50 research outputs found
Clustering Brain Signals: A Robust Approach Using Functional Data Ranking
In this paper, we analyze electroencephalograms (EEG) which are recordings of
brain electrical activity. We develop new clustering methods for identifying
synchronized brain regions, where the EEGs show similar oscillations or
waveforms according to their spectral densities. We treat the estimated
spectral densities from many epochs or trials as functional data and develop
clustering algorithms based on functional data ranking. The two proposed
clustering algorithms use different dissimilarity measures: distance of the
functional medians and the area of the central region. The performance of the
proposed algorithms is examined by simulation studies. We show that, when
contaminations are present, the proposed methods for clustering spectral
densities are more robust than the mean-based methods. The developed methods
are applied to two stages of resting state EEG data from a male college
student, corresponding to early exploration of functional connectivity in the
human brain
Role of sea quarks in the nucleon transverse spin
We present a phenomenological extraction of transversity distribution
functions and Collins fragmentation functions by simultaneously fitting to
semi-inclusive deep inelastic scattering and electron-positron annihilation
data. The analysis is performed within the transverse momentum dependent
factorization formalism, and sea quark transversity distributions are taken
into account for the first time. We find the quark favors a negative
transversity distribution while that of the quark is consistent with
zero according to the current accuracy. In addition, based on a combined
analysis of world data and simulated data, we quantitatively demonstrate the
impact of the proposed Electron-ion Collider in China on precise determinations
of the transversity distributions, especially for sea quarks, and the Collins
fragmentation functions
Unveiling the nucleon tensor charge at Jefferson Lab: A study of the SoLID case
Future experiments at the Jefferson Lab 12 GeV upgrade, in particular, the
Solenoidal Large Intensity Device (SoLID), aim at a very precise data set in
the region where the partonic structure of the nucleon is dominated by the
valence quarks. One of the main goals is to constrain the quark transversity
distributions. We apply recent theoretical advances of the global QCD
extraction of the transversity distributions to study the impact of future
experimental data from the SoLID experiments. Especially, we develop a simple
strategy based on the Hessian matrix analysis that allows one to estimate the
uncertainties of the transversity quark distributions and their tensor charges
extracted from SoLID data simulation. We find that the SoLID measurements with
the proton and the effective neutron targets can improve the precision of the
u- and d-quark transversity distributions up to one order of magnitude in the
range 0.05 < x < 0.6.Comment: 11 pages, 3 figures, published on Physics Letters
Spatially-coded Fourier ptychography: flexible and detachable coded thin films for quantitative phase imaging with uniform phase transfer characteristics
Fourier ptychography (FP) is an enabling imaging technique that produces
high-resolution complex-valued images with extended field coverages. However,
when FP images a phase object with any specific spatial frequency, the captured
images contain only constant values, rendering the recovery of the
corresponding linear phase ramp impossible. This challenge is not unique to FP
but also affects other common microscopy techniques -- a rather
counterintuitive outcome given their widespread use in phase imaging. The
underlying issue originates from the non-uniform phase transfer characteristic
inherent in microscope systems, which impedes the conversion of object
wavefields into discernible intensity variations. To address this challenge, we
present spatially-coded Fourier ptychography (scFP), a new method that
synergizes FP with spatial-domain coded detection for true quantitative phase
imaging. In scFP, a flexible and detachable coded thin film is attached atop
the image sensor in a regular FP setup. The spatial modulation of this thin
film ensures a uniform phase response across the entire synthetic bandwidth. It
improves reconstruction quality and corrects refractive index underestimation
issues prevalent in conventional FP and related tomographic implementations.
The inclusion of the coded thin film further adds a new dimension of
measurement diversity in the spatial domain. The development of scFP is
expected to catalyse new research directions and applications for phase
imaging, emphasizing the need for true quantitative accuracy with uniform
frequency response
Role of Protein Charge Density on Hepatitis B Virus Capsid Formation
The role of electrostatic interactions in the viral capsid assembly process was studied by comparing the assembly process of a truncated hepatitis B virus capsid protein Cp149 with its mutant protein D2N/D4N, which has the same conformational structure but four fewer charges per dimer. The capsid protein self-assembly was investigated under a wide range of protein surface charge densities by changing the protein concentration, buffer pH, and solution ionic strength. Lowering the protein charge density favored the capsid formation. However, lowering charge beyond a certain point resulted in capsid aggregation and precipitation. Interestingly, both the wild-type and D2N/D4N mutant displayed identical assembly profiles when their charge densities matched each other. These results indicated that the charge density was optimized by nature to ensure an efficient and effective capsid proliferation under the physiological pH and ionic strength