225 research outputs found
A Distributed and Incremental SVD Algorithm for Agglomerative Data Analysis on Large Networks
In this paper, we show that the SVD of a matrix can be constructed
efficiently in a hierarchical approach. Our algorithm is proven to recover the
singular values and left singular vectors if the rank of the input matrix
is known. Further, the hierarchical algorithm can be used to recover the
largest singular values and left singular vectors with bounded error. We also
show that the proposed method is stable with respect to roundoff errors or
corruption of the original matrix entries. Numerical experiments validate the
proposed algorithms and parallel cost analysis
Modewise Johnson-Lindenstrauss Embeddings for Nuclear Many-Body Theory
In this work, we explore modewise Johnson-Lindenstrauss embeddings (JLEs) as
a tool to reduce the computational cost and memory requirements of nuclear
many-body methods. JLEs are randomized projections of high-dimensional data
tensors onto low-dimensional subspaces that preserve key structural features.
Such embeddings allow for the oblivious and incremental compression of large
tensors, e.g., the nuclear Hamiltonian, into significantly smaller random
sketches that still allow for the accurate calculation of ground-state energies
and other observables. Their oblivious character makes it possible to compress
a tensor without knowing in advance exactly what observables one might want to
approximate at a later time. This opens the door for the use of tensors that
are much too large to store in memory, e.g., complete two-plus three-nucleon
Hamiltonians in large, symmetry-unrestricted bases. Such compressed
Hamiltonians can be stored and used later on with relative ease.
As a first step, we analyze the JLE's impact on the second-order Many-Body
Perturbation Theory (MBPT) corrections for nuclear ground-state observables.
Numerical experiments for a wide range of closed-shell nuclei, model spaces and
state-of-the-art nuclear interactions demonstrate the validity and potential of
the proposed approach: We can compress nuclear Hamiltonians hundred- to
thousand-fold while only incurring mean relative errors of 1\% or less in
ground-state observables. Importantly, we show that JLEs capture the relevant
physical information contained in the highly structured Hamiltonian tensor
despite their random characteristics. In addition to the significant storage
savings, the achieved compressions imply multiple order-of magnitude reductions
in computational effort when the compressed Hamiltonians are used in
higher-order MBPT or nonperturbative many-body methods.Comment: 23 pages, 14 figure
Functional redundancy of two C. elegans homologs of the histone chaperone Asf1 in germline DNA replication
AbstractEukaryotic genomes contain either one or two genes encoding homologs of the highly conserved histone chaperone Asf1, however, little is known of their in vivo roles in animal development. UNC-85 is one of the two Caenorhabditis elegans Asf1 homologs and functions in post-embryonic replication in neuroblasts. Although UNC-85 is broadly expressed in replicating cells, the specificity of the mutant phenotype suggested possible redundancy with the second C. elegans Asf1 homolog, ASFL-1. The asfl-1 mRNA is expressed in the meiotic region of the germline, and mutants in either Asf1 genes have reduced brood sizes and low penetrance defects in gametogenesis. The asfl-1, unc-85 double mutants are sterile, displaying defects in oogenesis and spermatogenesis, and analysis of DNA synthesis revealed that DNA replication in the germline is blocked. Analysis of somatic phenotypes previously observed in unc-85 mutants revealed that they are neither observed in asfl-1 mutants, nor enhanced in the double mutants, with the exception of enhanced male tail abnormalities in the double mutants. These results suggest that the two Asf1 homologs have partially overlapping functions in the germline, while UNC-85 is primarily responsible for several Asf1 functions in somatic cells, and is more generally involved in replication throughout development
Are we there yet? Laboratory preparedness for emerging infectious diseases
The West African Ebola virus epidemic of 2013β2016
was the most widespread epidemic of this disease in history;
it is estimated that this occurrence contributed to
more than 11000 deaths. During the epidemic, healthcare
workers (HCW)8 (including laboratorians) were
mobilized to care for individuals with suspected or confirmed
Ebola virus disease (EVD). However, at the
height of the epidemic, guidance on appropriate safety
measures for laboratory workers manipulating specimens
from EVD patients was sparse. This highlighted the need
for data and guidelines for laboratories testing specimens
not only for patients with EVD, but for any emerging
infectious disease. During the Ebola epidemic, questions
were raised about the roles and responsibilities of laboratories
in responding to highly infectious diseases, and the burden
of ongoing readiness for rare events. As the outbreak
decelerates, laboratorians must regroup, gather data, and
prepare for future outbreaks. We have asked 4 experts in this
field to share their thoughts on contemporary challenges in
laboratory preparedness for emerging infectious disease
New Insights into HTLV-1 Particle Structure, Assembly, and Gag-Gag Interactions in Living Cells
Human T-cell leukemia virus type 1 (HTLV-1) has a reputation for being extremely difficult to study in cell culture. The challenges in propagating HTLV-1 has prevented a rigorous analysis of how these viruses replicate in cells, including the detailed steps involved in virus assembly. The details for how retrovirus particle assembly occurs are poorly understood, even for other more tractable retroviral systems. Recent studies on HTLV-1 using state-of-the-art cryo-electron microscopy and fluorescence-based biophysical approaches explored questions related to HTLV-1 particle size, Gag stoichiometry in virions, and Gag-Gag interactions in living cells. These results provided new and exciting insights into fundamental aspects of HTLV-1 particle assemblyβwhich are distinct from those of other retroviruses, including HIV-1. The application of these and other novel biophysical approaches promise to provide exciting new insights into HTLV-1 replication
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