AERODYNAMIC DRAG AND STABILITY CHARACTERISTICS OF TOWED INFLATABLE DECELERATORS AT SUPERSONIC SPEEDS

Aerodynamic drag and stability of towed inflatable decelerators at supersonic speed

Conjugative transfer of ICESde3396 between three β-hemolytic streptococcal species

Background: Integrative conjugative elements (ICEs) are mobile genetic elements (MGEs) that possess all genes necessary for excision, transfer and integration into recipient genome. They also carry accessory genes that impart new phenotypic features to recipient strains. ICEs therefore play an important role in genomic plasticity and population structure. We previously characterised ICESde 3396, the first ICE identified in the β-hemolytic Streptococcus dysgalactiae subsp equisimilis (SDSE) and demonstrated its transfer to single isolates of Streptococcus pyogenes (group A streptococcus, GAS) and Streptococcus agalactiae (group B streptococcus, GBS). While molecular studies found the ICE in multiple SDSE and GBS isolates, it was absent in all GAS isolates examined. Results: Here we demonstrate that ICESde 3396:km is transferable from SDSE to multiple SDSE, GAS and GBS isolates. However not all strains of these species were successful recipients under the same growth conditions. To address the role that host factors may have in conjugation we also undertook conjugation experiments in the presence of A549 epithelial cells and DMEM. While Horizontal Gene Transfer (HGT) occurred, conjugation efficiencies were no greater than when similar experiments were conducted in DMEM. Additionally transfer to GAS NS235 was successful in the presence of DMEM but not in Todd Hewitt Broth suggesting that nutritional factors may also influence HGT. The GAS and GBS transconjugants produced in this study are also able to act as donors of the ICE. Conclusion: We conclude that ICEs are major sources of interspecies HGT between β-hemolytic streptococci, and by introducing accessory genes imparting novel phenotypic characteristics, have the potential to alter the population structure of these species

Mammalian behavior and physiology converge to confirm sharper cochlear tuning in humans

Frequency analysis of sound by the cochlea is the most fundamental property of the auditory system. Despite its importance, the resolution of this frequency analysis in humans remains controversial. The controversy persists because the methods used to estimate tuning in humans are indirect and have not all been independently validated in other species. Some data suggest that human cochlear tuning is considerably sharper than that of laboratory animals, while others suggest little or no difference between species. We show here in a single species (ferret) that behavioral estimates of tuning bandwidths obtained using perceptual masking methods, and objective estimates obtained using otoacoustic emissions, both also employed in humans, agree closely with direct physiological measurements from single auditory-nerve fibers. Combined with human behavioral data, this outcome indicates that the frequency analysis performed by the human cochlea is of significantly higher resolution than found in common laboratory animals. This finding raises important questions about the evolutionary origins of human cochlear tuning, its role in the emergence of speech communication, and the mechanisms underlying our ability to separate and process natural sounds in complex acoustic environments

Acoustic Mechanisms that Determine the Ear-Canal Sound Pressures Generated by Earphones

In clinical measurements of hearing sensitivity, a given earphone is assumed to produce essentially the same sound-pressure level in all ears. However, recent measurements [Voss et al., Ear and Hearing (in press)] show that with some middle-ear pathologies, ear-canal sound pressures can deviate by as much as 35 dB from the normal-ear value; the deviations depend on the earphone, the middle-ear pathology, and frequency. These pressure variations cause errors in the results of hearing tests. Models developed here identify acoustic mechanisms that cause pressure variations in certain pathological conditions. The models combine measurement-based Thevenin equivalents for insert and supra-aural earphones with lumped-element models for both the normal ear and ears with pathologies that alter the ear\u27s impedance (mastoid bowl, tympanostomy tube, tympanic-membrane perforation, and a \u27high- impedance\u27 ear). Comparison of the earphones\u27 Thevenin impedances to the ear\u27s input impedance with these middle-ear conditions shows that neither class of earphone acts as an ideal pressure source; with some middle-ear pathologies, the ear\u27s input impedance deviates substantially from normal and thereby causes abnormal ear-canal pressure levels. In general, for the three conditions that make the ear\u27s impedance magnitude lower than normal, the model predicts a reduced ear-canal pressure (as much as 35 dB), with a greater pressure reduction with an insert earphone than with a supra-aural earphone. In contrast, the model predicts that ear-canal pressure levels increase only a few dB when the ear has an increased impedance magnitude; the compliance of the air-space between the tympanic membrane and the earphone determines an upper limit on the effect of the middle-ear\u27s impedance increase. Acoustic leaks at the earphone-to-ear connection can also cause uncontrolled pressure variations during hearing tests. From measurements at the supra-aural earphone-to-ear connection, we conclude that it is unusual for the connection between the earphone cushion and the pinna to seal effectively for frequencies below 250 Hz. The models developed here explain the measured pressure variations with several pathologic ears. Understanding these mechanisms should inform the design of more accurate audiometric systems which might include a microphone that monitors the ear-canal pressure and corrects deviations from normal

iSchools and archival studies

Whispers and rumors about the iSchool movement lead some to fear that this represents yet another shift away from the valued traditions of library schools, threatening something far different than what library science pioneers ever envisioned. Predating the iSchool movement, however, were other programmatic shifts such as those that led to the formalization of graduate archival education. This essay argues that such evolution is essential to our future, as iSchools tackle the increasingly complex issues confronting a digital society. We consider the mission and history of iSchools and of archival studies, the basic elements and concepts of archival studies that are critical to iSchools, and the relationship between iSchools and the changing nature of personal and institutional archives. © 2009 Springer Science+Business Media B.V

Bacterial Leakage Evaluation of Three Root Canal Sealers with Two Obturation Techniques: An in Vitro Study

Background: The purpose of this study was to compare the quality of the coronal seal of three root canal sealers and two obturation techniques using the bacterial penetration method. Methods and Results: A total of 132 single-rooted human teeth with fully developed apices were used. The teeth were randomly assigned to three experimental groups according to the endodontic sealer used. Group 1: Samples (n=44) were obturated using a zinc oxide eugenol-based sealer, Pulp Canal Sealer EWT. Group 2: Samples (n=44) were obturated using an epoxy resin-based sealer, AH Plus. Group 3: Samples (n=44) were obturated using a bioceramic-based root canal sealer, Well-Root ST. Each group was subdivided into 2 equal subgroups in accordance with the obturation technique being used: the cold lateral condensation technique (CLCT) and Thermafil obturation technique (ThOT). Thus, 6 subgroups were formed: Sub-1A: Pulp Canal Sealer/CLCT; Sub-2A: AH Plus/CLCT; Sub-3A: Well-ROOT ST/CLCT; Sub-1B: Pulp Canal Sealer/ThOT; Sub-2B: Ah Plus/ThOT; Sub-3B: Well-ROOT ST/ThOT. A dual-chamber device was used to evaluate bacterial leakage. Fresh medium and E. faecalis were added to the upper chamber every 4 days. The broth was monitored for color change daily for 33 days. Significant differences were found among Sub-2A vs. Sub-1B (P=0.023), Sub-1A vs. Sub-3A (P=0.014), Sub-1A vs. Sub-2B (P=0.024), Sub-1A vs. Sub-3B (P=0.002), Sub-3A vs. Sub-1B (P=0.003), Sub-2B vs. Sub-1B (P=0.005), and Sub-1B vs. Sub-3B (P<0.0001). There was no significant difference in the average occurrence of turbidity between CLCT and ThOT (P=0.718) Conclusion: Regardless of the obturation technique, all root canal sealers exhibited leakage; however, the bioceramic-based root canal sealer appeared to perform better than the epoxy resin-based sealer and the zinc oxide eugenol-based sealer

On the relationships between kinetic schemes and two-state single molecule trajectories

Trajectories of a signal that fluctuates between two states which originate from single molecule activities have become ubiquitous. Common examples are trajectories of ionic flux through individual membrane-channels, and of photon counts collected from diffusion, activity, and conformational changes of biopolymers. By analyzing the trajectory, one wishes to deduce the underlying mechanism, which is usually described by a multi-substate kinetic scheme. In previous works, we divided kinetic schemes that generate two-state trajectories into two types: reducible schemes and irreducible schemes. We showed that all the information in trajectories generated from reducible schemes is contained in the waiting time probability density functions (PDFs) of the two states. It follows that reducible schemes with the same waiting time PDFs are not distinguishable. In this work, we further characterize the topologies of kinetic schemes, now of irreducible schemes, and further study two-state trajectories from the two types of scheme. We suggest various methods for extracting information about the underlying kinetic scheme from the trajectory (e. g., calculate the binned successive waiting times PDF and analyze the ordered waiting times trajectory), and point out the advantages and disadvantages of each. We show that the binned successive waiting times PDF is not only more robust than other functions when analyzing finite trajectories, but contains, in most cases, more information about the underlying kinetic scheme than other functions in the limit of infinitely long trajectories. For some cases however, analyzing the ordered waiting times trajectory may supply unique information about the underlying kinetic scheme

Exploring the limits of single emitter detection in fluorescence and extinction

We present an experimental comparison and a theoretical analysis of the signal-to-noise ratios in fluorescence and extinction spectroscopy of a single emitter. We show that extinction measurements can be advantageous if the emitter is weakly excited. Furthermore, we discuss the potential of this method for the detection and spectroscopy of weakly emitting systems such as rare earth ions.Comment: 11 pages, 5 figure