Collective Gradient Sensing in Fish Schools

Throughout the animal kingdom, animals frequently benefit from living in groups. Models of collective behaviour show that simple local interactions are sufficient to generate group morphologies found in nature (swarms, flocks and mills). However, individuals also interact with the complex noisy environment in which they live. In this work, we experimentally investigate the group performance in navigating a noisy light gradient of two unrelated freshwater species: golden shiners (Notemigonuscrysoleucas) and rummy nose tetra (Hemigrammus bleheri). We find that tetras outperform shiners due to their innate individual ability to sense the environmental gradient. Using numerical simulations, we examine how group performance depends on the relative weight of social and environmental information. Our results highlight the importance of balancing of social and environmental information to promote optimal group morphologies and performance

Illness reporting and demand for medical care in rural Burkina Faso

This is the post-print version of the final paper published in Social Science & Medicine. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2010 Elsevier B.V.The issue of illness reporting in modelling demand for health care in low- and middle-income countries can be handled according to either of two conceptually-different constructs: (a) considering illness reporting behaviour as endogenous to demand; or (b) considering demand itself as the outcome of a sample selection phenomenon. In this paper, we take the second viewpoint and estimate the demand for medical care with an estimator that uses Heckman-type. Empirical estimates based on household survey data from rural Burkina Faso suggest that there are some implications of illness reporting behaviour for modelling the demand for medical care.German Science Foundatio

Prevalence of Postpartum Family Planning Service Coverage in Selected Referral Facilities of Nepal

Introduction: Nepal Society of Obstetricians and Gynecologists jointly with the Nepalese government and with the support from the International Federation of Obstetrics and Gynecology has implemented an initiative to institutionalize postpartum family planning services in selected major referral facilities of Nepal to address the gap of low uptake of postpartum family planning in Nepal. The aim of the study is to find the prevalence of the service coverage of postpartum contraception in the selected facilities. Methods: A descriptive cross-sectional study was conducted in seven major referral facilities across Nepal. Data were collected from the hospital records of all women who delivered in these facilities between October 2018 and March 2019. Ethical approval for this study was obtained from Nepal Health Research Council. Data analysis was done with SPSS version 23. Results: Among the 29,072 deliveries from all the facilities, postpartum family planning counseling coverage was 27,301 (93.9%). The prevalence of uptake of Postpartum Intrauterine Device is 1581 (5.4%) and female sterilization is 1830 (6.3%). In total 11387 mothers (52.2%) had the intention to choose a postpartum family planning method. However, 36% of mothers neither used nor had the intention to choose a postpartum family planning method. Conclusions: The coverage of Postpartum Intrauterine Device counseling service coverage in Nepal is higher in 2018 as compared to 2016-2017 and in other countries implementing Postpartum Intrauterine Device initiatives. However, the prevalence of service coverage of immediate Postpartum Family Planning methods, mainly Postpartum Intrauterine Device in 2018 is lower in Nepal as compared to 2016-2017, and other countries implementing Postpartum Intrauterine Device initiative. More efforts are needed to encourage mothers delivering in the facilities to use the postpartum family planning method

Analyzing and Mimicking the Optimized Flight Physics of Soaring Birds: A Differential Geometric Control and Extremum Seeking System Approach with Real Time Implementation

For centuries, soaring birds -- such as albatrosses and eagles -- have been mysterious and intriguing for biologists, physicists, aeronautical/control engineers, and applied mathematicians. These fascinating biological organisms have the ability to fly for long-duration while spending little to no energy. This flight technique/maneuver is called dynamic soaring (DS). For biologists and physicists, the DS phenomenon is nothing but a wonder of the very elegant ability of the bird's interaction with nature and using its physical ether in an optimal way for better survival and energy efficiency. For the engineering community, it is a source of inspiration and an unequivocal promising chance for bio-mimicking. In literature, significant work has been done on modeling and constructing control systems that allow the DS maneuver to be mimicked. However, mathematical characterization of the DS phenomenon in literature has been limited to optimal control configurations that utilized developments in numerical optimization algorithms along with control methods to identify the optimal DS trajectory taken (or to be taken) by the bird/mimicking system. In this paper, we provide a novel two-layered mathematical approach to characterize, model, mimic, and control DS in a simple and real-time implementation. The first layer will be a differential geometric control formulation and analysis of the DS problem. The second layer will be a linkage between the DS philosophy and a class of dynamical control systems known as extremum seeking systems. We believe our framework captures more of the biological behavior of soaring birds and opens the door for geometric control theory and extremum seeking systems to be utilized in systems biology and natural phenomena. Simulation results are provided along with comparisons with powerful optimal control solvers to illustrate the advantages of the introduced method

Ferroelectric Switching Pathways and Domain Structure of SrBi2_2(Ta,Nb)2_2O9_9 from First Principles

Several families of layered perovskite oxide ferroelectrics exhibit a coupling between polarization and structural order parameters, such as octahedral rotation distortions. This coupling provides opportunities for novel electric field-based manipulation of material properties, and also stabilizes complex domain patterns and domain wall vortices. Amongst layered perovskites with such coupled orders, the Aurivillius-phase oxides SrBi$_2B_2$O$_9$ ($B$=Ta, Nb) are well-known for their excellent room temperature ferroelectric performance. This work combines group theoretic analysis with density functional theory calculations to examine the ferroelectric switching processes of SrBi$_2B_2$O$_9$. Low-energy two-step ferroelectric switching paths are identified, with polarization reversal facilitated by structural order parameter rotations. Analysis of the domain structure reveals how the relative energetics of the coupled order parameters translates into a network of several distinct domain wall types linked by domain wall vortex structures. Comparisons are made between the ferroelectric switching and domain structure of SrBi$_2B_2$O$_9$ and those of the layered $n$=2 Ruddlesden-Popper hybrid improper ferroelectrics. The results provide new insight into how ferroelectric properties may be optimized by engineering the complex crystal structures of Aurivllius-phase oxides

Control-Affine Extremum Seeking Control with Attenuating Oscillations

Control-affine Extremum Seeking Control (ESC) systems have been increasingly studied and applied in the last decade. Similar to classic ESC related structures, control-affine ESC systems are operable by assuming access to measurements of the objective function, and not necessarily its expression. In contrast to classic ESC related structures, in a control-affine ESC, the objective function -- or a map of it -- is incorporated within the system's vector fields themselves. This has invoked the use of tools from geometric control theory, namely Lie Bracket Systems (LBSs). Said LBSs play a crucial role in stability and performance characterization of ESCs. In a recent effort, many control-affine ESC structures have been generalized in a unifying class and analyzed through LBSs. In addition, this generalized class converge asymptotically to the extremum point; however, the extremum point has to be known a priori and guaranteeing vanishing control input at the extremum point requires the application of strong conditions. In this paper, we introduce a LBS-based ESC structure that: (1) does not require the extremum point a priori, (2) its oscillations attenuate structurally via a novel application of a geometric-based Kalman filter estimating LBSs; and (3) its stability is characterized by a time-dependent (one bound) condition that is verifiable via simulations and relaxed when compared to the generalized approach mentioned earlier. We provide numerical simulations of three problems to demonstrate the ability of our proposed ESC; these problems cannot be solved with vanishing oscillations using the above-mentioned generalized approach in literature

2.1μm Emission Spectral Properties of Tm and Ho Doped Transparent YAG Ceramic

Highly transparent Tm:Ho:YAG transparent ceramics were prepared using advanced ceramic technology and their spectroscopic properties were studied for infrared laser applications. Following the Judd-Ofelt procedure several spectroscopic properties such as the radiative transition probability (Arad), radiative decay time (τrad) and fluorescence branching ratio (β) are quantitatively obtained from the absorption spectrum. The absorption and emission cross sections corresponding to the 5I7 → 5I8 transition of Ho3+ at 2.1 μm have been evaluated following Mc Cumber theory and found that the obtained emission spectrum very well correlates to the simulated emission spectral data. The optical gain spectrum spread from 1800 nm to 2150 nm with a spectral width of over 107 nm and maximum gain coefficient of 0.44 cm–1. Thus it is expected that the Tm3+:Ho3+:YAG ceramics would be an appropriate host material to achieve infrared laser applications at 2.1 μm

Synthesis and Upconversion Spectroscopy of Yb Er Doped M2O2S (M = La, Gd, Y) Phosphors

Yb and Er doped M2O2S (M = Y, Gd, La) phosphor was synthesized by solid state flux fusion method and their up conversion spectral properties were studied as a function different Yb concentrations. The solid state flux fusion results in well crystallized hexagonal shaped phosphor particles of average size 4–6 μm. Upconversion spectral studies shows that all the compositions are stronger in green emission with the green emission intensity 1.7 times than the red in composition Gd2O2S:Yb(8)Er(1), Y2O2S:Yb(9)Er(1), La2O2S:Yb(3)Er(7) (All mol%). The internal upconversion efficiency for the green emission bands was calculated to be 74, 62, 100% respectively in Gd2O2S:Yb(8)Er(1), Y2O2S:Yb(8)Er(1), La2O2S:Yb(8)Er(1). Mechanisms of up conversion by two photon and energy transfer processes are interpreted and explained. The x, y color coordinates are measured and the color tunability was analyzed as a function of the 980 nm excitation power. Results shows that all phosphor offers power dependent color tuning properties where the emission color can be tuned from 490 nm to 550 nm by simply changing the 980 nm excitation power from 10–50 mW