1,269 research outputs found
Upper bound of the charge diffusion constant in holography
We investigate the upper bound of charge diffusion constant in holography.
For this purpose, we apply the conjectured upper bound proposal related to the
equilibration scales () to the
Einstein-Maxwell-Axion model. () is defined
as the collision point between the diffusive hydrodynamic mode and the first
non-hydrodynamic mode, giving rise to the upper bound of the diffusion constant
at low temperature as . We show
that the upper bound proposal also works for the charge diffusion and
(), at low , is determined by and the
scaling dimension of an infra-red operator as , as for
other diffusion constants. However, for the charge diffusion, we find that the
collision occurs at real , while it is complex for other
diffusions. In order to examine the universality of the conjectured upper
bound, we also introduce a higher derivative coupling to the
Einstein-Maxwell-Axion model. This coupling is particularly interesting since
it leads to the violation of the \textit{lower} bound of the charge diffusion
constant so the correction may also have effects on the \textit{upper} bound of
the charge diffusion. We find that the higher derivative coupling does not
affect the upper bound so that the conjectured upper bound would not be easily
violated.Comment: v1: 23 pages, 10 figures; v2: minor edits, references adde
The relationship of examinees’ individual characteristics and perceived acceptability of smart device-based testing to test scores on the practice test of the Korea Emergency Medicine Technician Licensing Examination
Purpose Smart device-based testing (SBT) is being introduced into the Republic of Korea’s high-stakes examination system, starting with the Korean Emergency Medicine Technician Licensing Examination (KEMTLE) in December 2017. In order to minimize the effects of variation in examinees’ environment on test scores, this study aimed to identify any associations of variables related to examinees’ individual characteristics and their perceived acceptability of SBT with their SBT practice test scores. Methods Of the 569 candidate students who took the KEMTLE on September 12, 2015, 560 responded to a survey questionnaire on the acceptability of SBT after the examination. The questionnaire addressed 8 individual characteristics and contained 2 satisfaction, 9 convenience, and 9 preference items. A comparative analysis according to individual variables was performed. Furthermore, a generalized linear model (GLM) analysis was conducted to identify the effects of individual characteristics and perceived acceptability of SBT on test scores. Results Among those who preferred SBT over paper-and-pencil testing, test scores were higher for male participants (mean± standard deviation [SD], 4.36± 0.72) than for female participants (mean± SD, 4.21± 0.73). According to the GLM, no variables evaluated— including gender and experience with computer-based testing, SBT, or using a tablet PC—showed a statistically significant relationship with the total score, scores on multimedia items, or scores on text items. Conclusion Individual characteristics and perceived acceptability of SBT did not affect the SBT practice test scores of emergency medicine technician students in Korea. It should be possible to adopt SBT for the KEMTLE without interference from the variables examined in this study
Holography and magnetohydrodynamics with dynamical gauge fields
Within the framework of holography, the Einstein-Maxwell action with
Dirichlet boundary conditions corresponds to a dual conformal field theory in
presence of an external gauge field. Nevertheless, in many real-world
applications, e.g., magnetohydrodynamics, plasma physics, superconductors, etc.
dynamical gauge fields and Coulomb interactions are fundamental. In this work,
we consider bottom-up holographic models at finite magnetic field and (free)
charge density in presence of dynamical boundary gauge fields which are
introduced using mixed boundary conditions. We numerically study the spectrum
of the lowest quasi-normal modes and successfully compare the obtained results
to magnetohydrodynamics theory in dimensions. Surprisingly, as far as the
electromagnetic coupling is small enough, we find perfect agreement even in the
large magnetic field limit. Our results prove that a holographic description of
magnetohydrodynamics does not necessarily need higher-form bulk fields but can
be consistently derived using mixed boundary conditions for standard gauge
fields.Comment: 54 pages, 22 figure
Epileptic nystagmus: A case report and systematic review
AbstractPurposeWe aimed to define the characteristics of epileptic nystagmus and correlate those with other clinical findings in a large number of patients.MethodsWe report a patient with epileptic nystagmus and additionally reviewed the reported clinical features of 36 more patients through a systematic literature search. We analyzed the characteristics of epileptic nystagmus and attempted correlations of those with alertness of the patients and epileptic foci on EEG.ResultsAll 33 patients with unilateral horizontal nystagmus showed nystagmus beating away from the side of ictal discharges. Epileptic nystagmus was preceded by gaze deviation in 21 patients, with contraversive in 19 and ipsiversive in 2. Seizures associated with epileptic nystagmus were mostly focal (25/29, 86.2%) with or without loss of awareness. Ictal discharges originated from the occipital (n=16), parietal (n=9), temporo-occipital (n=6), frontal (n=4), and temporal (n=3) areas, and two patients had multiple epileptic foci. Seizures were usually symptomatic (24/37, 64.9%). The presence of preceding gaze deviation and midline crossing of the nystagmus did not correlate with the ictal onset zone or alertness of the patients. Recording of epileptic nystagmus was available only in 6 patients, and the epileptic nystagmus could be localized to the saccadic areas in two and to the smooth pursuit areas in another two. Two patients showed the features of epileptic nystagmus from both areas.ConclusionEven though the localizing value of epileptic nystagmus seems limited in previous reports, the fast phase of epileptic nystagmus was almost always directed away from the epileptic focus that mostly arose from the posterior part of the cerebral hemisphere
Effect of the Er, Cr: YSGG Laser Parameters on Shear Bond Strength and Microstructure on Human Dentin Surface
The Effect of Photodynamic Therapy Using Indole-3-Acetic Acid and Green Light on Acne Vulgaris
Clinical characteristics and prevalence of vitamin D insufficiency in children less than two years of age
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