ABSTRACT
We have designed new chiral smectic mesogens with the -CH2O group near the chiral center. We synthesized two unique rod-like compounds. We determined the mesomorphic properties of these mesogens and confirmed the phase identification using dielectric spectroscopy. Depending on the length of the oligomethylene spacer (i.e., the number of methylene groups) in the achiral part of the molecules, the studied materials show different phase sequences. Moreover, the temperature ranges of the observed smectic phases are different. It can be seen that as the length of the alkyl chain increases, the liquid crystalline material shows more mesophases. Additionally, its clearing (isotropization) temperature increases. The studied compounds are compared with the structurally similar smectogens previously synthesized. The helical pitch measurements were performed using the selective reflection method. These materials can be useful and effective as chiral components and dopants in smectic mixtures targeted for optoelectronics and photonics.
ABSTRACT
The synthesis and characterization of new deuterated liquid crystal (LC) compounds based on phenyl tolane core is described in this paper. The work presents an alternative molecular approach to the conventional LC design. Correlations between molecular structure and mesomorphic and optical properties for compounds which are alkyl-hydrogen terminated and alkyl-deuterium, have been drawn. The compounds are characterized by mass spectrometry (electron ionization) analysis and infrared spectroscopy. They show enantiotropic nematic behavior in a broad temperature range, confirmed by a polarizing thermomicroscopy and differential scanning calorimetry. Detailed synthetic procedures are attached. Synthesized compounds show a significantly reduced absorption in the near-infrared (NIR) and medium-wavelength infrared (MWIR) radiation range, and stand as promising components of medium to highly birefringent liquid crystalline mixtures.
ABSTRACT
Stroke is one of the major public health problems worldwide. Determining the cerebrovascular risk factors (RF) is very important in the efforts of primary and secondary stroke prevention. The aim of the study was to establish the frequency of RF in patients with ischaemic (IS) or haemorrhagic stroke (HS) hospitalized in the stroke unit in the Department of Neurology of the Silesian Medical University from August 2000 to June 2002. We analysed data of 229 patients (29 with HS and 200 with IS). Functional outcome was evaluated by use of modified Rankin scale, Barthel Index and Scandinavian Neurological Stroke Scale at discharge. Statistical analysis was performed with Student's t-test, coefficient of correlation and multivariate logistic regression. 94.8% (n = 217) of all the patients had one or more RF. The most common RF were: hypertension (78.2%), coronary heart disease (54.2%), obesity (29.2%), diabetes mellitus (24.8%) and dyslipidaemia (24%). No correlation between the number of RF and functional outcome at discharge was observed. Cigarette smoking (p < 0.01) and alcohol abuse (p < 0.005) were more frequent in young patients (< 55 years). Previous ischaemic stroke was more common in older patients (>55 years). In male patients cigarette smoking and alcohol abuse were found more frequently than in female (p < 0.001). The mortality in examined patients was 22.2% (20.4% in patients with IS and 45.8% with HS). Male gender (p < 0.05), history of previous cardiac infarction (p < 0.05) and previous ischaemic stroke (p < 0.01) were associated with increased mortality. The other variables studied did not show significant differences.
