Submillimeter Atmospheric Transparency at Maunakea, at the South Pole, and at Chajnantor

For a systematic assessment of submillimeter observing conditions at different sites, we constructed tipping radiometers to measure the broad band atmospheric transparency in the window around 350 $\mu$m wavelength. The tippers were deployed on Maunakea, Hawaii, at the South Pole, and in the vicinity of Cerro Chajnantor in northern Chile. Identical instruments permit direct comparison of these sites. Observing conditions at the South Pole and in the Chajnantor area are better than on Maunakea. Simultaneous measurements with two tippers demonstrate conditions at the summit of Cerro Chajnantor are significantly better than on the Chajnantor plateau.Comment: Accepted by PAS

Repetitive Delone Sets and Quasicrystals

This paper considers the problem of characterizing the simplest discrete point sets that are aperiodic, using invariants based on topological dynamics. A Delone set whose patch-counting function N(T), for radius T, is finite for all T is called repetitive if there is a function M(T) such that every ball of radius M(T)+T contains a copy of each kind of patch of radius T that occurs in the set. This is equivalent to the minimality of an associated topological dynamical system with R^n-action. There is a lower bound for M(T) in terms of N(T), namely N(T) = O(M(T)^n), but no general upper bound. The complexity of a repetitive Delone set can be measured by the growth rate of its repetitivity function M(T). For example, M(T) is bounded if and only if the set is a crystal. A set is called is linearly repetitive if M(T) = O(T) and densely repetitive if M(T) = O(N(T))^{1/n}). We show that linearly repetitive sets and densely repetitive sets have strict uniform patch frequencies, i.e. the associated topological dynamical system is strictly ergodic. It follows that such sets are diffractive. In the reverse direction, we construct a repetitive Delone set in R^n which has M(T) = O(T(log T)^{2/n}(log log log T)^{4/n}), but does not have uniform patch frequencies. Aperiodic linearly repetitive sets have many claims to be the simplest class of aperiodic sets, and we propose considering them as a notion of "perfectly ordered quasicrystal".Comment: To appear in "Ergodic Theory and Dynamical Systems" vol.23 (2003). 37 pages. Uses packages latexsym, ifthen, cite and files amssym.def, amssym.te

Cousins Photometry and Temperatures for the Hyades, Coma, NGC 752, Praesepe, and M67

In this paper, new Cousins VRI data are presented for NGC 752 and Praesepe, and new and extant data are combined into an augmented database for M67. For those three clusters, catalogs containing Cousins VRI photometry, reddening-corrected values of (V -K)(J), and temperatures are produced. The same is done for Coma by using both previously published and newly derived Cousins photometry. An extant set of catalogs for the Hyades is updated to include V magnitudes and values of (R -I)(C) that were published after the original catalogs appeared. Finally, M67 V magnitudes published previously by Sandquist are corrected for an effect that depends on location on the face of the cluster. The corrected data and values of (V -I)(C) given by Sandquist are then set out in a supplementary catalog. Data files containing all of these catalogs are deposited in the CDS archives. To assess the quality of the data in the catalogs, the consistency of extant Cousins VRI databases is tested by performing analyses with the following features: (1) quantities as small as a few millimags are regarded as meaningful; (2) statistical analysis is applied; (3) no use is made of data other than VRI measurements and comparable results; (4) no inferences are drawn from color-magnitude comparisons; (5) pertinent data that have not been included previously are analyzed; and (6) results based on direct comparisons of stellar groups at the telescope are featured. In this way, it is found that our updated M67 color data and those of Sandquist are on the E region zero point. In contrast, values of (V -I)(C) from Montgomery and collaborators are found to be too red by 27 +/- 3 mmag, with an even larger offset being likely for unpublished data from Richer and his collaborators. Zero-point tests of our Cousins VRI colors for Coma, Praesepe, and NGC 752 are also satisfactory. Scale factor tests of the M67 colors are performed, and a likely scale factor error in the Montgomery et al. colors is found. However, it appears at present that the scale factors of our M67 colors and those of Sandquist are satisfactory. For the most part, zero-point tests of the assembled V magnitudes are also satisfactory, although it is found that further work on the V magnitudes for Praesepe and M67 would be useful. To put these results in perspective, it is pointed out that photometric tests that are satisfactory at the few-millimag level have been published for some two decades and so are not appearing for the first time in this paper.Astronom

Contralateral inhibition of click- and chirp-evoked human compound action potentials

Cochlear outer hair cells (OHC) receive direct efferent feedback from the caudal auditory brainstem via the medial olivocochlear (MOC) bundle. This circuit provides the neural substrate for the MOC reflex, which inhibits cochlear amplifier gain and is believed to play a role in listening in noise and protection from acoustic overexposure. The human MOC reflex has been studied extensively using otoacoustic emissions (OAE) paradigms; however, these measurements are insensitive to subsequent “downstream” efferent effects on the neural ensembles that mediate hearing. In this experiment, click- and chirp-evoked auditory nerve compound action potential (CAP) amplitudes were measured electrocochleographically from the human eardrum without and with MOC reflex activation elicited by contralateral broadband noise. We hypothesized that the chirp would be a more optimal stimulus for measuring neural MOC effects because it synchronizes excitation along the entire length of the basilar membrane and thus evokes a more robust CAP than a click at low to moderate stimulus levels. Chirps produced larger CAPs than clicks at all stimulus intensities (50–80 dB ppeSPL). MOC reflex inhibition of CAPs was larger for chirps than clicks at low stimulus levels when quantified both in terms of amplitude reduction and effective attenuation. Effective attenuation was larger for chirp- and click-evoked CAPs than for click-evoked OAEs measured from the same subjects. Our results suggest that the chirp is an optimal stimulus for evoking CAPs at low stimulus intensities and for assessing MOC reflex effects on the auditory nerve. Further, our work supports previous findings that MOC reflex effects at the level of the auditory nerve are underestimated by measures of OAE inhibition

Medical Implications of Space Radiation Exposure Due to Low Altitude Polar Orbits

Space radiation research has progressed rapidly in recent years, but there remain large uncertainties in predicting and extrapolating biological responses to humans. Exposure to cosmic radiation and Solar Particle Events may pose a critical health risk to future spaceflight crews and can have a serious impact to all biomedical aspects of space exploration. The relatively minimal shielding of the cancelled 1960's Manned Orbiting Laboratory program's space vehicle and the high inclination polar orbits would have left the crew susceptible to high exposures of cosmic radiation and high dose-rate SPEs that are mostly unpredictable in frequency and intensity. In this study, we have modeled the nominal and off-nominal radiation environment that a MOL-like spacecraft vehicle would be exposed to during a 30-day mission using high performance, multi-core computers. Projected doses from a historically large SPE (e.g. the August 1972 solar event) have been analyzed in the context of the MOL orbit profile, providing an opportunity to study its impact to crew health and subsequent contingencies.It is reasonable to presume that future commercial, government, and military spaceflight missions in low-Earth orbit will have vehicles with similar shielding and orbital profiles. Studying the impact of cosmic radiation to the mission's operational integrity and the health of MOL crewmembers provides an excellent surrogate and case-study for future commercial and military spaceflight missions.Comment: 6 pages, 4 figures, 2 table

Respite services and acquired brain injury in New South Wales : the perspectives of persons with acquired brain injury, their carers and service providers

Persons with acquired brain injury require continuing support and care in various aspects of their lives many years post-injury. Their care and support are mainly provided by family members. While respite is one of a range of critical support systems for carers and people with life-long disability, very little is known about respite in the area of acquired brain injury. The majority of the research on respite has been undertaken in developmental disability, mental health and in aged care, but there is no research to date about respite from the perspectives of the person with a disability, the carer and respite provider. There is also no research that examines these perspectives in the acquired brain injury literature. This study was aimed to address this gap in the literature by investigating respite from the perspectives of the person with acquired brain injury, the carer and the respite provider. It also examined the profile of respite services being provided in the Australian state of New South Wales as there had not been a comprehensive mapping of respite before. Survey methodology was used to gather information from persons with acquired brain injury and their carers who were members of the New South Wales Brain Injury Association, which is the peak advocacy association of people with brain injury. The same methodology was used to gather similar information from members of Interchange Respite Care New South Wales, which is a peak association representing respite providers in the state. The survey questionnaires were developed and designed after an extensive review of the literature, and were reviewed by experts in the fields of respite, disability and acquired brain injury. The survey questionnaire was also trialled on a sample of families. The survey questionnaires for the three participant groups shared several common sections, such as demographic information; factors influencing respite use; expectations of respite; and satisfaction with respite services used by persons or carers. The responses from the three participant groups were analysed and compared using logistic regression and descriptive statistics. The key findings of the study are (a) several characteristics or factors of the person with acquired brain injury and their carer were significantly associated with the use of respite, (b) there were several common factors that all three participant groups reported to influence respite use, and (c) there were several common expectations of respite among the three participant groups. Some of the characteristics or factors that were significantly associated with respite use included the severity of disability, the high level of dependency of the person with acquired brain injury, and the number of days spent in a coma. Common factors reported by all three participant groups to influence respite use included the stress level of the carer and the severity of disability. Factors reported to influence respite use appear to be consistent with the literature in developmental disability. There were common perspectives regarding the expectations of respite among all three participant groups, such as the need for trained and qualified respite staff; a wider range of respite services and more flexibility of respite service provision. The study also indicated a reported lack of sufficient respite for persons with acquired brain injury and their carers. Some of the findings of the study appeared to be consistent with the research literature on acquired brain injury; such as the majority of carers being mainly female; there is a reliance on informal networks for the care and support of the person with acquired brain injury; and the majority of the persons with acquired brain injury being male. The study also found that many respite providers in New South Wales had extensive experience in running a respite service. The findings of the study have important implications for policy direction and development, practice and service delivery, and research. In terms of policy direction and development, implications explored included: a flexible funding model that is responsive to the needs of carer and person with acquired brain injury, and adequately trained and qualified staff and volunteers play an important role in respite provision. Further research is required to understand empirically the benefits and quality of life outcomes over a period of time, such as what types and extent of respite are more beneficial for certain demographic profiles. The study highlights the perspectives of persons with acquired brain injury, their carers and respite providers. Respite is an important support system to enable persons with acquired brain injury to receive the continuing care and support from their carers. Respite in acquired brain injury is a new field that merits further research as it holds the potential for addressing the needs of people with acquired brain injury and their carers

Effects of Tornado Damage, Prescribed Fire, and Salvage Logging on Oak (Quercus Spp.) Saplings in Upland Oak Forests in Northern Mississippi

After European colonization and extensive logging folloby long periods of fire suppression, oak dominated forests, woodlands, and savannahs are being replaced by an unprecedented forest ecosystem. In Mississippi, these new forest systems are dominated in the mid- and understory by mesophytic species such as red maple (Acer rubrum L.) and sweetgum (Liquidambar styraciflua L.). Partial thinning of trees folloby prescribed fire can regenerate oaks in managed timber stands. A severe tornado occurred on a monitored oak stand in northern Mississippi. Of the damaged plots, some were treated with either prescribed fire or salvage logging or were left alone. I examined the effects of these treatments on oak regeneration. Species composition of saplings was measured to assess the impact of tornado damage and the treatments on sapling regeneration. All saplings, especially oaks, were reduced upon salvage logging which resulted in dominance by mesophytic species. Tornado damage increased all sapling densities, especially oaks, resulting in increased representation by upland oak species. In burned plots, oak saplings resisted and recovered from prescribed fire better than mesophytic saplings, but not enough to gain an overall height advantage. On poor soils, tornado damage alone may be enough to allow the regeneration of oak species without a prescribed fire. Results also indicate that natural regeneration of oaks may be incompatible with salvage logging, especially in areas that receive severe damage from high wind events