Sensitization of mesoporous nanocrystalline TiO(2) solar cells with quantum confined semiconductor nanocrystals (QDs) has some advantages over organic dyes or inorganic complex sensitizers, yet the reported efficiencies of laboratory devices are not currently competitive with those of dye sensitized cells. Several methods previously utilized to bind CdSe QDs to mesoporous TiO(2) films were investigated using low index faces of both anatase and rutile TiO(2) polytypes as model systems. The in situ ligand exchange method, where 3-mercaptopropionic acid (MPA) covered TiO(2) crystal surfaces are treated with trioctylphosphine (TOP)/trioctylphosphine oxide (TOPO) (TOP/TOPO)-capped CdSe QDs, resulted in very irreproducible and usually low sensitized photocurrents. The ex situ ligand exchange method, whereby MPA-capped QDs are synthesized and directly adsorbed onto bare TiO(2) single crystals, resulted in both reproducible sensitized photocurrents and surface coverages that are verified with atomic force microscopy (AFM). Purification of the nanocrystals and adjustment of the pH of the sensitization solution to >10.2 was found to prevent QD agglomeration and takes advantage of the dual chemical functionality of MPA to directly link the QDs to the TiO(2) surface. The spectral response of the incident photon to current efficiencies of CdSe QDs was directly compared to the commonly used sensitizer cis-di(thiocyanato)-bis(4,4;-dicarboxy-2,2'-bipyridine)ruthenium(II) (N3) on the same single crystals.

No abstract

Single-crystal anatase(101), (001) and rutile(100), (001) surfaces with atomically flat terraces were prepared and their structure verified with atomic force microscopy. A ruthenium complex dye, cis-di(thiocyanato)-bis( 2,2′ -bipyridyl- 4,4′ -dicarboxylate) ruthenium(II) (usually known as N3) was used to sensitize these surfaces. The N3 coverage dependence of the incident photon to current efficiencies (IPCE) was measured for all four surfaces. IPCE values were much higher on anatase(101) and rutile(100) than on the other two surfaces. The kinetics of N3 adsorption was also studied on the four surfaces. The adsorption kinetics for a slow adsorption step could be fit with a Langmuir kinetic model. The differences in the adsorption of N3 and the IPCE values are discussed based on the structure of the N3 and the geometry and reactivity of the binding sites on the four surfaces.

Spreading rumors on the Internet has become increasingly pervasive due to the proliferation of online social media. This paper investigates how rumors are amplified by a group of users who share similar interests or views, dubbed as an echo chamber. To this end, we identify and analyze 'rumor' echo chambers, each of which is a group of users who have participated in propagating common rumors. By collecting and analyzing 125 recent rumors from six popular fact-checking sites, and their associated 289,202 tweets/retweets generated by 176,362 users, we find that the rumors that are spread by rumor echo chamber members tend to be more viral and quickly propagated than those that are not spread by echo chamber members. We propose the notion of an echo chamber network that represents relations among rumor echo chambers. By identifying the hub rumor echo chambers (in terms of connectivity to other rumor echo chambers) in the echo chamber network, we show that the top 10% of hub rumor echo chambers contribute to propagation of 24% rumors by eliciting more than 36% of retweets, implying that core rumor echo chambers significantly contribute to rumor spreads. Online media such as social networks, online communities, instant messages, and e-mails have become popular vectors in disseminating news, content, political campaigns, scientific findings, or product advertisements. Due to the nature of such online media that spreads information quickly and widely 1-3 , there have been attempts to disseminate misinformation, false news, or rumors, the last of which are circulating stories of uncertain or ungrounded gossips 4,5. Such rumors usually affect people, society, or economics. For example, the misinformation about Hurricane Sandy on the east coast of the USA brought the storm of rumors and false photos on the Internet 6. Another well-known widespread rumor is about the Boston Marathon Bombing event. FBI requested for materials related to the suspects (as bombers), but many people reported and propagated a deluge of misinformation or rumors to that event at the moment 7. A false news about Barack Obama's injury due to the White House explosion was reported through Twitter by the Associated Press (AP), which brought monetary chaos in stock markets-$130 billion in stock values were wiped out 8. The growing importance in understanding rumor spreads has spurred research into analyzing rumor propagation patterns in online media. By analyzing the factors that are related to rumor propagation, researchers have investigated how different types of content 9,10 or initial propagation patterns 9 are associated with the rumor propagation. From a user perspective, the relations between rumor propagation patterns and individuals' interest (or political standpoint) 11,12 , behavioral characteristics 7,13 , or social structures 14 have been investigated. While these studies have provided valuable insights into understanding rumor spreads and their associated factors, relatively little attention has been paid to how a group of users that share...

No abstract

Four dicarboxylated cyanine dyes were used to sensitize single-crystal anatase (001), anatase (101), rutile (001), and rutile (100) surfaces. Incident photon to current efficiencies (IPCE) spectra and isotherms were gathered for the different combination of dyes and surfaces. The maximum coverage of the surface-bound dyes on the TiO2 crystal surfaces was determined by photochronocoulometric measurements. The IPCE spectra of the surface-bound dyes revealed that both the dye monomers and H-aggregates were both present and generated photocurrent. The relative abundance of dye monomers and H-aggregates was found to be strongly dependent on the crystallographic face used as the substrate for sensitization. The ratio of dye monomer to H-aggregate was quantified by fitting the IPCE spectra with a sum of the dye monomer and H-aggregate solution spectra. The trends in surface coverage were explained using a simple "lattice matching" model where the distance between the coordinatively unsaturated Ti binding sites on the various TiO2 crystallographic surfaces was compared with the distance between the carboxylate groups on the dyes. The rutile (100) surface had the highest coverage for all the dyes in agreement with the predictions of the lattice-matching model. Absorbed photon-to-current-efficiencies (APCEs) were calculated from the incident photon current efficiencies, the extinction coefficients and the measured surface coverages. The factors that affect the APCE values such as the relative injection yield for monomers and aggregate, the relative surface coverage values for monomers and aggregates, and semiconductor doping levels are discussed.

IMPORTANCE Suicide is a leading cause of death in the US. However, official national statistics on suicide rates are delayed by 1 to 2 years, hampering evidence-based public health planning and decision-making. OBJECTIVE To estimate weekly suicide fatalities in the US in near real time. DESIGN, SETTING, AND PARTICIPANTSThis cross-sectional national study used a machine learning pipeline to combine signals from several streams of real-time information to estimate weekly suicide fatalities in the US in near real time. This 2-phase approach first fits optimal machine learning models to each individual data stream and subsequently combines predictions made from each data stream via an artificial neural network. National-level US administrative data on suicide deaths, health

No abstract