Local Exchangeability

Exchangeability---in which the distribution of an infinite sequence is invariant to reorderings of its elements---implies the existence of a simple conditional independence structure that may be leveraged in the design of probabilistic models, efficient inference algorithms, and randomization-based testing procedures. In practice, however, this assumption is too strong an idealization; the distribution typically fails to be exactly invariant to permutations and de Finetti's representation theory does not apply. Thus there is the need for a distributional assumption that is both weak enough to hold in practice, and strong enough to guarantee a useful underlying representation. We introduce a relaxed notion of local exchangeability---where swapping data associated with nearby covariates causes a bounded change in the distribution. We prove that locally exchangeable processes correspond to independent observations from an underlying measure-valued stochastic process. We thereby show that de Finetti's theorem is robust to perturbation and provide further justification for the Bayesian modelling approach. Using this probabilistic result, we develop three novel statistical procedures for (1) estimating the underlying process via local empirical measures, (2) testing via local randomization, and (3) estimating the canonical premetric of local exchangeability. These three procedures extend the applicability of previous exchangeability-based methods without sacrificing rigorous statistical guarantees. The paper concludes with examples of popular statistical models that exhibit local exchangeability

Damage-growth-induced evolution of contact resistance of a RF MEMS switch

This study presented the evolution of the contact resistance induced by the growth of the contact damage between the switch contact tip and the drain surface in the lifetime of an ohmic RF MEMS switch. Omron 2SMES-01 commercial switch was selected for the experiment. All switches were operated under the hot-switching condition with a steeply rising actuation voltage. The voltage across the switch (switching voltage) was maintained as 20x of manufacturer’s specified value. Per million-cycle interval, the switching voltage, current, and contact resistance were recorded. The measurements showed three different situations of the contact resistance evolution: (i) the contact resistance monotonically decreases initially to a minimum and then monotonically increases; (ii) the resistance initially decreases to a local minimum, then increases to a local maximum, subsequently decreases to another local minimum, and finally increases; (iii) the resistance decreases initially and then increases until the switch fails in contact; the switch functions again after an intermitted response, and subsequently the resistance decreases again and then increases. A nonadhesive contact model is developed to explain these three situations. The modeling results show that the hot-switching condition changes properties of the contact materials, i.e., the elastic modulus and the yield strength, around the contact region and then causes some plastic deformation around the tip summit. The contact penetration and the contact area increase gradually due to the growth of the plastic deformation. Thus, the contact resistance which is reciprocally proportional to the contact area decreases in the initial stages of all cases. After unloading the tip per contact cycle, a residual depth is produced between the tip and the drain. The growth of the plastic deformation increases the residual depth. When the contact penetration reaches the value corresponding to the maximum contact area, the fixed electrostatic force cannot make the tip a deeper penetration due to a quite large residual depth. Consequently, the reduced contact penetration decreases the contact area. Therefore, the contact resistance dependent on the contact area rises gradually in the second stage as the first case. If the tip displacement caused by the electrostatic force is close to the tip–drain gap within a residual depth, a local minimum contact area will be produced to cause a local maximum contact resistance in the switch lifetime as the second case. A temporary failure in contact occurs when the tip displacement is smaller than the tip–drain gap within a residual depth. The slowing growth of the residual depth allows the tip–drain contact again as the third case

Employment and income support policies during the early phases of COVID-19: Lessons from the U.S., Denmark, and Taiwan

As COVID-19 spread across the world in 2020, health and economic activities have been impacted, and unemployment has risen across many countries. The consequences have been particularly harmful to vulnerable populations such as women, racial minorities, or part-time workers. While many governments enacted employment and income support policies as a response to this economic and health crisis, there has been a lack of comparative and evaluative reviews of how policies have addressed unemployment and inequality during the pandemic. In this study, we draw on Esping-Andersen’s (1990) frame of a liberal versus social-democratic welfare state to contextualize some employment and income support polices during the early phases of COVID-19 from the U.S., Denmark, and Taiwan, aiming to enhance the understanding of such policies. We found that the U.S., being more aligned with a liberal welfare state regime, relied on more market mechanisms to address labor and employment issues. Denmark and Taiwan, being more aligned with a social-democratic welfare state, enacted more interventions in and redistributions outside of the market to address employment problems. The human costs of unemployment and unemployment and labor market hysteresis are addressed in light of these two different approaches and outcomes

A Community-Based Walk-In Screening of Depression in Taiwan

Depression is a crucial public health problem because of its relatively high association with suicidal attempts, prolonged social isolation, poor physical health, and dementia. However, the available data and study on the prevalence of depression in Taiwan were mostly completed within the previous 1 to 2 decades, and these studies were limited to certain areas or populations. Little is known regarding the current status of depression in Taiwan. We used a brief tool, the Center for Epidemiological Studies Depression Scale (CES-D), to screen depression in 4 areas among the general and aged population. The results showed a higher CES-D score in the southern area among general (mean ± SD: 7.8 ± 8.4) or aged participants (mean ± SD: 7.2 ± 8.0) compared with other areas. The ratio of suspected depression patients was 16.4% of all recruited participants and 13.3% of aged participants. These results may provide information for this public health issue

Efficient Reactive Brownian Dynamics

We develop a Split Reactive Brownian Dynamics (SRBD) algorithm for particle simulations of reaction-diffusion systems based on the Doi or volume reactivity model, in which pairs of particles react with a specified Poisson rate if they are closer than a chosen reactive distance. In our Doi model, we ensure that the microscopic reaction rules for various association and disassociation reactions are consistent with detailed balance (time reversibility) at thermodynamic equilibrium. The SRBD algorithm uses Strang splitting in time to separate reaction and diffusion, and solves both the diffusion-only and reaction-only subproblems exactly, even at high packing densities. To efficiently process reactions without uncontrolled approximations, SRBD employs an event-driven algorithm that processes reactions in a time-ordered sequence over the duration of the time step. A grid of cells with size larger than all of the reactive distances is used to schedule and process the reactions, but unlike traditional grid-based methods such as Reaction-Diffusion Master Equation (RDME) algorithms, the results of SRBD are statistically independent of the size of the grid used to accelerate the processing of reactions. We use the SRBD algorithm to compute the effective macroscopic reaction rate for both reaction- and diffusion-limited irreversible association in three dimensions. We also study long-time tails in the time correlation functions for reversible association at thermodynamic equilibrium. Finally, we compare different particle and continuum methods on a model exhibiting a Turing-like instability and pattern formation. We find that for models in which particles diffuse off lattice, such as the Doi model, reactions lead to a spurious enhancement of the effective diffusion coefficients.Comment: To appear in J. Chem. Phy

Lack of Association between CLEC5A Gene Single-Nucleotide Polymorphisms and Kawasaki Disease in Taiwanese Children

Background. Kawasaki disease is characterized by systemic vasculitis of unknown etiology. Previous genetic studies have identified certain candidate genes associated with susceptibility to KD and coronary artery lesions. Host innate immune response factors are involved in modulating the disease outcome. The aim of this study was to investigate CLEC5A (C-type lectin domain family 5) genetic polymorphisms with regards to the susceptibility and outcome of KD. Methods. A total of 1045 subjects (381 KD patients and 664 controls) were enrolled to identify 4 tagging single-nucleotide polymorphisms (tSNPs) of CLEC5A (rs1285968, rs11770855, rs1285935, rs1285933) by using the TaqMan Allelic Discrimination Assay. The Hardy-Weinberg equilibrium was assessed in cases and controls, and genetic effects were evaluated by the chi-square test. Results. No significant associations were noted between the genotypes and allele frequency of the 4 CLEC5A tSNPs between controls and patients. In the patients, polymorphisms of CLEC5A showed no significant association with coronary artery lesion formation and intravenous immunoglobulin treatment response. Conclusions. This study showed for the first time that polymorphisms of CLEC5A are not associated with susceptibility to KD, coronary artery lesion formation, and intravenous immunoglobulin treatment response in a Taiwanese population