Growth Rates and Explosions in Sandpiles

We study the abelian sandpile growth model, where n particles are added at the origin on a stable background configuration in ? ^d . Any site with at least 2d particles then topples by sending one particle to each neighbor. We find that with constant background height h≤2d?2, the diameter of the set of sites that topple has order n ^1/d . This was previously known only for h<d. Our proof uses a strong form of the least action principle for sandpiles, and a novel method of background modification. We can extend this diameter bound to certain backgrounds in which an arbitrarily high fraction of sites have height 2d?1. On the other hand, we show that if the background height 2d?2 is augmented by 1 at an arbitrarily small fraction of sites chosen independently at random, then adding finitely many particles creates an explosion (a sandpile that never stabilizes).     

Redesigning the DNA‐Targeted Chromophore in Platinum–Acridine Anticancer Agents: A Structure–Activity Relationship Study

Platinum–acridine hybrid agents show low‐nanomolar potency in chemoresistant non‐small cell lung cancer (NSCLC), but high systemic toxicity in vivo. To reduce the promiscuous genotoxicity of these agents and improve their pharmacological properties, a modular build–click–screen approach was used to evaluate a small library of twenty hybrid agents containing truncated and extended chromophores of varying basicities. Selected derivatives were resynthesized and tested in five NSCLC cell lines representing large cell, squamous cell, and adenocarcinomas. 7‐Aminobenz[c]acridine was identified as a promising scaffold in a hybrid agent ( P1–B1 ) that maintained submicromolar activity in several of the DNA‐repair proficient and p53‐mutant cancer models, while showing improved tolerability in mice by 32‐fold compared to the parent platinum–acridine ( P1–A1 ). The distribution and DNA/RNA adduct levels produced by the acridine‐ and benz[c]acridine‐based analogues in NCI‐H460 cells (confocal microscopy, ICP‐MS), and their ability to bind G‐quadruplex forming DNA sequences (CD spectroscopy, HR‐ESMS) were studied. P1–B1 emerges as a less genotoxic, more tolerable, and potentially more target‐selective hybrid agent than P1–A1 .     

Determination of anionic surfactants during wastewater recycling process by ion pair chromatography with suppressed conductivity detection

A direct approach utilizing ion pairing reversed-phase chromatography coupled with suppressed conductivity detection was developed to monitor biodegradation of anionic surfactants during wastewater recycling through hydroponic plant growth systems and fixed-film bioreactors. Samples of hydroponic nutrient solution and bioreactor effluent with high concentrations (up to 120 mS electrical conductance) of inorganic ions can be analyzed without pretreatment or interference. The presence of non-ionic surfactants did not significantly affect the analysis. Dynamic linear ranges for tested surfactants [Igepon TC-42, ammonium lauryl sulfate, sodium laureth sulfate and sodium alkyl (C10-C16) ether sulfate] were 2 to approximately 500, 1 to approximately 500, 2.5 to approximately 550 and 3.0 to approximately 630 microg/ml, respectively.     

Axial segregation of granular materials

When mixtures of granular materials are rotated, it is often found that they segregate into bands, along the axis of rotation, which are rich in the various components. This effect is discussed experimentally and theoretically, with emphasis on a mechanism based on surface flow. The complimentary phenomenon of radial segregation is reviewed, and a mechanism is proposed. Finally, we consider the long-time behavior of rotating mixtures, particularly their anomolous coarsening. (c) 1999 American Institute of Physics.     

SURFACE POTENTIAL AND PHOTO-ADSORPTION ONTO SEMICONDUCTORS

Abstract— A theory of photo-adsorption onto semiconductors is developed using the kinetic expressions and the relations for steady state carrier concentrations in terms of the quasien Fermi levels. Expressions are derived which emphasize the importance of the surface potential. In particular it is shown that a significant quantity is the ratio of the surface potential to a critical quantity, Y_sc . An expression for the latter is given and it is shown that photoadsorption occurs if the ratio is greater than unity while desorption occurs if the ratio is less than unity. The theory also suggests a useful graphical representation of the effects of impurities and surface potential on adsorption.     

Dynamics of competitive evolution on a smooth landscape

We study competitive DNA sequence evolution directed by in vitro protein binding. The steady-state dynamics of this process is well described by a shape-preserving pulse which decelerates and eventually reaches equilibrium. We explain this dynamical behavior within a continuum mean-field framework. Analytical results obtained on the motion of the pulse agree with simulations. Furthermore, finite population correction to the mean-field results are found to be insignificant.