1,398 research outputs found
Field-dependent heat transport in the Kondo insulator SmB6 : phonons scattered by magnetic impurities
The thermal conductivity of the Kondo insulator SmB was measured
at low temperature, down to 70 mK, in magnetic fields up to 15 T, on single
crystals grown using both the floating-zone and the flux methods. The residual
linear term at is found to be zero in all samples, for
all magnetic fields, in agreement with previous studies. There is therefore no
clear evidence of fermionic heat carriers. In contrast to some prior data, we
observe a large enhancement of with increasing field. The effect of
field is anisotropic, depending on the relative orientation of field and heat
current (parallel or perpendicular), and with respect to the cubic crystal
structure. We interpret our data in terms of heat transport predominantly by
phonons, which are scattered by magnetic impurities.Comment: publish versio
High prevalence of scrapie in a dairy goat herd: tissue distribution of disease-associated PrP and effect of PRNP genotype and age
Following a severe outbreak of clinical scrapie in 2006–2007, a
large dairy goat herd was culled
and 200 animals were selected for post-mortem examinations in order to
ascertain the prevalence of infection,
the effect of age, breed and PRNP genotype on the susceptibility to scrapie,
the tissue distribution of diseaseassociated
PrP (PrP), and the comparative efficiency of different diagnostic methods.
As determined by immunohistochemical (IHC) examinations with Bar224 PrP antibody, the
prevalence of preclinical infection
was very high (72/200; 36.0%), with most infected animals being positive
for PrP in lymphoreticular system
(LRS) tissues (68/72; 94.4%) compared to those that were positive in
brain samples (38/72; 52.8%). The
retropharyngeal lymph node and the palatine tonsil showed the highest
frequency of PrP accumulation (87.3%
and 84.5%, respectively), while the recto-anal mucosa-associated lymphoid
tissue (RAMALT) was positive in
only 30 (41.7%) of the infected goats. However, the efficiency of rectal
and palatine tonsil biopsies taken
shortly before necropsy was similar. The probability of brain and RAMALT
being positive directly
correlated with the spread of PrP within the LRS. The prevalence of
infection was influenced by PRNP
genetics at codon 142 and by the age of the goats: methionine carriers older
than 60 months showed a much
lower prevalence of infection (12/78; 15.4%) than those younger than 60 months (20/42; 47.6%); these last
showed prevalence values similar to isoleucine homozygotes of any age
(40/80; 50.0%). Two of seven goats
with definite signs of scrapie were negative for PrP in brain but positive
in LRS tissues, and one goat showed
biochemical and IHC features of PrP different from all other infected
goats. The results of this study have
implications for surveillance and control policies for scrapie in goats
Correlation between bulk thermodynamic measurements and the low temperature resistance plateau in SmB6
Topological insulators are materials characterized by dissipationless,
spin-polarized surface states resulting from non-trivial band topologies.
Recent theoretical models and experiments suggest that SmB6 is the first
topological Kondo insulator, in which the topologically non-trivial band
structure results from electron-electron interactions via Kondo hybridization.
Here, we report that the surface conductivity of SmB6 increases systematically
with bulk carbon content. Further, addition of carbon is linked to an increase
in n-type carriers, larger low temperature electronic contributions to the
specific heat with a characteristic temperature scale of T* = 17 K, and a
broadening of the crossover to the insulating state. Additionally, X-ray
absorption spectroscopy shows a change in Sm valence at the surface. Our
results highlight the importance of phonon dynamics in producing a Kondo
insulating state and demonstrate a correlation between the bulk thermodynamic
state and low temperature resistance of SmB6
Incommensurate magnetism near quantum criticality in CeNiAsO
Two phase transitions in the tetragonal strongly correlated electron system
CeNiAsO were probed by neutron scattering and zero field muon spin rotation.
For = 8.7(3) K, a second order phase transition yields an
incommensurate spin density wave with wave vector . For = 7.6(3) K, we find co-planar commensurate order with a
moment of , reduced to of the saturation moment of the
Kramers doublet ground state, which we establish by
inelastic neutron scattering. Muon spin rotation in
shows the commensurate order only exists for x 0.1 so the transition at
= 0.4(1) is from an incommensurate longitudinal spin density wave to a
paramagnetic Fermi liquid
Cerebrovascular Pathology in Down Syndrome and Alzheimer Disease
People with Down syndrome (DS) are at high risk for developing Alzheimer disease (AD) with age. Typically, by age 40 years, most people with DS have sufficient neuropathology for an AD diagnosis. Interestingly, atherosclerosis and hypertension are atypical in DS with age, suggesting the lack of these vascular risk factors may be associated with reduced cerebrovascular pathology. However, because the extra copy of APP leads to increased beta-amyloid peptide (Aβ) accumulation in DS, we hypothesized that there would be more extensive and widespread cerebral amyloid angiopathy (CAA) with age in DS relative to sporadic AD. To test this hypothesis CAA, atherosclerosis and arteriolosclerosis were used as measures of cerebrovascular pathology and compared in post mortem tissue from individuals with DS (n = 32), sporadic AD (n = 80) and controls (n = 37). CAA was observed with significantly higher frequencies in brains of individuals with DS compared to sporadic AD and controls. Atherosclerosis and arteriolosclerosis were rare in the cases with DS. CAA in DS may be a target for future interventional clinical trials
Topological surface states in the Kondo insulator YbB revealed via planar tunneling spectroscopy
Planar tunneling spectroscopy of the Kondo insulator SmB suggests that an
interaction between the surface Dirac fermions and the bulk spin excitons
results in incompletely protected topological surface states. To gain further
insight into their true nature, it is necessary to study other topological
Kondo insulator candidates. Calculations of electronic energy bands predict
that the Kondo insulator YbB hosts topological surface states protected
by crystalline mirror symmetry. In this study, we present tunneling conductance
spectra obtained from the (001) surface of YbB single crystals and
discuss them in comparison to SmB. The linear conductance at low bias
provides strong evidence for the existence of surface Dirac fermions. The
double-hump structure in the negative bias region is associated with hybridized
band edges, in agreement with a calculated band structure. While these
similarities with SmB6 are suggestive of the existence of topological surface
states in YbB, in agreement with other experiments, some discrepancies
are also observed, which we attribute to a difference in their exact nature
from those in SmB.Comment: 25 pages, 7 figures, submitted to Physical Review
Experience and expectations of patients on weight loss: The Learning Health System Network Experience
Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152010/1/osp4364_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152010/2/osp4364.pd
First results from the MIT optical rapid imaging system (MORIS) on the IRTF: A stellar occultation by Pluto and a transit by exoplanet XO-2b
We present a high-speed, visible-wavelength imaging instrument: MORIS (the MIT Optical Rapid Imaging System). MORIS is mounted on the 3 m Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Its primary component is an Andor iXon camera, a nearly 60" square field of view with high quantum efficiency, low read noise, low dark current, and full-frame readout rates ranging from as slow as desired to a maximum of between 3.5 Hz and 35 Hz (depending on the mode; read noise of 6 pixel and 49 pixel with electron-multiplying gain = 1 , respectively). User-selectable binning and subframing can increase the cadence to a few hundred hertz. An electron-multiplying mode can be employed for photon counting, effectively reducing the read noise to subelectron levels at the expense of dynamic range. Data cubes, or individual frames, can be triggered to several-nanosecond accuracy using the Global Positioning System. MORIS is mounted on the side-facing exit window of SpeX, allowing simultaneous near-infrared and visible observations. Here, we describe the components, setup, and measured characteristics of MORIS. We also report results from the first science observations: the 2008 June 24 stellar occultation by Pluto and an extrasolar planetary transit by XO-2b. The Pluto occultation of a 15.8 magnitude star has a signal-to-noise ratio of 35 per atmospheric scale height and a midtime error of 0.32 s. The XO-2b transit reaches photometric precision of 0.5 mmag in 2 minutes and has a midtime timing precision of 23 s.United States. National Aeronautics and Space Administration (grant NNX07AK95G
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