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In September 2016, the annual meeting of the International Union for Quaternary Research’s Loess and Pedostratigraphy Focus Group, traditionally referred to as a LoessFest, met in Eau Claire, Wisconsin, USA. The 2016 LoessFest focused on “thin” loess deposits and loess transportation surfaces. This LoessFest included 75 registered participants from 10 countries. Almost half of the participants were from outside the United States, and 18 of the participants were students. This review is the introduction to the special issue for Quaternary Research that originated from presentations and discussions at the 2016 LoessFest. This introduction highlights current understanding and ongoing work on loess in various regions of the world and provides brief summaries of some of the current approaches/strategies used to study loess deposits.
The Deep Ice Sheet Coring (DISC) drill developed by Ice Coring and Drilling Services under contract with the US National Science Foundation is an electromechanical ice-drill system designed to take 122mm ice cores to depths of 4000 m. The new drill system was field-tested near Summit camp in central Greenland during the spring/summer of 2006. Testing was conducted to verify the performance of the DISC drill system and its individual components and to determine the modifications required prior to the system’s planned deployment for coring at the WAIS Divide site in Antarctica in the following year. The experiments, results and the drill crew’s experiences with the DISC drill during testing are described and discussed.
In the 1998-99 flight, BOOMERanG has produced maps of ∼4% of the sky at high Galactic latitudes, at frequencies of 90, 150, 240 and 410 GHz, with resolution ≳ 10'. The faint structure of the Cosmic Microwave Background at horizon and sub-horizon scales is evident in these maps. These maps compare well to the maps recently obtained at lower frequencies by the WMAP experiment. Here we compare the amplitude and morphology of the structures observed in the two sets of maps. We also outline the polarization sensitive version of BOOMERanG, which was flown early this year to measure the linear polarization of the microwave sky at 150, 240 and 350 GHz.
The Cosmic Background Imager (CBI) is an instrument designed to make images of the cosmic microwave background radiation and to measure its statistical properties on angular scales from about 3 arc minutes to one degree (spherical harmonic scales from l ˜ 4250 down to l ˜ 400). The CBI is a 13-element interferometer mounted on a 6 meter platform operating in ten 1-GHz frequency bands from 26 GHz to 36 GHz. The instantaneous field of view of the instrument is 45 arcmin (FWHM) and its resolution ranges from 3 to 10 arcmin; larger fields can be imaged by mosaicing. At this frequency and resolution, the primary foreground is due to discrete extragalactic sources, which are monitored at the Owens Valley Radio Observatory and subtracted from the CBI visibility measurements.
The instrument has been making observations since late 1999 of both primordial CMB fluctuations and the Sunyaev-Zeldovich effect in clusters of galaxies from its site at an altitude of 5080 meters near San Pedro de Atacama, in northern Chile. Observations will continue until August 2001 or later. We present preliminary results from the first few months of observations.
BOOMERanG has recently resolved structures on the last scattering surface at redshift ˜ 1100 with high signal to noise ratio. We review the technical advances which made this possible, and we focus on the current results for maps and power spectra, with special attention to the determination of the total mass-energy density in the Universe and of other cosmological parameters.
HST UV observations of V795 Her reveal a strong 2.6-h orbital variation in the prominent UV lines, in contrast to earlier (IUE) evidence of a 4.8-h period. Only the C IV line contains a strong blue-shifted, wind formed absorption component. Several lines exhibit a ‘narrow’ absorption feature near rest velocity which may originate in the disk, and a blue-shifted emission feature which accounts for most of the line profile variability.
In support of the disposal system safety case for a geological disposal facility (GDF) there is a requirement to consider 'what-if' hypothetical scenarios for post-closure nuclear criticality. Although all such scenarios are considered very unlikely, one 'what-if' scenario is the mobilization of fissile material from a number of waste packages and its slow accumulation within the GDF or the immediate surroundings. Should sufficient fissile material accumulate a quasi-steady-state (QSS) transient criticality event could result. A computer model has been developed to understand the evolution and consequences of such an event.
Since a postulated QSS criticality could persist for many millennia, building confidence in the modelling approach is difficult. However, the Oklo natural reactors in Africa operated for similar durations around two billion years ago, providing a natural analogue for comparison. This paper describes the modelling approach, its application to hypothetical criticality events for a GDF, and how the model can be compared to Oklo. The model results are found to be in agreement with the observational evidence from Oklo, building confidence in the use of the QSS model to simulate postulated post-closure criticality events in GDFs.
Tympanic middle ears have evolved multiple times independently among vertebrates, and share common features. We review flexibility within tympanic middle ears and consider its physiological and clinical implications.
The chain of conducting elements is flexible: even the ‘single ossicle’ ears of most non-mammalian tetrapods are functionally ‘double ossicle’ ears due to mobile articulations between the stapes and extrastapes; there may also be bending within individual elements.
Simple models suggest that flexibility will generally reduce the transmission of sound energy through the middle ear, although in certain theoretical situations flexibility within or between conducting elements might improve transmission. The most obvious role of middle-ear flexibility is to protect the inner ear from high-amplitude displacements.
Inter-ossicular joint dysfunction is associated with a number of pathologies in humans. We examine attempts to improve prosthesis design by incorporating flexible components.
Recent results on the diffuse scattering from single crystals of Fe1−xO at high temperatures reveal that the defect structure is in striking agreement with embedded cluster calculations by Ellis et al. The dominant defect is an imperfect 7:2 cluster. Mixtures of this and a larger complex (13:4) can explain the electrical properties. XANES studies of this oxide are in agreement with Ellis' theoretical work. However, in both FOx and MnxO it is not possible to use the shift of the cation K absorption edge to characterize valence. In fact in the latter case the shift passes through a minimum, perhaps indicating the onset of clustering.
We report on the use of lithium ion (Li+) drifting1 as a sensitive means to study Si self-interstitial (SiI) diffusion.2 Li+ properties in silicon are well known from extensive ion drift studies and Li+ interactions with dopants and point defects.3 We have used this low temperature (∼100°C) technique in combination with Si1 injection from oxides to delineate, identify and eliminate D defects4 in certain p-type floating zone (FZ) Si single crystals.5 Our results suggest Si1 diffusion occurs to a depth of at least 10 mm into the bulk during phosphorus (P) diffusion with oxidation (i.e., POCI3 process) at 950°C for 100 min. Process modeling of this lower bound SiI diffusion using SUPREM-IV9 results in a Sii diffusivity of 3.5×10−6 cm2/s at 950°C.
Laser-assisted dry etching ablation (LADEA) has been reviewed with an emphasis on its applicability for the microstructuring of III-V semiconductor compounds. The method is based on the application of an excimer laser ( λ= 308 nm) for pulsed heating of a wafer which is placed in a stream of Cl2/He gas. Both the products of chemical reaction and the depth to which a laser-induced reaction takes place depend on laser fluence. This makes possible the ablation of a well defined volume of the material. Little or no structural damage to the surface is observed because ablation is carried out with laser fluences below those required to melt the matrix material. The laser fluence dependence of the etch rate indicates that the process is primarily temperature driven with a characteristic energy for desorption. We have investigated LADEA as a method for in-situ processing of III-V semiconductors and the fabrication of nanostructures. An atomic force microscopy study has shown that atomically smooth surfaces can be obtained if the etch rate is near 1/2 atomic layer per laser pulse. The lateral resolution of LADEA has been found to be at least 20 nm. This, as well as the results of in-situ photoluminescence and Auger electron spectroscopy measurements, indicate that LADEA can be used for the direct (photoresist-free) fabrication of high quality microstructures and, ultimately, for the nanostructuring of III-V semiconductor compounds.
In-situ high temperature electrical conductivity and thermopower have been measured simultaneously on a number of ordered perovskite-like oxides containing double CUO4/2 sheets. Equilibrium measurements have been conducted as a function of oxygen partial pressure, temperature and chemical substitution in order to understand the relationships between the chemical architecture and the transport and defect properties. Data for LaBa2Cu2NbO8 and LaCa2Cu2GaO7 are presented and compared with those of known triple perovskite superconductors, Y1−xCaxSr2Cu2GaO7 and YBa2Cu3O7−δ, and several quadruple perovskites, Ln′Ln″Ba2Cu2M2O11 (Ln = Lanthanide, Y; M = Sn, Ti). These materials belong to a general family of superconductors which are constructed from similar ‘active’ layers (double perovskite blocks of square-pyramidal copper-oxygen sheets), and interleaved with fixed valence cations in perovskite-like ‘conditioning’ layers. Similarities in the transport properties of the non-superconducting and superconducting materials at elevated temperatures are illustrated, and the amount and types of defects, including carrier concentrations, are correlated with the internal chemistry and inner architecture of each material.
Layered copper-oxide superconductors exhibit the highest critical transition temperatures of any materials. Yet all of the known double perovskites A′A″B′B″O6 containing copper have a random or rock salt distribution of the B cations with the exception of the unique layered arrangement found in La2CuSnO6. Only the layered arrangement contains the CuO22- planes which are necessary for high-temperature superconductivity. The occurrence of layered or two dimensional structures increases markedly when vacancies are introduced on the oxygen sublattice, as evidenced in Ln2AEmCu2TimO5+3m (Ln = lanthanide, Y: AE = Ba, Ca: 2 ≤ m ≤ 4). Similarities among oxygen-deficient structures, especially those with two-dimensional solid-state features, are discussed. Combined conductivity and thermopower analysis are presented to elucidate their unique internal chemistry, defect structure, and conduction parameters. In particular, data for La2-xSrxCuSnO6 are presented and related to the crystal chemistry of the copper-oxygen layer. These data are compared with La2Ba2Cu2Sn2O11 and La2Ba2Cu2Ti2O11 to illustrate the significance of oxygen vacancies on the properties of the copper oxygen planes. New layered cuprates are discussed including the mixed A-site stoichiometries Ln′Ln″AEmCu2TimO5+3m (Ln = lanthanide, Y: AE = Ba, Ca: 2 ≤ m ≤ 4) which contain the smaller lanthanide (Ln″) ordered between the closely spaced, facing sheets of Cu-O square pyramids.
Crystalline diamond coatings and, increasingly, diamond like amorphous carbon (DLC) films are used for tribological and protective layers for their hardness and chemical inertness. They are also under investigation for their electron emitting properties, with possible applications in field emission displays. DLC films were deposited by laser ablation using a KrF excimer laser and fluences between 0.5 and 2 J/cm2. FTIR measurements did not show the presence of hydrogen in the films. Raman spectra allowed for the determination of the nature of the graphitic and diamond bonds (sp2 and sp3) as well as information about the disorder and short range order in the films. For a better determination of the sp3-content, which is often hidden in the Raman spectra, a correlation with optical properties in the near IR to near UV region was established. These values depended strongly on the substrate temperature and the laser fluence. DLC formation could be demonstrated even at substrate temperatures close to room temperature. Vickers hardness values and first measurements on the electron emissivity of the films can be correlated to the diamond character and the preparation method of the films.
In the microcrystalline regime, the behavior of grain boundary-controlled electroceramics is well described by the “brick layer model” (BLM). In the nanocrystalline regime, however, grain boundary layers can represent a significant volume fraction of the overall microstructure and simple layer models are no longer valid. This work describes the development of a pixel-based finite-difference approach to treat a “nested cube model” (NCM), which more accurately calculates the current distribution in polycrystalline ceramics when grain core and grain boundary dimensions become comparable. Furthermore, the NCM approaches layer model behavior as the volume fraction of grain cores approaches unity (thin boundary layers) and it matches standard effective medium treatments as the volume fraction of grain cores approaches zero. Therefore, the NCM can model electroceramic behavior at all grain sizes, from nanoscale to microscale. It can also be modified to handle multi-layer grain boundaries and property gradient effects (e.g., due to space charge regions).
We have recently observed spectrally resolved vibronic structure and luminescence intermittency from nanometer-size porous silicon nanocrystals. In this study we examine the quantum efficiency of a single nanoparticle and show that emitting nanoparticles do so with near unity quantum efficiency. This result suggests that the emission from porous Si nanoparticles, and thus bulk porous Si, results from a small number of high quantum efficiency emitters. In our previous work we have shown that our nanoparticles contain more than one coupled chromophore. In order to examine these effects more closely we employ several spectroscopy and microscopy techniques including: 1) single-particle spectroscopy, 2) shear-force microscopy, and 3) time-resolved spectroscopy, on a colloidal suspension of size-selected, surface-oxidized nanoparticles. In addition we apply statistical techniques to provide a more complete picture of the coupling between chromophores in a given nanoparticle.
The rich phase behaviour displayed by phospholipid bilayers and their structural relationship to biological membranes have made them fascinating objects of study. Despite being one of the most often examined of these model membrane systems, dipalmitoylphosphatidylcholine (DPPC) continues to be a source of interest for scientists. In particular, the ripple phase, Pβ′, of fully hydrated DPPC has generated a great deal of attention over the years as scientists have tried to understand the structural details of this novel phase1–5.