From micro to nano: properties and potential applications of micro- and nano-filled polymer ceramic composites in microsystem technology.

In microsystem technology, four important material classes are established either for the generation or the replication of microstructured surfaces: silicon, polymers, metals and ceramics. Composite materials consisting of a polymer matrix and ceramic fillers show improved thermomechanical properties in comparison to polymers and can be introduced as a new additional material class. The substitution of micro-sized ceramic fillers by nano-sized ceramics in composites has a strong influence on the composite's physical properties: the reduction of ceramic particle size down to the nanometre scale results in an improved sinter activity owing to the large surface area. The fabrication of dense ceramics is simplified and can be used for a rapid prototyping of microstructured ceramic parts. The addition of nano-sized ceramics with particle sizes of <40 nm to polymers allows the manufacturing of transparent polymer based composites with modified refractive indices for use in polymer waveguides. The influence of the ceramic particle size, the ceramic content and different dispersion methods on the composite's physical properties are discussed.

Second to fourth digit ratio: ethnic differences and family size in English, Indian and South African populations.

BACKGROUND: The second to fourth digit ratio (2D:4D) is lower in men than in women. 2D:4D may be established in utero and is negatively correlated with sperm counts and testosterone in men and positively correlated with oestrogen in men and women. Negative associations between male 2D:4D and family size and positive associations between female 2D:4D and family size have been found in some European populations. AIM: The study seeks to investigate the relationship between 2D:4D and family size in samples from Europe, Asia and Africa. SUBJECTS AND METHODS: Measurements of right hand 2D:4D were made in English (Merseyside, n = 403), Indian (Sugali and Yanadi, n= 160) and South African (Zulu,n = 258) populations. RESULTS: 2D:4D was weakly sexually dimorphic and showed strong ethnic differences. There were significant associations between 2D:4D and family size. For males these included negative associations in English and South African samples, and in the total sample. In females there was a positive association in the English sample, a negative association in the South African sample, and the total female sample showed a positive relationship between 2D:4D and family size. CONCLUSIONS: 2D:4D showed weak sex and strong ethnic differences. Low values of 2D:4D were associated with large family size in men. The situation was less clear in women but on balance there was evidence to support a relationship between high values of 2D:4D and large family size.

Melanin and HIV in sub-Saharan Africa.

HIV is common in sub-Saharan Africa. Sexually transmitted bacterial and fungal infections increase the chance of HIV infection. Melanin can prevent the penetration of skin and mucus membranes by microorganisms, and soluble melanin can inhibit HIV replication. We suggest that melanin may reduce the incidence of HIV infection through venereally acquired skin lesions, thus reducing the risk of sero-conversion and slow the progress to AIDS. Indigenous sub-Saharan peoples are highly melanized, but there is pigment variation between populations. We show that skin reflectance, a negative correlate of melanin, is positively associated with adult rate of HIV in sub-Saharan countries. There is no such relationship in populations outside sub-Saharan Africa. We suggest that melanin concentration in black people may correlate with resistance to HIV infection.

The ratio of 2nd to 4th digit length: a proxy for testosterone, and susceptibility to HIV and AIDS?

The incidence of HIV and AIDS is high in sub-Saharan Africa and in male homosexuals. It is suggested that testosterone-mediated immune dysfunction may account for this pattern. The ratio of the length of the 2nd and 4th digit (2D:4D) is negatively related to prenatal and adult testosterone concentrations. There is evidence that black South Africans have lower 2D:4D ratios than most other populations and male homosexuals have lower 2D:4D ratios than male heterosexuals. Men with low 2D:4D ratios may also be more sexually active and/or more fertile than men with high ratio. We suggest that men and women with low 2D:4D are susceptible to HIV infection and AIDS and babies with low 2D:4D ratio susceptible to vertical transmission. Infection rates may therefore be reduced by education and condom supply directed towards low 2D:4D adults.

The 2nd:4th digit ratio, sexual dimorphism, population differences, and reproductive success. evidence for sexually antagonistic genes?

The ratio between the length of the 2nd and 4th digit (2D:4D) is sexually dimorphic, with mean male 2D:4D lower than mean female 2D:4D. It recently was suggested that 2D:4D is negatively correlated with prenatal testosterone and positively correlated with prenatal estrogen. It is argued that high prenatal testosterone and low estrogen (indicated by low 2D:4D) favors the male fetus and low prenatal testosterone and high estrogen (indicated by high 2D:4D) favors the female fetus. The patterns of expression of 2D:4D are interpreted in terms of sexually antagonistic genes.We report data on the following. (a) reproductive success and 2D:4D from England, Germany, Spain, Hungary (ethnic Hungarians and Gypsy subjects), Poland, and Jamaica (women only). Significant negative associations were found between 2D:4D in men and reproductive success in the English and Spanish samples and significant positive relationships between 2D:4D in women and reproductive success in the English, German, and Hungarian samples. The English sample also showed that married women had higher 2D:4D ratios than unmarried women, suggesting male choice for a correlate of high ratio in women, and that a female 2D:4D ratio greater than male 2D:4D predicted high reproductive success within couples. Comparison of 2D:4D ratios of 62 father:child pairs gave a significant positive relationship. This suggested that genes inherited from the father had some influence on the formation of the 2D:4D ratio. Waist:hip ratio in a sample of English and Jamaican women was negatively related to 2D:4D. (b) Sex and population differences in mean 2D:4D in samples from England, Germany, Spain, Hungary (including ethnic Hungarians and Gypsy subjects), Poland, Jamaica, Finland, and South Africa (a Zulu sample). Significant sex and population differences in mean 2D:4D were apparent.