Apparent Dispersion Research Articles

Closed‐flow column experiments: A numerical sensitivity analysis of reactive transport and parameter uncertainty

AbstractThe identification of transport parameters by inverse modeling often suffers from equifinality or parameter correlation when models are fitted to measurements of the solute breakthrough in column outflow experiments. This parameter uncertainty can be approached by performing multiple experiments with different sets of boundary conditions, each provoking observations that are uniquely attributable to the respective transport processes. A promising approach to further increase the information potential of the experimental outcome is the closed‐flow column design. It is characterized by the recirculation of the column effluent into the solution supply vessel that feeds the inflow, which results in a damped sinusoidal oscillation in the breakthrough curve. In order to reveal the potential application of closed‐flow experiments, we present a comprehensive sensitivity analysis using common models for adsorption and degradation. We show that the sensitivity of inverse parameter determination with respect to the apparent dispersion can be controlled by the experimenter. For optimal settings, a decrease in parameter uncertainty as compared to classical experiments by an order of magnitude is achieved. In addition, we show a reduced equifinality between rate‐limited interactions and apparent dispersion. Furthermore, we illustrate the expected breakthrough curve for equilibrium and nonequilibrium adsorption, the latter showing strong similarities to the behavior found for completely mixed batch reactor experiments. Finally, breakthrough data from a reactive tracer experiment is evaluated using the proposed framework with excellent agreement of model and experimental results.

An investigation of dispersion characteristics in shallow coastal waters

Hydrodynamic dispersion has a significant impact on the mass transport of sediments and contaminants within coastal waters. In this study apparent horizontal dispersion in a tidally-dominated shallow estuary was investigated using field observations and a numerical model. A cluster of four Lagrangian drifters was released in two shallow regions inside Moreton Bay, Australia: between two small islands and in an open water area. During a 16-h tracking period, the drifters generally showed similar behaviour, initially moving with the dominant current and remaining together before spreading apart at the change of tide. Two dispersion regimes were identified, a slow dispersion during the earlier stage and a rapid dispersion during the latter stage of deployment. Such change in regime typically occurred during the succeeding ebb or flow tides, which may be attributable to residual eddies breaking down during reversal of tidal direction. In addition, a power function of the squared separation distance over the apparent dispersion coefficient produced an R2 exceeding 0.7, indicating a significant relationship between them.By applying a three-dimensional hydrodynamic model, the trajectories of artificial particles spreading in the bay were simulated, which allowed the calculation of dispersion coefficients throughout the entire bay. The study results demonstrate that the tidal effects on dispersion were dependent on the effect of tidal excursion and residual current. The tide was found to be the most dominant driver of dispersion in the bay when unobstructed by land; however, bathymetric and shoreline characteristics were also significant localised drivers of dispersion between the two islands as a result of island wake.

Apparent Attenuation and Dispersion Arising in Seismic Body-Wave Velocity Retrieval

The fact that seismologists often make measurements, using natural seismic solicitations, of properties of the Earth on rather large scales (laterally and in terms of depth) has led to interrogations as to whether attenuation of body waves is dispersive and even significant. The present study, whose aim is to clarify these complicated issues, via a controlled thought measurement, concerns the retrieval of a single, real body wave velocity of a simple geophysical configuration (involving two homogeneous, isotropic, non-dissipative media, one occupying the layer, the other the substratum), from its simulated response to pulsed plane wave probe radiation. This inverse problem is solved, at all frequencies within the bandwidth of the pulse. Due to discordance between the models associated with the assumed and trial responses, the imaginary part of the retrieved velocity turns out to be non-nil even when both the layer and substratum are non-lossy, and, in fact, to be all the greater, the larger is the discordance. The reason for this cannot be due to intrinsic attenuation, scattering, or geometrical spreading since these phenomena are absent in the chosen thought experiment, but rather to uncertainty in the measurement model.

The global spread of Zika virus: is public and media concern justified in regions currently unaffected?

BackgroundZika virus, an Aedes mosquito-borne flavivirus, is fast becoming a worldwide public health concern following its suspected association with over 4000 recent cases of microcephaly among newborn infants in Brazil.DiscussionPrior to its emergence in Latin America in 2015–2016, Zika was known to exist at a relatively low prevalence in parts of Africa, Asia and the Pacific islands. An extension of its apparent global dispersion may be enabled by climate conditions suitable to support the population growth of A. aegypti and A. albopictus mosquitoes over an expanding geographical range. In addition, increased globalisation continues to pose a risk for the spread of infection. Further, suspicions of alternative modes of virus transmission (sexual and vertical), if proven, provide a platform for outbreaks in mosquito non-endemic regions as well. Since a vaccine or anti-viral therapy is not yet available, current means of disease prevention involve protection from mosquito bites, excluding pregnant females from travelling to Zika-endemic territories, and practicing safe sex in those countries. Importantly, in countries where Zika is reported as endemic, caution is advised in planning to conceive a baby until such time as the apparent association between infection with the virus and microcephaly is either confirmed or refuted. The question arises as to what advice is appropriate to give in more economically developed countries distant to the current epidemic and in which Zika has not yet been reported.SummaryDespite understandable concern among the general public that has been fuelled by the media, in regions where Zika is not present, such as North America, Europe and Australia, at this time any outbreak (initiated by an infected traveler returning from an endemic area) would very probably be contained locally. Since Aedes spp. has very limited spatial dispersal, overlapping high population densities of mosquitoes and humans would be needed to sustain a focus of infection. However, as A. aegypti is distinctly anthropophilic, future control strategies for Zika should be considered in tandem with the continuing threat to human wellbeing that is presented by dengue, yellow fever and Japanese encephalitis, all of which are transmitted by the same vector species.Electronic supplementary materialThe online version of this article (doi:10.1186/s40249-016-0132-y) contains supplementary material, which is available to authorized users.

Preparation of commercially applicable slurry fuels from rapid hydrogasification char by blending with coal

The purpose of this work is first to investigate the slurryability of two chars produced from the rapid hydrogasification of two bituminous coals (YY coal and FG coal) in a pilot-scale entrained flow gasifier (abbreviated as RH char). Results showed that both RH chars had very poor slurryability mainly owing to the microporous and capillary structures of particles and the high water holding capacity, in sharp contrast to the properties of the parent coals and the char obtained from a common slow pyrolysis. The work thereafter aims at making a commercially usable water slurry by using the blends of RH char and YY coal. The slurry containing an adjusted solid blend of 60% total solid weight loading with 0.5% naphthalene sulfonate formaldehyde dispersant showed all satisfactory performances in the apparent viscosity, fluidity and static dispersion stability. Furthermore, it was found that the slurryability could be improved by an interactive effect between RH char and raw coal, which depended on the blending pairs and blending proportions.

Radial and tangential migration of telencephalic somatostatin neurons originated from the mouse diagonal area.

The telencephalic subpallium is the source of various GABAergic interneuron cohorts that invade the pallium via tangential migration. Based on genoarchitectonic studies, the subpallium has been subdivided into four major domains: striatum, pallidum, diagonal area and preoptic area (Puelles et al. 2013; Allen Developing Mouse Brain Atlas), and a larger set of molecularly distinct progenitor areas (Flames et al. 2007). Fate mapping, genetic lineage-tracing studies, and other approaches have suggested that each subpallial subdivision produces specific sorts of inhibitory interneurons, distinguished by differential peptidic content, which are distributed tangentially to pallial and subpallial target territories (e.g., olfactory bulb, isocortex, hippocampus, pallial and subpallial amygdala, striatum, pallidum, septum). In this report, we map descriptively the early differentiation and apparent migratory dispersion of mouse subpallial somatostatin-expressing (Sst) cells from E10.5 onward, comparing their topography with the expression patterns of the genes Dlx5, Gbx2, Lhx7-8, Nkx2.1, Nkx5.1 (Hmx3), and Shh, which variously label parts of the subpallium. Whereas some experimental results suggest that Sst cells are pallidal, our data reveal that many, if not most, telencephalic Sst cells derive from de diagonal area (Dg). Sst-positive cells initially only present at the embryonic Dg selectively populate radially the medial part of the bed nucleus striae terminalis (from paraseptal to amygdaloid regions) and part of the central amygdala; they also invade tangentially the striatum, while eschewing the globus pallidum and the preoptic area, and integrate within most cortical and nuclear pallial areas between E10.5 and E16.5.Electronic supplementary materialThe online version of this article (doi:10.1007/s00429-015-1086-8) contains supplementary material, which is available to authorized users.

Revisión de la producción científica sobre WebQuest en los últimos 20 años: análisis bibliométrico en Scopus y Web of Science

Tras la primera formulación en 1995 sobre qué es una Web Quest ¿cuál es el estado de su desarrollo en el campo de la educación? Esta pregunta exige muchas miradas y respuestas. Este trabajo busca ser parte de esta evaluación poniendo en evidencia el desarrollo de la producción científica sobre WebQuest en las dos principales bases de datos científicas: WOS (Web of Science) y Scopus desde su formulación hasta la actualidad (1995-2014). El método es el análisis bibliométrico en base a las siguientes variables: número de artículos publicados, número de citas recibidas, principales revistas citantes, promedio de citas por año, nombre y país de los autores más citados y palabras clave. Se ha procedido a la identificación del perfil y las características de las publicaciones científicas que lo tratan, sobre la conclusión de una evidente dispersión y atomización de resultados, destacando la existencia de una significativa comunidad científica sobre Webquest en España.

Anisotropic Dispersion and Upscaling for Miscible Displacement

Summary Dispersion is the irreversible mixing that occurs during miscible displacements. Dispersion can reduce local displacement efficiency by lessening solvent peak concentration or increase volumetric sweep efficiency by spreading of the injected solvent to more of the reservoir. Dispersion is therefore an important parameter in predicting and simulating miscible displacements. The difficulty of simulating miscible displacement and understanding the effect of dispersion is also compounded by numerical dispersion, which increases the apparent dispersion in finite-difference simulation models. This paper presents an approach to estimate the total longitudinal and transverse dispersion in large-scale media by use of continuous solvent injection in a medium of finite thickness. The simulations are based on the experimental arrangement of Blackwell (1962) to estimate transverse dispersion, with experiments consisting of coinjecting two miscible fluids into different sections of the medium at similar rates. This model arrangement, coupled with analytical solutions for the 2D convection/dispersion equation for a continuously injected solvent, allows us to determine longitudinal and transverse dispersivity simultaneously for the flow medium. In this manner, we investigate the effects of stochastic permeability distributions and other scaling groups affecting first-contact-miscible simulations on dispersion. Sensitivity analysis of dispersion in stochastic permeability fields confirms that both longitudinal and transverse dispersion are scale dependent. Results also show that the effect of increasing autocorrelation of cell permeability in the longitudinal direction (parallel to flow) is to increase longitudinal dispersion, as solvent travels through more continuous layers, while reducing transverse dispersion. Increasing autocorrelation in the transverse direction reduces dispersion in both directions. This reduction is caused by equilibration of solvent concentrations in continuous sections of the reservoir, resulting in reduced solute fingering and channeling. Finally, we developed a simple procedure to use the estimated dispersivities to determine a priori the maximum gridblock size that will maintain an equivalent level of dispersion between fine-scale models and upscaled coarse models. Large gridblock sizes can be used for highly heterogeneous and layered reservoir models. Nonuniform coarsening (upscaling) methods were also recommended and validated for reservoir models with sets of sequential but different permeability distributions. The procedure was extended to multicontact miscible simulations. The sweep and recovery from upscaled multicontact miscible simulations were comparable with those of fine-scale models.

Changes in P-wave velocity with different full waveform sonic transmitter centre frequency

Full waveform sonic logging, with the transmitter set at different centre frequencies, often provides different compressional wave velocities over the same interval. There may be several reasons why these velocity differences are recovered where the source has different frequency content. Examples include: intrinsic dispersion, scattering dispersion, geometric dispersion, processing artefacts and acquisition artefacts. We acquired and analysed multifrequency monopole full waveform sonic logging data from the cored drill hole intersecting a high-permeability sandy aquifer in the Northern Gnangara Mound, Perth Basin, Western Australia. A key interval of the shallow, sand-dominated Yarragadee Formation was selected and logged four times with transmitter centre frequencies set to 1, 3, 5 and 15 kHz. We compute apparent velocity dispersion as the percentage velocity differences in the P-wave velocity recovered from full waveform sonic logs completed at different dominant transmitter centre frequencies. We find that high-permeability sediments could be placed into broad groups: cross-bedded and non-cross-bedded sandstones.We find a distinctly different relationship between apparent P-wave velocity dispersion and permeability for cross-bedded and non-cross-bedded sandstones. Cross plots for the two sediment types show a general trend of increasing apparent dispersion with increasing permeability. Grouping the sandstone layers based on sediment type, as observed from core samples, illustrates different but positive correlation between the apparent P-wave velocity dispersion and permeability in these shallow, weakly-consolidated sandstones. The cross-bedded sandstone, for its part, has a wider range of permeability than the non-cross-bedded sandstone but a smaller range of apparent P-wave velocity dispersion. Given these results, our hypothesis is that while permeability plays a role, other factors such as geometric dispersion or scattering dispersion likely contribute the net value of P-wave dispersion recovered between any two receivers. Finally the results from these experiments have shown that there exists at least a weak empirical relationship between P-wave velocity dispersion and hydraulic permeability at the field site.

DNA-based species delimitation separates highly divergent populations within morphologically coherent clades of poorly dispersing beetles

We compared species-level entities recovered using distance, tree-based, and DNA-character based methods with morphologically defined species in poorly dispersing lyponiine net-winged beetles. The phylogenetic relationships were investigated using the cytochrome c oxidase 1–2 mtDNA fragment. We identified 31 species using a morphology-based concept and additional candidate species were delimited by the general mixed Yule-coalescent method and barcoding threshold within the morphologically coherent lineages owing to high genetic divergence (up to 10.97% within morphologically defined species, highest density 2.5–6.5%). Genetic divergence was positively correlated with geographical distance: lower in continental China where no apparent dispersal barriers are present (r2 = 0.172, P ≤ 0.001, average increase of genetic distance of 0.32% per 100 km) and much higher in Japan (r2 = 0.490, P ≤ 0.001, 1.81% per 100 km). We hypothesize that low dispersal propensity contributed to the high level of intraspecific, geographically structured divergence. DNA-based methods suggested a high number of morphologically undistinguishable species. The observed patterns agree with the model of neutral evolution. The poor dispersers produce gradually divergent populations across the range of the morphologically coherent lineages. We pose the question of what size of range and level of genetic difference justify formal acceptance of a species without morphological divergence from both the taxonomical and conservation management view points. © 2015 The Linnean Society of London

Analytical procedure of neon measurements on GV 5400 noble gas mass spectrometer and its evaluation by quartz standard CREU-1

Terrestrial in situ-produced stable cosmogenic isotope 21Ne can provide us lots of important geomorphologic information, while the prerequisite for the application of cosmogenic 21Ne in the surface process studies is the accurate measurements of three neon isotopes in the rock samples. To employ cosmogenic 21Ne in solving geological problems, we established a new analytical procedure of neon measurements on the GV 5400 noble gas mass spectrometer. Isobaric interferences on three neon isotopes have been quantified, and among them the correction for the major interference from 40Ar2+ on 20Ne+ was studied in more detail. Instead of the first-order correlation of 40Ar+/40Ar2+ ratio with the H2 partial pressure in the ion source section of the mass spectrometer reported by Professor Niedermann and co-workers in 1993, an excellent power function correlation of the 40Ar2+ counting to that of 40Ar+ has been established in our analytical system for determining the unresolved 40Ar2+ contribution by monitoring the 40Ar+ signal during sample analysis. The calibration experiment using air standard was performed, and then several aliquots of quartz standard CREU-1 were measured to assess the performance of our neon measurements. The average measured cosmogenic 21Ne concentration of CREU-1 (347±7.7×106atomg−1) is consistent with the published value (348±10×106atomg−1), which demonstrates the good analytical accuracy (0.3%) and high measurement precision (2.2%) of our neon measurements. And the MSWD value of 0.49 indicates the good agreement of the apparent dispersion of three aliquots data with their individual measurement errors. The establishment of this analytical procedure for neon measurement provides us a promising way for developing the cosmogenic 21Ne method in many fields of Earth sciences and beyond.

Velocity increase in the uppermost oceanic crust of subducting Philippine Sea plate beneath the Kanto region due to dehydration inferred from high-frequency trapped P waves

To investigate the detailed structural properties of the oceanic crust of subducting oceanic plate, we analyzed high-frequency (1 to 16 Hz) trapped P waves during earthquakes that occurred near the oceanic crust of the Philippine Sea plate. The distinct trapped P waves observed by the dense seismic network of the Kanto-Tokai region, Japan, did not show any apparent peak delay and frequency-dependent dispersion. These observations suggested that the oceanic crust around the source depths was characterized by a homogeneous velocity structure, rather than an inhomogeneous multiple-layered structure. This interpretation was examined by finite difference method simulations of seismic wave propagation using possible velocity structure models. The simulations demonstrated that a uniform velocity oceanic crust of the subducting Philippine Sea plate, which may result from the velocity increase in this layer at 30 to 40 km depth due to metamorphic-dehydration reactions, effectively trapped seismic energy as a short-distance waveguide and developed distinct pulse-like trapped P waves.

Arctic ground squirrel population collapse in the boreal forests of the Southern Yukon

Context The arctic ground squirrel (Urocitellus parryii) comprised 17% of the biomass of herbivores in the Yukon boreal forest during the summer months from 1987 to 1996 and was responsible for 23% of the energy flow at the herbivore level. By 2000, ground squirrel populations in this region collapsed to nearly zero and have remained there. Aims We summarise the population monitoring (since 1975) and recent experimental work that has been done on this key herbivore in the Kluane area of the southern Yukon to test one mechanistic hypothesis as the possible explanation for this population collapse and subsequent lack of recovery: predation. Methods Ground squirrels are the preferred summer prey of bird and mammal predators when snowshoe hare (Lepus americanus) populations are declining. We used translocations into formerly occupied habitat and radiotelemetry to determine movements and causes of death from 2009 to 2014. We surveyed 158 sites between 2008 and 2013 to measure the disappearance of colonies in alpine and forest habitats over 25 000 km2. Key results Ground squirrels from 2000 to 2013 comprised a small fraction of the herbivore biomass in the boreal forest zone, down from 17% earlier. Most forest populations (~95%) are currently extinct, whereas just over half (65%) of low-elevation meadow populations are locally extinct. One hypothesis is that ground squirrels in the forest have been driven into a predator pit from which they cannot recover. They remain abundant in alpine tundra (93% occupancy rate) and around airport runways and human habitations (97% occupancy), but there is no apparent dispersal from alpine areas down into the boreal forest. Conclusion The predator pit hypothesis is a likely explanation for the initial collapse and sustained decline in population size from 2000 to 2013. Recent attenuation of the hare cycle and milder winter climate have allowed shrubs to expand throughout the forest, thereby reducing visibility and increasing predation risk. This conclusion will be tested in further research using reintroductions to formerly occupied sites. Implication If the loss of this herbivore from the boreal forest is not reversed, predator pressure on the other major herbivores of the montane forest zone is likely to change significantly.

Effects of Soil Compaction and Organic Carbon Content on Preferential Flow in Loamy Field Soils

Preferential flow and transport through macropores affect plant water use efficiency and enhance leaching of agrochemicals and the transport of colloids, thereby increasing the risk for contamination of groundwater resources. The effects of soil compaction, expressed in terms of bulk density (BD), and organic carbon (OC) content on preferential flow and transport were investigated using 150 undisturbed soil cores sampled from 15 × 15–m grids on two field sites. Both fields had loamy textures, but one site had significantly higher OC content. Leaching experiments were conducted in each core by applying a constant irrigation rate of 10 mm h with a pulse application of tritium tracer. Five percent tritium mass arrival times and apparent dispersivities were derived from each of the tracer breakthrough curves and correlated with texture, OC content, and BD to assess the spatial distribution of preferential flow and transport across the investigated fields.Soils from both fields showed strong positive correlations between BD and preferential flow. Interestingly, the relationships between BD and tracer transport characteristics were markedly different for the two fields, although the relationship between BD and macroporosity was nearly identical. The difference was likely caused by the higher contents of fines and OC at one of the fields leading to stronger aggregation, smaller matrix permeability, and a more pronounced pipe-like pore system with well-aligned macropores.

Laboratory Estimation of Dispersivity Coefficients

The dispersion phenomena in aquifers through experimental activities have been extensively studied in the past; recently the availability of digital images of the transport process made possible the development of new techniques for the evaluation of the dispersivity coefficients (Sànchez et al., 2008, 2011). This work shows the application of an innovative procedure that allows a detailed estimation of longitudinal and transverse dispersivities in an experimental plume devised in a laboratory sandbox. The dataset was provided processing the results of a sandbox developed at the hydraulic laboratory of the University of Parma (DICATeA). The equipment represents a 2-D unconfined aquifer controlled through two constant head levels (upstream and downstream); it consists of a PMMA tank filled of 1mm glass beads as porous medium. An injector was placed inside the porous medium and sodium fluorescein salt was used as tracer. The tests consist of injecting a known solution discharge for a specific time duration and then observing the plume through the collection of side wall images obtained by means of a digital camera (see Citarella et al. (2010) and Cupola et al. (2014) for more details). The study case presented in this work considers a homogeneous porous media and a uniform flow in the vertical plane; the plume develops according to 2-D plane advection-dispersion equation. The pictures were collected with time interval equal to 5 s. Using the collected frames, it is possible to estimate the concentration in each point of the domain at different times and also the partial derivatives of the concentration in space and time. This information allows easily to estimate the two dispersivity coefficients using the Advection-Dispersion equation. This analysis was carried out for each picture collected during the test (about 650). The results showed, as expected, that the longitudinal dispersivity presents the same order of magnitude of the pore dimension and the ratio between longitudinal and transverse dispersivity is constant through the whole domain, although higher than that reported in literature. Even though the dispersivities are estimated for each pixel of the figures, only a few of them provide reliable information; in fact, only on the plume boundaries a significant variation in concentration could be detected. For this reason a selection criterion for the credibility of the results was developed. Future developments will estimate the apparent dispersivities considering a heterogeneous media.

Relations between macropore network characteristics and the degree of preferential solute transport

Abstract. The characteristics of the soil macropore network determine the potential for fast transport of agrochemicals and contaminants through the soil. The objective of this study was to examine the relationships between macropore network characteristics, hydraulic properties and state variables and measures of preferential transport. Experiments were carried out under near-saturated conditions on undisturbed columns sampled from four agricultural topsoils of contrasting texture and structure. Macropore network characteristics were computed from 3-D X-ray tomography images of the soil pore system. Non-reactive solute transport experiments were carried out at five steady-state water flow rates from 2 to 12 mm h−1. The degree of preferential transport was evaluated by the normalised 5% solute arrival time and the apparent dispersivity calculated from the resulting breakthrough curves. Near-saturated hydraulic conductivities were measured on the same samples using a tension disc infiltrometer placed on top of the columns. Results showed that many of the macropore network characteristics were inter-correlated. For example, large macroporosities were associated with larger specific macropore surface areas and better local connectivity of the macropore network. Generally, an increased flow rate resulted in earlier solute breakthrough and a shifting of the arrival of peak concentration towards smaller drained volumes. Columns with smaller macroporosities, poorer local connectivity of the macropore network and smaller near-saturated hydraulic conductivities exhibited a greater degree of preferential transport. This can be explained by the fact that, with only two exceptions, global (i.e. sample scale) continuity of the macropore network was still preserved at low macroporosities. Thus, for any given flow rate, pores of larger diameter were actively conducting solute in soils of smaller near-saturated hydraulic conductivity. This was associated with larger local transport velocities and, hence, less time for equilibration between the macropores and the surrounding matrix which made the transport more preferential. Conversely, the large specific macropore surface area and well-connected macropore networks associated with columns with large macroporosities limit the degree of preferential transport because they increase the diffusive flux between macropores and the soil matrix and they increase the near-saturated hydraulic conductivity. The normalised 5% arrival times were most strongly correlated with the estimated hydraulic state variables (e.g. with the degree of saturation in the macropores R2 = 0.589), since these combine into one measure the effects of irrigation rate and the near-saturated hydraulic conductivity function, which in turn implicitly depends on the volume, size distribution, global continuity, local connectivity and tortuosity of the macropore network.

The diagnostic value of diffusion-weighted magnetic resonance imaging and apparent diffusion coefficient values in children with cerebral infarction

Objective To explore the diffusion-weighted magnetic resonance imaging (DWI) and apparent dispersion coefficient (ADC) value in cerebral infarction diagnosis and judgment of cerebral infarction outcome and staging of the value. Methods According to different stages, 26 patients were divided into 3 phases, phaseⅠ (6~72 h) had 11 cases, phaseⅡ (4~10 d) had 12 cases, phase Ⅲ (10 d later) had 9 cases, of which 3 cases were reviewed, 3 cases were recurrence of cerebral infarction. Each patient′s MRI included T1 weighted imaging, T2 weighted imaging, DWI and ADC sequence scan image reconstruction, the ADC map obtained one regions of interest (ROI), and the mean ADC value of ROI were calculated, the average ADC value of the corresponding contralateral area were also calculated by the same method, and then the mean relative ADC value were calculated. Results DWI image of all cases showed high signal, 11 cases showed high signal and 1 case showed low signal in phase Ⅱ. In phase Ⅲ, 1 case showed normal signal and 1 case showed high signal, 2 cases showed mixed signal, 1 case were reduced, and the rest were all low signal. Compared with the contralateral corresponding region, the average ADC values were reduced in phase Ⅰ. The infarction average ADC values were 0.434 × 10-3mm2/s, 0.653 × 10-3mm2/s, 1.600 × 10-3mm2/s in phase Ⅰ, Ⅱ, Ⅲ respectively, and the average ADC values of contralateral corresponding region were 0.938 × 10-3mm2/s, 0.814 × 10-3mm2/s, 0.757× 10-3mm2/s respectively; the mean relative ADC values were (51.5±16.8)%, (79.2±30.0)%, (210.9±45.1)% in phase Ⅰ, Ⅱ, Ⅲ respectively (P<0.05). Conclusion ADC value of cerebral lesions area and relative ADC value of the variation in time provides an objective basis for the diagnosis of DWI, contributes to timely and accurately determine the age of cerebral lesions and pathophysiology of the changes. Key words: Cerebral infarction; Magnetic resonance imaging; Diffusion-weighted imaging; Apparent diffusion coefficient map; Apparent diffusion coefficient value; Relative apparent diffusion coefficient value; Children

Equivalence between the equilibrium dispersive and the transport model in describing band broadening in analytical gradient liquid chromatography

It is shown that the transport (TR) model may be equivalent to the equilibrium dispersive (ED) model in analytical gradient liquid chromatography when the column efficiency is not small. This result is obtained by assuming that the gradient profile is not distorted, the injection is an impulse, and the apparent axial dispersion coefficient (Da) of the ED model or the lumped kinetic coefficient (kfL) of the TR model varies with mobile phase composition. According to this equivalence, the plate height equation derived from the TR model in our previous work (Eq. (91) in Hao et al., 2013) is also suited for the ED model. This conclusion is confirmed by comparing the equation with the results obtained by Gritti and Guiochon from the ED model (Gritti and Guiochon, 2012).

Soft striped magnetic fluctuations competing with superconductivity inFe1+xTe

Neutron spectroscopy is used to investigate the magnetic fluctuations in ${\mathrm{Fe}}_{1+x}\mathrm{Te}$---a parent compound of chalcogenide superconductors. Incommensurate ``stripelike'' excitations soften with increased interstitial iron concentration. The energy crossover from incommensurate to stripy fluctuations defines an apparent hourglass dispersion. Application of sum rules of neutron scattering find that the integrated intensity is inconsistent with an $S=1\phantom{\rule{0.28em}{0ex}}{\mathrm{Fe}}^{2+}$ ground state and significantly less than $S=2$ predicted from weak crystal field arguments pointing towards the ${\mathrm{Fe}}^{2+}$ being in a superposition of orbital states. The results suggest that a highly anisotropic order competes with superconductivity in chalcogenide systems.

The Influence of Subsoil Structure and Acquisition Parameters in MASW Mode Mis-identification

Inversion of surface wave dispersion properties is commonly used to derive shear wave velocity depth profiles. However, one of the critical and yet rarely considered issues in this ill-posed inversion process is mode contamination. Rayleigh dispersion modes are the theoretically possible solutions of motion. Experimentally, we define Rayleigh dispersion properties from spectra energy maxima in some domain (as f–k), thus possibly producing only apparent experimental dispersion curves, where energy spreads onto several modes. If this phenomenon is not recognized, the inversion of an apparent dispersion curve can produce results unrelated to the actual subsurface structure. In this work, we present the results of synthetic tests that highlight the most common subsoil conditions and acquisition pitfalls that can give rise to surface wave mode contamination. In particular, we consider three typical subsoil structures that can produce this phenomenon: 1) a simple two-layer system with a strong impedance contrast, 2) a layered system with velocity inversion, and 3) a two-layer system having a lateral discontinuity. It is known that all such systems produce, to some extent, situations in which Rayleigh wave energy propagates at higher modes rather than on the fundamental mode. We also consider the impact of acquisition parameters, which influence mode contaminations mainly as a consequence of inadequate spatial sampling. This exercise leads to identifying the most critical subsoil characteristics that control ambiguous mode inversion. We finally propose possible a priori detectors and warnings for the most critical subsoil conditions leading to mode contamination.