Spontaneous and field-induced mesomorphism of a silyl-terminated bent-core liquid crystal as determined from second-harmonic generation and resonant X-ray scattering.

The polarity and structure of the phases of a liquid crystal constituted by thiophene-based bent-core molecules is investigated by means of optical second-harmonic generation (SHG), and resonant and conventional X-ray diffraction. The material studied is representative of a wide family of mesogens that contain silyl groups at the ends of the chains. These bulky terminal groups have been reported to give rise to smectic phases showing ferroelectric switching. However, the analysis of the SHG signal before and after application of electric fields has allowed us to establish unambiguously that the reported ferroelectricity is not intrinsic to the material but stabilized by the cell substrates once an electric field has been applied. In addition, the results obtained from resonant X-ray diffraction indicate that virgin samples have antiferroelectric undulated synclinic smectic structures.

[Initial clinical experiences with TIPS (transjugular intrahepatic portasystemic stent-shunt)]. / Erste klinische Erfahrungen mit TIPS (transjugulärer intrahepatischer portosystemischer Stent-Shunt).

15 patients with predominantly alcoholtoxic liver cirrhosis (mean age 50 years; 8 men and 7 women) were treated by the technically successful implantation of a transjugular portosystemic stent-shunt (TIPS) within a period of 1 year. The indications for TIPS implantation were the following: gastroesophageal bleedings in 12 cases (10 patients with recurrent variceal bleeding including 2 emergency cases with severe bleeding resistant to conventional therapy and 2 patients with exclusively gastral bleeding due to severe hypertensive gastropathy) and ascites resistant to conventional therapy in 3 cases. Portovenous pressure could be effectively reduced by mean of 37%. Within a mean observation period of 8 months 13 patients including the emergency cases remained without recurrent bleeding. Duplexsonography showed patent stents. 1 patient suffered from an early recurrent bleeding due to occlusion of the stent-shunt. The estimation of liver function according to the Child-Pugh-classification showed only minor changes. Before TIPS 9 patients were in class A, 4 in B, 2 in C; after TIPS 8 patients in A, 5 in B and 2 in C. Ascites resolved completely. Following TIPS all patients appeared to abstain from alcohol. After TIPS 5 from 14 surviving patients (36%) developed clinically manifest encephalopathy within the first 4-8 weeks (2 patients with previous episodes of encephalopathy, 2 other patients after withdrawal of lactulose). By enhanced conservative treatment (lactulose, paromomycine and protein restriction) encephalopathy could be overcome. 8 from 11 surviving patients investigated displayed characteristic MRI changes with an increased signal intensity in the basal ganglia (T1 weighted images). According to our preliminary results TIPS represents a new successful interventional regimen for the treatment of portal hypertension in selected cases.