Ultrafast relaxation of photoexcited superfluid He nanodroplets

The relaxation of photoexcited nanosystems is a fundamental process of light-matter interaction. Depending on the couplings of the internal degrees of freedom, relaxation can be ultrafast, converting electronic energy in a few fs, or slow, if the energy is trapped in a metastable state that decouples from its environment. Here, we study helium nanodroplets excited resonantly by femtosecond extreme-ultraviolet (XUV) pulses from a seeded free- electron laser. Despite their superfluid nature, we find that helium nanodroplets in the lowest electronically excited states undergo ultrafast relaxation. By comparing experimental pho- toelectron spectra with time-dependent density functional theory simulations, we unravel the full relaxation pathway: Following an ultrafast interband transition, a void nanometer-sized bubble forms around the localized excitation (He ) within 1 ps. Subsequently, the bubble collapses and releases metastable He at the droplet surface. This study highlights the high level of detail achievable in probing the photodynamics of nanosystems using tunable XUV pulses

Soft Chemical Control of Superconductivity in Lithium Iron Selenide Hydroxides Li1–x_{1–x}Fex_x(OH)Fe1–y_{1–y}Se

Hydrothermal synthesis is described of layered lithium iron selenide hydroxides Li$_{1–x}$Fex(OH)Fe$_{1–y}$Se (x$\sim$0.2; 0.02 < $y$ < 0.15) with a wide range of iron site vacancy concentrations in the iron selenide layers. This iron vacancy concentration is revealed as the only significant compositional variable and as the key parameter controlling the crystal structure and the electronic properties. Single crystal X-ray diffraction, neutron powder diffraction, and X-ray absorption spectroscopy measurements are used to demonstrate that superconductivity at temperatures as high as 40 K is observed in the hydrothermally synthesized samples when the iron vacancy concentration is low ($y$ < 0.05) and when the iron oxidation state is reduced slightly below +2, while samples with a higher vacancy concentration and a correspondingly higher iron oxidation state are not superconducting. The importance of combining a low iron oxidation state with a low vacancy concentration in the iron selenide layers is emphasized by the demonstration that reductive postsynthetic lithiation of the samples turns on superconductivity with critical temperatures exceeding 40 K by displacing iron atoms from the Li$_{1–x}$Fe$_x$(OH) reservoir layer to fill vacancies in the selenide layer

Characterization of liquid waste streams from shale gas development

Hydraulic fracturing has been practiced for over thirty years to improve effective porosity and stimulate oil and gas production. In the Appalachian Basin it has been used with horizontal drilling since 2008 to extract methane and natural gas liquids from source rock such as the Marcellus Formation. Hydraulic fracturing generates large volumes of waste water known as flowback: about 3,800 m3/well. Literature regarding the chemical composition of this waste stream is limited. This study examined injected hydraulic fracturing fluid from two wells and flow- back from four hydraulically fractured wells. Wells were sampled at various times during the flowback cycle and in sections of the basin known to produce either wet or dry gas, the former producing higher volumes of natural gas liquids. Concentrations were compared to available literature values and to drinking water standards as a basis for determining which parameters might compromise nearby, domestic wells in the event of an accidental release. Measured parameters included three classes: organic, inorganic ions and radioactive isotopes. Concentrations of all three classes of contaminants tended to increase during the flowback cycle. Organic contaminants including BTEX were substantially higher in the wet gas well. Radioactive isotopes, particularly alpha, beta, radium 226 and radium 228 increased during flowback. All contaminants were found in much higher concentrations in flowback water than in injected hydraulic fracturing fluids suggesting that the bulk of contaminants originate in the Marcellus formation rather than in the injected hydraulic fracturing fluids. Primary and secondary drinking water standards for all classes of contaminants were generally exceeded in flowback water. In addition to summarizing the chemical composition of flowback water, the presentation recommends practices for controlling the risk of environmental exposure

Germination of Seed of Three Varieties of Spotted Locoweed

Spotted locoweed (Astragalus lentiginosus Dougl.), one of the principal locoweeds of western rangelands, consists of 36 varieties. The objectives of this study included the definition of some of the factors influencing seed germination of the species. Five seed collections were studied; they represented five different geographical and edaphic locations. Three varieties of spotted locoweed were represented by these collections. The seed coat of the varieties studied was impermeable to water. Seed also contained a water-soluble germination inhibitor. Germination was not affected by light. Optimal germination occurred at the temperature regime 7/13 degrees C. However, at -1/4 and 21/27 degrees C, though it was slower, high percentage germination was ultimately achieved. Although salinity inhibited germination, seed from the different sources showed different tolerances to salinity.This material was digitized as part of a cooperative project between the Society for Range Management and the University of Arizona Libraries.The Journal of Range Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202

Alberta's approach to reclamation approvals and certification

Non UBCUnreviewedOthe

A comprehensive reclamation research program on coal mining disturbed lands

Kaiser Resources Ltd. has been conducting an intensive reclamation research program since 1975. Although many of its component projects are long-term, some experiments have already been completed. As a result, methods are now available for predicting the success of thirteen commonly-used revegetation species on Kaiser's disturbed areas. We also know at what elevations and aspects to expect the greatest success with currert reclamation practices. This may be helpful input in designing dumps and resloping efforts in the future. Kaiser's reclamation research group also conducts annual assessments of its former reclamation efforts in an attempt to monitor the development of the new plant communities. Extensive native and agronomic species test plots have been established in the subalpine zone. These will be augmented in the upcoming season by new treatments, including woody species cuttings, root plantings and grass-plug trials. A year-long study of the distribution, cycling and retention of plant nutrients has been initiated. This study should yield valuable information concerning future fertilization management as well as the stability of the reclamation plant communities.Non UBCUnreviewedOthe

Ultrafast relaxation of photoexcited superfluid He nanodroplets

The relaxation of photoexcited nanosystems is a fundamental process of light-matter interaction. Depending on the couplings of the internal degrees of freedom, relaxation can be ultrafast, converting electronic energy in a few fs, or slow, if the energy is trapped in a metastable state that decouples from its environment. Here, helium nanodroplets are resonantly excited by femtosecond extreme-ultraviolet (XUV) pulses from a seeded free-electron laser. Despite their superfluid nature, we find that helium nanodroplets in the lowest electronically excited states undergo ultrafast relaxation. By comparing experimental photoelectron spectra with time-dependent density functional theory simulations, we unravel the full relaxation pathway: Following an ultrafast interband transition, a void nanometer-sized bubble forms around the localized excitation (He*) within 1 ps. Subsequently, the bubble collapses and releases metastable He* at the droplet surface. This study highlights the high level of detail achievable in probing the photodynamics of nanosystems using tunable XUV pulses