Microwave rotational spectroscopy: A physical technique for specific pollutant monitoring

An attempt was made to present substantial evidence that microwave rotational spectroscopy can be developed for use in air pollution monitoring. Work with the diode-cavity spectrometer shows it to be capable to detecting small concentrations on NO2, SO2, H2,CO, and NH3 gas with very high specificity

Study of a Threshold Cherenkov Counter Based on Silica Aerogels with Low Refractive Indices

To identify $\pi^{\pm}$ and $K^{\pm}$ in the region of $1.0\sim 2.5$ GeV/c, a threshold Cherenkov counter equipped with silica aerogels has been investigated. Silica aerogels with a low refractive index of 1.013 have been successfully produced using a new technique. By making use of these aerogels as radiators, we have constructed a Cherenkov counter and have checked its properties in a test beam. The obtained results have demonstrated that our aerogel was transparent enough to make up for loss of the Cherenkov photon yield due to a low refractive index. Various configurations for the photon collection system and some types of photomultipliers, such as the fine-mesh type, for a read out were also tested. From these studies, our design of a Cherenkov counter dedicated to $\pi / K$ separation up to a few GeV/c %in the momentum range of $1.0 \sim 2.5$ GeV/c with an efficiency greater than $90$ \% was considered.Comment: 21 pages, latex format (article), figures included, to be published in Nucl. Instrm. Meth.

Peatland initiation and carbon accumulation in the Falkland Islands

The Falkland Islands in the South Atlantic Ocean contain extensive peatlands at the edge of their global climatic envelope, but the long-term carbon dynamics of these sites is poorly quantified. We present new data for ten sites, compile previously-published data and produce a new synthesis. Many peatlands in the Falkland Islands developed notably early, with a fifth of basal 14 C dates pre-Holocene. Falkland Islands peats have high ash content, high carbon content and high bulk density compared to global norms. In many sites carbon accumulation rates are extremely low, which may partly relate to low average rainfall, or to carbon loss through burning and aeolian processes. However, in coastal Tussac peatlands carbon accumulation can be extremely rapid. Our re-analysis of published data from Beauchene Island, the southernmost of the Falkland Islands, yields an exceptional long-term apparent carbon accumulation rate of 139 g C m −2 yr −1 , to our knowledge the highest recorded for any global peatland. This high accumulation might relate to the combination of a long growing-season and marine nutrient inputs. Given extensive coverage and carbon-dense peats the carbon stock of Falkland Islands peatlands is clearly considerable but robust quantification will require the development of a reliable peat map. Falkland Island peatlands challenge many standard assumptions and deserve more detailed study

Globally Anisotropic High Porosity Silica Aerogels

We discuss two methods by which high porosity silica aerogels can be engineered to exhibit global anisotropy. First, anisotropy can be introduced with axial strain. In addition, intrinsic anisotropy can result during growth and drying stages and, suitably controlled, it can be correlated with preferential radial shrinkage in cylindrical samples. We have performed small angle X-ray scattering (SAXS) to characterize these two types of anisotropy. We show that global anisotropy originating from either strain or shrinkage leads to optical birefringence and that optical cross-polarization studies are a useful characterization of the uniformity of the imposed global anisotropy.Comment: 18 pages, 14 figures, submitted to Journal of Non-Crystalline Solid

A rapid supercritical extraction process for the production of silica aerogels

Silica aerogels are a special class of porous materials in which both the pore size and interconnected particle size have nanometer dimensions. This structure imparts unique optical, thermal, acoustic, and electrical properties to these materials. Transmission electron microscopy and small angle x-ray scattering show that this nanostructure is sensitive to variations in processing conditions that influence crosslinking chemistry and growth processes prior to gelation. Recently, Lawrence Livermore National Laboratory (LLNL) has demonstrated that a Rapid Supercritical Extraction (RSCE) process can be used to prepare near-net shape silica aerogels in hours rather than days. Preliminary data from RSCE silica aerogels show that they have improved mechanical properties and slightly lower surface areas than their conventionally dried counterparts, while not compromising their optical and thermal performance

MOLYBDENUM DOPED CARBON AEROGELS WITH CATALYTIC POTENTIAL

Mo-doped carbon aerogels were obtained in the polycondensation reaction of aqueous resorcinol and formaldehyde by adding Mo-salt at two different stages of the synthesis: i) to the initial sol; ii) by incipient wetting impregnation of the supercritically dried polymer gel. Molybdenum added during the polymerization yielded a more compact gel structure with practically no mesoporosity. With post-impregnation, by contrast, mesopores of diameter 3-15 nm were generated. Carbonization appreciably enhanced the microporous character of both samples, but in the mesopore range their pore size distribution was conserved. The Mocontent of the samples was also different: Mo was lost during the solvent exchange before the supercritical drying (i.e., the Mo failed to bind chemically to the polymer matrix). The residual Mo congregated into 25-60 nm bulk clusters of α-Mo2C. In the other carbon aerogel, finely dispersed α-Mo2C and η-Mo3C2 crystals formed, of size 8-20 nm. On the surface of both carbons the Mo formed oxides. In the model test reaction (acetic acid hydroconversion) the catalytic activity of both carbon aerogels was enhanced by molybdenum. The more open pore structure, higher concentration and finer Mo distribution, as well as its chemical form, may all be responsible for the greater conversion and higher value products obtained with the post-impregnated sample

Falkland Island peatland development processes and the pervasive presence of fire

Palaeoecological analyses of Falkland Island peat profiles have largely been confined to pollen analyses. In order to improve understanding of long-term Falkland Island peat development processes, the plant macrofossil and stable isotope stratigraphy of an 11,550 year Falkland Island Cortaderia pilosa (‘whitegrass’) peat profile was investigated. The peatland developed into an acid, whitegrass peatland via a poor fen stage. Macrofossil charcoal indicate that local fires have frequently occurred throughout the development of the peatland. Raman spectroscopy analyses indicate changes in the intensity of burning which are likely to be related to changes in fuel types, abundance of fine fuels due to reduced evapotranspiration/higher rainfall (under weaker Southern Westerly Winds), peat moisture and human disturbance. Stable isotope and thermogravimetric analyses were used to identify a period of enhanced decomposition of the peat matrices dating from ∼7020 cal yr BP, which possibly reflects increasing strength of the Southern Westerly winds. The application of Raman spectroscopy and thermogravimetric analyses to the Falkland Island peat profile identified changes in fire intensity and decomposition which were not detectable using the techniques of macrofossil charcoal and plant macrofossil analyses.</p