Testing the adequacy of a simple theoretical model of dehydration optical clearing of collagen bundles: OCT measurements

Using optical coherence tomography, the scattering coefficients of collagen bundles are estimated at different levels of tissue hydration. We test the validity of a simple theoretical model of dehydration changes in the optical characteristics of a collagen bundle, which is considered as a system of parallel cylinders that model the collagen fibrils forming the bundle. The characteristics of scattering by individual scatterers are calculated using the Mie theory. To take into account the cooperative effects caused by the close packing of the scatterers, use is made of the standard packing function for a system of identical cylinders. The theoretical model also relies on a certain empirical law of changes in the hydration level of fibrils with a change in the water content in the tissue, which predetermines changes in the diameter and refractive index of fibrils during dehydration and rehydration of the tissue. It is shown that the theoretical estimates obtained using this model are in good agreement with the experimental data, which makes it possible to consider this model as reliable.

Majority-Minority Boards of Directors and Decision Making: The Effects of Homophily on Lending Decisions

In this study, I examine the role racial minorities in the boardroom can play in reducing social injustice by promoting more equal access to mortgage credit to minority households. I develop a simple theoretical model that posits directors who are racial minorities provide the credit unions they govern with a perspective that shapes lenders’ trust of minority applicants. This trust is shaped by homophily and the tendency of individuals to prefer interactions with similar individuals. Using mortgage loan data from a cross-section of credit unions in the United States from 185,446 applications, I find that credit unions where the majority of board members are minorities are less likely to reject a similarly qualified minority applicant than their counterparts. Governance by minority directors significantly reduces the effects of discrimination faced by minority applicants. The board’s effect is strongest in minority neighborhoods and where the homophily is stronger between directors and applicants.

Reconfigurable Surface Micropatterns Based on the Magnetic Field-Induced Shape Memory Effect in Magnetoactive Elastomers

A surface relief grating with a period of 30 µm is embossed onto the surface of magnetoactive elastomer (MAE) samples in the presence of a moderate magnetic field of about 180 mT. The grating, which is represented as a set of parallel stripes with two different amplitude reflectivity coefficients, is detected via diffraction of a laser beam in the reflection configuration. Due to the magnetic-field-induced plasticity effect, the grating persists on the MAE surface for at least 90 h if the magnetic field remains present. When the magnetic field is removed, the diffraction efficiency vanishes in a few minutes. The described effect is much more pronounced in MAE samples with larger content of iron filler (80 wt%) than in the samples with lower content of iron filler (70 wt%). A simple theoretical model is proposed to describe the observed dependence of the diffraction efficiency on the applied magnetic field. Possible applications of MAEs as magnetically reconfigurable diffractive optical elements are discussed. It is proposed that the described experimental method can be used as a convenient tool for investigations of the dynamics of magnetically induced plasticity of MAEs on the micrometer scale.

Deadlines and Memory Limitations

This paper presents the results of two natural field experiments at a dental clinic. Guided by a simple theoretical model, we exogenously vary deadlines and associated rewards for arranging checkup appointments. Our data show strong and systematic effects of deadlines on patients’ behavior. Imposing deadlines induces patients to act earlier and at a persistently higher frequency than without a deadline. We further document that individuals systematically respond to deadlines even if these are not tied to explicit rewards. Several of our findings suggest that individuals’ responses to deadlines are shaped by limitations in memory and attention. Our results illustrate that deadlines can be a powerful management tool to encourage timely task completion and to increase the cost effectiveness of performance-contingent rewards. This paper was accepted by Axel Ockenfels, behavioral economics and decision analysis.

An Empirical Note on the Long-Run Effects of Public and Private R&D on TFP

Several studies have examined the long-run effects of public and private R&D on TFP with mixed results. A common feature of these studies is that they measure public and private R&D activity using perpetual inventory stocks of public and private R&D capital, constructed under the assumption that the prices of GDP, public R&D, and private R&D move identically. This note argues that the results of these studies may be biased if the assumption of identical price movements is violated. The purpose and main contribution of this note is to estimate the long-run elasticities of TFP with respect to public and private R&D using both the stock of public/private R&D capital and an alternative measure of public/private R&D activity: the number of public/private sector researchers. In addition, this study contributes to the literature by developing a simple theoretical model that formalizes the intuition of how public and private R&D affect TFP, and by using both traditional and more recent panel methods. Contrary to previous studies, it is found—using numbers of researchers in the public and private sector—that there is strong evidence both of a significant positive long-run effect of both public and private R&D on TFP and of a greater effect of public R&D than private R&D. Consistent with the mixed evidence reported in the literature, it is also found that the use of public and private R&D stocks yields mixed results regarding the long-run effects of public and private R&D on TFP.

Inheritances, social classes, and wealth distribution

We consider a simple theoretical model to investigate the impact of inheritances on the wealth distribution. Wealth is described as a finite resource, which remains constant over different generations and is divided equally among offspring. All other sources of wealth are neglected. We consider different societies characterized by a different offspring probability distribution. We find that, if the population remains constant, the society reaches a stationary wealth distribution. We show that inequality emerges every time the number of children per family is not always the same. For realistic offspring distributions from developed countries, the model predicts a Gini coefficient of G ≈ 0.3. If we divide the society into wealth classes and set the probability of getting married to depend on the distance between classes, the stationary wealth distribution crosses over from an exponential to a power-law regime as the number of wealth classes and the level of class distinction increase.

Understanding the Size of the Government Spending Multiplier: It's in the Sign

This paper argues that an important, yet overlooked, determinant of the government spending multiplier is the direction of the fiscal intervention. Regardless of whether we identify government spending shocks from (i) a narrative approach, or (ii) a timing restriction, we find that the contractionary multiplier- the multiplier associated with a negative shock to government spending- is above 1 and largest in times of economic slack. In contrast, the expansionary multiplier- the multiplier associated with a positive shock- is substantially below 1 regardless of the state of the cycle. These results help understand seemingly conflicting results in the literature. A simple theoretical model with incomplete financial markets and downward nominal wage rigidities can rationalize our findings.

Ethology of morphogenesis reveals the design principles of cnidarian size and shape development

SummaryDuring development, organisms interact with their natural habitats while undergoing morphological changes, yet it remains unclear whether the interplay between developing systems and their environments impacts animal morphogenesis. Here, we use the cnidarian Nematostella vectensis as a developmental model to uncover a mechanistic link between organism size, shape and behavior. Using quantitative live imaging, including extensive behavioral profiling, combined with molecular and biophysical experiments, we demonstrate that the muscular hydraulic machinery that controls body movement directly drives larva-polyp morphogenesis. Unexpectedly, size and shape development are differentially controlled by antagonistic muscles. A simple theoretical model shows how a combination of slow-priming and fast-pumping pressures generated by muscular hydraulics acts as a global mechanical regulator that coordinates tissue remodeling. Altogether, our findings illuminate how dynamic behavioral modes in the environment can be harnessed to drive morphogenetic trajectories, establishing ethology as a critical component of organismal morphogenesis – termed ethology of morphogenesis.

Structure–Property Relationships for Weak Ferromagnetic Perovskites

Despite several decades of active experimental and theoretical studies of rare-earth orthoferrites, the mechanism of the formation of their specific magnetic, magnetoelastic, optical, and magneto-optical properties remains a subject of discussion. This paper provides an overview of simple theoretical model approaches to quantitatively describing the structure–property relationships—in particular, the interplay between FeO6 octahedral deformations/rotations and the main magnetic and optic characteristics, such as Néel temperature, overt and hidden canting of magnetic sublattices, magnetic and magnetoelastic anisotropy, and optic and photoelastic anisotropy.

Market Choices Driven by Reference Groups: A Comparison of Analytical and Simulation Results on Random Networks

The present paper reports simulation results for a simple model of reference group influence on market choices, e.g., brand selection. The model was simulated on three types of random graphs, Erdos–Renyi, Barabasi–Albert, and Watts–Strogatz. The estimates of equilibria based on the simulation results were compared to the equilibria of the theoretical model. It was verified that the simulations exhibited the same qualitative behavior as the theoretical model, and for graphs with high connectivity and low clustering, the quantitative predictions offered a viable approximation. These results allowed extending the results from the simple theoretical model to networks. Thus, by increasing the positive response towards the reference group, the third party may create a bistable situation with two equilibria at which respective brands dominate the market. This task is easier for large reference groups.