Non-detection Rate Research Articles

H spectropolarimetry of B[e] and Herbig Be stars

We present the results of medium-resolution (Δ v ≈ 60 km s−1) spectropolarimetric observations across H α of a sample of B[e] and Herbig Be objects. A change in linear polarization across H α is detected in a large fraction of the objects, with characteristics ranging from simple depolarization in a couple of Herbig Be stars, to more complex behaviour in the probable post-main-sequence B[e] stars. H α in the spectra of HD 37806 and 50138 each consist of a double-peaked polarized line and a superposed unpolarized single emission peak, suggesting two distinct line-forming regions. Multiple observations of HD 45677 allow for the separation of electron and dust scattering effects for the first time: the difference between derived intrinsic polarization angles of the two components indicates that the dust scattering region is clumpy. Two unexpected results are the non-detections of H α polarization changes in ω Ori, where depolarization has previously been detected, and in MWC 297, which exhibits source elongation at radio wavelengths. In ω Ori time variability is probably responsible such that the electron scattering disc of this star was much weakened at the time of observation. Two hypotheses are advanced that might explain the MWC 297 result. The general findings are that roughly half of the observed Herbig Be stars show polarization changes across Hα, implying immediately that their ionized envelopes are not spherically symmetric. This pattern, if confirmed by observations of a larger sample, could indicate that the non-detection rate is simply a consequence of sampling randomly oriented circumstellar discs able to scatter starlight within a few stellar radii. The deduced alignment of the disc of HD 53367 with the local interstellar magnetic field suggests an orderly star formation process in which the star ‘remembers’ the larger scale magnetic field direction. The stars classified as B[e] stars all show startling polarization changes across Hα. The details in each case are different, but the widely accepted concept of dense Hα-emitting equatorial discs around these objects is supported.

The survival of 1612-MHz OH masers in asymptotic giant branch plus white dwarf binaries

We have constructed a model of the OH distribution in an oxygen-rich outflow from an asymptotic giant branch star possessing a white dwarf companion. We assess the probability of 1612-MHz OH maser emission occurring despite the presence of a luminous accretion disc around the white dwarf. We find that the OH is resistant to photodissociation in all but the least massive winds, as a result of shielding by the dust component of the AGB outflow and self-shielding by H2O and OH molecules. This conclusion only partially supports the suggestion of Lewis that a ~ 40 per cent non-detection rate of OH 1612-MHz masers in potential OH/IR stars is due to photodissociation of OH. Our results are more compatible with the more tightly directed survey by Lewis & Engels of oxygen-rich OH/IR-star colour ‘mimics’, which shows a 1612-MHz detection rate of at least 75 per cent. We also postulate that other effects, such as the disruption of the velocity coherence of the wind, may be as important as photodissociation in inhibiting maser formation in AGB + WD binary systems.

Determination of the performance attributes of post-mortem meat inspection procedures

Traditional codes of post-mortem meat inspection are often inappropriate to the spectrum and prevalence of diseases and defects present in a particular class of livestock slaughtered in a specific geographical region. When a change in inspection procedures is proposed. a risk assessment model can provide a scientific basis for evaluation and generate important information for risk management decisions. A risk assessment of proposed new inspection procedures requires that all the grossly identifiable hazards that could be present in the tissues of interest be identified, and a trial be conducted to compare the performance characteristics of the inspection procedures. A confidence interval for the difference between the non-detection rates per N tissues that pass inspection provides the most meaningful comparison. A decision on the acceptability of a proposed new procedure is based on the worst case included in the confidence interval. Full matching and negative matching trial designs can be used, and each requires different statistical methods to determine confidence intervals for non-detection rates. Political and economic considerations may be involved in the determination of a level of acceptable risk, but determination of performance characteristics is independent of such considerations.

Fast clock synchroniser using initial phase presetting DPLL (IPP-DPLL) for burst signal reception

A fast clock synchroniser that quickly adjusts the initial phase of the DPLL output clock to the input signal (receiver detector output) at the beginning of acquisition is proposed for burst QDPSK signal reception. The synchroniser performance is given in terms of nondetection rate (NDR) of the unique word following the clock synchronisation preamble. Measured results clearly indicate that the proposed synchoniser achieves faster synchronisation than the conventional binary quantised DPLL clock synchroniser.

A risk-assessed evaluation of postmortem meat inspection procedures for ovine thysanosomiasis

Summary A risk assessment model was used to evaluate 4 meat inspection procedures for routine detection of Thysanosoma actinioides, a tapeworm that commonly infests the bile duct system of adult sheep in the United States. The overall sensitivities of different procedures ranged from 11.96 to 58.70%, and the nondetection rates per 1,000 viscera sets that passed inspection ranged from 38 to 77. On the basis of performance attributes for each procedure produced by the risk assessment model, the consumer was exposed to an aesthetic defect that was in 9 to 17 of every 1,000 livers passed for human consumption. The amount of wastage was also identified (3 to 39 livers/1,000 passed). Viewing of the incision site of the common hepatic duct was the most preferable routine inspection procedure, and matched pair analysis revealed that there was no additional benefit in combining this procedure with routine expression of a portion of bile from the gallbladder.

Test System Impact on System Availability

The specifications are presented for an imperfect automatic test system (ATS) (test frequency distribution, reliability, false alarm rate, nondetection rate) in order to account for the availability, readiness, mean time between unscheduled repairs (MTBUR), reliability, and maintenance of the system subject to monitoring and test. A time-dependent Markov model is presented, and applied in three cases, with examples of numerical results provided for preventive maintenance decisions, design of an automatic test system, buffer testing in computers, and data communications.