A simple technique for accurate and complete characterisation of a Fabry-Perot cavity.

It has become a significant challenge to accurately characterise the properties of recently developed very high finesse optical resonators (F > 10(6)). A similar challenge is encountered when trying to measure the properties of cavities in which either the probing laser or the cavity length is intrinsically unstable. We demonstrate in this article the means by which the finesse, mode-matching, free spectral range, mirror transmissions and dispersion may be measured easily and accurately even when the laser or cavity has a relatively poor intrinsic frequency stability.

Frequency stabilisation of a fibre-laser comb using a novel microstructured fibre.

There is great interest in developing high performance optical frequency metrology based around mode-locked fibre lasers because of their low cost, small size and long-term turnkey operation when compared to the solid-state alternative. We present a method for stabilising the offset frequency of a fibre-based laser comb using a 2 f - 3 f technique based around a unique fibre that exhibits strong resonant dispersive wave emission. This fibre requires lower power than conventional highly non-linear fibre to generate a suitable signal for offset frequency stabilisation and this in turn avoids the complexity of additional nonlinear steps. We generate an offset frequency signal from the mixing of a wavelength-shifted second harmonic comb with a third harmonic of the comb. Additionally, we have stabilised the repetition rate of the laser to a level better than 10(-14)/ radicaltau , limited by the measurement system noise floor.We present the means for complete and precise measurement of the transfer function of the laser frequency controls.

Invited article: design techniques and noise properties of ultrastable cryogenically cooled sapphire-dielectric resonator oscillators.

We review the techniques used in the design and construction of cryogenic sapphire oscillators at the University of Western Australia over the 18 year history of the project. We describe the project from its beginnings when sapphire oscillators were first developed as low-noise transducers for gravitational wave detection. Specifically, we describe the techniques that were applied to the construction of an interrogation oscillator for the PHARAO Cs atomic clock in CNES, in Toulouse France, and to the 2006 construction of four high performance oscillators for use at NMIJ and NICT, in Japan, as well as a permanent secondary frequency standard for the laboratory at UWA. Fractional-frequency fluctuations below 6 x 10(-16) at integration times between 10 and 200 s have been repeatedly achieved.

Helicobacter pylori and dyspepsia: a population-based study of the organism and host.

OBJECTIVE: The role of Helicobacter pylori (HP) infection in dyspepsia in the absence of peptic ulcer remains controversial. Specific attributes of the organism or the host response may be important. We aimed to determine whether HP infection overall, CagA status, serum gastrin, or serum pepsinogen levels are associated with dyspepsia in the community. METHODS: A self-report bowel disease questionnaire was mailed to a random sample of Olmsted County, Minnesota residents, aged 20-50 yr. All respondents who reported symptoms of dyspepsia or irritable bowel syndrome (cases) and all respondents without significant GI symptoms (controls) were invited to participate (n = 260). They were each assessed by a physician and their medical records reviewed. Serum was obtained to measure HP and CagA antibodies, pepsinogen I and II levels, and basal serum gastrin using validated assays. RESULTS: Of the 148 (57%) subjects who agreed to participate, 36 had dyspepsia (17 had ulcer-like dyspepsia), 35 had irritable bowel syndrome (IBS) without dyspepsia, and 77 were asymptomatic. The proportion who were seropositive for HP were 17% in dyspepsia (24% in ulcer-like dyspepsia), 20% in IBS, and 12% in asymptomatic controls. HP was not associated with dyspepsia, ulcer-like dyspepsia, or IBS after adjusting for age. Pepsinogen levels and serum gastrin were not associated with any of the conditions studied. However, CagA antibody positivity was associated with IBS (p < 0.05), and a borderline statistically significant association with dyspepsia was detected (p = 0.08). CONCLUSIONS: In this community, HP infection overall does not seem to explain dyspepsia, although the role of CagA-positive HP strains deserve further study.

Automated sampling and RNA isolation at room temperature for measurements of circadian rhythms in Chlamydomonas reinhardtii.

The development of techniques allowing the unattended collection of RNA from cell samples at room temperature makes practical accurate and facile monitoring of circadian rhythms in Chlamydomonas reinhardtii. The utility of these methods was demonstrated by collecting RNA samples for three days from cells maintained in continuous darkness. Every hour, cells were automatically collected and lysed with buffer containing SDS and proteinase K. Samples were maintained at room temperature with little or no evidence of degradation of RNA. Strong, non-damping circadian rhythms of cab mRNA abundance were measured. Free-running rhythms of about 24 h were measured from cultures maintained at 16, 20, 25 and 30 degrees C, thus demonstrating temperature compensation of circadian period. Simultaneous collections from cultures previously entrained to 12 h light/12 h dark cycles of opposite phase displayed circadian rhythms of cab mRNA abundance that were in phase with their previous entraining light cycles. Thus, this result suggests that the measured circadian rhythms of cab mRNA abundance was not an artifact of the collection procedure.