Substitution and atomic extension on greedy posets

In this paper, we study the operations of substitution and atomic extension on greedy posets. For the substitution operation, if P=(P ₁ , x, P ₂ )is a greedy poset, then P ₁ and P ₂ are greedy posets, the converse being false. However, for the atomic extension, P=P ₁ (x, P ₂ )is a greedy poset if and only if P ₁ and P ₂ are greedy posets. We prove also that the class of greedy semi-partitive lattices is the smallest one containing M _n (n2), B ₃ and closed by atomic extension. The class C _n of greedy posets with jump number n is infinite. However, we show that C _n can be obtained, in a very simple way, from a subclass D _n of finite cardinal ity. We construct D _n for n=1, 2.     

In situ observation of the internal structure and composition of biomineralized Emiliania huxleyi calcite by solid-state NMR Spectroscopy

Biomineralization, particularly the formation of calcium carbonate structures by organisms under ambient conditions, is of vast fundamental and applied interest. Organisms finely control all aspects of the formation of the biomaterials: composition, polymorph, morphology, and macroscopic properties. While in situ molecular-level characterization of the resulting biominerals is a formidable task, solid-state magic angle spinning NMR is one of the most powerful analytical techniques for this purpose. It is employed in this study to elucidate the structure and composition of biogenic calcite formed by Emiliania huxleyi, a unicellular alga distinguished by its exquisitely sculptured calcite cell coverings known as coccoliths. Strain 371 (CCMP) was grown and harvested from (15)N- and (13)C-enriched growth medium, with biosynthetic labeling to enhance the sensitivity of the NMR measurements. Crystalline and interfacial calcite environments were selectively probed using direct and indirect (cross-polarized) (13)C excitation, respectively. Different crystalline environments, in particular structural defect sites at concentrations of up to 1.4% with P and N moieties incorporated, were identified using (13)C rotational-echo double-resonance (REDOR) NMR. REDOR-derived geometrical constraints show that the P and N atoms at the defect sites are 3.2 and 2.3 (+/-0.2) A apart from a crystalline carbon carbonate. The phosphorus and nitrogen moieties within the biogenic calcite are identified as small, non-protonated moieties, attributed to inorganic ions such as PO4(3-) and NO3(-). The carbonates adjacent to these defects are chemically indistinguishable from bulk crystalline carbonates, yet their immediate environments experience reduced rigidity, as reflected by substantial T1((13)CO3(2-)) shortening. Interfacial carbonates, on the other hand, reside in structurally/chemically perturbed environments, as reflected by heterogeneous line broadening. This study is the first to directly unravel evidence on the incorporation of P/N moieties as structural defects within E. huxleyi biogenic calcite, and on the state of the adjacent crystalline carbonates.     

A DNAzyme cascade for the amplified detection of Pb(2+) ions or L-histidine

DNAzyme cascades activated by Pb(2+)- or L-histidine-dependent DNAzymes yield the horseradish peroxidase-mimicking catalytic nucleic acids that enable the colorimetric or chemiluminescence detection of Pb(2+) or L-histidine.     

A design of a two-dimensional,supersonic KH experiment on OMEGA-EP

An experiment meant to investigate the evolution of single mode Kelvin–Helmholtz (KH) instability in the supersonic regime is presented and theoretically analyzed. This experiment is intended to provide a direct measurement of the two-dimensional vortex evolution so that the high-Mach-number effects can be measured. The proposed design takes advantage of the ability of OMEGA-EP to drive experiments for up to 30 ns to produce steady conditions for KH that endure long enough to observe substantial growth. KH growth for the proposed design has been analyzed using two-dimensional numerical simulations. The results were compared to synthetic temporal KH numerical simulations using non-dimensional scaling in the low and high Mach number regime. The comparisons show that the growth in the high Mach number regime is expected to be suppressed by up to a factor of two. The effects of two-dimensional rarefactions from the lateral boundaries of the experimental system were also investigated. It was found that they introduce no major uncertainties or hazards to the experiment. We produced simulated radiographs, which show that the proposed experimental system will enable observation of the KH structures. An experiment of this kind has not yet been performed, and therefore would serve to validate numerical results and analytical models presented here and in the literature.     

Combustion behavior of ammonia blended with diethyl ether

Ammonia (NH₃) is recognized as a carbon-free hydrogen-carrier fuel with a high content of hydrogen atoms per unit volume. Recently, ammonia has received increasing attention as a promising alternative fuel for internal combustion engine and gas turbine applications. However, the viability of ammonia fueling future combustion devices has several barriers to overcome. To overcome the challenge of its low reactivity, it is proposed to blend it with a high-reactivity fuel. In this work, we have investigated the combustion characteristics of ammonia/diethyl ether (NH₃/DEE) blends using a rapid compression machine (RCM) and a constant volume spherical reactor (CVSR). Ignition delay times (IDTs) of NH₃/DEE blends were measured using the RCM over a temperature range of 620 to 942 K, pressures near 20 and 40 bar, equivalence ratios (Φ) of 1 and 0.5, and a range of mole fractions of DEE, χ_DEE, from 0.05 to 0.2 (DEE/NH₃ = 5 – 20%). Laminar burning velocities of NH₃/DEE premixed flames were measured using the CVSR at 298 K, 1 bar, Φ of 0.9 to 1.3, and χ_DEE from 0.1 to 0.4. Our results indicate that DEE promotes the reactivity of fuel blends resulting in significant shortening of the ignition delay times of ammonia under RCM conditions. IDTs expectedly exhibited strong dependence on pressure and equivalence ratio for a given blend. Laminar burning velocity was found to increase with increasing fraction of DEE. The burnt gas Markstein length increased with equivalence ratio for χ_DEE = 0.1 as seen in NH₃-air flames, while the opposite evolution of Markstein length was observed with Φ for 0.1 < χ_DEE ≤ 0.4, as observed in isooctane-air flames. A detailed chemical kinetics model was assembled to analyze and understand the combustion characteristics of NH₃/DEE blends.     

Diagram approach to character formulas for finite and compact groups

Some basic relations for the representation theory and the Wigner–Racah algebra of a finite or compact continuous group are discussed and transcribed in terms of diagrams. Special emphasis is placed on the case of a simply reducible group and all the diagrams are applicable to SU₂ without any change.