Kinetik der polykondensation von natriumsulfidhydrat und 1,4-dichlorbenzol zu poly(thio-1,4-phenylen)

The kinetics of the polycondensation of sodium sulfide hydrate and 1,4-dichlorobenzene to poly(thio-1,4-phenylene) in 1-methyl-2-pyrrolidone as solvent was studied in a differential scanning calorimeter at temperatures between 220 and 280°C. This polycondensation shows an autocatalytic behavior and the kinetics can be modelled by a first order reaction up to complete conversion. This is explained by the low solubility of sodium sulfide in l-methyl-2-pyrrolidone. The concentration of sodium sulfide is regarded as being constant during the whole course of the reaction. The autocatalytic effect can be explained by the increase of the condensation rate constant at the beginning of polycondensation due to the higher reactivity of the oligomers compared to the monomers. The number- and the weight-average molecular weight of the products formed during the course of the polycondensation can be modelled by means of stochastic methods. A simple model with only two different rate constants of the condensation process is assumed. The concentration of sodium sulfide in the reactive phase is found to be 2–5% of the value of dichlorobenzene at the beginning of the reaction and remains constant nearly until the end of polycondensation.     

A Study of Surface Deformation during Wire‐Rod Rolling of High Speed Steels using Experimental and Computational Techniques

The evolution of surface defects during shape rolling of high‐speed steel billets is studied using longitudinal surface defects prepared by machining and welding. The reduction of the defects during rolling in a production mill is compared to the total area reduction of the billets. Samples are collected after pass 4, 6, 8, 14, 19 and the final pass, 28, representing the finished 5.5mm wire. By inspecting the cross sections, the rotation of the billets from pass to pass is evaluated. Results from FE simulations on solid billets are compared to the experimental results. Generally, simulations predict less reduction than observed experimentally. In most cases cracks reduce most effectively followed by carbon steel welds and stainless steel welds.     

Note: flowing ion population from a resonance cavity source

The experimental low energy plasma for hemispherical analyzers nominal testing thermal plasma facility of Dartmouth College uses a microwave plasma source which generates an ionosphere-like plasma through a two-step process. The plasma is initially generated inside a cylindrical, insulated, resonance cavity. This initial plasma must pass through a sheath in order to enter the main experimental region. This process imparts a significant flow velocity to the ions which has been neglected in previous analysis of this plasma source. We predict the flow energy of the ions to be between 12-15 eV depending on conservation laws and show agreement with experimental results.     

Acetals as nucleating agents for polypropylene

Nucleating agents increase the impact strength, tensile strength, and tensile elasticity modulus of semicrystalline polymers. Nucleating agents also decrease product cycle times, resulting in a cost savings per product unit. We have synthesized and tested 15 compounds as nucleactors for polypropylene. Of these, trinapthylidene sorbitol, tri-(4-methyl-1-naphthylidene)sorbitol, tri-(4-methoxy-1-naphthylidene) sorbitol, and dibenzylidene xylitol are efficient nucleators of polypropylene. Trinaphthylidene sorbitol (tns) has two major diastereomers: The “S” diastereomer yields a faster crystallization rate for polypropylene than does the commercial nucleator dibenzylidene sorbitol (Millad 3905). Crystallization rates are 208 and 88, respectively (t min^?1 × 1000). The “R” diastereomer, however, is a poor nucleator and interferes with the nucleating activity of the “S” diastereomer. A 52/48 mixture of diastereomers does not nucleate polypropylene, even at twice the concentration. This is first time that the importance of stereochemistry has been demonstrated in the nucleating action. © 1994 John Wiley & Sons, Inc.     

Goal-driven automation of a deep space communications station: a case study in knowledge engineering for plan generation and execution

Abstract: This paper describes the application of Artificial Intelligence techniques for plan generation, plan execution, and plan monitoring to automate a Deep Space Communication Station. This automation allows a communication station to respond to a set of tracking goals by appropriately reconfiguring the communications hardware and software to provide the requested communications services. In particular this paper describes: (1) the overall automation architecture, (2) the plan generation and execution monitoring AI technologies used and implemented software components, and (3) the knowledge engineering process and effort required for automation. This automation was demonstrated in February 1995, at the DSS13 Antenna Station in Goldstone, CA on a series of Voyager tracks and the technologies demonstrated are being transferred to the operational Deep Space Network stations.     

Electron capture dissociation of tyrosine O-sulfated peptides complexed with divalent metal cations

We compare electron capture dissociation (ECD) of doubly protonated and divalent metal-adducted tyrosine O-sulfated peptides without basic amino acid residues. ECD of doubly protonated Tyr2-sulfated cholecystokinin (CCKS) and doubly protonated Tyr12-sulfated gastrin II (GST) resulted in complete loss of SO3 from all product ions. Thus, contrary to typical ECD behavior, localization of the sulfate groups was not possible. By contrast, ECD of Ca-, Mn-, Zn-, and Fe-adducted CCKS and ECD of deprotonated GST with two calcium adducts, i.e., [GST + 2Ca - H]3+, resulted in sulfated c'- and z.-type product ions with high sequence coverage, thereby allowing both sequencing and sulfate localization. In addition, divalent metal adduction provided improved positive mode ionization efficiency for these peptides. The drastically different fragmentation behavior observed in ECD of protonated and metal-adducted CCKS and GST, respectively, is proposed to be a consequence of the absence of basic amino acid residues, promoting a mobile proton-like fragmentation mechanism, including abundant sulfate loss, for protonated species. Retention of sulfate groups was also observed in electron detachment dissociation (EDD) of CCKS and GST. However, the EDD fragmentation efficiency was much lower than that of ECD and very limited fragmentation was observed in EDD of GST, precluding localization of the sulfate group in that peptide.     

Constraining Si Particles within Graphene Foam Monolith: Interfacial Modification for High‐Performance Li+ Storage and Flexible Integrated Configuration

Pulverization of electrode materials and loss of electrical contact have been identified as the major causes for the performance deterioration of alloy anodes in Li‐ion batteries. This study presents the hierarchical arrangement of spatially confining silicon nanoparticles (Si NPs) within graphene foam (GF) for alleviating these issues. Through a freeze‐drying method, the highly oriented GF monolith is engineered to fully encapsulate the Si NPs, serving not only as a robust framework with the well‐accessible thoroughfares for electrolyte percolation but also a physical blocking layer to restrain Si from direct exposure to the electrolyte. In return, the pillar effect of Si NPs prevents the graphene sheets from restacking while preserving the highly efficient electron/Li⁺ transport channels. When evaluated as a binder‐free anode, impressive cycle performance is realized in both half‐cell and full‐cell configurations. Operando X‐ray diffraction and in‐house X‐ray photoelectron spectroscopy confirm the pivotal protection of GF to sheathe the most volume‐expanded lithiated phase (Li₁₅Si₄) at room temperature. Furthermore, a free‐standing composite film is developed through readjusting the pore size in GF/Si monolith and directly integrated with nanocellulose membrane (NCM) separator. Because of the good electrical conductivity and structural integrity of the GF monolith as well as the flexibility of the NCM separator, the as‐developed GF/Si‐NCM electrode showcases the potential use in the flexible electronic devices.