Untersuchung der elektrischen Leitfähigkeit homologer N-(4-n-Alkyloxybenzyliden)-4'-n-butylaniline im nematischen und smektischen Phasenbereich / Investigation of the Electrical Conductivity of Homologous N-(4-n-alkoxybenzylidene)-4'-nbutylanilines in the Nematic and Smectic Phases

Investigation The electrical conductivity of the first eight homologous N-(4-n-alkoxybenzylidene)-4'-n-butylanilines is investigated in the isotropic, nematic and smectic phases using the electrolyte tetra-butylammonium picrate. The anisotropy ratio of the electrical conductivity shows pretransition behaviour in the nematic phases close to the transition to the smectic phases. This behaviour be-comes more distinct with increasing alkyl chain length of the liquid crystals. In the nematic phase of 40·4 an anisotropy ratio of V = 0.55 is determined at the lowest electrolyte concentration. Values of about V=0.05 were found in the smectic phases of several homologues. In the nematic phase, an increase of the electrolyte concentration effects an increase of the anisotropy ratio. This effect is systematically enhanced with increasing alkyl chain length.

Bericht: Die Auswertung von Elektronenresonanz-Spektren organischer Radikale

Die Methoden zur Auswertung linienreicher EPR-Spektren sind in den letzten Jahren bis zu einem Stand entwickelt worden, der ihre routinemäßige Anwendung erlaubt. Um dem Chemiker das Suchen nach den in der Literatur verstreuten Arbeiten zu ersparen, werden die Methoden zur Zuordnung der Linien zu den im Molekül vorhandenen Kernmomenten und zur Bestimmung der Radikalkonzentration unter Verzicht auf die quantentheoretischen Ableitungen zusammengestellt.

Zur Geschwindigkeit der Ausrichtung nematischer Flüssigkeiten durch Magnetfelder / Kinetics Of Alignment Of A Nematic Liquid Crystal In Magnetic Fields /

The rotation of the molecules in a nematic liquid crystal is studied after rotating the axis of the aligning magnetic field. The process of realignment is observed by doping the liquid crystal with an electrolyte and measuring the cross voltage U* which is induced perpendicular to the applied electric field. The resulting cross voltages are compared with the stationary values and it can be shown that the degree of order with respect to the rotating director remains almost constant. Therefore, the time dependence of the angle 0 between director and magnetic field can be calculated from the measured cross voltage using the steady state equation U* = U*(Φ) . Φ(t) satisfies the formula

ln | tan Φ | = ln | tan Φ0 | - (χa H2/γ1) t

which is derived from the differential equation for the rotation of the

director. This formula allows the calculation of the viscosity coefficient γ1, giving a value of 1.08 P for MBBA at 25 °C. An activation energy of 11.5 kcal mol -1 is determined from the temperature dependence of the viscosity coefficient.

Bestimmung elastischer Konstanten von MBBA und EBBA mit der elektrischen Leitfähigkeitsmethode / Determination of the Elastic Constants of MBBA and EBBA by Electric Conductivity Measurements

Several methods of studying the elastic behaviour of nematic liquid crystals by means of measuring the electric conductivity are discussed. The temperature dependence of the ratio of the splay and bend elastic constants to the anisotropy of the magnetic susceptibility is determined for N-(p-methoxybenzylidene) -p-n-butylaniline (MBBA), N-(p-ethoxybenzylidene) -p-n-butylaniline (EBBA) and mixtures of both.

Induced Smectic Phases II. Influence of the Amino Substituent on the Induction of Smectic Phases

The diagrams of state have been studied for some liquid crystal mixtures which show the induction of smectic phases. Each of the systems studied contains one component with an amino group which influences the polarity and the electron donor property of the molecules. The discussion of the diagrams of state, of the thickness of the smectic layers and of the colours of the mixtures, which indicate the formation of CT complexes, shows that existing models can not explain the induction of smectic phases.

Beobachtung von Inversionswänden in einer nematischen Flüssigkeit / Observation of inversion walls in nematic liquid, crystals

The magnetic field induced deformations of a homeotropic nematic liquid crystal layer are studied by means of the electric conductance. Its time dependence observed after rotating the magnetic field direction by 180° is explained by the formation of alignment inversion walls.

Kinetik der Reaktion von katalytisch aktiven Imidazol-SH-Verbindungen mit Bromacetamid

Die Geschwindigkeitskonstanten zweiter Ordnung für die Reaktion einfacher SH-Verbindungen sowie Imidazol-SH-Verbindungen mit Bromacetamid bei pH 7 und verschiedenen Temperaturen wurden bestimmt und daraus die Aktivierungsenergien sowie mit Hilfe der pKSH-Werte die pH-unabhängigen Geschwindigkeitskonstanten ermittelt. Die Ergebnisse zeigen, daß die nucleophile Reaktivität von SH-Gruppen durch ideal benachbarte Imidazolreste erhöht werden kann. Der Mechanismus dieser Aktivierung wird kurz diskutiert. - Eine nähere Untersuchung der Reaktivität von 4-Brom-5-nitroimidazol, das in der Literatur als Alkylierungsmittel vorgeschlagen wurde, zeigte, daß diese Verbindung unter den gewählten Bedingungen nicht mit SH-Gruppen reagiert

Induced Smectic Phases I. Polymorphism in Binary Mixtures of Alkyloxybenzylidene-alkylanilines with Alkyl- and Alkyloxy- cyanobiphenyls

The diagrams of state of mixtures of 4-n-alkyloxybenzylidene-4'-n-butylanilines with 4-n- alkyl- and 4-n-alkyloxy-4'-cyanobiphenyls are studied. The mixtures form induced smectic phases of type SA, SB and SE. In all three smectic phases the thickness of the smectic layers agrees with the mean values of the molecular lengths. In most cases the induced SA phases do not show uninterrupted miscibility with the SA phases of the pure components. For instance, the system 40 • 4/8 CBP exhibits three separate SA phase areas. The maximum transition temperatures of the induced smectic phases increase with increasing chain length of the azomethines, but remain constant in case of the SA and SB phases or even decrease in case of the SE phases with increasing chain length of the cyanobiphenyls

Zustandsdiagramme und röntgenographische Untersuchungen einiger induzierter smektischer Mischphasen / Phase Diagrams and X -R ay Studies of the Induced Smectic Phases of Liquid Crystal Mixtures

Phase diagrams of mixtures of terminal polar and terminal non-polar liquid crystals that exhibit smectic phases with very large ranges of stability are presented. X-ray studies show that the in­duced phases are of type SA, SB or SE. The determination of the layer thickness shows that the induced smectic phases are composed of monolayers, whereas the terminal polar components are composed of bilayers. A model for the formation of the induced smectic phases is proposed.

Progress of resonant ionization laser ion source development at GANIL

SPIRAL2 (Système de Production d'Ions Radioactifs Accélérés en Ligne) is a research facility under construction at GANIL (Grand Accélérateur National d'Ions Lourds) for the production of radioactive ion beams by isotope separation on-line methods and low-energy in-flight techniques. A resonant ionization laser ion source will be one of the main techniques to produce the radioactive ion beams. GISELE (GANIL Ion Source using Electron Laser Excitation) is a test bench developed to study a fully operational laser ion source available for Day 1 operations at SPIRAL2 Phase 2. The aim of this project is to find the best technical solution which combines high selectivity and ionization efficiency with small ion beam emittance and stable long term operation. Latest results about the new ion source geometry will be presented.

Open surgery for chronic limb ischemia: a review

This review considers the role of the different revascularization strategies in patients with chronic limb ischemia (CLI) and reveals that clinical evidence guiding therapeutic decision-making in CLI is poor and only careful basic recommendations can be made. For diffuse aortoiliac disease with occlusion of the aorta, aortobifemoral bypass remains the best option if the patient is fit for open surgery. Unilateral iliac occlusion should be treated by primary stenting, but an iliofemoral bypass may be the best option when the disease extends down to the common and deep femoral arteries. For infrainguinal revascularisation, bypass using the saphenous vein remains the best option for patients with occlusion of the superficial femoral artery >25 cm and for patients with multiple occlusions of the infrapopliteal arteries. In the absence of leg veins, arm veins should be used. Prosthetic grafts are the last option. Endovascular techniques are recommended in patients with short arterial lesions and limited life expectancy <2 years. Finally some patients with CLI are best treated by primary amputation. In conclusion, this review demonstrates that neither an endo- first nor a bypass-first attitude is appropriate in patients with CLI and suggests that these patients should be cared for by specialists in a multidisciplinary center in order to preserve their life and limbs, to conduct clinical trials and to control costs.

The diabetic foot: a review

Diabetic foot ulceration (DFU) is among the most frequent complications of diabetes. Neuropathy and ischaemia are the initiating factors and infection is mostly a consequence. We have shown in this review that any DFU should be considered to have vascular impairment. DFU will generally heal if the toe pressure is >55 mmHg and a transcutaneous oxygen pressure (TcPO2) <30 mmHg has been considered to predict that a diabetic ulcer may not heal. The decision to intervene is complex and made according to the symptoms and clinical findings. If both an endovascular and a bypass procedure are possible with an equal outcome to be expected, endovascular treatments should be preferred. Primary and secondary mid-term patency rates are better after bypass, but there is no difference in limb salvage. Bedridden patients with poor life expectancy and a non-revascularisable leg are indications for performing a major amputation. A deep infection is the immediate cause of amputation in 25% to 50% of diabetic patients. Patients with uncontrolled abscess, bone or joint involvement, gangrene, or necrotising fasciitis have a "foot-at risk" and need prompt surgical intervention with debridement and revascularisation. As demonstrated in this review, foot ulcer in diabetic is associated with high mortality and morbidity. Early referral, non-invasive vascular testing, imaging and intervention are crucial to improve DFU healing and to prevent amputation. Diabetics are eight to twenty-four times more likely than non-diabetics to have a lower limb amputation and it has been suggested that a large part of those amputations could be avoided by an early diagnosis and a multidisciplinary approach.