Rapid sea-level change in the Late Guadalupian (Permian) on the Tethyan side of South China: litho- and biostratigraphy of the Chaotian section in Sichuan

The Capitanian (Late Guadalupian) Maokou Formation at Chaotian in northern Sichuan, South China, is composed mainly of shallow marine shelf carbonates deposited on the Tethyan side of South China. By detailed field mapping and scientific drilling, we newly found out unique fossil assemblages and a sharp lithologic change in the upper part of the Maokou Formation. The main part of the Maokou Formation (over 130 m thick) is composed of algal packstone with Wordian-Capitanian large-tested fusulines, rugose corals and other sessile benthos, whereas the Uppermost Member (13 m thick) is composed of black limy mudstone/chert with Capitanian offshore biota (ammonoids, radiolarians, and conodonts). The topmost Capitanian conodont zones are missing; however, the Maokou Formation is disconformably overlain by 260+/-4 Ma volcanic ash (Wangpo bed) and the Early Lopingian Wujiaping Formation with plant-bearing coaly mudstone and shallow marine carbonates (packstone). The newly identified facies change indicates that northern Sichuan has experienced rapid sea-level changes in the late Guadalupian, i.e., first a transgression in the mid-Capitanian and then a regression across the Guadalupian-Lopingian boundary. As the end-Guadalupian is characterized by a global regression, such a volatile sea-level fluctuation, in particular the sea-level rise, is unique to the Tethyan side of South China. The newly recognized relatively deep-water late Guadalupian sequence adds new paleo-environmental information and further provides a paleotectonic interpretation of the low-latitude eastern Tethyan margin immediately before the end-Guadalupian mass extinction.     

Sources of primary production to Arctic bivalves identified using amino acid stable carbon isotope fingerprinting*

ABSTRACT

Benthic invertebrates are a crucial trophic link in Arctic marine food webs. However, estimates of the contribution of different primary production sources sustaining these organisms are not well characterised. We measured the stable carbon isotope values (δ¹³C) of essential amino acids (EAAs) in muscle tissue from two common bivalve genera (Macoma spp. and Astarte spp.) collected in Hanna Shoal in the northeastern Chukchi Sea. Mixing models comparing the δ¹³C_EAA fingerprints of the bivalves to a suite of primary production endmembers revealed relatively high contributions of EAAs from phytoplankton and bacteria in both species. We also examined whether δ¹³C_EAA fingerprints could be produced from the EAAs preserved in bivalve shells, which could allow primary production sources to be estimated from ancient bivalve shells. The δ¹³C_EAA fingerprints from a suite of paired modern bivalve shells and muscle from Macoma calcarea from across the Chukchi Sea revealed a correspondence between the estimates of the dominant primary production source of EAAs derived from analyses of these two tissue types. Our findings indicate that δ¹³C_EAA fingerprinting of marine bivalves can be used to examine dominant organic matter sources in the Arctic marine benthos in recent years as well as in deeper time.     

Structure and absorption spectra of substituted 2-hydroxy-2-trifluoromethylchroman-4-ones

UV absorption spectra of substituted 2-hydroxy-2-trifluoromethylchroman-4-ones (chromanones) in aqueous ethyleneglycol were studied. Replacement of hydrogen in the aromatic ring of the chromanones by CH₃ or CF₃ groups was shown to cause the molar extinction coefficients of the K, B, and C=O bands to shift from 16,160 to 27,980 and 30,250 dm³/mol·cm; from 12,750 to 17,920 and 16,130 dm³/mol·cm; and from 3850 to 3630 and 2760 dm³/mol·cm, respectively. Increasing the solution pH from 1 to 10.5 affected weakly the aromatic ring bands yet impacted greatly the chromanone carbonyl bands, causing their λ_max to shift from 311–326 nm to 342–346 nm and their extinction coefficients to increase from 2760–3850 dm³/mol·cm to 9940–10,160 dm³/mol·cm. A further rise in the pH resulted in hypochromia of the carbonyl band due to the destruction of the chromanones. The results were confirmed by NMR spectroscopy and GC methods.     

Extinction characteristics of isolated n-alkane fuel droplets during low temperature cool flame burning in air

Large carbon number n-alkanes are a notable component in all real transportation fuels, and their chemical structure fosters substantial low temperature kinetic reactivity. Normal alkanes have been studied in various canonical configurations but rarely in systems with strong coupling between low temperature chemistry and transport for pure as well as for multi-component n-alkane mixtures. The Flame Extinguishment (FLEX) experiments onboard the International Space Station provided a unique platform for investigating low temperature multi-phase n-alkane and iso-alkane combustion. Among the many interesting phenomena experimentally observed, cool flame extinction can occur, accompanied by the concurrent formation of a surrounding cloud of condensed vapor. In this work we conduct numerical simulations of high and low temperature combustion of large, initially single-component n-heptane, n-decane and n-dodecane droplets. The role of initial droplet diameter, operating pressure, and n-alkyl carbon number on the extinction of hot and low temperature flames is investigated and compared against the available experimental data. While all three fuels exhibit similar hot flame behavior, cool flame activity increases with the carbon number, resulting in an increased cool flame temperature and decreased extinction diameter. Multi-cyclic “hot/cool flame transitions” are found in air as pressure is slightly increased above one atmosphere. The cyclic behaviors correspond to continuously varying hot and cool flame transitions across the high, low, and negative temperature coefficient (NTC) kinetic regimes. Further increase in pressure results in a second stage steady “Warm flame” transition. The extinction of hot and cool flame has a strong non-linear dependence on ambient pressure but as the hot flame extinction diameter increases with pressure the extinction diameter of the cool flame decreases. The computational results are compared with a recent asymptotic analysis of FLEX n-alkane cool flames.     

The 12C+24Mg elastic scattering: An example of anomalous transparency at coulomb barrier energies

Fifteen complete angular distributions of the elastic scattering of ¹²C+²⁴Mg were measured at energies around the Coulomb barrier (E_cm = 10.67–16 MeV). The angular distributions are strongly oscillating and could be well described by an optical potential family, whose real part was determined without continuous ambiguity. The imaginary part of this optical potential is very shallow. At four energies the inelastic scattering angular distributions leading to the 2⁺ state of the ²⁴Mg were also measured and analysed with coupled-channels calculations. The volume integrals of the optical potentials used in the coupled-channels calculations present the threshold anomaly in their energy dependence, with a clear Q-value dependence.     

Kinetic effects of NO addition on n-dodecane cool and warm diffusion flames

The kinetic effects of NO addition on the flame dynamics and burning limits of n-dodecane cool and warm diffusion flames are investigated experimentally and computationally using a counterflow system. The results show that NO plays different roles in cool and warm flames due to their different reaction pathway sensitivities to the flame temperature and interactions with NO. We observe that NO addition decreases the cool flame extinction limit, delays the extinction transition from warm flame to cool flame, and promotes the ignition transition from warm flame to hot flame. In addition, jet-stirred reactor (JSR) experiments of n-dodecane oxidation with and without NO addition are also performed to develop and validate a n-dodecane/NO_x kinetic model. Reaction pathway and sensitivity analyses reveal that, for cool flames, NO addition inhibits the low-temperature oxidation of n-dodecane and reduces the flame temperature due to the consumption of RO₂ via NO+RO₂?NO₂+RO, which competes with the isomerization reaction that continues the peroxy radical branching sequence. The model prediction captures well the experimental trend of the inhibiting effect of NO on the cool flame extinction limit. For warm flames, two different kinds of warm flame transitions, the warm flame extinction transition to cool flame and the warm flame reignition transition to hot flame, were observed. The results suggest that warm extinction transition to cool flame is suppressed by NO addition while the warm flame reignition transition to hot flame is promoted. The kinetic model developed captures well the experimentally observed warm flame transitions to cool flame but fails to predict the warm flame reignition to hot flame at similar experimental conditions.     

Thermal annealing effect of on optical constants of vacuum evaporated Se75S25−xCdx chalcogenide thin films

Chalcogenide glasses are interesting materials due to their infrared transmitting properties and photo induced effects exhibited by them. Thin films with thickness of 3000 Å of the glasses Se₇₅S_25−xCd_x with x=6, 8 and 10 at% prepared by melt quench technique were evaporated by thermal evaporation onto glass substrates under a vacuum of 10⁻⁶ Torr. The optical constants (absorption coefficient, refractive index and extinction coefficient) of as-prepared and annealed films have been studied as a function of photon energy in the wave length region 400-1000 nm. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It has been found that the absorption coefficient and optical band gap increase with increasing annealing temperatures. The refractive index (n) and the extinction coefficient (k) were observed to decrease with increasing annealing temperature.     

Spectroscopic study of nanocrystalline V2O5·nH2O films doped with Li ions

Optical properties of nanocrystalline, Li_xV₂O₅·nH₂O films (0<x<22 mol%), are explored in the present work. These films have been produced by the sol–gel technique (colloidal route), which was used for the preparation of high purity and homogeneity films. Optical measurements were carried out using a double-beam spectrophotometer. The optical constants such as refractive index n, the extinction coefficient k, absorption coefficient α, and optical band gap of the films material have been evaluated. The optical absorption coefficient was calculated from the measured normal reflectance, R, and transmittance, T, spectra. The optical spectra of all samples exhibited two distinct regions: at high energy, which suggests a direct forbidden transition with optical gap ranging from 1.75 to 2.0 eV and increases with increase in Li-content. On the other hand a second low-energy band suggests a direct allowed transition with optical gap ranging from 0.40 to 0.42 eV. The width of the localized states (band tail) E_e was also estimated for all samples. Additional calculations applying the real part of the optical dielectric function led to the evaluation of the charge carrier concentration and their effective mass.     

Performance analysis of wavelength conversion using a light-injected laser diode based on improved rate equations

The extinction and signal to noise ratios, the two main figures-of-merit for a wavelength converted signal are analyzed on the basis of the improved rate equations. The model accurately considers the mutual coupling parameter β_m which indicates the efficiency of the wavelength conversion. A simple relationship among extinction ratio, signal to noise ratio and the mutual coupling parameter β_m is given. With the simulation results, we find that the high extinction and signal to noise ratios depends on higher pump (i.e. original) power, optimum probe (i.e. converted) power and less wavelength spacing between them, which is in accordance with the analysis of mutual coupling parameter β_m.     

Measurement of mean size and evaluation of polydispersity of gold nanoparticles from spectra of optical absorption and scattering

Two methods for determination of the mean size of gold nanoparticles, based on measurement of the wavelengths of the maxima λ_max of side scattering and extinction in the range 400–700 nm, are compared. Four sols with mean particle diameters d of about 15, 20, 25, and 30 nm, measured using the dynamic light-scattering technique, were studied experimentally. The slope of the size dependence λ_max(d) of the spectral position of the scattering peak exceeded that for the extinction peak by a factor of 2.4. This fact ensures a substantially higher accuracy of the scattering method. For simulating polydispersity, mixtures of three colloids with particle diameters of 20, 25, and 30 nm were used: sample S1, with a size distribution close to the normal one of around 25 nm, and sample S2, with equal concentrations of each of the components. The extinction spectra of mixtures S1 and S2 and the initial 25-nm sol (S0) were virtually identical, whereas their scattering spectra showed a pronounced increase in the peak amplitude in the series S0, S1, S2. These results agree with calculations based on the Mie theory. Thus, scattering spectra offer advantages over extinction spectra not only in measuring the mean size of gold particles but also in evaluating their polydispersity.     

Maximum coefficient of light extinction in a nonabsorbing dispersive medium

The maximum value of the light extinction coefficient μ, which can be observed in a dispersive medium with a relative refractive index n of the scattering particles, is studied within the framework of a quasi-crystalline approximation for nonabsorbing dispersive media consisting of monodisperse spherical scatterers. A change in the diffraction parameter x of the scattering particles and their volume concentration c _v is accompanied by nonmonotonic variations of the extinction coefficient, and the function μ(x, c _v ) exhibits several maxima. The dimensions and concentrations of particles are determined, for which the extinction coefficient reaches the absolute maximum μ^max. The μ^max value exhibits a monotonic growth with increasing relative refractive index n of the scattering particles. The conditions of validity of the Ioffe-Regel criterion of radiation localization have been studied. It is established that the localization in nonabsorbing dispersive media can be observed only for n ? 2.7. The intervals of x and c _v in which the criterion of radiation localization is satisfied in dispersive media consisting of particles with n = 3.0 and 3.5 are determined.     

Linear and nonlinear optical response of MgxZn1−xO: A density functional study

Total and partial density of states, frequency dependent complex refractive index including extinction coefficient, optical conductivity and transmission of Mg_xZn_1−xO (0≤x≤1) in rocksalt and wurtzite phases are calculated using full potential linearized augmented plane wave (FP-LAPW) method. The real part of refractive index decreases while the extinction coefficient, optical conductivity and transmission for rocksalt phase increases with the increase in Mg concentration. In wurtzite phase, ordinary and extraordinary indices decrease while extinction coefficient, optical conductivity and transmission increase in parallel as well as perpendicular to c-axis with the increase in the Mg concentration.     

Growth,fabrication, and testing of bismuth tri-iodide semiconductor radiation detectors

Bismuth tri-iodide (BiI₃) is an attractive material for high energy resolution radiation detectors. For the purpose of this research, detectors were fabricated using single crystals grown from ultra-pure BiI₃ powder; synthesized by the Physical Vapor Transport (PVT) technique. This technique yielded powder with total impurity level of 7.9 ppm. Efforts were also made to purify commercial BiI₃ powder using a custom-built Traveling Zone Refining (TZR) system. Initial trial runs were successful in reducing the total impurity level of the commercial powder from 200 ppm to less than 50 ppm. Using the modified vertical Bridgman technique and a customized sharp tip ampoule, a large BiI₃ single crystal was grown. The crystal had a surface area of 2.2 cm² and a thickness of 0.8 cm, which corresponds to a volume of 1.78 cm³. Radiation detectors were fabricated and then tested by measuring their electrical characteristics and radiation response. An alpha particle spectrum (using a ²⁴¹Am α-source) was recorded at room temperature with a BiI₃ detector 0.09 cm thick and with a surface area of 0.16 cm². The electron mobility was estimated to be 433 ± 79 cm²/V.     

Physical properties of ZnO thin films deposited by spray pyrolysis technique

Thin films of ZnO have been prepared on glass substrates at different thicknesses by spray pyrolysis technique using 0.2 M aqueous solution of zinc acetate. X-ray diffraction reveals that the films are polycrystalline in nature having hexagonal wurtzite type crystal structure. The resistivity at room temperature is of the order 10⁻² Ω cm and decreased as the temperature increased. Films are highly transparent in the visible region. The dependence of the refractive index, n, and extinction coefficient, k, on the wavelength for a sprayed film is also reported. Optical bandgap, E_g, has been reported for the films. A shift from E_g = 3.21 eV to 3.31 eV has been observed for deposited films.     

Towards dynamic control of magnetic fields to focus magnetic carriers to targets deep inside the body

Magnetic drug delivery has the potential to target therapy to specific regions in the body, improving efficacy and reducing side effects for treatment of cancer, stroke, infection, and other diseases. Using stationary external magnets, which attract the magnetic drug carriers, this treatment is limited to shallow targets (<5 cm below skin depth using the strongest possible, still safe, practical magnetic fields). We consider dynamic magnetic actuation and present initial results that show it is possible to vary magnets one against the other to focus carriers between them on average. The many remaining tasks for deep targeting in-vivo are then briefly noted.     

A DNS evaluation of mixing and evaporation models for TPDF modelling of nonpremixed spray flames

In the present work, nonpremixed temporally evolving planar spray jet flames are simulated using both direct numerical simulation (DNS) and the composition transported probability density function (TPDF) method. The objective is to assess the performance of various mixing and evaporation source term distribution models which are required to close the PDF transport equation in spray flames. Quantities which would normally be provided to the TPDF solver by spray models and turbulence models are provided from the DNS: the mean flow velocity, turbulent diffusivity, mixing frequency, and cell-mean evaporation source term. Two cases with different Damköhler numbers (Da) are considered. The low Da case (Da-) features extinction followed by reignition while extinction in the high Da case (Da+) is insignificant. The TPDF modelling considers two mixing models: interaction by exchange with the mean (IEM) and Euclidean minimum spanning trees (EMST). Three models for distribution of the evaporation source terms are considered: EQUAL which distributes them in proportion to notional particles’ mass weight, NEW which creates new particles of pure fuel, and SAT which distributes the sources preferentially to notional particles close to saturation. It is found that the IEM model overpredicts the extinction when used with any evaporation model for both Da- and Da+ cases. The EMST model captures well the trend for extinction and reignition for the Da- case when it is coupled with the EQUAL evaporation model, but it overpredicts the extinction when coupled with the NEW or SAT evaporation model. For the Da+ case, all evaporation models reasonably capture the flame dynamics when coupled with EMST. The flame temperature in the mixture fraction space was examined to further assess the model performance. In general the EMST model results in narrow PDFs with little conditional fluctuation, while the IEM model produces bimodal PDFs with burning and partial extinction branches.     

Localized states in InxGa1−xN epitaxial film

This study investigated localized states from In_0.36Ga_0.64N epitaxial film grown on a Si (111) substrate by performing macro-photoluminescence, micro-photoluminescence and time-resolved micro-photoluminescence experiments. Experimental data revealed two localized states — single and extended. The single localized state is a single-quantum-dot-like deep confined energy state, which is responsible for the bright line emissions. The extended localized state is a shallow confined energy state, which is related to a broad background emission. This work suggests that the origin of single and extended localized states is the indium-rich In_xGa_1?xN cluster and the spatial indium concentration fluctuation, respectively.     

Upper limit on the resistivity of La1.85Sr0.15CuO4

The stability of a shielding current in a hollow cylinder of La_1.85Sr_0.15CuO₄ has been studied with a superconducting quantum interference device (SQUID). From the observed lack of decay of the current an upper limit of 3×10^-17ω cm has been established on the resistivity at 4.2 K.     

Optical characterization of xTiO2-(60 − x)SiO2-40Na2O glasses: II. Absorption edge, Fermi level, electronic polarizability and optical basicity

In the present work different optical properties of xTiO₂-(60 − x)SiO₂-40Na₂O (wt%) optical glasses are determined. The characterization is done over a wide energy range, 0.41-6.2 eV. The refractive index and the extinction coefficient data are used to measure the absorption coefficient of the different glass compositions. Studying the UV-absorption edge, both direct and indirect allowed transitions with their optical energy gaps are carried out. In the same time, the Urbach energy is evaluated. From the extinction coefficient data, the Fermi energy of the glasses is calculated. The molar refraction, electronic polarizability and the optical basicity are obtained using the measured glass refractive indices.