Modeling many-particle mechanical effects of an interacting Rydberg gas

In a recent work [Phys. Rev. Lett. 98, 023004 (2007)] we have investigated the influence of attractive van der Waals interaction on the pair distribution and Penning ionization dynamics of ultracold Rydberg gases. Here we extend this description to atoms initially prepared in Rydberg states exhibiting repulsive interaction. We present calculations based on a Monte Carlo algorithm to simulate the dynamics of many atoms under the influence of both repulsive and attractive longrange interatomic forces. Redistribution to nearby states induced by black body radiation is taken into account, changing the effective interaction potentials. The model agrees with experimental observations, where the ionization rate is found to increase when the excitation laser is blue-detuned from the atomic resonance

Precast tile beam floor

The floor system3 described in this publication is the result of an attempt to obtain a floor of masonry materials, at a minimum cost in placing, which will successfully meet the loading requirements placed upon it. Most systems of masonry floor require considerable unproductive labor and materials which add to the cost but which do not contribute to the effectiveness of the ultimate structure. Forms must be built and dismantled. Even. where moveable and reusable forms are employed, the cost of assembling, dissembling and moving add to the charges which must be ultimately placed against the cost of the floor. This overhead becomes proportionally larger if the forms do not find continuous use

High-resolution spectroscopy of triplet states of Rb2 by femtosecond pump-probe photoionization of doped helium nanodroplets

The dynamics of vibrational wave packets in triplet states of rubidium dimers (Rb2) formed on helium nanodroplets are studied using femtosecond pump-probe photoionization spectroscopy. Due to fast desorption of the excited Rb2 molecules off the droplets and due to their low internal temperature, wave packet oscillations can be followed up to very long pump-probe delay times >1.5ns. In the first excited triplet state (1)^3\Sigma_g^+, full and fractional revivals are observed with high contrast. Fourier analysis provides high-resolution vibrational spectra which are in excellent agreement with ab initio calculations

Development, characteristics, and effects of the new Chatham Harbor inlet

A new tidal inlet into Chatham Harbor, Massachusetts, has developed from a breach in the barrier beach, Nauset Beach, that forms the outer shoreline of southeastern Cape Cod. Increased tidal range and wave energy resulting from the new inlet produced acute coastal erosion and channel shoaling within Chatham Harbor, with significant impacts on the fishing and boating industries, and on private and public propeny and interests. Study results are consistent with the hypothesis that the Nauset-Monomoy barrier beach system undergoes a long-term cycle of geomorphological change, and that a new cycle was initiated with the formation of this new inlet. Based on this new understanding, future changes in the system can be foreseen and provided to coastal resource managers.Funding was provided by the Commonwealth of Massachusetts, Department of Environmental Management, Division of Waterways; the Town of Chatham; Woods Hole Sea Grant Program; Massachusetts Office of Coastal Zone Management; U.S. Army Corps of Engineers (New England Division and Coastal Engineering Research Center); Town of Orleans; and Friends of Pleasant Bay

Coherent Population Trapping with Controlled Interparticle Interactions

We investigate Coherent Population Trapping in a strongly interacting ultracold Rydberg gas. Despite the strong van der Waals interactions and interparticle correlations, we observe the persistence of a resonance with subnatural linewidth at the single-particle resonance frequency as we tune the interaction strength. This narrow resonance cannot be understood within a meanfield description of the strong Rydberg--Rydberg interactions. Instead, a many-body density matrix approach, accounting for the dynamics of interparticle correlations, is shown to reproduce the observed spectral features

Site-specific DNA substrates for human excision repair: comparison between deoxyribose and base adducts

AbstractBackground: The genetic integrity of living organisms is maintained by a complex network of DNA repair pathways. Nucleotide excision repair (NER) is a versatile process that excises bulky base modifications from DNA. To study the substrate range of this system, we constructed bulky deoxyribose adducts that do not affect the chemistry of the corresponding bases. These novel adducts were incorporated into double-stranded DNA in a site-specific manner and the repair of the modified sites was investigated.Results: Using restriction enzymes as a probe for DNA modification, we confirmed that the resulting substrates contained the bulky deoxyribose adducts at the expected position. DNA containing these unique adducts did not stimulate DNA repair synthesis when mixed with an NER-competent human cell extract. Inefficient repair of deoxyribose adducts was confirmed by monitoring the release of single-stranded oligonucleotides during the excision reaction that precedes DNA repair synthesis. As a control, the same human cell extract was able to process a base adduct of comparable size.Conclusions: Our results indicate that modification of DNA bases rather than disruption of the sugar-phosphate backbone is an important determinant for damage recognition by the human NER system. Specific positions in DNA may thus be modified without eliciting NER responses. This observation suggests new strategies for anticancer drug design to generate DNA modifications that are refractory to repair processes