The anatomy of urban social networks and its implications in the searchability problem

The appearance of large geolocated communication datasets has recently increased our understanding of how social networks relate to their physical space. However, many recurrently reported properties, such as the spatial clustering of network communities, have not yet been systematically tested at different scales. In this work we analyze the social network structure of over 25 million phone users from three countries at three different scales: country, provinces and cities. We consistently find that this last urban scenario presents significant differences to common knowledge about social networks. First, the emergence of a giant component in the network seems to be controlled by whether or not the network spans over the entire urban border, almost independently of the population or geographic extension of the city. Second, urban communities are much less geographically clustered than expected. These two findings shed new light on the widely-studied searchability in self-organized networks. By exhaustive simulation of decentralized search strategies we conclude that urban networks are searchable not through geographical proximity as their country-wide counterparts, but through an homophily-driven community structure.

Membrane voltage initiates Ca2+ waves and potentiates Ca2+ increases with abscisic acid in stomatal guard cells

In higher plants changes and oscillations in cytosolic free Ca2+ concentration ([Ca2+]i) are central to hormonal physiology, including that of abscisic acid (ABA), which signals conditions of water stress and alters ion channel activities in guard cells of higher-plant leaves. Such changes in [Ca2+]i are thought to encode for cellular responses to different stimuli, but their origins and functions are poorly understood. Because transients and oscillations in membrane voltage also occur in guard cells and are elicited by hormones, including ABA, we suspected a coupling of [Ca2+]i to voltage and its interaction with ABA. We recorded [Ca2+]i by Fura2 fluorescence ratio imaging and photometry while bringing membrane voltage under experimental control with a two-electrode voltage clamp in intact Vicia guard cells. Free-running oscillations between voltages near −50 mV and −200 mV were associated with oscillations in [Ca2+]i, and, under voltage clamp, equivalent membrane hyperpolarizations caused [Ca2+]i to increase, often in excess of 1 μM, from resting values near 100 nM. Image analysis showed that the voltage stimulus evoked a wave of high [Ca2+]i that spread centripetally from the peripheral cytoplasm within 5–10 s and relaxed over 40–60 s thereafter. The [Ca2+]i increases showed a voltage threshold near −120 mV and were sensitive to external Ca2+ concentration. Substituting Mn2+ for Ca2+ to quench Fura2 fluorescence showed that membrane hyperpolarization triggered a divalent influx. ABA affected the voltage threshold for the [Ca2+]i rise, its amplitude, and its duration. In turn, membrane voltage determined the ability of ABA to raise [Ca2+]i. These results demonstrate a capacity for voltage to evoke [Ca2+]i increases, they point to a dual interaction with ABA in triggering and propagating [Ca2+]i increases, and they implicate a role for voltage in “conditioning” [Ca2+]i signals that regulate ion channels for stomatal function.

Solution of the pulse width modulation problem using orthogonal polynomials and Korteweg-de Vries equations

The mathematical underpinning of the pulse width modulation (PWM) technique lies in the attempt to represent “accurately” harmonic waveforms using only square forms of a fixed height. The accuracy can be measured using many norms, but the quality of the approximation of the analog signal (a harmonic form) by a digital one (simple pulses of a fixed high voltage level) requires the elimination of high order harmonics in the error term. The most important practical problem is in “accurate” reproduction of sine-wave using the same number of pulses as the number of high harmonics eliminated. We describe in this paper a complete solution of the PWM problem using Padé approximations, orthogonal polynomials, and solitons. The main result of the paper is the characterization of discrete pulses answering the general PWM problem in terms of the manifold of all rational solutions to Korteweg-de Vries equations.

High-Voltage Electron Tomography of Spindle Pole Bodies and Early Mitotic Spindles in the Yeast Saccharomyces cerevisiaeV⃞

The spindle pole body (SPB) is the major microtubule-organizing center of budding yeast and is the functional equivalent of the centrosome in higher eukaryotic cells. We used fast-frozen, freeze-substituted cells in conjunction with high-voltage electron tomography to study the fine structure of the SPB and the events of early spindle formation. Individual structures were imaged at 5–10 nm resolution in three dimensions, significantly better than can be achieved by serial section electron microscopy. The SPB is organized in distinct but coupled layers, two of which show ordered two-dimensional packing. The SPB central plaque is anchored in the nuclear envelope with hook-like structures. The minus ends of nuclear microtubules (MTs) are capped and are tethered to the SPB inner plaque, whereas the majority of MT plus ends show a distinct flaring. Unbudded cells containing a single SPB retain 16 MTs, enough to attach to each of the expected 16 chromosomes. Their median length is ∼150 nm. MTs growing from duplicated but not separated SPBs have a median length of ∼130 nm and interdigitate over the bridge that connects the SPBs. As a bipolar spindle is formed, the median MT length increases to ∼300 nm and then decreases to ∼30 nm in late anaphase. Three-dimensional models confirm that there is no conventional metaphase and that anaphase A occurs. These studies complement and extend what is known about the three-dimensional structure of the yeast mitotic spindle and further our understanding of the organization of the SPB in intact cells.

Voltage gating and permeation in a gap junction hemichannel.

Gap junction channels are formed by members of the connexin gene family and mediate direct intercellular communication through linked hemichannels (connexons) from each of two adjacent cells. While for most connexins, the hemichannels appear to require an apposing hemichannel to open, macroscopic currents obtained from Xenopus oocytes expressing rat Cx46 suggested that some hemichannels can be readily opened by membrane depolarization [Paul, D. L., Ebihara, L., Takemoto, L. J., Swenson, K. I. & Goodenough, D. A. (1991), J. Cell Biol. 115, 1077-1089]. Here we demonstrate by single channel recording that hemichannels comprised of rat Cx46 exhibit complex voltage gating consistent with there being two distinct gating mechanisms. One mechanism partially closes Cx46 hemichannels from a fully open state, gammaopen, to a substate, gammasub, about one-third of the conductance of gammaopen; these transitions occur when the cell is depolarized to inside positive voltages, consistent with gating by transjunctional voltage in Cx46 gap junctions. The other gating mechanism closes Cx46 hemichannels to a fully closed state, gammaclosed, on hyperpolarization to inside negative voltages and has unusual characteristics; transitions between gammaclosed and gammaopen appear slow (10-20 ms), often involving several transient substates distinct from gammasub. The polarity of activation and kinetics of this latter form of gating indicate that it is the mechanism by which these hemichannels open in the cell surface membrane when unapposed by another hemichannel. Cx46 hemichannels display a substantial preference for cations over anions, yet have a large unitary conductance (approximately 300 pS) and a relatively large pore as inferred from permeability to tetraethylammonium (approximately 8.5 angstroms diameter). These hemichannels open at physiological voltages and could induce substantial cation fluxes in cells expressing Cx46.

Are drawings dead? …and performance over aesthetics?

When the act of 'drawing' became what can only be called formalised, (whose growth can be said to have blossomed during the Renaissance), there developed a separation between the drawing and its procurement. Recently, David Ross Scheer, in his book ‘The Death of Drawing, Architecture in the Age of Simulation’ wrote: ‘…whereas architectural drawings exist to represent construction, architectural simulations exist to anticipate building performance.’ Meanwhile, Paolo Belardi, in his work ‘Why Architects Still Draw’ likens a drawing to an acorn, where he says: ‘It is the paradox of the acorn: a project emerges from a drawing – even from a sketch, rough and inchoate - just as an oak tree emerges from an acorn.’ He tells us that Giorgio Vasari would work late at night ‘seeking to solve the problems of perspective’ and he makes a passionate plea that this reflective process allows the concept to evolve, grow and/or develop. However, without belittling Belardi, the virtual model now needs this self-same treatment where it is nurtured, coaxed and encouraged to be the inchoate blueprint of the resultant oak tree. The model now too can embrace the creative process going through the first phase of preparation, where it focuses on the problem. The manipulation of the available material can then be incubated so that it is reasoned and generates feedback. This paper serves to align this shift in perception, methodologies and assess whether the 2D paper abstraction still has a purpose and role in today’s digital world!

Europe's growth problem (and what to do about it). Bruegel Policy Brief 2013/03, April 2013

The issue: The European Union's pre-crisis growth performance was disappointing enough, but the performance has been even more dismal since the onset of the crisis. Weak growth is undermining private and public deleveraging,and is fuelling continued banking fragility. Persistently high unemployment is eroding skills, discouraging labour market participation and undermining the EU’s long-term growth potential. Low overall growth is making it much tougher for the hard-hit economies in southern Europe to recover competitiveness and regain control of their public finances. Stagnation would reduce the attractiveness of Europe for investment. Under these conditions, Europe's social models are bound to prove unsustainable. Policy Challenge: The European Union's weak long-term growth potential and unsatisfactory recovery from the crisis represent a major policy challenge. Over and above the structural reform agenda, which vitally important, bold policy action is needed. The priority is to get bank credit going. Banking problems need to be assessed properly and bank resolution and recapitalisation should be pursued. Second, fostering the reallocation of factors to the most productive firms and the sectors that contribute to aggregate rebalancing is vital. Addressing intra-euro area competitiveness divergence is essential to support growth in southern Europe. Third, the speed of fiscal adjustment needs to be appropriate and EU funds should be front loaded to countries in deep recession, while the European Investment Bank should increase investment.

Holes in the skies over NATO's Central European member states. OSW Commentary No. 119, 22.10.2013

Over the past few months, four Central European states have made decisions which will determine the shape of their air forces over the next decade. On 11 October, Romania signed a contract under which it will buy twelve used US F-16A/B multi-role fighter aircraft from Portugal. In August, Slovakia signed contracts with Russia’s MiG for repairs and the limited modernisation of its twelve MiG-29 fighter aircraft currently in service. The Czech Republic entered into a preliminary agreement in July with Sweden on extending the lease of fourteen JAS-39 Gripen multi-role fighter aircraft (the new Czech government will hammer out the details following the parliamentary election). Bulgaria, which has been facing financial problems and political instability, in June postponed the purchase of new (non-Soviet) combat aircraft at least until the end of this year. If Sofia decides to buy any within the next few years, these will be not more than twelve relatively old and worn-out machines (most likely F-16A/B from Portuguese or Dutch army surplus). Given the fact that Hungary in 2012 made the same decision regarding its fourteen Gripen aircraft as the Czech Republic, there are good grounds to claim that the capabilities Central European NATO member states have to take action in airspace are durably limited. The region’s saturation with combat aircraft is the lowest when compared to the entire continent (with the exception of the Baltic states). Furthermore, the machines to be used in the coming decade will be the oldest and the least advanced technologically (all of them belong to the so-called “fourth generation”, the roots of which date back to the 1970s). The problem with gaining full interoperability within NATO has not been resolved in its Central European member states. By modernising its MiG-29 aircraft, Slovakia is to say the least postponing the achievement of interoperability once again. Bulgaria will gain interoperability by buying any Western combat aircraft. However, it is very unlikely to introduce new machines into service earlier than at the end of the present decade. Since the introduction of new fifth generation multi-role combat aircraft or transitional 4+ generation machines in the region’s air forces is unrealistic, the defence of the airspace of NATO member states in Central Europe can be termed an ever more porous sky.

A summary of the politico-economic changes taking place during Vladimir Putin's first term in office; Chechnya and Russia: The significance of the Chechen problem for contemporary Russia. OSW Study 11/2003

Putin's first term in office: The most significant achievement of Vladimir Putin's team over the three years of his term of office is the realisation of legislative changes, which may constitute a base for further - more detailed - political and economic reforms. This is, to a certain degree, a return to the economic tasks set out by a team of reformists in the early 1990s, which were impossible to realise at the time due to conflicts between the Kremlin and legislative powers. Chechnya and Russia: The purpose of this analysis is to examine the significance of the Chechen issue for contemporary Russia. Part I discusses the history of the conflict from 1991 to date and the impact of developments in the republic on Russia as a whole. Part II is an attempt to indicate the areas of Russian reality that are most deeply affected by the Chechen problem.

Germany’s ‘refugee’ problem. The most important test for Chancellor Merkel and the grand coalition. OSW COMMENTARY NUMBER 182/11.09.2015 2015-09-11

The rapid increase in the number of immigrants from outside of the EU coming to Germany has become the paramount political issue. According to new estimates, the number of individuals expected arrive in Germany in 2015 and apply for asylum there is 800,000, which is nearly twice as many as estimated in earlier forecasts. Various administrative, financial and social problems related to the influx of migrants are becoming increasingly apparent. The problem of ‘refugees’ (in public debate, the terms ‘immigrants’, ‘refugees’, ‘illegal immigrants’, ‘economic immigrants’ have not been clearly defined and have often been used interchangeably) has been culminating for over a year. Despite this, it was being disregarded by Angela Merkel’s government which was preoccupied with debates on how to rescue Greece. It was only daily reports of cases of refugee centres being set on fire that convinced Chancellor Merkel to speak and to make immigration problem a priority issue (Chefsache). Neither the ruling coalition nor the opposition parties have a consistent idea of how Germany should react to the growing number of refugees. In this matter, divisions run across parties. Various solutions have been proposed, from liberalisation of laws on the right to stay in Germany to combating illegal immigration more effectively, which would be possible if asylum granting procedures were accelerated. The proposed solutions have not been properly thought through, instead they are reactive measures inspired by the results of opinion polls. This is why their assumptions are often contradictory. The situation is similar regarding the actions proposed by Chancellor Merkel which involve faster procedures to expel individuals with no right to stay in Germany and a plan to convince other EU states to accept ‘refugees’. None of these ideas is new – they were already present in the German internal debate.

The problem of style,

"The six lectures reprinted in this volume were delivered [in their original form] in the School of English literature at Oxford ... in the summer term of 1921."--Prefatory note.

Spatial and temporal characteristics of summer precipitation over Central Europe in a suite of high-resolution climate models

High-impact, localized intense rainfall episodes represent a major socio-economic problem for societies worldwide, and at the same time these events are notoriously difficult to simulate properly in climate models. Here, the authors investigate how horizontal resolution and model formulation influence this issue by applying the HARMONIE regional climate model (HCLIM) with three different setups; two using convection parameterization at 15 and 6.25 km horizontal resolution (the latter within the “grey-zone” scale), with lateral boundary conditions provided by ERA-Interim reanalysis and integrated over a pan-European domain, and one with explicit convection at 2 km resolution (HCLIM2) over the Alpine region driven by the 15 km model. Seven summer seasons were sampled and validated against two high-resolution observational data sets. All HCLIM versions underestimate the number of dry days and hours by 20-40%, and overestimate precipitation over the Alpine ridge. Also, only modest added value were found of “grey-zone” resolution. However, the single most important outcome is the substantial added value in HCLIM2 compared to the coarser model versions at sub-daily time scales. It better captures the local-to-regional spatial patterns of precipitation reflecting a more realistic representation of the local and meso-scale dynamics. Further, the duration and spatial frequency of precipitation events, as well as extremes, are closer to observations. These characteristics are key ingredients in heavy rainfall events and associated flash floods, and the outstanding results using HCLIM in convection-permitting setting are convincing and encourage further use of the model to study changes in such events in changing climates.

Preventing adolescent depression: An evaluation of the problem solving for life program

This study evaluated the effectiveness of the Problem Solving For Life program as it universal approach to the prevention of adolescent depression. Short-term results indicated that participants with initially elevated depressions scores (high risk) who received the intervention showed a significantly greater decrease in depressive symptoms and increase in life problem-solving scores from pre- to postintervention compared with a high-risk control group. Low-risk participants who received the intervention reported a small but significant decrease in depression scores over the intervention period, whereas the low-risk controls reported an increase in depression scores. The low-risk group reported a significantly greater increase in problem-solving scores over the intervention period compared with low-risk controls. These results were not maintained, however, at 12-month follow-up.

Using a problem detection study (PDS) to identify and compare health care provider and consumer views of antihypertensive therapy

The objectives of this study were to ascertain consumer knowledge and behaviour about hypertension and treatment and to compare these with health care providers' perceptions (of 'most' consumers). The design for the study was a problem detection study (PDS): focus groups and then survey. Focus groups and survey participants were convenience samples of consumers, doctors, nurses and pharmacists. The main outcome measures were agreement on a 5-point Likert scale with statements about consumers' knowledge and behaviour about high blood pressure and medication. The survey identified areas of consensus and disagreement between consumers and health providers. While general knowledge and concordance with antihypertensive therapy among consumers was good, consequences such as eye and kidney disease, interactions with herbal medicines, and how to deal with missing a dose were less well known. Side effects were a problem for over one-quarter of participants, and cost was a problem in continuing therapy. Half the consumers had not received sufficient written information. Providers overall disagreed that most consumers have an adequate understanding of the condition. They agreed that most consumers adhere to therapy and can manage medicines; and about their own profession's role in information provision and condition management. Consumers confirmed positive provider behaviour, suggesting opportunities for greater communication between providers about actions taken with their consumers. In conclusion, the PDS methodology was useful in identifying consumer opinions. Differences between consumer and provider responses were marked, with consumers generally rating their knowledge and behaviour above providers' ratings of 'most' consumers. There are clear gaps to be targeted to improve the outcomes of hypertension therapy.

Problem solving in social interactions on the Internet: Rumor as social cognition

Rumor discourse has been conceptualized as an attempt to reduce anxiety and uncertainty via a process of social sensemaking. Fourteen rumors transmitted on various Internet discussion groups were observed and content analyzed over the life of each rumor With this (previously unavailable) more ecologically robust methodology, the intertwined threads of sensemaking and the gaining of interpretive control are clearly evident in the tapestry of rumor discourse. We propose a categorization of statements (the Rumor Interaction Analysis System) and find differences between dread rumors and wish rumors in anxiety-related content categories. Cluster analysis of these statements reveals a typology of voices (communicative postures) exhibiting sensemaking activities of the rumor discussion group, such as hypothesizing, skeptical critique, directing of activities to gain information, and presentation of evidence. These findings enrich our understanding of the long-implicated sensemaking function of rumor by clarifying the elements of communication that operate in rumor's social context.