All Who Wander: On the Prevalence and Characteristics of Multi-community Engagement

Although analyzing user behavior within individual communities is an active and rich research domain, people usually interact with multiple communities both on- and off-line. How do users act in such multi-community environments? Although there are a host of intriguing aspects to this question, it has received much less attention in the research community in comparison to the intra-community case. In this paper, we examine three aspects of multi-community engagement: the sequence of communities that users post to, the language that users employ in those communities, and the feedback that users receive, using longitudinal posting behavior on Reddit as our main data source, and DBLP for auxiliary experiments. We also demonstrate the effectiveness of features drawn from these aspects in predicting users' future level of activity. One might expect that a user's trajectory mimics the "settling-down" process in real life: an initial exploration of sub-communities before settling down into a few niches. However, we find that the users in our data continually post in new communities; moreover, as time goes on, they post increasingly evenly among a more diverse set of smaller communities. Interestingly, it seems that users that eventually leave the community are "destined" to do so from the very beginning, in the sense of showing significantly different "wandering" patterns very early on in their trajectories; this finding has potentially important design implications for community maintainers. Our multi-community perspective also allows us to investigate the "situation vs. personality" debate from language usage across different communities.Comment: 11 pages, data available at https://chenhaot.com/pages/multi-community.html, Proceedings of WWW 2015 (updated references

Moments of the Proton F2 Structure Function at Low Q2

The Q^2 dependence of inclusive electron-proton scattering F_2 structure function data in both the nucleon resonance region and the deep inelastic region, at momentum transfers below 5 (GeV/c)^2, is investigated. Moments of F_2 are constructed, down to momentum transfers of Q^2 ~ 0.1 (GeV/c)^2. The second moment is only slowly varying with Q^2 down to Q^2 ~ 1 (GeV/c)^2, which is a reflection of duality. Below Q^2 of 1 (GeV/c)^2, the Q^2 dependence of the moments is predominantly governed by the elastic contribution, whereas the inelastic channels still seem governed by local duality.Comment: 11 page paper, 1 LaTeX file, 10 postscript figure file

Cascades: A view from Audience

Cascades on online networks have been a popular subject of study in the past decade, and there is a considerable literature on phenomena such as diffusion mechanisms, virality, cascade prediction, and peer network effects. However, a basic question has received comparatively little attention: how desirable are cascades on a social media platform from the point of view of users? While versions of this question have been considered from the perspective of the producers of cascades, any answer to this question must also take into account the effect of cascades on their audience. In this work, we seek to fill this gap by providing a consumer perspective of cascade. Users on online networks play the dual role of producers and consumers. First, we perform an empirical study of the interaction of Twitter users with retweet cascades. We measure how often users observe retweets in their home timeline, and observe a phenomenon that we term the "Impressions Paradox": the share of impressions for cascades of size k decays much slower than frequency of cascades of size k. Thus, the audience for cascades can be quite large even for rare large cascades. We also measure audience engagement with retweet cascades in comparison to non-retweeted content. Our results show that cascades often rival or exceed organic content in engagement received per impression. This result is perhaps surprising in that consumers didn't opt in to see tweets from these authors. Furthermore, although cascading content is widely popular, one would expect it to eventually reach parts of the audience that may not be interested in the content. Motivated by our findings, we posit a theoretical model that focuses on the effect of cascades on the audience. Our results on this model highlight the balance between retweeting as a high-quality content selection mechanism and the role of network users in filtering irrelevant content

Local Duality Predictions for x ~ 1 Structure Functions

Recent data on the proton F_2 structure function in the resonance region suggest that local quark-hadron duality works remarkably well for each of the low-lying resonances, including the elastic, to rather low values of Q^2. We derive model-independent relations between structure functions at x ~ 1 and elastic electromagnetic form factors, and predict the x -> 1 behavior of nucleon polarization asymmetries and the neutron to proton structure function ratios from available data on nucleon electric and magnetic form factors.Comment: 10 pages, 2 figures, typos in Eq. (2) correcte

Quark-hadron duality in a relativistic, confining model

Quark-hadron duality is an interesting and potentially very useful phenomenon, as it relates the properly averaged hadronic data to a perturbative QCD result in some kinematic regions. While duality is well established experimentally, our current theoretical understanding is still incomplete. We employ a simple model to qualitatively reproduce all the features of Bloom-Gilman duality as seen in electron scattering. In particular, we address the role of relativity, give an explicit analytic proof of the equality of the hadronic and partonic scaling curves, and show how the transition from coherent to incoherent scattering takes place.Comment: This paper is dedicated to the memory of our collaborator Nathan Isgur. (34 pages, 13 figures

Retrosternal goiters

Clinica 1 Chirurgie, Clinica de Endocrinologie, Spitalul „Sf.Spiridon”, UMF ”Gr.T.Popa”, Iaşi, România, Al XII-lea Congres al Asociației Chirurgilor „Nicolae Anestiadi” din Republica Moldova cu participare internațională 23-25 septembrie 2015Introducere: Noțiunea de guşă retrosternală sau substernală reprezintă coborîrea a mai mult de 50% de glanda tiroidă în cavitatea toracică. Material şi metode: A fost efectuat un studiu retrospectiv a cazurilor de guşă retrosternală sau substernală din totalul de 2482 pacienți ce au suportat tiroidectomie în Clinica 1 Chirurgie din Iaşi în perioada 2000-2010. Guşa retrosternală a fost depistată la 54 (2,17%) pacienți. Toți bolnavii au fost îndreptați la operație din Clinica de Endocrinologie. Rezultate: Vîrsta medie a pacienților la momentul instalării diagnosticului a constituit 55,3±3,58 ani, majoritatea fiind femei – 83,3%. În manifestările clinice ale guşei retrosternale au dominat fenomenele de compresie. Dereglările funcției glandei tiroide au fost determinate prin teste hormonale efectuate în Clinica de Endocrinologie în 15 (27,7%) cazuri. Diagnoza de guşă retrosternală a fost suspectată în baza examenului clinic şi confirmată imagistic: radiografie toracică, ultrasonografie, computer tomografie. Abordul cervical a fost utilizat cu siguranță, sternotomia fiind necesară doar în 8 (14,8%) cazuri. Morbiditatea postoperatorie a constituit 5,5% (3 cazuri) cu mortalitate nulă. Durata medie de spitalizare a fost 4,3 zile. Noi am comparat datele noastre recente cu raportul privind tratamentul guşei retrosternale şi toracice în Clinica 1 Chirurgie din Iaşi în perioada anilor 1950-1979, publicat în revista „Chirurgia” în 1981. Concluzii: Guşa retrosternală reprezintă o formă specifică de patologie a glandei tiroide cu o incidență scăzută. Diagnosticul şi tratamentul guşei retrosternale implică o abordare multidisciplinară. Medicul endocrinolog are un rol important în diagnosticul şi supravegherea postoperatorie. Deşi intervenția chirurgicală este o metoda curativă de elecție pentru guşa substernală, persistă controverse privind abordul chirurgical şi rata complicațiilor. Abordul cervical poate fi utilizat cu siguranță aproape în toate cazurile, sternotomia fiind efectuată fără ezitare în caz de necesitate.Introduction: The term of retrosternal or substernal goiter means that more than 50% of thyroid gland descends in the thorax. Material and methods: There is a retrospective study on retrosternal and substernal goiter and its pathological features among 2482 patients who underwent thyroidectomy between 2000 and 2010 in the First Surgery Clinic of Iasi. Retrosternal goiter was diagnosed in 54 (2.17%) patients. All patients were referred to surgery from the Clinic of Endocrinology. Results: Mean age at diagnosis was 55.3±3.58 years, and most cases were found in women – 83.3%). The clinical picture of retrosternal goiter was dominated by compressive disorders. Thyroid function abnormalities were identified by hormonal assays performed on Endocrinology Clinic Iasi in 15 (27.7%) cases. The diagnosis of retrosternal goiter was suggested by clinical examination and confirmed by imaging: chest X-ray, ultrasound, CT scan. The cervical approach was safely performed. Only in 8 cases (14.8%), sternotomy was necessary. There was no mortality, and morbidity was 5.5% (3 cases). The length of stay in the hospital was 4.3 days. We compared our recent data with a previous report on retrosternal and thoracic goiter treated in First Surgery Clinic of Iasi during 1950 to 1979 and published in the journal “Chirurgia” in 1981. Conclusions: Retrosternal goiter is a particular form of thyroid surgical pathology presented with reduced incidence. Diagnosis and treatment of retrosternal goiter involve a multidisciplinary team. The endocrinologist has an important role in diagnosis and postoperative follow-up. Surgery is the treatment of choice for substernal goiters, but there are still some controversies on surgical approach, and complication rate. The cervical approach can be safely performed in almost all cases but when required, sternotomy should be performed without hesitation

Comment on "Nucleon elastic form factors and local duality"

We comment on the papers "Nucleon elastic form factors and local duality" [Phys. Rev. {\bf D62}, 073008 (2000)] and "Experimental verification of quark-hadron duality" [Phys. Rev. Lett. {\bf 85}, 1186 (2000)]. Our main comment is that the reconstruction of the proton magnetic form factor, claimed to be obtained from the inelastic scaling curve thanks to parton-hadron local duality, is affected by an artifact.Comment: to appear in Phys. Rev.

Perturbative QCD Analysis of Local Duality in a fixed W^2 Framework

We study the global Q^2 dependence of large x, F_2 nucleon structure function data, with the aim of providing a perturbative-QCD based, quantitative analysis of parton-hadron duality. As opposed to previous analyses at fixed x, we use a framework in fixed W^2. We uncover a breakdown of the twist-4 approximation with a renormalon type improvement at O(1/Q^4) which, by affecting the initial evolution of parton distributions, will have consequences for pQCD analyses also at large x and very large Q^2.Comment: RevTex4, 8 pages, 3 figure