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The blend of an industrial cooligomer side chain cholesteric material with a polar small molecule liquid crystal of reversed chirality induces a low temperature smectic A phase [1]. We present here the change in the textural characteristics at the SA-Ch transition observed by optical microscopy between untreated glass slides: particular fingers, different from those recently described [2], are obtained for a slow increase of temperature, starting from an unperturbed spontaneous homeotropic SA domain. These fingers, coexisting with large SA domains, are understandable as 180° Bloch walls introducing progressively the helicity in the medium. Over a large temperature domain, these chiral fingers coexist in an apparent thermodynamic equilibrium with the normal SA phase, suggesting the occurrence of an analogue [3,4] of the Shubnikov superconducting phase: probably due to the presence of the glass slides, the geometry of the screw dislocations, comparable to the vortex of type 2 superconductors, is di...

Archimedian spiral wave instabilities have been discovered in chemical [1] and biological systems [2]. We present here the first example of such an instability pattern, encountered in a physical medium [3]. This instability is directly observed by polarized optical microscopy, on a positive dielectric anisotropy smectic A sample with homeotropic organization between parallel glass slides. The arm of the spiral is probably constituted of a 180° Bloch wall, separating indistinguishable smectic domains, and incorporating progressively the helicity of the cholesteric phase, excluded from the smectic.

We have shown recently that a side chain chiral industrial co-oligosiloxane exhibits an original blue phase behaviour at the cholesteric-isotropic transition [1–3]. This same material has been studied dissolved in various polar small molecule nematic or cholesteric liquid crystals and it was shown that these associations are responsible for a large induced smectic domain. These systems allow the adjustment of the smectic A-cholesteric transition temperature from 180°C to room temperature, depending on the nature and concentration of the associated small molecule liquid crystal. Moreover the kinetics of this transition is strongly slowed down at high co-oligomer concentrations, suggesting, as confirmed by a preliminary X-ray study on the pure material, that the presumed glass transition allowing for the quenching of the Bragg optical properties at room temperature is in fact strongly associated with strong smectic correlations between the mesogenic parts.

Placental abruption is a syndrome, which occurs in the third trimester of the pregnancy or during labour. It is the main cause of pregnancy last term bleeding and is also responsible for a high stillbirth rate. The objective is to describe the epidemiological, clinical, paraclinical and therapeutic characteristics in order to decrease the fetal and maternal mortality and morbidity.It is a prospective and descriptive study in continuous series, over a twelve-month period, from 1st January 2003 to 31st December 2003, at Issaka Gazobi maternity of Niamey, Niger.During the study period, 3255 deliveries have been done. One hundred and eighteen placental abruptions have been observed, which corresponds to a frequency of 3.6% with the highest rate during raining season. The average age and parity were: 31 years and 5th with a predominance of grand multiparous (38.2%). The majority of the patients were in-utero transfers (83,1%) and had done at least 10 km before arriving. One hundred and eleven patients had a caesarean section (94,1%) and 7 delivered through the vaginal route (5.9%). The fetal prognosis was characterized by a high stillbirth rate of 71.3% (87/122), fetal hypotrophy (64.8%) and prematurity (23.8%). The main cause of maternal morbidity was anaemia (76.3%) and Disseminated Intravascular Coagulation (5.9%). Further, 81 patients have been transfused (68.7%). The maternal mortality was 5.1% (6/118).Placental abruption, a medical and obstetrical emergency, is a serious obstetric condition, especially in our country. Physicians must be aware that patients with high blood pressure, preeclampsia, eclampsia, particularly in case of multiparity are at increased risk of placental abruption. Early diagnosis, prenatal follow-up and caesarean section improve the maternal and fetal prognosis.