Interactions 2019

In each issue of Interactions, the School’s annual magazine you will find stories about students, faculty and alumni from each of our disciplines. Learn about the ways our students, faculty and alumni are impacting their communities through health care outreach. Read about their research and how they are contributing to advances in patient care. Meet our Alumni of the Year and get to know our faculty.https://scholarlycommons.pacific.edu/interactions/1010/thumbnail.jp

Evaluating the Success of Compensatory Wetland Mitigation in the California Coastal Zone

Compensatory mitigation is a practice whereby a government agency requires the creation, restoration, enhancement, or preservation of ecological resources to offset unavoidable adverse impacts to environmentally sensitive habitat caused by some form of development. Compensatory wetland mitigation programs have slowed the rate of wetland loss in California and elsewhere, but they have largely failed to offset impacts with a sufficient amount of functional mitigation acreage. In California, more than 90% of the state’s historical wetlands have been drained, diked, filled, or dredged over the past 100 years. This report evaluates the success of compensatory wetland mitigation required by the California Coastal Commission between 2012 and 2018. Methods involved reviewing permits and preparing a database to index all compensatory mitigation projects in the study period; locating all available mitigation plans and monitoring reports for those projects; statistically evaluating each project’s compliance with performance criteria and “no net loss” policies; and performing a literature review to contextualize these findings. As permitted, the Coastal Commission’s compensatory mitigation program appears to have resulted in a net gain of wetlands; however, incomplete monitoring data suggests that the net gain may be lower than reported. Fulfillment of performance criteria was about 70% as reported by annual monitoring reports from 20% of projects. Performance criteria focused mainly on vegetation. Requiring a more diverse range of criteria—including hydrology, soil, and wildlife-based metrics in addition to vegetation—could improve tracking of ecological function. This research also reveals opportunities to improve accountability through technical and procedural reforms, including maintaining a centralized storage system for mitigation monitoring data, requiring that compliance reports be reviewed by technical staff, encouraging clearer descriptions of mitigation requirements, and making compensatory mitigation data more accessible to the public

Hardness of Bichromatic Closest Pair with Jaccard Similarity

Consider collections $\mathcal{A}$ and $\mathcal{B}$ of red and blue sets, respectively. Bichromatic Closest Pair is the problem of finding a pair from $\mathcal{A}\times \mathcal{B}$ that has similarity higher than a given threshold according to some similarity measure. Our focus here is the classic Jaccard similarity $|\textbf{a}\cap \textbf{b}|/|\textbf{a}\cup \textbf{b}|$ for $(\textbf{a},\textbf{b})\in \mathcal{A}\times \mathcal{B}$. We consider the approximate version of the problem where we are given thresholds $j_1>j_2$ and wish to return a pair from $\mathcal{A}\times \mathcal{B}$ that has Jaccard similarity higher than $j_2$ if there exists a pair in $\mathcal{A}\times \mathcal{B}$ with Jaccard similarity at least $j_1$. The classic locality sensitive hashing (LSH) algorithm of Indyk and Motwani (STOC '98), instantiated with the MinHash LSH function of Broder et al., solves this problem in $\tilde O(n^{2-\delta})$ time if $j_1\ge j_2^{1-\delta}$. In particular, for $\delta=\Omega(1)$, the approximation ratio $j_1/j_2=1/j_2^{\delta}$ increases polynomially in $1/j_2$. In this paper we give a corresponding hardness result. Assuming the Orthogonal Vectors Conjecture (OVC), we show that there cannot be a general solution that solves the Bichromatic Closest Pair problem in $O(n^{2-\Omega(1)})$ time for $j_1/j_2=1/j_2^{o(1)}$. Specifically, assuming OVC, we prove that for any $\delta>0$ there exists an $\varepsilon>0$ such that Bichromatic Closest Pair with Jaccard similarity requires time $\Omega(n^{2-\delta})$ for any choice of thresholds $j_2<j_1<1-\delta$, that satisfy $j_1\le j_2^{1-\varepsilon}$

Frequency tunable electronic sources working at room temperature in the 1 to 3 THz band

Compact, room temperature terahertz sources are much needed in the 1 to 3 THz band for developing multi-pixel heterodyne receivers for astrophysics and planetary science or for building short-range high spatial resolution THz imaging systems able to see through low water content and non metallic materials, smoke or dust for a variety of applications ranging from the inspection of art artifacts to the detection of masked or concealed objects. All solid-sate electronic sources based on a W-band synthesizer followed by a high-power W-band amplifier and a cascade of Schottky diode based THz frequency multipliers are now capable of producing more than 1 mW at 0.9THz, 50 μW at 2 THz and 18 μW at 2.6 THz without the need of any cryogenic system. These sources are frequency agile and have a relative bandwidth of 10 to 15%, limited by the high power W-band amplifiers. The paper will present the latest developments of this technology and its perspective in terms of frequency range, bandwidth and power

Trading Determinism for Time in Space Bounded Computations

Savitch showed in $1970$ that nondeterministic logspace (NL) is contained in deterministic $\mathcal{O}(\log^2 n)$ space but his algorithm requires quasipolynomial time. The question whether we can have a deterministic algorithm for every problem in NL that requires polylogarithmic space and simultaneously runs in polynomial time was left open. In this paper we give a partial solution to this problem and show that for every language in NL there exists an unambiguous nondeterministic algorithm that requires $\mathcal{O}(\log^2 n)$ space and simultaneously runs in polynomial time.Comment: Accepted in MFCS 201

Polynomial Threshold Functions for Decision Lists

For $S \subseteq \{0,1\}^n$ a Boolean function $f \colon S \to \{-1,1\}$ is a polynomial threshold function (PTF) of degree $d$ and weight $W$ if there is an integer polynomial $p$ of degree $d$ and with sum of absolute coefficients $W$ such that $f(x) = \text{sign } p(x)$ for all $x \in S$. We study representation of decision lists as PTFs over Boolean cube $\{0,1\}^n$ and over Hamming ball $\{0,1\}^{n}_{\leq k}$. As our first result we show that for all $d = O\left( \left( \frac{n}{\log n}\right)^{1/3}\right)$ any decision list over $\{0,1\}^n$ can be represented by a PTF of degree $d$ and weight $2^{O(n/d^2)}$. This improves the result by Klivans and Servedio by a $\log^2 d$ factor in the exponent of the weight. Our bound is tight for all $d = O\left( \left( \frac{n}{\log n}\right)^{1/3}\right)$ due to the matching lower bound by Beigel. For decision lists over a Hamming ball $\{0,1\}^n_{\leq k}$ we show that the upper bound on the weight above can be drastically improved to $n^{O(\sqrt{k})}$ for $d = \Theta(\sqrt{k})$. We also show that similar improvement is not possible for smaller degree by proving the lower bound $W = 2^{\Omega(n/d^2)}$ for all $d = O(\sqrt{k})$.Comment: 14 page

Multivariate Fractionally Integrated APARCH Modeling of Stock Market Volatility: A multi-country study

Tse (1998) proposes a model which combines the fractionally integrated GARCH formulation of Baillie, Bollerslev and Mikkelsen (1996) with the asymmetric power ARCH speci¯cation of Ding, Granger and Engle (1993). This paper analyzes the applicability of a multivariate constant conditional correlation version of the model to national stock market returns for eight countries. We ¯nd this multivariate speci¯cation to be generally applicable once power, leverage and long-memory e®ects are taken into consideration. In addition, we ¯nd that both the optimal fractional di®erencing parameter and power transformation are remarkably similar across countries. Out-of-sample evidence for the superior forecasting ability of the multivariate FIAPARCH framework is provided in terms of forecast error statistics and tests for equal forecast accuracy of the various models.Asymmetric Power ARCH, Fractional integration, Stock returns, Volatility forecast evaluation

HVDC links between North Africa and Europe: Impacts and benefits on the dynamic performance of the European system

This document is the Accepted Manuscript version of the following article: Mokhtar Benasla, Tayeb Allaoui, Mostefa Brahami, Mouloud Denai, and Vijay K. Sood, ‘HVDC links between North Africa and Europe: Impacts and benefits on the dynamic performance of the European system’, Renewable and Sustainable Energy Reviews, November 2017. Under embargo. Embargo end date: 20 November 2018. The published version is available online at doi: DOI: https://doi.org/10.1016/j.rser.2017.10.075. Published by Elsevier Ltd. This manuscript version is distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (http://creativecommons.org/licenses/by-nc-nd/4.0/ ), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.In the last decade, there have been several initiatives for the deployment of cross-Mediterranean HVDC (High Voltage Direct Current) links to enable the transmission of electrical power from renewable energy sources between North Africa and Europe. These initiatives were mainly driven by the potential economic, environmental and technical benefits of these HVDC interconnections. In previous studies on these projects, some technical aspects of critical importance have not been addressed or studied in sufficient detail. One of these key aspects relates to the impact and possible benefit of these HVDC links on the dynamic performance of the European system which is the major focus of this paper. Several issues relating to the dynamic performance of the system are addressed here. Based on the experience gained from existing AC/DC projects around the world, this paper shows that the HVDC links between North Africa and Europe can greatly improve the dynamic performance of the European system especially in the southern regions. In addition, some challenges on the operation and control of these HVDC links are highlighted and solutions to overcome these challenges are proposed. This review paper, therefore, serves as a preliminary study for further detailed investigation of specific impacts or benefits of these interconnections on the overall performance of the European system.Peer reviewe