Μm Portion Research Articles

A REVIEW OF DEPOSIT VELOCITY PREDICTION METHODS FOR MEDIUM PARTICLE SIZE SLURRIES IN PIPES

Methods of predicting the deposit velocity for wide particle size slurries with maximum particle size up to about 1 mm and maximum d50 size around 0.3 mm are outlined. These slurries generally possess non-Newtonian properties, typically modelled as Bingham plastics, and typically flow pseudo-homogeneously in turbulent flow down to the deposit velocity. Because they flow pseudo-homogeneously, pressure gradient prediction is relatively easy once a suitable operating velocity is selected. Consequently, the deposit velocity is the most important parameter as it determines the operating velocity. Beginning with Durand and Condolios [6], the historical development of the major methods for predicting the deposit velocity for mono-size particles in water are first reviewed, and their advantages and limitations discussed. Methods of extending predictions to mono-size particles in viscous Newtonian fluids are then reviewed. Next, prediction techniques relevant to deposition are reviewed for non-Newtonian slurries. These include prediction of the transition velocity between laminar and turbulent flow, and the critical pressure gradient required to prevent deposition under laminar flow conditions. Finally, these prediction techniques are combined to apply to minus 1 mm, wide size distribution, viscous slurries, commonly encountered in the mining industry. Two deposit velocity prediction techniques for these types of slurries are discussed. The first technique, based on determining the inherent viscosity of the slurry and assuming the weighted mean particle size of the total slurry represented the relevant coarse particle dimension, was found to predict performance in an operating 593 mm ID pipeline. The second technique, based on assuming the minus 75 µm portion represented the “carrier” fluid and assuming the median size of the plus 75 µm portion represented the relevant coarse particle dimension, was found to give very good predictions of the observed deposition trends of Goosen and Paterson [8] for a minus 300 µm gold tailings tested in 100 mm, 152 mm and 242 mm test loops.

Impact of nanominerals on the migration and distribution of cadmium on soil aggregates

Soil aggregates play an important role in the migration and transformation of heavy metals. In this paper, solution adsorption and incubation experiments were carried out to explore the effects of soil texture (sandy loam and clay loam), nanominerals (nanomontmorillonite [nMt] and nanohydroxyapatite [nHA]), and pollution levels (5, 10, and 15 mg/kg) on the surface migration and transformation of cadmium in soil aggregates with different sized particles. The aim is to clarify the dynamics of cadmium in various particle size soil aggregates of different texture soils and demonstrate the positive effect of nanominerals on the partitioning and geochemical fractions of cadmium between the aggregates. The results showed that as the particle size decreased, the ability of the soil aggregates to carry cadmium initially decreased and then increased. Organic matter was the main factor influencing the cadmium distribution among the soil aggregates, whereas soil texture had no significant effect on the adsorption capacity of Cd2+ in the soil particles. The soil aggregates with sizes <15 μm had the highest cadmium accumulation capacity. As the cadmium concentration increased, cadmium ions were more likely to accumulate in soil aggregates with small particles (<15 μm). The application of nanominerals promoted the migration of cadmium to <15 μm particles from 2000 to 45 μm particles in sandy loam and 75-15 μm particles in clay. nHA also significantly improved the content of residual cadmium in the <15 μm portion of both soil textures. This study provides a theoretical basis for the use of nano-fixatives in environmental restoration applications.

High Responsivity of InP/InAsP Nanowire Array Broadband Photodetectors Enhanced by Optical Gating.

High-performance photodetectors operating in the near-infrared (0.75-1.4 μm) and short-wave infrared (1.4-3.0 μm) portion of the electromagnetic spectrum are key components in many optical systems. Here, we report on a combined experimental and theoretical study of square millimeter array infrared photodetectors comprising 3 million n+-i-n+ InP nanowires grown by MOVPE from periodically ordered Au seed particles. The nominal i-segment, comprising 20 InAs0.40P0.60 quantum discs, was grown by use of an optimized Zn doping to compensate the nonintentional n-doping. The photodetectors exhibit bias- and power-dependent responsivities reaching record-high values of 250 A/W at 980 nm/20 nW and 990 A/W at 532 nm/60 nW, both at 3.5 V bias. Moreover, due to the embedded quantum discs, the photoresponse covers a broad spectral range from about 0.70 to 2.5 eV, in effect outperforming conventional single InGaAs detectors and dual Si/Ge detectors. The high responsivity, and related gain, results from a novel proposed photogating mechanism, induced by the complex charge carrier dynamics involving optical excitation and recombination in the quantum discs and interface traps, which reduces the electron transport barrier between the highly doped n+ contact and the i-segment. The experimental results obtained are in perfect agreement with the proposed theoretical model and represent a significant step forward toward understanding gain in nanoscale photodetectors and realization of commercially viable broadband photon detectors with ultrahigh gain.

Inhalation bioaccessibility of Cd, Cu, Pb and Zn and speciation of Pb in particulate matter fractions from areas with different pollution characteristics in Henan Province, China

Windowsill particulate matter (PM) samples were collected from an area near large lead-smelting facilities in Jiyuan (JP), the urban area of Jiyuan (JU) and the peri-urban area of Mianchi (MC) in Henan, China to investigate the concentration and inhalation bioaccessibility of Cd, Cu, Pb and Zn. The <10 μm portions of the samples were extracted with simulated lung fluid to assess the in vitro inhalation bioaccessibility. Lower concentrations of heavy metals were found in the MC samples than in the JP and the JU samples. The average concentrations of Pb, Cd and Cu in the portions of the same size are in the order of JP samples > JU samples > MC samples. For Pb, Cd and Zn, the maximum inhalation bioaccessibility fraction values are all found in the MC samples, which ranged 3.87–8.79%, while those of the JP and the JU samples are <2%. The Pb speciation analysis with X-ray absorption spectrometry indicate mineral bound Pb, PbS and Pb3(PO4)2 are the predominant Pb species in the JP samples; for the JU sample, organic bound Pb is the predominant Pb species in the 45–125 μm portion, while mineral bound Pb is the predominant Pb species in the 10–45 μm portion; for the MC samples, organic bound Pb is the predominant Pb species, followed by PbS. The results indicate that there is significant accumulation of Pb, Cd, Cu and Zn associated with PM in the area near the lead smelter and in the urban area of Jiyuan, especially Pb and Cd, however, the inhalation bioaccessibility of these metals in samples from the lead smelting impacted area is low, this may be due to the higher proportion of less soluble species of the metals in the samples from this area. However, organic matter bound Pb found in some samples has higher bioaccessibility than other Pb species.

Characteristics and controlling factors of reservoir space of mudstone and shale in Es3x in the Zhanhua Sag

Zhanhua Sag is a widely accepted target zone with huge exploration and development potential for shale oil and shale gas resources. Many detailed studies have been undertaken around the geochemistry of the lower section of the third member of the Shahejie Formation (Es3x), while few studies have focused on the reservoir. In this study, based on the mineralogical features and geochemical characteristics, and by using statistical methods, the characteristics and controlling factors of reservoir space of mudstone and shale in Es3x in the Zhanhua Sag are explored through field-emission scanning electron microscopy (FE-SEM), high pressure mercury injection capillary pressure (MICP), and nuclear magnetic resonance (NMR) techniques. Three major findings were obtained. ① There are micropores and microfractures in the reservoir space, which include intergranular pores, clay intercrystal pores, pyrite intercrystal pores, dissolved pores, structural microfractures, and bedding microfractures. ② According to the features of pore size distribution (PSD), the pore distribution can be divided into the following three categories: 0–50 nm, 50 nm–2 μm, and >2 μm; the average volumes of these components are 0.01079 mL g−1, 0.00361 mL g−1, and 0.00355 mL g−1, respectively, thus showing that the pores whose radii are distributed at 0–50 nm form the most important reservoir space (though those with the 50 nm–2 μm and >2 μm radii are also important and cannot be ignored). ③ There are different controlling factors when it comes to different scale pores. Based on statistics and FE-SEM results, the dissolved pores in calcite were determined to be the controlling factor for the 0–50 nm portion, the intercrystalline pores in clay and pyrite, and intergranular pores between authigenic minerals (calcite, dolomite, and pyrite) and clastic minerals (calcite and dolomite) were determined to be the controlling factors for the 50 nm–2 μm portion, and the structural microfractures and bedding microfractures were determined to be the main factors for the >2 μm portion. Furthermore, it is the brittle minerals content and bedded structure that control the microfractures. This study thus clarifies the types and characteristics of reservoir space and identifies pore structure controlling factors of mudstone and shale in Es3x in the Zhanhua Sag; this information has important significance for future reservoir evaluations.

A facile sonochemical synthesis of shell-stabilized reactive microbubbles using surface-thiolated bovine serum albumin with the Traut’s reagent

The short lifetime of proteinaceous microbubbles produced using conventional sonication method has hindered their applications in drug delivery and metal removal from wastewater. In this study, we aimed to synthesize stable proteinaceous microbubbles and to demonstrate their reactivity. Our model protein, bovine serum albumin (BSA) was treated with 2-iminothiolane hydrochloride (Traut’s reagent) to convert primary amines to thiols before the synthesis of microbubbles. Microbubbles produced with the Traut’s reagent-treated BSA (BSA-SH MBs) were initially concentrated at median sizes of 0.5 and 2.5μm. The 0.5μm portion quickly vanished, and the 2.5μm portion gradually shrank to ∼850nm in ∼3days and became stabilized afterward for several months under 4°C. Characterizations of BSA-SH MBs by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) indicated the presence of free unbound thiols and primary amines on their surface, implying the possibility of further surface modification. Based on the zeta potential measurement, the isoelectric point (IEP) of BSA-SH MBs was determined to be 4.5. The attachments of BSA-SH MBs on alumina, silica, and gold surfaces in different pH environments were carried out with a quartz crystal microbalance with dissipation monitoring (QCM-D), demonstrating the reactivities of BSA-SH MBs. At pH 6, the negatively charged BSA-SH MBs were adsorbed onto the alumina surface by electrostatic interaction. Analogously, at pH 4, the adsorption of the positively charged BSA-SH MBs on the silica surface was confirmed. Compared with the electrostatic interaction, the adsorption of BSA-SH MBs on the gold surface is attributed to the strong gold-thiol bonding effect. This is the first time that a universal approach for stabilizing protein-shelled microbubbles was reported using only one single step of surface treatment of proteins with the Traut’s reagent.

Dynamic Measurements of the Position, Orientation, and DNA Content of Individual Unlabeled Bacteriophages.

A complete understanding of the cellular pathways involved in viral infections will ultimately require a diverse arsenal of experimental techniques, including methods for tracking individual viruses and their interactions with the host. Here we demonstrate the use of holographic microscopy to track the position, orientation, and DNA content of unlabeled bacteriophages (phages) in solution near a planar, functionalized glass surface. We simultaneously track over 100 individual λ phages at a rate of 100 Hz across a 33 μm × 33 μm portion of the surface. The technique determines the in-plane motion of the phage to nanometer precision, and the height of the phage above the surface to 100 nm precision. Additionally, we track the DNA content of individual phages as they eject their genome following the addition of detergent-solubilized LamB receptor. The technique determines the fraction of DNA remaining in the phage to within 10% of the total 48.5 kilobase pairs. Analysis of the data reveals that under certain conditions, λ phages move along the surface with their heads down and intermittently stick to the surface by their tails, causing them to stand up. Furthermore, we find that in buffer containing high concentrations of both monovalent and divalent salts, λ phages eject their entire DNA in about 7 s. Taken together, these measurements highlight the potential of holographic microscopy to resolve the fast kinetics of the early stages of phage infection.

Trace metal concentration and partitioning in the first 1.5 m of hydrothermal vent plumes along the Mid-Atlantic Ridge: TAG, Snakepit, and Rainbow

To determine the significance of metal fluxes from hydrothermal vents, understanding the speciation, reactivity, and possible transformations of metals and metal sulfides within the hydrothermal plume is critical. In this study, we measure the concentration and partitioning of trace metals (Fe, Mn, Cu, Cd, Co, Pb, Ni) and sulfide phases within the first 1.5m of the rising plume at three vent fields (TAG, Snakepit, and Rainbow) along the Mid-Atlantic Ridge. A HCl/HNO3 leaching method was used to differentiate metals present in metal mono-sulfides from those in pyrite and chalcopyrite. At all three vent sites, Mn and Fe are primarily in the <0.2μm (filtered) portion, whereas Cu, Co, Cd, and Pb are mainly in the unfiltered fraction. Significant concentrations of HNO3-extractable metals were found in the <0.2μm fraction at all three vent sites, indicating that they likely exist in a recalcitrant nanoparticulate phase such as pyrite or chalcopyrite. At TAG and Snakepit, Cu is correlated with Co, as Co enters into chalcopyrite and other CuFeS phases and Zn is correlated with Cd and Pb as they form discrete metal sulfide phases. At Rainbow, Zn, Cd, and Pb are correlated, but Cu and Co are not correlated. The Rainbow data are consistent with the higher metal to sulfide ratio found at Rainbow. These speciation differences are significant as both mineral type and size will affect the amount of metal transported from the vent site and its availability for biogeochemical processes.

Fast flotation of coal at low pulp density using the Reflux Flotation Cell

Fast particle flotation is accomplished by maximising three fundamental aspects: the kinetics of particle–bubble attachment, the bubble interfacial flux for particle extraction, and the rate of bubble–liquid segregation. In practice, it has been impossible to extend all three aspects simultaneously using conventional flotation devices. Hence, significantly higher processing rates using a single flotation cell has not been possible. Here, the Reflux Flotation Cell has been used in this work to address all three aspects in unison in a single stage of separation. This novel system permits throughput rates well beyond conventional flotation standards. Stable operation using extreme gas and feed fluxes is accomplished using a system of parallel inclined channels located below the vertical portion of the cell. In this paper a highly diluted coal feed comprised of well-liberated coal particles at 0.35wt% solids, was prepared from hydrocyclone overflow. The volumetric feed flux was increased to nearly 10 times the typical conventional level, achieving an extremely low cell residence time, in the order of 25s. Very good combustible recoveries were obtained, with the +38μm portion increasing from 92.3% to 98.5% with increasing gas flux. The partitioning of particles below 38μm decreased with decreasing particle size until separation became governed by hydraulic entrainment, clearly evident at a particle diameter of ∼1.65μm.

Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life

Exoplanet discovery has made remarkable progress, with the first rocky planets having been detected in the central star's liquid water habitable zone. The remote sensing techniques used to characterize such planets for potential habitability and life rely solely on our understanding of life on Earth. The vegetation red edge from terrestrial land plants is often used as a direct signature of life, but it occupies only a small niche in the environmental parameter space that binds life on present-day Earth and has been widespread for only about 460 My. To more fully exploit the diversity of the one example of life known, we measured the spectral characteristics of 137 microorganisms containing a range of pigments, including ones isolated from Earth's most extreme environments. Our database covers the visible and near-infrared to the short-wavelength infrared (0.35-2.5 µm) portions of the electromagnetic spectrum and is made freely available from biosignatures.astro.cornell.edu. Our results show how the reflectance properties are dominated by the absorption of light by pigments in the visible portion and by strong absorptions by the cellular water of hydration in the infrared (up to 2.5 µm) portion of the spectrum. Our spectral library provides a broader and more realistic guide based on Earth life for the search for surface features of extraterrestrial life. The library, when used as inputs for modeling disk-integrated spectra of exoplanets, in preparation for the next generation of space- and ground-based instruments, will increase the chances of detecting life.

Fate of colloids during estuarine mixing in the Arctic

Abstract. The estuarine behavior of organic carbon (OC) and trace elements (TE) was studied for the largest European sub-Arctic river, which is the Severnaya Dvina; this river has a deltaic estuary covered in ice during several hydrological seasons: summer (July 2010, 2012) and winter (March 2009) baseflow, and the November–December 2011 ice-free period. Colloidal forms of OC and TE were assessed for three pore size cutoffs (1, 10, and 50 kDa) using an in situ dialysis procedure. Conventionally dissolved (&lt; 0.22 μm) fractions demonstrated clear conservative behavior for Li, B, Na, Mg, K, Ca, Sr, Mo, Rb, Cs, and U during the mixing of freshwater with the White Sea; a significant (up to a factor of 10) concentration increase occurs with increases in salinity. Si and OC also displayed conservative behavior but with a pronounced decrease in concentration seawards. Rather conservative behavior, but with much smaller changes in concentration (variation within ±30%) over a full range of salinities, was observed for Ti, Ni, Cr, As, Co, Cu, Ga, Y, and heavy REE. Strong non-conservative behavior with coagulation/removal at low salinities (&lt; 5‰) was exhibited by Fe, Al, Zr, Hf, and light REE. Finally, certain divalent metals exhibited non-conservative behavior with a concentration gain at low (~ 2–5‰, Ba, Mn) or intermediate (~ 10–15‰, Ba, Zn, Pb, Cd) salinities, which is most likely linked to TE desorption from suspended matter or sediment outflux. The most important result of this study is the elucidation of the behavior of the "truly" dissolved low molecular weight LMW&lt; 1 kDa fraction containing Fe, OC, and a number of insoluble elements. The concentration of the LMW fraction either remains constant or increases its relative contribution to the overall dissolved (&lt; 0.22 μm) pool as the salinity increases. Similarly, the relative proportion of colloidal (1 kDa–0.22 μm) pool for the OC and insoluble TE bound to ferric colloids systematically decreased seaward, with the largest decrease occurring at low (&lt; 5‰) salinities. Overall, the observed decrease in the colloidal fraction may be related to the coagulation of organo-ferric colloids at the beginning of the mixing zone and therefore the replacement of the HMW1 kDa–0.22 μm portion by the LMW&lt; 1 kDa fraction. These patterns are highly reproducible across different sampling seasons, suggesting significant enrichment of the mixing zone by the most labile (and potentially bioavailable) fraction of the OC, Fe and insoluble TE. The size fractionation of the colloidal material during estuarine mixing reflects a number of inorganic and biological processes, the relative contribution of which to element speciation varies depending on the hydrological stage and time of year. In particular, LMW&lt; 1 kDa ligand production in the surface horizons of the mixing zone may be linked to heterotrophic mineralization of allochthonous DOM and/or photodestruction. Given the relatively low concentration of particulate versus dissolved load of most trace elements, desorption from the river suspended material was less pronounced than in other rivers in the world. As a result, the majority of dissolved components exhibited either conservative (OC and related elements such as divalent metals) or non-conservative, coagulation-controlled (Fe, Al, and insoluble TE associated with organo-ferric colloids) behavior. The climate warming at high latitudes is likely to intensify the production of LMW&lt; 1 kDa organic ligands and the associated TE; therefore, the delivery of potentially bioavailable trace metal micronutrients from the land to the ocean may increase.

Computational analysis of the effect of surface roughness on the deflection of a gold coated silicon micro-cantilever

Numerical simulations were performed to study the effects of surface roughness on the deflection of gold coated silicon cantilevers due to molecular adsorption. The cantilever was modeled using a ball and spring system where the spring constants for the Si-Si, Si-Au, and Au-Au bonds were obtained from first principal calculations. The molecular adsorption process was simulated by elongating the natural bond length of the surface bonding sites by 0.5%. Increasing the bond length created a surface stress on the cantilever causing it to deflect. The system studied consisted of a 1 μm portion of a cantilever of various surface roughnesses with variable boundary condition and was processed in parallel on the Atlantic Computational Excellence Network cluster. The results have indicated that cantilevers with a rougher gold surface deflected more than those with a smoother surface. The increase in deflection is attributed to an increase in stress raisers in the gold film localized around the surface features. The onset of stress raisers increases the differential stress between the top and bottom surfaces and results in an increase in the deflection of the cantilever.

Characterization of lunar dust and a synopsis of available lunar simulants

Understanding the formation and evolution of the soil and dust of the Moon addresses the fundamental question of the interactions of space with the surface of an airless body. The physical and chemical properties of the lunar dust, the <20 μm portion of lunar soil, are key properties necessary for studies of the toxicity and the electrostatic charging of the dust. These properties have been largely overlooked until recent years. Although chemical and physical studies of the <20 μm portion of lunar soil have been the topic of several studies, there is still need for further studies, primarily of the <1 μm particles. This paper presents a review of the studies of lunar dust that have been conducted to date. As many preparations for future exploration or science activities on the Moon require testing using lunar soil/dust simulants, we also include a brief review of past and current simulants.

Spectrum of hot water in the 4750-13 000 cm−1wavenumber range (0.769-2.1 μm)

The high resolution laboratory spectrum of hot water vapour has been recorded in the 500–13 000 cm−1 wavenumber range and we report on the analysis of the 4750–13 000 cm−1 (0.769–2.1 μm) portion. The emission spectrum was recorded using an oxy-acetylene welding torch and a Fourier transform spectrometer. Line assignments in the laboratory spectrum as well as in an absorption spectrum of a sunspot umbra were made with the help of the BT2 line-list. Our torch spectrum is the first laboratory observation of the 9300 Å ‘steam bands’ seen in M-stars and brown dwarfs.

Quantitative Analysis of Cell Division and Cell Death in Seminal Root of Rye under Salt Stress

Cell division and cell death in the cell division zone of the roots of rye seedlings under salt stress were analyzed quantitatively. Cell division was examined by immunological staining with anti-5-bromo-2'-deoxyuridine (BrdU) and cell death by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL). In the 0-700 µm portion from the root tip, which is the cell division zone, the frequency of cell division increased linearly during BrdU treatment. Therefore, the frequency of cell division under salt stress was compared with that in the control at 7 hours after application of BrdU. In the 250 mM NaCl solution (salt stress), the frequency of cell division was decreased and that of cell death was increased as compared with the control resulting in the inhibition of root elongation. In the presence of 50 and 100 mM NaCl, the frequency of cell division was also significantly increased and cell death was hardly detected, and root growth was unchanged as compared with the control. These results suggested that the increase of cell division complemented the decrease of cell elongation due to salt stress, and consequently maintained root growth under mild salt stress conditions.

Mid-infrared (2.5 ≤ λ ≤ 12.5 μm) optical absorption enhancement of textured silicon surfaces coated with an antireflective thin film

High-performance solar cells and optical detection devices frequently incorporate microscopic surface texturing and antireflective (AR) thin films to reduce the reflection of incident radiation and, thus, enhance optical absorption. Using conventional electrochemical and single-crystal silicon micromachining techniques, porous silicon (PS) and textured surfaces composed of randomly spaced and sized pyramids (RSSPs) were fabricated and optically characterized over the mid-infrared (2.5 ≤ λ ≤ 12.5 μm) portion of the optical spectrum. The utility of a 1.53 ± 0.03 μm thick yttrium oxide (Y 2O 3) AR thin film was also investigated in an attempt to enhance optical absorption. The optical measurements were accomplished using a 21 ° incident illumination angle (measured with respect to the sample's normal) and a Bomem® total integrating sphere to quantify the total (specular and diffuse) reflectance ( R). A highly-polished, uncoated, single-crystal silicon wafer was used as a reference surface ( R ave = 0.436 with R σ = 0.033). The performance of the uncoated PS samples revealed R ave = 0.205 with R σ = 0.078, and the RSSP samples manifested R ave = 0.090 with R σ = 0.003. The AR coating significantly improved the performance of the reference and the RSSP textured surfaces: reference sample, ( R ave = 0.251 with R σ = 0.040; RSSP samples, ( R ave = 0.024 with R σ = 0.017). The AR coating did not improve the mid-infrared optical performance of the PS samples; however, the R characteristics for the 0.5 ≤ λ ≤ 2.5 μm portion of the optical spectrum were reduced by more than 50%.

Determination of inorganic sulfate in detergent products by capillary electrophoresis

We have been able to show that capillary electrophoresis (CE) can be used for the rapid determination of sulfate in granular detergents. With this method, an aqueous solution of the detergent (5 g/l) is prepared and a small, filtered (0.2 μm) portion is used for the assay. The total analysis time per sample by CE is less than 15 min using duplicate injections, with 2-min washes between each injection. The analytical method and a comparison of results between CE and gravimetric determinations, will be discussed. Sodium sulfate was quantitated by CE and by a BaCl 2 gravimetric method using 26 different granular detergents with levels ranging from 2 to 40% Na 2SO 4. A least squares fit of the gravimetric data plotted versus the CE data resulted in r 2 = 0.991, m = 0.92 ± 0.02 and b = − 0.41 ± 0.24 (SEE = 0.864), where m = slope, b = y-intercept, and SEE = standard error of estimate. Day-to-day CE results varied by less than 1.0% Na 2SO 4. Within a given day, results from replicate samples varied typically by less than 0.5% Na 2SO 4. The optimum linear range for this method is between 10 to 100 μg/ml, even though the response is linear up to and beyond 180 μg/ml. Sulfate concentrations above 100 μg/ml result in poor resolution for samples with multiple ions.

The behaviour of platinum group elements in the surficial environment at Ferguson Lake, N.W.T., Rottenstone Lake, Sask. and Sudbury, Ont., Canada

A multidisciplinary geochemical study of the distribution, dispersion, and glacial dispersal, of the pge and associated elements has been undertaken within soil, till, humus, vegetation and water at Ferguson Lake, Northwest Territories, Rottenstone Lake, Saskatchewan and Sudbury, Ontario. As the pge generally are present at low levels in surficial materials, development work on analytical techniques was an essential part of this study. At Ferguson Lake, the spatial distribution patterns of Au, Pt and Pd in till clearly indicate the exposed gossan zones, as expected, but also indicate a possible extension of the zone beneath a peat bog- and till-covered area. Down-ice dispersal of Au, Pt and Pd is limited to one to two hundred metres, in the <63 μm component of the till samples collected from frost boils. In vegetation the pge enrichment extends for several hundred metres down-ice and is best defined by Pd in birch twigs. Detectable, although extremely low, levels of Pt (2.8 ppt) and Pd (2.0 ppt) are present in waters in the vicinity of the gossanous zones at Ferguson Lake. At Rottenstone Lake, moderate to high concentrations of pge, Au, and base metals were found in ashed twigs of black spruce and the hmc of the tills for a distance of less than two hundred metres down-ice of the mineralization. Low Pd and Au concentrations were present in ashed spruce twigs about one kilometre down-ice of the mineralization, where only the hmc of the tills yielded anomalous concentrations of Pt and Au. There appears to be only limited dispersal of the pge and Au. These data indicate that only the hmc and the spruce twigs are of value in detecting Pt and Au in this area. Palladium presents a different picture, being detectable in only some of the soils, absent in the tills and hmc, yet appreciably enriched in the twig ash. The inference is that Pd is moving in solution and is being somewhat adsorbed in the soil but is much more significantly being taken up by the plant roots. At the Sudbury areas the pge, hosted in the Ni-Cu mineralization, are best reflected by elevated levels in the ashed humus of almost all elements examined. There is only minimal response in pge and Au to the mineralization from any of the fractions of the soil; whereas the <2 μm fraction of the B-horizon soil reflects the mineralization by elevated levels of As, Sb, Se, Cr, Co, Ni, Cu, Pb and Zn. Only hmc from the tills show elevated pge, Au and variable enhancement in As, Sb, Se and the base metals. The < 2 μm portion of the tills tends to be highest in As, Se, Cr and the base metals. This ongoing study shows that surficial materials and vegetation are effective in identifying areas of concealed pge mineralization. Various pathfinder elements, primarily Cu and Ni, but perhaps also As, Se, Sb and the other base metals, in the < 2 μm B-horizon soils and tills, may be informative in a preliminary evaluation of the pge potential of an area, prior to undertaking the more expensive precious-metal analyses. Humus and vegetation both appear extremely effective, and most cost efficient, and heavy-mineral concentrates ( hmc) appear effective, for identifying areas with pge potential, whereas hmc from tills appear most effective for zeroing in on the site of the pge mineralization.

Rapid-tuning device for CO2 heterodyne detection lidar

A device for rapid-tuning cw, Q-switched lasers for a CO2 heterodyne detection lidar is presented. It is shown that it is possible to utilize galvanometer-driven mirrors to rapidly switch wavelengths over randomly selected lasing transitions in the 9–11 μm portion of the spectrum. Both a transmitter and a local oscillator are simultaneously switched between transitions while still achieving the frequency stability typically required for a coherent lidar system.

DNA synthesis catalyzed in vitro by yeast extracts using A 2 ?m DNA containing plasmid as template for enzymatic DNA synthesis

Partially purified cell-free extracts prepared from growing cells of the yeast Saccharomyces cerevisiae catalyze DNA synthesis directed by the chimeric plasmid BTYP-2 containing the whole 2 μm DNA sequence. The biochemical properties of the reaction have been examined and inactivation studies indicate that DNA synthesis is only due to protein factors. Analysis of the products of the DNA synthesis reaction demonstrates that part of the in vitro synthesized DNA is not covalently linked to the template, thus suggesting initiation of new DNA chains. The analysis of the distribution of the labelled products at early times of reaction showed a preferential synthesis on the 2 μm portion of the BTYP-2 DNA template.