1,936 research outputs found
A threshold model of plastic waste fragmentation: New insights into the distribution of microplastics in the ocean and its evolution over time
Plastic pollution in the aquatic environment has been assessed for many years
by ocean waste collection expeditions around the globe or by river sampling.
While the total amount of plastic produced worldwide is well documented, the
amount of plastic found in the ocean, the distribution of particles on its
surface and its evolution over time are still the subject of much debate. In
this article, we propose a general fragmentation model, postulating the
existence of a critical size below which particle fragmentation becomes
extremely unlikely. In the frame of this model, an abundance peak appears for
sizes around 1mm, in agreement with real environmental data. Using, in
addition, a realistic exponential waste feed to the ocean, we discuss the
relative impact of fragmentation and feed rates, and the temporal evolution of
microplastics (MP) distribution. New conclusions on the temporal trend of MP
pollution are drawn.Comment: 14 pages, 14 figure
Hydrogeochemical characteristics of shallow groundwater in volcanic rock aquifer systems in the western and northern flanks of Mount Meru, Tanzania
FIRST RESULTS OF SPACE CHARGE SIMULATIONS FOR THE NOVEL MULTI-TURN INJECTION
Recently, a novelmulti-turn injection technique was proposed. It is based on beam merging via resonance crossing. The various beamlets are successively injected and merged back by crossing a stable resonance generated by non-linear magnetic fields. Space charge is usually a crucial effect at injection in a circular machine and it could have an adverse impact on the phase space topology required for merging the various beamlets. Numerical simulations were performed to assess the stability of the merging process as a function of injected beam charge. The results are presented and discussed in this paper
Changes in the starch-protein interface depending on common wheat grain hardness revealed using atomic force microscopy
The Atomic Force Microscope tip was used to progressively abrade the surface of non-cutted starch granules embedded in the endosperm protein matrix in grain sections from wheat near-isogenic lines differing in the puroindoline b gene and thus hardness. In the hard near-isogenic wheat lines, starch granules exhibited two distinct profiles corresponding either to abrasion in the surrounding protein layer or the starch granule. An additional profile, only identified in soft lines, revealed a marked stop in the abrasion at the protein-starch transition similar to a lipid interface playing a lubricant role. It was related to the presence of both wild-type puroindolines, already suggested to act at the starch-protein interface through their association with polar lipids.This study revealed, for the first time, in situ differences in the nano-mechanical properties at the starch-protein interface in the endosperm of wheat grains depending on the puroindoline allelic status
Micromechanisms of fracture propagation in glassy polymers
While most glassy polymers are nominally brittle at macroscopic scales, they are known to exhibit plastic deformation in indentation, scratching, and microcutting when the loaded region is sufficiently small. The same applies to the micrometer size process zone at the tip of a propagating crack. While the presence and approximate size of this microscale plastic zone is well described by the Dugdale model, the prediction of the toughness of these materials is not possible without accounting for the details of the local large strain field and the work hardening behaviour of these polymers, which can be inferred from their response to compressive tests. Strain localization mechanisms such as crazing or shear banding should also be taken into account to properly model toughness. Finally, viscoplastic creep plays a major role in determining the dependence of the toughness on crack propagation velocity, as well as the important difference between the initiation and propagation toughness, which is responsible for the occurrence of a characteristic stick-slip propagation under some loading conditions.
Please click Additional Files below to see the full abstract
Recommended from our members
A framework for estimating societyâs economic welfare following the introduction of an animal disease: the case of Johneâs disease
Animal diseases are global issues affecting the productivity and financial profitability of affected farms. Johneâs disease is distributed on farms worldwide and is an endemic contagious bacterial infection in ruminants caused by Mycobacterium avium subspecies paratuberculosis. In cattle, the clinical disease manifests itself as chronic enteritis resulting in reduced production, weight loss, and eventually death. Johneâs disease is prevalent in the UK, including Scotland. Direct costs and losses associated with Johneâs disease have been estimated in previous research, confirming an important economic impact of the disease in UK herds. Despite this, the distributional impact of Johneâs disease among milk consumers and producers in Scotland has not been estimated. In this paper, we evaluate the change in societyâs economic welfare, namely to dairy producers (i.e. infected and uninfected herds) and milk consumers in Scotland induced by the introduction of Johneâs disease in the national Scottish dairy herd. At the national-level, we conclude that the economic burden falls mainly on producers of infected herds and, to a lesser extent, milk consumers, while producers of uninfected herds benefit from the presence of Johneâs. An infected producerâs loss per cow is approximately two times larger in magnitude than that of an uninfected producerâs gain. Such economic welfare estimates are an important comparison of the relative costs of national herd prevalence and the wider economic welfare implications for both producers and consumers. This is particularly important from a policy, public good, cost sharing, and human health perspective. The economic welfare framework presented in this paper can be applied to other diseases to examine the relative burden of societyâs economic welfare of alternative livestock disease scenarios. In addition, the sensitivity analysis evaluates uncertainty in economic welfare given limited data and uncertainty in the national herd prevalence, and other input parameters, associated with Johneâs disease in Scotland. Therefore, until the prevalence of Johneâs is better understood, the full economic cost to Scottish dairy herds remains uncertain but in the meantime the sensitivity analysis evaluates the robustness of economic welfare to such uncertainties
Fracture propagation in glassy polymers: From nanometer to centimeter
Please click Additional Files below to see the full abstract
Composite macroH2A/NRF-1 Nucleosomes Suppress Noise and Generate Robustness in Gene Expression
SummaryThe histone variant macroH2A (mH2A) has been implicated in transcriptional repression, but the molecular mechanisms that contribute to global mH2A-dependent genome regulation remain elusive. Using chromatin immunoprecipitation sequencing (ChIP-seq) coupled with transcriptional profiling in mH2A knockdown cells, we demonstrate that singular mH2A nucleosomes occupy transcription start sites of subsets of both expressed and repressed genes, with opposing regulatory consequences. Specifically, mH2A nucleosomes mask repressor binding sites in expressed genes but activator binding sites in repressed genes, thus generating distinct chromatin landscapes that limit genetic or extracellular inductive signals. We show that composite nucleosomes containing mH2A and NRF-1 are stably positioned on gene regulatory regions and can buffer transcriptional noise associated with antiviral responses. In contrast, mH2A nucleosomes without NRF-1 bind promoters weakly and mark genes with noisier gene expression patterns. Thus, the strategic position and stabilization of mH2A nucleosomes in human promoters defines robust gene expression patterns
Geochemical processes controlling the groundwater chemistry and fluoride contamination in the aquifer systems on the eastern, western and northern flanks of Mount Meru, Tanzania
In the Arusha volcanic region in northern Tanzania, within the eastern branch of the East African Rift, water shortage is common and much of the surface water carries unacceptable levels of dissolved ïŹuoride; hence groundwater is the main source of drinking water. Unfortunately, the quality of groundwater in this region is also very poor due to a high fluoride (Fâ») content because of natural contamination from the surrounding geological environment. Consumption of this water leads to dental and skeletal fluorosis among the local population.
Existing borehole completion reports and field stratigraphic description of sub-surface sediments during the digging of new hand dug wells were used to characterise the geology of aquifers. On the western flank, the main aquifer is a fractured and weathered basalt while on the south-western and north-eastern flanks the aquifers are composed of volcanic deposits (ash, tuffs, pumice, lapilli) and fractured and weathered basalt.
A total of 158 groundwater samples from 113 water points (61 hand-dug wells and 52 springs) were collected for chemical analysis. Laboratory results show Sodium (Na+) and bicarbonate (HCO3â») are the dominant ions hence the main water type in this area is Sodium bicarbonate (NaHCO3). Preliminary results show strong contrasts in pH, EC, TDS and Fâ» concentration across the study area, with some spatial patterns for water samples from springs (on the north-eastern flank) where pH, EC, TDS and Fâ» concentration increase with a decrease in elevation.
In all 158 groundwater samples, 91% (143 samples) have Fâ» concentration higher than the WHO limit (1.5 mg/l) recommended for drinking water. The 9% (15 samples) with Fâ» concentration lower than the WHO limit are water from the springs found in the recharge area at higher elevation on the eastern flanks of Mount Meru inside the Arusha National Park.
The chemistry of the groundwater shows that weathering and dissolution of silicate minerals (especially chemical weathering of Na-K-rich volcanic rocks), dissolution of fluoride-rich minerals and calcite precipitation play great roles on the chemical evolution of groundwater in the study area while long residence time and nature of the geological formations (including degree of weathering) play great roles in the groundwater fluoride contamination in the area
- âŠ