2,547 research outputs found
Diastereofacial selectivity in reactions of substituted cyclohexyl radicals. An experimental and theoretical study
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
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
Hydrodynamical Modeling of a MultipleâInlet Estuary/Barrier System: Insight Into Tidal Inlet Formation and Stability
Two specific questions are addressed concerning the role of tidal hydrodynamics in determining the longâterm morphologic evolution of the Nauset BeachâMonomoy Island barrier system and the Chatham HarborâPleasant Bay tidal estuary, Massachusetts: (1) why do the barrier and estuary exhibit a longâterm (âŒ150 yr) cycle of new inlet formation, and (2) once a new inlet forms, why is the resulting multiple inlet system unstable? To address these questions, a branched 1âd numerical model is used to recreate the basic flow patterns in the tidal estuary at tenâyear intervals during the last half century and also to recreate flow conditions shortly before and shortly after the formation of the new inlet. Results suggest that an inlet will form through Nauset Beach once southerly elongation of the barrier has led to a critical head across the barrier at high tide. If this critical head (enhanced by storm surge and wave setâup) exists at high tide during consecutive tidal cycles, flood currents can deepen the overwash channel sufficiently to enable the stronger ebb currents to complete the formation process. Once a new inlet has formed, the surface gradient and tidal discharge are drastically reduced along the preâexisting channel to the south of the inlet. This reduction eliminates the tidal scouring action needed to keep the channel open. Rapid shoaling within the channel to the south of the new inlet completes the hydrodynamic decoupling of the northern and southern sections of the estuary.https://scholarworks.wm.edu/vimsbooks/1037/thumbnail.jp
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