Excess-entropy scaling of dynamics for a confined fluid of dumbbell-shaped particles

We use molecular simulation to study the ability of excess entropy scaling relationships to describe the kinetic properties of a confined molecular system. We examine a model for a confined fluid consisting of dumbbell-shaped molecules that interact with atomistically detailed pore walls via a Lennard-Jones potential. We obtain kinetic, thermodynamic, and structural properties of the system at three wall-fluid interaction strengths and over a temperature range that includes sub-and super-critical conditions. Four dynamic properties are considered: translational and rotational diffusivities, a characteristic relaxation time for rotational motion, and a collective relaxation time stemming from analysis of the coherent intermediate scattering function. We carefully consider the reference state used to define the excess entropy of a confined fluid. Three ideal-gas reference states are considered, with the cases differentiated by the extent to which one-body spatial and orientational correlations are accounted for in the reference state. Our results indicate that a version of the excess entropy that includes information related to the one-body correlations in a confined fluid serves as the best scaling variable for dynamic properties. When adopting such a definition for the reference state, to a very good approximation, bulk and confined data for a specified dynamic property at a given temperature collapse onto a common curve when plotted against the excess entropy.National Science Foundation CBET-0828979Welch Foundation F-1696David and Lucile Packard FoundationChemical Engineerin

Aging as a consequence of misrepair -- A novel theory of aging

It is now increasingly realized that the underlying mechanisms which govern aging is a complex interplay of genetic regulation and damage accumulation. Aging as a result of accumulation of ‘faults’ on cellular and molecular levels, has been proposed in the damage (fault)-accumulation theory by Kirkwood 2006. However, this theory fails to explain some aging phenotypes such as fibrosis and premature aging, since terms such as ‘damage’ and ‘fault’ are not specified. Therefore we introduce here a specification of the underlying mechanism of aging and arrive at a novel theory: aging of the body is a result of the accumulation of Misrepair of tissue. It emphasizes: a) it is Misrepair, not the original damage, that accumulates and leads to aging; and b) aging can occur at different levels, however aging of the body takes place at least on the tissue level, but not necessarily on cellular/molecular level. The novel concept of Misrepair introduced here unifies the understanding of the roles of environmental damage, repair, gene regulation, and multicellular structure in the aging process. The Misrepair-accumulation theory introduced in the present paper gives explanations for the aging phenotypes, premature aging, and the difference of longevity in different species, and is consistent with the point of view of physical theory of complex systems

Shipping information pipeline: initial design principles

This paper presents a design science approach to solving persistent problems in the international shipping eco system by creating the missing common information infrastructures. Specifically, this paper reports on an ongoing dialogue between stakeholders in the shipping industry and information systems researchers engaged in the design and development of a prototype for an innovative IT-artifact called Shipping Information Pipeline which is a kind of “an internet” for shipping information. The instrumental aim is to enable information seamlessly to cross the organizational boundaries and national borders within international shipping which is a rather complex domain. The intellectual objective is to generate and evaluate the efficacy and effectiveness of design principles for inter-organizational information infrastructures in the international shipping domain that can have positive impacts on global trade and local economies

Geometric principles of second messenger dynamics in dendritic spines.

Dendritic spines are small, bulbous protrusions along dendrites in neurons and play a critical role in synaptic transmission. Dendritic spines come in a variety of shapes that depend on their developmental state. Additionally, roughly 14-19% of mature spines have a specialized endoplasmic reticulum called the spine apparatus. How does the shape of a postsynaptic spine and its internal organization affect the spatio-temporal dynamics of short timescale signaling? Answers to this question are central to our understanding the initiation of synaptic transmission, learning, and memory formation. In this work, we investigated the effect of spine and spine apparatus size and shape on the spatio-temporal dynamics of second messengers using mathematical modeling using reaction-diffusion equations in idealized geometries (ellipsoids, spheres, and mushroom-shaped). Our analyses and simulations showed that in the short timescale, spine size and shape coupled with the spine apparatus geometries govern the spatiotemporal dynamics of second messengers. We show that the curvature of the geometries gives rise to pseudo-harmonic functions, which predict the locations of maximum and minimum concentrations along the spine head. Furthermore, we showed that the lifetime of the concentration gradient can be fine-tuned by localization of fluxes on the spine head and varying the relative curvatures and distances between the spine apparatus and the spine head. Thus, we have identified several key geometric determinants of how the spine head and spine apparatus may regulate the short timescale chemical dynamics of small molecules that control synaptic plasticity

Sec6 mutations and the Drosophila exocyst complex

To allow a detailed analysis of exocyst function in multicellular organisms, we have generated sec6 mutants in Drosophila. We have used these mutations to compare the phenotypes of sec6 and sec5 in the ovary and nervous system, and we find them to be similar. We also find that Sec5 is mislocalized in sec6 mutants. Additionally, we have generated an epitope-tagged Sec8 that localized with Sec5 on oocyte membranes and was mislocalized in sec5 and sec6 germ-line clones. This construct further revealed a genetic interaction of sec8 and sec5. These data, taken together, provide new information about the organization of the exocyst complex and suggest that Sec5, Sec6 and Sec8 act as a complex, each member dependent on the others for proper localization and function

Learning Image-Conditioned Dynamics Models for Control of Under-actuated Legged Millirobots

Millirobots are a promising robotic platform for many applications due to their small size and low manufacturing costs. Legged millirobots, in particular, can provide increased mobility in complex environments and improved scaling of obstacles. However, controlling these small, highly dynamic, and underactuated legged systems is difficult. Hand-engineered controllers can sometimes control these legged millirobots, but they have difficulties with dynamic maneuvers and complex terrains. We present an approach for controlling a real-world legged millirobot that is based on learned neural network models. Using less than 17 minutes of data, our method can learn a predictive model of the robot's dynamics that can enable effective gaits to be synthesized on the fly for following user-specified waypoints on a given terrain. Furthermore, by leveraging expressive, high-capacity neural network models, our approach allows for these predictions to be directly conditioned on camera images, endowing the robot with the ability to predict how different terrains might affect its dynamics. This enables sample-efficient and effective learning for locomotion of a dynamic legged millirobot on various terrains, including gravel, turf, carpet, and styrofoam. Experiment videos can be found at https://sites.google.com/view/imageconddy

A game theoretic rationale for Henderson's rule of three and four

Includes bibliographical references (p. 13-14)

Need a Lift? An Elevator Queueing Problem

Various aspects of the behavior and dispatching of elevators (lifts) were studied. Monte Carlo simulation was used to study the statistics of the several models for the peak demand at uppeak times. Analytical models problems were used to prove or disprove whether schemes were optimal. A mostly integer programming problem was formulated but not studied further