High Field Site Research Articles

Impact of Cr3+ substitution on the nephelauxetic ratio and Racah parameter of Cr-Mn-Zn nanoferrites

For the first time, we present the ligand field splitting (10Dq) nephelauxetic ratio (β), Racah parameter (B) and stability of Cr3+ within Mn–Zn nanoferrite which synthesized using the citrate route. These parameters were determined via optical absorption spectra. The obtained bands in the significance range of optical absorption spectra are wide as well as asymmetric; therefore the deconvolution process becomes a necessary task. The values of 10Dq and B have been estimated from the produced bands. The values of 10Dq are observed to increase from 16366.61 to 16447.37 cm−1 whereas, B values are observed to decrease from 829.81 to 760.80 cm−1 with additional Cr3+ substitution. The increasing 10Dq and decreasing B values, evidence for bonds between Cr3+ ions with their environments became a further covalent (less ionic). Moreover, the values of β are observed to decrease for further Cr3+ substitution. This decrease of β produces less stability between Cr3+ and its ligand. Furthermore, Dq/B values declare that Cr3+ centers are in the low-field sites by a slight tendency towards the high-field sites with further Cr/Fe substitution process. Therefore, it was suggested that Cr3+ substituted Mn–Zn nanoferrites are excellent candidates for diverse optical applications such as a tunable laser.

Optical spectroscopy of chromium doped bismuth-lithium borate glasses

The optical absorption, photoluminescence, and electron spin resonance spectroscopies were used to investigate the effect of Bismuth oxide on a chromium doped borate glass system of composition 14.5% Li2O – 0.5% Cr2O3 – (85-x)% B2O3 – (x)% Bi2O3, x = 0.0, 1.0, 3.0, 5.0 and 8.0, synthesized by conventional melt quenching technique. Two sets of Cr characteristic absorption bands were identified in the ultraviolet and visible regions. The intensity and/or peak position for these transitions could be readily tuned through Bi2O3 additives. The ligand field analysis applied to the absorption spectra revealed high field sites for Cr ions as inferred from the resulting Dq/B values. The presence of Cr6+ and Cr3+ ions is further supported by the development of well-defined photoluminescence peaks. The electron spin resonance spectra complement these optical findings and clearly identify resonance signals ascribed to Cr3+ and Cr5+, the latter in particular evolves monotonically with Bi2O3 content.

Blue, Red, and Green Emission from Chromium and Copper Metal Doped Lithium Borate Glass

The influence of copper metal on the structural and optical properties (absorption and emission) of the lithium borate glass samples containing chromium considered. The analysis of FTIR spectra measured, indicated the copper and chromium ions act as network former and modifier depend on the concentration of everyone in the sample content. The ratio between the BO4 groups to the total boron groups (BO4+BO3) decreases with the copper content increases up to 2 mol % and then increase. The optical properties that the Dq/B decreases with the increase the copper and higher than 2.3 which indicates the glass samples containing Cr3+ions in the high-field sites and produce conventional laser action. The emission spectra show the intensity emission bands at 440 nm, 540 nm, and 730 nm for relative strong blue, green and red bands respectively.

Compatibility of pellet fuelling with ELM suppression by RMPs in the ASDEX Upgrade tokamak

It is demonstrated that tokamak plasma can be fuelled by pellets while simultaneously maintaining ELM suppression by external resonant magnetic perturbations (RMPs). Pellets are injected vertically from high field site and deposited at outer part of plasma cross section. Each pellet triggers a benign MHD event followed by a short lived ELM-free phase. The ELM suppression phase with pellet fuelling lasts 11 pellet cycles and is terminated by intentionally increasing the pellet rate to cause a transition to the ELMy phase.

Interactions between vortex and magnetic rings at high kinetic and magnetic Reynolds numbers

Interactions between magnetic and vortex rings are studied over a wide interval of interaction parameter values ranging from negligible magnetic effects on vorticity structure, to very strong effects. The employed interaction parameter measures the strength of the Lorentz force in units of the inertial force. At small interaction parameters, the vortex ring shapes part of the magnetic ring into a dissipative, curved, magnetic sheet structure. At high interaction parameters, the Lorentz force acts as an agent of proliferation of vortex rings, since it generates two vortex rings adjacent to the original magnetic structure, one of which is pulled (together with the advected magnetic field) into the wake of the original vortex ring, while the other escapes, ready to interact with another magnetic ring. Once within the initial vortex ring wake, both magnetic and vorticity structures are stretched into spirals, whilst the Lorentz force continuously generates new, intense vorticity at high magnetic field sites.

Wheat black point: Role of environment and genotype

Wheat black point is an important quality defect in many areas of the world. The aims of this study were to identify grain tissues involved and to develop a better understanding of the genetic and environmental mechanisms that control black point. Results (of microscopic and genetic investigations) were consistent with control of pigment synthesis being resident in the tissues comprising the grain coat. Analysis of data for a black point susceptible variety revealed a strong correlation between black point and rainfall 20–30 days after anthesis. Application of overhead misting to wheat plots during grain ripening in field experiments appeared to validate this relationship and black point symptoms preceded the appearance of any fungal infestation. A 3-years trials at a high risk field site involving commercial varieties and a doubled haploid population derived from a resistant x susceptible cross indicated significant contributions from genotype, environment and genotype x environment. Germination rate of black pointed developing and ripe grains increased, with no apparent impact on seed viability. The results suggest that black point development can be independent of fungal presence. Furthermore, dark pigment synthesis in susceptible genotypes appears to occur if specific environmental conditions coincide with a sensitive period in grain development.

Nitrogen use efficiency and productivity of first year switchgrass and big bluestem from low to high soil nitrogen

Despite an abundance of research on the biomass response to nitrogen fertilizer in established switchgrass fields, there is a dearth of knowledge of the first year response in switchgrass, and nothing yet available for big bluestem. Based on differences in their C4 photosynthetic subtypes, big bluestem may show greater photosynthetic (PNUE) and above-ground whole plant nitrogen use efficiency (NUE) over switchgrass. Here we report the first year biomass response to nitrogen fertilizer for two cultivars of upland switchgrass and three cultivars of big bluestem. We first performed a greenhouse experiment with four nitrogen treatments ranging from 1.5 dmol m−3 to 16 mol m−3 aqueous nitrogen solutions. Here we measured PNUE mid-way through the experiment and harvested plants green to measure above-ground whole plant NUE. We also compared these cultivars at two field sites with contrasting soil nitrogen content. At low soil nitrogen, big bluestem “Prairie View” achieved both the highest NUE in the greenhouse and greatest biomass in the field. Switchgrass produced significantly more biomass than big bluestem at the high nitrogen field site, whereas biomass production was similar for both species at the low nitrogen field site. Although both species responded positively to increasing soil nitrogen, switchgrass did increasingly more so compared to big bluestem, with a 20% greater biomass stimulation in the greenhouse from low to high soil nitrogen. Net CO2 assimilation rates showed a similar response with biomass production to the nitrogen treatments, allowing switchgrass “Sunburst” to achieve a slightly greater PNUE compared to big bluestem “Prairie View”.

High Salinity Relaying to Reduce Vibrio parahaemolyticus and Vibrio vulnificus in Chesapeake Bay Oysters (Crassostrea virginica).

Cases of Vibrio infections in the United States have tripled from 1996 to 2009 and these infections are most often associated with the consumption of seafood, particularly oysters (Crassostrea virginica). Information is needed on how to reduce numbers of Vibrio parahaemolyticus and Vibrio vulnificus in bi-valve molluscan shellfish (for example, oysters). The purpose of this study was to evaluate the effectiveness of high salinity relaying or treatment in recirculating aquaculture systems (RASs) as methods to reduce the abundance of V. parahaemolyticus and V. vulnificus in oysters. For relaying field trials, oysters were collected from approved harvest waters, temperature abused outside under a tarp for 4 h, and then transferred to high (29 to 33 ppt.) and moderate (12 to 19 ppt.) salinities. For RAS treatment trial, oysters were transferred to 32 to 34 ppt. salinity at 15 °C. After 7, 14, 21, and in some instances 28 d, oysters were collected and analyzed for V. parahaemolyticus and V. vulnificus levels using multiplex real-time PCR. Initial levels of V. parahaemolyticus and V. vulnificus ranged from 3.70 to 5.64 log10 MPN/g, and were reduced by 2 to 5 logs after 21 to 28 d in high salinity water (29 to 34 ppt.). Oyster mortalities averaged 4% or less, and did not exceed 7%. Relaying of oysters to high salinity field sites or transfer to high salinity RAS tanks was more effective in reducing V. vulnificus compared with V. parahaemolyticus. These results suggest that high salinity relaying of oysters is more effective in reducing V. vulnificus than V. parahaemolyticus in the oyster species used in this study.

Does fire alter soil water repellency in subtropical coastal sandy environments?

AbstractIrregular wetting, water repellency, and preferential flow are well‐documented properties of coastal sandy podzols, though little is known about the effect of fire on unsaturated zone processes in this environment. This study investigates water repellency at and below the soil surface in two coastal sandy podzols following bushfire. Water drop penetration time tests were applied to burned and unburned soils at a high dune field site in South East Queensland, Australia. It was found that the mean water drop penetration time of the burned soil was four times that of the unburned soil, but both soils were largely non‐repellent. Post‐fire repellency peaked below the surface in a patchy layer, in contrast to the laterally extensive layer reported in other studies, and high organic matter content in the soil did not appear to significantly influence repellency post‐burn. Non‐parametric statistics were used to quantify the high spatial variability in water repellency, which was ultimately insufficiently captured by atypically large (n = 1000 drop) datasets. This study confirms the presence of naturally occurring repellency and patchy infiltration in sandy soils while demonstrating that conclusively describing the influence of fire is challenging in a soil with heterogeneous infiltration characteristics. With respect to this uncertainty, it appears that fire does not increase soil water repellency such that infiltration and runoff processes due to fire‐induced water repellency would differ post‐burn.

Physical and spectroscopic studies of Cr3+ doped mixed alkaline earth oxide borate glasses

A series of mixed alkaline earth oxide glasses xMgO-(30-x)BaO-69.8B2O3-0.2Cr2O3 were prepared and studied using electron paramagnetic resonance (EPR), optical absorption, Raman spectroscopy and photoluminescence experimental techniques. The optical absorption spectra revealed the characteristic octahedral symmetry of Cr3+ions through three broad band transitions 4A2g(F)→ 4T2g(F), 4A2g(F)→ 4T1g(F), and 4A2g(F)→ 2T1g(P). The crystal field (Dq) and Racah parameters (B and C), the optical band gap and Urbach energies of the glass samples were also reported along with the physical properties like density and molar volume. In the EPR spectra three resonance signals corresponding to Cr3+ ions were observed. A broad signal with g = 5.110 was observed which belongs to the isolated Cr3+ centers localized in the strongly distorted octahedral (rhombic) sites of the glass network, a narrow signal (g = 1.960) corresponding to the Cr3+ centers in the weekly distorted (cubic) sites of the glass network, and a third very broad signal (g = 2.210) was also observed corresponding to Cr3+- Cr3+ paired centers coupled by magnetic dipolar interaction. Another resonance signal with effective value g ≈ 4.220 was attributed to Fe3+ ions impurity. The number of spins (N) participating in the resonance and susceptibility (χ) values at room temperature were reported and their values varied in a non-linear manner with the composition exhibiting mixed oxide effect. The estimated molecular bonding coefficients (α) values indicated stronger ionic contribution. The Raman spectral investigations were carried out. The Photoluminescence spectra bands near 690 and 750 nm correspond to the Cr3+ centers in high and low field sites respectively.

Evolution of the optical properties of chromium doped calcium tetraborate glass under high pressure

In this contribution, we present luminescence properties of calcium tetraborate glass (CaB4O7) activated with Cr3+ ions. Excitation spectra, steady state and time resolved luminescence spectra at temperatures between 10K and 300K and at high hydrostatic pressure up to 120kbar were measured. The excitation spectrum consists of two broad bands peaking at 420nm and 580nm related to transitions from the 4A2g ground state to 4T1g and 4T2g excited states, respectively. Ambient pressure luminescence spectrum consists of two bands peaking at 690nm and 850nm. First band is related to the spin forbidden 2Eg→4A2g transition, whereas the second broad band is related to the spin allowed 4T2g→4A2g transition. Widths of both bands are significantly greater than natural due to inhomogeneous broadening. The ratio between intensities of these bands is strongly temperature and pressure dependent. At pressure below 50 kbar relative contribution of the 2Eg→4A2g luminescence decreases with increasing temperature and increases when pressure is applied. For pressure higher than 50 kbar only the emission related to the 2Eg→4A2g transition is observed. Analysis of luminescence lineshape and kinetics allowed to estimate the width of the crystal field distribution and show that even at ambient pressure most of the Cr3+ ions occupy high field sites with energy of the 4T2g higher than the energy of the 2Eg state.

Low and high field sites of Cr3+ ions in calcium tetraborate glasses

This paper presents electron paramagnetic resonance and detailed optical spectroscopic characterization of CaB4O7 glasses doped with Cr3+. The luminescence excitation spectrum consists of two broad bands related to transitions from the ground state 4A2g to the excited states 4T1g and 4T2g of the octahedrally coordinated Cr3+ ions. The photoluminescence spectrum is a superposition of the R line related to the 2Eg→4A2g transition and broad band related to the 4T2g→4A2g transition. The analysis of electron paramagnetic resonance spectra allowed to distinguish different Cr3+ sites, whereas the analysis of luminescence and luminescence excitation spectra allowed to characterize the crystal field distribution in the glass host.

Atmospheric black carbon and sulfate concentrations in Northeast Greenland

Abstract. Measurements of equivalent black carbon (EBC) in aerosols at the high Arctic field site Villum Research Station (VRS) at Station Nord in North Greenland showed a seasonal variation in EBC concentrations with a maximum in winter and spring at ground level. Average measured concentrations were about 0.067 ± 0.071 for the winter and 0.011 ± 0.009 for the summer period. These data were obtained using a multi-angle absorption photometer (MAAP). A similar seasonal pattern was found for sulfate concentrations with a maximum level during winter and spring analyzed by ion chromatography. Here, measured average concentrations were about 0.485 ± 0.397 for the winter and 0.112 ± 0.072 for the summer period. A correlation between EBC and sulfate concentrations was observed over the years 2011 to 2013 stating a correlation coefficient of R2 = 0.72. This finding gives the hint that most likely transport of primary emitted BC particles to the Arctic was accompanied by aging of the aerosols through condensational processes. BC and sulfate are known to have only partly similar sources with respect to their transport pathways when reaching the high Arctic. Aging processes may have led to the formation of secondary inorganic matter and further transport of BC particles as cloud processing and further washout of particles is less likely based on the typically observed transport patterns of air masses arriving at VRS. Additionally, concentrations of EC (elemental carbon) based on a thermo-optical method were determined and compared to EBC measurements. EBC measurements were generally higher, but a correlation between EC and EBC resulted in a correlation coefficient of R2 = 0.64. Model estimates of the climate forcing due to BC in the Arctic are based on contributions of long-range transported BC during spring and summer. The measured concentrations were here compared with model results obtained by the Danish Eulerian Hemispheric Model, DEHM. Good agreement between measured and modeled concentrations of both EBC/BC and sulfate was observed. Also, the correlation between BC and sulfate concentrations was confirmed based on the model results observed over the years 2011 to 2013 stating a correlation coefficient of R2 = 0.74. The dominant source is found to be combustion of fossil fuel with biomass burning as a minor, albeit significant source.

Variation in isotopologues of atmospheric nitric acid in passively collected samples along an air pollution gradient in southern California

The sources and oxidation pathways of atmospheric nitric acid (HNO3) can be evaluated using the isotopic signatures of oxygen (O) and nitrogen (N). This study evaluated the ability of Nylasorb nylon filters to passively collect unbiased isotopologues of atmospheric HNO3 under controlled and field conditions. Filters contained in passive samplers were exposed in continuous stirred tank reactors (CSTRs) at high (16 μg/m3) and moderate (8 μg/m3) HNO3 concentrations during 1–4 week deployment times. Filters were concurrently exposed at high and low N deposition sites along a gradient in the Sonoran Desert. Filters deployed in CSTRs at moderate HNO3 concentrations for 1–2 weeks had greater variation of δ18O relative to the 3–4 week deployments, while high concentration samples were consistent across weeks. All deployment means were within 2‰ of the source solution. The δ15N of all weekly samples were within 0.5‰ of the source solution. Thus, when deployed for longer than 3 weeks, Nylasorb filters collected an isotopically unbiased sample of atmospheric HNO3. The initial HNO3 samples at the high deposition field sites had higher δ15N and δ18O values than the low deposition sites, suggesting either two independent sources of HNO3 were mixing or that heavier isotopologues of HNO3 were preferentially lost from the gas phase through physical deposition or equilibrium chemical reactions. Subsequent HNO3 samples were subject to summer monsoon conditions leading to variation of isotopic signatures of N and O following 2-source mixing dynamics. Both sites mixed with a source that dominated during the two discrete precipitation events. The high number of lightning strikes near the samplers during the monsoon events suggested that lightning-created HNO3 was one of the dominant mixing sources with an approximate isotopic signature of 21.6‰ and −0.6‰ for δ18O and δ15N respectively. Two-source mixing models suggest that lightning-created HNO3 made up between 40 and 42% of atmospheric HNO3 at the high deposition sites and 59–63% at the low deposition during the 4 week exposure.

Assessment of the consistency of H 2O line intensities over the near-infrared using sun-pointing ground-based Fourier transform spectroscopy

We report on the consistency of water vapour line intensities in selected spectral regions between 800–12,000 cm −1 under atmospheric conditions using sun-pointing Fourier transform infrared spectroscopy. Measurements were made across a number of days at both a low and high altitude field site, sampling a relatively moist and relatively dry atmosphere. Our data suggests that across most of the 800–12,000 cm −1 spectral region water vapour line intensities in recent spectral line databases are generally consistent with what was observed. However, we find that HITRAN-2008 water vapour line intensities are systematically lower by up to 20% in the 8000–9200 cm −1 spectral interval relative to other spectral regions. This discrepancy is essentially removed when two new linelists (UCL08, a compilation of linelists and ab-initio calculations, and one based on recent laboratory measurements by Oudot et al. (2010) [10] in the 8000–9200 cm −1 spectral region) are used. This strongly suggests that the H 2O line strengths in the HITRAN-2008 database are indeed underestimated in this spectral region and in need of revision. The calculated global-mean clear-sky absorption of solar radiation is increased by about 0.3 W m −2 when using either the UCL08 or Oudot line parameters in the 8000–9200 cm −1 region, instead of HITRAN-2008. We also found that the effect of isotopic fractionation of HDO is evident in the 2500–2900 cm −1 region in the observations.

Effect of Nanocrystal Structures on Interface of Cr-Doped Yttrium Aluminum Garnet Double-Clad Crystal Fiber

In this study, we investigated both the microstructure and the chemistry of the core/inner cladding interface in Cr-doped yttrium aluminum garnet (Cr:YAG) double-clad crystal fiber by high-resolution transmission electron microscopy. In the axial direction, two contrasting layers were found between the SiO2 inner cladding and the YAG crystal core (with or without heat treatment). Cr3+:γ-Al2O3 nanocrystals were observed; these nanodomains were slightly tilted at an angle of about 2° from the core YAG structures at the original interface. Subsequently, amorphous oxide layers were formed during codrawing laser-heated pedestal growth. The Cr3+:γ-Al2O3 nanocrystals had different lattice parameters and showed various structures during growth. The defect density of the core YAG near the interface was reduced after appropriate heat treatment. These results indicated that the growth kinetics can critically affect the interface chemistry in this crystal fiber. The relative fluorescence spectrum of Cr4+ in both low- and high-field sites was significantly affected by the nanocrystal distribution.

Starving the soil of plant inputs for 50 years reduces abundance but not diversity of soil bacterial communities

If soil communities rely on plant-derived carbon, is biodiversity lost when this primary source is removed? Soil microbial and mesofaunal communities at the Rothamsted Highfield site were compared under a mixed grass sward, arable rotation and a section maintained as a bare-fallow for the past 50 years by regular tillage. Organic matter reserves have been degraded and microbial and mesofaunal numbers and mite diversity have declined in this unique bare-fallow site, where fresh carbon inputs have been drastically reduced. However, it supports a species-rich metabolically active bacterial community of similar diversity to that in soil maintained as grass sward. Thus in contrast to soil mesofauna, bacterial diversity (but not abundance) is apparently independent of plant inputs.

Broadband Near-Infrared Emission from TransparentNi2+-Doped Sodium Aluminosilicate Glass Ceramics

Broadband near-infrared emission from transparent Ni2+-dopedsodium aluminosilicate glass-ceramics is observed. The broad emissionis centred at 1290 nm and covers the whole telecommunication wavelengthregion (1100–1700 nm) with full width at half maximum of about 340 nm.The observed infrared emission could be attributed to the 3T2(F)→3A2(F) transition of octahedral Ni2+ ions thatoccupy high-field sites in nanocrystals. The product of the lifetime andthe stimulated emission cross section is 2.15×10−24 cm2s.It is suggested that Ni2+-doped sodium aluminosilicate glassceramics have potential applications in tunable broadband light sourcesand broadband amplifiers.

Composition dependence of the microspectroscopy of Cr ions in double-clad Cr:YAG crystal fiber

We have demonstrated the use of microspectroscopy for measuring the Cr3+ and Cr4+ fluorescence spectra in double-clad Cr:YAG crystal fiber. The emission spectra of Cr3+ and Cr4+ are detected from core and inner cladding. The Cr3+ spectrum in the inner cladding shows a broad-band emission from 650to950nm, while the emission of Cr4+ occurs in the range of 1.15–1.55μm with a peak around 1.22μm. The characteristic of Cr ion at high-field sites shows a narrow-band emission (E2→A24 for Cr3+; E1→A23 for Cr4+), whereas that at low-field sites shows a broad-band emission (T24→A24 for Cr3+; T23→A23 for Cr4+). The emission intensity ratio of high-field sites to low-field sites in the inner cladding with different compositions has been investigated. It varies from 20% to 29% for Cr3+ and from 7.1% to 11.3% for Cr4+ when the concentration of SiO2 increases from 26.9to43.0wt%.

Optical spectroscopy and crystal-field strength of Cr 3+ in various solid matrixes

Abstract The Cr 3+:BeAl 2O 4 crystal, Cr 3:LiNbO 3 crystal, and ZnO-Al 2O 3-SiO 2 glass-ceramic were obtained by the Czochralski technique, Bridgman method, and melting processing, respectively. The optical absorption and emission spectra of the above Cr 3-incorporated solid-state materials were recorded. The technical parameters for growing high-quality Cr 3+:BeAl 2O 4 and Cr 3+:LINbO 3 crystals were obtained. The results indicate that the optical absorption and fluorescence spectra of Cr 3+ show quite a few differences in various matrixes. The sharp line emissions were observed in the Cr 3+:BeAl 2O 4 and Cr 3+:LiNbO 3 crystals. The crystal-field parameters ( D q) for Cr 3+ in different matrixes were calculated from their corresponding spectra. It is indicated that Cr 3+:BeAl 2O 4 and Cr 3+:LiNbO 3 belong to the high-field site crystal, while the Cr 3+:ZnO-Al 2O 3-SiO 2 glass and glass-ceramic belong to the weak-field site crystal.