Models for Dispersion in Flow Injection Analysis Part 1. Basic Requirements and Study of Factors Affecting Dispersion

The various approaches adopted for accounting for dispersion behaviour in flow injection analysis are examined and the advantages of a modelling approach are discussed. The variation of the dispersion coefficient as a function of (a) flow-rate, (b) tube length, (c) tube inner diameter and (d) method of injection obtained under typical flow injection conditions are studied and discussed. Explanations for some of the effects observed are presented in terms of molecular diffusion and convective flow patterns. The advantages of time injection over the more usual slug injection are clearly demonstrated and the use of the single well stirred tank model to describe the relationship between volume injected and dispersion coefficient under conditions of time injection are examined. The applications of this model to describing the entire curve shape for slug injection and of the potentially more versatile two-tank model are briefly introduced

Models for Dispersion in Flow Injection Analysis. Part 2. The Two Tanks in Parallel Model

The application of two models based on the stirred mixing tanks, the well stirred tank and the two tanks in parallel models, is discussed, and results are presented for flow manifolds with both flame atomic absorption spectrometric and solution spectrophotometric detectors. Both models can be applied to the description of the dispersion generated by the nebuliser/spray chamber of a flame atomic absorption spectrometer. They can also be applied to flow injection manifolds under conditions giving rise to peaks having exponential-like rise and fall curves

A 3D MHD model of astrophysical flows: algorithms, tests and parallelisation

In this paper we describe a numerical method designed for modelling different kinds of astrophysical flows in three dimensions. Our method is a standard explicit finite difference method employing the local shearing-box technique. To model the features of astrophysical systems, which are usually compressible, magnetised and turbulent, it is desirable to have high spatial resolution and large domain size to model as many features as possible, on various scales, within a particular system. In addition, the time-scales involved are usually wide-ranging also requiring significant amounts of CPU time. These two limits (resolution and time-scales) enforce huge limits on computational capabilities. The model we have developed therefore uses parallel algorithms to increase the performance of standard serial methods. The aim of this paper is to report the numerical methods we use and the techniques invoked for parallelising the code. The justification of these methods is given by the extensive tests presented herein.Comment: 17 pages with 21 GIF figures. Accepted for publication in A&

ANALISIS SATURASI AIR PADA SAMPEL TANAH MENGGUNAKAN MICRO CT-SKYSCAN 1173

Teknologi pemindaian Micro CT-Scan dalam beberapa dekade terakhir telah terbukti berkembang secara pesat dalam memvisualisasikan dan mengkuantifikasi struktur tanah. Penelitian ini bertujuan untuk mengetahui pengaruh penambahan air pada sampel tanah terhadap struktur pori-pori sampel tanah tersebut. Sampel yang digunakan dalam penelitian ini berupa sampel tanah andosol yang berasal dari Parongpong dan sampel tanah mediteran yang berasal dari Batu kapur Subang. Kemudian sampel tanah tersebut dipindai dengan menggunakan Micro CT-Skyscan 1173 dan didapatkan citra digital. Setelah citra digital sampel tanah didapatkan kemudian direkonstruksi menggunakan perangkat lunak NRecon. Selanjutnya citra hasil rekonstruksi dengan software CTAn dianalisis parameter porositas serta total volume pori sampel tersebut. Kemudian sampel tanah tersebut dipindai kembali dengan saturasi air sebesar 10 %, 25 %, 50 %, 75%, 90 % dan 100% dari volume pori untuk melihat pengaruh penambahan persentase air terhadap pori-pori sampel tanah. Selanjutnya dianalisis struktur pori-pori masing-masing penambahan air dengan menggunakan perangkat lunak CTAn. Sehingga didapatkan kesimpulan bahwa semakin bertambahnya saturasi air pada sampel tanah maka semakin bertambah pula porositas tanah tersebut.-----Micro CT Scan scanning technology in the last few decades has proven to be growing rapidly in visualizing and quantifying the soil structure. This study aims to determine the effect of adding water on soil samples to the structure of the pores of the soil sample. The samples used in this study are andosol soil samples from Parongpong and mediteran soil samples from Batu Kapur Subang. Then the soil samples were scanned using Micro CT-Skyscan 1173 and obtained digital images. Once the digital image of the soil sample is obtained it is then reconstructed using NRecon software. Furthermore, the image of reconstruction with CTAn software was analyzed porosity parameter and total pore volume of the sample. Then the soil is scanned again with water addition of 10%, 25%, 50%, 75%, 90% and 100% of pore volume to see the effect of adding water percentage to soil sample pores. Next we analyzed the structure of the pores of each water addition by using CTAn software. So it can be concluded that the more water in the soil sample the more porosity of the soil

From transcriptome to biological function: environmental stress in an ectothermic vertebrate, the coral reef fish Pomacentrus moluccensis

BackgroundOur understanding of the importance of transcriptional regulation for biological function is continuously improving. We still know, however, comparatively little about how environmentally induced stress affects gene expression in vertebrates, and the consistency of transcriptional stress responses to different types of environmental stress. In this study, we used a multi-stressor approach to identify components of a common stress response as well as components unique to different types of environmental stress. We exposed individuals of the coral reef fish Pomacentrus moluccensis to hypoxic, hyposmotic, cold and heat shock and measured the responses of approximately 16,000 genes in liver. We also compared winter and summer responses to heat shock to examine the capacity for such responses to vary with acclimation to different ambient temperatures.ResultsWe identified a series of gene functions that were involved in all stress responses examined here, suggesting some common effects of stress on biological function. These common responses were achieved by the regulation of largely independent sets of genes; the responses of individual genes varied greatly across different stress types. In response to heat exposure over five days, a total of 324 gene loci were differentially expressed. Many heat-responsive genes had functions associated with protein turnover, metabolism, and the response to oxidative stress. We were also able to identify groups of co-regulated genes, the genes within which shared similar functions.ConclusionThis is the first environmental genomic study to measure gene regulation in response to different environmental stressors in a natural population of a warm-adapted ectothermic vertebrate. We have shown that different types of environmental stress induce expression changes in genes with similar gene functions, but that the responses of individual genes vary between stress types. The functions of heat-responsive genes suggest that prolonged heat exposure leads to oxidative stress and protein damage, a challenge of the immune system, and the re-allocation of energy sources. This study hence offers insight into the effects of environmental stress on biological function and sheds light on the expected sensitivity of coral reef fishes to elevated temperatures in the future

Symplectic integrators in the shearing sheet

The shearing sheet is a model dynamical system that is used to study the small-scale dynamics of astrophysical disks. Numerical simulations of particle trajectories in the shearing sheet usually employ the leapfrog integrator, but this integrator performs poorly because of velocity-dependent (Coriolis) forces. We describe two new integrators for this purpose; both are symplectic, time-reversible and second-order accurate, and can easily be generalized to higher orders. Moreover, both integrators are exact when there are no small-scale forces such as mutual gravitational forces between disk particles. In numerical experiments these integrators have errors that are often several orders of magnitude smaller than competing methods. The first of our new integrators (SEI) is well-suited for disks in which the typical inter-particle separation is large compared to the particles' Hill radii (e.g., planetary rings), and the second (SEKI) is designed for disks in which the particles are on bound orbits or the separation is smaller than the Hill radius (e.g., irregular satellites of the giant planets).Comment: 9 pages, 6 figures, accepted for publication in MNRAS, v2: discussion/tests for symmetrized and modified leapfrog integrators adde

Two-Dimensional Hydrodynamic Simulations of Convection in Radiation-Dominated Accretion Disks

The standard equilibrium for radiation-dominated accretion disks has long been known to be viscously, thermally, and convectively unstable, but the nonlinear development of these instabilities---hence the actual state of such disks---has not yet been identified. By performing local two-dimensional hydrodynamic simulations of disks, we demonstrate that convective motions can release heat sufficiently rapidly as to substantially alter the vertical structure of the disk. If the dissipation rate within a vertical column is proportional to its mass, the disk settles into a new configuration thinner by a factor of two than the standard radiation-supported equilibrium. If, on the other hand, the vertically-integrated dissipation rate is proportional to the vertically-integrated total pressure, the disk is subject to the well-known thermal instability. Convection, however, biases the development of this instability toward collapse. The end result of such a collapse is a gas pressure-dominated equilibrium at the original column density.Comment: 10 pages, 7 figures, accepted for publication in ApJ. Please send comments to [email protected]

Retrospective evaluation of weight loss in Maine Medical Center Cancer Institute (MMCCI) patients receiving radiation treatment for head and neck cancer

Treatment for head and neck cancer often results in weight loss as a side effect. One option to mitigate this weight loss is placement of a percutaneous endoscopic gastrostomy (PEG) tube placement. Radiation oncologists at a academic tertiary medical center discuss the option of PEG placement during patient consultation. A retrospective evaluation of weight loss in patients receiving radiation was conducted over a two-year period. The goal of this data collection was to create a standard for oncology consultations regarding PEG tube placement. Baseline metrics and a root cause analysis drove subsequent data collection steps. After analyzing the raw data, variables of interest and descriptors of PEG tube placement were identified. Patients and providers reported many benefits of having more information during consultations. Findings will be reviewed with all radiation oncologists with the plan to incorporate them into patient-physician discussions during consultations and treatment visits