Wait-Free Concurrent Graph Objects with Dynamic Traversals

Graphs are versatile data structures that allow the implementation of a variety of applications, such as computer-aided design and manufacturing, video gaming, or scientific simulations. However, although data structures such as queues, stacks, and trees have been widely studied and implemented in the concurrent context, multi-process applications that rely on graphs still largely use a sequential implementation where accesses are synchronized through the use of global locks or partitioning, thus imposing serious performance bottlenecks. In this paper we introduce an innovative concurrent graph model that provides addition and removal of any edge of the graph, as well as atomic traversals of a part (or the entirety) of the graph. We further present Dense, a concurrent graph implementation that aims at mitigating the two aforementioned implementation drawbacks. Dense achieves wait-freedom by relying on helping and provides the inbuilt capability of performing a partial snapshot on a dynamically determined subset of the graph

Brief Announcement: Persistent Software Combining

We study the performance power of software combining in designing recoverable algorithms and data structures. We present two recoverable synchronization protocols, one blocking and another wait-free, which illustrate how to use software combining to achieve both low persistence and synchronization cost. Our experiments show that these protocols outperform by far state-of-the-art recoverable universal constructions and transactional memory systems. We built recoverable queues and stacks, based on these protocols, that exhibit much better performance than previous such implementations

Development of the Brief Ageing Perceptions Questionnaire (B-APQ): a confirmatory factor analysis approach to item reduction.

BACKGROUND: This paper aimed to develop a short version of the 32-item Ageing Perceptions Questionnaire (APQ), a multi-dimensional measure based on Leventhal\u27s self-regulation model. Ageing perceptions are a key area of interest for large-scale surveys of ageing populations. As these studies capture a broad range of health and social variables, included instruments need to be as concise as possible. METHODS: Data from the Irish Longitudinal Study of Ageing (TILDA), a representative sample of community-dwelling individuals aged 50+ (n = 6,718), was used to revise the scale. Items for exclusion were identified by examining conceptual content, descriptive statistics, and by detecting sources of poor model fit using confirmatory factor analysis (CFA). Potential combinations of dimensions were also tested using CFA. Finally, we identified any dimensions that could be excluded without limiting the conceptual coverage and coherence of the scale. Model modifications were done sequentially and with regard to theoretical considerations. Internal consistency and construct validity of the concise scale were compared with the longer version. RESULTS: Initially, 11 items were excluded on the basis of conceptual and empirical overlap with other items. CFA indicated that the negative-control and negative-consequences dimensions could be combined, allowing us to exclude a further item from this dimension. The 5-item timeline-cyclical dimension was also excluded, as it was less well-established conceptually and empirically than the other dimensions. The final 17-item, 5-dimension model was consistent with the original conceptual model and fit the data well (chi-sq = 1433.54, df(109), p CONCLUSIONS: The Brief-APQ (B-APQ) is a concise, multi-dimensional measure of ageing perceptions, which is psychometrically valid for use with the Irish population aged 50+. The concise version preserved the internal consistency and construct validity of the original. Its brevity makes it particularly suitable for use with large-scale adult population surveys. The psychometric analysis supports the application of the self-regulation model to ageing perceptions, but also the existence of distinct \u22physical decline\u22 and \u22ongoing development\u22 dimensions of perceptions

The Grid Elegies

Immigrants are a key component in New York City’s pandemic. Historically, New York is a city of immigrants and their children. In the latter part of the 20th Century, more immigrants arrived due to changes in migration policy. There was also an increased outmigration through second and third generations, which mirrors an economic trajectory seen in previous points in history, mainly in the 1970s. At that time, there was the lure of government policies – from federal mortgage agencies that graded white suburban areas as safer areas for banks to make loans than racially mixed urban areas, to road construction that literally paved the way for an outflow from the city. This collection attempts to narrate the flow of migrants in New York City and its Eastern suburban sprawl throughout time, with a consideration of the natural formation of the land and its peoples. The capstone originated in unexpected study during the COVID-19 pandemic in New York City where the work asks the question, does New York’s moving population of immigrants change when they move here, and how do people on the move change the land

Testing the Assumption of Measurement Invariance in the SAMHSA Mental Health and Alcohol Abuse Stigma Assessment in Older Adults

This study examined the assumption of measurement invariance of the SAMSHA Mental Health and Alcohol Abuse Stigma Assessment. This is necessary to make valid comparisons across time and groups. The data come from the Primary Care Research in Substance Abuse and Mental Health for Elderly trial, a longitudinal multisite, randomized trial examining two modes of care (Referral and Integrated). A sample of 1,198 adults over the age of 65 who screened positive for depression, anxiety, and/or at-risk drinking was used. Structural equation modeling was used to assess measurement invariance in a two-factor measurement model (Perceived Stigma, Comfort Level). Irrespective of their stigma level, one bias indicated that with time, respondents find it easier to acknowledge that it is difficult to start treatment if others know they are in treatment. Other biases indicated that sex, mental quality of life and the subject of stigma had undue influence on respondents' feeling people would think differently of them if they received treatment and on respondents' comfort in talking to a mental health provider. Still, in the present study, these biases in response behavior had little effect on the evaluation of group differences and changes in stigma. Stigma decreased for patients of both the Referral and Integrated care group

insights into assembly processes

Changes in species diversity following volcanic eruptions have been studied extensively, but our knowledge on functional diversity and community assembly under such conditions is very limited. Here, we study the processes following the destruction of vegetation after a volcanic eruption. Specifically, we investigate (1) the temporal patterns of taxonomic and functional diversity over time since a previous eruption (alpha diversity) and beta diversity, (2) the temporal patterns of 26 individual traits (vegetative characteristics, plant taxa ecological preferences, and regenerative characteristics) providing more detailed information on species strategies at the initial and later stages of succession, and (3) the processes driving species assembly and whether they changed over time since the eruption an eruption. We analyzed data recorded during five floristic censuses that took place between 1911 and 2011, calculated alpha and beta facets of taxonomic and functional diversity and examined how community structure changed over time, using 26 functional characteristics, based on their ability to discern primary from later colonists, including longevity, growth form, Ellenberg's indicator values, seed production and weight, flower size and sex, pollination type, and dispersal mode. Null model analysis was used to test whether the observed functional diversity deviates from random expectations. Alpha diversity, both taxonomic and functional, increased over time after an eruption, while beta diversity did not display a clear trend. This finding indicates that mainly abiotic processes determine species assembly over time after an eruption (at least for the time span studied here), contrary to theoretical expectations. It is most interesting that, simultaneously, some aspects of diversity indicated the effect of biotic interactions (facilitation and competition) on the assembly of species a few years after an eruption. This finding implies a legacy effect, since a high percentage of perennial species was noticed in the assemblage right after the eruption, as well as the effect of the harsh environmental conditions on the assembly of the plant communities. In conclusion, our results indicate the role of legacy effects in succession (most probably through the survival of underground plant parts) and underline the importance of disturbance history in providing the context needed for understanding effects of past events on succession