Relative Density Difference Research Articles

Influence of k-space trajectory corrections on proton density mapping with ultrashort echo time imaging: Application for imaging of short T2 components in white matter

PurposeTo evaluate the impact of MR gradient system imperfections and limitations for the quantitative mapping of short T2* signals performed by ultrashort echo time (UTE) acquisition approach. Materials and methodsThe measurement of short T2* signals from a phantom and a healthy volunteer study (8 subjects of average age 28 ± 4 years) were performed on a 3T scanner. The characteristics of the gradient system were obtained using calibration method performed directly on the measured subject or phantom. This information was used to calculate the actual sampling trajectory with the help of a parametric eddy current model. The actual sample positions were used to reconstruct corrected images and compared with uncorrected data. ResultsComparison of both approaches, i.e., without and with correction of k-space sampling trajectories revealed substantial improvement when correction was applied. The phantom experiments demonstrate substantial in-plane signal intensity variations for uncorrected sampling trajectories. In the case of the volunteer study, this led to significant differences in relative proton density (RPD) estimation between the uncorrected and corrected data (P = 0.0117 by Wilcoxon matched-pairs test) and provides for about ~15% higher values for short T2* components of white matter (WM) in the case of uncorrected images. ConclusionThe imperfection of the applied gradients could induce errors in k-space data sampling which further propagates into the fidelity of the UTE images and jeopardizes precision of quantification. However, the study proved that measurement of gradient errors together with correction of sample positions can contribute to increased accuracy and unbiased characterization of short T2* signals.

Associations between quantitative sleep EEG and subsequent cognitive decline in older women.

The pathophysiological processes of Alzheimer's dementia predate its clinical manifestation. Sleep disturbances can accelerate the aging process and are common features of dementia. This study examined whether quantitative sleep electroencephalogram changes predate the clinical development of mild cognitive impairment and/or incident dementia. We collected data from a nested case-control sample of women (mean age 83years) from the Sleep and Cognition Study, an ancillary study to the longitudinal Study of Osteoporotic Fractures, who were characterized as cognitively normal at the time of a baseline polysomnography study (Study of Osteoporotic Fractures visit 8) based on a Mini-Mental Status Exam (MMSE) score >24. Cases (n=85) were women who developed new mild cognitive impairment or dementia by objective cognitive testing 5years after polysomnography. Controls were women with no mild cognitive impairment/dementia (n=85) at baseline or at follow-up. Differences in electroencephalogram absolute and relative power density were observed between the two groups. Specifically, higher electroencephalogram power values were found in the dementia/mild cognitive impairment group, for the alpha (p=.01) and theta bands (p=.04) in non-rapid eye movement sleep, as well as alpha (p=.04) and sigma (p=.04) bands in rapid eye movement sleep. In contrast, there were no group differences in traditional polysomnography measures of sleep architecture and sleep stage distribution, as well as sleep apnea and periodic limb movement indices. Our results provide evidence for quantitative electroencephalogram changes, which precede the clinical onset of cognitive decline and the diagnosis of dementia in elderly women, and support the application of quantitative sleep electroencephalogram analysis as a promising biomarker for imminent cognitive decline.

A tidal pump for artificial downwelling: Theory and experiment

Coastal hypoxia is on the rise around the world, reducing secondary production and ecosystem services in estuarine and coastal regions. We propose a tidal pump consisting of a 90° bend and a vertical downwelling pipe that potentially mitigates hypoxia in bottom waters. Downwelling kinetic head presents an approximate linear dependence on incident kinetic head. Experiments were carried out on a physical model at 1:80 scale covering a wide range of current speeds and density difference heads. Experimental findings confirm the theoretical model. Downwelling flow rate mainly depends on tidal current speed, relative density difference, the immersed length of the pump below the pycnocline and the pump geometry, the latter two of which allow engineers actively regulate downwelling flow. In the Changjiang estuary where hypoxia frequently occurs below the pycnocline during late summers, surface oxygen-rich water could be pumped into a depth 15.36 m below the pycnocline at a flow rate of 0.4 m3/s for 1.2 m pipe diameter. Further study will focus on the deployment of the tidal pump to obtain the optimal dissolved oxygen (DO) concentration field in bottom waters.

Computed tomography in equine orthopaedics – the next great leap?

SummaryComputed tomography (CT) generates sectional, multiplanar images based on x‐ray attenuation properties of the subject. Contrast within images is based on differences in relative tissue density. It can resolve subtle structural abnormalities within bone and soft tissue and, as such, it has potential, among other uses, to screen for pathology within bones of the appendicular skeleton in racehorses, which could predispose to catastrophic fractures. Recent technological advances have made the possibility of performing CT imaging in the standing horse a viable clinical alternative. This commentary reviews some recent developments in this field of clinical imaging in the horse.

Influence of Carbon Addition to Fe‐Mn‐Si Type Alloy on the Structure and Shape Memory Effect

The study presented is focused on the influence of carbon addition on properties of the Fe‐Mn‐Si type intelligent materials with basic composition of Fe64Mn30Si6 (wt. %). Three alloys were prepared, starting from elemental powders, with 0, 0.1, and 0.3 wt. % of carbon, at corresponding silicon content reduction. For the synthesis, the mechanical alloying, sintering, and annealing were applied. Further process involved deformation and subsequent heating in a furnace. High temperature X‐ray diffraction patterns, obtained at room temperature and up to 600°C, showed evolution of α′, γ, and ε phase peaks. The study revealed that a small carbon addition (of 0.1 wt. %), could increase shape recovery stress, even up to 1.8% after one cycle of training. The higher carbon content leads to a deterioration of the property. Also, relative density differences are observed between the sintered Fe64Mn30Si6 (wt. %) alloys with before/after annealing with/without mechanical alloying involvement.

Performance of ground-based and aerial survey methods for monitoring wildlife assemblages in a conservation area of northern Tanzania

Validating and improving field-sampling techniques for estimating wildlife community composition and population size is essential for wildlife management and conservation. We conducted ground distance sampling surveys along line transects and block counts from a small aircraft in Manyara Ranch in Northern Tanzania and contrasted estimates of species richness and species-specific densities from both sampling techniques. We used regression analyses (logistic regression and generalized linear mixed models) and model selection to investigate whether a species’ body size, group size, body color, as well as vegetation cover explained the variation in species presence/absence and relative density differences in aerial vs. ground-based sampling. Ground surveys detected significantly more species than aerial surveys. However, aerial surveys detected three species that were missed by ground surveys (African lions, African buffalo, and spotted hyena). Model selection suggested that species with smaller body mass and small group sizes were more likely to be missed in aerial surveys. Densities estimated from the aerial surveys were generally but non-significantly lower than the densities estimated from the ground surveys, with the exception of density estimates for African elephants which were slightly higher from aerial surveys. Density differences between the two methods were greater for species with small group size, light body color, and in areas with denser vegetation cover; these variables explained 75% of the variation in density differences between the two survey methods. Albeit being similar in operational costs in our relatively small study area, ground surveys yielded (1) more complete information with respect to wildlife community composition and (2) density estimates were mostly higher and (3) more precise and (4) appear more feasible to be implemented in community-based conservation schemes.

In situ stabilization of NAPL contaminant source-zones as a remediation technique to reduce mass discharge and flux to groundwater

Widely used flushing and in-situ destruction based remediation techniques (i.e. pump-and treat, enhanced-solubilization, and chemical oxidation/reduction) for sites contaminated by nonaqueous phase liquid (NAPL) contaminant sources have been shown to be ineffective at complete mass removal and reducing aqueous-phase contaminant of concern (COC) concentrations to levels suitable for site closure. A remediation method was developed to reduce the aqueous solubility and mass-flux of COCs within NAPL through the in-situ creation of a NAPL mixture source-zone. In contrast to remediation techniques that rely on the rapid removal of contaminant mass, this technique relies on the stabilization of difficult-to-access NAPL sources to reduce COC mass flux to groundwater. A specific amount (volume) of relatively insoluble n-hexadecane (HEXDEC) or vegetable oil (VO) was injected into a trichloroethene (TCE) contaminant source-zone through a bench-scale flow cell port (i.e. well) to form a NAPL mixture of targeted mole fraction (TCE:HEXDEC or TCE:VO). NAPL-aqueous phase batch tests were conducted prior to the flow-cell experiments to evaluate the effects of various NAPL mixture ratios on equilibrium aqueous-phase concentrations of TCE to design optimal NAPL (HEXDEC or VO) injection volumes for the flow-cell experiments. The NAPL-stabilization flow-cell experiments initiated and sustained significant reductions in COC concentration and mass flux due to a combination of both reduced relative permeability (increased NAPL-saturation) and via modification of NAPL composition (decreased TCE mole fraction). Variations in remediation performance (i.e. impacts on TCE concentration and mass flux reduction) between the different HEXDEC injection volumes were relatively minor, and therefore inconsistent with Raoult's Law predictions. This phenomenon likely resulted from non-uniform mixing of the injected HEXDEC with TCE in the source-zone. VO injection caused TCE concentrations and mass-flux to decrease more rapidly than with HEXDEC injections. This phenomenon occurred because the injected VO was observed to mix more uniformly with TCE in the source-zone due to a lower mobilization potential. The relative lower density differences (buoyancy effects) between VO and the flushing solution (water) was the primary factor contributing to the lower mobilization potential for VO. Overall, this study indicated that the delivery of HEXDEC or VO into the toxic TCE source-zone was effective in significantly reducing contaminant aqueous-phase concentration and mass-flux. However, the effectiveness of this in-situ NAPL stabilization technique depends on source delivery, uniform mixing of amendment, and that the amendment remains immobilized within and around the NAPL contaminant source.

Phytostabilization Ability of Baccharis linearis and Its Relation to Properties of a Tailings-Derived Technosol

Spontaneous colonization of mine tailing dams by plants is a potential tool for phytostabilization of such reservoirs. However, the physical and chemical properties of each mine tailings deposit determine the success of natural plant establishment. The plant Baccharis linearis is the main native nanophanerophyte species (evergreen sclerophyllous shrub) that naturally colonizes abandoned copper tailings dams in arid to semiarid north-central Chile. This study compare growth of B. linearis against the physical and chemical properties of a Technosol derived from copper mine tailings. Five sites inside the deposit were selected based on B. linearis vegetation density (VD), at two soil sampling depths under the canopy of adult individuals. Physical and chemical properties of tailings samples and nutrient concentrations in tailings and plants were each determined. Some morphological features of the plants (roots and aerial parts) were also quantified. There were significant differences in soil available water capacity (AW) and relative density (Rd) at different VD. Sites with low AW and high Rd had lower nutrient concentrations and higher Zn content in tailings, decreased infection by arbuscular mycorrhizal fungi, and increased fine root abundance and root hair length in individual plants. In contrast, higher AW, which was positively correlated with fine particles and organic matter content, had a positive effect on vegetation coverage, increased N and P contents in tailings, and increased N contents in leaf tissues, even when available N and P levels in tailings were low. Multiple constraints, such as low AW, N, P, and B contents and high Zn concentrations in the tailings restricted vegetation coverage, but no phenotypic differences were observed between individuals. Thus, in order to promote dense coverage by B. linearis, water retention in these tailings must be improved by increasing colloidal particles (organic and/or inorganic) contents, which have a positive effect on colonization by this species.

Invited Commentary

Mitral annuloplasty ring dehiscence may occur in 1% to 10% of all mitral surgeries, but can have severe and potentially fatal consequences when it does. In this issue of The Annals, Pierce and colleagues [1Pierce E.L. Siefert A.W. Paul D.M. et al.How local annular force and collagen density govern mitral annuloplasty ring dehiscence risk.Ann Thorac Surg. 2016; 102: 518-526Abstract Full Text Full Text PDF PubMed Scopus (25) Google Scholar] examine the mechanisms underlying mitral annuloplasty ring dehiscence. In this manuscript, “How Local Annular Force and Collagen Density Govern Mitral Annuloplasty Ring Dehiscence Risk,” Pierce and colleagues examine causative factors governing mitral annular ring suture dehiscence in a sheep model. Possible mechanisms contributing to dehiscence such as cyclic force, loading, annular flexion, and left ventricular pressures, among others, were quantified and correlated with relative collagen density differences at multiple points around the mitral ovine annulus. From this data, a propensity for mitral annular suture pull out and force margins of safety was developed. The results showed that the anterior annular holding strength exceeded posterior annular holding strength and that the overall pullout force required exhibited a strong correlation to local collagen density. Surprisingly, trigonal sutures were less secure (less resistant to pullout) than would have been predicted or thought by the authors, due to a combination of reduced collagen in the trigonal area and higher overall annular rigidity. This goes against popular belief that the trigones are the most secure area. This finding reinforces their finding that the inter-trigonal anterior annular tissue may be a superior anchor for a mitral annular ring. This fact may help guide clinicians in selection of type of ring (complete versus partial) and for future rings and mitral prostheses. Furthermore, this manuscript is also important as it brings up more questions to be considered. For example, ring dehiscence appears to be more common in the tricuspid annular position than mitral. What are the corresponding pullout forces in the tricuspid position? Are there significant differences between the ovine and the human annulus? What happens to pullout force when the annulus is overdistended and dilated, as is often seen in human congestive heart failure. All of these questions should be examined carefully as our field moves forward to possible percutaneous therapy for mitral and tricuspid disease. Data such as in the present manuscript will help with the technology of percutaneous implantations of mitral and tricuspid rings when annular ring implantation technique no longer includes direct visualization. The scientific quantitation of long-held popular beliefs in cardiac surgery is well warranted. The questioning and validation or abandonment of our standard practice should be a continual quality process. It is in this manner that we will best serve our future mitral patients. How Local Annular Force and Collagen Density Govern Mitral Annuloplasty Ring Dehiscence RiskThe Annals of Thoracic SurgeryVol. 102Issue 2PreviewAnnuloplasty ring dehiscence is a well described mode of mitral valve repair failure. Defining the mechanisms underlying dehiscence may facilitate its prevention. Full-Text PDF

Sustained gravity currents in a channel

Gravitationally driven motion arising from a sustained constant source of dense fluid in a horizontal channel is investigated theoretically using shallow-layer models and direct numerical simulations of the Navier–Stokes equations, coupled to an advection–diffusion model of the density field. The influxed dense fluid forms a flowing layer underneath the less dense fluid, which initially filled the channel, and in this study its speed of propagation is calculated; the outflux is at the end of the channel. The motion, under the assumption of hydrostatic balance, is modelled using a two-layer shallow-water model to account for the flow of both the dense and the overlying less dense fluids. When the relative density difference between the fluids is small (the Boussinesq regime), the governing shallow-layer equations are solved using analytical techniques. It is demonstrated that a variety of flow-field patterns are feasible, including those with constant height along the length of the current and those where the height varies continuously and discontinuously. The type of solution realised in any scenario is determined by the magnitude of the dimensionless flux issuing from the source and the source Froude number. Two important phenomena may occur: the flow may be choked, whereby the excess velocity due to the density difference is bounded and the height of the current may not exceed a determined maximum value, and it is also possible for the dense fluid to completely displace all of the less dense fluid originally in the channel in an expanding region close to the source. The onset and subsequent evolution of these types of motions are also calculated using analytical techniques. The same range of phenomena occurs for non-Boussinesq flows; in this scenario, the solutions of the model are calculated numerically. The results of direct numerical simulations of the Navier–Stokes equations are also reported for unsteady two-dimensional flows in which there is an inflow of dense fluid at one end of the channel and an outflow at the other end. These simulations reveal the detailed mechanics of the motion and the bulk properties are compared with the predictions of the shallow-layer model to demonstrate good agreement between the two modelling strategies.

Analysis of direct transformation from graphite to diamond crystal

The lattice parameters of cubic diamond and rhombohedral graphite under the probable direct transformation synthesis conditions have been obtained by means of linear expansion coefficient and elastic constant. Based on the empirical electron theory in solid and molecules, the valence electron structures (VESs) of graphite and diamond, the covalent electron densities (CEDs), and the relative electron density differences (REDDs) of the diamond growth interfaces have been calculated. It has been found that the REEDs of graphite/diamond interfaces were awfully large and the CEDs were discontinuous at the first order approximation. Not any meaningful atomic state of graphite structure, which satisfied the bond length difference formula, existed on the detonation synthetic conditions. Accordingly, it was considered that the direct transformation from graphite to diamond could not come true from the perspective of VES. In addition, the mechanism of synthesis diamond by explosive detonation was discussed based on the VESs of graphite and diamond.

How Local Annular Force and Collagen Density Govern Mitral Annuloplasty Ring Dehiscence Risk

Annuloplasty ring dehiscence is a well described mode of mitral valve repair failure. Defining the mechanisms underlying dehiscence may facilitate itsprevention. Factors that govern suture dehiscence were examined with an ovine model. After undersized ring annuloplasty in live animals (n= 5), cyclic force (FC) that acts on sutures during cardiac contraction was measured with custom transducers. FC was measured at ten suture positions, throughout cardiac cycles with peak left ventricular pressure (LVPmax) of 100, 125, and 150 mm Hg. Suture pullout testing was conducted on explanted mitral annuli (n= 12) to determine suture holding strength at each position. Finally, relative collagen density differences at suture sites around the annulus were assessed by two-photon excitation fluoroscopy. Anterior FC exceeded posterior FC at each LVPmax (eg, 2.8 ± 1.3 N versus 1.8 ± 1.2 N atLVPmax= 125 mm Hg, p < 0.01). Anterior holding strength exceeded posterior holding strength (6.4 ± 3.6 N versus 3.9 ± 1.6 N, p<0.0001). On the basis of FC at LVPmax of 150 mm Hg, margin of safety before suture pullout was vastly higher between the trigones (exclusive) versus elsewhere (4.8 ± 0.9N versus 1.9± 0.5 N, p < 0.001). Margin of safety exhibited strong correlation to collagen density (R(2)= 0.947). Despite lower cyclic loading on posterior sutures, the weaker posterior mitral annular tissue creates higher risk of dehiscence, apparently because of reduced collagen content. Sutures placed atop the trigones are less secure than predicted, because of a combination of reduced collagen and higher overall rigidity in this region. These findings highlight the inter-trigonal tissue as the superior anchor and have implications on the design and implantation techniques for next-generation mitral prostheses.

A preliminary assessment of using conservation drones for Sumatran orang-utan (Pongo abelii) distribution and density

To conserve biodiversity, scientists monitor wildlife populations and their habitats. Current methods have constraints, such as the costs of ground or aerial surveys, limited resolution of freely available satellite images, and expensive high-resolution satellite images. Recently researchers started to use unmanned aerial vehicles (UAVs or drones) for wildlife and habitat monitoring. Here we tested whether we could detect nests of the critically endangered Sumatran orang-utan on imagery acquired from a camera-mounted drone to determine distribution and density. Our results show that the distribution of nests compares well between aerial and ground-based surveys and that relative density (nest/km) shows a significant correlation between these two survey types. The results also indicate that both methods can be used to detect significant differences in relative density between previously degraded reforested and enriched areas. We conclude that orang-utan nest surveys from drones are a promising survey method to determine distribution and (relative) density of Sumatran orang-utans and perhaps other ape species.

Adult tonsillectomy: postoperative pain depends on indications

IntroductionIntense pain is one of the most important postoperative complaints after tonsillectomy. It is often described by patients as comparable to the pain that accompanies an acute tonsillitis. Although recurrent tonsillitis is the most frequent indication for surgery, many tonsillectomies are performed due to other indications and these patients may be unfamiliar with such pain. ObjectiveTo verify whether individuals with recurrent tonsillitis experience different post-tonsillectomy pain intensity than those with other indications for surgery, with no history of episodes of acute tonsillitis. MethodsA total of 61 tonsillectomies were performed under general anesthesia, using a potassium titanyl phosphate (KTP) laser (to eliminate the potential influence on the study results of forceful dissection of fibrotic tonsils in patients with history of recurrent tonsillitis) and multiple ligations of blood vessels within the tonsillar beds. The patients received 37.5mg Tramadoli hydrochloridum+325mg Paracetamol tablets for 10 days. Postoperative variables included the duration of hospital stay, postoperative hemorrhage and readmission rate. The patients reported pain intensity on consecutive days, pain duration, weight loss on postoperative day 10, character, intensity and duration of swallowing difficulties, and the need for additional doses of painkillers. Healing was also assessed. Capsular nerve fibers were histologically examined in the resected tonsils by immunostainings for general and sensory markers. ResultsIndications for the surgery were: recurrent acute tonsillitis (34 patients), no history of recurrent tonsillitis: focus tonsil (20) and intense malodour (7). Pain intensity on postoperative days 3–4 and incidence of readmissions due to dehydration were significantly higher in the group with no history of recurrent tonsillitis. No significant differences in relative densities of protein gene product (PGP) 9.5- and calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers were observed. ConclusionPatients with recurrent tonsillitis qualified for tonsillectomy reported lower pain intensity than those without recurrent tonsillitis and the pain scores were unrelated to nerve fibers density.

Does habitat disturbance affect stress, body condition and parasitism in two sympatric lemurs?

Understanding how animals react to human-induced changes in their environment is a key question in conservation biology. Owing to their potential correlation with fitness, several physiological parameters are commonly used to assess the effect of habitat disturbance on animals’ general health status. Here, we studied how two lemur species, the fat-tailed dwarf lemur (Cheirogaleus medius) and the grey mouse lemur (Microcebus murinus), respond to changing environmental conditions by comparing their stress levels (measured as hair cortisol concentration), parasitism and general body condition across four habitats ordered along a gradient of human disturbance at Kirindy Forest, Western Madagascar. These two species previously revealed contrasting responses to human disturbance; whereas M. murinus is known as a resilient species, C. medius is rarely encountered in highly disturbed habitats. However, neither hair cortisol concentrations nor parasitism patterns (prevalence, parasite species richness and rate of multiple infections) and body condition varied across the gradient of anthropogenic disturbance. Our results indicate that the effect of anthropogenic activities at Kirindy Forest is not reflected in the general health status of both species, which may have developed a range of behavioural adaptations to deal with suboptimal conditions. Nonetheless, a difference in relative density among sites suggests that the carrying capacity of disturbed habitat is lower, and both species respond differently to environmental changes, with C. medius being more negatively affected. Thus, even for behaviourally flexible species, extended habitat deterioration could hamper long-term viability of populations.

Study of hydrodynamic instabilities with a multiphase lattice Boltzmann model

Rayleigh–Taylor and Kelvin–Helmholtz hydrodynamic instabilities are frequent in many natural and industrial processes, but their numerical simulation is not an easy challenge. This work simulates both instabilities by using a lattice Boltzmann model on multiphase fluids at a liquid-vapour interface, instead of multicomponent systems like the oil–water one. The model, proposed by He, Chen and Zhang (1999) [1] was modified to increase the precision by computing the pressure gradients with a higher order, as proposed by McCracken and Abraham (2005) [2] . The resulting model correctly simulates both instabilities by using almost the same parameter set. It also reproduces the relation γ ∝ A between the growing rate γ of the Rayleigh–Taylor instability and the relative density difference between the fluids (known as the Atwood number A ), but including also deviations observed in experiments at low density differences. The results show that the implemented model is a useful tool for the study of hydrodynamic instabilities, drawing a sharp interface and exhibiting numerical stability for moderately high Reynolds numbers.

Density Effects on Dilution and Height of Vertical Fountains

AbstractThe effects of relative density difference on the dilution and height of vertical negative buoyant jets were investigated experimentally. These effects, which are related to fluid density, occurred in addition to the buoyancy effects commonly parameterized by the densimetric Froude number. The density effects have generally been ignored in previous investigations and in practice on the basis of Boussinesq’s approximation. The density effects could, however, be relevant in connection to hypersaline discharges from desalination plants and dense discharges from oil and potash mining industries. A series of seven upward fountain experiments were performed in the laboratory to carry out this investigation. The flow was turbulent, the relative density difference varied from 0.0014 to 0.064, and the densimetric Froude number varied from 2.13 to 15.7. The results showed that an increase in the relative density difference reduced both the minimum return dilution and maximum height of the fountains. The obs...

Alterations in sociability and functional brain connectivity caused by early-life seizures are prevented by bumetanide

There is a well-described association between infantile epilepsy and pervasive cognitive and behavioral deficits, including a high incidence of autism spectrum disorders. Despite the robustness of the relationship between early-life seizures and the development of autism, the pathophysiological mechanism by which this occurs has not been explored. As a result of increasing evidence that autism is a disorder of brain connectivity we hypothesized that early-life seizures would interrupt normal brain connectivity during brain maturation and result in an autistic phenotype. Normal rat pups underwent recurrent flurothyl-induced seizures from postnatal (P)days 5–14 and then tested, along with controls, for developmental alterations of development brain oscillatory activity from P18–P25. Specifically we wished to understand how normal changes in rhythmicity in and between brain regions change as a function of age and if this rhythmicity is altered or interrupted by early life seizures.In rat pups with early-life seizures, field recordings from dorsal and ventral hippocampus and prefrontal cortex demonstrated marked increase in coherence as well as a decrease in voltage correlation at all bandwidths compared to controls while there were minimal differences in total power and relative power spectral densities. Rats with early-life seizures had resulting impairment in the sociability and social novelty tests but demonstrated no evidence of increased activity or generalized anxiety as measured in the open field. In addition, rats with early-life seizures had lower seizure thresholds than controls, indicating long-standing alterations in the excitatory/inhibition balance. Bumetanide, a pharmacological agent that blocks the activity of NKCC1 and induces a significant shift of ECl toward more hyperpolarized values, administration at the time of the seizures precluded the subsequent abnormalities in coherence and voltage correlation and resulted in normal sociability and seizure threshold. Taken together these findings indicate that early-life seizures alter the development of oscillations and result in autistic-like behaviors. The altered communication between these brain regions could reflect the physiological underpinnings underlying social cognitive deficits seen in autism spectrum disorders.

Lubricated viscous gravity currents

AbstractWe present a theoretical and experimental study of viscous gravity currents lubricated by another viscous fluid from below. We use lubrication theory to model both layers as Newtonian fluids spreading under their own weight in two-dimensional and axisymmetric settings over a smooth rigid horizontal surface and consider the limit in which vertical shear provides the dominant resistance to the flow in both layers. There are contributions from Poiseuille-like flow driven by buoyancy and Couette-like flow driven by viscous coupling between the layers. The flow is self-similar if both fluids are released simultaneously, and exhibits initial transient behaviour when there is a delay between the initiation of flow in the two layers. We solve for both situations and show that the latter converges towards self-similarity at late times. The flow depends on three key dimensionless parameters relating the relative dynamic viscosities, input fluxes and density differences between the two layers. Provided the density difference between the two layers is bounded away from zero, we find an asymptotic solution in which the front of the lubricant is driven by its own gravitational spreading. There is a singular limit of equal densities in which the lubricant no longer spreads under its own weight in the vicinity of its nose and ends abruptly with a non-zero thickness there. We explore various regimes, from thin lubricating layers underneath a more viscous current to thin surface films coating an underlying more viscous current and find that although a thin film does not greatly influence the more viscous current if it forms a surface coating, it begins to cause interesting dynamics if it lubricates the more viscous current from below. We find experimentally that a lubricated gravity current is prone to a fingering instability.

Population structure of two bamboo species in relation to topographical units in the Republic of Benin (West Africa): implications for sustainable management

A study was carried out in two phytodistricts (Ouémé-valley and Plateau) to assess the population structure of two bamboo species (Oxytenanthera abyssinica (A. Rich.) Munro and Bambusa vulgaris Schrad. ex J.C. Wendl. in two topographical units: plateau and wetlands. In each phytodistrict, bamboo stands were randomly selected in each topographical unit for inventory using a 0.25-ha square plot. Structural parameters of bamboos were computed and compared using a Wilcoxon rank test. Spatial distribution of the two bamboos was also assessed using the method of neighbourhood density in relation to a focal point. The observed culm diameter distribution was established for each stand and adjusted to the two-parameter Weibull distribution. Oxytenanthera abyssinica showed the highest culm and clump density values in both wetlands and plateau whereas B. vulgaris showed greater values of mean diameter and dominant height whatever the habitat. Diameter structures of bamboo stands showed a right asymmetric distribution and bamboo spatial distribution was highly aggregative, especially in wetlands. No significant difference in mean relative neighbourhood density between species was noted. However, a significant difference was observed between wetlands and plateau (p < 0.001) indicating strong influence of the topographical units on the relative neighbourhood density of bamboo species. All of these findings are determinants in designing suitable management strategies for bamboo populations in Benin, particularly with the increasing demand to build fish-traps and shelter in the traditional fishing systems “Acadja”.