Fast evaluation of union-intersection expressions

We show how to represent sets in a linear space data structure such that expressions involving unions and intersections of sets can be computed in a worst-case efficient way. This problem has applications in e.g. information retrieval and database systems. We mainly consider the RAM model of computation, and sets of machine words, but also state our results in the I/O model. On a RAM with word size $w$, a special case of our result is that the intersection of $m$ (preprocessed) sets, containing $n$ elements in total, can be computed in expected time $O(n (\log w)^2 / w + km)$, where $k$ is the number of elements in the intersection. If the first of the two terms dominates, this is a factor $w^{1-o(1)}$ faster than the standard solution of merging sorted lists. We show a cell probe lower bound of time $\Omega(n/(w m \log m)+ (1-\tfrac{\log k}{w}) k)$, meaning that our upper bound is nearly optimal for small $m$. Our algorithm uses a novel combination of approximate set representations and word-level parallelism

Anatomy of coping: evidence from people living through the crises of 2008-11

This paper surveys qualitative crisis monitoring data from sites in 17 developing and transition countries to describe crisis impacts and analyze the responses and sources of support used by people to cope. These crises included shocks to export sectors as a result of the global financial crisis, as well as food and fuel price volatility, in the period from 2008 to early 2011. Respondents reported the crisis had resulted in significant hardships in the form of foregone meals, education, and health care, food insecurity, asset losses, stress, and worsening crime and community cohesion. Although the export-oriented formal sector was most exposed to the global economic downturn, the crises impacts were more damaging for informal sector workers, and some of the adverse impacts will be long-lasting and possibly irreversible. There were important gender and age differences in the distribution of impacts and coping responses, some of which diverged from what has been seen in previous crisis coping responses. The more common sources of assistance were family, friends, and community-based and religious organizations; formal social protection and finance were not widely cited as sources of support in most study countries. However, as the crisis deepened, the traditional informal safety nets of the poor became depleted because of the large and long-lasting shocks that ensued, pointing to the need for better formal social protection systems for coping with future shocks.

Simulating Uniform Hashing in Constant Time and Optimal Space

Many algorithms and data structures employing hashing have been analyzed under the uniform hashing assumption, i.e., the assumption that hash functions behave like truly random functions. In this paper it is shown how to implement hash functions that can be evaluated on a RAM in constant time, and behave like truly random functions on any set of n inputs, with high probability. The space needed to represent a function is O(n) words, which is the best possible (and a polynomial improvement compared to previous fast hash functions). As a consequence, a broad class of hashing schemes can be implemented to meet, with high probability, the performance guarantees of their uniform hashing analysis

Linear probing with constant independence

Hashing with linear probing dates back to the 1950s, and is among the most studied algorithms. In recent years it has become one of the most important hash table organizations since it uses the cache of modern computers very well. Unfortunately, previous analyses rely either on complicated and space consuming hash functions, or on the unrealistic assumption of free access to a truly random hash function. Already Carter and Wegman, in their seminal paper on universal hashing, raised the question of extending their analysis to linear probing. However, we show in this paper that linear probing using a pairwise independent family may have expected logarithmic cost per operation. On the positive side, we show that 5-wise independence is enough to ensure constant expected time per operation. This resolves the question of finding a space and time efficient hash function that provably ensures good performance for linear probing

Modulatory effects on dendritic cells by human herpesvirus 6

Human herpesvirus 6A and 6B are β-herpesviruses approaching 100% seroprevalance worldwide. These viruses are involved in several clinical syndromes and have important immunomodulatory effects. Dendritic cells (DC) are key players in innate and adaptive immunity. Accordingly, DC are implicated in the pathogenesis of many human diseases, including infections. In this review the effects of HHV-6 infection on DC will be discussed