Indicators of replicative damage in equine tendon fibroblast monolayers

<p>Background: Superficial digital flexor tendon (SDFT) injuries of horses usually follow cumulative matrix microdamage; it is not known why the reparative abilities of tendon fibroblasts are overwhelmed or subverted. Relevant in vitro studies of this process require fibroblasts not already responding to stresses caused by the cell culture protocols. We investigated indicators of replicative damage in SDFT fibroblast monolayers, effects of this on their reparative ability, and measures that can be taken to reduce it.</p> <p>Results: We found significant evidence of replicative stress, initially observing consistently large numbers of binucleate (BN) cells. A more variable but prominent feature was the presence of numerous gammaH2AX (γH2AX) puncta in nuclei, this being a histone protein that is phosphorylated in response to DNA double-stranded breaks (DSBs). Enrichment for injury detection and cell cycle arrest factors (p53 (ser15) and p21) occurred most frequently in BN cells; however, their numbers did not correlate with DNA damage levels and it is likely that the two processes have different causative mechanisms. Such remarkable levels of injury and binucleation are usually associated with irradiation, or treatment with cytoskeletal-disrupting agents.</p> <p>Both DSBs and BN cells were greatest in subconfluent (replicating) monolayers. The DNA-damaged cells co-expressed the replication markers TPX2/repp86 and centromere protein F. Once damaged in the early stages of culture establishment, fibroblasts continued to express DNA breaks with each replicative cycle. However, significant levels of cell death were not measured, suggesting that DNA repair was occurring. Comet assays showed that DNA repair was delayed in proportion to levels of genotoxic stress.</p> <p>Conclusions: Researchers using tendon fibroblast monolayers should assess their “health” using γH2AX labelling. Continued use of early passage cultures expressing initially high levels of γH2AX puncta should be avoided for mechanistic studies and ex-vivo therapeutic applications, as this will not be resolved with further replicative cycling. Low density cell culture should be avoided as it enriches for both DNA damage and mitotic defects (polyploidy). As monolayers differing only slightly in baseline DNA damage levels showed markedly variable responses to a further injury, studies of effects of various stressors on tendon cells must be very carefully controlled.</p&gt

Tundra water budget and implications of precipitation underestimation

Difficulties in obtaining accurate precipitation measurements have limited meaningful hydrologic assessment for over a century due to performance challenges of conventional snowfall and rainfall gauges in windy environments. Here, we compare snowfall observations and bias adjusted snowfall to end-of-winter snow accumulation measurements on the ground for 16 years (1999–2014) and assess the implication of precipitation underestimation on the water balance for a low-gradient tundra wetland near Utqiagvik (formerly Barrow), Alaska (2007–2009). In agreement with other studies, and not accounting for sublimation, conventional snowfall gauges captured 23–56% of end-of-winter snow accumulation. Once snowfall and rainfall are bias adjusted, long-term annual precipitation estimates more than double (from 123 to 274 mm), highlighting the risk of studies using conventional or unadjusted precipitation that dramatically under-represent water balance components. Applying conventional precipitation information to the water balance analysis produced consistent storage deficits (79 to 152 mm) that were all larger than the largest actual deficit (75 mm), which was observed in the unusually low rainfall summer of 2007. Year-to-year variability in adjusted rainfall (±33 mm) was larger than evapotranspiration (±13 mm). Measured interannual variability in partitioning of snow into runoff (29% in 2008 to 68% in 2009) in years with similar end-of-winter snow accumulation (180 and 164 mm, respectively) highlights the importance of the previous summer's rainfall (25 and 60 mm, respectively) on spring runoff production. Incorrect representation of precipitation can therefore have major implications for Arctic water budget descriptions that in turn can alter estimates of carbon and energy fluxes

Dynamical electron transport through a nanoelectromechanical wire in a magnetic field

We investigate dynamical transport properties of interacting electrons moving in a vibrating nanoelectromechanical wire in a magnetic field. We have built an exactly solvable model in which electric current and mechanical oscillation are treated fully quantum mechanically on an equal footing. Quantum mechanically fluctuating Aharonov-Bohm phases obtained by the electrons cause nontrivial contribution to mechanical vibration and electrical conduction of the wire. We demonstrate our theory by calculating the admittance of the wire which are influenced by the multiple interplay between the mechanical and the electrical energy scales, magnetic field strength, and the electron-electron interaction

Charging effects in quantum wires

We investigate the role of charging effects in a voltage-biased quantum wire. Both the finite range of the Coulomb interaction and the long-ranged nature of the Friedel oscillation imply a finite capacitance, leading to a charging energy. While observable Coulomb blockade effects are absent for a single impurity, they are crucial if islands are present. For a double barrier, we give the resonance condition, fully taking into account the charging of the island.Comment: 6 Pages RevTeX, no figures, Phys. Rev. B (in press

Hydrology and Meteorology of the Central Alaskan Arctic: Data Collection and Analysis

The availability of environmental data for unpopulated areas of Alaska can best be described as sparse; however, these areas have resource development potential. The central Alaskan Arctic region north of the Brooks Range (referred to as the North Slope) is no exception in terms of both environmental data and resource potential. This area was the focus of considerable oil/gas exploration immediately following World War II. Unfortunately, very little environmental data were collected in parallel with the exploration. Soon after the oil discovery at Prudhoe Bay in November 1968, the U.S. Geological Survey (USGS) started collecting discharge data at three sites in the neighborhood of Prudhoe Bay and one small watershed near Barrow. However, little complementary meteorological data (like precipitation) were collected to support the streamflow observations. In 1985, through a series of funded research projects, researchers at the University of Alaska Fairbanks (UAF), Water and Environmental Research Center (WERC), began installing meteorological stations on the North Slope in the central Alaskan Arctic. The number of stations installed ranged from 1 in 1985 to 3 in 1986, 12 in 1996, 24 in 2006, 23 in 2010, and 7 in 2014. Researchers from WERC also collected hydrological data at the following streams: Imnavait Creek (1985 to present), Upper Kuparuk River (1993 to present), Putuligayuk River (1999 to present, earlier gauged by USGS), Kadleroshilik River (2006 to 2010), Shaviovik River (2006 to 2010), No Name River (2006 to 2010), Chandler River (2009 to 2013), Anaktuvuk River (2009 to 2013), Lower Itkillik River (2012 to 2013), and Upper Itkillik River (2009 to 2013). These catchments vary in size, and runoff generation can emanate from the coastal plain, the foothills or mountains, or any combination of these locations. Snowmelt runoff in late May/early June is the most significant hydrological event of the year, except at small watersheds. For these watersheds, rain/mixed snow events in July and August have produced the floods of record. Ice jams are a major concern, especially in the larger river systems. Solid cold season precipitation is mostly uniform over the area, while warm season precipitation is greater in the mountains and foothills than on the coastal plain (roughly 3:2:1, mountains:foothills: coastal plain).The results reported here are primarily for the drainages of the Itkillik, Anaktuvuk, and Chandler River basins, where a proposed transportation corridor is being considered. Results for 2011 and before can be found in earlier reports.ABSTRACT ..................................................................................................................................... i LIST OF FIGURES ........................................................................................................................ v LIST OF TABLES .......................................................................................................................... x ACKNOWLEDGMENTS AND DISCLAIMER ........................................................................ xiii CONVERSION FACTORS, UNITS, WATER QUALITY UNITS, VERTICAL AND HORIZONTAL DATUM, ABBREVIATIONS, AND SYMBOLS ........................................... xiv ABBREVIATIONS, ACRONYMS, AND SYMBOLS .............................................................. xvi 1 INTRODUCTION ................................................................................................................... 1 2 PRIOR RELATED PUBLICATIONS .................................................................................... 5 3 STUDY AREA ........................................................................................................................ 7 4 PREVIOUS STUDIES .......................................................................................................... 11 5 METHODOLOGY AND EQUIPMENT .............................................................................. 15 5.1 Acoustic Doppler Current Profiler ................................................................................. 17 5.2 Discharge Measurements ............................................................................................... 17 5.3 Suspended Sediments ..................................................................................................... 20 5.3.1 River Sediment ........................................................................................................ 21 5.3.2 Suspended Sediment Observations ......................................................................... 21 5.3.3 Suspended Sediment Discharge .............................................................................. 22 5.3.4 Turbidity ................................................................................................................. 23 5.3.5 Bed Sediment Distribution ...................................................................................... 23 5.3.6 Suspended Sediment Grain-Size Distribution ........................................................ 24 6 RESULTS .............................................................................................................................. 25 6.1 Air Temperature and Relative Humidity ........................................................................ 25 6.2 Wind Speed and Direction ............................................................................................. 30 6.3 Net Radiation .................................................................................................................. 38 6.4 Warm Season Precipitation ............................................................................................ 40 6.5 Cold Season Precipitation .............................................................................................. 46 6.6 Annual Precipitation ....................................................................................................... 52 6.7 Soil ................................................................................................................................. 55 6.7.1 Soil Temperature ..................................................................................................... 56 6.7.1.1 Results ................................................................................................................. 57 6.7.2 Soil Moisture ........................................................................................................... 60 6.7.2.1 Results ................................................................................................................. 61 6.8 North Slope Climatology ............................................................................................... 63 6.8.1 Air Temperature ...................................................................................................... 63 6.8.2 Precipitation ............................................................................................................ 65 6.8.2.1 Warm Season Precipitation ................................................................................. 65 6.8.2.2 Cold Season Precipitation ................................................................................... 68 6.8.2.3 Annual Total Precipitation .................................................................................. 70 6.9 Surface Water Hydrology ............................................................................................... 72 6.9.1 Itkillik River ............................................................................................................ 73 6.9.2 Upper Itkillik River ................................................................................................. 74 6.9.2.1 Dye Trace Results, Upper Itkillik River .............................................................. 81 6.9.3 Lower Itkillik River 2013 Breakup and Spring Flood ............................................ 84 6.9.4 Anaktuvuk River ..................................................................................................... 91 6.9.5 Chandler River ...................................................................................................... 100 6.9.6 Additional Field Observations .............................................................................. 107 6.10 River Sediment Results ................................................................................................ 117 6.10.1 Correlation between Isco and Depth-Integrated Samples ..................................... 117 6.10.2 Suspended Sediment Rating Curves ..................................................................... 118 6.10.3 Suspended Sediment Concentrations .................................................................... 119 6.10.4 Suspended Sediment Discharge ............................................................................ 125 6.10.5 Turbidity ............................................................................................................... 129 6.10.6 Bed Sediment Distribution .................................................................................... 134 6.10.7 Suspended Sediment Grain-Size Distribution ...................................................... 136 7 HYDROLOGIC ANALYSIS .............................................................................................. 139 7.1 Precipitation Frequency Analysis ................................................................................. 139 7.2 Manning’s Roughness Coefficient (n) Calculations Revisited .................................... 142 7.3 Hydrological Modeling ................................................................................................ 147 8 CONCLUSIONS ................................................................................................................. 157 9 REFERENCES .................................................................................................................... 163 10 APPENDICES ..................................................................................................................... 169 Appendix A – Air Temperature and Relative Humidity Appendix B – Wind Speed and Direction: Wind Roses Appendix C – Cumulative Warm Season Precipitation for All Years at Each Station and Cumulative Warm Season Precipitation by Year for All Stations, 2007 to 2013 Appendix D – Soil Temperature and Moisture Content Appendix E – Rating Curves and Discharge Measurement Summarie

How backscattering off a point impurity can enhance the current and make the conductance greater than e^2/h per channel

It is well known that while forward scattering has no effect on the conductance of one-dimensional systems, backscattering off a static impurity suppresses the current. We study the effect of a time-dependent point impurity on the conductance of a one-channel quantum wire. At strong repulsive interaction (Luttinger liquid parameter g<1/2), backscattering renders the linear conductance greater than its value e^2/h in the absence of the impurity. A possible experimental realization of our model is a constricted quantum wire or a constricted Hall bar at fractional filling factors nu=1/(2n+1) with a time-dependent voltage at the constriction.Comment: 7 pages, 2 figure

Fabry-Perot interference and spin filtering in carbon nanotubes

We study the two-terminal transport properties of a metallic single-walled carbon nanotube with good contacts to electrodes, which have recently been shown [W. Liang et al, Nature 441, 665-669 (2001)] to conduct ballistically with weak backscattering occurring mainly at the two contacts. The measured conductance, as a function of bias and gate voltages, shows an oscillating pattern of quantum interference. We show how such patterns can be understood and calculated, taking into account Luttinger liquid effects resulting from strong Coulomb interactions in the nanotube. We treat back-scattering in the contacts perturbatively and use the Keldysh formalism to treat non-equilibrium effects due to the non-zero bias voltage. Going beyond current experiments, we include the effects of possible ferromagnetic polarization of the leads to describe spin transport in carbon nanotubes. We thereby describe both incoherent spin injection and coherent resonant spin transport between the two leads. Spin currents can be produced in both ways, but only the latter allow this spin current to be controlled using an external gate. In all cases, the spin currents, charge currents, and magnetization of the nanotube exhibit components varying quasiperiodically with bias voltage, approximately as a superposition of periodic interference oscillations of spin- and charge-carrying ``quasiparticles'' in the nanotube, each with its own period. The amplitude of the higher-period signal is largest in single-mode quantum wires, and is somewhat suppressed in metallic nanotubes due to their sub-band degeneracy.Comment: 12 pages, 6 figure

Reconstructing the origin of Helianthus deserticola: Survival and selection on the desert floor

The diploid hybrid species Helianthus deserticola inhabits the desert floor, an extreme environment relative to its parental species Helianthus annuus and Helianthus petiolaris. Adaptation to the desert floor may have occurred via selection acting on transgressive, or extreme, traits in early hybrids between the parental species. We explored this possibility through a field experiment in the hybrid species' native habitat using H. deserticola, H. annuus, H. petiolaris, and two populations of early-generation (BC2) hybrids between the parental species, which served as proxies for the ancestral genotype of the ancient hybrid species. Character expression was evaluated for each genotypic class. Helianthus deserticola was negatively transgressive for stem diameter, leaf area, and flowering date, and the latter two traits are likely to be advantageous in a desert environment. The BC 2 hybrids contained a range of variation that overlapped these transgressive trait means, and an analysis of phenotypic selection revealed that some of the selective pressures on leaf size and flowering date, but not stem diameter, would move the BC2 population toward the H. deserticola phenotype. Thus, H. deserticola may have originated from habitat-mediated directional selection acting on hybrids between H. annuus and H. petiolaris in a desert environment