Challenge For Experimentalists Research Articles

Enhancing the reactivity of carbon-nanotube for carbon monoxide detection by mono- and co-doping of boron and nitrogen heteroatoms: A DFT and TD-DFT study

Carbon nanotube (CNT) doped with boron (p-type) and nitrogen (n-type) atoms (BxNy@CNT) have attracted the attention of many experimental and theoretical researchers for variety of industrial applications such as catalytic processes in fuel cells and detection of environmental pollutants. BxNy@CNTs can be synthesized with different concentrations (i.e. x/y ratios) and various configurations (i.e. relative position of B to N atoms), and therefore, BxNy@CNTs show an unpredictable reactivity in physical and chemical reactions. Hence, the selection of an appropriate BxNy@CNTs combination to achieve the most efficiency for a specific application is a challenge for experimentalists. In this regard, herein, we investigated theoretically different combinations of BxNy@CNT (x, y = 0, 1), i.e. single doped boron (B@CNT) and nitrogen (N@CNT) along with multi-doped boron and nitrogen BN@CNT, in three ortho, meta and para-BN@CNT configurations for detection and removing of monoxide carbon (CO) as a diatomic toxic gas. Theoretical calculations were done based on the quantum calculations in DFT and TD-DFT levels of theory using M06-2X (and B3LYP-D3)/6-31+G(d,p) functional/basis set. We focused on variations in electrical (useable for electronic based nano-sensor devices) and optical (useable for optical based nano-sensor devices) properties after adsorption of CO gas. Results indicate that, compared to the other combinations, co-doping of boron in para position relative to nitrogen (para-BN@CNT) can significantly activate the inert-CNT toward CO sensing. Theoretical results of this work can help experimental scientists in the synthesis and selection of the appropriate BxNy@CNT combinations for applying in nanotube based nano-sensors.

A general way of analyzing EPR spectroscopy for a pair of magnetically equivalent lanthanide ions in crystal: A case study of BaY2F8:Yb3+ crystal

Electron paramagnetic resonance (EPR) is an important tool to study the complex interactions (e.g., exchange and magnetic dipole-dipole interactions) for a pair of lanthanide (Ln) ions in crystals. How to analyze these EPR spectra and obtain the strength of each interaction is a challenge for experimentalists. In this work, a general way of calculating the EPR lines for two magnetically equivalent Ln ions is given by us to solve this problem. In order to explain their EPR spectra and obtain exchange interaction parameters Ji (i = x, y, z) between them, we deduce the analytic formulas for computing the angular dependent EPR lines for such Ln pairs under the condition of weak coupling (|Ji| ≪ hv, where v is the microwave frequency in the EPR experiment) and set up the spin-Hamiltonian energy matrix that should be diagonalized to obtain these lines if intermediate (|Ji| ∼ hv) and strong (|Ji| > hv) couplings are encountered. To verify our method, the experimental EPR spectra for the Yb3+ doped BaY2F8 crystal are considered by us and the EPR lines from the isolated Yb3+ ion and Yb3+-Yb3+ pair with distance R equal to 0.371 nm are identified clearly. Moreover, exchange interaction parameters (Jx ≈ –0.04 cm–1, Jy ≈ –0.24 cm–1, and Jz ≈ –0.1 cm–1) for such a pair are also determined by our calculations. This case study demonstrates that the theoretical method given in this work would be useful and could be applied to understand interactions between Ln ions in crystals.

Two-dimensional hexagonal smectic structure formed by topological defects.

A two-dimensional hexagonal smectic structure formed by point topological defects and intersecting defect walls was discovered. This unique structure was predicted theoretically about 30 years ago but not observed. For a long time the hexagonal structure was a challenge for experimentalists. A different type of self-organization in smectic films was found and used to form the hexagonal structure. Methods applied for building the hexagonal phase can be used for the formation of complicated liquid-crystal structures.

Carbodiphosphorane Analogues E(PPh3)2 with E=C–Pb: A Theoretical Study with Implications for Ligand Design

Quantum-chemical calculations at the BP86/TZVPP level have been carried out for the heavy Group 14 homologues of carbodiphosphorane E(PPh(3))(2), where E=Si, Ge, Sn, Pb, which are experimentally unknown so far. The results of the theoretical investigation suggest that the tetrelediphosphoranes E(PPh(3))(2) (1E) are stable compounds that could become isolated in a condensed phase. The molecules possess donor-acceptor bonds Ph(3)P→E←PPh(3) to a bare tetrele atom E, which retains its four valence electrons as two electron lone pairs. The analysis of the bonding situation and the calculation of the chemical reactivity indicate that the molecules 1E belong to the class of divalent E(0) compounds (ylidones). All molecules 1C-1Pb have very large first but also very large second proton affinities, which distinguishes them from the N-heterocyclic carbene homologues, in which the donor atom is a divalent E(II) species that possesses only one electron lone pair. Compounds 1E are powerful double donors that strongly bind Lewis acids such as BH(3) and AuCl in the complexes 1E(BH(3))(n) and 1E(AuCl)(n) (n=1, 2). The bond dissociation energies (BDEs) of the second BH(3) and AuCl molecules are only slightly less than the BDE of the first BH(3) and AuCl. The results of this work are a challenge for experimentalists.

Comparing observed and modelled growth of larval herring (<i>Clupea harengusz</i>): Testing individual-based model parameterisations

Experiments that directly test larval fish individual-based model (IBM) growth predictions are uncommon since it is difficult to simultaneously measure all relevant metabolic and behavioural attributes. We compared observed and modelled somatic growth of larval herring ( Clupea harengus ) in short-term (50 degree-day) laboratory trials conducted at 7 and 13°C in which larvae were either unfed or fed ad libitum on different prey sizes (~100 to 550 µm copepods, Acartia tonsa ). The larval specific growth rate (SGR, % DW d -1 ) was generally overestimated by the model, especially for larvae foraging on large prey items. Model parameterisations were adjusted to explore the effect of 1) temporal variability in foraging of individuals, and 2) reduced assimilation efficiency due to rapid gut evacuation at high feeding rates. With these adjustments, the model described larval growth well across temperatures, prey sizes, and larval sizes. Although the experiments performed verified the growth model, variability in growth and foraging behaviour among larvae shows that it is necessary to measure both the physiology and feeding behaviour of the same individual. This is a challenge for experimentalists but will ultimately yield the most valuable data to adequately model environmental impacts on the survival and growth of marine fish early life stages.

Ab Initio Study of Molecular Properties and Decomposition Products of 1-AzidoalkynesA Challenge for Experimentalists

In this publication, a characterization of different azidoalkyne compounds using high-level ab initio quantum chemical methods is presented. For this purpose, the molecular structures and the 13C NMR chemical shifts have been calculated at the MP2 and CCSD(T) level of theory and the influence of zero-point vibration as well as the solvent on the chemical shifts are discussed. Furthermore, a comparison of the energy barriers of the decomposition under N2 separation for a set of 1-azidoalkynes with different functional groups has been carried out. The molecular structures and properties of the resultant decomposition products have been investigated. It is remarkable that large deviations of the NMR chemical shifts of ethylthioethynyl azide occur in comparison to the experiment. These deviations are far outside of the error bars. Electron correlation effects are of high importance if an accurate description of the chemical shifts of 1-azidoalkynes shall be obtained. A comparison of the energy barriers of the decomposition under N2 separation of 1-azidoalkynes with different functional groups indicates that the stability of 1-azidoalkynes is not increased by typical donor or acceptor groups but rather by silyl or phenyl substituents. The molecular geometries of the decomposition products indicate that the equilibrium structures are of carbene character. Some of the results presented here are in contradiction to previous experimental publications and cast a new light on some open challenges for experimentalists.

A panorama of lineage‐specific transcription in hematopoiesis

The hematopoietic system consists of more than ten differentiated cell types, all of which are derived from a single type of hematopoietic stem cell. The accessibility and interest of this system have made it a model for understanding normal and abnormal differentiation of mammalian cells. Newer techniques have generated a mass of data that requires integrative approaches for analysis and interpretation. The traditional view of the differentiation program holds that a small number of regulators are involved in each stage of cell specification. However, this may not be the case. Recent analyses have shown that almost all substantial subsets of genes, including the set of broadly expressed transcription factors, are expressed in patterns that are unique for each lineage. Further, much of this difference between lineages can be captured in two-dimensional graphs. Understanding the biologic significance, mechanisms and constraints underlying these differences is a challenge for experimentalists and computational biologists alike.

From Opals to Optics: Colloidal Photonic Crystals

Over a decade ago, theorists predicted that photonic crystals active at visible and near-infrared wavelengths would possess a variety of exciting optical properties. Only in the last several years, however, have experimentalists begun to build materials that realize this potential in the laboratory. This lag between experiment and theory is primarily due to the to the challenges associated with fabricating these unique materials. As the term “crystal” suggests, these samples must consist of highly perfect ordered arrays of solids. However, unlike conventional crystals, which exhibit order on the angstrom length scale, photonic crystals must have order on the submicrometer length scale. In addition, many of the most valuable properties of photonic crystals are only realized when samples possess a “full” photonic bandgap. For such systems, large dielectric contrasts and particular crystal symmetries create a range of frequencies over which light cannot propagate. Realizing the nanoscopic architectures required to form such systems is a challenge for experimentalists. As a result, fabrication schemes that rely on lithographic techniques or spontaneous assembly have been a focus in the development of the field.