Die Diazobenzolreaction des Harns

Ohne Zusammenfassung     

Many-body potential for point defect clusters in Fe-C alloys

Modeling the consequences of crystalline defects requires efficient interaction sampling. Empirical potentials can identify relevant pathways if the energetics and configurations of competing defects are captured. Here, we develop such a potential for an alloy of arbitrary point defect concentration, body-centered cubic alpha-Fe supersaturated in C. This potential successfully calculates energetically favored defects, and predicts formation energies and configurations of multicarbon-multivacancy clusters that were not attainable with existing potentials or identified previously via ab initio methods.     

PLIF imaging of mean temperature and pressure in a supersonic bluff wake

 Planar laser-induced fluorescence (PLIF) of seeded nitric oxide was used to obtain mean 2-D temperature and pressure fields in the near-wake region of a thick flat plate in a Mach 3 flow. A two-line ratio technique was used to obtain the temperature field, while an image obtained at the limit of low quenching rate was used to infer the pressure field. An analysis shows that these time-average measurements can suffer from significant weighted averaging bias errors in regions where there are large temperature fluctuations; however, these bias errors can be minimized by judicious selection of the absorption lines used. The resulting temperature field reveals the warm upstream boundary layer, the temperature jump across the recompression shocks and the expected minimum and maximum temperatures in the expansion and recirculation regions, respectively. The pressure measurements indicate a uniform low pressure in the base region, a rapid increase near reattachment, followed by a gradual approach to the free stream value farther downstream. Received: 25 July 1996 / Accepted: 11 September 1997     

Spontaneous Formation of RNA Strands,Peptidyl RNA,and Cofactors

How the biochemical machinery evolved from simple precursors is an open question. Here we show that ribonucleotides and amino acids condense to peptidyl RNAs in the absence of enzymes under conditions established for genetic copying. Untemplated formation of RNA strands that can encode genetic information, formation of peptidyl chains linked to RNA, and formation of the cofactors NAD⁺, FAD, and ATP all occur under the same conditions. In the peptidyl RNAs, the peptide chains are phosphoramidate‐linked to a ribonucleotide. Peptidyl RNAs with long peptide chains were selected from an initial pool when a lipophilic phase simulating the interior of membranes was offered, and free peptides were released upon acidification. Our results show that key molecules of genetics, catalysis, and metabolism can emerge under the same conditions, without a mineral surface, without an enzyme, and without the need for chemical pre‐activation.     

Coupled Orientation and Stretching of Chains in Mesoscale Models of Polydisperse Linear Polymers in Startup of Steady Shear Flow Simulations

Polydisperse linear polymers are studied in startup of steady shear flow simulations using dissipative particle dynamics. The results show that with an increase in polydispersity the stress overshoot declines while the steady‐state stress increases. Various physical characteristics of the systems are studied including frequency of nonbonded interactions, gyration radius data, flow alignment angles, and average bond lengths. The patterns in the data suggest higher forces are necessary to orient and stretch long chain fractions in the flow direction. Relaxation modulus data prove the broad range of relaxation mechanisms in polydisperse systems. Linear viscoelasticity theory is used to quantify the relaxation spectrum. The results indicate an increase in the longest relaxation time in systems with higher polydispersity. The steady‐state shear viscosity results show higher viscosities with an increase in polydispersity at all shear‐rates. The good agreement of the characteristic behaviors of modeled polydisperse polymers with experiments is encouraging for future work.

     

Nanotechnology for Electroanalytical Biosensors of Reactive Oxygen and Nitrogen Species

Over the past several decades, nanotechnology has contributed to the progress of biomedicine, biomarker discovery, and the development of highly sensitive electroanalytical / electrochemical biosensors for in vitro and in vivo monitoring, and quantification of oxidative and nitrosative stress markers like reactive oxygen species (ROS) and reactive nitrogen species (RNS). A major source of ROS and RNS is oxidative stress in cells, which can cause many human diseases, including cancer. Therefore, the detection of local concentrations of ROS (e. g. superoxide anion radical; O₂^•−) and RNS (e. g. nitric oxide radical; NO^• and its metabolites) released from biological systems is increasingly important and needs a sophisticated detection strategy to monitor ROS and RNS in vitro and in vivo. In this review, we discuss the nanomaterials‐based ROS and RNS biosensors utilizing electrochemical techniques with emphasis on their biomedical applications.