Structural design of concrete filled steel elliptical hollow sections

This paper presents the behaviour and design of axially loaded elliptical steel hollow sections filled with normal and high strength concrete. The experimental investigation was conducted with three nominal wall thickness (4mm, 5mm and 6.3mm) and different infill concrete cube strengths varied from 30 to 100 MPa. The effect of steel tube thickness, concrete strength, and confinement were discussed together with column strengths and load-axial shortening curves were evaluated. The study is limited to cross-section capacity and has not been validated at member level. Comparisons of the tests results together with other available results from the literature have been made with current design method used for the design of composite circular steel sections in Eurocode 4 and AISC codes. It was found that existing design guidance for concrete filled circular hollow sections may generally be safely applied to concrete filled elliptical steel tubes

Enhanced 3-epi-25-hydroxyvitamin D3 signal leads to overestimation of its concentration and amplifies interference in 25-hydroxyvitamin D LC-MS/MS assays

Background 3-epi-25-hydroxyvitamin D3 (3-epi-25OHD3) interferes in most liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays for 25-hydroxyvitamin D (25OHD). The clinical significance of this is unclear, with concentrations from undetectable to 230 nmol/L reported. Many studies have quantified 3-epi-25OHD3 based on 25OHD3 calibrators or other indirect methods, and we speculated that this contributes to the observed variability in reported 3-epi-25OHD3 concentrations. Methods We compared continuous MS/MS infusions of 3-epi-25OHD3 and 25OHD3 solutions, spiked both analytes into the same serum matrix and analysed patient samples to assess the effect of three different quantitation methods on 3-epi-25OHD3 concentration. Experiments were performed on an LC-MS/MS system using a phenyl column which does not resolve 3-epi-25OHD3, and a modified method utilizing a Zorbax SB-CN column that chromatographically resolves 3-epi-25OHD3 from 25OHD3. Results A greater 3-epi-25OHD3 signal, compared with 25OHD3, was observed during equimolar post-column continuous infusion of analyte solutions, and following analysis of a serum pool spiked with both analytes. 3-epi-25OHD3 signal enhancement was dependent on mobile phase composition. Compared with 3-epi-25OHD3 calibrators, indirect quantitation methods resulted in up to 10 times as many samples having 3-epi-25OHD3 concentrations ≥ 10 nmol/L, and an approximately fourfold increase in the maximum observed 3-epi-25OHD3 concentration to 95 nmol/L. Conclusions Enhanced 3-epi-25OHD3 signal leads to overestimation of its concentrations in the indirect quantitation methods used in many previous studies. The enhanced signal may contribute to greater interference in some 25OHD LC-MS/MS assays than others. We highlight that equimolar responses cannot be assumed in LC-MS/MS systems, even if two molecules are structurally similar

The totally nonnegative Grassmannian is a ball

We prove that three spaces of importance in topological combinatorics are homeomorphic to closed balls: the totally nonnegative Grassmannian, the compactification of the space of electrical networks, and the cyclically symmetric amplituhedron.Comment: 19 pages. v2: Exposition improved in many place

Regularity theorem for totally nonnegative flag varieties

We show that the totally nonnegative part of a partial flag variety $G/P$ (in the sense of Lusztig) is a regular CW complex, confirming a conjecture of Williams. In particular, the closure of each positroid cell inside the totally nonnegative Grassmannian is homeomorphic to a ball, confirming a conjecture of Postnikov.Comment: 63 pages, 2 figures; v2: Minor changes; v3: Final version to appear in J. Amer. Math. So

Communication and Coordination in the Laboratory Collective Resistance Game

This paper presents a laboratory collective resistance (CR) game to study how different forms of non-binding communication among responders can help coordinate their collective resistance against a leader who transgresses against them. Contrary to the predictions of analysis based on purely self-regarding preferences, we find that non-binding communication about intended resistance increases the incidence of no transgression even in the one-shot laboratory CR game. In particular, we find that the incidence of no transgression increases from 7 percent with no communication up to 25-37 percent depending on whether communication occurs before or after the leader’s transgression decision. Responders’ messages are different when the leaders can observe them, and the leaders use the observed messages to target specific responders for transgression.Communication ; Cheap Talk ; Collective Resistance ; Laboratory Experiment ; Social Preferences

COMMUNICATION AND COORDINATION IN THE LABORATORY COLLECTIVE RESISTANCE GAME

This paper presents a laboratory collective resistance (CR) game to study how different forms of non-binding communication among responders can help coordinate their collective resistance against a leader who transgresses against them. Contrary to the predictions of analysis based on purely self-regarding preferences, we find that non-binding communication about intended resistance increases the incidence of no transgression even in the one-shot laboratory CR game. In particular, we find that the incidence of no transgression increases from 7 percent with no communication up to 25-37 percent depending on whether communication occurs before or after the leader’s transgression decision. Responders’ messages are different when the leaders can observe them, and the leaders use the observed messages to target specific responders for transgression.Communication, Cheap Talk, Collective Resistance, Laboratory Experiment, Social Preferences

COORDINATING COLLECTIVE RESISTANCE THROUGH COMMUNICATION AND REPEATED INTERACTION

This paper presents a laboratory collective resistance (CR) game to study how different forms of repeated interactions, with and without communication, can help coordinate subordinates' collective resistance to a ???divide-and-conquer??? transgression against their personal interests. In the one-shot CR game, a first???mover (the ???leader???) decides whether to transgress against two responders. Successful transgression increases the payoff of the leader at the expense of the victim(s) of transgression. The two responders then simultaneously decide whether to challenge the leader. The subordinates face a coordination problem in that their challenge against the leader's transgression will only succeed if both of them incur the cost to do so. The outcome without transgression can occur in equilibrium with standard money-maximizing preferences with repeated interactions, but this outcome is not an equilibrium with standard preferences when adding non-binding subordinate ???cheap talk??? communication in the one-shot game. Nevertheless, we find that communication (in the one-shot game) is at least as effective as repetition (with no communication) in reducing the transgression rate. Moreover, communication is better than repetition in coordinating resistance, because it makes it easier for subordinates to identify others who have social preferences and are willing to incur the cost to punish a violation of social norms.Communication, Cheap Talk, Collective Resistance, Divide-and-Conquer, Laboratory Experiment, Repeated Games, Social Preferences

Uncertainty and Resistance to Reform in Laboratory Participation Games

This paper presents a participation game experiment to study the impact of uncertainty and costly political participation on the incidence of reform. Fernandez and Rodrik (1991) show that uncertainty about who will ultimately gain or lose as a result of a reform can prevent its adoption. We introduce intra-group conflict into this framework by incorporating costly political participation, which creates a natural incentive for free-riding on fellow group members’ efforts to influence policy outcomes. An agent, however, may still be willing to participate if her participation is likely to affect the policy outcome given the probabilities of participation by others. Our experimental findings show that uncertainty reduces the incidence of reform even with costly political participation, and that an increase in the cost of participation reduces the participation of all agents, regardless of whether they belong to the majority and minority. This second result cannot be reconciled with the standard mixed strategy Nash equilibrium, but is consistent with the quantal response equilibrium.Reform, Uncertainty, Experiment, Participation Game, Bounded Rationality, Quantal Response Equilibrium