The Online Simple Knapsack Problem with Reservation and Removability

In the online simple knapsack problem, a knapsack of unit size 1 is given and an algorithm is tasked to fill it using a set of items that are revealed one after another. Each item must be accepted or rejected at the time they are presented, and these decisions are irrevocable. No prior knowledge about the set and sequence of items is given. The goal is then to maximize the sum of the sizes of all packed items compared to an optimal packing of all items of the sequence. In this paper, we combine two existing variants of the problem that each extend the range of possible actions for a newly presented item by a new option. The first is removability, in which an item that was previously packed into the knapsack may be finally discarded at any point. The second is reservations, which allows the algorithm to delay the decision on accepting or rejecting a new item indefinitely for a proportional fee relative to the size of the given item. If both removability and reservations are permitted, we show that the competitive ratio of the online simple knapsack problem rises depending on the relative reservation costs. As soon as any nonzero fee has to be paid for a reservation, no online algorithm can be better than 1.5-competitive. With rising reservation costs, this competitive ratio increases up to the golden ratio (? ? 1.618) that is reached for relative reservation costs of 1-?5/3 ? 0.254. We provide a matching upper and lower bound for relative reservation costs up to this value. From this point onward, the tight bound by Iwama and Taketomi for the removable knapsack problem is the best possible competitive ratio, not using any reservations

Summary of large-scale nonplanar reinforced concrete wall tests

Nonplanar wall configurations are prevalent in engineering practice, yet relatively little research has addressed nonplanar walls and the earthquake response of these components remains poorly understood. A recent experimental test program conducted by the authors investigated the earthquake response of modern, ACI Code compliant C‐shaped walls subjected to unidirectional and bidirectional lateral loading. To compare the results of this study with previous experimental investigations conducted by others, this document examines laboratory tests of slender nonplanar walls available in the literature. Response histories, damage patterns, drift capacity and failure mechanisms are used to characterize the behavior of each nonplanar wall test specimen. The impact on behavior of various design parameters as well as unidirectional versus bidirectional load history is investigated. Results are synthesized to provide improved understanding of behavior and guidance for design of nonplanar walls. Section 2 provides an overview of the nonplanar wall test found in the literature. Section 3 provides a more in‐depth overview of C‐ and U‐shaped walls, including the C‐shaped wall tests conducted as part of this study. Section 4 presents failure and response mechanism observed during nonplanar wall tests. Section 5 summarizes observations and presents conclusions about nonplanar wall behavior

Summary of large-scale C-shaped reinforced concrete wall tests

Flexural concrete walls (i.e., walls the yield in flexural prior to failure) are used commonly as the lateral load resisting system for mid‐ and high‐rise buildings on the West Coast. They are relatively stiff under service‐level loading, can take on various configurations to accommodate architectural constraints, and are generally assumed to exhibit ductile response under severe earthquake loading. Despite heavy reliance on concrete walls, relatively little research has been done to investigate the earthquake performance of walls with modern design details. Few data exist characterizing the performance of modern walls under variable levels of earthquake loading or the impact of various design parameters on this performance. Few data exist to support evaluation and validation of numerical models for modern walls. In 2004 a research study funded by the National Science Foundation (NSF), through the Network for Earthquake Engineering Simulation Research (NEESR) program, was initiated to investigate the earthquake performance of slender modern walls. This study is being conducted primarily by faculty and graduate students at the Universities of Washington and Illinois, with experimental testing conducted using the NSF‐funded NEES laboratory at the University of Illinois, Urbana‐Champaign (UIUC). The objectives of this study are to generate experimental data characterizing the seismic response and performance of modern concrete walls, develop numerical models for simulating wall response to support design and research, and develop recommendations for performance‐based seismic design of these systems. The NSF‐funded study included experimental testing of planar rectangular walls, a planar coupled wall, and a C‐shaped wall, with experimental testing limited to unidirectional lateral loading and constant axial loading. In 2009 the Charles Pankow Foundation (CPF) provided supplemental funding to expand the scope of this study to include investigation of the impact of bidirectional loading on the earthquake performance of isolated C‐shaped walls and C‐shaped walls in coupled core‐wall systems. This document presents the results of the three C‐shaped wall tests conducted as part of the NSF and CPF funded study. All three specimens had nominally the same design. The specimens were designed to represent C‐shaped walls in a coupled core‐wall system in a modern mid‐rise building. Specifically, specimens represented the bottom three stories of a C‐shaped wall in a ten‐story core‐wall building; loads were applied to the top of the specimen to achieve a load pattern at the base of the specimen representative of that which would develop in the ten‐story building. All three specimens were subjected to quasi‐static cyclic lateral loading in combination with axial loading. The first specimen, identified as Wall 6 of the NSF‐CPF project, was subjected to unidirectional lateral loading in the direction of the web of the C‐shaped wall and a constant axial load. The second specimen, Wall 7, was subjected to a cruciform lateral load pattern (i.e. loading in the direction of the web of the wall followed by loading in the direction of the wall flanges) as well as bidirectional lateral loading and a constant axial load. The third specimen, Wall 8, was subjected to a cruciform lateral load pattern, bidirectional loading and varying axial load. For Wall 8, a constant axial load was applied when the wall was subject to lateral loading in the direction of the web of the wall; a varying axial load was applied when the wall was subjected to lateral loading in the direction of the wall flanges to simulate the variation in axial load resulting from coupling action in the core‐wall system. The response of test specimens was monitored using multiple instrumentation systems. Multiple fixed and roaming still cameras were used to document damage. A close range photogrammetric system and 2 a Nikon metrology / Krypton system were used to generate displacement field data. Displacement transducers were used to measure specimen deformation and specimen displacement. External concrete strain gages and embedded steel strain gages were used to monitor local strains. Load cells were used to monitor applied loads. This report employs data from load cells and displacement transducers as well as still camera images to characterize wall behavior and provide a preliminary assessment of performance. In the future, data from other instrumentation systems will be employed to refine the preliminary characterization and performance assessment. All data will be archived and made available to the public via NEEShub (http://www.neeshub.org). The presentation of the C‐shaped wall tests is organized as follows. Section 2 presents the specimen design and construction. Section 3 presents material data for the concrete and steel used in specimen construction. Section 4 presents the test setup and the loading protocol used for the tests. Section 5 presents the instrumentation systems and data collection protocol. Section 6, 7, and 8 presents results for the individual wall tests. Section 9 compares the observed behavior of the three specimens. Section 10 presents preliminary conclusions of the experimental investigation

Empirically derived effective stiffness expressions for concrete walls

In most cases, analysis to determine component demands for seismic design of concrete buildings employs linear elastic models in which reduced, effective component stiffnesses are used. This document i) reviews the recommendations for defining the effective flexural, shear and axial stiffness of concrete walls that are included in current design codes, standards and guidelines and ii) compares these recommendations with stiffness expressions derived directly from experimental data by the authors and others. Section 2 reviews existing empirically derived and code‐, standard‐, and guideline‐based expressions for the effective stiffness of concrete walls. Section 3 presents the process used by the authors to compute effective stiffness values from laboratory data. Sections 4 through 6 present effective stiffness values derived from laboratory test data for C‐shaped wall specimens tested as part of this study, for planar wall specimens tested by the authors as part of a previous study, and for non‐planar wall specimens tested by others. Section 7 presents the results of a study in which recommended effective stiffness values were used to compute the yield displacements of seven coupled‐wall specimens tested in the laboratory by the authors and others. Section 8 summarizes the results of this investigation

Delaying Decisions and Reservation Costs

We study the Feedback Vertex Set and the Vertex Cover problem in a natural variant of the classical online model that allows for delayed decisions and reservations. Both problems can be characterized by an obstruction set of subgraphs that the online graph needs to avoid. In the case of the Vertex Cover problem, the obstruction set consists of an edge (i.e., the graph of two adjacent vertices), while for the Feedback Vertex Set problem, the obstruction set contains all cycles. In the delayed-decision model, an algorithm needs to maintain a valid partial solution after every request, thus allowing it to postpone decisions until the current partial solution is no longer valid for the current request. The reservation model grants an online algorithm the new and additional option to pay a so-called reservation cost for any given element in order to delay the decision of adding or rejecting it until the end of the instance. For the Feedback Vertex Set problem, we first analyze the variant with only delayed decisions, proving a lower bound of $4$ and an upper bound of $5$ on the competitive ratio. Then we look at the variant with both delayed decisions and reservation. We show that given bounds on the competitive ratio of a problem with delayed decisions impliy lower and upper bounds for the same problem when adding the option of reservations. This observation allows us to give a lower bound of $\min{\{1+3\alpha,4\}}$ and an upper bound of $\min{\{1+5\alpha,5\}}$ for the Feedback Vertex Set problem. Finally, we show that the online Vertex Cover problem, when both delayed decisions and reservations are allowed, is $\min{\{1+2\alpha, 2\}}$-competitive, where $\alpha \in \mathbb{R}_{\geq 0}$ is the reservation cost per reserved vertex.Comment: 14 Pages, submitte

The Correlation Between Poverty and Access to Essential Surgical Care in Ghana: A Geospatial Analysis.

BACKGROUND: Surgical disease burden falls disproportionately on individuals in low- and middle-income countries. These populations are also the least likely to have access to surgical care. Understanding the barriers to access in these populations is therefore necessary to meet the global surgical need. METHODS: Using geospatial methods, this study explores the district-level variation of two access barriers in Ghana: poverty and spatial access to care. National survey data were used to estimate the average total household expenditure (THE) in each district. Estimates of the spatial access to essential surgical care were generated from a cost-distance model based on a recent surgical capacity assessment. Correlations were analyzed using regression and displayed cartographically. RESULTS: Both THE and spatial access to surgical care were found to have statistically significant regional variation in Ghana (p < 0.001). An inverse relationship was identified between THE and spatial access to essential surgical care (β -5.15 USD, p < 0.001). Poverty and poor spatial access to surgical care were found to co-localize in the northwest of the country. CONCLUSIONS: Multiple barriers to accessing surgical care can coexist within populations. A careful understanding of all access barriers is necessary to identify and target strategies to address unmet surgical need within a given population

Impact of Bi-directional Loading on the Seismic Performance of C-shaped Piers of Core Walls

Reinforced concrete structural walls are commonly used as the primary lateral load resisting system in modern buildings constructed in high seismic regions. Most walls in high-rise buildings are C-shaped to accommodate elevators or other architectural features. C-shaped walls have complex loading and response including: (1) symmetric response in the direction of the web, (2) asymmetric response in the direction of the flange and (3) high compression and shear demands when used as a pier in a coupled-wall configuration. A research study was conducted on C-shaped walls tested under (1) uni-directional and (2) bi-directional loading of an isolated walls and (3) bi-directional loading of a c-shaped pier in a coupled wall system. Each of the walls failed in flexure with strength loss resulting from low-cycle fatigue of the boundary element longitudinal reinforcement with buckling followed by fracture. The damage progression was as follows: (1) cracking at the wall-foundation interface, (2) concrete spalling in the web, (3) buckling and fracture of web reinforcement, (4) spalling in the flanges, (5) buckling and fracture of the bars in the boundary elements. Concrete spalling and steel bar damage occurred at lower strong-axis drift levels for the bi-directionally loaded, resulting in lower drift capacities for these loading protocols. However, for the strong-axis direction, bi-directional loading does not reduce flexural or shear effective stiffness values suggesting that current values are appropriate for design and evaluation of buildings with c-shaped walls

Function and Regulation of Chloroplast Peroxiredoxin IIE

Peroxiredoxins (PRX) are thiol peroxidases that are highly conserved throughout all biological kingdoms. Increasing evidence suggests that their high reactivity toward peroxides has a function not only in antioxidant defense but in particular in redox regulation of the cell. Peroxiredoxin IIE (PRX-IIE) is one of three PRX types found in plastids and has previously been linked to pathogen defense and protection from protein nitration. However, its posttranslational regulation and its function in the chloroplast protein network remained to be explored. Using recombinant protein, it was shown that the peroxidatic Cys121 is subjected to multiple posttranslational modifications, namely disulfide formation, S-nitrosation, S-glutathionylation, and hyperoxidation. Slightly oxidized glutathione fostered S-glutathionylation and inhibited activity in vitro. Immobilized recombinant PRX-IIE allowed trapping and subsequent identification of interaction partners by mass spectrometry. Interaction with the 14-3-3 υ protein was confirmed in vitro and was shown to be stimulated under oxidizing conditions. Interactions did not depend on phosphorylation as revealed by testing phospho-mimicry variants of PRX-IIE. Based on these data it is proposed that 14-3-3υ guides PRX‑IIE to certain target proteins, possibly for redox regulation. These findings together with the other identified potential interaction partners of type II PRXs localized to plastids, mitochondria, and cytosol provide a new perspective on the redox regulatory network of the cell