We report radio frequency ͑rf͒ electrical readout of graphene mechanical resonators. The mechanical motion is actuated and detected directly by using a vector network analyzer, employing a local gate to minimize parasitic capacitance. A resist-free doubly clamped sample with resonant frequency ϳ34 MHz, quality factor ϳ10 000 at 77 K, and signal-to-background ratio of over 20 dB is demonstrated. In addition to being over two orders of magnitude faster than the electrical rf mixing method, this technique paves the way for use of graphene in rf devices such as filters and oscillators.

In this study, bulk bone collagen carbon (δ 13 C) and nitrogen (δ 15 N) isotope data from 49 individuals, recovered from two Medieval burial grounds in Hereford, England, are coupled with incremental dentine data from five individuals with high δ 15 N bone values who survived into old age, to see whether the high δ 15 N values were consistent throughout their childhood and adolescence. There are statistically insignificant differences between mean bone δ 13 C and δ 15 N values from the two Hereford populations, exhumed at Cathedral Close and St. Guthlac's Priory, despite temporal and demographic differences (St Guthlac's mean: δ 13 C -19.4 ± 0.5‰ and δ 15 N 10.9 ± 1.2‰. Hereford Cathedral mean: δ 13 C -19.6 ± 0.4‰ and δ 15 N 10.4 ± 0.9‰, 1σ). In comparison to other contemporary urban populations, the Hereford individuals present significantly lower but more variable δ 15 N values, suggesting a diet low in protein from high trophic level foods such as meat and milk, possibly the result of differing social status or geographic factors. The approximately 23-year long incremental dentine profiles all show considerable fluctuation in stable isotope values during childhood and adolescence for all individuals until around age 20, suggesting possible influence by physiological processes related to growth and development.

No abstract

PDF of the full book of Elements' Fall 2014 journal