5,528 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
Universality of dispersive spin-resonance mode in superconducting BaFe2As2
Spin fluctuations in superconducting BaFe2(As1-xPx)2 (x=0.34, Tc = 29.5 K)
are studied using inelastic neutron scattering. Well-defined commensurate
magnetic signals are observed at ({\pi},0), which is consistent with the
nesting vector of the Fermi surface. Antiferromagnetic (AFM) spin fluctuations
in the normal state exhibit a three-dimensional character reminiscent of the
AFM order in nondoped BaFe2As2. A clear spin gap is observed in the
superconducting phase forming a peak whose energy is significantly dispersed
along the c-axis. The bandwidth of dispersion becomes larger with approaching
the AFM ordered phase universally in all superconducting BaFe2As2, indicating
that the dispersive feature is attributed to three-dimensional AFM
correlations. The results suggest a strong relationship between the magnetism
and superconductivity.Comment: 5 pages, 5 figure
Local magnetic anisotropy in BaFeAs: a polarized inelastic neutron scattering study
The anisotropy of the magnetic excitations in BaFeAs was studied by
polarized inelastic neutron scattering which allows one to separate the
components of the magnetic response. Despite the in-plane orientation of the
static ordered moment we find the in-plane polarized magnons to exhibit a
larger gap than the out-of-plane polarized ones indicating very strong
single-ion anisotropy within the layers. It costs more energy to rotate a spin
within the orthorhombic {\it a-b} plane than rotating it perpendicular to the
FeAs layers.Comment: 4 pages, 4 figure
Recommended from our members
Combined Banzhaf & Diversity Index (CBDI) for critical node detection
Critical node discovery plays a vital role in assessing the vulnerability of a computer network to malicious attacks and failures and provides a useful tool with which one can greatly improve network security and reliability. In this paper, we propose a new metric to characterize the criticality of a node in an arbitrary computer network which we refer to as the Combined Banzhaf & Diversity Index (CBDI). The metric utilizes a diversity index which is based on the variability of a node׳s attributes relative to its neighbours and the Banzhaf power index which characterizes the degree of participation of a node in forming shortest paths. The Banzhaf power index is inspired from the theory of voting games in game theory. The proposed metric is evaluated using analysis and simulations. The criticality of nodes in a network is assessed based on the degradation in network performance achieved when these nodes are removed. We use several performance metrics to evaluate network performance including the algebraic connectivity which is a spectral metric characterizing the connectivity robustness of the network. Extensive simulations in a number of network topologies indicate that the proposed CBDI index chooses more critical nodes which, when removed, degrade network performance to a greater extent than if critical nodes based on other criticality metrics were removed
Recommended from our members
Spectral Partitioning for Node Criticality
Finding critical nodes in a network is a significant task, highly relevant to network vulnerability and security. We consider the node criticality problem as an algebraic connectivity minimization problem where the objective is to choose nodes which minimize the algebraic connectivity of the resulting network. Previous suboptimal solutions of the problem suffer from the computational complexity associated with the implementation of a maximization consensus algorithm. In this work, we use spectral partitioning concepts introduced by Fiedler, to propose a new suboptimal solution which significantly reduces the implementation complexity. Our approach, combined with recently proposed distributed Fiedler vector calculation algorithms enable each node to decide by itself whether it is a critical node. If a single node is required then the maximization algorithm is applied on a restricted set of nodes within the network. We derive a lower bound for the achievable algebraic connectivity when nodes are removed from the network and we show through simulations that our approach leads to algebraic connectivity values close to this lower bound. Similar behaviour is exhibited by other approaches at the expense, however, of a higher implementation complexity
Conditions of Teaching and Research in Economics: Some Preliminary Findings
This paper reports onthe preliminary findings of a study
initiated two years ago, at the initiative of the P.LD.E. to review the
problems of teaching and research in economics and related subjects
(ERS)! during the last two decades. The need for such a study has been
felt for some time not only because of the common perception of
declining standards in higher education generally and, economics, in
particular, but also from the perceived competition economics has faced
from other disciplines, especially business studies and computer science
as a passport to the job market. After having enjoyed a relatively
robust period of growth in the 1960s largely through the assistance of
foreign donors such as the Ford Foundation, ERS in Pakistan have
suffered in their development not only from the comparative paucity of
resources allocated to them, but also as a result of an adverse change
in the perceptions about the primacy of their usefulness for policy
purposes. The demand for economics has also suffered some decline as a
result of the diminished importance of the public sector and of planned
development during the last two decades. While special branches of
economics, such as finance, project evaluation, transport and energy
economics have shown increased demand, mainly in the private sector or
donor-related institutions, the demand for general economic analysts is
not as strong as in the past and does not provide many gainful
opportunities for professional advancement. Due to the continued
disadvantage in terms of salaries and other rewards, the academic
profession, remains unattractive
Client Satisfaction Towards Quality of Health Services: an Assessment at Primary Healthcare of District Gujranwala
This survey designed to evaluate the satisfaction level and the factors that affect the patient satisfaction regarding health care delivery services with the aim to improve the services in the primary health care settings of Gujranwala. A Cross Sectional Study done on randomly selected patients attending the basic health units of Gujranwala, with more than18 years of age. Pretested structured "Liker scale questionnaire" was used for data collection. Out of total respondents, 62 (41.3%) clients were satisfied with the services provided by the basic health units of Gujranwala. The factors identified to determine patient satisfaction were accessibility of services, behavior of staff, health education, level of cleanliness, drug availability and miscellaneous services. Not a single ranked area of satisfaction noticed. Client\u27s occupation and income had significant relationship with the patient satisfaction level. Gender, age, and education of clients were not contributing factors; they not affect the client satisfaction level.Less than half clients were satisfied with the services provided by the basic health units. Management of health facilities needs to improve the services
AEGRP: an enhanced geographical routing protocol for vanet
Vehicular ad hoc network (VANET), is a derivative type of mobile ad hoc networks with its unique characteristics and an essential part of intelligent transportation system (ITS). In VANET, the vehicles can disseminate information to certain or all vehicles within a region for different applications. Applications can be categorized as safety, convenience and comfort of the driver and passengers such as traffic conditions, accident detection, roadway safety, mobile sensing, and infotainment. These promising applications require intelligent and efficient routing protocols, which are capable of adapting rapidly changing topologies, high mobility in the network. Geographic routing protocols have become a popular routing type because of its simplicity and low overhead features, but recent research has recognized these protocols are not considering many particular constraints of the vehicular environment. However, existing routing protocols offered limited performance due to frequent disconnectivity, high signal interference in the presence of obstacles and lead to network delay and overhead issues. The main objective of this paper is to design an enhanced geographical routing protocol that addresses the network delay problems and provide necessary improvements over conventional geographic routing in light of constraints of these environments
Recommended from our members
Adding the reliability on tree based topology construction algorithms for wireless sensor networks
Topology control is a technique used in wireless sensor networks to maximize energy efficiency and network lifetime. In previous literature, many tree based techniques have been proposed to save energy and increase the network lifetime. In tree based algorithms, the most promising solution is the formation of a network backbone, which serves on behalf of rest of the nodes in the network and therefore leading towards Connected Dominating Set (CDS) formulation. However, one imminent problem with all tree based solution is a compromise on network reliability. Therefore, to address reliability issues in tree based solutions, in this paper, we propose Poly3 which maintains cliques of size three in order to achieve network reliability on top of the CDS algorithm. This makes the network more robust to link removal. Our empirical and mathematical analysis reveals that Poly3 provides better reliability than algorithms of the same kind
- …