Determination of lateral inflows in the Kuparuk River watershed, a study in the Alaskan Arctic

Thesis (M.S.) University of Alaska Fairbanks, 2015The objectives of this research were to investigate the relationships between lateral inflows and watershed characteristics within the Kuparuk watershed of Arctic Alaska, as well as to quantify the lateral inflows to be used as an input for calibrating and running a process-based instream water temperature model. Determination of lateral inflows was accomplished by constructing hydrographs at multiple locations along Imnavait Creek and the Kuparuk River using stage and discharge field measurements. The hydrographs were then routed between gauging stations downstream (starting upstream) using the Muskingum routing method; and finally subtracting the routed hydrograph from the downstream measured hydrograph to calculate any additional water that had entered the reach between gauging stations. Results showed, as a general trend, that reaches within the northern foothills of the Brooks Range experienced larger lateral inflow contributions per square kilometer and had larger runoff ratios than subsequent reaches to the north where the terrain flattens out and transitions into the coastal plain. Two reaches within the watershed contradicted the general trend. The low-gradient reach nearest to the Arctic Ocean experienced larger lateral inflows throughout the summer that were unaffected by rainfall precipitation events; this is believed to be caused by snowmelt water initially stored in the low gradient terrain and slowly released into the drainage network during summer months. This area is rich with wetlands, ponds, and lakes and snow-damming during break up is prevalent. The other reach was located upstream of the Kuparuk aufeis field and was observed to lose water during the summer of 2013, supporting a hypothesis that the aufeis formation in this area is fed throughout the winter by a large talik upstream

Enhanced structural correlations accelerate diffusion in charge-stabilized colloidal suspensions

Theoretical calculations for colloidal charge-stabilized and hard sphere suspensions show that hydrodynamic interactions yield a qualitatively different particle concentration dependence of the short-time self-diffusion coefficient. The effect, however, is numerically small and hardly accessible by conventional light scattering experiments. Applying multiple-scattering decorrelation equipment and a careful data analysis we show that the theoretical prediction for charged particles is in agreement with our experimental results from aqueous polystyrene latex suspensions.Comment: 1 ps-file (MS-Word), 14 page

Phase Behaviour of Amphiphilic Monolayers: Theory and Simulation

Coarse grained models of monolayers of amphiphiles (Langmuir monolayers) have been studied theoretically and by computer simulations. We discuss some of the insights obtained with this approach, and present new simulation results which show that idealised models can successfully reproduce essential aspects of the generic phase behaviour of Langmuir monolayers.Comment: To appear in J. Phys.: Cond. Matte

Coherent Versus Incoherent Ladar Detection at 2.09 μm

A 2.09-μm ladar system is built to compare coherent to incoherent detection. The 2.09-μm wavelength is of interest because of its high atmospheric transmission and because it is eyesafe. The 2.09-μm system presented is capable of either a coherent or incoherent operational mode, is tunable in a small region around 2.09 μm, and is being used to look at the statistical nature of the ladar return pulses for typical glint and speckle targets. To compare coherent to incoherent detection the probability of detection is investigated as the primary performance criterion of interest. The probability of detection is dependent on both the probability of false alarm and the probability density function, representing the signal current output from the detector. These probability distributions are different for each detection technique and for each type of target. Furthermore, the probability of detection and the probability of false alarm are both functions of the dominating noise source(s) in the system. A description of the theoretical expectations of this system along with the setup of the ladar system and how it is being used to collect data for both coherent and incoherent detection is presented

A primer on choosing goals and indicators to evaluate ecological restoration success

We discuss aspects of one of the most important issues in ecological restoration: how to evaluate restoration success. This rst requires clearly stated and justied restoration goals and targets; this may seem “obvious” but in our experience, this step is often elided. Indicators or proxy variables are the typical vehicle for monitoring; these must be justied in the context of goals and targets and ultimately compared against those to allow for an evaluation of outcome (e.g. success or failure). The monitoring phase is critical in that a project must consider how the monitoring frequency and overall design will allow the postrestoration trajectories of indicators to be analyzed. This allows for real‐time management adjustments—adaptive management (sensu lato)—to be implemented if the trajectories are diverging from the targets. However, as there may be large variation in early postrestoration stages or complicated (nonlinear) trajectory, caution is needed before committing to management adjustments. Ideally, there is not only a goal and target but also a model of the expected trajectory—that only can occur if there are sucient data and enough knowledge about the ecosystem or site being restored. With so many possible decision points, we focus readers' attention on one critical step—how to choose indicators. We distinguish generalizable and specic indicators which can be qualitative, semiquantitative, or quantitative. The generalizable indicators can be used for meta‐analyses. There are many options of indicators but making them more uniform would help mutual comparisons among restoration projects

On the Application of a Monolithic Array for Detecting Intensity-Correlated Photons Emitted by Different Source Types

It is not widely appreciated that many subtleties are involved in the accurate measurement of intensity-correlated photons; even for the original experiments of Hanbury Brown and Twiss (HBT). Using a monolithic 4x4 array of single-photon avalanche diodes (SPADs), together with an off-chip algorithm for processing streaming data, we investigate the difficulties of measuring second-order photon correlations g2 in a wide variety of light fields that exhibit dramatically different correlation statistics: a multimode He-Ne laser, an incoherent intensity-modulated lamp-light source and a thermal light source. Our off-chip algorithm treats multiple photon-arrivals at pixel-array pairs, in any observation interval, with photon fluxes limited by detector saturation, in such a way that a correctly normalized g2 function is guaranteed. The impact of detector background correlations between SPAD pixels and afterpulsing effects on second-order coherence measurements is discussed. These results demonstrate that our monolithic SPAD array enables access to effects that are otherwise impossible to measure with stand-alone detectors.Comment: 17 pages, 6 figure

Chiral and herringbone symmetry breaking in water-surface monolayers

We report the observation from monolayers of eicosanoic acid in the L′2 phase of three distinct out-of-plane first-order diffraction peaks, indicating molecular tilt in a nonsymmetry direction and hence the absence of mirror symmetry. At lower pressures the molecules tilt in the direction of their nearest neighbors. In this region we find a structural transition, which we tentatively identify as the rotator-herringbone transition L2d−L2h

Trion formation dynamics in monolayer transition metal dichalcogenides

We report charged exciton (trion) formation dynamics in doped monolayer transition metal dichalcogenides, specifically molybdenum diselenide (MoSe2), using resonant two-color pump-probe spectroscopy. When resonantly pumping the exciton transition, trions are generated on a picosecond time scale through exciton-electron interaction. As the pump energy is tuned from the high energy to low energy side of the inhomogeneously broadened exciton resonance, the trion formation time increases by ∼50%. This feature can be explained by the existence of both localized and delocalized excitons in a disordered potential and suggests the existence of an exciton mobility edge in transition metal dichalcogenides

Long-term spectral and timing properties of the soft gamma-ray repeater SGR 1833-0832 and detection of extended X-ray emission around the radio pulsar PSR B1830-08

SGR 1833-0832 was discovered on 2010 March 19 thanks to the Swift detection of a short hard X-ray burst and follow-up X-ray observations. Since then, it was repeatedly observed with Swift, Rossi X-ray Timing Explorer, and XMM-Newton. Using these data, which span about 225 days, we studied the long-term spectral and timing characteristics of SGR 1833-0832. We found evidence for diffuse emission surrounding SGR 1833-0832, which is most likely a halo produced by the scattering of the point source X-ray radiation by dust along the line of sight, and we show that the source X-ray spectrum is well described by an absorbed blackbody, with temperature kT=1.2 keV and absorbing column nH=(10.4+/-0.2)E22 cm^-2, while different or more complex models are disfavoured. The source persistent X-ray emission remained fairly constant at about 3.7E-12 erg/cm^2/s for the first 20 days after the onset of the bursting episode, then it faded by a factor 40 in the subsequent 140 days, following a power-law trend with index alpha=-0.5. We obtained a phase-coherent timing solution with the longest baseline (225 days) to date for this source which, besides period P=7.5654084(4) s and period derivative dP/dt=3.5(3)E-12 s/s, includes higher order period derivatives. We also report on our search of the counterpart to the SGR at radio frequencies using the Australia Telescope Compact Array and the Parkes radio telescope. No evidence for radio emission was found, down to flux densities of 0.9 mJy (at 1.5 GHz) and 0.09 mJy (at 1.4 GHz) for the continuum and pulsed emissions, respectively, consistently with other observations at different epochs.Comment: 12 pages, 7 colour figures and 3 tables, accepted for publication in MNRAS. Figure 6 in reduced quality and abstract abridged for astro-ph submissio

Conductive Hybrid Cu-HHTP-TCNQ Metal–Organic Frameworks for Chemiresistive Sensing

Electrically conductive metal–organic frameworks (MOFs) and MOF-like coordination polymers are an emerging class of materials that combine good electrical charge transport with unique properties such as nanoporosity. The combination of different metal nodes and organic linkers allows tailoring MOFs to specific properties and applications in electronics, like selective chemiresistive sensing. The intrinsic crystallinity of MOFs, which usually promotes efficient charge transport, makes them also difficult to integrate into flexible systems, as crystalline MOFs are often brittle. The present study reports on a fast and reliable interfacial synthesis of conductive MOF films composed of two different organic ligands, 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) and 7,7,8,8-tetracyanoquinodimethane (TCNQ), lacking long-range periodic order while preserving good electrical conductivity of 0.033 S cm−1 at room temperature and chemiresistive response toward ambient changes. The hybrid nature of the discontinuous film is investigated multiparametrically by electron and atomic force microscopy as well as by Raman spectroscopy. This study demonstrates that including different types of MOFs is a good compromise between structural order and conductivity, thus making hybrid framework architectures to a promising active material for chemiresistive sensors without the need for high crystallinity