222 research outputs found
Detecting corrupted pages in M replicated large files
A file in a distributed database system is replicated on M sites and may contain corrupted pages. Abdel-Ghaffar and El Abbadi gave a detection scheme assuming that the number of corrupted pages f < M l 2. We replace this assumption by a much weaker one, that, for each page, the majority of copies are correct. Our schemes are based on the structure of the Reed-Solomon code, as proposed by Abdel-Ghaffar and El Abbadi for M= 2. © 1997 IEEE.published_or_final_versio
Optimal competitiveness for the Rectilinear Steiner Arborescence problem
We present optimal online algorithms for two related known problems involving
Steiner Arborescence, improving both the lower and the upper bounds. One of
them is the well studied continuous problem of the {\em Rectilinear Steiner
Arborescence} (). We improve the lower bound and the upper bound on the
competitive ratio for from and to
, where is the number of Steiner
points. This separates the competitive ratios of and the Symetric-,
two problems for which the bounds of Berman and Coulston is STOC 1997 were
identical. The second problem is one of the Multimedia Content Distribution
problems presented by Papadimitriou et al. in several papers and Charikar et
al. SODA 1998. It can be viewed as the discrete counterparts (or a network
counterpart) of . For this second problem we present tight bounds also in
terms of the network size, in addition to presenting tight bounds in terms of
the number of Steiner points (the latter are similar to those we derived for
)
Improved Average Complexity for Comparison-Based Sorting
This paper studies the average complexity on the number of comparisons for
sorting algorithms. Its information-theoretic lower bound is . For many efficient algorithms, the first term is easy to
achieve and our focus is on the (negative) constant factor of the linear term.
The current best value is for the MergeInsertion sort. Our new value
is , narrowing the gap by some . An important building block of
our algorithm is "two-element insertion," which inserts two numbers and
, , into a sorted sequence . This insertion algorithm is still
sufficiently simple for rigorous mathematical analysis and works well for a
certain range of the length of for which the simple binary insertion does
not, thus allowing us to take a complementary approach with the binary
insertion.Comment: 21 pages, 2 figure
Improved Adaptive Group Testing Algorithms with Applications to Multiple Access Channels and Dead Sensor Diagnosis
We study group-testing algorithms for resolving broadcast conflicts on a
multiple access channel (MAC) and for identifying the dead sensors in a mobile
ad hoc wireless network. In group-testing algorithms, we are asked to identify
all the defective items in a set of items when we can test arbitrary subsets of
items. In the standard group-testing problem, the result of a test is
binary--the tested subset either contains defective items or not. In the more
generalized versions we study in this paper, the result of each test is
non-binary. For example, it may indicate whether the number of defective items
contained in the tested subset is zero, one, or at least two. We give adaptive
algorithms that are provably more efficient than previous group testing
algorithms. We also show how our algorithms can be applied to solve conflict
resolution on a MAC and dead sensor diagnosis. Dead sensor diagnosis poses an
interesting challenge compared to MAC resolution, because dead sensors are not
locally detectable, nor are they themselves active participants.Comment: Expanded version of a paper appearing in ACM Symposium on Parallelism
in Algorithms and Architectures (SPAA), and preliminary version of paper
appearing in Journal of Combinatorial Optimizatio
Massive stars as thermonuclear reactors and their explosions following core collapse
Nuclear reactions transform atomic nuclei inside stars. This is the process
of stellar nucleosynthesis. The basic concepts of determining nuclear reaction
rates inside stars are reviewed. How stars manage to burn their fuel so slowly
most of the time are also considered. Stellar thermonuclear reactions involving
protons in hydrostatic burning are discussed first. Then I discuss triple alpha
reactions in the helium burning stage. Carbon and oxygen survive in red giant
stars because of the nuclear structure of oxygen and neon. Further nuclear
burning of carbon, neon, oxygen and silicon in quiescent conditions are
discussed next. In the subsequent core-collapse phase, neutronization due to
electron capture from the top of the Fermi sea in a degenerate core takes
place. The expected signal of neutrinos from a nearby supernova is calculated.
The supernova often explodes inside a dense circumstellar medium, which is
established due to the progenitor star losing its outermost envelope in a
stellar wind or mass transfer in a binary system. The nature of the
circumstellar medium and the ejecta of the supernova and their dynamics are
revealed by observations in the optical, IR, radio, and X-ray bands, and I
discuss some of these observations and their interpretations.Comment: To be published in " Principles and Perspectives in Cosmochemistry"
Lecture Notes on Kodai School on Synthesis of Elements in Stars; ed. by Aruna
Goswami & Eswar Reddy, Springer Verlag, 2009. Contains 21 figure
The Functional DRD3 Ser9Gly Polymorphism (rs6280) Is Pleiotropic, Affecting Reward as Well as Movement
Abnormalities of motivation and behavior in the context of reward are a fundamental component of addiction and mood disorders. Here we test the effect of a functional missense mutation in the dopamine 3 receptor (DRD3) gene (ser9gly, rs6280) on reward-associated dopamine (DA) release in the striatum. Twenty-six healthy controls (HCs) and 10 unmedicated subjects with major depressive disorder (MDD) completed two positron emission tomography (PET) scans with [11C]raclopride using the bolus plus constant infusion method. On one occasion subjects completed a sensorimotor task (control condition) and on another occasion subjects completed a gambling task (reward condition). A linear regression analysis controlling for age, sex, diagnosis, and self-reported anhedonia indicated that during receipt of unpredictable monetary reward the glycine allele was associated with a greater reduction in D2/3 receptor binding (i.e., increased reward-related DA release) in the middle (anterior) caudate (p<0.01) and the ventral striatum (p<0.05). The possible functional effect of the ser9gly polymorphism on DA release is consistent with previous work demonstrating that the glycine allele yields D3 autoreceptors that have a higher affinity for DA and display more robust intracellular signaling. Preclinical evidence indicates that chronic stress and aversive stimulation induce activation of the DA system, raising the possibility that the glycine allele, by virtue of its facilitatory effect on striatal DA release, increases susceptibility to hyperdopaminergic responses that have previously been associated with stress, addiction, and psychosis
Inhibition of Proliferation and Induction of Apoptosis in Multiple Myeloma Cell Lines by CD137 Ligand Signaling
BACKGROUND: Multiple myeloma (MM) is a malignancy of terminally-differentiated plasma cells, and the second most prevalent blood cancer. At present there is no cure for MM, and the average prognosis is only three to five years. Current treatments such as chemotherapy are able to prolong a patient's life but rarely prevent relapse of the disease. Even hematopoietic stem cell transplants and novel drug combinations are often not curative, underscoring the need for a continued search for novel therapeutics. CD137 and its ligand are members of the Tumor Necrosis Factor (TNF) receptor and TNF superfamilies, respectively. Since CD137 ligand cross-linking enhances proliferation and survival of healthy B cells we hypothesized that it would also act as a growth stimulus for B cell cancers. METHODOLOGY/PRINCIPAL FINDINGS: Proliferation and survival of B cell lymphoma cell lines were not affected or slightly enhanced by CD137 ligand agonists in vitro. But surprisingly, they had the opposite effects on MM cells, where CD137 ligand signals inhibited proliferation and induced cell death by apoptosis. Furthermore, secretion of the pro-inflammatory cytokines, IL-6 and IL-8 were also enhanced in MM but not in non-MM cell lines in response to CD137 ligand agonists. The secretion of these cytokines in response to CD137 ligand signaling was consistent with the observed activation of the classical NF-kappaB pathway. We hypothesize that the induction of this pathway results in activation-induced cell death, and that this is the underlying mechanism of CD137-induced MM cell death and growth arrest. CONCLUSIONS/SIGNIFICANCE: These data point to a hitherto unrecognized role of CD137 and CD137 ligand in MM cell biology. The selective inhibition of proliferation and induction of cell death in MM cells by CD137 ligand agonists may also warrant a closer evaluation of their therapeutic potential
High Extracellular Ca2+ Stimulates Ca2+-Activated Cl− Currents in Frog Parathyroid Cells through the Mediation of Arachidonic Acid Cascade
Elevation of extracellular Ca2+ concentration induces intracellular Ca2+ signaling in parathyroid cells. The response is due to stimulation of the phospholipase C/Ca2+ pathways, but the direct mechanism responsible for the rise of intracellular Ca2+ concentration has remained elusive. Here, we describe the electrophysiological property associated with intracellular Ca2+ signaling in frog parathyroid cells and show that Ca2+-activated Cl− channels are activated by intracellular Ca2+ increase through an inositol 1,4,5-trisphophate (IP3)-independent pathway. High extracellular Ca2+ induced an outwardly-rectifying conductance in a dose-dependent manner (EC50∼6 mM). The conductance was composed of an instantaneous time-independent component and a slowly activating time-dependent component and displayed a deactivating inward tail current. Extracellular Ca2+-induced and Ca2+ dialysis-induced currents reversed at the equilibrium potential of Cl− and were inhibited by niflumic acid (a specific blocker of Ca2+-activated Cl− channel). Gramicidin-perforated whole-cell recording displayed the shift of the reversal potential in extracellular Ca2+-induced current, suggesting the change of intracellular Cl− concentration in a few minutes. Extracellular Ca2+-induced currents displayed a moderate dependency on guanosine triphosphate (GTP). All blockers for phospholipase C, diacylglycerol (DAG) lipase, monoacylglycerol (MAG) lipase and lipoxygenase inhibited extracellular Ca2+-induced current. IP3 dialysis failed to induce conductance increase, but 2-arachidonoylglycerol (2-AG), arachidonic acid and 12S-hydroperoxy-5Z,8Z,10E,14Z-eicosatetraenoic acid (12(S)-HPETE) dialysis increased the conductance identical to extracellular Ca2+-induced conductance. These results indicate that high extracellular Ca2+ raises intracellular Ca2+ concentration through the DAG lipase/lipoxygenase pathway, resulting in the activation of Cl− conductance
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