1,208 research outputs found
Recent advances in experimental techniques to probe fast excited-state dynamics in biological molecules in the gas phase : dynamics in nucleotides, amino acids and beyond
In many chemical reactions, an activation barrier must be overcome before a chemical transformation can occur. As such, understanding the behaviour of molecules in energetically excited states is critical to understanding the chemical changes that these molecules undergo. Among the most prominent reactions for mankind to understand are chemical changes that occur in our own biological molecules. A notable example is the focus towards understanding the interaction of DNA with ultraviolet radiation and the subsequent chemical changes. However, the interaction of radiation with large biological structures is highly complex, and thus the photochemistry of these systems as a whole is poorly understood. Studying the gas-phase spectroscopy and ultrafast dynamics of the building blocks of these more complex biomolecules offers the tantalizing prospect of providing a scientifically intuitive bottom-up approach, beginning with the study of the subunits of large polymeric biomolecules and monitoring the evolution in photochemistry as the complexity of the molecules is increased. While highly attractive, one of the main challenges of this approach is in transferring large, and in many cases, thermally labile molecules into vacuum. This review discusses the recent advances in cutting-edge experimental methodologies, emerging as excellent candidates for progressing this bottom-up approach
Synthesis and Evaluation of Radamide Analogues, A Chimera of Radicicol and Geldanamycin
Previously, we reported the Hsp90 inhibitory activity of radamide, an open chain amide chimera of geldanamycin and radicicol. Attempts to further expand upon structure–activity relationships for this class of Hsp90 inhibitors led to the preparation of a series of radamide analogues focused on differing tether lengths and quinone mimics. In addition, the cup-shaped conformation adopted by the two natural products when bound to the Hsp90 N-terminal ATP binding pocket suggests that conformationally biased compounds may demonstrate improved binding and inhibition. The preparation and evaluation of radamide analogues with cis/trans α,β-unsaturated amides yielded compounds that exhibit improved antiproliferative activity. In addition, several analogues demonstrated the ability to induce degradation of Hsp90-dependent oncogenic signaling proteins in vitro, a hallmark of Hsp90 N-terminal inhibition
Strategies for Monitoring Multiuse Trail Networks: Implications for Practice
Many municipalities, park districts, and nonprofit organizations have begun monitoring nonmotorized traffic on multiuse trails as the need for information about the use of facilities has grown and relatively low-cost sensors for automated monitoring have become available. As they have gained experience, they have begun to move from site-specific monitoring on individual trails to a more comprehensive monitoring of trail networks. This case study review compares strategies developed by 10 organizations for monitoring traffic on multiuse trails, including local, multicounty, statewide, and multistate trail networks. The focus is on approaches to the design of monitoring networks, particularly the rationales or objectives for monitoring and the selection of monitoring sites. It is shown that jurisdictions are following principles of monitoring established by FHWA and that the design of monitoring networks is evolving to meet new challenges, including monitoring large-scale networks. Relevant outcomes and implications for practice are summarized. The researchers concluded that FHWA guidelines can be adapted to many circumstances and can increase information for decision making. Trail monitoring is informing decisions related to facility planning, investment, and safety
Integrated waveguides and deterministically positioned nitrogen vacancy centers in diamond created by femtosecond laser writing
Diamond's nitrogen vacancy (NV) center is an optically active defect with
long spin coherence times, showing great potential for both efficient nanoscale
magnetometry and quantum information processing schemes. Recently, both the
formation of buried 3D optical waveguides and high quality single NVs in
diamond were demonstrated using the versatile femtosecond laser-writing
technique. However, until now, combining these technologies has been an
outstanding challenge. In this work, we fabricate laser written photonic
waveguides in quantum grade diamond which are aligned to within micron
resolution to single laser-written NVs, enabling an integrated platform
providing deterministically positioned waveguide-coupled NVs. This fabrication
technology opens the way towards on-chip optical routing of single photons
between NVs and optically integrated spin-based sensing
The gold standard: accurate stellar and planetary parameters for eight Kepler M dwarf systems enabled by parallaxes
We report parallaxes and proper motions from the Hawaii Infrared Parallax Program for eight nearby M dwarf stars with transiting exoplanets discovered by Kepler. We combine our directly measured distances with mass-luminosity and radius–luminosity relationships to significantly improve constraints on the host stars’ properties. Our astrometry enables the identification of wide stellar companions to the planet hosts. Within our limited sample, all the multi-transiting planet hosts (three of three) appear to be single stars, while nearly all (four of five) of the systems with a single detected planet have wide stellar companions. By applying strict priors on average stellar density from our updated radius and mass in our transit fitting analysis, we measure the eccentricity probability distributions for each transiting planet. Planets in single-star systems tend to have smaller eccentricities than those in binaries, although this difference is not significant in our small sample. In the case of Kepler-42bcd, where the eccentricities are known to be ≃0, we demonstrate that such systems can serve as powerful tests of M dwarf evolutionary models by working in L⋆ − ρ⋆ space. The transit-fit density for Kepler- 42bcd is inconsistent with model predictions at 2.1σ (22%), but matches more empirical estimates at 0.2σ (2%), consistent with earlier results showing model radii of M dwarfs are underinflated. Gaia will provide high-precision parallaxes for the entire Kepler M dwarf sample, and TESS will identify more planets transiting nearby, late-type stars, enabling significant improvements in our understanding of the eccentricity distribution of small planets and the parameters of late-type dwarfs.Support for Program number HST-HF2-51364.001-A was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.Some of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST). STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX09AF08G and by other grants and contracts. This paper includes data collected by the Kepler mission. Funding for the Kepler mission is provided by the NASA Science Mission directorate. The authors acknowledge the Texas Advanced Computing Center (TACC) at The University of Texas at Austin for providing HPC resources that have contributed to the research results reported within this paper. URL: http://www.tacc.utexas.edu. (HST-HF2-51364.001-A - NASA through Space Telescope Science Institute; NAS5-26555 - NASA; NNX09AF08G - NASA Office of Space Science; NASA Science Mission directorate
Polarized micro-Raman studies of femtosecond laser written stress-induced optical waveguides in diamond
Understanding the physical mechanisms of the refractive index modulation
induced by femtosecond laser writing is crucial for tailoring the properties of
the resulting optical waveguides. In this work we apply polarized Raman
spectroscopy to study the origin of stress-induced waveguides in diamond,
produced by femtosecond laser writing. The change in the refractive index
induced by the femtosecond laser in the crystal is derived from the measured
stress in the waveguides. The results help to explain the waveguide
polarization sensitive guiding mechanism, as well as providing a technique for
their optimization.Comment: 5 pages, 4 figure
Challenges in Monitoring Regional Trail
This study reports traffic monitoring results at 30 locations on a 972-mi shared-use trail network across the east-central United States. We illustrate challenges in adapting the principles in the Federal Highway Administration’s Traffic Monitoring Guide to a regional trail network. We make four contributions: 1) we use factor analysis and k-means clustering to implement a stratified random process for selecting monitoring sites; 2) we illustrate quality assurance procedures and the challenges of obtaining valid results from a multi-state monitoring system; 3) we describe variation in trail traffic volumes across five land use classes in response to daily weather and seasons; and 4) we report two performance measures for the network: annual average daily trail traffic and trail miles traveled. The Rails to Trails Conservancy deployed passive infrared traffic monitors in 2015 through 2017. Site-specific regression models were used to impute missing daily traffic volumes. The effects of weather were consistent across land use classes but the effects of temporal variables, including weekend and season of year, varied. A plan for short-duration monitoring is presented. Results confirm the FHWA monitoring principles and the difficulties of implementing them regionally
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