Free Aluminum Research Articles

Средообразующая активность корневой системы регенерантов ячменя в условиях токсичности кислых почв

Regenerative lines of barley 917-01, 781-04, 441-05, 530-98 obtained by cell selection on acid selective media with aluminum, were evaluated with regard to the original sorts 999-93, Novichok and standard Bios 1 in the laboratory, vegetative and field experiments. The dynamics of changes in the medium acidity by the roots of barley seedlings and their biometric indicators against the control (pH 6.0) and stress (pH 4.0 and pH 4.0 + Al 3+ 20 mg/l) backgrounds were studied in the aquatic culture. Regenerated 917-01 and 781-04 were alkalinizing water actively (by 2.4-2.5 pH units) against the background of intensive root growth compared to the control (43%) and biomass accumulation (10%). The solution acidity of Novichok and its regenerantive genotype 441-05 was changing slightly. In vegetation experiments, the environment-forming activity of the regenerative line 530-98 in changing the acidity and content of free aluminum in the zone of the rhizosphere was studied. On soil background with pH 3.9 and A1 3+ 5.6 mg/100 g of soil the level of alkalization reached 0.7 units of pH at decrease in amount of free aluminum by 4.23 mg / 100 g of soil that 1.8 times exceeded the similar indicators of the standard Bios 1. With stress intensification, the increased productivity of the regenerant relative to the standard up to 2 times was revealed (by 0.66 t/ha on the soil background at pH 3.7 and Al 21 mg/100 g of soil). In favorable conditions of cultivation, the productivity of regenerants decreased relative to the standard. In the competitive tests the regenerative genotypes 917-01 and 530-98, possessing high medium forming activity of the root system, were among the best breeding numbers. Line 917-01 received the status of the sort (the Forward). Not all regenerants possessed breeding value. Selection in vitro of Al- resistant sort Novichok has not led to positive results. The conclusion about expediency of involvement in cellular selection of genotypes with low level of stress resistance and potentially high adaptive variability has been made.

Effect of rapid Solidification on mechanical properties of free machining lead free aluminum alloys for improved machinability

There have been very few reports describing the free machining lead free aluminum alloys containing minimal amounts of tin and indium melt spun process. Our paper describes the effect of fundamental factors on the machinability of free machining lead free aluminum alloys rapidly solidified from melt. Structural and thermal properties have been investigated by x-ray diffraction (XRD) and differential scanning calorimetry (DSC) techniques. Tensile test machine used in studies the mechanical properties such as ultimate tensile strength, elastic constants, yield strength and critical shear stress for Al-Zn-Sn-In alloys. It is noticed that mechanical and thermal properties attributed to fine grained structure, reduced levels of segregation and presence of new intermetallic compounds (IMC) such as AlZn and SnZn due to high casting rate by rapid solidification processes. The determination of mechanical properties was suggested to be attributed to the gradual increase of α-Al crystals. We evaluated the tensile properties using tensile test machine of the melt-spun ribbons at varied stress-strain rates to determine the underlying deformation mechanisms .Critical shear stress (CSS) was also calculated .It was found that it is equal to 9.29 GPa for annealed ribbons at 262 0C for 9 hrs. The results showed that several combination of tensile strength ,yield strength ,elastic moduli can be generated from Al- 0.1wt% Zn-1.5 wt% Sn- 1.63 wt% In alloys before and after heat treatment at (262 0C for 3,6,9 hrs) to meet the needs of free machining aluminum alloy applications.

Investigation of the Reversible Lithiation of an Oxide Free Aluminum Anode by a LiBH4 Solid State Electrolyte

In this study, we analyze and compare the physical and electrochemical properties of an all solid-state cell utilizing LiBH4 as the electrolyte and aluminum as the active anode material. The system was characterized by galvanostatic lithiation/delithiation, cyclic voltammetry (CV), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). Constant current cycling demonstrated that the aluminum anode can be reversibly lithiated over multiple cycles utilizing a solid-state electrolyte. An initial capacity of 895 mAh/g was observed and is close to the theoretical capacity of aluminum. Cyclic voltammetry of the cell was consistent with the constant current cycling data and showed that the reversible lithiation/delithiation of aluminum occurs at 0.32 V and 0.38 V (vs. Li+/Li) respectively. XRD of the aluminum anode in the initial and lithiated state clearly showed the formation of a LiAl (1:1) alloy. SEM-EDS was utilized to examine the morphological changes that occur within the electrode during cycling. This work is the first example of reversible lithiation of aluminum in a solid-state cell and further emphasizes the robust nature of the LiBH4 electrolyte. This demonstrates the possibility of utilizing other high capacity anode materials with a LiBH4 based solid electrolyte in all-solid-state batteries.

Selective binding behavior of humic acid removal by aluminum coagulation.

The reactivity characteristics of humic acid (HA) with aluminium coagulants at different pH values was investigated. It revealed that the linear complexation reaction occurred between aluminum and humic acid at pH<7, and the reaction rate increased as the pH increased from 2 to 6. While at pH=7, most of the dosed aluminum existed in the form of free aluminum and remained unreacted in the presence of HA until the concentration reached to trigger Al(OH)3(s) formation. Differentiating the change of functional groups of HA by 1H nuclear magnetic resonance spectroscopy and X-ray photoelectron spectra analysis, it elucidated that there was a selective complexation between HA and Al with lower Al dosage at pH 5, which was probably due to coordination of the activated functional groups onto aluminium. While almost all components were removed proportionally by sweep adsorption without selectivity at pH 7, as well as that with higher Al dosage at pH 5. This study provided a promising pathway to analyse the mechanism of the interaction between HA and metal coagulants in future.

Impact of an Artificial Digestion Procedure on Aluminum-Containing Nanomaterials.

Aluminum has gathered toxicological attention based on relevant human exposure and its suspected hazardous potential. Nanoparticles from food supplements or food contact materials may reach the human gastrointestinal tract. Here, we monitored the physicochemical fate of aluminum-containing nanoparticles and aluminum ions when passaging an in vitro model of the human gastrointestinal tract. Small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), ion beam microscopy (IBM), secondary ion beam mass spectrometry (TOF-SIMS), and inductively coupled plasma mass spectrometry (ICP-MS) in the single-particle mode were employed to characterize two aluminum-containing nanomaterials with different particle core materials (Al0, γAl2O3) and soluble AlCl3. Particle size and shape remained unchanged in saliva, whereas strong agglomeration of both aluminum nanoparticle species was observed at low pH in gastric fluid together with an increased ion release. The levels of free aluminum ions decreased in intestinal fluid and the particles deagglomerated, thus liberating primary particles again. Dissolution of nanoparticles was limited and substantial changes of their shape and size were not detected. The amounts of particle-associated phosphorus, chlorine, potassium, and calcium increased in intestinal fluid, as compared to nanoparticles in standard dispersion. Interestingly, nanoparticles were found in the intestinal fluid after addition of ionic aluminum. We provide a comprehensive characterization of the fate of aluminum nanoparticles in simulated gastrointestinal fluids, demonstrating that orally ingested nanoparticles probably reach the intestinal epithelium. The balance between dissolution and de novo complex formation should be considered when evaluating nanotoxicological experiments.

Microwave absorbing performance enhancement of Fe75Si15Al10 composites by selective surface oxidation

An excessively large dielectric constant is a challenge to improve the performances of the Fe-based absorbing material. Here, we propose a selective surface oxidation method to reduce the permittivity without sacrificing the permeability, by annealing under 5%H2—95%N2 (H2/N2). It is found that a thin layer of aluminum and silicon oxides formed on the surface of Fe75Si15Al10 particles during annealing in the range of 500–780 °C under H2/N2, thereby leading to an obvious decrease of permittivity of the Fe75Si15Al10 composite. According to Gibbs free energy, aluminum and silicon oxides are formed and iron oxides are reduced during annealing under H2/N2 at above 500 °C. Interestingly, the XPS result shows that the atomic ratio of Fe decreases significantly on the particle surface, which infers that the reduced Fe atoms diffuse to the interior of the particles. The surface oxide layer can protect the inner part of the alloy from further oxidation, which contributes to a high permeability. Meanwhile, the XRD result shows the formation of DO3-type ordering, which leads to the promotion of permeability. The two reasons lead to the improvement of permeability of the Fe75Si15Al10 composite after annealing. The composite is confirmed to have high permeability and low permittivity, exhibiting better electromagnetic wave absorption properties.

Clusia criuva Cambess. (Clusiaceae): anatomical characterization, chemical prospecting and antioxidant activity.

This study aims the anatomical description and chemical characterization of aerial parts of Clusia criuva Cambess., Clusiaceae in addition to the evaluation of the antioxidant activity of crude extracts, correlated to the flavonoid content. The morphological characterization was performed using traditional techniques of plant anatomy. For phytochemical studies, crude extracts were obtained by static maceration and analyzed by thin layer chromatography. The antioxidant activity and the flavonoids content were determined by colorimetric methods involving, respectively, 2,2-diphenyl-1-picrylhydrazyl free radical and aluminum chloride. C. criuva has uniseriate epidermis, paracytic stomata, hypostomatic leaves, cuticular flanges and cordiform vascular cylinder with accessory bundles. Chemical prospecting confirmed the abundant presence of terpenes and phenols in the extracts of leaves and of fruits. The methanolic extract of seeds showed the lowest EC50 value, but the methanolic extract of pericarps exhibited the highest maximum antioxidant activity. The results suggested a high percentage of flavonoids in the hexanic extract of pericarps, however, this could represent, in fact, the presence of benzophenones. Secretory ducts and the shape of the midrib are diagnostic for C. criuva. The antioxidant activity is not directly related to the flavonoids. The results indicate the importance of future studies with C. criuva chemical constituents.

&lt;i&gt;In vitro&lt;/i&gt; Antioxidant Activity in Seven Selected Local Ghanaian Spices and an Artificial Spice, Shrimp Cube

Many spices have been shown to have harmless sources of natural antioxidants and have been of great help in preventing the pathological effects caused by free radicals and their associated oxidative stress. The total antioxidant activity, total phenolic content and flavonoid content in ethanol extract of seven (7) local spices (clove, rosemary, anise seeds, calabash nutmeg, Ethiopian pepper, bayleaf and fermented African locust beans) and one artificial spice in Ghana; (shrimp cube) were determined in vitro by the 1, 1 diphenyl-2-picryl hydrazyl (DPPH) free radical scavenging assay, the Folin-Ciocalteau and aluminium chloride colorimetric methods respectively. The total phenolic content estimated for each spice decreased in the order clove > rosemary > bayleaf > anise seeds > calabash nutmeg > Ethiopian pepper > fermented African locust beans > shrimp cube with a statistically significant p- value of 0.003. The total flavonoid contents decreased significantly in the order clove >calabash nutmeg > rosemary > Ethiopian pepper > bayleaf > anise seeds > fermented African locust beans > shrimp cube (p= 0.002). The free radical scavenging activity of the spices also decreased significantly in the order clove > rosemary > bayleaf > anise seeds > Ethiopian pepper > calabash nutmeg > fermented African locust > shrimp cube (p=0.040). Statistically significant linear correlations were observed between total phenolic content and DPPH scavenging activity (r = 0.976, p=0.000) and flavonoid content and DPPH scavenging activity (r =0.693, p=0.003).These findings suggest that local plant-based spices are available sources of natural antioxidants than the shrimp cube. Of the seven local spices analysed, cloves had the highest antioxidant activity. Future studies should investigate the antioxidant activity of these spices in vivo.

A hybrid multiple damages detection method for plate structures

A hybrid method is proposed to properly identify multiple damages for plate structures in this work. In the stage of damage localization, singular value decomposition (SVD) is applied to reveal singularities in modal shapes, and hence to detect the damage locations. In the stage of damage quantification, based on the detected location information ant colony optimization (ACO) algorithm is introduced to estimate damage severity by searching for damage evaluation database, which reveals the relationship between the natural frequencies and the damage severity. The modal shapes and the natural frequencies required in damage localization and quantification are obtained via the wavelet finite element method. The numerical simulation and experimental investigation are carried out to test the performance of the hybrid method for free aluminum plates with multiple damages. And the results indicate that the proposed method is effective to identify multiple damages of plate structures with reasonable precision.

Superatoms: Electronic and Geometric Effects on Reactivity.

The relative role of electronic and geometric effects on the stability of clusters has been a contentious topic for quite some time, with the focus on electronic structure generally gaining the upper hand. In this Account, we hope to demonstrate that both electronic shell filling and geometric shell filling are necessary concepts for an intuitive understanding of the reactivity of metal clusters. This work will focus on the reactivity of aluminum based clusters, although these concepts may be applied to clusters of different metals and ligand protected clusters. First we highlight the importance of electronic shell closure in the stability of metallic clusters. Quantum confinement in small compact metal clusters results in the bunching of quantum states that are reminiscent of the electronic shells in atoms. Clusters with closed electronic shells and large HOMO-LUMO (highest occupied molecular orbital-lowest unoccupied molecular orbital) gaps have enhanced stability and reduced reactivity with O2 due to the need for the cluster to accommodate the spin of molecular oxygen during activation of the molecule. To intuitively understand the reactivity of clusters with protic species such as water and methanol, geometric effects are needed. Clusters with unsymmetrical structures and defects usually result in uneven charge distribution over the surface of the cluster, forming active sites. To reduce reactivity, these sites must be quenched. These concepts can also be applied to ligand protected clusters. Clusters with ligands that are balanced across the cluster are less reactive, while clusters with unbalanced ligands can result in induced active sites. Adatoms on the surface of a cluster that are bound to a ligand result in an activated adatom that reacts readily with protic species, offering a mechanism by which the defects will be etched off returning the cluster to a closed geometric shell. The goal of this Account is to argue that both geometric and electronic shell filling concepts serve as valuable organizational principles that explain a wide variety of phenomena in the reactivity of clusters. These concepts help to explain the fundamental interactions that allow for specific clusters to be described as superatoms. Superatoms are clusters that exhibit a well-defined valence. A superatom cluster's properties may be intuitively understood and predicted based on the energy gained when the cluster obtains its optimal electronic and geometric structure. This concept has been found to be a unifying principle among a wide variety of metal clusters ranging from free aluminum clusters to ligand protected noble metal clusters and even metal-chalcogenide ligand protected clusters. Thus, the importance of electronic and geometric shell closing concepts supports the superatom concept, because the properties of certain clusters with well-defined valence are controlled by the stability that is enhanced when they retain their closed electronic and geometric shells.

ALKALI AND POTASSIUM ALMATES ARE PERSPECTIVE HYDROGEN SUBSTITUTES

The statistical theory of phase transformations of the potassium alanate KAlH4 temperature decomposition leading to the formation of a more complex alanate K3AlH6 and potassium hydride KH and to further dehydrogenation of the latter with free hydrogen release, pure potassium and aluminum was developed on the basis of molecular-kinetic concepts. The free energies values of the decay phases are calculated, dependence of the decay phases and temperature, pressure, composition on metals, hydrogen concentration, activity of its atoms and energy parameters are found. Bialkaline alanates K2MAlH6 (M = Na, Li) and Na2LiAlH6 were also studied. A number of literary experimental graphs of the thermal decomposition processes for the alanates are given, from which the averaged values of the temperatures for the phase transformations are estimated. Plots of the free energies values of the phases at the different temperatures are plotted vs the concentration of hydrogen, the minima of which determine the equilibrium states. The possibility of two such minima appearance corresponding to the stable and metastable states of the phase is established. The temperature dependence of the equilibrium concentration for hydrogen was found, its specificity in the region of hydrogen concentration c = 0.5 was revealed. The graphs of the temperature dependence of free hydrogen releasing from each phase are obtained and such a graph for all chemical reactions of the alanate decomposition that occur also. On the latter one, fractures were found at the points of phase transitions, which can be experimentally manifested in the form of bends. Isotherms of hydrogen absorption-desorption processes and hydrogen content isoplets in phases are also constructed. The possibility of hysteresis effect is established. The results of calculations are compared with the experimental data, their qualitative correspondence is obtained.

Castability and mechanical properties of new 7xxx aluminum alloys for automotive chassis/body applications

To develop an aluminum alloy that combines excellent mechanical properties with good castability for near-net-shape casting of automotive structural parts, new Cu–free medium Mg 7xxx aluminum alloys with minor Zr (0.1%) and Ti (0, 0.1, and 0.2%) (all contents in wt% unless stated otherwise) elemental content were investigated as potential candidates. The effects of a vulnerable temperature interval and grain refinement on the hot tearing susceptibility (HTS) were investigated in this work to prevent hot tearing. Al–6Zn–(1.3–1.5)Mg–0.1Zr–(0.1–0.2)Ti alloys show 140–150% of ultimate tensile strength (370–390 MPa), 150–180% of elongation (10–12%), 60–80% of medium-thick-wall fluidity, and equivalent thin-wall fluidity, compared to the respective properties of the commercial A356 alloy. Medium-thick-wall fluidity depended on the heat release upon solidification of the alloy investigated, and thin-wall fluidity depended on the surface energy of the alloy in molten state. When the Ti content was increased, a concave variation in the medium-thick-wall fluidity and a monotonic increase in the thin-wall fluidity were observed. In terms of hot tearing, Ti addition led to a decrease in the HTS, which eventually reached zero. By adding 3% Si, hot tearing could be prevented; however, at the same time, elongation was found to decrease to less than 4%. The grain size reduction and morphology alteration due to the combined addition of 0.2% Ti and 0.1% Zr led to an improvement in castability because of a delay in crystal coherency, decrease in solidification time and vulnerable time period, and suppression of Fe-containing intermetallic and T phase crystallization.

Geological, geotechnical, and mechanical characterization of lateritic gravels from Eastern Cameroon for road construction purposes

Petrographic, mineralogical (X-ray diffraction), and chemical analyses performed on granite-derived lateritic gravels of the Nganke–Bonis road section show that those materials consist of quartz (26–41 wt%), kaolinite (30–41 wt%), goethite (10–14 wt%), hematite (9–11 wt%), and gibbsite (7–8 wt%). The values of the relative rock virtual weathering degree (30.03–43.12%), potential importance of free aluminum (18.85–19.57%), and potential importance of free ferric iron (18.65–23.08%) indicate that these materials are poorly to moderately altered, plastic, and clearly rupture under loading. The values of the silica/sesquioxide ratio (2.65–3.68 > 2) indicate that these lateritic gravels are suitable for use as sub-base layer materials. The geological data are corroborated by the results of geotechnical and mechanical tests on those materials: fine particles 18–30%, liquid limit 53–64%, plasticity index 22–32%, California bearing ratio 47–69%, uniaxial compressive strength 1.22–1.28 MPa, and tensile strength 0.80–0.84 MPa. A combination of 25–30 wt% of grain-fraction 5/20 granite aggregates (Los Angeles abrasion <30%) with 70–75 wt% of lateritic gravels provides concrete with California bearing ratio values of between 82 and 87, thus making the studied materials of Nganke–Bonis area suitable for use as base layers on roads ranging from Cameroon to the Central African Republic.

English

The free aluminum (Al) content in soil can reach levels that are toxic to plants, and this has frequently limited increased productivity of cultures. Four genes encoding nitrate reductase (NR) were identified, named ZmNR1&ndash;4. With the aim of evaluating NR activity and the transcriptional modulation of the ZmNR1, ZmNR2, ZmNR3, and ZmNR4 genes in leaves, 30-day-old hybrid maize BRAS 3010 plants were irrigated with a solution of Al2(SO4)3.18H2O for 16 days. The transcriptional levels of ZmNR2, ZmNR3, and ZmNR4 and NR activity will exhibit standard changes similar in the leaves, where, from the second week of stress onwards, there was a decrease in enzymatic activity and in the accumulation of transcripts. An increase ZmNR1 mRNA levels were observed, indicating that this gene may be associated with other metabolic pathways. This study resulted in the identification and characterization of different genes that encode NR and are involved in nitrogen metabolism in maize, in which the ZmNR2, ZmNR3, and ZmNR4 genes regulate the activity of NR in response to aluminum stress. The characterization of these genes may help in our understanding of the genetic-molecular and physiological mechanisms of maize subjected to aluminum stress. Key words: Abiotic stress, Al, gene expression, nitrogen, metal toxicity, mineral nutrition.

Evaluation of phosphorus sorption characteristics of soils from the Bambouto sequence (West Cameroon)

The evaluation of phosphorus sorption characteristics of soils and their relation to soil properties from the Bambouto sequence of Baranka 1, Baranka 2, Femock 1 and Femock 2 has been studied. Phosphorus, an essential plant nutrient, is often not readily available to plants and this deficiency tends to limit plant growth. It is thus, necessary to investigate the quantity that is readily available to plants in order to avoid excesses and reduce water pollution by fertilizers. The Freundlich, Langmuir, Temkin, Van Huay and Linear adsorption isotherms were used to describe the P adsorption processes. Phosphorus adsorption capacity decreased in the order Femock 2 &gt; Femock 1 &gt; Baranka 2 &gt; Baranka 1 with maximum adsorption values of 3464.21, 3112.17, 2866.00 and 2758.38 mg kg-1 respectively. Accuracy of fitness of data of the four soil series into the adsorption equations increased in the order Langmuir, Linear, Van Huay, Temkin and Freundlich isotherm. The capacity of each soil sample to adsorb phosphorus was significantly correlated with the clay content (r = 0.949*) of the soils. The use of organic materials and liming as a basis for phosphorus sorption reduction will be useful for crop production in the Bambouto sequence.© 2016 International Formulae Group. All rights reserved.Keywords: Phosphorus fixation, volcanic soil, free aluminium, clay, soil pH

Comparison of different phosphorous adsorption models in acid forest soils of Bityili (Southern – Cameroon) and their relationship with soil properties

This study was designed to compare the phosphorous fixation capacity of three soils series named Tyele, Minkonmingon and Mekoto in the south region of Cameroon and to determine the soil properties that are the main predictors of the P activity of those soils. Five adsorption equations viz. Linear, Langmuir, Van Huay, Freundlich and Temkin were used to describe P adsorption processes. The results of the study showed that maximum adsorbed P of Minkonmingon, Tyele and Mekoto was 936.09, 311.15 and 823.37 mg kg -1 of soils respectively with the mean of 690.20 mg kg -1 of soils. By applying various models, P adsorption data revealed that for low concentration range, the Freundlich equation show a better fit followed by the Langmuir, Van Huay, Temkin and Linear equations. It can be thus concluded from the adsorption and Spearman correlation analysis that the soil of Minkonmingon has a greater capacity to fix P followed by those of Mekoto and Tyele respectively with silt, exchangeable acidity, free aluminum, potassium and soil organic carbon and pH KCl being the main predictors of P activity in these soils. © 2016 International Formulae Group. All rights reserved. Keywords: Phosphorous fixation, adsorption isotherms, soil characteristics, correlation, acid soils, Cameroon

(Invited) Innovations in Ionic Liquids Electrodeposition of Metals

A novel pathway for the high energy efficiency electrodeposition of metals from metal oxides and metal compounds by means of electrolysis in ionic liquids at low temperatures was investigated. Experimental results for electrochemical deposition of Zn from ZnO and Cu from Cu2O, Pb from PbO using Urea ((NH2)2CO) and Choline chloride (HOC2H4N(CH3)3 +Cl-) or (ChCl) are discussed. The results showed that pure metal was deposited on the cathode. Successful deposition of metal from metal oxide dissolved in Urea/ChCl (2:1) was accomplished with efficiency greater than 87%. Electrodeposition of aluminium and titanium using imidazolium chloride ionic liquids with the addition of AlCl3 and TlCl4 were carried out at low temperatures. The cathode deposits obtained were dendrite free pure aluminium (>99.9% pure) and Al-Ti (up to 37 wt %) alloy. Cathode current densities of up to 500 A/m2for electrowinning of aluminium were achieved. The surface modification of electrodes not only improved the cathode current density but also eliminated the dendritic deposition of metals. Use of glassy surface finish, aluminum cathode and aluminum alloy anode improved the current density of the process. The critical cathode overpotential and limiting current density at which aluminum dendritic growth begins was determined as -0.53 V and 518 A/m2, respectively. Lower overpotentials (<0.42 V) prevent the dendrite formation in the aluminum deposits. It was concluded that the overpotential is the key in preventing dendrite formation. A 3-D mathematical model (CFD) was developed for the batch reactor electrodeposition of metals process. The optimum conditions for electrodeposition of metals and alloys were determined. The model results are in good agreement with the experimental data for the Al electrowinning process. The advantages of the electrodeposition of metals using ionic liquids compared to industrial aqueous metals processes are low temperature, low energy consumption, and low pollutant emissions.

GHz spurious mode free AlN lamb wave resonator with high figure of merit using one dimensional phononic crystal tethers

This letter reports a spurious mode free GHz aluminum nitride (AlN) lamb wave resonator (LWR) towards high figure of merit (FOM). One dimensional gourd-shape phononic crystal (PnC) tether with large phononic bandgaps is employed to reduce the acoustic energy dissipation into the substrate. The periodic PnC tethers are based on a 1 μm-thick AlN layer with 0.26 μm-thick Mo layer on top. A clean spectrum over a wide frequency range is obtained from the measurement, which indicates a wide-band suppression of spurious modes. Experimental results demonstrate that the fabricated AlN LWR has an insertion loss of 5.2 dB and a loaded quality factor (Q) of 1893 at 1.02 GHz measured in air. An impressive ratio of the resistance at parallel resonance (Rp) to the resistance at series resonance (Rs) of 49.8 dB is obtained, which is an indication of high FOM for LWR. The high Rp to Rs ratio is one of the most important parameters to design a radio frequency filter with steep roll-off.

Comparing Empetro nigri-Pinetum and Vaccinio uliginosi-Betuletum pubescentis soils in terms of organic matter stocks and ecochemical indices in the Słowiński National Park

Abstract We conducted comparative studies on soil organic matter stocks and indices of the soil’s ecochemical state under Empetro nigri-Pinetum (En-P) and Vaccinio uliginosi-Betuletum pubescentis (Vu-Bp) in the Słowiński National Park. The investigated plant communities are associated with Arenosols that developed from eolian sands and are exposed to high groundwater levels. The presence of fossil Histosol at a depth of 75 cm in the Vu-Bp stand, which lies below the current groundwater level, is the factor that sets both stands apart. The fossil soil strongly differs from Arenosol in terms of its chemical composition. A high abundance of nutrients in bioavailable forms in the soil is one of the reasons for natural renewal of downy birch in the stand, which presence in turn affects the turnover of elements and the properties of Arenosol. The results of our studies confirm the existence of strong feedback between the soil and plant communities. Soils under the mixed pine-birch Vu-Bp stand are characterized by smaller stocks of organic matter and total organic carbon (TOC) contained in the ectohumus as compared to the soils under the pure pine En-P stand. The opposite is found in the humic horizon. Additionally, in the Vu-Bp stand we observed greater accumulation of total nitrogen (TN) in ectohumus, which is reflected in lower TOC:TN ratios. The contents of TN and TOC:TN ratios in humic horizons were similar in both stands. The soils under En-P were more strongly acidified, especially in O-horizons. Mineral horizons in both stands were characterized by a very small sorptive capacity, which increased in ectohumus and fossil soil. Significant differences between the stands were observed in the ionic composition of sorptive complexes. The soils under Vu-Bp stand were more strongly saturated with basic cations, predominantly calcium. In soil solums of both stands, we observed a deficit of bioavailable potassium and magnesium, which was partially compensated by significant amounts of these components in ectohumus and fossil soil in the Vu-Bp stand. Despite a strongly acidic pH, molar Ca:Al ratios suggest that there are no phytotoxic effects due to free aluminium in ectohumus, while they are unlikely in mineral horizons. The risk of phytotoxic effects is reduced by the influx of calcium from groundwater.

A Novel Feature in Aluminum Cluster Photoionization Spectra and Possibility of Electron Pairing at T ≳ 100 K

A unique property of size-resolved metal nanocluster particles is their "superatom"-like electronic shell structure. The shell levels are highly degenerate, and it has been predicted that this can enable exceptionally strong superconducting-type electron pair correlations in certain clusters composed of just tens to hundreds of atoms. Here we report on the observation of a possible spectroscopic signature of such an effect. A bulge-like feature appears in the photoionization yield curve of a free cold aluminum cluster and shows a rapid rise as the temperature approaches ≈100 K. This is an unusual effect, not previously reported for clusters. Its characteristics are consistent with an increase in the effective density of states accompanying a pairing transition, which suggests a high-temperature superconducting state with Tc ≳ 100 K. Our results highlight the promise of metal nanoclusters as high-Tc building blocks for materials and networks.