2,630 research outputs found
Electronic Liquid Crystal Phases of a Doped Mott Insulator
The character of the ground state of an antiferromagnetic insulator is
fundamentally altered upon addition of even a small amount of charge. The added
charges agglomerate along domain walls at which the spin correlations, which
may or may not remain long-ranged, suffer a phase shift. In two
dimensions, these domain walls are ``stripes'' which are either insulating, or
conducting, i.e. metallic rivers with their own low energy degrees of freedom.
However, quasi one-dimensional metals typically undergo a transition to an
insulating ordered charge density wave (CDW) state at low temperatures. Here it
is shown that such a transition is eliminated if the zero-point energy of
transverse stripe fluctuations is sufficiently large in comparison to the CDW
coupling between stripes. As a consequence, there exist novel,
liquid-crystalline low-temperature phases -- an electron smectic, with
crystalline order in one direction, but liquid-like correlations in the other,
and an electron nematic with orientational order but no long-range positional
order. These phases, which constitute new states of matter, can be either high
temperature supeconductors or two-dimensional anisotropic ``metallic''
non-Fermi liquids. Evidence for the new phases may already have been obtained
by neutron scattering experiments in the cuprate superconductor,
La_{1.6-x}Nd_{0.4}Sr_xCuO_{4}.Comment: 5 pages in RevTex with two figures in ep
Vanishing of phase coherence in underdoped Bi_2Sr_2CaCu_2O_8+d
Coherent time-domain spectroscopy is used to measure the screening and
dissipation of high-frequency electromagnetic fields in a set of underdoped
Bi_2Sr_2CaCu_2O_8+d thin films. The measurements provide direct evidence for a
phase-fluctuation driven transition from the superconductor to normal state,
with dynamics described well by the Berezinskii-Kosterlitz-Thouless theory of
vortex-pair unbinding.Comment: Nature, Vol. 398, 18 March 1999, pg. 221 4 pages with 4 included
figure
From correlation functions to Wilson loops
We start with an n-point correlation function in a conformal gauge theory. We
show that a special limit produces a polygonal Wilson loop with sides. The
limit takes the points towards the vertices of a null polygonal Wilson loop
such that successive distances . This produces a fast moving
particle that generates a "frame" for the Wilson loop. We explain in detail how
the limit is approached, including some subtle effects from the propagation of
a fast moving particle in the full interacting theory. We perform perturbative
checks by doing explicit computations in N=4 super-Yang-Mills.Comment: 37 pages, 10 figures; typos corrected, references adde
Initial fixation placement in face images is driven by top-down guidance
The eyes are often inspected first and for longer period during face exploration. To examine whether this saliency of the eye region at the early stage of face inspection is attributed to its local structure properties or to the knowledge of its essence in facial communication, in this study we investigated the pattern of eye movements produced by rhesus monkeys (Macaca mulatta) as they free viewed images of monkey faces. Eye positions were recorded accurately using implanted eye coils, while images of original faces, faces with scrambled eyes, and scrambled faces except for the eyes were presented on a computer screen. The eye region in the scrambled faces attracted the same proportion of viewing time and fixations as it did in the original faces, even the scrambled eyes attracted substantial proportion of viewing time and fixations. Furthermore, the monkeys often made the first saccade towards to the location of the eyes regardless of image content. Our results suggest that the initial fixation placement in faces is driven predominantly by ‘top-down’ or internal factors, such as the prior knowledge of the location of “eyes” within the context of a face
The connection between superconducting phase correlations and spin excitations in YBaCuO: A magnetic field study
One of the most striking universal properties of the
high-transition-temperature (high-) superconductors is that they are all
derived from the hole-doping of their insulating antiferromagnetic (AF) parent
compounds. From the outset, the intimate relationship between magnetism and
superconductivity in these copper-oxides has intrigued researchers. Evidence
for this link comes from neutron scattering experiments that show the
unambiguous presence of short-range AF correlations (excitations) in cuprate
superconductors. Even so, the role of such excitations in the pairing mechanism
and superconductivity is still a subject of controversy. For
YBaCuO, where controls the hole-doping level, the most
prominent feature in the magnetic excitations spectra is the ``resonance''.
Here we show that for underdoped YBaCuO, where and
are below the optimal values, modest magnetic fields suppress the resonance
significantly, much more so for fields approximately perpendicular rather than
parallel to the CuO planes. Our results indicate that the resonance
measures pairing and phase coherence, suggesting that magnetism plays an
important role in the superconductivity of cuprates. The persistence of a field
effect above favors mechanisms with preformed pairs in the normal state
of underdoped cuprates.Comment: 12 pages, 4 figures, Nature (in press
Lithofacies uncertainty modeling in a siliciclastic reservoir setting by incorporating geological contacts and seismic information
Deterministic modeling lonely provides a unique boundary layout, depending on the geological interpretation or interpolation
from the hard available data. Changing the interpreter’s attitude or interpolation parameters leads to displacing the
location of these borders. In contrary, probabilistic modeling of geological domains such as lithofacies is a critical aspect
to providing information to take proper decision in the case of evaluation of oil reservoirs parameters, that is, applicable
for quantification of uncertainty along the boundaries. These stochastic modeling manifests itself dramatically beyond this
occasion. Conventional approaches of probabilistic modeling (object and pixel-based) mostly suffers from consideration
of contact knowledge on the simulated domains. Plurigaussian simulation algorithm, in contrast, allows reproducing the
complex transitions among the lithofacies domains and has found wide acceptance for modeling petroleum reservoirs.
Stationary assumption for this framework has implications on the homogeneous characterization of the lithofacies. In this
case, the proportion is assumed constant and the covariance function as a typical feature of spatial continuity depends only
on the Euclidean distances between two points. But, whenever there exists a heterogeneity phenomenon in the region, this
assumption does not urge model to generate the desired variability of the underlying proportion of facies over the domain.
Geophysical attributes as a secondary variable in this place, plays an important role for generation of the realistic contact
relationship between the simulated categories. In this paper, a hierarchical plurigaussian simulation approach is used to construct
multiple realizations of lithofacies by incorporating the acoustic impedance as soft data through an oil reservoir in Iran.This research was funded by the National Elites Foundation of Iran in collaboration with research Institute Petroleum of Industry in Iran under the project number of 9265005
Stimulation of GLP-1 secretion downstream of the ligand-gated ion channel TRPA1.
Stimulus-coupled incretin secretion from enteroendocrine cells plays a fundamental role in glucose homeostasis and could be targeted for the treatment of type 2 diabetes. Here, we investigated the expression and function of transient receptor potential (TRP) ion channels in enteroendocrine L cells producing GLP-1. By microarray and quantitative PCR analysis, we identified trpa1 as an L cell-enriched transcript in the small intestine. Calcium imaging of primary L cells and the model cell line GLUTag revealed responses triggered by the TRPA1 agonists allyl-isothiocyanate (mustard oil), carvacrol, and polyunsaturated fatty acids, which were blocked by TRPA1 antagonists. Electrophysiology in GLUTag cells showed that carvacrol induced a current with characteristics typical of TRPA1 and triggered the firing of action potentials. TRPA1 activation caused an increase in GLP-1 secretion from primary murine intestinal cultures and GLUTag cells, an effect that was abolished in cultures from trpa1(-/-) mice or by pharmacological TRPA1 inhibition. These findings present TRPA1 as a novel sensory mechanism in enteroendocrine L cells, coupled to the facilitation of GLP-1 release, which may be exploitable as a target for treating diabetes.This is an author-created, uncopyedited electronic version of an article accepted for publication in Diabetes. The American Diabetes Association (ADA), publisher of Diabetes, is not responsible for any errors or omissions in this version of the manuscript or any version derived from it by third parties. The definitive publisher-authenticated version will is available in Diabetes online at http://diabetes.diabetesjournals.org/content/early/2014/10/13/db14-0737.short?rss=1&patientinform-links=yes&legid=diabetes;db14-0737v1
Longer fixation duration while viewing face images
The spatio-temporal properties of saccadic eye movements can be influenced by the cognitive demand and the characteristics of the observed scene. Probably due to its crucial role in social communication, it is argued that face perception may involve different cognitive processes compared with non-face object or scene perception. In this study, we investigated whether and how face and natural scene images can influence the patterns of visuomotor activity. We recorded monkeys’ saccadic eye movements as they freely viewed monkey face and natural scene images. The face and natural scene images attracted similar number of fixations, but viewing of faces was accompanied by longer fixations compared with natural scenes. These longer fixations were dependent on the context of facial features. The duration of fixations directed at facial contours decreased when the face images were scrambled, and increased at the later stage of normal face viewing. The results suggest that face and natural scene images can generate different patterns of visuomotor activity. The extra fixation duration on faces may be correlated with the detailed analysis of facial features
Physical activity and fitness in women with metastatic breast cancer.
PURPOSE: This study aimed to explore differences in physical activity and fitness between women with metastatic breast cancer compared to healthy controls and factors associated with their physical activity levels. METHODS: Seventy-one women with metastatic breast cancer, aged (mean (SD)) 57.7 (9.5) and 2.9 (3.1) years after the onset of metastatic disease, and 71 healthy controls aged 55.0 (9.4) years participated. Of those with metastatic disease, 27% had bone-only metastases, 35% visceral-only metastases and 38% bone and visceral metastases. Patient-reported outcomes and physical measures of muscle strength and aerobic fitness assessments were obtained. Participants wore a SenseWear® physical activity monitor over 7 days, and the average steps/day and the time spent in moderate-to-vigorous intensity physical activity were determined. RESULTS: Women with metastases were significantly (i) less aerobically fit than the control group (25.3 (5.4) vs. 31.9 (6.1) mL • kg(-1) • min(-1); P < 0.001); (ii) weaker (e.g. lower limb strength for the metastatic and control groups was 53.5 (23.7) vs. 76.0 (27.4) kg, respectively; P < 0.001); (iii) less active, with the metastatic group attaining only 56% of the mean daily step counts of the healthy women; and (iv) more symptomatic, reporting higher levels of fatigue and dyspnoea (P < 0.001). CONCLUSION: Women living in the community with metastatic breast cancer possessed lower aerobic fitness, reduced muscular strength and less daily physical activity compared to healthy counterparts. They also experienced poorer functioning and higher symptom burden. IMPLICATIONS FOR CANCER SURVIVORS: Women living with metastatic breast cancer may benefit from a physical activity programme to address their physical impairments
<i>Trypanosoma brucei rhodesiense</i> transmitted by a single tsetse fly bite in vervet monkeys as a model of human African trypanosomiasis
Sleeping sickness is caused by a species of trypanosome blood parasite that is transmitted by tsetse flies. To understand better how infection with this parasite leads to disease, we provide here the most detailed description yet of the course of infection and disease onset in vervet monkeys. One infected tsetse fly was allowed to feed on each host individual, and in all cases infections were successful. The characteristics of infection and disease were similar in all hosts, but the rate of progression varied considerably. Parasites were first detected in the blood 4-10 days after infection, showing that migration of parasites from the site of fly bite was very rapid. Anaemia was a key feature of disease, with a reduction in the numbers and average size of red blood cells and associated decline in numbers of platelets and white blood cells. One to six weeks after infection, parasites were observed in the cerebrospinal fluid (CSF), indicating that they had moved from the blood into the brain; this was associated with a white cell infiltration. This study shows that fly-transmitted infection in vervets accurately mimics human disease and provides a robust model to understand better how sleeping sickness develops
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