Te Method Research Articles

Optical properties of metamaterial-based devices modulated by a liquid crystal

Due to the fact that it is possible to manipulate light with photonic crystals (PCs), PCs hold a great potential for designing new optical devices. There has been an increase in research on tuning the optical properties of PCs to design devices. We presented a numerical study of optical properties of metamaterial-based devices by liquid crystal infiltration. The plane wave expansion method and finite-difference time-domain method for both TE and TM modes revealed optical properties in photonic crystal structures in an air background for a square lattice. E7 type has been used as a nematic liquid crystal and SrTiO3 as a ferroelectric material. We showed the possibility of the metamaterials for a two-dimensional photonic crystal cavity on a ferroelectric base infiltrated with a nematic liquid crystal.

ESTIMATION OF ATOSIBAN ACETATE IN PARENTERALS BY RP HPLC

A simple, precise, rapid and accur a te reverse phase HPLC method was developed for the estimation of Atosiban Acetate in dosage form. A n XTerra MS C18 analytical column ( 250 x 4.6 mm , 5 μm partical size ) with mobile phase consisting of mixture of buffer 0.0 3 M Potassium Dihydrogen Orthophosphate in water and pH adjusted to 3.20 with o rtho - phosphoric acid and acetonitrile in the gradient program was used. The flow rate was 1.0 mL /min an d the effluents were monitored at 2 2 0 nm . The retention time was 1 1.3 min . The detector response was linear in the concentration of 15 - 225 mc g/ mL . The respective linear regression equation being y = 1286.9 x - 1290 . 8 . The limit of detection (LOD) and limit of quantification (LOQ) for Atosiban Acet ate were found to be 1.5 mcg/mL and 4.5 mcg/mL respectively . The percentage ass ay of Atosiban Acetate was 99. 6 %. The method was validated by determining its accuracy, precision and linearity . The results of the stu dy showed that the proposed RP - HPLC method is simple, rapid , precise and accurate, which is useful for the

ESTIMATION OF TRIMEBUTINE MALEATE IN TABLET DOSAGE FORM BY RP HPLC

A simple, precise, rapid and accur a te reverse phase HPLC method was developed for the estimation of Trimebutine Maleate in tablet dosage form. A n XTerra(R) C18 analytical column ( 250 x 4.6 mm , 5 μm partical size ) with mobile phase consisting of mixture of buffer 0.0 2 M Ammonium Acetate in water and acetonitrile in the gradient program was used. The flow rate was 1.0 mL /min and the effluents were monitored at 275 nm . The retention time was 17.0 min utes . The detector response was linear in the concentration of 2 0 - 3 0 0 mc g/ mL . The respective linear regression equation being y = 1914.1 x - 1911 . The limit of detection and limit of quantification was 0. 5 mcg /mL and 1.5 mc g/ mL respectively. The percenta ge ass ay of Trimebutine Maleate was 99. 8 %. The method was validated by determining its accuracy, precision and system suitability . The results of the study showed that the proposed RP - HPLC method is simple, rapid , precise and accurate, which is useful for the routine determination of Trimebutine Maleate in bulk drug and in its pharmaceutical dosage form.

Emission spectrum of ionized gas in the irregular galaxy Holmberg II

We study the ionized gas spectrum of star forming regions in the Holmberg II galaxy using the optical long-slit spectroscopic observations made at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). We estimate the oxygen, nitrogen, sulphur, neon, and argon abundances in individual HII regions and find the average metallicity in the galaxy to be Z=0.1 or 0.3 Zsun depending on the estimation method employed. We use these observations combined with the results of our earlier studies of the Irr galaxy IC 10 and BCD galaxy VII Zw 403 to compare the currently most popular methods of gas metallicity estimation in order to select among them the techniques that are most reliable for analysing Irr galaxies. To this end, we use the "direct" Te method and six empirical and theoretical methods. The results of our observations mostly confirm the conclusions of Lopez-Sanchez et al. (2012) based on the analysis of systematic deviations of metallicity estimates derived by applying different methods to "model" HII regions.

RECALIBRATION OF PAGEL'S METHOD FOR H II REGIONS CONSIDERING THE THERMAL STRUCTURE, THE IONIZATION STRUCTURE, AND THE DEPLETION OF O INTO DUST GRAINS

Using a sample of 28 HII regions from the literature with measured temperature inhomogeneity parameter, t^2, we present a statistical correction to the chemical abundances determined with the Te(4363/5007) method. We used the t^2 values to correct the oxygen gaseous abundances and consider the oxygen depletion into dust to calculate the total abundances for these objects. This correction is used to obtain a new calibration of Pagel's strong-line method, R_{23}, to determine oxygen abundances in HII regions. Our new calibration simultaneously considers the temperature structure, the ionization structure, and the fraction of oxygen depleted into dust grains. Previous calibrations in the literature have included one or two of these factors; this is the first time all three are taken into account. This recalibration conciliates the systematic differences among the temperatures found from different methods. We find that the total correction due to thermal inhomogeneities and dust depletion amounts to an increase in the O/H ratio of HII regions by factors of 1.7 to 2.2 (or 0.22 to 0.35 dex). This result has important implications in various areas of astrophysics such as the study of the higher end of the initial mass function, the star formation rate, and the mass-metallicity relation of galaxies, among others.

Abundance determination from global emission-line SDSS spectra: exploring objects with high N/O ratios

We have compared the oxygen and nitrogen abundances derived from global emission-line SDSS spectra of galaxies using (1) the Te method and (2) two recent strong line calibrations: the ON and NS calibrations. Using the Te method, anomously high N/O abundances ratios have been found in some SDSS galaxies. To investigate this, we have Monte Carlo simulated the global spectra of composite nebulae by a mix of spectra of individual components, based on spectra of well-studied HII regions in nearby galaxies. We found that the Te method results in an underestimated oxygen abundance (and hence in an overestimated nitrogen-to-oxygen ratio) if HII regions with different physical properties contribute to the global spectrum of composite nebulae. This effect is somewhat similar to the small-scale temperature fluctuations in HII regions discussed by Peimbert. Our work thus suggests that the high Te-based N/O abundances ratios found in SDSS galaxies may not be real. However, such an effect is not expected to be present in dwarf galaxies since they have generally an uniform chemical composition. The ON and NS calibrations give O and N abundances in composite nebulae which agree with the mean luminosity-weighted abundances of their components to within 0.2 dex.

Platinum group elements (Pt, Pd, Rh) in airborne particulate matter in rural vs. urban areas of Germany: Concentrations and spatial patterns of distribution

This study examines platinum group element concentrations (PGE) (i.e. platinum (Pt), palladium (Pd) and rhodium (Rh)) and their spatial distribution in airborne particulate matter fractions (PM) of human health concern in urban and rural areas of Germany. Fractionated airborne dust and PM10, PM2.5 and PM1 samples were collected along a busy road in Frankfurt am Main from July 2008 to April 2010. PM10 was also sampled in Deuselbach and Neuglobsow between January 2008 and July 2009 to examine their concentrations at rural locations and potential for long-range transport.Pt, Pd and Rh were isolated and pre-enriched in samples using a combination of Te and Hg co-precipitation methods. Concentrations were determined using isotope dilution ICP-Q-MS (in collision mode with He).The highest airborne PGE concentrations were measured in PM10 from Frankfurt (e.g. 12.4pg Pt/m3 (mean)), while the rural locations of Deuselbach and Neuglobsow exhibited the lowest levels (e.g. 2pg Pt/m3 (mean)). PGE concentrations were observed to decline with increasingly smaller PM size fractions from PM10 to PM1. All size fractions generally contained higher levels of Pd compared to Pt and Rh, an element of greater concern due to its solubility. PM2.5 collected in Frankfurt had a mean of 16.1pg Pd/m3, compared to 9.4pg/m3 for Pt. PGE concentrations also demonstrated a distinct seasonal relationship, with the greatest levels occurring in winter. Compared to a previous study in 2002, PGE concentrations in fractionated airborne dust have significantly increased over time. Elevated PGE levels were also measured for PM10 sampled in Neuglobsow and Deuselbach, which could not be attributed to local emission sources. Using the diagnostic meteorological model, CALMET, trajectory analyses confirmed our hypothesis that PGE are being transported over longer distances from other areas of Europe.

Advanced fluid-typing methods for NMR logging

In recent years, nuclear magnetic resonance (NMR) has been increasingly used for fluidtyping in well-logging because of the improved generations of NMR logging tools. This paper first discusses the applicable conditions of two one-dimensional NMR methods: the dual TW method and dual TE method. Then, the two-dimensional (T2, D) and (T2, T1) NMR methods are introduced. These different typing methods for hydrocarbon are compared and analyzed by numerical simulation. The results show that the dual TW method is not suitable for identifying a macroporous water layer. The dual TE method is not suitable for typing gas and irreducible water. (T2, T1) method is more effective in typing a gas layer. In an oil-bearing layer of movable water containing big pores, (T2, T1) method can solve the misinterpretation problem in the dual TW method between a water layer with big pores and an oil layer. The (T2, T1) method can distinguish irreducible water from oil of a medium viscosity, and the viscosity range of oil becomes wide in contrast with that of the dual TW method. The (T2, D) method is more effective in typing oil and water layers. In a gas layer, when the SNR is higher than a threshold, the (T2, D) method can resolve the overlapping T2 signals of irreducible water and gas that occurs due to the use of the dual TE method. Two-dimensional NMR for fluid-typing is an important development of well logging technology.

Improvements in routine uranium isotope ratio measurements using the modified total evaporation method for multi-collector thermal ionization mass spectrometry

A new version of the “modified total evaporation” (MTE) method for isotopic analysis of uranium samples by multi-collector thermal ionization mass spectrometry (TIMS), with high analytical performance and designed in a more user-friendly and routinely applicable way, is described in detail. It is mainly being used for nuclear safeguards measurements, but can readily be applied in other scientific areas like geochemistry. The development of the MTE method was organized in collaboration of several “key nuclear mass spectrometry laboratories”, namely the New Brunswick Laboratory (NBL), the Safeguards Analytical Laboratory (SAL, now SGAS—Safeguards Analytical Services) of the International Atomic Energy Agency (IAEA), the Institute for Transuranium Elements (ITU/JRC), and the Institute for Reference Materials and Measurements (IRMM/JRC), with IRMM taking the leading role. Due to the use of the “total evaporation” (TE) principle the measurement of the “major” ratio n(235U)/n(238U) is routinely being performed with an accuracy of 0.02%. In contrast to the TE method, in the MTE method the total evaporation process is interrupted on a regular basis to allow for correction for background from peak tailing, internal calibration of a secondary electron multiplier (SEM) detector versus the Faraday cups, peak-centering, and ion source re-focusing. Therefore, the most significant improvement using the MTE method is in the measurement performance achieved for the “minor” ratios n(234U)/n(238U) and n(236U)/n(238U). The n(234U)/n(238U) ratio is measured using Faraday cups only with the result that the (relative) measurement uncertainty (k = 2) is better than 0.12%, which is an improvement by a factor of about 5–10 compared to TE measurements. Furthermore, the IAEA requirement for the “measurement performance”, defined here as the sum of the (absolute) deviation of the measured from the true (certified) value plus the (absolute) measurement uncertainty (k = 2), for n(236U)/n(238U) ratio measurements is 1 × 10−6, but the MTE method provides a measurement performance which is, depending on the ratio, by several orders of magnitude superior compared to this limit and to the TE method. For routine MTE measurements a detection limit of 3 × 10−9 was achieved using an SEM detector for detecting the isotope 236U. The MTE method is now routinely being used at all collaborating laboratories with the hope that more laboratories will implement this capability in the future as well. Additional applications for the MTE method are presented in this paper, e.g., for absolute Ca isotope measurements.

Detection of citrus yellow mosaic virus by PCR and nucleic acid spot hybridisation using non-radioactive probes in commercial citrus species

Citrus yellow mosaic virus (CYMV) was detected by polymerase chain reaction (PCR) in leaf samples of sweet orange, Rangpurlime, Pumello pink and acid lime and also in twig bark, fruit rind, fruit juice except fruit rag of sweet orange cv. Sathgudi, where all the positive samples showed bright amplification of the 726 bp band except in fruit rind. The CYMV could be detected by the biotin labelled probe of CYMV up to 1:100 dilutions by TE and TNE extraction methods in sweet orange cv. Sathgudi as well as Rangpurlime.

Quantitative Characterization of the Achilles Tendon in Cadaveric Specimens: T1 and T2* Measurements Using Ultrashort-TE MRI at 3 T

The objective of our study was to provide a quantitative means of evaluating the intrinsic T1 and T2(*) values of the Achilles tendon through the measurement of T1 recovery and T2(*) relaxation times, respectively, using ultrashort-TE (UTE) MRI at 3 T with histologic correlation. Six cadaveric specimens underwent MRI at 3 T. The MRI protocol included standard MRI and UTE pulse sequences. For T1 measurement, a saturation recovery time method was applied (saturation recovery time range, 10-1,600 milliseconds), and for T2(*) measurements, a constant TR-varying TE method was used (TE, 100 microseconds-15 milliseconds). An analysis algorithm written in Matlab was executed offline on axial DICOM images for the T1 and T2(*) measurements in areas of normal tendon. The cadaveric specimens were subsequently frozen to -40 degrees C. They were sectioned with the slice thickness corresponding to the MR images. Anatomic sections were photographed and visually inspected. Specimens were then processed for histology. MR images, specimen photographs, and histology results were reviewed by two musculoskeletal radiologists and one pathologist. Compared with histology results, the combination of UTE and standard MRI provided an accurate means of identifying normal tendon. The mean T1 measurement was 621 milliseconds and the mean T2(*) measurement was 2.18 milliseconds in histologically proven regions of normal tendon. The UTE MR sequence offers structural information about and allows reproducible quantitative evaluation of tissues with short T2 components, such as tendons, that are inaccessible on conventional MRI. This technique showed T1 and T2(*) measurements in the normal Achilles tendon and allowed correlation with structural status by histology. Because of the small number of specimens, this is considered a feasibility study.

Scattering of Electromagnetic Waves by Dielectric Gratings with Dielectric Rectangular Cylinders Sandwiched between Two Multilayers

In this paper, we propose an improved method to analyze the scattering problem by dielectric gratings with dielectric rectangular cylinders sandwiched between two multilayers, by combining an improved Fourier series expansion method and multilayer method for both TM and TE waves.Numerical results are given for the influence of incident angle and frequency of the transmitted power in terms of the parameters e 3/e 0 of rectangular cylinders in the middle layer, yielding the basic characteristics of resonance peak for switching or frequency selective devices for both TM and TE cases.

Andromeda IV: A new local volume very metal-poor galaxy

And IV is a low surface brightness (LSB) dwarf galaxy at a distance of 6.1 Mpc, projecting close to M 31. In this paper the results of spectroscopy of the And IV two brightest HII regions with the SAO 6-m telescope (BTA) are presented. In spectra of both of them the faint line [OIII]λ4363 Å was detected and this allowed us to determine their O/H by the classical Te method. Their values for 12+log(O/H) are equal to 7.49±0.06 and 7.55±0.23, respectively. The comparison of the direct O/H calculations with the two most reliable semi-empirical and empirical methods shows the good consistency between these methods. For And IV absolute blue magnitude, MB = −12.6, our value for O/H corresponds to the ‘standard’ relation between O/H and LB for dwarf irregular galaxies (DIGs). And IV appears to be a new representative of the extremely metal-deficient gas-rich galaxies in the Local Volume. The very large range of M(HI) for LSB galaxies with close metallicities and luminosities indicates that simple models of LSBG chemical evolution are too limited to predict such striking diversity.

The Oxygen Abundance of Nearby Galaxies from Sloan Digital Sky Survey Spectra

We have derived the oxygen abundance for a sample of nearby galaxies in Data Release 5 of the Sloan Digital Sky Survey (SDSS) that possess at least two independent spectra of one or several H II regions with a detected [O III] λ4363 auroral line. Since, for nearby galaxies, the [O II] λ3727 nebular line is out of the observed wavelength range, we propose a method to derive (O/H)ff abundances using the classic Te method coupled with the flux-flux (ff) relation. (O/H)7325 abundances have also been determined, based on the [O II] λλ7320, 7330 line intensities and using a small modification of the standard Te method. The (O/H)ff and (O/H)7325 abundances have been derived with both the one- and two-dimensional t2-t3 relations. It was found that the (O/H)ff abundances derived with the parametric two-dimensional t2-t3 relation are the most reliable. Oxygen abundances have been determined in 29 nearby galaxies on the basis of 84 individual abundance determinations in H II regions. Because of our selection methods, the metallicity of our galaxies lies in the narrow range 8.2 12 + log(O/H) 8.4. The radial distribution of oxygen abundances in the disk of the spiral galaxy NGC 4490 is determined for the first time.

The direct oxygen abundances of metal-rich galaxies derived from electron temperature

Context. Direct measurement of oxygen abundance for metal-rich galaxies from electron temperature is difficult or impossible since temperature-sensitive auroral lines generally become too weak to be measured. Aims. We aim to derive the electron temperature (Te) in the gas of metal-rich star-forming galaxies, which can be obtained from their ratios of auroral lines [O ii]λλ7320, 7330 to nebular lines [O ii]λ3727, in order to establish a more robust massmetallicity relationship, and compare the Te-based (O/H) abundances with those from empirical strong-line calibrations, such as R23 (=([O ii]λ3727+[O iii]λλ4959, 5007)/Hβ). Methods. We obtained 27 spectra by stacking the spectra of several hundred (even several thousand) star-forming galaxies selected from the SDSS-DR4 in each of the 27 stellar mass bins from log(M∗) ∼ 8.0 to 10.6 (in units of log(M� )). This “stack” method sufficiently improves the signal-to-noise ratio of the auroral lines [O ii]λλ7320, 7330. Using a two-zone model for the temperature structure, we derive the electron temperature t2 in the low ionization region from the [O ii]λλ7320, 7330/[O ii]λ3727 ratio, and then use a relation derived by fitting H ii region models to estimate the electron temperature t3 in the high ionization region from t2. Then, the direct (O/H) abundances are obtained from t2, t3 and the related line-ratios. The emission lines have been carefully corrected for dust extinction using the Balmer line ratio after correcting for the underlying stellar absorption. Results. Combining our results with those from the literature with lower metallicities, we are able to provide a new relationship between the direct measurements of (O/H) and R23, which still shows an upper and a lower branch with the transition around 12 + log(O/H) ∼ 8.0−8.2. It also shows that the empirical R23 method will overestimate log(O/H) by 0.2 to 0.6 dex. The new metal-mass relationship of the galaxies with moderate metallicities is fitted by a linear fit (12 + log(O/H) = 6.223 + 0.231 × log(M∗)) confirming that empirical methods significantly overestimate (O/H). We also derived their (N/O) abundance ratios on the basis of the Te method, which are consistent with the combination of the primary and secondary components of nitrogen. Conclusions. This study provides for the first time a method to calibrate direct O/H abundances (from Te) for a large range of galaxies

Probabilistic Modeling of Knee Muscle Moment Arms: Effects of Methods, Origin–Insertion, and Kinematic Variability

In musculoskeletal modeling, reliable estimates of muscle moment arms are an important step in accurately predicting muscle forces and joint moments. The degree of agreement between the two common methods of calculating moment arms-tendon excursion (TE) and geometric origin-insertion, is currently unknown for the muscles crossing the knee joint. Further, measured moment arm data are subject to variability in estimation of attachment sites as points from irregular surfaces on the bones, and due to differences in joint kinematics observed in vivo. Thus, the objectives of the present study were to compare moment arms of major muscles crossing the knee joint obtained from TE and geometric methods using a finite element-based lower extremity model, and to quantify the effects of potential muscle origin-insertion and tibiofemoral kinematic variability on the predicted moment arms using probabilistic methods. A semiconstrained, fixed bearing, posterior cruciate-retaining total knee arthroplasty was included due to available in vivo kinematic data. In this study, muscle origin and insertion locations and kinematic variables were represented as normal distributions with standard deviations of 5 mm for origin-insertion locations and up to 1.6 mm and 3.0 degrees for the kinematic parameters. Agreement between the deterministic moment arm calculations from the two methods was excellent for the flexors, while differences in trends and magnitudes were observed for the extensor muscles. Model-predicted deterministic moment arms from both methods agreed reasonably with the experimental values from available literature. The uncertainty in input parameters resulted in substantial variability in predicted moment arms, with the size of 1-99% confidence interval being up to 41.3 and 35.8 mm for the TE and geometric methods, respectively. The sizeable range of moment arm predictions and associated excursions has the potential to affect a muscle's operating range on the force-length curve, thus affecting joint moments. In this study, moment arm predictions were more dependent on muscle origin-insertion locations than the kinematic variables. The important parameters from the TE method were the origin and insertion locations in the sagittal plane, while the insertion location in the sagittal plane was the dominant parameter using the geometric method.

A two-step procedure for extracting genomic DNA from dried blood spots on filter paper for polymerase chain reaction amplification

-based diagnostic tests. Traditionally alarge volume of blood is collected in tubes and DNA isextracted from white blood cells using a phenol–chloro-form method [1] or a “salting-out” rapid puri Wcation proce-dure [2]. While these methods are able to provide milligramquantities of puriWed DNA, this amount generally exceedsthat required for successful PCR and the methods are alsomore time consuming and expensive, and hence less suit-able for rapid PCR diagnosis, especially for multiple bloodsamples.The use of dried blood spots on Wlter paper becomes anattractive alternative to blood collection in tubes for PCRanalyses. First, only a small amount of blood is needed, andimmediate processing is not required. Second, there are notransfer steps once the blood is applied onto the paper andhence the chance for mislabeling or sample mixing is low.Third, sample transport and storage for dried blood spots iseasy and less expensive. As a result of these advantages, col-lection of blood on Wlter paper has been widely used for thePCR-based genetic screening [3–5].As blood samples contain a variety of substances thatmay inhibit PCR, separation of these substances fromDNA is generally necessary prior to ampli Wcation. To over-come this problem, a number of methods have been devel-oped for DNA extraction from dried blood spots on Wlterpaper, including the methanol method [6], the protease Kmethod [7], the Chelex-100 method [8], and the TE method[9]. Commercial products are also available, such as FTAcards and puriWcation reagent (Whatman, Middlesex, UK),but these products are relatively expensive, and the puriW-cation procedure requires multiple washing steps. Multisteppipetting is not only time consuming and incompatible withlarge numbers of samples, but will also increase the likeli-hood of cross-contamination.In this paper, we describe a simple but eYcient method(called the NaOH method in short) for extracting genomicDNA from dried blood samples stored for up to 5 years,which involves only one step of incubation in 20mMNaOH solution followed by a single wash with TE

A Simple Bi-directional Mode Expansion Propagation Algorithm Based on Modes of a Parallel-plate Waveguide

The bi-directional mode expansion propagation algorithm (BEP) is known to be an accurate and efficient method for modelling field distribution in high-index contrast waveguide structures with strong back-reflections like Bragg gratings and photonic crystals. The main difficulty of this method is that for lossy structures, the propagation constants of modes are to be searched in the complex plane. To speed-up this procedure, a two-step algorithm for eigenmode calculation based on the expansion into the modes of an empty metallic waveguide has recently been proposed. Proper truncation rules possessing good convergence of the expansion method for both TE and TM modes have also been recently published. In this contribution, both these approaches are combined in the development of an extremely simple version of the two-dimensional BEP method that makes use of the field expansion into the eigenmodes of a parallel-plate waveguide. The method is strictly reciprocal and appeared to be computationally reliable also for strongly lossy structures. High numerical stability is ensured using the scattering matrix formalism, and an efficient method of calculating Bloch modes for symmetric as well as asymmetric periodic waveguide structures is adopted. A wide range of applicability of the method is demonstrated by a few examples.

Spectrophotometry of Sextans A and B: Chemical Abundances of HiiRegions and Planetary Nebulae

We present the results of high-quality long-slit spectroscopy of planetary nebulae (PNe) and H II regions in the two dwarf irregular (dIrr) galaxies Sextans A and B, which belong to a small group of galaxies just outside the Local Group. The observations were obtained with the New Technology Telescope ESO Multi-Mode Instrument. In Sextans A we obtained the element abundances in its only known PN and in three H II regions with the classical Te method. The oxygen abundances in these three H II regions of Sextans A are all consistent within the individual rms uncertainties, with an average 12 + log(O/H) = 7.54 ± 0.06. The oxygen abundance of the PN in Sextans A is, however, significantly higher: 12 + log(O/H) = 8.02 ± 0.05. This PN is even more enriched in nitrogen and helium, suggesting a classification as a PN of type I. The PN abundances of S and Ar, which are presumably unaffected by nucleosynthesis in the progenitor star, are well below those in the H II regions, indicating lower metallicity at the epoch of the PN progenitor formation (~1.5 Gyr ago, according to our estimates based on the PN parameters). In Sextans B we obtained spectra of one PN and six H II regions. Element abundances with the Te method could be derived for the PN and three of the H II regions. For two of these H II regions, which have a separation of only ~70 pc in projection, the oxygen abundances do not differ within the rms uncertainties, with a mean of 12 + log(O/H) = 7.53 ± 0.05. The third H II region, which is about 0.6 kpc northeast of the first two, is twice as metal-rich, with 12 + log(O/H) = 7.84 ± 0.05. This suggests considerable inhomogeneity in the present-day metallicity distribution in Sextans B. Whether this implies a general chemical inhomogeneity among populations of comparable age in Sextans B, and thus a metallicity spread at a given age, or whether we happen to see the short-lived effects of freshly ejected nucleosynthesis products prior to their dispersal and mixing with the ambient interstellar medium will require further study. For the PN we measured an O/H ratio of 12 + log(O/H) = 7.47 ± 0.16, consistent with that of the low-metallicity H II regions. We discuss the new metallicity data for the H II regions and PNe in the context of the published star formation histories and published abundances of the two dIrr galaxies. Both dIrrs show generally similar star formation histories in the sense of continuous star formation with amplitude variations but differ in their detailed enrichment timescales and star formation rates as a function of time. If we combine the photometrically derived estimates for the mean metallicity of the old red giant branch population in both dIrrs with the present-day metallicity of the H II regions, both dIrrs have experienced chemical enrichment by at least 0.8 dex (lower limit) throughout their history.

Spectroscopic study of blue compact galaxies

This is the fifth paper in a series studying the stellar components, star formation histories, star formation rates and metallicities of a blue compact galaxy (BCG) sample. Based on our high-quality ground-based spectroscopic observations, we have determined the electron temperatures, electron densities, nitrogen abundances and oxygen abundances for 72 star-forming BCGs in our sample, using different oxygen abundance indicators. The oxygen abundance covers the range , and nitrogen is found to be mostly a product of secondary nucleosynthesis for and apparently a product of primary nucleosynthesis for . To assess the possible systematic differences among different oxygen abundance indicators, we have compared oxygen abundances of BCGs obtained with the Te method, R23 method, P method, N2 method and O3N2 method. The oxygen abundances derived from the Te method are systematically lower by 0.1-0.25 dex than those derived from the strong line empirical abundance indicators, consistent with previous studies based on region samples. We confirm the existence of the metallicity-luminosity relation in BCGs over a large range of abundances and luminosities. Our sample of galaxies shows that the slope of the metallicity-luminosity relation for the luminous galaxies (~-0.05) is slightly shallower than that for the dwarf galaxies (~-0.17). An offset was found in the metallicity-luminosity relation of the local galaxies and that of the intermediate redshift galaxies. It shows that the metallicity-luminosity relation for the emission line galaxies at high redshift is displaced to lower abundances, higher luminosities, or both.