Statistical Methodology for Optimal Sensor Locations for Damage Detection in Structures

A Bayesian statistical methodology is presented for optimally locating the sensors in a structure for the purpose of extracting the most information about the model parameters which can be used in model updating and in damage detection and localization. This statistical approach properly handles the unavoidable uncertainties in the measured data as well as the uncertainties in the mathematical model used to represent the structural behavior. The optimality criterion for the sensor locations is based on information entropy which is a measure of the uncertainty in the model parameters. The uncertainty in these parameters is computed by the Bayesian statistical methodology and then the entropy measure is minimized over the set of possible sensor configurations using a genetic algorithm. Results presented illustrate how both the minimum entropy of the parameters and the optimal sensor configuration depend on the location of sensors, number of sensors, number and type of contributing modes and the structural parameterization (substructuring) scheme used

Zero Lattice Sound

We study the N_f-flavor Gross-Neveu model in 2+1 dimensions with a baryon chemical potential mu, using both analytical and numerical methods. In particular, we study the self-consistent Boltzmann equation in the Fermi liquid framework using the quasiparticle interaction calculated to O(1/N_f), and find solutions for zero sound propagation for almost all mu > mu_c, the critical chemical potential for chiral symmetry restoration. Next we present results of a numerical lattice simulation, examining temporal correlation functions of mesons defined using a point-split interpolating operator, and finding evidence for phonon-like behaviour characterised by a linear dispersion relation in the long wavelength limit. We argue that our results provide the first evidence for a collective excitation in a lattice simulation.Comment: 18 pages, 6 figure

Quantifying the Drivers of Star Formation on Galactic Scales. I. The Small Magellanic Cloud

We use the star formation history of the Small Magellanic Cloud (SMC) to place quantitative limits on the effect of tidal interactions and gas infall on the star formation and chemical enrichment history of the SMC. The coincident timing of two recent (< 4 Gyr) increases in the star formation rate and SMC/Milky Way(MW) pericenter passages suggests that global star formation in the SMC is driven at least in part by tidal forces due to the MW. The Large Magellanic Cloud (LMC) is the other potential driver of star formation, but is only near the SMC during the most recent burst. The poorly constrained LMC-SMC orbit is our principal uncertainty. To explore the correspondence between bursts and MW pericenter passages further, we model star formation in the SMC using a combination of continuous and tidally-triggered star formation. The behavior of the tidally-triggered mode is a strong inverse function of the SMC-MW separation (preferred behavior ~ r^-5, resulting in a factor of ~100 difference in the rate of tidally-triggered star formation at pericenter and apocenter). Despite the success of these closed-box evolutionary models in reproducing the recent SMC star formation history and current chemical abundance, they have some systematic shortcomings that are remedied by postulating that a sizable infall event (~ 50% of the total gas mass) occured about 4 Gyr ago. Regardless of whether this infall event is included, the fraction of stars in the SMC that formed via a tidally triggered mode is > 10% and could be as large as 70%.Comment: Accepted for publication in Ap

Working time regimes: A panel discussion on continuing problems

This article records a panel discussion at the Organizational Working Time Regimes conference on 31 March 2017 at the University of Graz, Austria. The discussion was moderated by Sara Louise Muhr and the panelists were Jana Costas, Susanne Ekman, Laura Empson and Dan Kärreman. The discussion both departed from yet centred on the concept of time itself: how we understand time as academics, employees and managers, and how the notion of time guides and controls all of us in various ways. Through the different perspectives that the panelists have on time and work regimes, it became evident that time – and discussions of time – is complex and context-dependent and needs to be researched as such. The discussion passionately weaved in and out of key questions on work intensification, inequality regimes and resistance to working time regimes that are deeply entwined with dynamic dialectics such as personal/professional, past/future, individual/organizational, worker/leader, good/bad. The panel in this way takes the reader through difficult discussions about what is ‘extreme’, for whom is it extreme and what interventions (if any) can be made by academics. Doing so, the panelists sensitively drew attention to our own line of work, academia, and the work regimes controlling academics

Is your EPL attractive? Classification of publications through download statistics

Here we consider the download statistics of EPL publications. We find that papers in the journal are characterised by fast accumulations of downloads during the first couple of months after publication, followed by slower rates thereafter, behaviour which can be represented by a model with predictive power. We also find that individual papers can be classified in various ways, allowing us to compare categories for open-access and non-open-access papers. For example, for the latter publications, which comprise the bulk of EPL papers, a small proportion (2%) display intense bursts of download activity, possibly following an extended period of less remarkable behaviour. About 18% have an especially high degree of attractiveness over and above what is typical for the journal. One can also classify the ageing of attractiveness by examining download half-lives. Approximately 18% have strong interest initially, waning in time. A further 20% exhibit "delayed recognition" with relatively late spurs in download activity. Although open-access papers enjoy more downloads on average, the proportions falling into each category are similar.Comment: 6 pages, 8 figures, accepted for publication in EP

Failure of Mean Field Theory at Large N

We study strongly coupled lattice QCD with $N$ colors of staggered fermions in 3+1 dimensions. While mean field theory describes the low temperature behavior of this theory at large $N$, it fails in the scaling region close to the finite temperature second order chiral phase transition. The universal critical region close to the phase transition belongs to the 3d XY universality class even when $N$ becomes large. This is in contrast to Gross-Neveu models where the critical region shrinks as $N$ (the number of flavors) increases and mean field theory is expected to describe the phase transition exactly in the limit of infinite $N$. Our work demonstrates that close to second order phase transitions infrared fluctuations can sometimes be important even when $N$ is strictly infinite.Comment: 4 pages, 3 figure

Education Policy and Intergenerational Transfers in Equilibrium

This paper compares partial and general equilibrium effects of alternative financial aid policies intended to promote college participation. We build an overlapping generations life-cycle, heterogeneous-agent, incomplete-markets model with education, labor supply, and consumption/saving decisions. Altruistic parents make inter vivos transfers to their children. Labor supply during college, government grants and loans, as well as private loans, complement parental transfers as sources of funding for college education. We find that the current financial aid system in the U.S. improves welfare, and removing it would reduce GDP by two percentage points in the long-run. Any further relaxation of government-sponsored loan limits would have no salient effects. The short-run partial equilibrium effects of expanding tuition grants (especially their need-based component) are sizeable. However, long-run general equilibrium effects are 3-4 times smaller. Every additional dollar of government grants crowds out 20-30 cents of parental transfers

Education Policy and Intergenerational Transfers in Equilibrium

This paper examines the equilibrium effects of alternative financial aid policies intended to promote college participation. We build an overlapping generations life cycle model with education, labor supply, and consumption/saving decisions. Cognitive and non-cognitive skills of children depend on the cognitive skills and education of parents, and affect education choice and labor market outcomes. Driven by both altruism and paternalism, parents make transfers to their children which can be used to fund education, supplementing grants, loans and the labor supply of the children themselves during college. The crowding out of parental transfers by government programs is sizable and thus cannot be ignored when designing policy. The current system of federal aid is valuable: removing either grants or loans would each reduce output by 2% and welfare by 3% in the long-run. An expansion of aid towards ability-tested grants would be markedly superior to either an expansion of student loans or a labor tax cut. This result is, in part, due to the complementarity between parental education and ability in the production of skills of future generations

Education Policy and Intergenerational Transfers in Equilibrium

This paper examines the equilibrium effects of alternative financial aid policies intended to promote college participation. We build an overlapping generations life-cycle, heterogeneous-agent, incomplete-markets model with education, labor supply, and consumption/saving decisions. Driven by both altruism and paternalism, parents make inter vivos transfers to their children. Both cognitive and non-cognitive skills determine the non-pecuniary cost of schooling. Labor supply during college, government grants and loans, as well as private loans, complement parental resources as means of funding college education. We find that the current financial aid system in the U.S. improves welfare, and removing it would reduce GDP by 4-5 percentage points in the long-run. Further expansions of government-sponsored loan limits or grants would have no salient aggregate effects because of substantial crowding-out: every additional dollar of government grants crowds out 30 cents of parental transfers plus an equivalent amount through a reduction in student’s labor supply. However, a small group of high-ability children from poor families, especially girls, would greatly benefit from more generous federal aid