Polymers-Copolymer as Flow Improvers for Fuel Oils and Their Electrical Conductivity

In order to find efficient cold flow improvers for fuel oil, polymethylmethacrylate (PMMA), polystyrene (PS), and a copolymer [styrene (S)–methylmethacrylate (MMA) were prepared. The structure of these polymers and the copolymer were characterized by infrared spectral analysis and their molecular weights were measured. These polymers-copolymer were used as additives for fuel oils in order to lower their pour point. Accordingly, they were evaluated as flow improvers for fuel oil. The results indicated that PMMA possesses less performance as pour point depressant. While the addition of PS and the copolymer (S–MMA) yield excellent pour point depressants for fuel oil. Upon studying the prepared additives and their properties, it was found that the electrical properties of the copolymer were changed due to the presence of polar ion in MMA effect on the electrical properties. The highest electrical conductivity was found when styrene:MMA molar ratio was 1:1.     

Microrheology and electrical conductivity of a dilute PNIPAM suspension

We study on a suspension of poly(N-isopropylacrylamide) at a low concentration using particle-tracking microrheology in two modalities: at constant temperatures and during a heating ramp. The dilute suspensions do not present a glass state at low temperatures, and at high temperatures, the polymer particles collapse, giving rise to entropic forces that induce aggregation of the tracking colloids. The viscoelastic moduli of the system, which drastically change with temperature, allow us to follow this dynamics. Furthermore, the viscosity of the system remains approximately constant with temperature but suddenly increases as it passes the lower critical solution temperature (LCST). Such effect is probably associated to hydration before the collapse of the polymer, as verified by electrical conductivity measurements.     

Trigonometrische Doppelreihen

Ohne Zusammenfassung     

Zur expliziten Lösung nicht orthogonaler Randwertprobleme

Ohne Zusammenfassung     

On triazoles. VII Synthesis of novel tri- and tetracyclic ring systems

The ring-closure of the 5-amino-1-(2-aminophenyl)-3-methylthio-1H-1,2,4-triazole derivatives 3 and 4 with different simple and cyclic C₁ components lead to the formation of 1,2,4-triazolo[1,5-α]-1,3,5-benzotriazepines 5–6 , their 4,5-dihydro- 7 , different 5-spiro-homocyclic- 8–13 , and 5-spiro-heterocyclic- 14-15 analogues. The structure of the compounds obtained was proved with the use of their ir, uv, ¹H-nmr and ¹³C-nmr spectra.     

Sensitive spectrophotometric determination of ascorbic acid in fruit juices and pharmaceutical formulations using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP)

A simple and very sensitive method has been developed for the determination of ascorbic acid based on the oxidation of ascorbic acid to dehydroascorbic acid by iron(III), followed by a complexation of iron(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol(Br-PADAP). The iron(II) complex is formed immediately, with absorption maxima at 560 and 748 nm and a molar absorptivity of 1.31 × 10⁵ l mole^–1cm^–1 and 5.69 × 10⁴ l mole^–1cm^–1, respectively. The ascorbic acid determination is possible with a linear range up to 2.4 μg ml^–1, a calibration sensitivity of 0.744 ml μg^–1 at 560 nm and 0.323 ml μg^–1 at 748 nm, and a detection limit of 15 ng ml^–1 and 44 ng ml^–1, respectively. The procedure was used for the ascorbic acid determination in several fruit juices and pharmaceutical formulations. The results demonstrated a good precision (R.S.D. < 1%) and are in agreement with those obtained with others methods. The Br-PADAP method proposed is six times more sensitive than the method using the iron(II)-1,10-phenanthroline system. Received: 7 May 1996 / Revised: 1 July 1996 / Accepted: 8 August 1996     

Polymorphism in Dethoxyprone,a steroidal anesthetic. II. Crystal and molecular structure of 11α-dimethylamino-2β-ethoxy-3α-hydroxy-5α-pregnan-20-one (Dethoxyprone,form II)

The crystal and molecular structure of 11-dimethylamino-2-ethoxy-3-hydroxy-5-pregnan-20-one (Dethoxyprone, formII) (C₂₅H₄₃NO₃) has been determined by direct methods, and refined to a finalR of 0.067 for 4508 observed reflections. The compound crystallizes in space groupP2₁2₁2₁ with cell dimensionsa=10.830 (2),b=12.703 (2),c=17.490 (1) Å;Z=4,D _x =1.12 g cm^–3, (CuK )=5.28 cm^–1. The rings of the steroid skeleton are trans connected. Rings A, B, and C have chair conformations, while ring D has a half-chair conformation. The molecules are hydrogen bonded in a head to tail fashion through the hydroxy and keto groups.     

The influence of hubs in the structure of a neuronal network during an epileptic seizure

In this work, we propose changes in the structure of a neuronal network with the intention to provoke strong synchronization to simulate episodes of epileptic seizure. Starting with a network of Izhikevich neurons we slowly increase the number of connections in selected nodes in a controlled way, to produce (or not) hubs. We study how these structures alter the synchronization on the spike firings interval, on individual neurons as well as on mean values, as a function of the concentration of connections for random and non-random (hubs) distribution. We also analyze how the post-ictal signal varies for the different distributions. We conclude that a network with hubs is more appropriate to represent an epileptic state.