Average Mz Research Articles

Impact of the cation field strength on physical properties and structures of alkali and alkaline-earth borosilicate glasses

The impact of the cation field strength (CFS) of the glass network-modifier cations on the structure and properties of borosilicate glasses (BS) were examined for a large ensemble of mixed-cation (R/2)M(2)O–(R/2)Na2O–B2O3–KSiO2 glasses with M+ ={Li+, Na+, K+, Rb+} and M2+ ={Mg2+, Ca2+, Sr2+, Ba2+} from four series of {K, R} combinations of K = n(SiO2)/n(B2O3) = {2.0, 4.0} and R =[n(M(2)O) ​+ ​n(Na2O)]/n(B2O3) = {0.75, 2.1}. Combined with results from La3+ bearing glasses enabled the probing of physical-property variations across a wide CFS range, encompassing the glass transition temperature (Tg), density, molar volume and compactness, as well as the hardness (H) and Young's modulus (E). We discuss the inferred composition–structure/CFS–property relationships. Each of Tg, H, and E revealed a non-linear dependence against the CFS and a strong Tg/H correlation, where each property is maximized for the largest alkaline-earth metal cations, i.e., Sr2+ and Ba2+, along with the high-CFS La3+ species. The 11B MAS NMR-derived fractional BO4 populations decreased linearly with the average Mz+/Na+ CFS within both K–0.75 glass branches, whereas the NBO-rich K–2.1 glasses manifested more complex trends. Comparisons with results from RM2O–B2O3–KSiO2 glasses suggested no significant “mixed alkali effect”.

Coarsening of sediments from the Huanghe (Yellow River) delta-coast and its environmental implications

We studied temporal-spatial variations in the grain size of sediments from the Huanghe (Yellow River) delta-coast. Four sediment push-cores and more than 200 surface sediment samples were collected. Key factors that control the sediment variability were revealed, as well as their environmental significance. Analytical results indicated that sediments of the Huanghe delta-coast have coarsened over the past decades, and that this coarsening has intensified in recent years. The average mean grain size (Mz) of two cores in the offshore area from the abandoned delta lobe increased by approximately 18%–32% in the 2010s compared to the 1990s. Surface sediments in the nearshore area were coarsened by about 25% on average from 28.6 μm in 1992 to 35.7 μm in 2000. The sediment coarsening of the abandoned delta lobe began in the 1990s due to the extensive erosion caused by the absence of riverine-sediment supply. Coarse-grained sediments that were resuspended and transported offshore also made the sediment of the abandoned delta lobe coarser. In contrast, sediments of two cores in the offshore area of the active delta lobe were coarsened by more than 30% in the 2010s compared to the 1990s. The average Mz of surface sediments in the nearshore area increased by more than 22% from 23.5 μm in 1992 to 28.7 μm in 2000. The sediment coarsening of the active delta lobe began in the 1990s and became more significant in the 2000s. This trend was due to the rapid decrease of the sediment load from the Huanghe, as well as the coarsening of river-delivered sediments (from 17.7 μm to 22.9 μm) caused by the Water-Sediment Regulation Scheme that has been in place since 2002. Increasing coastal hydrodynamics and the loss of riverine sediment also account for the coarsening of sediments of the delta lobe. Our data clearly indicate that the critical bed-shear stress of the Huanghe delta-coast increased significantly. As a result, it was more difficult to initiate motion of the seabed sediments, leading to the decline of resuspension and erosion. Moreover, since the content of sedimentary organic carbon is negatively correlated with sediment grain size, the coarsening sediment of the study area will have inevitably degraded the carbon-related biogeochemical processes of the Huanghe delta-coast. Our findings have significant implications for the evolution of large river deltas, which are now threatened by sediment starvation and erosion.

Granulometric and pebble morphometric applications to Benin Flank sediments in western Anambra Basin, Nigeria: proxies for paleoenvironmental reconstruction.

Integrated granulometric and pebble morphometric study of Late Cretaceous rocks of the Benin Flank, Nigeria, were used to delineate depositional process and environment of the rocks in the study area. Granulometric analysis reveals that the sandstones of the Lokoja Bassange Formation have an average graphic mean (Mz) of 0.59Φ (coarse grains), inclusive graphic standard deviation (δi) of 1.36Φ (poorly sorted), graphic kurtosis (Ka) of 1.12Φ (leptokurtic), and inclusive graphic skewness (Ski) of - 0.14Φ (stongly coarse skewed). The sandstones for the Mamu Formation have an average Mz of 1.42Φ (medium grains), inclusive graphic standard deviation (δi) of 0.74Φ (moderately sorted), graphic kurtosis (Ka) of 1.43Φ (leptokurtic), and inclusive graphic skewness (Ski) of 0.02Φ (nearly symetrical). The sandstones for the Ajali Formation have an average Mz of 1.23Φ (medium grains), inclusive graphic standard deviation (δi) of 1.21Φ (poorly sorted), graphic kurtosis (Ka) of 1.46Φ (leptokurtic), and inclusive graphic skewness (Ski) of - 0.17Φ (nearly symetrical). Pebble morphometric analysis of the larger grains reveals that the mean values of elongation ratio (ER) = 0.69, coefficient of flatness (FI) = 54.90%, oblate-prolate index (OPI) = 3.34, the maximum projection sphericity index (MPSI) = 0.75, form = 0.67, and roundness (ρ) = 36.28% for the Lokoja Bassange Formation; ER = 0.76, FI = 37.07%, OPI = -3.20, the MPSI = 0.53, form = 0.38, and ρ = 52.93% for the Mamu Formation; and ER = 0.72, FI = 47.44%, OPI = 1.12, the MPSI = 0.67, form = 0.54 and ρ = 42.68% for the Ajali Formation. The integration of the various granulometric and pebble morphometric data, different bivariate and ternary plots indicate fluvial environment for the Lokoja Bassange Formation, dominantly shallow marine environment for the Mamu Formation and fluvial - shallow marine environment for the Ajali Formation. This study shows that the Benin Flank, western Anambra Basin has a depositional setting radiating between fluvial and shallow marine environments.

Spin-orbit torque in Pt/CoNiCo/Pt symmetric devices.

Current induced magnetization switching by spin-orbit torques offers an energy-efficient means of writing information in heavy metal/ferromagnet (FM) multilayer systems. The relative contributions of field-like torques and damping-like torques to the magnetization switching induced by the electrical current are still under debate. Here, we describe a device based on a symmetric Pt/FM/Pt structure, in which we demonstrate a strong damping-like torque from the spin Hall effect and unmeasurable field-like torque from Rashba effect. The spin-orbit effective fields due to the spin Hall effect were investigated quantitatively and were found to be consistent with the switching effective fields after accounting for the switching current reduction due to thermal fluctuations from the current pulse. A non-linear dependence of deterministic switching of average Mz on the in-plane magnetic field was revealed, which could be explained and understood by micromagnetic simulation.

Shelf Sediments of Alexandria Region, Egypt: Explorations and Evaluation of Offshore Sand Sources for Beach Nourishment and Transport Dispersion

Textural and compositional characteristics of beach and bottom sediments collected from the beach-continental shelf of Alexandria region on the Mediterranean coast of Egypt were examined to search for quality nourishment borrow material, and to initially assess its compatibility with the existing native beaches. Sediment characteristics and carbonate content combined with analyses of coastal processes (waves and currents) and seabed morphology are also explored to interpret sediment transport pathways. Three sediment types composed of carbonate material are identified on the Alexandria shelf based on their texture and compositional characteristics. These are: Late Holocene to modern fine to medium sand (average Mz = 0.23 mm; range of 0.063–0.4 mm), a relict late Pleistocene to mid-Holocene shelly coarser material, coarse to very coarse sand (average Mz = 0.7 mm; range of 0.41–3.3 mm), and relict mud to very fine sand (average Mz = < 0.051 mm; < 0.063 mm). Textural and compositional evaluations indicate that the coarse-grained relict sand (54 km2) is locally found just seaward of the Alexandria Metropolitan area between water depths of ∼10 and 70 m; corresponds to 1 to 10 km distance from the coastline, and could be used as a nourishment and borrow material for eroded beaches of Alexandria that have experienced prolonged sediment deficiency combined with anthropogenic influences. Compatibility analysis indicates that the characteristics of the defined borrow material and those of the native beach are generally compatible with each other. With respect to the quality standards, the borrow material is similar to and slightly coarser than the native beach sand and also matches the same range of sorting (0.25–2.37 Ø) and carbonate content (8.0 to 99.9%); therefore it is compatible to use as a sand source for beach nourishment. Moreover, estimated overfill factor (RA) implies that eroded beaches would maintain a stable state following the sand-filling operation with a re-nourishment factor (Rj) of 0.39. Our observations indicate that shelf sediments, both relict and modern, are displaced northeasterly in the alongshore and offshore directions by the N and NW wave-induced currents in conjunction with the counter-clockwise geostrophic East Mediterranean current. These sediments are reworked and deposited as mixed carbonate and biogenic sands on the irregular rocky seafloor of the submerged ridges that characterize the inner shelf and are considered as the major source of sediment in the study region.

Effect of Pitch Length on the Behavior of Rotary Triple Helix Root Canal Instruments

The behavior of nickel-titanium instruments depends largely on the cross-section of the working part. The effect of pitch length was evaluated using two instruments with the same cross-section (triple helix; 0.6% taper). One had a short pitch (0.5 mm at the tip to 0.9 mm at 16 mm at the end of the working part). The other had a long pitch (1.18 mm/2 mm). A dynamometer recorded tensional stress (MHz) and the tendency to screw in (Fz) during simulated canal preparations. Rotational speed was kept constant, and a continuous pecking movement was used. At the end of the preparations, the average Fz was 5.02 N for the short-pitch instrument and 1.47 N for the long-pitch instrument (p < 0.001). The average Mz varied from 0.88 N (short pitch) to 0.35 N (long pitch). Increasing the pitch decreased torsional load sharing and the tendency to screw in.

A comparison between matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry and size exclusion chromatography in the mass characterisation of synthetic polymers with narrow molecular-mass distributions: Poly(methyl methacrylate) and poly(styrene)

A series of poly(methyl methacrylate)s and poly(styrene)s (masses 1000‐12,000 Da) with narrow molecular-mass distributions have been analysed by matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) mass spectrometry and size exclusion chromatography (SEC). The resultant number average Mn, mass (weight) average Mw, and z average Mz molecular masses as determined from the two techniques are presented and compared. These data show MALDI-TOF mass spectrometry and size exclusion chromatography (SEC) to be in good agreement, typically to within 10% for the analyses of these types of polymers.

Texture of River and Beach Sediments Seaward from Active Volcanic Highlands, Southwestern Guatemala: ABSTRACT

Sedimentologists have investigated grain-size distributions of sediments from various environments in an attempt to gain uniformitarian insight for reconstruction of ancient environments. However, modern river and beach sediments occurring seaward from active volcanic highlands have been little studied even though ancient analogues may be common locally. The Pacific coastal plain in Central America is widest in Guatemala where it is abruptly terminated 10-30 mi inland by the steep slopes of a row of active Quaternary volcanoes. The slopes are locally bare of vegetation, and the strongly seasonal, torrential rainfall provides abundant bed load to low-sinuosity streams that discharge onto the coastal plain and flow seaward in a roughly parallel pattern. Guatemala river and beach-face sands are mostly moderately to moderately well sorted (river average ^sgrI = 0.87^phgr units; beach average ^sgrI = 0.54^phgr units), near symmetrical, mesokurtic, medium-grained (river average Mz = 1.44^phgr; beach average Mz = 1.45^phgr) volcanic arenites, composed predominantly of unweathered grains of angular volcanic rock fragments, plagioclase, and ferromagnesian and opaque minerals. River sands can be distinguished from beach sands by plotting mean size versus sorting, by coarsest percentile (C) versus median percentile (M), and by inspection of cumulative probability curves. Curves for river sands commonly show subpopulations inferred to reflect sliding and/or suspension populations. Saltation populations, in both river and each sands, are usually polymodal because of mixing of grain populations differing in specific gravity and shape. Published bivariant plots and other techniques are assessed in terms of the Guatemalan sands. End_of_Article - Last_Page 634------------