Sensing and decision-making in random search

While microscopic organisms can use gradient-based search to locate resources, this strategy can be poorly suited to the sensory signals available to macroscopic organisms. We propose a framework that models search-decision making in cases where sensory signals are infrequent, subject to large fluctuations, and contain little directional information. Our approach simultaneously models an organism's intrinsic movement behavior (e.g. Levy walk) while allowing this behavior to be adjusted based on sensory data. We find that including even a simple model for signal response can dominate other features of random search and greatly improve search performance. In particular, we show that a lack of signal is not a lack of information. Searchers that receive no signal can quickly abandon target-poor regions. Such phenomena naturally give rise to the area-restricted search behavior exhibited by many searching organisms

A Stochastic Compartmental Model for Fast Axonal Transport

In this paper we develop a probabilistic micro-scale compartmental model and use it to study macro-scale properties of axonal transport, the process by which intracellular cargo is moved in the axons of neurons. By directly modeling the smallest scale interactions, we can use recent microscopic experimental observations to infer all the parameters of the model. Then, using techniques from probability theory, we compute asymptotic limits of the stochastic behavior of individual motor-cargo complexes, while also characterizing both equilibrium and non-equilibrium ensemble behavior. We use these results in order to investigate three important biological questions: (1) How homogeneous are axons at stochastic equilibrium? (2) How quickly can axons return to stochastic equilibrium after large local perturbations? (3) How is our understanding of delivery time to a depleted target region changed by taking the whole cell point-of-view

Deep desulfurization of petroleum feedstocks by selective adsorption and extraction

The ability of Ru(NH3)5(H2O) 2+ to bind to thiophenes has been used in an extraction process in which a solution of Ru(NH3)5(H2O) 2+ in 70% DMF and 30% H2O is contacted with a simulated petroleum feedstock (45% toluene/55% hexanes) containing 400 ppm of DBT. Five successive extractions reduce the amount of DBT in the simulated feedstock from 400 ppm to 25 ppm. The Ru(NH3)5(H2O) 2+ extractant can be regenerated from the Ru(NH3) 5(DBT)2+ either by air-oxidation followed by H2-reduction or by displacement of the DBT by adding H2O to the DMF/H2 O phase.;Complexes CpRu(CO)2(BF4) and CpFe(CO)2(THF) 2+ were adsorbed onto a mesoporous silica substrate. When these modified silica surfaces are stirred with a simulated gasoline feedstock containing 400 ppm(S) DBT, they form CpRu(CO)2(DBT)+ and CpFe(CO) 2(DBT)+ on the silica surface and lower DBT levels by 98% and 70% respectively, as determined by GC. These metal-complex modified surfaces behave as solid phase extractants (SPEs) towards sulfur impurities in gasoline and diesel fuels. The surface metal-DBT complexes, have been characterized by CP MAS 13C NMR and XPS. Through their independent synthesis, the X-ray structures of CpRu(CO)2(DBT)+ and CpFe(CO) 2(DBT)+ were solved.;Finally, we report the use of solid phase extractants (SPE) consisting of Ag+ salts (SPE-Ag) adsorbed on mesoporus SBA-15 or amorphous silica for the removal of DBT and 4,6-Me2DBT from a simulated diesel feedstocks. In these extractions SPE-Ag was stirred with DBT in decanes. It was observed that within 1 min, the DBT level was reduced from 400 ppm to 72 (+/-9) ppm, while 4,6-Me2DBT was reduced to 75 (+/-6) ppm. The active SPE-Ag may be regenerated by washing with diethylether, thereby separating the DBT from the petroleum feedstocks. The easy regeneration of these adsorbents makes them attractive for the deep desulfurization of petroleum feedstocks

Geometric erogdicity of a bead-spring pair with stochastic Stokes forcing

We consider a simple model for the uctuating hydrodynamics of a exible polymer in dilute solution, demonstrating geometric ergodicity for a pair of particles that interact with each other through a nonlinear spring potential while being advected by a stochastic Stokes uid velocity field. This is a generalization of previous models which have used linear spring forces as well as white-in-time uid velocity fields. We follow previous work combining control theoretic arguments, Lyapunov functions, and hypo-elliptic diffusion theory to prove exponential convergence via a Harris chain argument. To this, we add the possibility of excluding certain "bad" sets in phase space in which the assumptions are violated but from which the systems leaves with a controllable probability. This allows for the treatment of singular drifts, such as those derived from the Lennard-Jones potential, which is an novel feature of this work

Harry Truman's 1948 non-political tour

Honors thesi