753 research outputs found
Unified greedy approximability beyond submodular maximization
We consider classes of objective functions of cardinality constrained
maximization problems for which the greedy algorithm guarantees a constant
approximation. We propose the new class of --augmentable
functions and prove that it encompasses several important subclasses, such as
functions of bounded submodularity ratio, -augmentable functions, and
weighted rank functions of an independence system of bounded rank quotient - as
well as additional objective functions for which the greedy algorithm yields an
approximation. For this general class of functions, we show a tight bound of
on
the approximation ratio of the greedy algorithm that tightly interpolates
between bounds from the literature for functions of bounded submodularity ratio
and for -augmentable functions. In paritcular, as a by-product, we
close a gap left in [Math.Prog., 2020] by obtaining a tight lower bound for
-augmentable functions for all . For weighted rank
functions of independence systems, our tight bound becomes
, which recovers the known bound of for
independence systems of rank quotient at least
Overproduction and characterization of a recombinant D -amino acid oxidase from Arthrobacter protophormiae
A screening of soil samples for d-amino acid oxidase (d-AAO) activity led to the isolation and identification of the gram-positive bacterium Arthrobacter protophormiae. After purification of the wild-type d-AAO, the gene sequence was determined and designated dao. An alignment of the deduced primary structure with eukaryotic d-AAOs and d-aspartate oxidases showed that the d-AAO from A. protophormiae contains five of six conserved regions; the C-terminal type 1 peroxisomal targeting signal that is typical for d-AAOs from eukaryotic origin is missing. The dao gene was cloned and expressed in Escherichia coli. The purified recombinant d-AAO had a specific activity of 180U mg proteinâ1 for d-methionine and was slightly inhibited in the presence of l-methionine. Mainly, basic and hydrophobic d-amino acids were oxidized by the strictly enantioselective enzyme. After a high cell density fermentation, 2.29âĂâ106U of d-AAO were obtained from 15l of fermentation brot
Incremental Maximization via Continuization
We consider the problem of finding an incremental solution to a
cardinality-constrained maximization problem that not only captures the
solution for a fixed cardinality, but also describes how to gradually grow the
solution as the cardinality bound increases. The goal is to find an incremental
solution that guarantees a good competitive ratio against the optimum solution
for all cardinalities simultaneously. The central challenge is to characterize
maximization problems where this is possible, and to determine the
best-possible competitive ratio that can be attained. A lower bound of
and an upper bound of are known on the competitive
ratio for monotone and accountable objectives [Bernstein et al., Math. Prog.,
2022], which capture a wide range of maximization problems. We introduce a
continuization technique and identify an optimal incremental algorithm that
provides strong evidence that is the best-possible competitive
ratio. Using this continuization, we obtain an improved lower bound of
by studying a particular recurrence relation whose characteristic polynomial
has complex roots exactly beyond the lower bound. Based on the optimal
continuous algorithm combined with a scaling approach, we also provide a
-competitive randomized algorithm. We complement this by a randomized
lower bound of via Yao's principle
Maintained partial protection against Streptococcus pneumoniae despite Bâcell depletion in mice vaccinated with a pneumococcal glycoconjugate vaccine
Objectives: Anti-CD20 monoclonal antibody therapy rapidly depletes >â95% of CD20+ B cells from the circulation. B-cell depletion is an effective treatment for autoimmune disease and B-cell malignancies but also increases the risk of respiratory tract infections. This effect on adaptive immunity could be countered by vaccination. We have used mouse models to investigate the effects of B-cell depletion on pneumococcal vaccination, including protection against infection and timing of vaccination in relation to B-cell depletion. // Methods: C57BL/6 female mice were B-cell depleted using anti-CD20 antibody and immunized with two doses of Prevnar-13 vaccine either before or after anti-CD20 treatment. B-cell repertoire and Streptococcus pneumoniaeâspecific IgG levels were measured using whole-cell ELISA and flow cytometry antibody-binding assay. Protection induced by vaccination was assessed by challenging the mice using a S.âpneumoniae pneumonia model. // Results: Antibody responses to S.âpneumoniae were largely preserved in mice B-cell depleted after vaccination resulting in full protection against pneumococcal infections. In contrast, mice vaccinated with Prevnar-13 while B cells were depleted (with >â90% reduction in B-cell numbers) had decreased circulating antiâS.âpneumoniae IgG and IgM levels (measured using ELISA and flow cytometry antibody binding assays). However, some antibody responses were maintained, and, although vaccine-induced protection against S.âpneumoniae infection was impaired, septicaemia was still prevented in 50% of challenged mice. // Conclusions: This study showed that although vaccine efficacy during periods of profound B-cell depletion was impaired some protective efficacy was preserved, suggesting that vaccination remains beneficial
Potential sources of interference with the highly sensitive detection and quantification of alphaâsynuclein seeds by qRTâQuIC
Parkinsonâs disease (PD) is a progressive neurodegenerative disease which is histologically characterized by loss of dopaminergic neurons in the substantia nigra and deposition of aggregated alphaâsynuclein (aSyn) in the brain. The detection of aSyn in well accessible fluids has been one of the central approaches in the development of biomarkers for PD. Recently, realâtime quakingâinduced conversion (RTâQuIC) has been successfully adapted for use with aSyn seeds. Here, we systematically analysed parameters potentially impacting the reliability of this assay by using quantitative realâtime quakingâinduced conversion (qRTâQuIC) with in vitroâformed aSyn seeds. Seeds diluted in cerebrospinal fluid (CSF) accelerated the seeding reaction and slightly increased the sensitivity without affecting specificity. Repeated freezeâthaw cycles decreased the apparent lag times of seeds diluted in ddH2O but did not alter the seeding activity of seeds diluted in CSF. High levels of artificial contamination with blood resulted in prolonged apparent lag times, while sensitivity and specificity were unaffected. Altogether, qRTâQuIC with aSyn seems to be robust concerning sensitivity and specificity in our model system, but quantitative interpretation might be limited under certain conditions
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