133 research outputs found
Deductive synthesis of recursive plans in linear logic
Linear logic has previously been shown to be suitable for describing and deductively solving planning problems involving conjunction and disjunction. We introduce a recursively defined datatype and a corresponding induction rule, thereby allowing recursive plans to be synthesised. In order to make explicit the relationship between proofs and plans, we enhance the linear logic deduction rules to handle plans as a form of proof term
Hydrosomes: femtoliter containers for fluorescence spectroscopy studies
We report on improvements and innovations in the use of hydrosomes to encapsulate and study single molecules. Hydrosomes are optically-trappable aqueous nanodroplets. The droplets are suspended in a fluorocarbon medium that is immiscible with water and has an index of refraction lower than water, so hydrosomes are stable and optically trapped by a focused laser beam (optical tweezers). Using optical tweezers, we hold the hydrosomes within a confocal observation volume and interrogate the encapsulated molecule by fluorescence excitation. This method allows for long observation times of a molecule without the need for surface immobilization or liposome encapsulation. We have developed a new way for creating hydrosomes on demand by inertially launching them into the fluorocarbon matrix using a piezo-activated micropipette. Time-resolved fluorescence anisotropy studies are carried out to characterize the effects of the hydrosome interface boundary on biological molecules and to determine whether molecules encapsulated within hydrosomes diffuse freely throughout the available volume. We measured the fluorescence anisotropy decay of 20mer DNA duplexes, and enhanced green fluorescent protein (GFP). We conclude that the molecules rotate freely inside the nanodroplets and do not stick or aggregate at the boundary
Hydrosomes: femtoliter containers for fluorescence spectroscopy studies
We report on improvements and innovations in the use of hydrosomes to encapsulate and study single molecules. Hydrosomes are optically-trappable aqueous nanodroplets. The droplets are suspended in a fluorocarbon medium that is immiscible with water and has an index of refraction lower than water, so hydrosomes are stable and optically trapped by a focused laser beam (optical tweezers). Using optical tweezers, we hold the hydrosomes within a confocal observation volume and interrogate the encapsulated molecule by fluorescence excitation. This method allows for long observation times of a molecule without the need for surface immobilization or liposome encapsulation. We have developed a new way for creating hydrosomes on demand by inertially launching them into the fluorocarbon matrix using a piezo-activated micropipette. Time-resolved fluorescence anisotropy studies are carried out to characterize the effects of the hydrosome interface boundary on biological molecules and to determine whether molecules encapsulated within hydrosomes diffuse freely throughout the available volume. We measured the fluorescence anisotropy decay of 20mer DNA duplexes, and enhanced green fluorescent protein (GFP). We conclude that the molecules rotate freely inside the nanodroplets and do not stick or aggregate at the boundary
Structural Properties of Ego Networks
The structure of real-world social networks in large part determines the
evolution of social phenomena, including opinion formation, diffusion of
information and influence, and the spread of disease. Globally, network
structure is characterized by features such as degree distribution, degree
assortativity, and clustering coefficient. However, information about global
structure is usually not available to each vertex. Instead, each vertex's
knowledge is generally limited to the locally observable portion of the network
consisting of the subgraph over its immediate neighbors. Such subgraphs, known
as ego networks, have properties that can differ substantially from those of
the global network. In this paper, we study the structural properties of ego
networks and show how they relate to the global properties of networks from
which they are derived. Through empirical comparisons and mathematical
derivations, we show that structural features, similar to static attributes,
suffer from paradoxes. We quantify the differences between global information
about network structure and local estimates. This knowledge allows us to better
identify and correct the biases arising from incomplete local information.Comment: Accepted by SBP 2015, to appear in the proceeding
Evidence for ambient dark aqueous SOA formation in the Po Valley, Italy
Laboratory experiments suggest that water-soluble products from the gas-phase oxidation of volatile organic compounds can partition into atmospheric waters where they are further oxidized to form low volatility products, providing an alternative route for oxidation in addition to further oxidation in the gas phase. These products can remain in the particle phase after water evaporation, forming what is termed as aqueous secondary organic aerosol (aqSOA). However, few studies have attempted to observe ambient aqSOA. Therefore, a suite of measurements, including near-real-time WSOC (water-soluble organic carbon), inorganic anions/cations, organic acids, and gas-phase glyoxal, were made during the PEGASOS (Pan-European Gas-AeroSOls-climate interaction Study) 2012 campaign in the Po Valley, Italy, to search for evidence of aqSOA. Our analysis focused on four periods: Period A on 19–21 June, Period B on 30 June and 1–2 July, Period C on 3–5 July, and Period D on 6–7 July to represent the first (Period A) and second (Periods B, C, and D) halves of the study. These periods were picked to cover varying levels of WSOC and aerosol liquid water. In addition, back trajectory analysis suggested all sites sampled similar air masses on a given day. The data collected during both periods were divided into times of increasing relative humidity (RH) and decreasing RH, with the aim of diminishing the influence of dilution and mixing on SOA concentrations and other measured variables. Evidence for local aqSOA formation was only observed during Period A. When this occurred, there was a correlation of WSOC with organic aerosol (R2 = 0.84), aerosol liquid water (R2 = 0.65), RH (R2 = 0.39), and aerosol nitrate (R2 = 0.66). Additionally, this was only observed during times of increasing RH, which coincided with dark conditions. Comparisons of WSOC with oxygenated organic aerosol (OOA) factors, determined from application of positive matrix factorization analysis on the aerosol mass spectrometer observations of the submicron non-refractory organic particle composition, suggested that the WSOC differed in the two halves of the study (Period A WSOC vs. OOA-2 R2 = 0.83 and OOA-4 R2 = 0.04, whereas Period C WSOC vs. OOA-2 R2 = 0.03 and OOA-4 R2 = 0.64). OOA-2 had a high O ∕ C (oxygen ∕ carbon) ratio of 0.77, providing evidence that aqueous processing was occurring during Period A. Key factors of local aqSOA production during Period A appear to include air mass stagnation, which allows aqSOA precursors to accumulate in the region; the formation of substantial local particulate nitrate during the overnight hours, which enhances water uptake by the aerosol; and the presence of significant amounts of ammonia, which may contribute to ammonium nitrate formation and subsequent water uptake and/or play a more direct role in the aqSOA chemistry
Model Selection for Degree-corrected Block Models
The proliferation of models for networks raises challenging problems of model
selection: the data are sparse and globally dependent, and models are typically
high-dimensional and have large numbers of latent variables. Together, these
issues mean that the usual model-selection criteria do not work properly for
networks. We illustrate these challenges, and show one way to resolve them, by
considering the key network-analysis problem of dividing a graph into
communities or blocks of nodes with homogeneous patterns of links to the rest
of the network. The standard tool for doing this is the stochastic block model,
under which the probability of a link between two nodes is a function solely of
the blocks to which they belong. This imposes a homogeneous degree distribution
within each block; this can be unrealistic, so degree-corrected block models
add a parameter for each node, modulating its over-all degree. The choice
between ordinary and degree-corrected block models matters because they make
very different inferences about communities. We present the first principled
and tractable approach to model selection between standard and degree-corrected
block models, based on new large-graph asymptotics for the distribution of
log-likelihood ratios under the stochastic block model, finding substantial
departures from classical results for sparse graphs. We also develop
linear-time approximations for log-likelihoods under both the stochastic block
model and the degree-corrected model, using belief propagation. Applications to
simulated and real networks show excellent agreement with our approximations.
Our results thus both solve the practical problem of deciding on degree
correction, and point to a general approach to model selection in network
analysis
Testing Propositions Derived from Twitter Studies: Generalization and Replication in Computational Social Science
Replication is an essential requirement for scientific discovery. The current study aims to generalize and replicate 10 propositions made in previous Twitter studies using a representative dataset. Our findings suggest 6 out of 10 propositions could not be replicated due to the variations of data collection, analytic strategies employed, and inconsistent measurements. The study’s contributions are twofold: First, it systematically summarized and assessed some important claims in the field, which can inform future studies. Second, it proposed a feasible approach to generating a random sample of Twitter users and its associated ego networks, which might serve as a solution for answering social-scientific questions at the individual level without accessing the complete data archive.published_or_final_versio
- …