198 research outputs found
Schema architecture and their relationships to transaction processing in distributed database systems
We discuss the different types of schema architectures which could be supported by distributed database systems, making a clear distinction between logical, physical, and federated distribution. We elaborate on the additional mapping information required in architecture based on logical distribution in order to support retrieval as well as update operations. We illustrate the problems in schema integration and data integration in multidatabase systems and discuss their impact on query processing. Finally, we discuss different issues relevant to the cooperation (or noncooperation) of local database systems in a heterogeneous multidatabase system and their relationship to the schema architecture and transaction processing
Finding the KT partition of a weighted graph in near-linear time
In a breakthrough work, Kawarabayashi and Thorup (J.~ACM'19) gave a
near-linear time deterministic algorithm for minimum cut in a simple graph . A key component is finding the -KT partition of ,
the coarsest partition of such that for every
non-trivial -near minimum cut with sides it
holds that is contained in either or , for .
Here we give a near-linear time randomized algorithm to find the
-KT partition of a weighted graph. Our algorithm is quite
different from that of Kawarabayashi and Thorup and builds on Karger's
framework of tree-respecting cuts (J.~ACM'00).
We describe applications of the algorithm. (i) The algorithm makes progress
towards a more efficient algorithm for constructing the polygon representation
of the set of near-minimum cuts in a graph. This is a generalization of the
cactus representation initially described by Bencz\'ur (FOCS'95). (ii) We
improve the time complexity of a recent quantum algorithm for minimum cut in a
simple graph in the adjacency list model from to
. (iii) We describe a new type of randomized algorithm
for minimum cut in simple graphs with complexity . For
slightly dense graphs this matches the complexity of the current best algorithm which uses a different approach based on random
contractions.
The key technical contribution of our work is the following. Given a weighted
graph with edges and a spanning tree , consider the graph whose
nodes are the edges of , and where there is an edge between two nodes of
iff the corresponding 2-respecting cut of is a non-trivial near-minimum cut
of . We give a time deterministic algorithm to compute a
spanning forest of
Parallel Evaluation of Multi-join Queries
A number of execution strategies for parallel evaluation of multi-join queries have been proposed in the literature. In this paper we give a comparative performance evaluation of four execution strategies by implementing all of them on the same parallel database system, PRISMA/DB. Experiments have been done up to 80 processors. These strategies, coming from the literature, are named: Sequential Parallel, Synchronous Execution, Segmented Right-Deep, and Full Parallel. Based on the experiments clear guidelines are given when to use which strategy.
This is an extended abstract; the full paper appeared in Proc. ACM SIGMOD'94, Minneapolis, Minnesota, May 24–27, 199
The Wellesley News (01-19-1933)
https://repository.wellesley.edu/news/1936/thumbnail.jp
On analog quantum algorithms for the mixing of Markov chains
The problem of sampling from the stationary distribution of a Markov chain
finds widespread applications in a variety of fields. The time required for a
Markov chain to converge to its stationary distribution is known as the
classical mixing time. In this article, we deal with analog quantum algorithms
for mixing. First, we provide an analog quantum algorithm that given a Markov
chain, allows us to sample from its stationary distribution in a time that
scales as the sum of the square root of the classical mixing time and the
square root of the classical hitting time. Our algorithm makes use of the
framework of interpolated quantum walks and relies on Hamiltonian evolution in
conjunction with von Neumann measurements.
There also exists a different notion for quantum mixing: the problem of
sampling from the limiting distribution of quantum walks, defined in a
time-averaged sense. In this scenario, the quantum mixing time is defined as
the time required to sample from a distribution that is close to this limiting
distribution. Recently we provided an upper bound on the quantum mixing time
for Erd\"os-Renyi random graphs [Phys. Rev. Lett. 124, 050501 (2020)]. Here, we
also extend and expand upon our findings therein. Namely, we provide an
intuitive understanding of the state-of-the-art random matrix theory tools used
to derive our results. In particular, for our analysis we require information
about macroscopic, mesoscopic and microscopic statistics of eigenvalues of
random matrices which we highlight here. Furthermore, we provide numerical
simulations that corroborate our analytical findings and extend this notion of
mixing from simple graphs to any ergodic, reversible, Markov chain.Comment: The section concerning time-averaged mixing (Sec VIII) has been
updated: Now contains numerical plots and an intuitive discussion on the
random matrix theory results used to derive the results of arXiv:2001.0630
Efficiency of the EmERGE Pathway of Care in Five European HIV Centres
Objective: We aimed to calculate the efficiency of the EmERGE Pathway of Care in five European HIV clinics, developed and implemented for medically stable people living with HIV.
Methods: Participants were followed up for 1 year before and after implementation of EmERGE, between April 2016 and October 2019. Micro-costing studies were performed in the outpatient services of the clinics. Unit costs for outpatient services were calculated in national currencies and converted to US purchasing parity prices. Primary and secondary outcome measures of participants did not change during the study.
Conclusions: EmERGE is acceptable and provided cost savings in different socio-economic settings. Antiretroviral drug costs remain the main cost drivers in medically stable people living with HIV. While antiretroviral drug prices in local currencies did not differ that much between countries, conversion to US$ purchasing parity prices revealed antiretroviral drugs were more expensive in the least wealthy countries. This needs to be taken into consideration when countries negotiate drug prices with pharmaceutical vendors. Greater efficiencies can be anticipated by extending the use of the EmERGE Pathway to people with complex HIV infection or other chronic diseases. Extending such use should be systematically monitored, implementation should be evaluated and funding should be provided to monitor and evaluate future changes in service provision.info:eu-repo/semantics/publishedVersio
Tropical Peatland Hydrology Simulated With a Global Land Surface Model
Tropical peatlands are among the most carbon-dense ecosystems on Earth, and their water storage dynamics strongly control these carbon stocks. The hydrological functioning of tropical peatlands differs from that of northern peatlands, which has not yet been accounted for in global land surface models (LSMs). Here, we integrated tropical peat-specific hydrology modules into a global LSM for the first time, by utilizing the peatland-specific model structure adaptation (PEATCLSM) of the NASA Catchment Land Surface Model (CLSM). We developed literature-based parameter sets for natural (PEATCLSM(Trop,Nat)) and drained (PEATCLSM(Trop,Drain)) tropical peatlands. Simulations with PEATCLSM(Trop,Nat) were compared against those with the default CLSM version and the northern version of PEATCLSM (PEATCLSM(North,Nat)) with tropical vegetation input. All simulations were forced with global meteorological reanalysis input data for the major tropical peatland regions in Central and South America, the Congo Basin, and Southeast Asia. The evaluation against a unique and extensive data set of in situ water level and eddy covariance-derived evapotranspiration showed an overall improvement in bias and correlation compared to the default CLSM version. Over Southeast Asia, an additional simulation with PEATCLSM(Trop,Drain) was run to address the large fraction of drained tropical peatlands in this region. PEATCLSM(Trop,Drain) outperformed CLSM, PEATCLSM(North,Nat), and PEATCLSM(Trop,Nat) over drained sites. Despite the overall improvements of PEATCLSM(Trop,Nat) over CLSM, there are strong differences in performance between the three study regions. We attribute these performance differences to regional differences in accuracy of meteorological forcing data, and differences in peatland hydrologic response that are not yet captured by our model.Peer reviewe
Quality of life in Maltese Adults with Congenital Heart Disease : a Second Look – An APPROACH-IS Substudy
Background
A first quality of life (QOL) study among Maltese adults with congenital heart disease (ACHD) in 2016 found no significant differences when compared to the general population. The aims of the present study were to (1) compare QOL between Maltese and other European ACHD patients and (2) investigate medical predictors (i.e. number of surgical/non-surgical interventions, heart failure, arrhythmias, pacemaker/implantable cardioverter-defibrillator, cardiac hospitalisation during preceding year, follow-up frequency, other medical conditions, mood/anxiety/psychiatric disorders) of QOL in Maltese patients.
Methods
Data collected during \u201cAssessment of Patterns of Patient-Reported Outcomes in Adults with Congenital Heart disease\u2013International Study\u201d (APPROACH-IS) was used. QOL was measured using linear analog scale (LAS) and Satisfaction With Life Scale (SWLS). QOL in 109 Maltese and 1510 European participants was compared. Multivariable logistic regression was used to test the predictive value of medical factors on QOL in Maltese patients.
Results
There were no significant differences in QOL between the two cohorts [mean LAS Malta 80.51 (95% CI 77.96,83.07) vs. European 79.43 (95% CI 78.65,80.21) (p=0.776); mean SWLS Malta 26.00 (95% CI 24.94,27.06) vs. European 26.26 (95% CI 25.95,26.57) (p=0.288)] and no significant differences when cohorts were divided by gender and age. Only a mood/anxiety/other psychiatric disorder significantly predicted poorer QOL on both scales in Maltese patients (LAS (
f=-.389, p<0.001), SWLS (
f=-.352, p=0.001)).
Conclusions
Maltese ACHD patients have a good QOL comparable to that of European counterparts. Mood, anxiety and other psychiatric
disorders can negatively impact Maltese patients\u2019 QOL. Better access to clinical psychology services should be ensured
- …