Stochastic models of intracellular transport

The interior of a living cell is a crowded, heterogenuous, fluctuating environment. Hence, a major challenge in modeling intracellular transport is to analyze stochastic processes within complex environments. Broadly speaking, there are two basic mechanisms for intracellular transport: passive diffusion and motor-driven active transport. Diffusive transport can be formulated in terms of the motion of an over-damped Brownian particle. On the other hand, active transport requires chemical energy, usually in the form of ATP hydrolysis, and can be direction specific, allowing biomolecules to be transported long distances; this is particularly important in neurons due to their complex geometry. In this review we present a wide range of analytical methods and models of intracellular transport. In the case of diffusive transport, we consider narrow escape problems, diffusion to a small target, confined and single-file diffusion, homogenization theory, and fractional diffusion. In the case of active transport, we consider Brownian ratchets, random walk models, exclusion processes, random intermittent search processes, quasi-steady-state reduction methods, and mean field approximations. Applications include receptor trafficking, axonal transport, membrane diffusion, nuclear transport, protein-DNA interactions, virus trafficking, and the self–organization of subcellular structures

Channel modeling for diffusive molecular communication - a tutorial review

Molecular communication (MC) is a new communication engineering paradigm where molecules are employed as information carriers. MC systems are expected to enable new revolutionary applications such as sensing of target substances in biotechnology, smart drug delivery in medicine, and monitoring of oil pipelines or chemical reactors in industrial settings. As for any other kind of communication, simple yet sufficiently accurate channel models are needed for the design, analysis, and efficient operation of MC systems. In this paper, we provide a tutorial review on mathematical channel modeling for diffusive MC systems. The considered end-to-end MC channel models incorporate the effects of the release mechanism, the MC environment, and the reception mechanism on the observed information molecules. Thereby, the various existing models for the different components of an MC system are presented under a common framework and the underlying biological, chemical, and physical phenomena are discussed. Deterministic models characterizing the expected number of molecules observed at the receiver and statistical models characterizing the actual number of observed molecules are developed. In addition, we provide channel models for timevarying MC systems with moving transmitters and receivers, which are relevant for advanced applications such as smart drug delivery with mobile nanomachines. For complex scenarios, where simple MC channel models cannot be obtained from first principles, we investigate simulation-driven and experiment-driven channel models. Finally, we provide a detailed discussion of potential challenges, open research problems, and future directions in channel modeling for diffusive MC systems

Index to 1985 NASA Tech Briefs, volume 10, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1985 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

The Development and Application of Microwave Heating

Microwave heating has found many applications ranging from the microwave ovens in kitchen to heat food, to a sterilization apparatus for medical treatment, to materials processing in the various fields. In those applications, microwave heating demonstrates significant advantages over conventional methods in reduced processing time and less environmental impacts. This book is comprised of eight chapters within three parts highlighting different aspects covering both the basic understandings and the advanced applications. The included discussion on the application of microwave heating in the field of food-, chemical engineering-, agricultural-, forestry- and mineral processing industry will provide a passage for future research. As a monograph, it is designed to be a fundamental reference book, aiming to help the readers to concentrate on the key aspects behind the success in microwave heating

Cross-talk-free dual-color fluorescence cross-correlation spectroscopy for high-throughtput screening

High throughput processing of chemical/biochemical information is critical in many areas, such as genome sequencing, drug discovery and clinical diagnostics. Integral to collecting information at high rates with the necessary throughput is the development of systems that can not only monitor the results with high precision and accuracy, but also prepare and process samples prior to the analytical measurement. To achieve the required throughput, we have conducted work directed toward developing a system that provides detection sensitivity at the single-molecule detection (SMD) level. The research was first focused on the development of a sensitive strategy for the detection of proteins (thrombin) at the SMD level. Nucleic acid-based fluorescence sensors were used as recognition elements for the detection of single protein molecules with single-pair fluorescence resonance energy transfer. The technique provided higher analytical sensitivity compared to bulk analog measurements due to the digital readout format (i.e., molecular counting) and also reduced assay turn-around-time. Research was then directed toward the design and construction of a two-color FCCS system, which employed two spectrally separate fluorophores, Cy3 (λabs = 532 nm, λem= 560 nm) and IRD800 (λabs = 780 nm, λem= 810 nm). The system provided negligible color cross-talk (cross-excitation and/or cross-emission) and/or fluorescence resonance energy transfer (FRET). To provide evidence of cross-talk free operation, the system was evaluated using microspheres and quantum dots. Experimental results indicated no color leakage from the microspheres or quantum dots into inappropriate color channels. The enzymatic activity of APE1 was monitored by FCCS using a double-stranded DNA substrate that was dual labeled with Cy3 and IRD800. Activity of APE1 was also monitored in the presence of an inhibitor (7-nitroindole-2-carboxylic acid). To improve sample processing throughput, a multi-phase (water-in-oil) segmented flow microfluidic chip was studied using the FCCS system to monitor APE1 enzyme activity. Aqueous droplets were generated in a perfluorocarbon (FC-3283) carrier fluid with a nonionic surfactant (Perfluorooctanol, 10% v/v) in a polymer microchip. The optical system successfully monitored the controlled generation of highly regular droplets loaded with fluorescent beads at delivery rates ranging from 40 - 60 droplets per sec

Mechanical Behavior of Materials

This text serves to cover in more detail solid mechanics concepts and specifically the material response to stress and strain. This text spans solid mechanics concepts from stress and strain at an atomistic length scale, to linear elasticity, anisotropy, linear viscoelasticity, plasticity, dislocation generation and interactions, and fracture.https://scholarlycommons.pacific.edu/open-textbooks/1015/thumbnail.jp

Acoustic Confinement and Characterization of a Microwave Plasma

High amplitude acoustic fields are used to confine, characterize, and manipulate collisional plasmas with temperatures of a few thousand Kelvin. This dissertation describes the theory, experimental techniques, and apparatus necessary both to generate high amplitude sound in a few thousand Kelvin plasma and to use that sound field to manipulate the plasma within a resonant acoustic cavity. The acoustic field in a spherically symmetric oscillating plasma has been measured to have a Mach number of .03, which is sufficient to cause acoustic radiation pressure effects to confine the plasma to the center of its container. This field also generates convection in the conducting gas, which we study by measuring its effect on the acoustic spectrum, watching the convection occur on high speed video, and by measuring the microwave signal reflected off of the convecting plasma. I also discuss how the varying electrical conductivity due to a high amplitude acoustic field in a plasma may enable a new type of 3D thermoacoustic oscillation