The limits of validity of the Frequency Ratio Method: The particular case of γ Doradus stars

This work provides a general vision of the limits of validity of the Frequency Ratio Method applied to the g‐mode pulsators in asymptotic regime, the γ Doradus stars. In particular, the work is mainly focused on the role of rotation which is found one of the most important source of uncertainty of the method. The particular case of the moderately rotating γ Doradus star HD48501 is discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sensitive Ion‐Flotation Separation of Ag(I) Traces Using 2‐(2‐Methoxyphenyl)benzimidazole before Flame Atomic Absorption Spectrometric Determination in Water

A sensitive, reliable, and environmentally friendly method for simple separation and preconcentration of Ag(I) traces in aqueous samples is presented prior to their flame atomic absorption spectrometric determinations. At pH 7.0, Ag(I) was separated with 2‐(2‐methoxyphenyl)benzimidazole (MPBI) as a new complexing agent and floated after adding sodium dodecyl sulfate (SDS) as a foaming reagent. The floated layer was then dissolved in proper amount of concentrated nitric acid in methanol and introduced to the flame atomic absorption spectrometer (FAAS). The effects of pH, concentration of MPBI, type and amount of surfactant as the floating agent, type and amount of eluting agent, and influence of foreign ions on the recovery of the analyte ion were investigated. Also, using a nonlinear curve fitting method, the formation constant of 1.62 × 10⁶ was obtained for Ag(I)–MPBI complex. The analytical curve was linear in the range of 1.8 × 10^?7–1.7 × 10^?6 mol/L for determination of Ag(I). The relative standard deviation (RSD; N = 10) corresponding to 0.7 × 10^?6 mol/L of Ag(I), the limit of detection (10 blanks), and the enrichment factor were obtained as 1.7%, 2.9 × 10^?8 mol/L, and 43.0, respectively. The proposed procedure was then applied successfully for determination of silver ions in different water samples.     

A numerical investigation of a moderate coastal storm with intense precipitation

Abstract

In this study, the development of a moderate coastal storm with intense precipitation that occurred during 12–14 February 1993 is examined using a high‐resolution version of the Canadian Regional Finite‐element (RFE) model with more realistic physical representations. It is shown that the improved RFE model predicts well the coastal cyclogenesis events and also the distribution and intensity of heavy mixed precipitation (rain and snow) associated with the storm. It is found that the cyclogenesis takes place in response to the low‐level inshore advection of high‐θ_e air from the maritime boundary layer, and the approach of a mid‐level shortwave trough with a warm pool above that is previously associated with a decaying cyclone upstream. More rapid deepening of the cyclone ensues as intense precipitation falls along the warm and cold fronts near the cyclone centre.

Diagnosis of the control and sensitivity simulations reveals that the low‐level inshore warm advection and the propagation of the stratospheric warm pool contribute more significantly to the surface pressure falls during the incipient stage, whereas the mid‐level shortwave trough plays an important role in the cyclogenesis at later stages. Overall, latent heat release accounts for about 50% of the cyclone's total deepening, in agreement with the presence of a moderate baroclinic environment and the generation of intense precipitation.

The diabatic and kinematic structures near the rain‐snow boundary are examined to gain insight into the influence of melting snow on the cyclogenesis. It is shown that the improved RFE model reproduces well the rain‐snow boundary structures as previously observed. Moreover, a thermally indirect circulation (perturbation) can be seen in the vicinity of the rain‐snow boundary. It is found, however, that melting of snow tends to produce a weak negative or negligible impact on the cyclogenesis, as opposed to previous hypotheses.     

THE CLASSROOM AS THE FIELD FOR STUDYING GEOGRAPHICAL EDUCATION

ABSTRACT. Recent attempts by U.S. politicians to reform the nation'sschools have shifted the goal of education to school accountability as assessed in standardized testing. Such an emphasis undermines geographical education in schools because of geography'ssuperficial representation in tests and in the social studies curriculum. Fieldwork done in the classroom can point to means of circumventing this dilemma. Collaborative fieldwork between college faculty members and public‐school teachers has the potential for adding geography to the social studies curriculum in a substantive way. Work conducted jointly by Hartwick College and the Oneonta (New York) Middle School exemplifies such a partnership.     

Evaporation from seasonally frozen bare and vegetated ground at various groundwater table depths in the Ordos Basin,Northwest China

In cold climates, the process of freezing–thawing significantly affects the ground surface heat balance and water balance. To better understand the mechanism of evaporation from seasonally frozen soils, we performed field experiments at different water table depths on vegetated and bare ground in a semiarid region in China. Soil moisture and temperature, air temperature, precipitation, and water table depths were measured over a 5‐month period (November 1, 2016, to March 14, 2017). The evaporation, which was calculated by a mass balance method, was high in the periods of thawing and low in the periods of freezing. Increased water table depth in the freezing period led to high soil moisture in the upper soil layer, whereas lower initial groundwater levels during freezing–thawing decreased the cumulative evaporation. The extent of evaporation from the bare ground was the same in summer as in winter. These results indicate that a noteworthy amount of evaporation from the bare ground is present during freezing–thawing. Finally, the roots of Salix psammophila could increase the soil temperature. This study presents an insight into the joint effects of soil moisture, temperature, ground vegetation, and water table depths on the evaporation from seasonally frozen soils. Furthermore, it also has important implications for water management in seasonally frozen areas.     

Weichselian interstadials at Riipiharju,northern Sweden – interpretation of vegetation and climate from fossil and modern pollen records

Hättestrand, M. & Robertsson, A.‐M. 2010: Weichselian interstadials at Riipiharju, northern Sweden – interpretation of vegetation and climate from fossil and modern pollen records. Boreas, 10.1111/j.1502‐3885.2009.00129.x. ISSN 0300‐9483. The most complete records of Weichselian ice‐free conditions in northern Sweden have been retrieved from kettleholes in the Riipiharju esker. In an earlier study, the Riipiharju I core was described as containing two Weichselian interstadials and Riipiharju was chosen as type site for the second Weichselian interstadial in northern Sweden. Here, we present a palynological investigation of two new sediment cores (Riipiharju II and III) retrieved from Riipiharju. Together, the new cores comprise a late cold part of the first Weichselian interstadial recorded in northeastern Sweden (Tärendö I, earlier correlated with Peräpohjola in Finland) as well as a long sequence of the second Weichselian interstadial (Tärendö II, earlier named Tärendö). The results indicate that the climate during deposition of the Tärendö II sequence was more variable than earlier suggested. According to the present interpretation it was relatively warm in the early part of Tärendö II; thereafter a long cold phase persisted, and finally the climate was warmer again in the late part of Tärendö II. The warm phases are characterized by Betula‐dominant pollen assemblages, while the cold phase is characterized by high percentages of Artemisia and Gramineae pollen. Since there is still no firm chronology established of the interstadials in northeastern Sweden, two possible correlations are discussed; either Tärendö I and II are correlated with Brörup (MIS 5c) and Odderade (MIS 5a), or, perhaps more likely, they are correlated with Odderade and early Middle Weichselian (MIS 3) time.     

Supraglacial weathering crust dynamics inferred from cryoconite hole hydrology

Water levels in cryoconite holes were monitored at high resolution over a 3‐week period on Austre Brøggerbreen (Svalbard). These data were combined with melt and energy balance modelling, providing insights into the evolution of the glacier's near‐surface hydrology and confirming that the hydrology of the near‐surface, porous ice known as the ‘weathering crust’ is dynamic and analogous to a shallow‐perched aquifer. A positive correlation between radiative forcing of melt and drainage efficiency was found within the weathering crust. This likely resulted from diurnal contraction and dilation of interstitial pore spaces driven by variations in radiative and turbulent fluxes in the surface energy balance, occasionally causing ‘sudden drainage events’. A linear decrease in water levels in cryoconite holes was also observed and attributed to cumulative increases in near‐surface ice porosity over the measurement period. The transport of particulate matter and microbes between cryoconite holes through the porous weathering crust is shown to be dependent upon weathering crust hydraulics and particle size. Cryoconite holes therefore yield an indication of the hydrological dynamics of the weathering crust and provide long‐term storage loci for cryoconite at the glacier surface. This study highlights the importance of the weathering crust as a crucial component of the hydrology, ecology and biogeochemistry of the glacier ecosystem and glacierized regions and demonstrates the utility of cryoconite holes as natural piezometers on glacier surfaces. Copyright © 2015 John Wiley & Sons, Ltd.     

Abundance and isotopic composition of noble gases in metal and graphite of the Bohumilitz IAB iron meteorite

Abstract— Abundances and isotopic compositions of noble gases in metal and graphite of the Bohumilitz IAB iron meteorite were measured. The abundance ratios of spallogenic components in metal reveal a ³He deficiency which is due to the diffusive loss of parent isotopes, that is, tritium (Tilles, 1963; Schultz, 1967). The diffusive loss likely has been induced by thermal heating by the Sun during cosmic‐ray exposure (～160 Ma; Lavielle et al, 1999). Thermal process such as impact‐induced partial loss may have affected the isotopic composition of spallogenic Ne. The ¹²⁹Xe/¹³¹Xe ratio of cosmogenic components in the metal indicates an enhanced production of epi‐thermal neutrons. The abundance ratios of spallogenic components in the graphite reveal that it contained small amounts of metal and silicates. The isotopic composition of heavy noble gases in graphite itself was obtained from graphite treated with HF/HCl. The isotopic composition of the etched graphite shows that it contains two types of primordial Xe (i.e., Q‐Xe and El Taco Xe). The isotopic heterogeneity preserved in the Bohumilitz graphite indicates that the Bohumilitz graphite did not experience any high‐temperature event and, consequently, must have been emplaced into the metal at subsolidus temperatures. This situation is incompatible with an igneous model as well as the impact melting models for the IAB‐IIICD iron meteorites as proposed by Choi et al. (1995) and Wasson et al (1980).     

New insights into geochemical behaviour in ancient marine carbonates (Upper Jurassic Ammonitico Rosso): Novel proxies for interpreting sea‐level dynamics and palaeoceanography

Elemental concentrations in Phanerozoic sea water are known to fluctuate both in time and space. With regard to carbonates precipitated from marine fluids, elemental concentrations in the carbonate crystal lattice are affected by a complex array of equilibrium and non‐equilibrium as well as post‐depositional alteration processes. To assess the potential of carbonate elemental chemostratigraphy, seven Upper Jurassic sections were investigated along a proximal to distal transect across the south‐east Iberian palaeomargin. The aim was to explore stratigraphic and spatial variations in calcium, strontium, magnesium, iron and manganese elemental abundances. The epicontinental geochemical record is influenced by the combination of continental runoff and a significant diagenetic overprint. In contrast, the epioceanic geochemical record agrees with reconstructed open marine sea water values, reflecting a moderate degree of syn‐depositional to early marine pore water diagenesis. Establishing a fair degree of preservation of matrix micrite, a thorough statistical approach was applied and elemental associations tested for their environmental significance. Principal component and hierarchical cluster analyses revealed a persistent relation between carbonate magnesium, iron and strontium abundances. Processes related to early diagenetic nodulation in Ammonitico Rosso facies most probably account for the incorporation of these elements in the calcium carbonate lattice. The clear decoupling of carbonate manganese abundance with respect to the remaining elements is documented and related to high sea floor spreading rates and hydrothermal activity during the Late Jurassic. The investigation of potential time‐fluctuation of geochemical patterns was approached through variogram computation. The observed temporal behaviour is most likely to be forced by relative sea‐level dynamics, reflecting Late Jurassic palaeoceanographic conditions and potential planetary interactions. The data obtained in this study highlight the utility of elemental data from carbonate matrix micrites as geochemical proxies for studying the influence of remote trigger factors.     

Tectonics of a fast spreading center: A Deep-Tow and sea beam survey on the East Pacific rise at 19°30′ S

Sea Beam and Deep-Tow were used in a tectonic investigation of the fast-spreading (151 mm yr^-1) East Pacific Rise (EPR) at 19°30 S. Detailed surveys were conducted at the EPR axis and at the Brunhes/Matuyama magnetic reversal boundary, while four long traverses (the longest 96 km) surveyed the rise flanks. Faulting accounts for the vast majority of the relief. Both inward and outward facing fault scarps appear in almost equal numbers, and they form the horsts and grabens which compose the abyssal hills. This mechanism for abyssal hill formation differs from that observed at slow and intermediate spreading rates where abyssal hills are formed by back-tilted inward facing normal faults or by volcanic bow-forms. At 19°30 S, systematic back tilting of fault blocks is not observed, and volcanic constructional relief is a short wavelength signal (less than a few hundred meters) superimposed upon the dominant faulted structure (wavelength 2–8 km). Active faulting is confined to within approximately 5–8 km of the rise axis. In terms of frequency, more faulting occurs at fast spreading rates than at slow. The half extension rate due to faulting is 4.1 mm yr^-1 at 19°30 S versus 1.6 mm yr^-1 in the FAMOUS area on the Mid-Atlantic Ridge (MAR). Both spreading and horizontal extension are asymmetric at 19°30 S, and both are greater on the east flank of the rise axis. The fault density observed at 19°30 S is not constant, and zones with very high fault density follow zones with very little faulting. Three mechanisms are proposed which might account for these observations. In the first, faults are buried episodically by massive eruptions which flow more than 5–8 km from the spreading axis, beyond the outer boundary of the active fault zone. This is the least favored mechanism as there is no evidence that lavas which flow that far off axis are sufficiently thick to bury 50–150 m high fault scarps. In the second mechanism, the rate of faulting is reduced during major episodes of volcanism due to changes in the near axis thermal structure associated with swelling of the axial magma chamber. Thus the variation in fault spacing is caused by alternate episodes of faulting and volcanism. In the third mechanism, the rate of faulting may be constant (down to a time scale of decades), but the locus of faulting shifts relative to the axis. A master fault forms near the axis and takes up most of the strain release until the fault or fault set is transported into lithosphere which is sufficiently thick so that the faults become locked. At this point, the locus of faulting shifts to the thinnest, weakest lithosphere near the axis, and the cycle repeats.