MINORITIZED GROUPS AND SOCIAL INTEGRATION AND RECOVERY CAPITAL DEVELOPMENT IN MUTUAL AID FELLOWSHIPS

The aim of this study was to examine the relationship between the level of engagement in recovery oriented mutual aid self-help groups one has, and the development of Recovery Capital (RC), an important variable in the recovery process from substance use disorders (SUDs). This study further assessed the correlation between self-help engagement and RC development for persons from minoritized groups. Results of this study can help social workers understand the efficacy of referrals to free, community-based mutual aid recovery programs for individuals from different demographic backgrounds, particularly those from minoritized groups, who often face barriers to treatment. A survey of a non- probability sample of 215 individuals who self-identify as in recovery was utilized to collect information on demographic characteristics, level of engagement in self-help recovery groups, and level of recovery capital. Quantitative analyses were conducted to compare correlation coefficients between self-help involvement and recovery capital development amongst minoritized groups. The results of this study support the correlation between self-help engagement with RC, as well as the findings indicate that there is no significant difference in results with varying ethnic backgrounds. This study provides evidence that self-help groups such as 12-step meetings are a valuable resource regardless of being from an ethnically minoritized group

Untying Knotted DNA with Elongational Flows

We present Brownian dynamics simulations of initially knotted double-stranded DNA molecules untying in elongational flows. We show that the motions of the knots are governed by a diffusion–convection equation by deriving scalings that collapse the simulation data. When being convected, all knots displace nonaffinely, and their rates of translation along the chain are topologically dictated. We discover that torus knots “corkscrew” when driven by flow, whereas nontorus knots do not. We show that a simple mechanism can explain a coupling between this rotation and the translation of a knot, explaining observed differences in knot translation rates. These types of knots are encountered in nanoscale manipulation of DNA, occur in biology at multiple length scales (DNA to umbilical cords), and are ubiquitous in daily life (e.g., hair). These results may have a broad impact on manipulations of such knots via flows, with applications to genomic sequencing and polymer processing.Singapore-MIT Alliance for Research and Technology (SMART)National Science Foundation (U.S.) (Grant CBET-1335938

Mathematical Models of Physiological Responses to Exercise

This paper develops empirical mathematical models for physiological responses to exercise. We first find single-input single-output models describing heart rate variability, ventilation, oxygen consumption and carbon dioxide production in response to workload changes and then identify a single-input multi-output model from workload to these physiological variabilities. We also investigate the possibility of the existence of a universal model for physiological variability in different individuals during treadmill running. Simulations based on real data substantiate that the obtained models accurately capture the physiological responses to workload variations. In particular, it is observed that (i) different physiological responses to exercise can be captured by low-order linear or mildly nonlinear models; and (ii) there may exist a universal model for oxygen consumption that works for different individuals

Λ\Lambda-Enhanced Imaging of Molecules in an Optical Trap

We report non-destructive imaging of optically trapped calcium monofluoride (CaF) molecules using in-situ $\Lambda$-enhanced gray molasses cooling. $200$ times more fluorescence is obtained compared to destructive on-resonance imaging, and the trapped molecules remain at a temperature of $20\,\mu\text{K}$. The achieved number of scattered photons makes possible non-destructive single-shot detection of single molecules with high fidelity.Comment: 6 pages, 4 figure

Metastable Tight Knots in Semiflexible Chains

Knotted structures can spontaneously occur in polymers such as DNA and proteins, and the formation of knots affects biological functions, mechanical strength and rheological properties. In this work, we calculate the equilibrium size distribution of trefoil knots in linear DNA using off-lattice simulations. We observe metastable knots on DNA, as predicted by Grosberg and Rabin. Furthermore, we extend their theory to incorporate the finite width of chains and show an agreement between our simulations and the modified theory for real chains. Our results suggest localized knots spontaneously occur in long DNA and the contour length in the knot ranges from 600 to 1800 nm.National Science Foundation (U.S.) (NSF Grant No. 1335938)Singapore. National Research FoundationSingapore-MIT Alliance for Research and Technology (SMART

Origin of Metastable Knots in Single Flexible Chains

Recent theoretical progress has explained the physics of knotting of semiflexible polymers, yet knotting of flexible polymers is relatively unexplored. We herein develop a new theory for the size distribution of knots on a flexible polymer and the existence of metastable knots. We show the free energy of a flexible molecule in a tube can be mapped to quantitatively reproduce the free energy distribution of a knot on a flexible chain. The size distribution of knots on flexible chains is expected to be universal and might be observed at a macroscopic scale, such as a string of hard balls.Singapore-MIT Alliance for Research and TechnologyNational Science Foundation (U.S.) (Grant 1335938

Translocation dynamics of knotted polymers under a constant or periodic external field

We perform Brownian dynamics simulations to examine how knots alter the dynamics of polymers moving through nanopores under an external field. In the first part of this paper, we study the situation when the field is constant. Here, knots halt translocation above a critical force with jamming occurring at smaller forces for twist topologies compared to non-twist topologies. Slightly below the jamming transition, the polymer's transit times exhibit large fluctuations. This phenomenon is an example of the knot's molecular individualism since the conformation of the knot plays a large role in the chain's subsequent dynamics. In the second part of the paper, we study the motion of the chain when one cycles the field on and off. If the off time is comparable to the knot's relaxation time, one can adjust the swelling of the knot at the pore and hence design strategies to ratchet the polymer in a controllable fashion. We examine how the off time affects the ratcheting dynamics. We also examine how this strategy alters the fluctuations in the polymer's transit time. We find that cycling the force field can reduce fluctuations near the knot's jamming transition, but can enhance the fluctuations at very high forces since knots get trapped in metastable states during the relaxation process. The latter effect appears to be more prominent for non-torus topologies than torus ones. We conclude by discussing the feasibility of this approach to control polymer motion in biotechnology applications such as sequencing.Singapore-MIT Alliance for Research and Technology (SMART)National Science Foundation (U.S.) (Grant CBET-1335938