/pdf/handbook-of-plant-nutrition-1uozdhlhhi.pdf

Handbook of Plant Nutrition

High-precision Sr/Ca ratios are reported for Porites corals from Davies Reef, at ∼19°S on the midshelf of the Great Barrier Reef, Australia. Skeletal growth parameters were also determined from coral slabs using X ray photographs and γ-densitometry measurements. A calibration of the Sr/Ca thermometer has been obtained, using in situ measured sea surface temperatures, which gives Sr/Ca × 10³ = 10.48 (±0.01) − 0.0615 (±0.0004) × T, whereT is in °C. This calibration applies to different species of Porites and a large range of annual extension and calcification rates, provided sampling follows a major growth axis. Biases of 1°–2°C have been observed in the low-density margins where growth is hampered by interfering fans of corallites. The analytical and the long-term reproducibility of Sr/Ca-derived temperatures are both better than ±0.3°C (2σ). Coral growth parameters such as the extension rate or density generally appear to respond to environmental changes such as rainfall but do not affect the Sr/Ca partitioning between coralline aragonite and seawater. No correlation has been found between calcification rate and Sr/Ca variations, consistent with Sr/Ca being mainly controlled by temperature. In the Great Barrier Reef, the interannual variability in SST is primarily related to the El Nino-Southern Oscillation phenomenon and is typically marked by a cold anomaly during the winter preceding the mature warm phase. Instrumental records show that the surface waters of the Coral Sea around 19°S have experienced a significant cooling associated with the El Ninos of 1965, 1972, and 1982-1983 which the Porites corals record faithfully. The coral-derived temperatures for the period from 1965 to 1993 show an increase of 1.3°C, which has occurred mainly since 1979. This warming is larger in magnitude but consistent with the trend for the southern hemisphere land and marine temperature records, which shows an increase of around 0.4°C.

Strontium/calcium ratios in modern Porites corals from the Great Barrier Reef as a proxy for sea surface temperature: calibration of the thermometer and monitoring of ENSO

Applications of laser-induced breakdown spectroscopy for geochemical and environmental analysis: A comprehensive review

Thin Friction The rubbing motion between two surfaces is always hindered by friction, which is caused by continuous contacting and attraction between the surfaces. These interactions may only occur over a distance of a few nanometers, but what happens when the interacting materials are only that thick? Lee et al. (p. 76; see the Perspective by Müser and Shakhvorostov) explored the frictional properties of a silicon tip in contact with four atomically thin quasi–two dimensional materials with different electrical properties. For all the materials, the friction was seen to increase as the thickness of the film decreased, both for flakes supported by substrates and for regions placed above holes that formed freely suspended membranes. Placing graphene on mica, to which it strongly adheres, suppressed this trend. For these thin, weakly adhered films, out-of-plane buckling is likely to dominate the frictional response, which leads to this universal behavior. A universal trend is observed for the friction properties of thin films on weakly adhering substrates. Using friction force microscopy, we compared the nanoscale frictional characteristics of atomically thin sheets of graphene, molybdenum disulfide (MoS2), niobium diselenide, and hexagonal boron nitride exfoliated onto a weakly adherent substrate (silicon oxide) to those of their bulk counterparts. Measurements down to single atomic sheets revealed that friction monotonically increased as the number of layers decreased for all four materials. Suspended graphene membranes showed the same trend, but binding the graphene strongly to a mica surface suppressed the trend. Tip-sample adhesion forces were indistinguishable for all thicknesses and substrate arrangements. Both graphene and MoS2 exhibited atomic lattice stick-slip friction, with the thinnest sheets possessing a sliding-length–dependent increase in static friction. These observations, coupled with finite element modeling, suggest that the trend arises from the thinner sheets’ increased susceptibility to out-of-plane elastic deformation. The generality of the results indicates that this may be a universal characteristic of nanoscale friction for atomically thin materials weakly bound to substrates.

Frictional Characteristics of Atomically-Thin Sheets

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Good practices in LIBS analysis: Review and advices

Graphene-based micro-electromechanical systems (MEMS) are very promising candidates for next generation miniaturized, lightweight, and ultra-sensitive devices. In this review, we review the progress to date of the assessment of the mechanical, electromechanical, and thermomechanical properties of graphene for application in graphene-based MEMS. Graphene possesses a plethora of outstanding properties—such as a 1 TPa Young's modulus, exceptionally high 2D failure strength that stems from its sp2 hybridization, and strong sigma bonding between carbon atoms. Such exceptional mechanical properties can enable, for example, graphene-based sound sources capable of generating sound beyond the audible range. The recently engineered piezoelectric properties of atomic force microscope tip-pressed graphene membranes or supported graphene on SiO2 substrates, have paved the way in fabricating graphene-based nano-generators and actuators. On the other hand, graphene's piezoresistive properties have enabled miniaturized pressure and strain sensors. 2D graphene nano-mechanical resonators can potentially measure ultralow forces, charges and potentially detect single atomic masses. The exceptional tribology of graphene can play a significant role in achieving superlubricity. In addition, the highest reported thermal conductivity of graphene is amenable for use in chips and providing better performing MEMS, as heat is efficiently dissipated. On top of that, graphene membranes could be nano-perforated to realize specialized applications like DNA translocation and desalination. Finally, to ensure stability and reliability of the graphene-based MEMS, adhesion is an important mechanical property that should be considered. In general, graphene could be used as a structural material in resonators, sensors, actuators and nano-generators with better performance and sensitivity than conventional MEMS.

/pdf/mechanical-and-electromechanical-properties-of-graphene-and-ktv4n4uvwl.pdf

Mechanical and electromechanical properties of graphene and their potential application in MEMS

Laser-induced breakdown spectroscopy (LIBS) is an emerging and promising tool for rapid and efficient elemental analysis. We used the LIBS technique to analyze the raw monazite sands collected from the beaches in southern Bangladesh. We have detected a number of rare earths (lanthanides) such as cerium, lanthanum, praseodymium, neodymium, yttrium, ytterbium, gadolinium, dysprosium and erbium, in addition to other metallic elements such as zirconium, chromium, titanium, magnesium, manganese, niobium and aluminum. To the best of our knowledge, this is the first time multiple rare earths have been identified in a natural mineral by LIBS.

Identification of multiple rare earths and associated elements in raw monazite sands by laser-induced breakdown spectroscopy

LIBS technique coupled with adsorption has been applied for the efficient detection of arsenic in liquid. Several adsorbents like tea leaves, bamboo slice, charcoal and zinc oxide have been used to enable sensitive detection of arsenic presence in water using LIBS. Among these, zinc oxide and charcoal show the better results. The detection limits for arsenic in water were 1 ppm and 8 ppm, respectively, when ZnO and charcoal were used as adsorbents of arsenic. To date, the determination of 1 ppm of As in water is the lowest concentration of detected arsenic in water by the LIBS technique. The detection limit of As was lowered to even less than 100 ppb by a combination of LIBS technique, adsorption by ZnO and concentration enhancement technique. Using the combination of these three techniques the ultimate concentration of arsenic was found to be 0.083 ppm (83 ppb) for arsenic polluted water collected from a tube-well of Farajikandi union (longitude 90.64°, latitude 23.338° north) of Matlab Upozila of Chandpur district in Bangladesh. This result compares fairly well with the finding of arsenic concentration of 0.078 ppm in the sample by the AAS technique at the Bangladesh Council of Scientific and Industrial Research (BCSIR) lab. Such a low detection limit (1 ppm) of trace elements in liquid matrix has significantly enhanced the scope of LIBS as an analytical tool.

Detection of trace amount of arsenic in groundwater by laser-induced breakdown spectroscopy and adsorption

Laser-induced breakdown spectroscopic (LIBS) technique was used to study the elemental proﬁle of coral skeletons. Apart from calcium and carbon, which are the main elemental constituents of coral skeleton, elements like Sr, Na, Mg, Li, Si, Cu, Ti, K, Mn, Zn, Ba, Mo, Br and Fe were detected in the coral skeletons from the Inani Beach and the Saint Martin’s island of Bangladesh and the coral from the Philippines. In addition to the qualitative analysis, the quantitative analysis of the main elemental constituent, calcium (Ca), was done. The result shows the presence of (36.15±1.43)% by weight of Ca in the coral skeleton collected from the Inani Beach, Cox’s Bazar, Bangladesh. It was determined by using six calibration curves, drawn for six emission lines of Ca I (428.301 nm, 428.936 nm, 431.865 nm, 443.544 nm, 443.569 nm, and 445.589 nm), by standard analyte additive method. Also from AAS measurement the percentage content of Ca in the same sample of coral skeleton obtained was 39.87% by weight which compares fairly well with the result obtained by the analyte additive method.

Determination of Ca content of coral skeleton by analyte additive method using the LIBS technique

Lifetimes of the excited 2P2 (3P) 3p 4S3/2 level of a nitrogen atom corresponding to transitions to different lower states have been estimated by measuring the line intensity of a transition as a function of the delay time between the Q-switching of the laser and the gating of the window of the ICCD. This novel time resolved laser-induced breakdown spectroscopic technique is explained in the paper. The lifetimes of the upper level 2P2 (3P) 3p 4S3/2 corresponding to the three transitions to 2P2 (3P) 3s 4P1/2 (742.346 nm), 2P2 (3P) 3s 4P3/2 (744.27 nm) and 2P2 (3P) 3s 4P5/2 (746.851 nm) were measured by this technique. The corresponding average lifetimes (τ) of these transitions were 199 ns, 105 ns and 68 ns. These values compare pretty well with the calculated lifetimes of 203.8 ns, 96.7 ns and 59.2 ns for the above three transitions as reported by Hibbert et al. The plasma temperature (atomic excitation temperature) decay time was found to be 1133 ns. This novel technique of estimating the lifetime of an excited state of an atom/ion is yet another very useful application of LIBS as a versatile analytical tool.

Z.H. Khan

Papers

Mechanical and electromechanical properties of graphene and their potential application in MEMS

Identification of multiple rare earths and associated elements in raw monazite sands by laser-induced breakdown spectroscopy

Detection of trace amount of arsenic in groundwater by laser-induced breakdown spectroscopy and adsorption

Determination of Ca content of coral skeleton by analyte additive method using the LIBS technique

Radiative lifetime measurement of excited neutral nitrogen atoms by time resolved laser-induced breakdown spectroscopy