3,395 research outputs found
AdS Taub-Nut Space and the O(N) Vector Model on a Squashed 3-Sphere
In this note, motivated by the Klebanov-Polyakov conjecture we investigate
the strongly coupled O(N) vector model at large on a squashed three-sphere
and its holographic relation to bulk gravity on asymptotically locally
spaces. We present analytical results for the action of the field theory as the
squashing parameter , when the boundary becomes effectively one
dimensional. The dual bulk geometry is AdS-Taub-NUT space in the corresponding
limit. In this limit we solve the theory exactly and show that the action of
the strongly coupled boundary theory scales as .
This result is remarkably close to the scaling of the
Einstein gravity action for AdS-Taub-NUT space. These results explain the
numerical agreement presented in hep-th/0503238, and the soft logarithmic
departure is interpreted as a prediction for the contribution due to higher
spin fields in the bulk geometry.Comment: 11 pages, 3 figures. References adde
Effective actions on the squashed three-sphere
The effective actions of a scalar and massless spin-half field are determined
as functions of the deformation of a symmetrically squashed three-sphere. The
extreme oblate case is particularly examined as pertinant to a high temperature
statistical mechanical interpretation that may be relevant for the holographic
principle. Interpreting the squashing parameter as a temperature, we find that
the effective `free energies' on the three-sphere are mixtures of thermal
two-sphere scalars and spinors which, in the case of the spinor on the
three-sphere, have the `wrong' thermal periodicities. However the free energies
do have the same leading high temperature forms as the standard free energies
on the two-sphere. The next few terms in the high-temperature expansion are
also explicitly calculated and briefly compared with the Taub-Bolt-AdS bulk
result.Comment: 23 pages, JyTeX. Conclusion slightly amended, one equation and minor
misprints correcte
A cortical potential reflecting cardiac function
Emotional trauma and psychological stress can precipitate cardiac arrhythmia and sudden death through arrhythmogenic effects of efferent sympathetic drive. Patients with preexisting heart disease are particularly at risk. Moreover, generation of proarrhythmic activity patterns within cerebral autonomic centers may be amplified by afferent feedback from a dysfunctional myocardium. An electrocortical potential reflecting afferent cardiac information has been described, reflecting individual differences in interoceptive sensitivity (awareness of one's own heartbeats). To inform our understanding of mechanisms underlying arrhythmogenesis, we extended this approach, identifying electrocortical potentials corresponding to the cortical expression of afferent information about the integrity of myocardial function during stress. We measured changes in cardiac response simultaneously with electroencephalography in patients with established ventricular dysfunction. Experimentally induced mental stress enhanced cardiovascular indices of sympathetic activity (systolic blood pressure, heart rate, ventricular ejection fraction, and skin conductance) across all patients. However, the functional response of the myocardium varied; some patients increased, whereas others decreased, cardiac output during stress. Across patients, heartbeat-evoked potential amplitude at left temporal and lateral frontal electrode locations correlated with stress-induced changes in cardiac output, consistent with an afferent cortical representation of myocardial function during stress. Moreover, the amplitude of the heartbeat-evoked potential in the left temporal region reflected the proarrhythmic status of the heart (inhomogeneity of left ventricular repolarization). These observations delineate a cortical representation of cardiac function predictive of proarrhythmic abnormalities in cardiac repolarization. Our findings highlight the dynamic interaction of heart and brain in stress-induced cardiovascular morbidity
The Alternate Arm Converter: A New Hybrid Multilevel Converter With DC-Fault Blocking Capability
This paper explains the working principles, supported by simulation results, of a new converter topology intended for HVDC applications, called the alternate arm converter (AAC). It is a hybrid between the modular multilevel converter, because of the presence of H-bridge cells, and the two-level converter, in the form of director switches in each arm. This converter is able to generate a multilevel ac voltage and since its stacks of cells consist of H-bridge cells instead of half-bridge cells, they are able to generate higher ac voltage than the dc terminal voltage. This allows the AAC to operate at an optimal point, called the “sweet spot,” where the ac and dc energy flows equal. The director switches in the AAC are responsible for alternating the conduction period of each arm, leading to a significant reduction in the number of cells in the stacks. Furthermore, the AAC can keep control of the current in the phase reactor even in case of a dc-side fault and support the ac grid, through a STATCOM mode. Simulation results and loss calculations are presented in this paper in order to support the claimed features of the AAC
The effects of crossbow impacts onto a common automotive vehicle side window—a preliminary study
In recent times, the number of criminal incidents involving crossbows in the UK has increased with many incidents resulting in either injuries or fatalities. Whilst the effects of crossbow bolts on the body are well understood, there is a limited understanding on how these projectiles interact with the wider environment. One area of particular interest is the interaction between common vehicle side windows and bolts. In this study, the penetrability of two distinct bolts using an off-the-shelve crossbow against a common automotive side window was explored, where velocity loss up to 25 m/s post impact was recorded. All windows failed through radial glass fracture at a rate up to 1600 m/s, whilst bolt damage varied from tip holder decoupling, shaft damage, and traumatic fletching removal. No distinct relationship between bolt type, velocity, and window damage was identified
Analyzing Recent Coronary Heart Disease Mortality Trends in Tunisia between 1997 and 2009.
BACKGROUND: In Tunisia, Cardiovascular Diseases are the leading causes of death (30%), 70% of those are coronary heart disease (CHD) deaths and population studies have demonstrated that major risk factor levels are increasing.
OBJECTIVE: To explain recent CHD trends in Tunisia between 1997 and 2009.
METHODS: DATA SOURCES: Published and unpublished data were identified by extensive searches, complemented with specifically designed surveys.
ANALYSIS: Data were integrated and analyzed using the previously validated IMPACT CHD policy model. Data items included: (i)number of CHD patients in specific groups (including acute coronary syndromes, congestive heart failure and chronic angina)(ii) uptake of specific medical and surgical treatments, and(iii) population trends in major cardiovascular risk factors (smoking, total cholesterol, systolic blood pressure (SBP), body mass index (BMI), diabetes and physical inactivity).
RESULTS: CHD mortality rates increased by 11.8% for men and 23.8% for women, resulting in 680 additional CHD deaths in 2009 compared with the 1997 baseline, after adjusting for population change. Almost all (98%) of this rise was explained by risk factor increases, though men and women differed. A large rise in total cholesterol level in men (0.73 mmol/L) generated 440 additional deaths. In women, a fall (-0.43 mmol/L), apparently avoided about 95 deaths. For SBP a rise in men (4 mmHg) generated 270 additional deaths. In women, a 2 mmHg fall avoided 65 deaths. BMI and diabetes increased substantially resulting respectively in 105 and 75 additional deaths. Increased treatment uptake prevented about 450 deaths in 2009. The most important contributions came from secondary prevention following Acute Myocardial Infarction (AMI) (95 fewer deaths), initial AMI treatments (90), antihypertensive medications (80) and unstable angina (75).
CONCLUSIONS: Recent trends in CHD mortality mainly reflected increases in major modifiable risk factors, notably SBP and cholesterol, BMI and diabetes. Current prevention strategies are mainly focused on treatments but should become more comprehensive
The O(N) model on a squashed S^3 and the Klebanov-Polyakov correspondence
We solve the O(N) vector model at large N on a squashed three-sphere with a
conformal mass term. Using the Klebanov-Polyakov version of the AdS_4/CFT_3
correspondence we match various aspects of the strongly coupled theory with the
physics of the bulk AdS Taub-NUT and AdS Taub-Bolt geometries. Remarkably, we
find that the field theory reproduces the behaviour of the bulk free energy as
a function of the squashing parameter. The O(N) model is realised in a
symmetric phase for all finite values of the coupling and squashing parameter,
including when the boundary scalar curvature is negative.Comment: 1+27 pages. 6 figures. LaTeX. References adde
Neural activity relating to generation and representation of galvanic skin conductance responses: A functional magnetic resonance imaging study
Modulation of emotional appraisal by false physiological feedback during fMRI
BACKGROUND
James and Lange proposed that emotions are the perception of physiological reactions. Two-level theories of emotion extend this model to suggest that cognitive interpretations of physiological changes shape self-reported emotions. Correspondingly false physiological feedback of evoked or tonic bodily responses can alter emotional attributions. Moreover, anxiety states are proposed to arise from detection of mismatch between actual and anticipated states of physiological arousal. However, the neural underpinnings of these phenomena previously have not been examined.
METHODOLOGY/PRINCIPAL FINDINGS
We undertook a functional brain imaging (fMRI) experiment to investigate how both primary and second-order levels of physiological (viscerosensory) representation impact on the processing of external emotional cues. 12 participants were scanned while judging face stimuli during both exercise and non-exercise conditions in the context of true and false auditory feedback of tonic heart rate. We observed that the perceived emotional intensity/salience of neutral faces was enhanced by false feedback of increased heart rate. Regional changes in neural activity corresponding to this behavioural interaction were observed within included right anterior insula, bilateral mid insula, and amygdala. In addition, right anterior insula activity was enhanced during by asynchronous relative to synchronous cardiac feedback even with no change in perceived or actual heart rate suggesting this region serves as a comparator to detect physiological mismatches. Finally, BOLD activity within right anterior insula and amygdala predicted the corresponding changes in perceived intensity ratings at both a group and an individual level.
CONCLUSIONS/SIGNIFICANCE
Our findings identify the neural substrates supporting behavioural effects of false physiological feedback, and highlight mechanisms that underlie subjective anxiety states, including the importance of the right anterior insula in guiding second-order "cognitive" representations of bodily arousal state
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