ABSTRACT
The complex refractive indices of two benchmark nematic liquid crystal,4-4 '-n-pentyl-cyanobiphenyl (5CB) and 4-(trans-4'pentylcyclohexyl)-benzonitrile (PCH5) have been determinedin the frequency range from 0.2 to 0.8 THz. The technique of coherent THztime-domain spectroscopy (THz-TDS) was used. We show that the birefringenceof 5CB is in the range of 0.15 to 0.21, while that of PCH is from 0.01 to0.08. Both liquid crystals exhibit relatively small absorption in thisfrequency range. The large birefringence of 5CB indicates possible applications of liquid-crystal-based devices for modulation and polarizationcontrol of electromagnetic radiation in the THz frequency range.
ABSTRACT
A population-based case-control interview study of 486 adult leukemia cases and 502 healthy controls was carried out in Shanghai, People's Republic of China during 1987-89 to evaluate the etiologic role of prior medical conditions, medications, and diagnostic X-rays. Risks were examined separately for 236 cases with acute non-lymphocytic leukemia (ANLL), 79 with chronic myeloid leukemia (CML), 81 with acute lymphocytic leukemia (ALL), and 21 with chronic lymphocytic leukemia (CLL). Little difference was found between cases and controls for prior history of diabetes, hypertension, allergic conditions, most medications, and diagnostic X-rays. A few significant associations were observed for appendectomy, tuberculosis, and for several other chronic disorders with specific leukemia cell types, but the odds ratio estimates for most of these ranged from two to three and, with the exception of the two specified above, were based generally on five or fewer exposed controls. In contrast to an association with childhood leukemia in Shanghai, prior use of chloramphenicol was not linked with ANLL or other forms of adult leukemia. Further research is needed to clarify the relation of specific medical conditions and exposures with particular subtypes of leukemia, and to examine reasons for the low incidence of CLL in China and other Asian populations.
Subject(s)
Disease , Leukemia/epidemiology , Adolescent , Adult , Age Factors , Aged , Appendectomy/statistics & numerical data , Case-Control Studies , China/epidemiology , Female , Humans , Hyperthyroidism/epidemiology , Leukemia, Lymphocytic, Chronic, B-Cell/epidemiology , Leukemia, Myelogenous, Chronic, BCR-ABL Positive/epidemiology , Leukemia, Myeloid, Acute/epidemiology , Male , Middle Aged , Population Surveillance , Precursor Cell Lymphoblastic Leukemia-Lymphoma/epidemiology , Risk Factors , Salicylates/adverse effects , Tuberculosis/epidemiologyABSTRACT
We demonstrate two interferometric methods for measuring the thickness of nematic liquid crystal films with a free surface. The accuracy of either method is better than +/-1 %.
