Narrow Column Research Articles

Statistical Validation of the Mixing Length Concept in Bubble Columns Operated in the Transition Flow Regime

A new statistical parameter was de ned in order to determine the range of applicability of the mixing length concept in two bubble columns. Gas holdup time series (60,000 points) were measured in two bubble columns (0.15 and 0.4 m in i.d.) by a conductivity wire-mesh sensors. The new statistical parameter Φ was de ned as the ratio of the mean value of the signal to three times the average absolute deviation (3AAD) and it was correlated to the mixing length. It was found that this new correlation was not valid in all hydrodynamic regimes. It is applicable only in the transition ow regime. Such a clari cation has not been provided in the literature so far. In the narrow bubble column, the results were also conrmed on the basis of the Kolmogorov entropy and another statistical parameter. The new parameter Φ was also used for ow regime identi cation. In the narrow bubble column, the rst transition velocity Utrans was identi ed at 0.034 m/s; whereas, the second Utrans occurred at 0.112 m/s. In the large bubble column, the two Utrans values were identi ed at 0.045 and 0.101 m/s, respectively.

Open tubular lab-on-column/mass spectrometry for targeted proteomics of nanogram sample amounts.

A novel open tubular nanoproteomic platform featuring accelerated on-line protein digestion and high-resolution nano liquid chromatography mass spectrometry (LC-MS) has been developed. The platform features very narrow open tubular columns, and is hence particularly suited for limited sample amounts. For enzymatic digestion of proteins, samples are passed through a 20 µm inner diameter (ID) trypsin + endoproteinase Lys-C immobilized open tubular enzyme reactor (OTER). Resulting peptides are subsequently trapped on a monolithic pre-column and transferred on-line to a 10 µm ID porous layer open tubular (PLOT) liquid chromatography LC separation column. Wnt/ß-catenein signaling pathway (Wnt-pathway) proteins of potentially diagnostic value were digested+detected in targeted-MS/MS mode in small cell samples and tumor tissues within 120 minutes. For example, a potential biomarker Axin1 was identifiable in just 10 ng of sample (protein extract of ∼1,000 HCT15 colon cancer cells). In comprehensive mode, the current OTER-PLOT set-up could be used to identify approximately 1500 proteins in HCT15 cells using a relatively short digestion+detection cycle (240 minutes), outperforming previously reported on-line digestion/separation systems. The platform is fully automated utilizing common commercial instrumentation and parts, while the reactor and columns are simple to produce and have low carry-over. These initial results point to automated solutions for fast and very sensitive MS based proteomics, especially for samples of limited size.

Fabricating High-Performance Silicon Thin-Film Transistor by Meniscus Force Mediated Layer Transfer Technique

INTRODUCTION. If such a Silicon (Si) metal-oxide-semiconductor field-effect transistor (MOSFET) technology, namely, high-performance single crystalline silicon (c-Si) MOSFETs formed locally at the required position at low temperature (150°C or less) on flexible substrates, were established, so-called “flexible electronics” could be further advanced. Moreover, this technology could also be applied to system integration, namely, simultaneously mounting different devices such as integrated circuits and sensors[1]. We have proposed a novel layer transfer of the (100)-oriented c-Si thin film to a flexible substrate at very low process temperature[2]. In this study, by applying above-mentioned technology, the performance of flexible MOSFETs fabricated by using a c-Si film transferred by meniscus force was verified experimentally. EXPERIMENTAL. The SOI layer [p-type Si(100), 10-30 W∙cm] was patterned to form a 3-µm-wide and 5-µm-long dog-bone shape with 20×20 µm2 square regions at both ends. This pattern is applicable to MOSFET fabrication to form a source, a channel, and a drain. To form supporting columns, holes with size of 2 × 2 µm2 were made at intervals of 3 µm in the square regions. The 300 nm-thick buried-oxide (BOX) layer was isotropically etched by 33% hydrofluoric acid at room temperature for 90 seconds by using the patterned SOI layer as a mask for the midair cavity. As a result of the etching of the BOX layer below the patterned SOI layer, the narrow SiO2 columns can be formed underneath both end regions of the film. Figure 1 schematically shows the meniscus force(F=πR 2 γ[(1/R)-(2cosθE/H)]+2πR2γ sinθE ) mediated layer transfer (MLT) of SOI layer to a flexible substrate[2]. The starting and counter PET substrates were in close face-to-face contact with the filling water, and these substrates were heated on a hot plate at 80°C. RESULTS AND DISCUSSION. When the starting SOI wafer and the PET substrate were separated, it was confirmed that the original form and position of the SOI layer were completely maintained after the film transfer. The electron-backscatter-diffraction (EBSD) pattern map confirms that a (100)-oriented c-Si thin film was successfully formed on PET substrate at 80°C. Here, to confirm the adaptability of this layer transfer technique to thin-film devices, MOSFET were fabricated on a PET substrate. The source and drain regions were implanted with phosphorus ions at a dosage of 1×1015 cm-2. To control the threshold voltage, boron ions were injected (at a dosage of 1×1011 cm-2) into the channel region. After impurities in the source, channel, and drain regions were activated by heating at 1000 ºC in nitrogen ambient for 10 minutes, the BOX layer was isotropically etched by 33% hydrofluoric acid at room temperature for 90 seconds by using the patterned SOI layer as a mask for the midair cavity. As a result of the etching of the BOX layer below the patterned SOI layer, the narrow SiO2 columns can be formed underneath both end regions of the film. Here, the key process is the thermal oxidation of the SOI layer on the midair cavity. An 11-nm-thick gate insulator was formed on a SOI wafer temperature at 1000 ºC in dry oxygen ambient for four minutes[3]. By thermally oxidizing the SOI layer, the SOI layer can be covered on both surfaces with SiO2. After that, the forming gas annealing was performed at 400 ºC in a 3%-hydrogen/nitrogen mixture for 30 min. The thermal oxidation and subsequent hydrogen anneal ensure a good MOS interface, and the SiO2 layer works as a “blocking” layer that blocks contamination from PET. After the SOI layer was transferred to the PET substrate by MLT technique, a 200-nm-thick SiO2 film was deposited at 130 ºC by remote plasma chemical vapor deposition (RPCVD). After the contact holes are opened, the gate, source, and drain electrodes are formed by aluminum evaporation and wet etching. The MOSFET dimensions are length (L) of 3.7 µm and width (W) of 3 µm, and the maximum temperature of the fabrication process is 130ºC. Figure 2 shows Id-Vg characteristics of the MOSFETs fabricated on a transferred Si film. The MOSFET dimensions are L = 3.7 µm and W = 3 µm. The MOSFET showed a mobility of 343 cm2V-1s-1. A CKNOWLEDGEMENTS.A part of this work was supported by Research Institute for Nanodevice and Bio Systems, Hiroshima University and Funding Program for Next Generation World-Leading Researchers (NEXT Program) from the Japan Society for the Promotion of Science (JSPS). This work was supported by JSPS KAKENHI Grant Number 252156. REFERENCES. [1] T. Fukushima, et. al., IEDM Tech. Dig., 1 (2008). [2] K. Sakaike el al., Jpn. J. Appl. Phys. 53, 018004 (2014). [3] K. Sakaike el al., Appl. Phys. Lett., 103, 233510 (2014).

Development and validation of a quick, easy, cheap, effective, rugged and safe method for the determination of imidacloprid and its metabolites in soil.

A simplified quick, easy, cheap, effective, rugged and safe method was standardized and validated for the estimation of residues of imidacloprid and its metabolites from different types of soil comprising sandy loam, loamy sand and clay loam soil. The samples were extracted with acetonitrile, clean up by treatment with primary secondary amine sorbent and graphitized carbon. High-performance liquid chromatography (HPLC) is a technique to separate and quantitate residues of polar, nonvolatile and thermolabile chemical compounds, using high-pressure pumps, short and narrow columns packed with microparticulate phases and a detector. The residues were estimated using HPLC equipped with a photodiode array detector system, C18 column. Acetonitrile and water (30 : 70) were used as an isocratic mobile phase at 0.3 mL/min. Imidacloprid and its metabolites presented distinct peaks at retention factors of 4.93 min (6-chloronicotinic acid), 7.91 min (nitroguanidine), 9.12 min (olefin), 11.32 min (nitrosimine), 13.82 min (urea), 15.45 min (5-hydroxy) and 22.47 min (imidacloprid). Consistent recoveries above 80% for imidacloprid and its metabolites were observed when samples were spiked at 0.01, 0.05 and 0.10 mg/kg levels. The limit of quantification of the method was 0.01 mg/kg. The analytical method was validated in terms of parameters including selectivity, linearity, precision and accuracy of the detection system.

Development of a new green non-dispersive ionic liquid microextraction method in a narrow glass column for determination of cadmium prior to couple with graphite furnace atomic absorption spectrometry

Easy and innovative non-dispersive ionic liquid based microextraction (NDILME) has been developed for preconcentration of trace level of cadmium (Cd) in aqueous real surface water samples prior to couple with graphite furnace atomic absorption spectrometry (GFAAS). A 200cm long narrow glass column containing aqueous solution of standard/sample was used to increase phase transfer ratio by providing more contact area between two medium (aqueous and extractive), which drastically improve the recoveries of labile hydrophobic chelate of Cd ammonium pyrrolidinedithiocarbamate (APDC), into ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [C4mim][PF6]. Different aspect of the desire method have been investigated and optimized. Under the optimized key experimental variables, limit of detection (LOD) and enhancement factor (EF) were achieved to be 0.5ngL−1 and 150, respectively. Reliability of the model method was checked by relative standard deviation (%RSD), which was found to be <5%. Validity and accuracy of the developed method was checked by analysis of certified reference water samples (SLRS-4 Riverine water) using standard addition method.Application of the model method was productively performed by analysis of Cd in real surface water samples (tap and sea).

New Evidence for the Mixing Length Concept in a Narrow Bubble Column Operated in the Transition Regime

New Evidence for the Mixing Length Concept in a Narrow Bubble Column Operated in the Transition Regime

Study of a continuous spectrum of low pressure glow discharge in hydrogen and helium in a longitudinal magnetic field

The influence of a longitudinal magnetic field on electron temperature and density and on the continuous spectral radiance of a negative glow discharge in the visible spectrum range was studied. The electron temperature and density were determined by the double probe method. It was found that the discharge is compressed to a narrow column under the action of the magnetic field and its glow intensity increases by ∼100 times. This is accompanied by an increase in the electron temperature and density. The total voltage at the discharge decreases by two or three times. The study of the influence of a longitudinal magnetic field on the spectral radiance of the continuous spectrum is of greatest interest in this work. For the given conditions of the studied glow discharge (low pressure and small degree of ionization ∼10−6), bremsstrahlung radiation was shown to make the largest contribution to continuous spectral radiance upon electron scattering on a neutral particle. The measured quantity of the continuous spectral radiance of the discharge was compared with the calculated quantity of bremsstrahlung radiation for neutral particles. The measured quantity was found to be larger than the calculated one by 102–103 times, and the largest discrepancy was observed in the absence of the magnetic field. A hypothesis is proposed to explain such a strong discrepancy between the measured and calculated spectral radiance of the continuum spectrum.

Simulation of High Impact Rainfall Events Over Southeastern Hilly Region of Bangladesh Using MM5 Model

Simulation of high impact rainfall events over southeastern hilly region of Bangladesh has been carried out using Fifth-Generation PSU/NCAR Mesoscale Model (MM5) conducting two historical rainfall events, namely, 21 June, 2004 and 11 July, 2004. These extraordinary rainfall events were localized over the Rangamati region and recorded 304 mm and 337 mm rainfall on 21 June, 2004 and 11 July, 2004, respectively, over Rangamati within a span of 24 h. The model performance was evaluated by examining the different predicted and derived parameters. It is found that the seasonal monsoon trough has northerly position compared to normal and pass through Bangladesh extending up to northeast India for both cases. The heat low was found to be intense (996 hPa) with strong north-south pressure gradient (12–15 hPa). The analysis of the geopotential height field at 200 hPa shows that the Tibetan high is shifted towards south by 7-8° latitudes with axis along 22–25°N for both cases. The analysis of the wind field shows that the areas of high impact rainfall exhibit strong convergence of low level monsoon circulation (~19–58 knots). The strong southwesterlies were found to exist up to 500 hPa level in both cases. The lower troposphere (925–500 hPa) was characterized by the strong vertical wind shear (~9–18 ms−1) and high relative vorticity (~20–40 × 10−5 s−1). The analysis also shows that the areas of high impact rainfall events and neighbourhoods are characterized by strong low level convergence and upper level divergence. The strong southwesterly flow causes transportation of large amount of moisture from the Bay of Bengal towards Bangladesh, especially over the areas of Rangamati and neighbourhoods. The high percentage of relative humidity extends up to the upper troposphere along a narrow vertical column. Model produced details structure of the spatial patterns of rainfall over Bangladesh reasonably well though there are some biases in the rainfall pattern. The model suggests that the highly localized high impact rainfall was the result of an interaction of the mesoscale severe convective processes with the large scale active monsoon system.

NuSTARDISCOVERY OF A LUMINOSITY DEPENDENT CYCLOTRON LINE ENERGY IN VELA X-1

We present NuSTAR observations of Vela X-1, a persistent, yet highly variable, neutron star high-mass X-ray binary (HMXB). Two observations were taken at similar orbital phases but separated by nearly a year. They show very different 3-79 keV flux levels as well as strong variability during each observation, covering almost one order of magnitude in flux. These observations allow, for the first time ever, investigations on kilo-second time-scales of how the centroid energies of cyclotron resonant scattering features (CRSFs) depend on flux for a persistent HMXB. We find that the line energy of the harmonic CRSF is correlated with flux, as expected in the sub-critical accretion regime. We argue that Vela X-1 has a very narrow accretion column with a radius of around 0.4 km that sustains a Coulomb interaction dominated shock at the observed luminosities of Lx ~ 3x10^36 erg/s. Besides the prominent harmonic line at 55 keV the fundamental line around 25 keV is clearly detected. We find that the strengths of the two CRSFs are anti-correlated, which we explain by photon spawning. This anti-correlation is a possible explanation for the debate about the existence of the fundamental line. The ratio of the line energies is variable with time and deviates significantly from 2.0, also a possible consequence of photon spawning, which changes the shape of the line. During the second observation, Vela X-1 showed a short off-state in which the power-law softened and a cut-off was no longer measurable. It is likely that the source switched to a different accretion regime at these low mass accretion rates, explaining the drastic change in spectral shape.

Exact predictions from the Edwards ensemble versus realistic simulations of tapped narrow two-dimensional granular columns

We simulate, via a discrete element method, the tapping of a narrow column of disks under gravity. For frictionless disks, this system has a simple analytical expression for the density of states in the Edwards volume ensemble. We compare the predictions of the ensemble at constant compactivity against the results for the steady states obtained in the simulations. We show that the steady states cannot be properly described since the microstates sampled are not in correspondence with the predicted distributions, suggesting that the postulates of flat measure and ergodicity are, either or both, invalid for this simple realization of a static granular system. However, we show that certain qualitative features of the volume fluctuations which are difficult to predict from simple arguments are captured by the theory.

Enrichment of Y‐Chromosome‐Bearing Bull Spermatozoa by Swim‐up Through a Column

With the advancement of assisted reproductive biotechnologies, preselecting the sex of offspring has become an important goal for cattle and other livestock breeding as well as for research. The aim of this study was to investigate the feasibility of producing enriched pools of X- or Y-chromosome-bearing sperm by vertical swim-up through a long, narrow column. Sperm recovered from the top portion of the column was predominantly Y-bearing (60%, p<0.05), which were capable of fertilizing matured oocytes and produce significantly more male embryos compared with standard swim-up protocol.

Seismic response of exterior RC wide beam–narrow column joints: Earthquake-resistant versus as-built joints

This paper presents the results of a two-part experimental investigation undertaken for evaluating the seismic behavior of exterior wide beam–narrow column connections of the type constructed in Middle Eastern region. In the first part of the investigation, two full-scale gravity – load designed or “as-built” joints were tested under quasi-static cyclic loading. The joints failed prematurely by developing joint shear failure at considerably low drift ratios between 1.0% and 1.5% and therefore their resistance against lateral earthquake load was deemed insignificant. In the second part of the investigation, guided by the test results of the as-built joints, two additional “earthquake-resistant” joints were tested. The corresponding joints were designed assuming gravity load similar to the “as-built” joints, except that their reinforcing detailing were slightly improved particularly by adding transverse steel reinforcement within the joint core and increasing the development lengths of the beam reinforcement, partly in accordance with the recommendations of ACI 318-08 and ACI-ASCE 352-02. Despite violating the requirements of joint dimensions set forth in ACI 318-08, the “earthquake-resistant” joints performed considerably better than the “as-built” joints by preventing or delaying joint shear failure; developing higher lateral load, deformation, and energy absorption and dissipation capacities; and displaying stable overall hysteretic response.

DEATH BECOMES HER: ON THE PROGRESSIVE POTENTIAL OF VICTORIAN MOURNING

On the occasion of her Golden Jubilee, Queen Victoria was depicted in a woodcut by William Nicholson that was to become extremely popular (Figure 1). So stout that her proportions approach those of a cube, the Queen is dressed from top to toe in her usual black mourning attire, the white of her gloved hands punctuating the otherwise nearly solid black rectangle of her body. Less than thirty years later, another simple image of a woman in black would prove to be equally iconic: the lithe, narrow column of Chanel's black dress (Figure 2). Comparing the dresses depicted in the two images – the first a visual reminder of the desexualized stolidity of Victorian fidelity, the second image an example of women's burgeoning social and sexual liberation – might lead one to conclude that the only thing they have in common is the color black. And yet, twentieth- and twenty-first-century fashion historians suggest that Victorian mourning is the direct antecedent of the sexier fashions that followed. Jill Fields writes, for example, that “the move to vamp black became possible because the growing presence of black outerwear for women in the nineteenth century due to extensive mourning rituals merged with the growing sensibility that dressing in black was fashionable” (144). Valerie Mendes is more direct: “Traditional mourning attire blazed a trail for the march of fashionable black and the little black dress” (9). These are provocative claims given that most scholarly accounts of Victorian mourning attire – whether from the perspective of literary analysis, fashion history or theory, or social history or theory – offer no indication that such progressive possibilities were inherent in widows’ weeds. Instead, those accounts focus almost exclusively on chasteness and piety, qualities required of the sorrowful widow, as the only message communicated by her attire: “Widows’ mourning clothes announced the ongoing bonds of fidelity, dependence, and grieving that were expected to tie women to their dead husbands for at least a year” (Bradbury 289). The disparity in the two accounts raises the question: how could staid, cumbersome black Victorian mourning attire lead to dresses understood to embrace sexuality and mobility?

Hypertrophic Lichen Sclerosus With Dyskeratosis and Parakeratosis—A Common Presentation of Vulvar Lichen Sclerosus Not Associated With a Significant Risk of Malignancy

Epithelial hyperplasia, individual necrotic keratocytes, and parakeratosis are common findings in lichen sclerosus. When those changes are prominent, they may pose diagnostic problems, especially because such lesions often show no or only minimal sclerosis. Necrotic keratocytes are often numerous and are found in all reaches of the epidermis, presenting themselves as eosinophilic globules with or without remnants of pyknotic nuclei. Because those changes tend to be accentuated focally above dermal papillae, they often give rise to narrow columns of parakeratosis in the overlying cornified layer. Within those columns, individual necrotic keratocytes with pyknotic nuclei are preserved as distinct dyskeratotic parakeratotic cells. That constellation of findings is fairly characteristic of hypertrophic lichen sclerosus. It was found, at least subtle and focally, in 14 of 70 consecutive biopsy specimens of lichen sclerosus, most of which came from the vulva of elderly women. Although similar cases have been described as differentiated vulvar intraepithelial neoplasia (VIN) in the literature, there was no significant nuclear atypia, no crowding of nuclei, and no significant mitotic activity in any of those lesions. Follow-up of at least 5 years in 8 patients revealed no development of squamous cell carcinoma. Hypertrophic lichen sclerosus with dyskeratosis and parakeratosis seems to be a relatively common presentation of vulvar lichen sclerosus not associated with a significant risk of malignancy.

Simulation of a flood producing rainfall event of 29 July 2010 over north-west Pakistan using WRF-ARW model

Simulation of a flood producing rainfall event of 29 July 2010 over north-west Pakistan has been carried out using the Weather Research and Forecasting (WRF) model. This extraordinary rainfall event was localized over north-west Pakistan and recorded 274 mm of rainfall at Peshawar (34.02°N, 71.58°E), within a span of 24 h on that eventful day where monthly July normal rainfall is only 46.1 mm. The WRF model was run with the triple-nested domains of 27, 9, and 3 km horizontal resolution using Kain–Fritsch cumulus parameterization scheme having YSU planetary boundary layer. The model performance was evaluated by examining the different simulated parameters. The model-derived rainfall was compared with Pakistan Meteorological Department–observed rainfall. The model suggested that this flood producing heavy rainfall event over north-west region of Pakistan might be the result of an interaction of active monsoon flow with upper air westerly trough (mid-latitude). The north-west Pakistan was the meeting point of the southeasterly flow from the Bay of Bengal following monsoon trough and southwesterly flow from the Arabian Sea which helped to transport high magnitude of moisture. The vertical profile of the humidity showed that moisture content was reached up to upper troposphere during their mature stage (monsoon system usually did not extent up to that level) like a narrow vertical column where high amounts of rainfall were recorded. The other favourable conditions were strong vertical wind shear, low-level convergence and upper level divergence, and strong vorticity field which demarked the area of heavy rainfall. The WRF model might be able to simulate the flood producing rainfall event over north-west Pakistan and associated dynamical features reasonably well, though there were some spatial and temporal biases in the simulated rainfall pattern.

Toward Improved Closure Relations for the Turbulent Kinetic Energy Equation in Bubble‐Driven Flows

AbstractThere is a considerable interest within both academia and industry to develop improved computational fluid dynamic methods for gas‐liquid flows in bubble columns in order to support their scale‐up and optimal design. One main model limitation in current Eulerian two‐fluid and multi‐fluid models concerns adequate closure relations for turbulence in bubble‐driven flows. This article highlights some special features of bubble‐induced turbulence, discusses shortcomings of common concepts for closure of the liquid phase turbulence kinetic energy equation and presents an approach for development and validation of improved models. Some problematic issues related to the direct numerical simulation of bubble swarms in narrow bubble columns are also discussed.

Layer Transfer and Simultaneous Crystallization Technique for Amorphous Si Films with Midair Structure Induced by Near-Infrared Semiconductor Diode Laser Irradiation and Its Application to Thin-Film Transistor Fabrication

A novel layer transfer and simultaneous crystallization of amorphous silicon (a-Si) films induced by near-infrared semiconductor-diode-laser (SDL) irradiation has been investigated. The a-Si films supported by narrow quartz columns on a starting quartz substrate and a counter substrate [glass and poly(ethylene terephthalate)] were in face-to-face contact, and an SDL irradiated the a-Si films with midair structure. After SDL irradiation, the Si films were completely transferred and crystallized simultaneously on the counter substrates. In-situ monitoring revealed that the layer transfer took place either in the solid phase or the liquid phase followed by phase transformation in the cooling period. High performance polycrystalline Si thin-film transistors were successfully fabricated on the transferred Si films, which showed a high on/off ratio of more than 105 and a field-effect mobility as high as 268 cm2 V-1 s-1.

Near-field modification of femtosecond laser beam to enhance single-shot pulse filamentation in glass medium

In this paper, a study of the effect of a transparent dielectric medium (soda-lime glass placed after an objective lens) on femtosecond pulse filamentation in Corning Eagle2000 glass is presented. The dielectric medium placed after the objective lens increases the effective numerical aperture of the focusing lens and tightly focuses the beam to elevate the power density in a tiny focal volume. A single-shot narrow filamentary void of diameter 3.8 μm is observed to propagate as long as 700 μm in Corning Eagle2000 glass. Elevated optical intensity confined in the small focal volume and low ionization losses per unit length in the narrow plasma column collectively enhance the filamentary propagation of the ultra-short pulse in bulk glass. The applied technique also offers an approach to control the length and width of a filamentary void structure in a transparent dielectric medium.

Semi-automated solid phase extraction method for the mass spectrometric quantification of 12 specific metabolites of organophosphorus pesticides, synthetic pyrethroids, and select herbicides in human urine

Organophosphate and pyrethroid insecticides and phenoxyacetic acid herbicides represent important classes of pesticides applied in commercial and residential settings. Interest in assessing the extent of human exposure to these pesticides exists because of their widespread use and their potential adverse health effects. An analytical method for measuring 12 biomarkers of several of these pesticides in urine has been developed. The target analytes were extracted from one milliliter of urine by a semi-automated solid phase extraction technique, separated from each other and from other urinary biomolecules by reversed-phase high performance liquid chromatography, and detected using tandem mass spectrometry with isotope dilution quantitation. This method can be used to measure all the target analytes in one injection with similar repeatability and detection limits of previous methods which required more than one injection. Each step of the procedure was optimized to produce a robust, reproducible, accurate, precise and efficient method. The required selectivity and sensitivity for trace-level analysis (e.g., limits of detection below 0.5ng/mL) was achieved using a narrow diameter analytical column, higher than unit mass resolution for certain analytes, and stable isotope labeled internal standards. The method was applied to the analysis of 55 samples collected from adult anonymous donors with no known exposure to the target pesticides. This efficient and cost-effective method is adequate to handle the large number of samples required for national biomonitoring surveys.

Structures in compressible magnetoconvection and the nature of umbral dots

Structures seen in idealized numerical experiments on compressible magnetoconvection in an imposed strong vertical magnetic field show important differences from those detected in observations or realistic numerical simulations of sunspot umbrae. To elucidate the origin of these discrepancies, we present a series of idealized 3D compressible magnetoconvection experiments that differ from previous such experiments in several details, bringing them closer to realistic solar conditions. An initially vertical magnetic field B 0 is imposed on a time snapshot of fully developed solar-like turbulent convection in a layer bounded by a stable layer from above. Upon relaxation to a statistically steady state, the structure of the flow field and magnetic field is examined. Instead of the vigorous granular convection (GRC) well known to take place in magnetized or weakly magnetized convection, for high values of B0 heat is transported by small-scale convection (SSC) in the form of narrow, persistent convective columns consisting of slender upflows accompanied by adjacent downflow patches, which are reminiscent of the 'convectons' identified in earlier semianalytic models. For moderate field strengths, flux separation (FXS) is observed: isolated field-free inclusions of GRC are embedded in a strongly magnetized plasma with SSC. Between the SSC and FXS regimes, a transitional regime (F/S) is identified where convectons dynamically evolve into multiply segmented granular inclusions and back. Our results agree in some aspects more closely with observed umbral structures than earlier idealized models, because they do reproduce the strong localized, patchy downflows immediately adjacent to the narrow convective columns. Based on recent observations of umbral dots, we suggest that in some cases the conditions in sunspot umbrae correspond to the newly identified F/S transitional regime.