arising from the monotonic effects can be removed from the combined uncertainty. A strategy is given for determining the relationships among measurement results and specification limits. An example is given to demonstrate the application of the criterion
Solar flare hard X-ray spikes observed by RHESSI: a statistical study
Context. Hard X-ray (HXR) spikes refer to fine time structures on timescales
of seconds to milliseconds in high-energy HXR emission profiles during solar
flare eruptions. Aims. We present a preliminary statistical investigation of
temporal and spectral properties of HXR spikes. Methods. Using a three-sigma
spike selection rule, we detected 184 spikes in 94 out of 322 flares with
significant counts at given photon energies, which were detected from
demodulated HXR light curves obtained by the Reuven Ramaty High Energy Solar
Spectroscopic Imager (RHESSI). About one fifth of these spikes are also
detected at photon energies higher than 100 keV. Results. The statistical
properties of the spikes are as follows. (1) HXR spikes are produced in both
impulsive flares and long-duration flares with nearly the same occurrence
rates. Ninety percent of the spikes occur during the rise phase of the flares,
and about 70% occur around the peak times of the flares. (2) The time durations
of the spikes vary from 0.2 to 2 s, with the mean being 1.0 s, which is not
dependent on photon energies. The spikes exhibit symmetric time profiles with
no significant difference between rise and decay times. (3) Among the most
energetic spikes, nearly all of them have harder count spectra than their
underlying slow-varying components. There is also a weak indication that spikes
exhibiting time lags in high-energy emissions tend to have harder spectra than
spikes with time lags in low-energy emissions.Comment: 16 pages, 13 figure
Chromospheric Evaporation in an X1.0 Flare on 2014 March 29 Observed with IRIS and EIS
Chromospheric evaporation refers to dynamic mass motions in flare loops as a
result of rapid energy deposition in the chromosphere. These have been observed
as blueshifts in X-ray and extreme-ultraviolet (EUV) spectral lines
corresponding to upward motions at a few tens to a few hundreds of km/s. Past
spectroscopic observations have also revealed a dominant stationary component,
in addition to the blueshifted component, in emission lines formed at high
temperatures (~10 MK). This is contradictory to evaporation models predicting
predominant blueshifts in hot lines. The recently launched Interface Region
Imaging Spectrograph (IRIS) provides high resolution imaging and spectroscopic
observations that focus on the chromosphere and transition region in the UV
passband. Using the new IRIS observations, combined with coordinated
observations from the EUV Imaging Spectrometer, we study the chromospheric
evaporation process from the upper chromosphere to corona during an X1.0 flare
on 2014 March 29. We find evident evaporation signatures, characterized by
Doppler shifts and line broadening, at two flare ribbons separating from each
other, suggesting that chromospheric evaporation takes place in successively
formed flaring loops throughout the flare. More importantly, we detect dominant
blueshifts in the high temperature Fe XXI line (~10 MK), in agreement with
theoretical predictions. We also find that, in this flare, gentle evaporation
occurs at some locations in the rise phase of the flare, while explosive
evaporation is detected at some other locations near the peak of the flare.
There is a conversion from gentle to explosive evaporation as the flare
evolves.Comment: ApJ in pres
Computational structure‐based drug design: Predicting target flexibility
The role of molecular modeling in drug design has experienced a significant revamp in the last decade. The increase in computational resources and molecular models, along with software developments, is finally introducing a competitive advantage in early phases of drug discovery. Medium and small companies with strong focus on computational chemistry are being created, some of them having introduced important leads in drug design pipelines. An important source for this success is the extraordinary development of faster and more efficient techniques for describing flexibility in three‐dimensional structural molecular modeling. At different levels, from docking techniques to atomistic molecular dynamics, conformational sampling between receptor and drug results in improved predictions, such as screening enrichment, discovery of transient cavities, etc. In this review article we perform an extensive analysis of these modeling techniques, dividing them into high and low throughput, and emphasizing in their application to drug design studies. We finalize the review with a section describing our Monte Carlo method, PELE, recently highlighted as an outstanding advance in an international blind competition and industrial benchmarks.We acknowledge the BSC-CRG-IRB Joint Research Program in Computational Biology. This work was supported by a grant
from the Spanish Government CTQ2016-79138-R.J.I. acknowledges support from SVP-2014-068797, awarded by the Spanish Government.Peer ReviewedPostprint (author's final draft
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