18 research outputs found
Multiversion Concurrency with Bounded Delay and Precise Garbage Collection
In this paper we are interested in bounding the number of instructions taken
to process transactions. The main result is a multiversion transactional system
that supports constant delay (extra instructions beyond running in isolation)
for all read-only transactions, delay equal to the number of processes for
writing transactions that are not concurrent with other writers, and
lock-freedom for concurrent writers. The system supports precise garbage
collection in that versions are identified for collection as soon as the last
transaction releases them. As far as we know these are first results that bound
delays for multiple readers and even a single writer. The approach is
particularly useful in situations where read-transactions dominate write
transactions, or where write transactions come in as streams or batches and can
be processed by a single writer (possibly in parallel).
The approach is based on using functional data structures to support multiple
versions, and an efficient solution to the Version Maintenance (VM) problem for
acquiring, updating and releasing versions. Our solution to the VM problem is
precise, safe and wait-free (PSWF).
We experimentally validate our approach by applying it to balanced tree data
structures for maintaining ordered maps. We test the transactional system using
multiple algorithms for the VM problem, including our PSWF VM algorithm, and
implementations with weaker guarantees based on epochs, hazard pointers, and
read-copy-update. To evaluate the functional data structure for concurrency and
multi-versioning, we implement batched updates for functional tree structures
and compare the performance with state-of-the-art concurrent data structures
for balanced trees. The experiments indicate our approach works well in
practice over a broad set of criteria
Loneliness and the Emotional Experience of Absence
In this paper, we develop an analysis of the structure and content of loneliness. We argue that this is an emotion of absence-an affective state in which certain social goods are regarded as out of reach for the subject of experience. By surveying the range of social goods that appear to be missing from the lonely person's perspective, we see what it is that can make this emotional condition so subjectively awful for those who undergo it, including the profound sense of being unable to realise oneself, in collaboration with others
Homochirality and the need of energy
The mechanisms for explaining how a stable asymmetric chemical system can be
formed from a symmetric chemical system, in the absence of any asymmetric
influence other than statistical fluctuations, have been developed during the
last decades, focusing on the non-linear kinetic aspects. Besides the absolute
necessity of self-amplification processes, the importance of energetic aspects
is often underestimated. Going down to the most fundamental aspects, the
distinction between a single object -- that can be intrinsically asymmetric --
and a collection of objects -- whose racemic state is the more stable one --
must be emphasized. A system of strongly interacting objects can be described
as one single object retaining its individuality and a single asymmetry; weakly
or non-interacting objects keep their own individuality, and are prone to
racemize towards the equilibrium state. In the presence of energy fluxes,
systems can be maintained in an asymmetric non-equilibrium steady-state. Such
dynamical systems can retain their asymmetry for times longer than their
racemization time.Comment: 8 pages, 7 figures, submitted to Origins of Life and Evolution of
Biosphere
Expanded protein information at SGD: new pages and proteome browser
The recent explosion in protein data generated from both directed small-scale studies and large-scale proteomics efforts has greatly expanded the quantity of available protein information and has prompted the Saccharomyces Genome Database (SGD; ) to enhance the depth and accessibility of protein annotations. In particular, we have expanded ongoing efforts to improve the integration of experimental information and sequence-based predictions and have redesigned the protein information web pages. A key feature of this redesign is the development of a GBrowse-derived interactive Proteome Browser customized to improve the visualization of sequence-based protein information. This Proteome Browser has enabled SGD to unify the display of hidden Markov model (HMM) domains, protein family HMMs, motifs, transmembrane regions, signal peptides, hydropathy plots and profile hits using several popular prediction algorithms. In addition, a physico-chemical properties page has been introduced to provide easy access to basic protein information. Improvements to the layout of the Protein Information page and integration of the Proteome Browser will facilitate the ongoing expansion of sequence-specific experimental information captured in SGD, including post-translational modifications and other user-defined annotations. Finally, SGD continues to improve upon the availability of genetic and physical interaction data in an ongoing collaboration with BioGRID by providing direct access to more than 82 000 manually-curated interactions