27,112 research outputs found
Write-limited sorts and joins for persistent memory
To mitigate the impact of the widening gap between the memory needs of CPUs and what standard memory technology can deliver, system architects have introduced a new class of memory technology termed persistent memory. Persistent memory is byteaddressable, but exhibits asymmetric I/O: writes are typically one order of magnitude more expensive than reads. Byte addressability combined with I/O asymmetry render the performance profile of persistent memory unique. Thus, it becomes imperative to find new ways to seamlessly incorporate it into database systems. We do so in the context of query processing. We focus on the fundamental operations of sort and join processing. We introduce the notion of write-limited algorithms that effectively minimize the I/O cost. We give a high-level API that enables the system to dynamically optimize the workflow of the algorithms; or, alternatively, allows the developer to tune the write profile of the algorithms. We present four different techniques to incorporate persistent memory into the database processing stack in light of this API. We have implemented and extensively evaluated all our proposals. Our results show that the algorithms deliver on their promise of I/O-minimality and tunable performance. We showcase the merits and deficiencies of each implementation technique, thus taking a solid first step towards incorporating persistent memory into query processing. 1
Stability of Influence Maximization
The present article serves as an erratum to our paper of the same title,
which was presented and published in the KDD 2014 conference. In that article,
we claimed falsely that the objective function defined in Section 1.4 is
non-monotone submodular. We are deeply indebted to Debmalya Mandal, Jean
Pouget-Abadie and Yaron Singer for bringing to our attention a counter-example
to that claim.
Subsequent to becoming aware of the counter-example, we have shown that the
objective function is in fact NP-hard to approximate to within a factor of
for any .
In an attempt to fix the record, the present article combines the problem
motivation, models, and experimental results sections from the original
incorrect article with the new hardness result. We would like readers to only
cite and use this version (which will remain an unpublished note) instead of
the incorrect conference version.Comment: Erratum of Paper "Stability of Influence Maximization" which was
presented and published in the KDD1
Zika Virus: Can Artificial Contraception Be Condoned?
As the Zika virus pandemic continues to bring worry and fear to health officials and medical scientists, Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) have recommended that residents of the Zika-infected countries, e.g., Brazil, and those who have traveled to the area should delay having babies which may involve artificial contraceptive, particularly condom. This preventive policy, however, is seemingly at odds with the Roman Catholic Churchâs position on the contraceptive. As least since the promulgation of Paul VIâs 1968 encyclical, Humanae Vitae, the Church has explicitly condemned artificial birth control as intrinsic evil. However, the current pontiff, Pope Francis, during his recent visit to Latin America, remarked that the use of artificial contraception may not be in contradiction to the teaching of Humanae Vitae while drawing a parallel between the current Zika Crisis and the 1960âs Belgian Congo Nun Controversy. The pope mentioned that the traditional ethical principle of the lesser of two evils may be the doctrine that justified the exceptions. The authors of this paper attempt to expand the theological rationale of the popeâs suggestion. In so doing, the authors rely on casuistical reasoning as an analytic tool that compares the Belgian Congo Nun case and the given Zika case, and suggest that the former is highly similar to, if not the same as, the latter in terms of normative moral feature. That is, in both cases the use of artificial contraception is theologically justified in reference to the criteria that the doctrine of the lesser of two evils requires. The authors wish that the paper would provide a solid theological-ethical ground based on which condom-use as the most immediate and effective preventive measure can be recommended in numerous Catholic hospitals as well as among Catholic communities in the world, particularly the most Zika-affected and largest Catholic community in the world, Brazil â 123 million present Brazilian citizens are reported to be Roman Catholic
Multi giant graviton systems, SUSY breaking and CFT
In this article, we describe giant gravitons in AdS_5 x S^5 moving along
generic trajectories in AdS_5. The giant graviton dynamics is solved by proving
that the D3-brane effective action reduces to that of a massive point particle
in AdS_5 and therefore the solutions are in one to one correspondence with
timelike geodesics of AdS_5. All these configurations are related via
isometries of the background, which induce target space symmetries in the world
volume theory of the D-brane. Hence, all these configurations preserve the same
amount of supersymmetry as the original giant graviton, i.e. half of the
maximal supersymmetry. Multiparticle configurations of two or more giant
gravitons are also considered. In particular, a binary system preserving one
quarter of the supersymmetries is found, providing a non trivial time-dependent
supersymmetric solution. A short study on the dual CFT description of all the
above states is given, including a derivation of the exact induced isometry map
in the CFT side of the correspondence.Comment: latex, 27+1 pages. v2: comment on mixing of states in section 4.3
added, reference added, typos corrected, final versio
Measuring Integration and Efficiency in Maize Grain Markets: The Case of South Africa and Mozambique
Price transmission between the South African market and other regional markets is not as straightforward, despite South Africaâs role of a surplus producer for the region. There appears to be a host of local factors that must be taken into account in order to anticipate the likely level of regional food prices. This article assesses the degree of market integration and the speed of price adjustment to spatial price differentials between the SAFEX maize price in South Africa and maize grain and maize meal prices in Maputo, Mozambique. The findings of this study indicate that under certain trading regimes, there is no evidence of a long-run relationship between Mozambican and South African maize grain prices. This implies that any large deviations, within these regimes, which exceed transaction costs, could continue to grow with no tendency towards equilibrium. However, the trade volume data indicates maize grain exports from South Africa into Mozambique in every month except for three within the sample set. Hence, the empirical findings of this paper are unexpected given a simple arbitrage argument. Possible reasons for these findings are highlighted in the article. It is interesting to note that when the same empirical analysis is undertaken for the SAFEX maize prices and maize meal prices in Maputo then there is in fact evidence of a long-run relationship between these prices in a high import regime. These findings are not surprising and are what we would expect since two of the largest milling companies, located in Maputo are responsible for the majority of the volume of maize grain imported into the country from South Africa.price transmission, market integration, cointegration, trade regimes, Crop Production/Industries,
Digesting the Message about Contaminants and Country Foods in the Canadian North: A Review and Recommendations for Future Research and Action
Communicating the risks of environmental contaminants in the food chain to northern Aboriginal peoples poses significant challenges for communities at risk and environment and health professionals alike. Reported results of poor risk communication practice on this issue include increased fear and confusion in northern communities, changes in the dietary behaviour and traditional lifestyles of their residents, and associated impacts on their society, economy, and health. A review of past communication research and activities on this issue in the Canadian North reveals a general ad hoc âlearning by doingâ approach to primarily one-way communication events. The lack of focused communication research on an issue that has garnered great focus and effort elsewhere in the country and continent has forced health professionals and communicators to rely on assumptions about the reception and level of comprehension of important health messages previously disseminated. The importance of this information is increasing as research begins to detect subtle health effects from exposure to these substances among newborns in some northern regions. Thus planning and evaluation are needed for risk communication, and possibly changes to the scale at which communication work is done in northern communities.Le fait dâinformer les peuples autochtones du Nord des risques associĂ©s Ă la prĂ©sence de contaminants de lâenvironnement dans la chaĂźne alimentaire pose un dĂ©fi de taille pour les collectivitĂ©s exposĂ©es Ă ces risques, tout comme pour les professionnels de lâenvironnement et de la santĂ©. Les rĂ©sultats dĂ©jĂ rapportĂ©s dâune piĂštre pratique de divulgation des risques sur cette question mentionnent une augmentation de la peur et de la confusion dans les collectivitĂ©s nordiques, des changements dans le comportement alimentaire et le style de vie traditionnel des rĂ©sidents, et les impacts qui en rĂ©sultent sur leur sociĂ©tĂ©, leur Ă©conomie et leur santĂ©. Un examen de la recherche en communications et des activitĂ©s de divulgation antĂ©rieures sur cette question dans le Nord rĂ©vĂšle que la communication est principalement unilatĂ©rale et se fait de façon improvisĂ©e sur le tas. Le manque dâune recherche en communications bien ciblĂ©e, sur une question ayant pris beaucoup dâampleur et donnĂ© lieu Ă une importante mobilisation ailleurs Ă lâĂ©chelle du pays et du continent, ce manque donc a obligĂ© les professionnels de la santĂ© et les spĂ©cialistes en communications dans le domaine Ă se fier Ă des hypothĂšses quant Ă la rĂ©ception et au niveau de comprĂ©hension dâimportants messages relatifs Ă la santĂ© diffusĂ©s antĂ©rieurement. Cette information acquiert de plus en plus dâimportance Ă mesure que la recherche commence Ă dĂ©tecter des effets tĂ©nus sur la santĂ© dus Ă une exposition Ă ces contaminants chez les nouveau-nĂ©s dans certaines rĂ©gions du Nord. Il faut donc procĂ©der Ă une planification et Ă une Ă©valuation de la divulgation des risques, voire Ă des changements dans lâĂ©chelle Ă laquelle sâeffectue la communication dans les collectivitĂ©s du Nord
signals at LEP2 energies in the Minimal Supersymmetric Standard Model
In this paper we compare and into four-fermion production
at centre-of-mass energies typical of LEP2 and somewhat larger. The theoretical
framework considered is the Minimal Supersymmetric Standard Model. The interest
in exploiting the CERN collider at values of greater than
192 GeV could come from the discovery of Supersymmetric signals during runs at
lower energy. If these indicate that a charged Higgs boson exists in the mass
range \MH\approx95-105 GeV, then a few years of running at
GeV and nominal luminosity could make the detection of such scalars feasible,
in the purely leptonic channel and, for small
\tb's, also in the semi-hadronic(leptonic) one . Charged
Higgs bosons of the above nature cannot be produced by the beam energies
approved at present for LEP2. However, if runs beyond the so-called `192 GeV
cryogenic limit' will be approved by the CERN Council, our selection procedure
will enable us to establish the presence, or otherwise, of charged Higgs bosons
in the mentioned mass rangeComment: 30 pages, latex, epsfig, 12 postscript figures, complete paper
available at ftp://axpa.hep.phy.cam.ac.uk/stefano/cavendish_9615 and at
http://www.hep.phy.cam.ac.uk/theory/papers
Quality engineering of a traction alternator by robust design
Robust design is an engineering methodology for improving productivity during research and development so that high-quality products can be developed and produced quickly and at low cost. A large electrical company was developing traction alternators for a diesel electrical engine. Customer requirement was to obtain very high efficiency which, in turn, was influenced by several design parameters. The usual approach of the 'design-build-test' cycle was considered time-consuming and costly; it used to take anywhere from 4 months to 1 year before finalizing the product design parameters as it involved physical assembly and also testing. Instead, the authors used Taguchi's parameter design approach. This approach took about 8 weeks to arrive at optimum design parameter values; clearly demonstrating the cutting edge of this methodology over the traditional design-build-test approach. The prototype built and tested accordingly gave satisfactory overall performance, meeting and even exceeding customer requirements
Finite energy/action solutions of Yang-Mills equations on Schwarzschild and deSitter backgrounds for dimension
Physically relevant gauge and gravitational theories can be seen as special
members of hierarchies of more elaborate systems. The Yang-Mills (YM) system is
the first member of a hierarchy of Lagrangians which we will index by ,
and the Einstein-Hilbert (EH) system of general relativity is the first member
of another hierarchy which we index by . In this paper, we study the
classical equations of the YM hierarchy considered in the
background of special geometries (Schwarzschild, deSitter,anti-deSitter) of the
EH hierarchy. Solutions are obtained in various dimensions and lead
to several examples of non-self-dual YM fields. When self-dual
solutions exist in addition. Their action is equal to the Chern-Pontryagin
charge and can be compared with that of the non-self-dual solutions.Comment: LaTeX, 25 pages, 2 figures, new title, minor change
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