198 research outputs found
A distributed directory scheme for information access in mobile computers
In this paper, we discuss the design aspects of a dynamic distributed directory scheme (DDS) to facilitate efficient and transparent access to information files in mobile environments. The proposed directory interface enables users of mobile computers to view a distributed file system on a network of computers as a globally shared file system. In order to counter some of the limitations of wireless communications, we propose improvised invalidation schemes that avoid false sharing and ensure uninterrupted usage under disconnected and low bandwidth conditions
BatchRank: A Novel Batch Mode Active Learning Framework for Hierarchical Classification
Active learning algorithms automatically identify the salient
and exemplar instances from large amounts of unlabeled
data and thus reduce human annotation effort in inducing
a classification model. More recently, Batch Mode Active
Learning (BMAL) techniques have been proposed, where a
batch of data samples is selected simultaneously from an un-
labeled set. Most active learning algorithms assume a
at
label space, that is, they consider the class labels to be in-
dependent. However, in many applications, the set of class
labels are organized in a hierarchical tree structure, with
the leaf nodes as outputs and the internal nodes as clusters
of outputs at multiple levels of granularity. In this paper,
we propose a novel BMAL algorithm (BatchRank) for hi-
erarchical classification. The sample selection is posed as
an NP-hard integer quadratic programming problem and a
convex relaxation (based on linear programming) is derived,
whose solution is further improved by an iterative truncated
power method. Finally, a deterministic bound is established
on the quality of the solution. Our empirical results on sev-
eral challenging, real-world datasets from multiple domains,
corroborate the potential of the proposed framework for real-
world hierarchical classification applications
Adaptive gene regulatory networks
Regulatory interactions between genes show a large amount of cross-species
variability, even when the underlying functions are conserved: There are many
ways to achieve the same function. Here we investigate the ability of
regulatory networks to reproduce given expression levels within a simple model
of gene regulation. We find an exponentially large space of regulatory networks
compatible with a given set of expression levels, giving rise to an extensive
entropy of networks. Typical realisations of regulatory networks are found to
share a bias towards symmetric interactions, in line with empirical evidence.Comment: 5 pages RevTe
The Human Cytomegalovirus Chemokine vCXCL-1 Modulates Normal Dissemination Kinetics of Murine Cytomegalovirus In Vivo
Human cytomegalovirus (HCMV) is a betaherpesvirus that is a significant pathogen within newborn and immunocompromised populations. Morbidity associated with HCMV infection is the consequence of viral dissemination. HCMV has evolved to manipulate the host immune system to enhance viral dissemination and ensure long-term survival within the host. The immunomodulatory protein vCXCL-1, a viral chemokine functioning primarily through the CXCR2 chemokine receptor, is hypothesized to attract CXCR2+ neutrophils to infection sites, aiding viral dissemination. Neutrophils harbor HCMV in vivo; however, the interaction between vCXCL-1 and the neutrophil has not been evaluated in vivo. Using the mouse model and mouse cytomegalovirus (MCMV) infection, we show that murine neutrophils harbor and transfer infectious MCMV and that virus replication initiates within this cell type. Utilizing recombinant MCMVs expressing vCXCL-1 from the HCMV strain (Toledo), we demonstrated that vCXCL-1 significantly enhances MCMV dissemination kinetics. Through cellular depletion experiments, we observe that neutrophils impact dissemination but that overall dissemination is largely neutrophil independent. This work adds neutrophils to the list of innate cells (i.e., dendritic and macrophages/monocytes) that contribute to MCMV dissemination but refutes the hypothesis that neutrophils are the primary cell responding to vCXCL-1
If cooperation is likely punish mildly: Insights from economic experiments based on the snowdrift game
Punishment may deter antisocial behavior. Yet to punish is costly, and the
costs often do not offset the gains that are due to elevated levels of
cooperation. However, the effectiveness of punishment depends not only on how
costly it is, but also on the circumstances defining the social dilemma. Using
the snowdrift game as the basis, we have conducted a series of economic
experiments to determine whether severe punishment is more effective than mild
punishment. We have observed that severe punishment is not necessarily more
effective, even if the cost of punishment is identical in both cases. The
benefits of severe punishment become evident only under extremely adverse
conditions, when to cooperate is highly improbable in the absence of sanctions.
If cooperation is likely, mild punishment is not less effective and leads to
higher average payoffs, and is thus the much preferred alternative. Presented
results suggest that the positive effects of punishment stem not only from
imposed fines, but may also have a psychological background. Small fines can do
wonders in motivating us to chose cooperation over defection, but without the
paralyzing effect that may be brought about by large fines. The later should be
utilized only when absolutely necessary.Comment: 15 pages, 6 figures; accepted for publication in PLoS ON
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Microstructural characterization of high energy product Nd-Fe-B rapidly solidified ribbons
The bonded Nd-Fe-B market has experienced the fastest growth of any permanent magnet market. Rapidly solidified Nd-Fe-B forms the basis for this bonded magnet industry. Rapid solidification is carried out by melt spinning, producing a highly stable and magnetically hard microstructure. This study focuses on a microstructural analysis of this melt spun ribbon using transmission and scanning electron microscopy (TEM and SEM), atom probe field ion microscopy (APFIM) and Auger electron spectroscopy (AES). The ribbons showed a uniform grain size and shape distribution through the thickness of the melt spun ribbon. Grain sizes ranged from 20 to 40 nm. AES showed neodymium enrichment on a fracture surface and corresponding iron and boron depletion suggesting that the eutectic 70Nd-30Fe phase is present with a thickness of approximately 1 nm. Atom probe composition analysis of grain interiors gave results very close to the nominal composition and some preliminary evidence of a grain boundary phase
If players are sparse social dilemmas are too: Importance of percolation for evolution of cooperation
Spatial reciprocity is a well known tour de force of cooperation promotion. A
thorough understanding of the effects of different population densities is
therefore crucial. Here we study the evolution of cooperation in social
dilemmas on different interaction graphs with a certain fraction of vacant
nodes. We find that sparsity may favor the resolution of social dilemmas,
especially if the population density is close to the percolation threshold of
the underlying graph. Regardless of the type of the governing social dilemma as
well as particularities of the interaction graph, we show that under pairwise
imitation the percolation threshold is a universal indicator of how dense the
occupancy ought to be for cooperation to be optimally promoted. We also
demonstrate that myopic updating, due to the lack of efficient spread of
information via imitation, renders the reported mechanism dysfunctional, which
in turn further strengthens its foundations.Comment: 6 two-column pages, 5 figures; accepted for publication in Scientific
Reports [related work available at http://arxiv.org/abs/1205.0541
Sustainable institutionalized punishment requires elimination of second-order free-riders
Although empirical and theoretical studies affirm that punishment can elevate
collaborative efforts, its emergence and stability remain elusive. By
peer-punishment the sanctioning is something an individual elects to do
depending on the strategies in its neighborhood. The consequences of
unsustainable efforts are therefore local. By pool-punishment, on the other
hand, where resources for sanctioning are committed in advance and at large,
the notion of sustainability has greater significance. In a population with
free-riders, punishers must be strong in numbers to keep the "punishment pool"
from emptying. Failure to do so renders the concept of institutionalized
sanctioning futile. We show that pool-punishment in structured populations is
sustainable, but only if second-order free-riders are sanctioned as well, and
to a such degree that they cannot prevail. A discontinuous phase transition
leads to an outbreak of sustainability when punishers subvert second-order
free-riders in the competition against defectors.Comment: 7 two-column pages, 3 figures; accepted for publication in Scientific
Report
Benevolent characteristics promote cooperative behaviour among humans
Cooperation is fundamental to the evolution of human society. We regularly
observe cooperative behaviour in everyday life and in controlled experiments
with anonymous people, even though standard economic models predict that they
should deviate from the collective interest and act so as to maximise their own
individual payoff. However, there is typically heterogeneity across subjects:
some may cooperate, while others may not. Since individual factors promoting
cooperation could be used by institutions to indirectly prime cooperation, this
heterogeneity raises the important question of who these cooperators are. We
have conducted a series of experiments to study whether benevolence, defined as
a unilateral act of paying a cost to increase the welfare of someone else
beyond one's own, is related to cooperation in a subsequent one-shot anonymous
Prisoner's dilemma. Contrary to the predictions of the widely used inequity
aversion models, we find that benevolence does exist and a large majority of
people behave this way. We also find benevolence to be correlated with
cooperative behaviour. Finally, we show a causal link between benevolence and
cooperation: priming people to think positively about benevolent behaviour
makes them significantly more cooperative than priming them to think
malevolently. Thus benevolent people exist and cooperate more
Surface Tension of Seawater
New measurements and a reference correlation for the surface tension of seawater at atmospheric pressure are presented in this paper. Surface tension of seawater was measured across a salinity range of 20 ⩽ S ⩽ 131 g/kg and a temperature range of 1 ⩽ t ⩽ 92 °C at atmospheric pressure using the Wilhelmy plate method. The uncertainty within measurements varied from 0.18 to 0.37 mN/m with the average uncertainty being 0.22 mN/m. The experimental procedures were validated with tests conducted on ACS reagent grade water and aqueous sodium chloride solutions. Literature data and present measurements were evaluated and a reference correlation was developed expressing surface tension of seawater as a function of temperature and salinity. The average absolute percentage deviation between measurements and the correlation was 0.19% while the maximum deviation was 0.60%.Center for Clean Water and Clean Energy at MIT and KFUPM (Project R13-CW-10
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