Terms Of Stoichiometry Research Articles

MAPLE deposition of hybrid PLGA-Fe3O4- Cypress-PEDOT: PSS coatings

We report on the Matrix Assisted Pulsed Laser Evaporation, laser technology for depositing biocompatible, antimicrobial, hydrophilic, and biodegradable complex hybrid polymeric system loaded with essential cypress-oil and magnetite nanoparticles as resorbable implants, capable of targeting possible hyperthermia applications, an anticancer moderate field heating therapy. Magnetite nanoparticles based on iron oxide (Fe3O4) coated with Cypress essential oil (denoted: Fe3O4- Cypress) and embedded in PLGA (poly(lactic-co-glycolic acid) (denoted: PLGA-Fe3O4- Cypress-) and PLGA - poly(3,4-ethylene dioxythiophene) doped with poly(styrene sulfonate) anions) (PEDOT: PSS) mixture (denoted: PLGA-Fe3O4- Cypress- PEDOT: PSS) were used as MAPLE targets. The controlled drug delivery of the active Cypress oil, an antimicrobial therapeutic agent from Fe3O4- Cypress nanoparticles could be possible by applying an external radio frequency (RF) magnetic field. The Fe3O4-Cypress-based powders as well as the final hybrid coatings have been characterized in terms of stoichiometry, morphology, magnetic, antimicrobial properties, biocompatibility, and response to external physical stimuli. FTIR analyses confirmed the quasi-stoichiometric laser transfer of organic compounds while the XRD evidenced the semicrystalline structure of deposited thin films. SEM and AFM images evidence that conductive polymer addition led to the films' relief flattening and a decrease in the coatings' thickness and roughness by changing the polymeric packaging. The samples containing conductive polymer exhibited 3 times higher current and corrosion rate values. All coatings are hydrophilic and revealed enhanced cellular viability when cultured with osteoblast-like MG-63 cells. The composite structures exhibited significant antimicrobial activity against Gram-positive (Staphylococcus aureus), and Gram-negative (Escherichia coli) bacteria, as well as to the opportunistic yeast Candida albicans.

Differentiated Zn(II) binding affinities in animal, plant, and bacterial metallothioneins define their zinc buffering capacity at physiological pZn.

Metallothioneins (MTs) are small, Cys-rich proteins present in various but not all organisms, from bacteria to humans. They participate in zinc and copper metabolism, toxic metals detoxification, and protection against reactive species. Structurally, they contain one or multiple domains, capable of binding a variable number of metal ions. For experimental convenience, biochemical characterization of MTs is mainly performed on Cd(II)-loaded proteins, frequently omitting or limiting Zn(II) binding features and related functions. Here, by choosing 10 MTs with relatively well-characterized structures from animals, plants, and bacteria, we focused on poorly investigated Zn(II)-to-protein affinities, stability-structure relations, and the speciation of individual complexes. For that purpose, MTs were characterized in terms of stoichiometry, pH-dependent Zn(II) binding, and competition with chromogenic and fluorescent probes. To shed more light on protein folding and its relation with Zn(II) affinity, reactivity of variously Zn(II)-loaded MTs was studied by (5,5'-dithiobis(2-nitrobenzoic acid) oxidation in the presence of mild chelators. The results show that animal and plant MTs, despite their architectural differences, demonstrate the same affinities to Zn(II), varying from nano- to low picomolar range. Bacterial MTs bind Zn(II) more tightly but, importantly, with different affinities from low picomolar to low femtomolar range. The presence of weak, moderate, and tight zinc sites is related to the folding mechanisms and internal electrostatic interactions. Differentiated affinities of all MTs define their zinc buffering capacity required for Zn(II) donation and acceptance at various free Zn(II) concentrations (pZn levels). The data demonstrate critical roles of individual Zn(II)-depleted MT species in zinc buffering processes.

The impact of outgassing on the nano-oxides kinetics of ferritic oxide dispersion strengthened steel

Oxide Dispersion Strengthened (ODS) steels are studied for their application in fission and fusion nuclear power plants. These steels are processed by powder metallurgy involving a high energy milling of Fe-Cr with oxides powders, followed by outgazing and hot consolidation. The temperature increase during these last two stages triggers the precipitation of a fine dispersion of nano-oxides. The outgazing stage is generally conducted at temperature between 300 and 800 °C for several hours, which can already trigger the formation of nano-oxides, and thus may have an influence on the final nano-oxide characteristics. In this work we assess the nano-oxides size by Small Angle X-Ray Scattering (SAXS) and get insight on the nano-oxides chemical and structural properties by comparison between SAXS and Atom Probe Tomography (APT) during a thermal treatment at 700 °C for 5 h, simulating the outgazing stage. We show that despite that the nano-oxides slightly grow during the 700 °C heating, the final properties of the nano-oxides in term of size and number density are extremely close to those where no 700 °C isothermal was applied. Moreover, the growth rate of the nano-oxides is surprisingly higher at 700 °C than 1100 °C. APT and SAXS comparison shows that the nano-oxides do not stabilize in terms of stoichiometry and structure in the studied conditions, and that a small quantity of Al remain in the precipitates during this 700 °C isothermal treatment. Both of these factors could influence the nano-oxides kinetics at low temperature. • The outgazing shows no influence on the final nano-oxides size and number density. • No stabilization of the nano-oxides is observed at 700 °C after 5 h isothermal. • The nano-oxides growth rate is surprisingly higher at 700 °C than at 1100 °C. • Nano-oxides contains Al on the 700 °C isothermal, which is removed after heating at 1100°C. • TiC or Ti(C,N) is likely to form after the outgazing, between 700 and 1100 °C.

Solid State Synthesis of Aluminum Doped Li7La3Zr2O12 Garnet with Enhanced Thermal Processing Stability

Lithium lanthanum zirconium oxide garnet (LLZO) is a solid-state lithium ion conducting electrolyte being studied extensively for all-solid-state batteries (ASSB) owing to its high lithium conductivity and chemical stability against lithium metal anodes. This material, though useful, is highly sensitive to lithium stoichiometry in terms of crystalline stability and functional properties including conductivity. Stabilizing agents such as aluminum oxide and excess lithium are needed to preserve the cubic phase and compensate for lithium volatility during high temperature processing. Material engineering that allows LLZO to be fabricated with lower sensitivity to processing conditions is an important enabler in ultimate implementation of this material.Given the range of ceramic materials processing constraints such as ball milling, calcination, and sintering at temperatures above 1000oC, lithium volatility can drive deleterious phase formation. This study was designed to consider mechanisms that reduce the processing sensitivities of aluminum doped LLZO along its path to being utilized in a ceramic-manufacturing optimal ASSB. Processing sensitivities ameliorated via direct incorporation of excess lithium within LLZO lattice provides a key advantage towards the densification over topical additions of excess lithium precursors. By utilizing thermogravimetric analysis in conjunction with in-situ XRD analysis of solid state LLZO precursor synthesis the sensitivity of the LLZO cubic phase to lithium volatility can be reduced via early incorporation of excess lithium carbonate during initial formation. Details of in-situ phase evolution of LLZO from precursors were further clarified via temperature resolved mapping of diffraction patterns. The improved suppression of lithium volatilization has helpful implications for the scalable production of LLZO powders and assembly of ASSBs.

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Revealing phase evolution mechanism for stabilizing formamidinium-based lead halide perovskites by a key intermediate phase

Analysis of the drying process for precursors of Cu2ZnSn(S,Se)4 layers by low cost non vacuum fabrication technique

Cu2ZnSn(S,Se)4 solar cells were fabricated by a non-vacuum solution-based spin coating technique followed by annealing in selenium atmosphere without H2S treatment. The effects of the drying time after spin coating on physical and electrical properties of the cells were investigated. Structural and morphological properties were investigated by X-ray diffraction, Raman spectroscopy, energy dispersive X-ray analysis, atomic force microscopy and scanning electron microscopy. The physical properties, in terms of stoichiometry, crystal structure, morphology and orientation of the grains were shown to be influenced by the different drying times.Consequently, current–voltage characteristics show that the drying time of the precursors has a significant involvement in the device performance. The highest efficiency has been measured for 5 min drying time (with a 4.73% efficiency is obtained with Voc = 320 mV, Jsc = 28.6 mA/cm2 and FF = 52%), while samples with longer or shorter drying time have lower efficiencies. A further increase in efficiency, exceeding 5%, is obtained by inserting a contact grid on the front contact. Also accelerated stability tests (performed in a black box with one sun illumination at 80 °C) show different effects in light soaking, almost no degradation is observed for all the three cases. In this paper we highlight the connection of the different physical to the electrical properties generated just by the different drying times of the precursor for the CZTS absorbers.

Chemical evaluation of the quality of nanostructures synthesized on the surface of indium phosphide

Purpose: The article proposes a methodology for determining the chemical quality criterion of porous layers synthesized on the surface of semiconductors, based on taking into account the chemical parameters of the surface that can affect the properties of nanostructures. Design/methodology/approach: The chemical quality criterion was evaluated in terms of stoichiometry, stability of structures over time, uniformity of distribution over the surface, and the presence of an oxide phase. As an example, a calculation is demonstrated for the por-InP/InP structure synthesized on a mono-InP surface. The results of calculating the chemical quality criterion were evaluated using the Harrington scale to rank samples by quality level. Findings: A chemical criterion for the quality of porous layers synthesized on the surface of semiconductors has been developed. This criterion contains a set of indicators sufficient for a comprehensive assessment of the surface condition and is universal in nature. The studies carried out make it possible to reasonably approach the determination of the modes of electrochemical processing of semiconductors and open up new perspectives in the construction of a model of self-organization of a porous structure. Research limitations/implications: The chemical quality criterion does not allow evaluating the obtained nanostructures in terms of geometric parameters. Therefore, in the future, there is a need to develop a morphological quality criterion and determine a methodology for assessing a generalized quality criterion for nanostructures synthesized on the surface of semiconductors, which may include economic, environmental, technological indicators, and the like. Practical implications: Study results are expedient from a practical point of view, since they make it possible to reasonably approach the determination of the modes of electrochemical processing of semiconductors, synthesize nanostructures with predetermined properties, and create standard samples of nanomaterial composition.Originality/value: Methodology for assessing the quality of porous semiconductors by a chemical criterion has been applied for the first time in engineering science. The article will be useful to engineers, who are engaged in the synthesis of nanostructures, researchers and scientists, as well as specialists in nanometrology.

Flying Viruses - from Biophysical to Structural Characterization

Viruses affect basically all organisms on earth. Some are detrimental to human development, whereas those targeting pathogenic bacteria or crop pathogens can be beneficial for us. An integral part of icosahedral viruses is the capsid protein shell protecting the genome. Many copies of the capsid protein often self-assemble into shells of defined size. Low binding affinity of individual subunits allows efficient assembly and gives rise to highly stable particles. These capsids can be studied by native and hydrogen/deuterium exchange mass spectrometry (MS) in terms of stoichiometry, dynamics, assembly pathways and stability.

Translation machinery reprogramming in programmed cell death in Saccharomyces cerevisiae

Programmed cell death involves complex molecular pathways in both eukaryotes and prokaryotes. In Escherichia coli, the toxin–antitoxin system (TA-system) has been described as a programmed cell death pathway in which mRNA and ribosome organizations are modified, favoring the production of specific death-related proteins, but also of a minor portion of survival proteins, determining the destiny of the cell population. In the eukaryote Saccharomyces cerevisiae, the ribosome was shown to change its stoichiometry in terms of ribosomal protein content during stress response, affecting the relative proportion between ohnologs, i.e., the couple of paralogs derived by a whole genome duplication event. Here, we confirm the differential expression of ribosomal proteins in yeast also during programmed cell death induced by acetic acid, and we highlight that also in this case pairs of ohnologs are involved. We also show that there are different trends in cytosolic and mitochondrial ribosomal proteins gene expression during the process. Moreover, we show that the exposure to acetic acid induces the differential expression of further genes coding for products related to translation processes and to rRNA post-transcriptional maturation, involving mRNA decapping, affecting translation accuracy, and snoRNA synthesis. Our results suggest that the reprogramming of the overall translation apparatus, including the cytosolic ribosome reorganization, are relevant events in yeast programmed cell death induced by acetic acid.

Intraspecific variation in litter palatability to macroarthropods in response to grazing and soil fertility

Abstract Clarifying the functional consequences of intraspecific trait variability in response to interacting trophic levels would provide a significant improvement in our understanding of above‐ground–below‐ground linkages. In particular, the effects of grazing on plant traits may translate into altered litter quality, with potentially important consequences for litter‐feeding decomposers. Plant and litter variability in response to grazing is expected to depend on soil fertility levels, with tolerance and defensive strategies more commonly expressed on fertile and poorer soils, respectively. However, how grazing and fertility interactively alter litter quality and palatability to detritivores has not been explored yet. We conducted a cafeteria experiment with three common millipede (Diplopoda) species feeding on leaf litter from two plant species, the grass Bromopsis erecta and the forb Potentilla verna. Each millipede was offered a binary choice between litter types produced by the same plant species, but sampled in plots with distinct herbivory and fertilization status: litter originating from grazed areas or from 1‐year sheep exclosures, both in native areas and in adjacent paddocks that received chemical N and P fertilization, as well as litter from a 25‐year sheep exclosures in the native area. We found that fertilization and herbivore exclusion interactively affected Bromopsis litter quality and palatability, whereas Potentilla was much less affected. Bromopsis litter palatability was not affected by grazing when litter was collected in native plots, except for the long‐term exclosure which led to low palatability. In contrast, and in line with our expectations, herbivory was associated with much higher palatability in fertilized plots. The changes in palatability were associated with important alterations of litter quality. Overall, our study demonstrates that intraspecific variation in litter can have profound consequences for soil functioning. It emphasizes the role of grazing as a key, but plant species‐specific factor controlling litter intraspecific variability, and its complex interaction with soil fertility level. Moreover, our results advocate for a better understanding of the response of the different organisms involved in the decomposition process, in particular litter‐feeding macro‐detritivores. We encourage future studies aiming at disentangling the various and complex relationships between above‐ground processes such as herbivory and soil functioning.

PGE Mineralization of Massive Chromitites of the Iov Dunite Body (Northern Urals)

This work presents the results of the first comprehensive study of PGE mineralization from massive chromitites of the Iov dunite body (Northern Urals). The chromitites are composed of chromespinelides with a higher content of Cr2O3 with respect to those from other zonal clinopyroxenite–dunite massifs of the Urals. However, the composition of chromespinelides fits the trend that is characteristic of the dunite–clinopyroxenite–gabbro formation. PGE minerals, in particular Pt–Fe solid solutions, were identified in chromitites and in chromespinelides in the form of crystals and aggregates of a complex non-crystallographic habit and less often of an idiomorphic cubic habit. In terms of stoichiometry, Pt–Fe minerals correspond to ferroplatinum (Pt2Fe) and isoferroplatinum (Pt3Fe). The minerals of the isomorphic tetraferroplatinum–tulameenite–nickelferroplatinum series are widely distributed. Thus, the PGE mineralization of the Iov dunite body has features that are characteristic of clinopyroxenite–dunite massifs of the Urals.

Terbium chelation, a specific fluorescent tagging of human transferrin. Optimization of conditions in view of its application to the HPLC analysis of carbohydrate-deficient transferrin (CDT).

Transferrin (Tf) is the major iron-transporting protein in the human body and, for this reason, has been extensively studied in biomedicine. This protein undergoes a complex glycosylation process leading to several glycoforms, some of which are important in the diagnosis of alcohol abuse and of congenital glycosylation defects under the collective name of carbohydrate-deficient transferrin (CDT). Exploiting the Tf ability to bind not only iron but also other ions, specific attention has been devoted to binding activity towards Tb3+, which was reported to greatly enhance its intrinsic fluorescence upon the interaction with Tf. However, the structural properties of the Tb3+-Tf complex have not been described so far. In the present work, the formation of the Tf-Tb3+ complex has been investigated by the employment of several biophysical techniques, such as fluorescence resonance energy transfer (FRET), "native" mass spectrometry (MS), and near-UV circular dichroism (CD). Each method allowed the detection of the Tf-Tb3+ complex, yielding a specific signature. The interaction of Tb3+ with Fe3+-free Tf (apoTf) has been described in terms of stoichiometry, affinity, and structural effects in comparison with Fe3+. These experiments led to the first direct detection of the Tf-Tb3+ complex by MS, indicating a 1:2 stoichiometry and allowing the investigation of structural effects of metal binding. Either Tb3+ or Fe3+ binding affected protein conformation, inducing structural compaction to a similar extent. Nevertheless, near-UV CD and pH-dependence profiles suggested subtle differences in the coordination of the two metals by Tf side chains. Experimental conditions that promote complex formation have been identified, highlighting the importance of alkaline pH and synergistic ions, such as carbonate. On the basis of these studies, sample pretreatment, separation, and detection conditions of a high-performance liquid chromatographic method for CDT analysis are optimized, achieving relevant increase (by a factor of ∼3) of analytical sensitivity. Graphical abstract Schematic representation of HPLC-separated transferrin glycoforms detected by fluorescence emission of the terbium ions bound to the protein.

Effects of spatially restricted Ni nanocrystals within ordered mesopores on the production of syngas

Ordered mesoporous silica (OMS) materials such as SBA-15, MSU-H, KIT-6, and MSU-F were utilized as catalyst supports for the catalytic partial oxidation of methane (CPOM) to produce syngas and hydrogen. The 2-D hexagonal ordered mesoporous structure was found to play a crucial role in evenly distributing Ni nanocrystals during the preparation. The OMS supports also helped maintain the position and size of the Ni nanocrystals even after partial oxidation at elevated temperatures. Various characterization techniques were utilized to assess the catalytic performance as well as to investigate the deactivation phenomena. The 2-D hexagonal and 3-D bicontinuous OMS-supported catalysts were found to have great resistance against carbon deposition. In addition, the 2-D hexagonal mesostructured catalysts showed greater resistance against sintering than other OMS-supported and the conventional refractory material-supported catalysts. Under oxygen deficient conditions in terms of stoichiometry, the OMS-supported Ni catalysts were shown to be less deactivated and more resistant against coke formation compared with Ni catalysts with conventional refractory materials.

陕西省3种主要树种叶片、凋落物和土壤N、P化学计量特征

PDF HTML阅读 XML下载 导出引用 引用提醒 陕西省3种主要树种叶片、凋落物和土壤N、P化学计量特征 DOI: 10.5846/stxb201507171508 作者: 作者单位: 西北农林科技大学林学院,西北农林科技大学黄土高原土壤侵蚀与旱地农业国家重点实验室,西北农林科技大学黄土高原土壤侵蚀与旱地农业国家重点实验室,西北农林科技大学林学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目（41201088，41371506）；中国科学院西部之光资助项目（K301021304）；中国科学院陕西省森林固碳现状、速率和潜力研究（XDA05050203-05） N and P stoichiometric characteristics of leaves, litter, and soil for three dominant tree species in the Shaanxi Province Author: Affiliation: College of Forestry,Northwest ADdDdF University,Yangling,Shaanxi,Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources,Yangling,Shaanxi,Institute of Soil and Water Conservation,Chinese Academy of Sciences and Ministry of Water Resources,Yangling,Shaanxi, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以陕西省29个县（市）39个样点的刺槐、辽东栎和油松林为研究对象，分析比较不同树种乔木叶片、凋落物与土壤N、P化学计量特征及其与经纬度、海拔、年均温度和年降水等环境因子间关系的异同以及三者之间可能存在的关系，以期为认识陕西省主要森林树种养分限制状况、制定合理的植被管理和恢复措施提供理论依据。结果表明：3树种叶片N、P含量及比值均为刺槐 > 辽东栎 > 油松，与叶片相比，凋落物中N、P含量变化幅度较小，为刺槐 > 辽东栎 > 油松，N：P比值为油松 > 辽东栎 > 刺槐。10-20 cm与0-10 cm土层相比，3树种中除辽东栎中P含量差异不显著外，其它指标N、P含量及N：P比值均显著下降（P < 0.05）。刺槐、辽东栎和油松叶片N、P含量与土壤N、P含量均没有显著相关性，以刺槐、辽东栎和油松3种植物叶片为总体来说，P含量与土壤P含量显著正相关（P < 0.05）。叶片N、P含量均大致表现出随着年均温度和年降水的增加而增加，随着经纬度的增加而降低的趋势，这一点在刺槐叶中最为明显。凋落物N含量随着年均温度和年降水的增加而增加，随着纬度和经度的增加而降低；P含量随着年降水和经度的增加而降低；N：P比值随着年均温度和年降水的增加而增加，随着纬度的增加而降低。研究区内，土壤N、P含量随着纬度、海拔的增加和年均温度、年降水、经度的降低而增加，N：P比值则呈相反的趋势。3树种土壤N、P含量及N：P比值中，P含量比N含量受环境影响更大，且0-10 cm和10-20 cm土层N、P含量及N：P比值与各环境因子的关系基本一致。 Abstract:Plant nutrient stoichiometry can be used to distinguish the biological entities based on element composition and responses to environmental factors. We determined the N and P stoichiometry for leaves, litter, and soil associated with 3 dominant tree species:Robinia pseucdoacacia, Quercus liaotungensis, and Pinus tabulaeformis, at 39 sites in 29 county-level cites of the Shaanxi Province. We aimed to distinguish the differences in leaf, litter, and soil N and P stoichiometry among the different tree species, and their relationships with environmental factors in the Shaanxi Province. Leaf N and P concentrations and their ratios, were Robinia pseucdoacacia > Quercus liaotungensis > Pinus tabulaeformis. Compared with plant leaves, the range and quantity of litter N and P concentration significantly reduced (P < 0.05), and the order was still Robinia pseucdoacacia > Quercus liaotungensis > Pinus tabulaeformis, while the order for the N:P ratio was Pinus tabulaeformis > Quercus liaotungensis > Robinia pseucdoacacia. There were no significant correlations (P < 0.05) between Robinia pseucdoacacia, Quercus liaotungensis, and Pinus tabulaeformis leaf N (or P) and soil N (or P), indicating that their growth was not limited by N or P. In total, there were significant correlations between leaf P and soil P (P < 0.05), which indicated that the growth of the plant was limited by P in the Shaanxi Province. Leaf N and P increased with mean annual temperature and precipitation, especially for Robinia pseucdoacacia. The leaf N:P ratio for the 3 tree species did not clearly correlate with the environmental factors. Litter N increased with mean annual temperature and precipitation, and decreased depending on the latitude and longitude. Although litter P showed no significant relationships with temperature and latitude (P < 0.05), it declined with precipitation and longitude. Litter N:P ratio increased with temperature and precipitation and decreased with latitude. Soil N and P increased with latitude and altitude, and decreased with mean annual temperature, mean annual precipitation, and longitude. The soil N:P ratios demonstrated an opposite trend. Soil P was more closely correlated with environmental factors than N, and the relationship between the 0-10 cm and 10-20 cm N and P stoichiometry in terms of environmental factors was almost the same. 参考文献 相似文献 引证文献

Characterization of RF sputtered thin film potassium sodium niobate (KNN) with silicon and nickel electrodes

A low cost recipe for thin film deposition of Potassium Sodium Niobate, (Na,K)NbO3 (KNN) is pursued. The use of expensive noble metals as electrodes was avoided and instead highly doped silicon was used for both the structural layer and the bottom electrode. Nickel was used for the top electrode. In order to evaluate the outcome, the films were studied in terms of stoichiometry, crystal structure and leakage current density. RF sputtering of thin films of KNN at room temperature was successfully done. Proper crystal structure (Perovskite structure) was achieved after post deposition annealing. Though the leakage current density exhibited high dependency on the polarity of the applied voltage, a leakage current density of 1 × 10ź6 A/cm2 at 100 kV/cm was measured. A stoichiometry study revealed that the relative ratio of the volatile elements (Na and K) in the samples was within the acceptable range, however, a total loss of about 25---33ź% was observed.

Generating functions for stoichiometry and structure of single- and double-layer sheet-silicates

AbstractTwo-dimensional nets may be used to generate the stoichiometry and structure of single-layer and double-layer sheet-silicate minerals. Many sheet-silicate minerals are based on the 3-connected plane nets 63, 4.82, (4.6.8)2(6.82)1and (52.8)1(5.82)1, and some more complicated nets, e.g. (5.6.7)4(5.72)1(62.7)1, (4.122)2(42.12)1, (52.8)1(5.62)1(5.6.8)2(62.8)1,have one or two representative structures. Many complicated sheet-silicate minerals are based on sheets of 2-, 3- and 4-connected tetrahedra that may be developed from 3- and 4-connected plane nets by a series of oikodoméic operations on 3- or 4-connected nets that change the topologyof the parent net. There are three classes of oikodoméic operations: (1) insertion of 2- and 3-connected vertices into 3- and 4-connected plane nets; (2,3) replication of single-layer sheets by topological mirror or two-fold-rotation operators, and condensation of the resulting twosingle-layer sheets to form double-layer sheets. The topological aspects of these sheet structures may be described by functions that express stoichiometry in terms of tetrahedron connectivities (formula-generating functions) and functions that associate these formula-generating functionswith specific two-dimensional nets. Using these functions, we may generate formulae and structural arrangements of single-layer and double-layer silicate structures with specific local and long-range topological features.

Plant fertilization interacts with life history: variation in stoichiometry and performance in nettle-feeding butterflies.

Variation in food stoichiometry affects individual performance and population dynamics, but it is also likely that species with different life histories should differ in their sensitivity to food stoichiometry. To address this question, we investigated the ability of the three nettle-feeding butterflies (Aglais urticae, Polygonia c-album, and Aglais io) to respond adaptively to induced variation in plant stoichiometry in terms of larval performance. We hypothesized that variation in larval performance between plant fertilization treatments should be functionally linked to species differences in host plant specificity. We found species-specific differences in larval performance between plant fertilization treatments that could not be explained by nutrient limitation. We showed a clear evidence of a positive correlation between food stoichiometry and development time to pupal stage and pupal mass in A. urticae. The other two species showed a more complex response. Our results partly supported our prediction that host plant specificity affects larval sensitivity to food stoichiometry. However, we suggest that most of the differences observed may instead be explained by differences in voltinism (number of generations per year). We believe that the potential of some species to respond adaptively to variation in plant nutrient content needs further attention in the face of increased eutrophication due to nutrient leakage from human activities.

Probing the Minimum Geometric Requirements for T-Cell Stimulation

The immune recognition process involves an elaborate arrangement of adhesion, costimulatory and signaling molecules organized into a stereotypic geometric structure known as the immunological synapse (IS). We have developed a versatile engineered platform to probe the minimum geometric requirements (in terms of spacing and stoichiometry) for T-cell stimulation. Arrays of metallic nanodots, ∼ 2-10 nm in size, to which a UCHT1 Fab antibody was bound, were created by nanolithography. These served as individual T-cell receptor (TCR) binding sites. The adhesion molecule ICAM-1 was either statically bound to a PEG-silane brush surrounding the nanodots, or it was allowed to move freely within the arrays in a supported lipid bilayer. T-cells were plated on arrays comprising individual TCR binding sites, small clusters and extended hexagonal close packed arrays, with spacings ranging from 40 nm and below to 1 μm. TCR signaling strength was monitored by measuring phosphorylated tyrosine (pY) intensity. T-cell adhesion was assessed by the number of cells bound to the arrays, as well as by the area of spread cells.Systematic variation of the spacing and cluster size of TCR binding sites in the arrays enabled determination of the minimum conditions that support T-cell signaling and the formation of the IS. TCR signaling increased with decreasing spacing below a threshold spacing ∼ 60 nm. For clusters with these spacings the formation of the stereotypic “bullseye” geometry that characterizes the immune synapse became evident, with ICAM-1 excluded to the periphery. In terms of stoichiometry, at least 4 TCR-binding sites (within ∼ 60 nm) were required for T-cell adhesion and spreading. Further, in the absence of ICAM-1 (or at low concentrations), a threshold density of agonist sites was found, above which the TCR apparently plays a dual role of immune activity and adhesion.

Sodium intercalation chemistry in graphite

The solvated-Na-ion intercalation in graphite is investigated in terms of stoichiometry, staging structure, and solvated ion configuration using combined experimental and theoretical studies.

Microbial respiration per unit biomass increases with carbon-to-nutrient ratios in forest soils

The ratio of carbon-to-nutrient in forest floors is usually much higher than the ratio of carbon-to-nutrient that soil microorganisms require for their nutrition. In order to understand how this mismatch affects carbon (C) cycling, we investigated the respiration rate per unit soil microbial biomass – the metabolic quotient (qCO2) – in relation to the soil carbon-to-nitrogen (C:N) and carbon-to-phosphorus (C:P) ratio in temperate forests. For this purpose, cores of beech, spruce, and mixed spruce-beech forest soils were cut into slices of 1 cm from the litter layer down to 5 cm in the mineral soil, and the relationship between the qCO2 and the soil C:N and the soil C:P ratio was analyzed. We found that the qCO2 was positively correlated with soil C:N ratio in spruce soils (R = 0.72), and with the soil C:P ratio in beech (R = 0.93), spruce (R = 0.80) and mixed forest soils (R = 0.96). We also observed a close correlation between the qCO2 and the soil C concentration in all three forest types. Yet, the qCO2 decreased less with depth than the C concentration in all three forest types, suggesting that the change in qCO2 is not only controlled by the soil C concentration. We conclude that microorganisms increase their respiration rate per unit biomass with increasing soil C:P ratio and C concentration, which adjusts the substrate to their nutritional demands in terms of stoichiometry.