1,735 research outputs found
The State of State Science Standards 2012
American science performance is lagging as the economy becomes increasingly high tech, but our current science standards are doing little to solve the problem. Reviewers evaluated science standards for every state for this report and their findings were deeply troubling: The majority of states earned Ds or Fs for their standards in this crucial subject, with only six jurisdictions receiving As. Explore all the state report cards and see how your state performed
Brain oscillations differentially encode noxious stimulus intensity and pain intensity
Noxious stimuli induce physiological processes which commonly translate into pain. However, under certain conditions, pain intensity can substantially dissociate from stimulus intensity, e.g. during longer-lasting pain in chronic pain syndromes. How stimulus intensity and pain intensity are differentially represented in the human brain is, however, not yet fully understood. We therefore used electroencephalography (EEG) to investigate the cerebral representation of noxious stimulus intensity and pain intensity during 10 min of painful heat stimulation in 39 healthy human participants. Time courses of objective stimulus intensity and subjective pain ratings indicated a dissociation of both measures. EEG data showed that stimulus intensity was encoded by decreases of neuronal oscillations at alpha and beta frequencies in sensorimotor areas. In contrast, pain intensity was encoded by gamma oscillations in the medial prefrontal cortex. Contrasting right versus left hand stimulation revealed that the encoding of stimulus intensity in contralateral sensorimotor areas depended on the stimulation side. In contrast, a conjunction analysis of right and left hand stimulation revealed that the encoding of pain in the medial prefrontal cortex was independent of the side of stimulation. Thus, the translation of noxious stimulus intensity into pain is associated with a change from a spatially specific representation of stimulus intensity by alpha and beta oscillations in sensorimotor areas to a spatially independent representation of pain by gamma oscillations in brain areas related to cognitive and affective-motivational processes. These findings extend the understanding of the brain mechanisms of nociception and pain and their dissociations during longer-lasting pain as a key symptom of chronic pain syndromes
Prefrontal gamma oscillations encode tonic pain in humans
Under physiological conditions, momentary pain serves vital protective functions. Ongoing pain in chronic pain states, on the other hand, is a pathological condition that causes widespread suffering and whose treatment remains unsatisfactory. The brain mechanisms of ongoing pain are largely unknown. In this study, we applied tonic painful heat stimuli of varying degree to healthy human subjects, obtained continuous pain ratings, and recorded electroencephalograms to relate ongoing pain to brain activity. Our results reveal that the subjective perception of tonic pain is selectively encoded by gamma oscillations in the medial prefrontal cortex. We further observed that the encoding of subjective pain intensity experienced by the participants differs fundamentally from that of objective stimulus intensity and from that of brief pain stimuli. These observations point to a role for gamma oscillations in the medial prefrontal cortex in ongoing, tonic pain and thereby extend current concepts of the brain mechanisms of pain to the clinically relevant state of ongoing pain. Furthermore, our approach might help to identify a brain marker of ongoing pain, which may prove useful for the diagnosis and therapy of chronic pain
High-performance 3D waveguide architecture for astronomical pupil-remapping interferometry
The detection and characterisation of extra-solar planets is a major theme
driving modern astronomy, with the vast majority of such measurements being
achieved by Doppler radial-velocity and transit observations. Another technique
-- direct imaging -- can access a parameter space that complements these
methods, and paves the way for future technologies capable of detailed
characterization of exoplanetary atmospheres and surfaces. However achieving
the required levels of performance with direct imaging, particularly from
ground-based telescopes which must contend with the Earth's turbulent
atmosphere, requires considerable sophistication in the instrument and
detection strategy. Here we demonstrate a new generation of photonic
pupil-remapping devices which build upon the interferometric framework
developed for the {\it Dragonfly} instrument: a high contrast waveguide-based
device which recovers robust complex visibility observables. New generation
Dragonfly devices overcome problems caused by interference from unguided light
and low throughput, promising unprecedented on-sky performance. Closure phase
measurement scatter of only has been achieved, with waveguide
throughputs of . This translates to a maximum contrast-ratio
sensitivity (between the host star and its orbiting planet) at
(1 detection) of (when a conventional
adaptive-optics (AO) system is used) or (for typical
`extreme-AO' performance), improving even further when random error is
minimised by averaging over multiple exposures. This is an order of magnitude
beyond conventional pupil-segmenting interferometry techniques (such as
aperture masking), allowing a previously inaccessible part of the star to
planet contrast-separation parameter space to be explored
Heterotic-Heterotic String Duality and Multiple K3 Fibrations
A type IIA string compactified on a Calabi-Yau manifold which admits a K3
fibration is believed to be equivalent to a heterotic string in four
dimensions. We study cases where a Calabi-Yau manifold can have more than one
such fibration leading to equivalences between perturbatively inequivalent
heterotic strings. This allows an analysis of an example in six dimensions due
to Duff, Minasian and Witten and enables us to go some way to prove a
conjecture by Kachru and Vafa. The interplay between gauge groups which arise
perturbatively and nonperturbatively is seen clearly in this example. As an
extreme case we discuss a Calabi-Yau manifold which admits an infinite number
of K3 fibrations leading to infinite set of equivalent heterotic strings.Comment: 13 pages, LaTe
Minimum Distances in Non-Trivial String Target Spaces
The idea of minimum distance, familiar from R 1/R duality when the string
target space is a circle, is analyzed for less trivial geometries. The
particular geometry studied is that of a blown-up quotient singularity within a
Calabi-Yau space and mirror symmetry is used to perform the analysis. It is
found that zero distances can appear but that in many cases this requires other
distances within the same target space to be infinite. In other cases zero
distances can occur without compensating infinite distances.Comment: 21 pages, IASSNS-HEP-94/1
The SO(32) Heterotic String on a K3 Surface
The SO(32) heterotic string on a K3 surface is analyzed in terms of the dual
theory of a type II string (or F-theory) on an elliptically fibred Calabi-Yau
manifold. The results are in beautiful agreement with earlier work by Witten
using very different methods. In particular, we find gauge groups of SO(32) x
Sp(k) appearing at points in the moduli space identified with point-like
instantons and see hypermultiplets in the (32,2k) representation becoming
massless at the same time. We also discuss some aspects of the E8 x E8 case.Comment: 12 pages, LaTeX, 1 figure, refs modifie
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