Brownian coagulation at high concentration.

Particle growth by Brownian coagulation at high concentration in the continuum regime is investigated by solving the Langevin dynamics (LD) equations for each particle trajectory of polydisperse suspensions. By monitoring the LD attainment of the self-preserving size distribution (SPSD), it is shown that the classic Smoluchowski collision frequency function is accurate for dilute particle volume fractions, phis, below 0.1%. At higher phis, coagulation is about 4 and 10 times faster than for the classic theory at phis = 10 and 20%, respectively. For complete particle coalescence upon collision, SPSDs develop even in highly concentrated suspensions (up to phis = 35%), as with dilute ones, but are broadened with increasing phis. At high particle concentration, an overall coagulation rate is proposed that reduces to the classic one at low concentration. Detailed collision frequency functions are also obtained at various phis values. Fractal-like agglomerates undergoing coagulation at constant fractal dimension attain an SPSD only temporarily because their effective volume fraction continuously increases, approaching gelation in the absence of restructuring or fragmentation.

High concentration agglomerate dynamics at high temperatures.

The dynamics of agglomerate aerosols are investigated at high solids concentrations that are typical in industrial scale manufacture of fine particles (precursor mole fraction larger than 10 mol %). In particular, formation and growth of fumed silica at such concentrations by chemical reaction, coagulation, and sintering is simulated at nonisothermal conditions and compared to limited experimental data and commercial product specifications. Using recent chemical kinetics for silica formation by SiCl4 hydrolysis and neglecting aerosol polydispersity, the evolution of the diameter of primary particles (specific surface area, SSA), hard- and soft-agglomerates, along with agglomerate effective volume fraction (volume occupied by agglomerate) is investigated. Classic Smoluchowski theory is fundamentally limited for description of soft-agglomerate Brownian coagulation at high solids concentrations. In fact, these high concentrations affect little the primary particle diameter (or SSA) but dominate the soft-agglomerate diameter, structure, and volume fraction, leading to gelation consistent with experimental data. This indicates that restructuring and fragmentation should affect product particle characteristics during high-temperature synthesis of nanostructured particles at high concentrations in aerosol flow reactors.

[The German Orthopedics Society 1918-1932. Developments and trends]. / Die Deutsche Orthopädische Gesellschaft von 1918-1932. Entwicklungen und Strömungen.

The German Orthopedic Society was founded in 1901. The period between 1918 and 1932 was characterized by the aftermath of World War I. Up to the middle of the 2nd decade, orthopedic surgeons mainly treated soldiers and civilians affected by the war. Almost every congress dealt with amputations and artificial limbs. At the same time, orthopedic surgery became a specialty at the German universities, legitimizing it as a subject of its own. Besides the large number of victims of the First World War who had to be treated by orthopedic surgeons, there was a second group of patients, the so-called cripples. These handicapped people had not previously been treated in general. A new law established in 1920 guaranteed the government's support for treatment and education of these patients. This law was called "Krüppel-Fürsorge-Gesetz," which entailed welfare but also resocialization of the handicapped, including their return to work. The German nation recognized the economic benefit of this law and accepted the financial burden. During this period, German orthopedic surgeons developed many important surgical techniques, diagnostic tests, and technical findings for the production of orthoses and artificial limbs. Some examples of techniques are described in the article: UVirradiation for the treatment of rickets according to K. Huldschinsky, Borggreve's rotationplasty of the leg (Umkehrplastik), hallux valgus arthroplasty according to Brandes, and Bragard's sign.

A new biologic prosthesis for vascular substitute in mongrel dogs.

New glutaraldehyde-treated vascular prosthesis tubes of bovine pericardium were placed in the abdominal aortas of 29 mongrel dogs and observed for 30 to 540 days. Clinical evaluation was performed during follow-up, and histologic and arteriographic studies were done at the end of the study. Patency was shown by arteriography in 27 of 29 tubes (93.1%). Neoendothelialization was found in all grafts, and there was a mixed effect, characterized by both rejection and foreign body reaction in the prostheses from 180 days onward. Both the handling and consistency of the grafts were excellent for implantation. Graft procoagulation and animal anticoagulation were not necessary.

Uso de un antitrombotico a largo plazo en pacientes con insuficiencia arterial de miembros inferiores. / A long term use of an antithrombotic agent in patients with arterial insufficiency

Se exponen las experiencias de mas de 10 anos con el empleo de un antitrombotico, dipiridamol, administrado a largo plazo (promedio 72 meses), en pacientes sujetos a cirugia por arteriopatia oclusiva arteriosclerotica o tromboembolica. Un grupo testigo, sin medicacion antitrombotica, sirve de control. El grupo A muestra una incidencia muy baja de fenomenos tromboembolicos, durante los periodos en que se administra el dipiridamol y alta incidencia cuando se suspende este medicamento.El grupo B, sin medicacion antitrombolica, presenta el segundo episodio oclusivo en mas del 50% de los pacientes

Enzymatic epimerization of D-erythro-dihydroneopterin triphosphate to L-threo-dihydroneopterin triphosphate.

An enzyme has been discovered in Escherichia coli that catalyzes the conversion of the triphosphate ester of 2-amino-4-hydroxy-6-(D-erythro-1',2',3'-trihydroxypropyl)-7,8-dihydropteridine, (i.e. D-erythro-dihydroneopterin triphosphate) to an epimer of this compound, L-threo-dihydroneopterin triphosphate. The enzyme, which is here named "D-erythro-dihydroneopterin triphosphate 2'-epimerase," needs a divalent cation (Mg2+ or Mn2+ is most effective) for maximal activity. Its molecular weight is estimated at 87 000-89 000. Little or no activity can be detected if either the monophosphate or the phosphate-free form of the substrate is incubated with the enzyme. Evidence is presented to establish that all three phosphate residues of the substrate are retained in the product and that the product is of the L-threo configuration.