Balanced Families of Perfect Hash Functions and Their Applications

The construction of perfect hash functions is a well-studied topic. In this paper, this concept is generalized with the following definition. We say that a family of functions from $[n]$ to $[k]$ is a $\delta$-balanced $(n,k)$-family of perfect hash functions if for every $S \subseteq [n]$, $|S|=k$, the number of functions that are 1-1 on $S$ is between $T/\delta$ and $\delta T$ for some constant $T>0$. The standard definition of a family of perfect hash functions requires that there will be at least one function that is 1-1 on $S$, for each $S$ of size $k$. In the new notion of balanced families, we require the number of 1-1 functions to be almost the same (taking $\delta$ to be close to 1) for every such $S$. Our main result is that for any constant $\delta > 1$, a $\delta$-balanced $(n,k)$-family of perfect hash functions of size $2^{O(k \log \log k)} \log n$ can be constructed in time $2^{O(k \log \log k)} n \log n$. Using the technique of color-coding we can apply our explicit constructions to devise approximation algorithms for various counting problems in graphs. In particular, we exhibit a deterministic polynomial time algorithm for approximating both the number of simple paths of length $k$ and the number of simple cycles of size $k$ for any $k \leq O(\frac{\log n}{\log \log \log n})$ in a graph with $n$ vertices. The approximation is up to any fixed desirable relative error

Some results on (a:b)-choosability

A solution to a problem of Erd\H{o}s, Rubin and Taylor is obtained by showing that if a graph $G$ is $(a:b)$-choosable, and $c/d > a/b$, then $G$ is not necessarily $(c:d)$-choosable. Applying probabilistic methods, an upper bound for the $k^{th}$ choice number of a graph is given. We also prove that a directed graph with maximum outdegree $d$ and no odd directed cycle is $(k(d+1):k)$-choosable for every $k \geq 1$. Other results presented in this article are related to the strong choice number of graphs (a generalization of the strong chromatic number). We conclude with complexity analysis of some decision problems related to graph choosability

Admission Control to Minimize Rejections and Online Set Cover with Repetitions

We study the admission control problem in general networks. Communication requests arrive over time, and the online algorithm accepts or rejects each request while maintaining the capacity limitations of the network. The admission control problem has been usually analyzed as a benefit problem, where the goal is to devise an online algorithm that accepts the maximum number of requests possible. The problem with this objective function is that even algorithms with optimal competitive ratios may reject almost all of the requests, when it would have been possible to reject only a few. This could be inappropriate for settings in which rejections are intended to be rare events. In this paper, we consider preemptive online algorithms whose goal is to minimize the number of rejected requests. Each request arrives together with the path it should be routed on. We show an $O(\log^2 (mc))$-competitive randomized algorithm for the weighted case, where $m$ is the number of edges in the graph and $c$ is the maximum edge capacity. For the unweighted case, we give an $O(\log m \log c)$-competitive randomized algorithm. This settles an open question of Blum, Kalai and Kleinberg raised in \cite{BlKaKl01}. We note that allowing preemption and handling requests with given paths are essential for avoiding trivial lower bounds

The political economy of Food subsidy reform in Egypt

Subsidies Egypt ,Food aid ,Food policy ,Food relief Government policy Cost effectiveness ,Poor Government policy ,

Current definitions of “transdiagnostic” in treatment development: A search for consensus

Research in psychopathology has identified psychological processes that are relevant across a range of Diagnostic and Statistical Manual (DSM) mental disorders, and these efforts have begun to produce treatment principles and protocols that can be applied transdiagnostically. However, review of recent work suggests that there has been great variability in conceptions of the term “transdiagnostic” in the treatment development literature. We believe that there is value in arriving at a common understanding of the term “transdiagnostic.” The purpose of the current manuscript is to outline three principal ways in which the term “transdiagnostic” is currently used, to delineate treatment approaches that fall into these three categories, and to consider potential advantages and disadvantages of each approachFirst author draf

Multilateral development banks and environmental policymaking in Central and Eastern Europe

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Political Science, 1999.Includes bibliographical references (p. 298-312).The dissertation is a comparative study of three multilateral development banks (MDBs)-the World Bank, European Bank for Reconstruction and Development (EBRD), and European Investment Bank (EIB)-and their struggles to operationalize and implement relatively new environmental mandates. MDBs are increasingly being relied upon to address environmental issues in their activities, while at the same time facing criticism for allegedly promoting serious environmental degradation in borrowing countries. The dissertation focuses on the activities of these banks in Central and Eastern Europe, where the fall of the Iron Curtain revealed the most polluted countries in Europe, and where these MDBs are among the top donors. There is significant variation in the degree to which these MDBs have incorporated environmental goals into their work. The World Bank has played an important role in providing policy support for environmental reform in the region, while financing the largest scope of "green" projects of the three banks. The EIB has responded to its environmental goals in minimal ways, and the EBRD has an intermediate position between the other two. I argue that external pressure from major shareholder countries, usually supported or pushed by NGOs, is a key factor determining the depth of an MDB's commitment to new mandates, such as the environment. However, shareholder commitment is a necessary but not sufficient condition in explaining the banks' environmental behavior. Governance structures for all three banks are diffuse, and, as a result, institutional design and incentive systems play critical roles in how environmental objectives are translated into activities. In all three cases, the banks' internal incentive systems are poorly aligned with their environmental goals, and even where institutional variables are structured to promote greater awareness of environmental issues within the banks, they do not always work as envisioned. Theoretically, the dissertation argues that different causal variables matter at different stages of the policy process. Neorealist approaches have the most explanatory power in accounting for how environmental ideas are brought to the MDBs, but are insufficient in explaining outcomes. Approaches drawn from institutionalist and organizational theories, in turn, provide guidance in analyzing the mechanisms by which environmental objectives are translated into practice. The argument calls for a better integration of international relations theories emphasizing the importance of shareholder politics with theories that focus on how institutional arrangements shape behavior.by Tamar L. Gutner.Ph.D

The effect of bacteria on planula-larvae settlement and metamorphosis in the octocoral Rhytisma fulvum fulvum

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Freire, I., Gutner-Hoch, E., Muras, A., Benayahu, Y., & Otero, A. The effect of bacteria on planula-larvae settlement and metamorphosis in the octocoral Rhytisma fulvum fulvum. Plos One, 14(9), (2019): e0223214, doi:10.1371/journal.pone.0223214.While increasing evidence supports a key role of bacteria in coral larvae settlement and development, the relative importance of environmentally-acquired versus vertically-transferred bacterial population is not clear. Here we have attempted to elucidate the role of post-brooding-acquired bacteria on the development of planula-larvae of the octocoral Rhytisma f. fulvum, in an in vitro cultivation system employing different types of filtered (FSW) and autoclaved (ASW) seawater and with the addition of native bacteria. A good development of larvae was obtained in polystyrene 6-well cell culture plates in the absence of natural reef substrata, achieving a 60–80% of larvae entering metamorphosis after 32 days, even in bacteria-free seawater, indicating that the bacteria acquired during the brooding period are sufficient to support planulae development. No significant difference in planulae attachment and development was observed when using 0.45 μm or 0.22 μm FSW, although autoclaving the 0.45 μm FSW negatively affected larval development, indicating the presence of beneficial bacteria. Autoclaving the different FSW homogenized the development of the larvae among the different treatments. The addition of bacterial strains isolated from the different FSW did not cause any significant effect on planulae development, although some specific strains of the genus Alteromonas seem to be beneficial for larvae development. Light was beneficial for planulae development after day 20, although no Symbiodinium cells could be observed, indicating either that light acts as a positive cue for larval development or the presence of beneficial phototrophic bacteria in the coral microbiome. The feasibility of obtaining advanced metamorphosed larvae in sterilized water provides an invaluable tool for studying the physiological role of the bacterial symbionts in the coral holobiont and the specificity of bacteria-coral interactions.This work was supported by: EU FP7-Research Infrastructure Initiative Assemble (Association of European marine biological laboratories); EU FP7 Project Byefouling (grant agreement no 612717); Xunta de Galicia, Consellería de Cultura, Educación e Ordenación Universitaria (grant number ED431D 2017/22). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript