25,199 research outputs found
Remove-Win: a Design Framework for Conflict-free Replicated Data Collections
Internet-scale distributed systems often replicate data within and across
data centers to provide low latency and high availability despite node and
network failures. Replicas are required to accept updates without coordination
with each other, and the updates are then propagated asynchronously. This
brings the issue of conflict resolution among concurrent updates, which is
often challenging and error-prone. The Conflict-free Replicated Data Type
(CRDT) framework provides a principled approach to address this challenge.
This work focuses on a special type of CRDT, namely the Conflict-free
Replicated Data Collection (CRDC), e.g. list and queue. The CRDC can have
complex and compound data items, which are organized in structures of rich
semantics. Complex CRDCs can greatly ease the development of upper-layer
applications, but also makes the conflict resolution notoriously difficult.
This explains why existing CRDC designs are tricky, and hard to be generalized
to other data types. A design framework is in great need to guide the
systematic design of new CRDCs.
To address the challenges above, we propose the Remove-Win Design Framework.
The remove-win strategy for conflict resolution is simple but powerful. The
remove operation just wipes out the data item, no matter how complex the value
is. The user of the CRDC only needs to specify conflict resolution for
non-remove operations. This resolution is destructed to three basic cases and
are left as open terms in the CRDC design skeleton. Stubs containing
user-specified conflict resolution logics are plugged into the skeleton to
obtain concrete CRDC designs. We demonstrate the effectiveness of our design
framework via a case study of designing a conflict-free replicated priority
queue. Performance measurements also show the efficiency of the design derived
from our design framework.Comment: revised after submissio
Entropy fluctuation formulas of fermionic Gaussian states
We study the statistical behaviour of quantum entanglement in bipartite
systems over fermionic Gaussian states as measured by von Neumann entropy. The
formulas of average von Neumann entropy with and without particle number
constrains have been recently obtained, whereas the main results of this work
are the exact yet explicit formulas of variances for both cases. For the latter
case of no particle number constrain, the results resolve a recent conjecture
on the corresponding variance. Different than existing methods in computing
variances over other generic state models, the key ingredient in proving the
results of this work relies on a new simplification framework. The framework
consists of a set of new tools in simplifying finite summations of what we
refer to as dummy summation and re-summation techniques. As a byproduct, the
proposed framework leads to various new transformation formulas of
hypergeometric functions.Comment: 64 pages, 3 figure
Gamma-ray bursts: postburst evolution of fireballs
The postburst evolution of fireballs that produce -ray bursts is
studied, assuming the expansion of fireballs to be adiabatic and relativistic.
Numerical results as well as an approximate analytic solution for the evolution
are presented. Due to adoption of a new relation among , and
(see the text), our results differ markedly from the previous studies.
Synchrotron radiation from the shocked interstellar medium is attentively
calculated, using a convenient set of equations. The observed X-ray flux of GRB
afterglows can be reproduced easily. Although the optical afterglows seem much
more complicated, our results can still present a rather satisfactory approach
to observations. It is also found that the expansion will no longer be highly
relativistic about 4 days after the main GRB. We thus suggest that the
marginally relativistic phase of the expansion should be investigated so as to
check the afterglows observed a week or more later.Comment: 17 pages, 4 figures, MNRAS in pres
Impact of template backbone heterogeneity on RNA polymerase II transcription.
Variations in the sugar component (ribose or deoxyribose) and the nature of the phosphodiester linkage (3'-5' or 2'-5' orientation) have been a challenge for genetic information transfer from the very beginning of evolution. RNA polymerase II (pol II) governs the transcription of DNA into precursor mRNA in all eukaryotic cells. How pol II recognizes DNA template backbone (phosphodiester linkage and sugar) and whether it tolerates the backbone heterogeneity remain elusive. Such knowledge is not only important for elucidating the chemical basis of transcriptional fidelity but also provides new insights into molecular evolution. In this study, we systematically and quantitatively investigated pol II transcriptional behaviors through different template backbone variants. We revealed that pol II can well tolerate and bypass sugar heterogeneity sites at the template but stalls at phosphodiester linkage heterogeneity sites. The distinct impacts of these two backbone components on pol II transcription reveal the molecular basis of template recognition during pol II transcription and provide the evolutionary insight from the RNA world to the contemporary 'imperfect' DNA world. In addition, our results also reveal the transcriptional consequences from ribose-containing genomic DNA
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