851 research outputs found
The Tolman-Eichenbaum Machine: Unifying Space and Relational Memory through Generalization in the Hippocampal Formation
The hippocampal-entorhinal system is important for spatial and relational memory tasks. We formally link these domains, provide a mechanistic understanding of the hippocampal role in generalization, and offer unifying principles underlying many entorhinal and hippocampal cell types. We propose medial entorhinal cells form a basis describing structural knowledge, and hippocampal cells link this basis with sensory representations. Adopting these principles, we introduce the Tolman-Eichenbaum machine (TEM). After learning, TEM entorhinal cells display diverse properties resembling apparently bespoke spatial responses, such as grid, band, border, and object-vector cells. TEM hippocampal cells include place and landmark cells that remap between environments. Crucially, TEM also aligns with empirically recorded representations in complex non-spatial tasks. TEM also generates predictions that hippocampal remapping is not random as previously believed; rather, structural knowledge is preserved across environments. We confirm this structural transfer over remapping in simultaneously recorded place and grid cells
The First Detections of the Extragalactic Background Light at 3000, 5500, and 8000A (II): Measurement of Foreground Zodiacal Light
We present a measurement of the absolute surface brightness of the zodiacal
light (3900-5100A) toward a fixed extragalactic target at high ecliptic
latitude based on moderate resolution (~1.3A per pixel) spectrophotometry
obtained with the du Pont 2.5m telescope at Las Campanas Observatory in Chile.
This measurement and contemporaneous Hubble Space Telescope data from WFPC2 and
FOS comprise a coordinated program to measure the mean flux of the diffuse
extragalactic background light (EBL). The zodiacal light at optical wavelengths
results from scattering by interplanetary dust, so that the zodiacal light flux
toward any extragalactic target varies seasonally with the position of the
Earth. This measurement of zodiacal light is therefore relevant to the specific
observations (date and target field) under discussion. To obtain this result,
we have developed a technique that uses the strength of the zodiacal Fraunhofer
lines to identify the absolute flux of the zodiacal light in the
multiple-component night sky spectrum. Statistical uncertainties in the result
are 0.6% (1 sigma). However, the dominant source of uncertainty is systematic
errors, which we estimate to be 1.1% (1 sigma). We discuss the contributions
included in this estimate explicitly. The systematic errors in this result
contribute 25% in quadrature to the final error in our coordinated EBL
measurement, which is presented in the first paper of this series.Comment: Accepted for publication in ApJ, 22 pages using emulateapj.sty,
version with higher resolution figures available at
http://www.astro.lsa.umich.edu/~rab/publications.html or at
http://nedwww.ipac.caltech.edu/level5/Sep01/Bernstein2/frames.htm
Mechanisms of cerebellar tonsil herniation in patients with Chiari malformations as guide to clinical management
Background The pathogenesis of Chiari malformations is incompletely understood. We tested the hypothesis that different etiologies have different mechanisms of cerebellar tonsil herniation (CTH), as revealed by posterior cranial fossa (PCF) morphology. Methods In 741 patients with Chiari malformation type I (CM-I) and 11 patients with Chiari malformation type II (CM-II), the size of the occipital enchondrium and volume of the PCF (PCFV) were measured on reconstructed 2D-CT and MR images of the skull. Measurements were compared with those in 80 age- and sex-matched healthy control individuals, and the results were correlated with clinical findings. Results Significant reductions of PCF size and volume were present in 388 patients with classical CM-I, 11 patients with CM-II, and five patients with CM-I and craniosynostosis. Occipital bone size and PCFV were normal in 225 patients with CM-I and occipitoatlantoaxial joint instability, 55 patients with CM-I and tethered cord syndrome (TCS), 30 patients with CM-I and intracranial mass lesions, and 28 patients with CM-I and lumboperitoneal shunts. Ten patients had miscellaneous etiologies. The size and area of the foramen magnum were significantly smaller in patients with classical CM-I and CM-I occurring with craniosynostosis and significantly larger in patients with CM-II and CM-I occurring with TCS. Conclusions Important clues concerning the pathogenesis of CTH were provided by morphometric measurements of the PCF. When these assessments were correlated with etiological factors, the following causal mechanisms were suggested: (1) cranial constriction; (2) cranial settling; (3) spinal cord tethering; (4) intracranial hypertension; and (5) intraspinal hypotension
Silicate dust in the environment of RS Ophiuchi following the 2006 eruption
We present further Spitzer Space Telescope observations of the recurrent nova
RS Ophiuchi, obtained over the period 208-430 days after the 2006 eruption. The
later Spitzer IRS data show that the line emission and free-free continuum
emission reported earlier is declining, revealing incontrovertible evidence for
the presence of silicate emission features at 9.7 and 18microns. We conclude
that the silicate dust survives the hard radiation impulse and shock blast wave
from the eruption. The existence of the extant dust may have significant
implications for understanding the propagation of shocks through the red giant
wind and likely wind geometry.Comment: 12 pages, 4 figures, accepted for publication in ApJ (Letters
The application of predictive modelling for determining bio-environmental factors affecting the distribution of blackflies (Diptera: Simuliidae) in the Gilgel Gibe watershed in Southwest Ethiopia
Blackflies are important macroinvertebrate groups from a public health as well as ecological point of view. Determining the biological and environmental factors favouring or inhibiting the existence of blackflies could facilitate biomonitoring of rivers as well as control of disease vectors. The combined use of different predictive modelling techniques is known to improve identification of presence/absence and abundance of taxa in a given habitat. This approach enables better identification of the suitable habitat conditions or environmental constraints of a given taxon. Simuliidae larvae are important biological indicators as they are abundant in tropical aquatic ecosystems. Some of the blackfly groups are also important disease vectors in poor tropical countries. Our investigations aim to establish a combination of models able to identify the environmental factors and macroinvertebrate organisms that are favourable or inhibiting blackfly larvae existence in aquatic ecosystems. The models developed using macroinvertebrate predictors showed better performance than those based on environmental predictors. The identified environmental and macroinvertebrate parameters can be used to determine the distribution of blackflies, which in turn can help control river blindness in endemic tropical places. Through a combination of modelling techniques, a reliable method has been developed that explains environmental and biological relationships with the target organism, and, thus, can serve as a decision support tool for ecological management strategies
A spectral atlas of post-main-sequence stars in omega Centauri: kinematics, evolution, enrichment and interstellar medium
We present a spectral atlas of the post-main-sequence population of the most
massive Galactic globular cluster, omega Centauri. Spectra were obtained of
more than 1500 stars selected as uniformly as possible from across the (B, B-V)
colour-magnitude diagram of the proper motion cluster member candidates of van
Leeuwen et al. (2000). The spectra were obtained with the 2dF multi-fibre
spectrograph at the Anglo Australian Telescope, and cover the approximate range
lambda~3840-4940 Angstroem. We measure the radial velocities, effective
temperatures, metallicities and surface gravities by fitting ATLAS9 stellar
atmosphere models. We analyse the cluster membership and stellar kinematics,
interstellar absorption in the Ca II K line at 3933 Angstroem, the RR Lyrae
instability strip and the extreme horizontal branch, the metallicity spread and
bimodal CN abundance distribution of red giants, nitrogen and s-process
enrichment, carbon stars, pulsation-induced Balmer line emission on the
asymptotic giant branch (AGB), and the nature of the post-AGB and UV-bright
stars. Membership is confirmed for the vast majority of stars, and the radial
velocities clearly show the rotation of the cluster core. We identify
long-period RR Lyrae-type variables with low gravity, and low-amplitude
variables coinciding with warm RR Lyrae stars. A barium enhancement in the
coolest red giants indicates that 3rd dredge-up operates in AGB stars in omega
Cen. This is distinguished from the pre-enrichment by more massive AGB stars,
which is also seen in our data. The properties of the AGB, post-AGB and
UV-bright stars suggest that RGB mass loss may be less efficient at very low
metallicity, [Fe/H]<<-1, increasing the importance of mass loss on the AGB. The
catalogue and spectra are made available via CDS.Comment: accepted for publication in MNRA
Hypertrophic cardiomyopathy in myosin-binding protein C (MYBPC3) Icelandic founder mutation carriers
Objective: The myosin-binding protein C (MYBPC3) c.927-2A>G founder mutation accounts for >90% of sarcomeric hypertrophic cardiomyopathy (HCM) in Iceland. This cross-sectional observational study explored the penetrance and phenotypic burden among
carriers of this single, prevalent founder mutation.
Methods: We studied 60 probands with HCM caused by MYBPC3 c.927-2A>G and 225 first-degree relatives. All participants underwent comprehensive clinical evaluation and relatives were genotyped.
Results: Genetic and clinical evaluation of relatives identified 49 genotype-positive (G+) relatives with left ventricular hypertrophy (G+/LVH+), 59 G+without LVH (G+/LVH−) and 117 genotype-negative relatives (unaffected). Compared with HCM probands, G+/
LVH+ relatives were older at HCM diagnosis, had less LVH, a less prevalent diastolic dysfunction, fewer ECG abnormalities, lower serum N-terminal pro-B-type natriuretic peptide (NT-proBNP) and high-sensitivity cardiac troponin I levels, and fewer symptoms. The penetrance of HCM was influenced by age and sex; specifically, LVH was present in 39%
of G+males but only 9% of G+females under age 40 years (p=0.015), versus 86% and 83%, respectively, after age 60 (p=0.89). G+/LVH− subjects had normal wall thicknesses, diastolic function and NT-proBNP levels, but subtle changes in LV geometry and more ECG
abnormalities than their unaffected relatives.
Conclusions: Phenotypic expression of the Icelandic MYBPC3 founder mutation varies by age, sex and proband status. Men are more likely to have LVH at a younger age, and disease manifestations were more prominent in probands than in relatives identified via
family screening. G+/LVH− individuals had subtle clinical differences from unaffected relatives well into adulthood, indicating subclinical phenotypic expression of the pathogenic mutation
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The effects of tannin-containing ground pine bark diet upon nutrient digestion, nitrogen balance, and mineral retention in meat goats
Background
Pine bark is a rich source of phytochemical compounds including tannins, phenolic acids, anthocyanins, and fatty acids. These phytochemicals have potential to significantly impact on animal health and animal production. The goal of this work is to measure the effects of tannins in ground pine bark as a partial feed replacement on feed intake, dietary apparent digestibility, nitrogen balance, and mineral retention in meat goats.
Results
Eighteen Kiko cross goats (initial BW = 31.8 ± 1.49 kg) were randomly assigned to three treatment groups (n = 6). Dietary treatments were tested: control (0 % pine bark powder (PB) and 30 % wheat straw (WS)); 15 % PB and 15 % WS, and 30 % PB and 0 % WS. Although dry matter (DM) intake and digestibility were not affected (P > 0.10) by feeding PB, neutral detergent fiber (linear; P = 0.01), acid detergent fiber (linear; P = 0.001) and lignin digestibility (linear; P = 0.01) decreased, and crude protein (CP) digestibility tended to decrease (P = 0.09) as PB increased in the diet, apparent retention of Ca (P = 0.09), P (P = 0.03), Mg (P = 0.01), Mn (P = 0.01), Zn (P = 0.01) and Fe (P = 0.09) also increased linearly. Nitrogen intake and fecal N excretion were not affected (P > 0.05) by addition of PB in the diet, but N balance in the body was quadratically increased (P < 0.01) in the 15 % PB diet compared to other diets. This may be due to more rumen escape protein and less excreted N in the urine with the 15 % PB diet. The study showed that a moderate level of tannin-containing pine bark supplementation could improve gastrointestinal nitrogen balance with the aim of improving animal performance.
Conclusion
These results suggest that tannin-containing PB has negative impact on fiber, lignin, and protein digestibility, but positively impacted on N-balance
The Spitzer Spectroscopic Survey of S-type Stars
S-type AGB stars are thought to be in the transitional phase between M-type
and C-type AGB stars. Because of their peculiar chemical composition, one may
expect a strong influence of the stellar C/O ratio on the molecular chemistry
and the mineralogy of the circumstellar dust. In this paper, we present a large
sample of 87 intrinsic galactic S-type AGB stars, observed at infrared
wavelengths with the Spitzer Space Telescope, and supplemented with
ground-based optical data. On the one hand, we derive the stellar parameters
from the optical spectroscopy and photometry, using a grid of model
atmospheres. On the other, we decompose the infrared spectra to quantify the
flux-contributions from the different dust species. Finally, we compare the
independently determined stellar parameters and dust properties. For the stars
without significant dust emission, we detect a strict relation between the
presence of SiS absorption in the Spitzer spectra and the C/O ratio of the
stellar atmosphere. These absorption bands can thus be used as an additional
diagnostic for the C/O ratio. For stars with significant dust emission, we
define three groups, based on the relative contribution of certain dust species
to the infrared flux. We find a strong link between group-membership and C/O
ratio. We show that these groups can be explained by assuming that the
dust-condensation can be cut short before silicates are produced, while the
remaining free atoms and molecules can then form the observed magnesium
sulfides or the carriers of the unidentified 13 and 20 micron features.
Finally, we present the detection of emission features attributed to molecules
and dust characteristic to C-type stars, such as molecular SiS, hydrocarbons
and magnesium sulfide grains. We show that we often detect magnesium sulfides
together with molecular SiS and we propose that it is formed by a reaction of
SiS molecules with Mg.Comment: Accepted for publication in A&
Pneumonic Tularemia in Rabbits Resembles the Human Disease as Illustrated by Radiographic and Hematological Changes after Infection
Background: Pneumonic tularemia is caused by inhalation of the gram negative bacterium, Francisella tularensis. Because of concerns that tularemia could be used as a bioterrorism agent, vaccines and therapeutics are urgently needed. Animal models of pneumonic tularemia with a pathophysiology similar to the human disease are needed to evaluate the efficacy of these potential medical countermeasures. Principal Findings: Rabbits exposed to aerosols containing Francisella tularensis strain SCHU S4 developed a rapidly progressive fatal pneumonic disease. Clinical signs became evident on the third day after exposure with development of a fever (>40.5°C) and a sharp decline in both food and water intake. Blood samples collected on day 4 found lymphopenia and a decrease in platelet counts coupled with elevations in erythrocyte sedimentation rate, alanine aminotransferase, cholesterol, granulocytes and monocytes. Radiographs demonstrated the development of pneumonia and abnormalities of intestinal gas consistent with ileus. On average, rabbits were moribund 5.1 days after exposure; no rabbits survived exposure at any dose (190-54,000 cfu). Gross evaluation of tissues taken at necropsy showed evidence of pathology in the lungs, spleen, liver, kidney and intestines. Bacterial counts confirmed bacterial dissemination from the lungs to the liver and spleen. Conclusions/Significance: The pathophysiology of pneumonic tularemia in rabbits resembles what has been reported for humans. Rabbits therefore are a relevant model of the human disease caused by type A strains of F. tularensis. © 2011 Reed et al
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