2,225 research outputs found
Hydrological controls of in situ preservation of waterlogged archaeological deposits
Environmental change caused by urban development, land drainage, agriculture or climate change may result in accelerated decay of
in situ archaeological remains. This paper reviews research into impacts of environmental change on hydrological processes of relevance
to preservation of archaeological remains in situ. It compares work at rural sites with more complex urban environments. The research
demonstrates that both the quantity and quality of data on preservation status, and hydrological and chemical parameters collected during
routine archaeological surveys need to be improved. The work also demonstrates the necessity for any archaeological site to be placed
within its topographic and geological context. In order to understand preservation potential fully, it is necessary to move away from
studying the archaeological site as an isolated unit, since factors some distance away from the site of interest can be important for
determining preservation. The paper reviews what is known about the hydrological factors of importance to archaeological preservation
and recommends research that needs to be conducted so that archaeological risk can be more adequately predicted and mitigated. Any
activity that changes either source pathways or the dominant water input may have an impact not just because of changes to the water
balance or the water table, but because of changes to water chemistry. Therefore, efforts to manage threatened waterlogged environments
must consider the chemical nature of the water input into the system. Clearer methods of assessing the degree to which buried
archaeological sites can withstand changing hydrological conditions are needed, in addition to research which helps us understand what
triggers decay and what controls thresholds of response for different sediments and types of artefact
eLISA Telescope In-field Pointing and Scattered Light Study
The orbital motion of the three spacecraft that make up the eLISA Observatory constellation causes long-arm line of sight variations of approximately one degree over the course of a year. The baseline solution is to package the telescope, the optical bench, and the gravitational reference sensor (GRS) into an optical assembly at each end of the measurement arm, and then to articulate the assembly. An optical phase reference is exchanged between the moving optical benches with a single mode optical fiber (backlink fiber). An alternative solution, referred to as in-field pointing, embeds a steering mirror into the optical design, fixing the optical benches and eliminating the backlink fiber, but requiring the additional complication of a two-stage optical design for the telescope. We examine the impact of an in-field pointing design on the scattered light performance
In vivo model for microbial invasion of tooth root dentinal tubules
ABSTRACT Objective Bacterial penetration of dentinal tubules via exposed dentine can lead to root caries and promote infections of the pulp and root canal system. The aim of this work was to develop a new experimental model for studying bacterial invasion of dentinal tubules within the human oral cavity. Material and Methods Sections of human root dentine were mounted into lower oral appliances that were worn by four human subjects for 15 d. Roots were then fixed, sectioned, stained and examined microscopically for evidence of bacterial invasion. Levels of invasion were expressed as Tubule Invasion Factor (TIF). DNA was extracted from root samples, subjected to polymerase chain reaction amplification of 16S rRNA genes, and invading bacteria were identified by comparison of sequences with GenBank database. Results All root dentine samples with patent tubules showed evidence of bacterial cell invasion (TIF value range from 5.7 to 9.0) to depths of 200 mm or more. A spectrum of Gram-positive and Gram-negative cell morphotypes were visualized, and molecular typing identified species of Granulicatella, Streptococcus, Klebsiella, Enterobacter, Acinetobacter, and Pseudomonas as dentinal tubule residents. Conclusion A novel in vivo model is described, which provides for human root dentine to be efficiently infected by oral microorganisms. A range of bacteria were able to initially invade dentinal tubules within exposed dentine. The model will be useful for testing the effectiveness of antiseptics, irrigants, and potential tubule occluding agents in preventing bacterial invasion of dentine
Hypothermic cardiopulmonary bypass: A comparison between alpha and pH stat regulation in the dog
The accepted normal pH of 7.40 may not be optimal at lower temperatures. This study evaluated the effect of maintaining pH in the accepted normal range at hypothermia (group 1, pH stat) or at normothermia (group 2, alpha stat) on organ blood flow and hemodynamics in dogs. The desired pH was achieved at all temperatures by adjusting pCO2. Hypothermia to 20[deg]C was induced by high flow bypass in both groups followed by 45 min of reduced flow before rewarming. In group 1 (n = 10), pH was 7.45 +/- 0.02 at 20[deg]C and in group 2 (n = 11) it was 7.64 +/- 0.01. A greater base excess developed by the end of the low flow period in pH stat animals (-9.4 +/- 1.1 vs -2.8 +/- 0.8, P P P P P P P P pCO2 control between alpha and pH stat regulation assume lesser importance for regional blood flow when normal systemic flow is maintained during cooling and rewarming.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26870/1/0000435.pd
In vivo model for microbial invasion of tooth root dentinal tubules
Objective Bacterial penetration of dentinal tubules via exposed dentine can lead to root caries and promote infections of the pulp and root canal system. The aim of this work was to develop a new experimental model for studying bacterial invasion of dentinal tubules within the human oral cavity. Material and Methods Sections of human root dentine were mounted into lower oral appliances that were worn by four human subjects for 15 d. Roots were then fixed, sectioned, stained and examined microscopically for evidence of bacterial invasion. Levels of invasion were expressed as Tubule Invasion Factor (TIF). DNA was extracted from root samples, subjected to polymerase chain reaction amplification of 16S rRNA genes, and invading bacteria were identified by comparison of sequences with GenBank database. Results All root dentine samples with patent tubules showed evidence of bacterial cell invasion (TIF value range from 5.7 to 9.0) to depths of 200 mm or more. A spectrum of Gram-positive and Gram-negative cell morphotypes were visualized, and molecular typing identified species of Granulicatella, Streptococcus, Klebsiella, Enterobacter, Acinetobacter, and Pseudomonas as dentinal tubule residents. Conclusion A novel in vivo model is described, which provides for human root dentine to be efficiently infected by oral microorganisms. A range of bacteria were able to initially invade dentinal tubules within exposed dentine. The model will be useful for testing the effectiveness of antiseptics, irrigants, and potential tubule occluding agents in preventing bacterial invasion of dentine
The CRIRES Search for Planets Around the Lowest-Mass Stars. I. High-Precision Near-Infrared Radial Velocities with an Ammonia Gas Cell
Radial velocities measured from near-infrared spectra are a potentially
powerful tool to search for planets around cool stars and sub-stellar objects.
However, no technique currently exists that yields near-infrared radial
velocity precision comparable to that routinely obtained in the visible. We
describe a method for measuring high-precision relative radial velocities of
these stars from K-band spectra. The method makes use of a glass cell filled
with ammonia gas to calibrate the spectrograph response similar to the "iodine
cell" technique that has been used very successfully in the visible. Stellar
spectra are obtained through the ammonia cell and modeled as the product of a
Doppler-shifted template spectrum of the object and a spectrum of the cell,
convolved with a variable instrumental profile model. A complicating factor is
that a significant number of telluric absorption lines are present in the
spectral regions containing useful stellar and ammonia lines. The telluric
lines are modeled simultaneously as well using spectrum synthesis with a
time-resolved model of the atmosphere over the observatory. The free parameters
in the complete model are the wavelength scale of the spectrum, the
instrumental profile, adjustments to the water and methane abundances in the
atmospheric model, telluric spectrum Doppler shift, and stellar Doppler shift.
Tests of the method based on the analysis of hundreds of spectra obtained for
late M dwarfs over six months demonstrate that precisions of ~5 m/s are
obtainable over long timescales, and precisions of better than 3 m/s can be
obtained over timescales up to a week. The obtained precision is comparable to
the predicted photon-limited errors, but primarily limited over long timescales
by the imperfect modeling of the telluric lines.Comment: Accepted for publication in Ap
Non-equilibrium Phase Transitions with Long-Range Interactions
This review article gives an overview of recent progress in the field of
non-equilibrium phase transitions into absorbing states with long-range
interactions. It focuses on two possible types of long-range interactions. The
first one is to replace nearest-neighbor couplings by unrestricted Levy flights
with a power-law distribution P(r) ~ r^(-d-sigma) controlled by an exponent
sigma. Similarly, the temporal evolution can be modified by introducing waiting
times Dt between subsequent moves which are distributed algebraically as P(Dt)~
(Dt)^(-1-kappa). It turns out that such systems with Levy-distributed
long-range interactions still exhibit a continuous phase transition with
critical exponents varying continuously with sigma and/or kappa in certain
ranges of the parameter space. In a field-theoretical framework such
algebraically distributed long-range interactions can be accounted for by
replacing the differential operators nabla^2 and d/dt with fractional
derivatives nabla^sigma and (d/dt)^kappa. As another possibility, one may
introduce algebraically decaying long-range interactions which cannot exceed
the actual distance to the nearest particle. Such interactions are motivated by
studies of non-equilibrium growth processes and may be interpreted as Levy
flights cut off at the actual distance to the nearest particle. In the
continuum limit such truncated Levy flights can be described to leading order
by terms involving fractional powers of the density field while the
differential operators remain short-ranged.Comment: LaTeX, 39 pages, 13 figures, minor revision
Mindfulness is Inversely Associated with Alcohol Attentional Bias Among Recovering Alcohol-Dependent Adults
Although mindfulness has been linked with salutary clinical outcomes, less is known about its relation to cognitive mechanisms implicated in the onset and maintenance of alcohol dependence. Because trait mindfulness is associated with attentional control and emotion regulation, we hypothesized that trait mindfulness would be inversely associated with attentional bias towards visual alcohol cues. We tested this hypothesis in a sample of alcohol-dependent adults residing in a treatment facility, who completed questionnaires on trait mindfulness, craving, and stress, as well as a spatial cueing task designed to assess alcohol attentional bias. Recovering alcohol-dependent individuals high in trait mindfulness exhibited less alcohol attentional bias (AB), stress, and craving, and greater alcohol-related self-efficacy, than their counterparts low in trait mindfulness. Multiple linear regression analyses indicated that trait mindfulness was more predictive of alcohol AB than stress, craving, alcohol-related self-efficacy, time in treatment, or pre-treatment level of alcohol consumption. Identification of malleable traits that can offset automatic cognitive mechanisms implicated in addiction may prove to be crucial to treatment development efforts
The Exotic Eclipsing Nucleus of the Ring Planetary Nebula SuWt2
SuWt2 is a planetary nebula (PN) consisting of a bright ionized thin ring
seen nearly edge-on. It has a bright (V=12) central star, too cool to ionize
the PN, which we discovered to be an eclipsing binary. A spectrum from IUE did
not reveal a UV source. We present extensive ground-based photometry and
spectroscopy of the central binary collected over the ensuing two decades,
resulting in the determination that the orbital period of the eclipsing pair is
4.9 d, and consists of two nearly identical A1 V stars, each of mass ~2.7
M_sun. The physical parameters of the A stars, combined with evolutionary
tracks, show that both are in the short-lived "blue-hook" evolutionary phase
that occurs between the main sequence and the Hertzsprung gap, and that the age
of the system is about 520 Myr. One puzzle is that the stars' rotational
velocities are different from each other, and considerably slower than
synchronous with the orbital period. It is possible that the center-of-mass
velocity of the eclipsing pair is varying with time, suggesting that there is
an unseen third orbiting body in the system. We propose a scenario in which the
system began as a hierarchical triple, consisting of a ~2.9 M_sun star orbiting
the close pair of A stars. Upon reaching the AGB stage, the primary engulfed
the pair into a common envelope, leading to a rapid contraction of the orbit
and catastrophic ejection of the envelope into the orbital plane. In this
picture, the exposed core of the initial primary is now a white dwarf of ~0.7
M_sun, orbiting the eclipsing pair, which has already cooled below the
detectability possible by IUE at our derived distance of 2.3 kpc and a
reddening of E(B-V)=0.40. The SuWt2 system may be destined to perish as a Type
Ia supernova. (Abridged)Comment: 60 pages, 11 figure, to appear in the Astronomical Journa
Classical and relativistic long-term time variations of some observables for transiting exoplanets
We analytically work out the long-term, i.e. averaged over one orbital
revolution, time variations of some direct observable quantities Y induced by
classical and general relativistic dynamical perturbations of the two-body
pointlike Newtonian acceleration in the case of transiting exoplanets moving
along elliptic orbits. More specifically, the observables with which we
deal are the transit duration, the radial velocity and the time interval
between primary and secondary eclipses. The dynamical effects considered are
the centrifugal oblateness of both the star and the planet, their tidal bulges
mutually raised on each other, a distant third body X, and general relativity
(both Schwarzschild and Lense-Thirring). We take into account the effects due
to the perturbations of all the Keplerian orbital elements involved in a
consistent and uniform way. First, we explicitly compute their instantaneous
time variations due to the dynamical effects considered and plug them in the
general expression for the instantaneous change of Y; then, we take the overall
average over one orbital revolution of the so-obtained instantaneous rate specialized to the perturbations considered. Instead, somewhat hybrid
expressions can be often found in literature: in them, the secular precession
of, typically, the periastron only is straightforwardly inserted into
instantaneous formulas. Numerical evaluations of the obtained results are given
for a typical star-planet scenario and compared with the expected observational
accuracies over a time span 10 yr long. Our results are, in principle, valid
also for other astronomical scenarios. They may allow, e.g., for designing
various tests of gravitational theories with natural and artificial bodies in
our solar system. (Abridged)Comment: LaTex2e, 19 pages, 5 figures, 2 tables. Some references updated. To
appear in Monthly Notices of the Royal Astronomical Society (MNRAS
- …