1,607 research outputs found
Fermi coordinates and modified Franklin transformation : A comparative study on rotational phenomena
Employing a relativistic rotational transformation to study and analyze
rotational phenomena, instead of the rotational transformations based on
consecutive Lorentz transformations and Fermi coordinates, leads to different
predictions. In this article, after a comparative study between Fermi metric of
a uniformly rotating eccentric observer and the spacetime metric in the same
observer's frame obtained through the modified Franklin transformation, we
consider rotational phenomena including transverse Doppler effect and Sagnac
effect in both formalisms and compare their predictions. We also discuss length
measurements in the two formalisms.Comment: 21 pages, 2 figures, replaced with the published versio
Electronic states in a graphene flake strained by a Gaussian bump
The effect of strain in graphene is usually modeled by a pseudo-magnetic
vector potential which is, however, derived in the limit of small strain. In
realistic cases deviations are expected in view of graphene's very high strain
tolerance, which can be up to 25%. Here we investigate the pseudo-magnetic
field generated by a Gaussian bump and we show that it exhibits significant
differences with numerical tight-binding results. Furthermore, we calculate the
electronic states in the strained region for a hexagon shaped flake with
armchair edges. We find that the six-fold symmetry of the wave functions inside
the Gaussian bump is directly related to the different effect of strain along
the fundamental directions of graphene: zigzag and armchair. Low energy
electrons are strongly confined in the armchair directions and are localized on
the carbon atoms of a single sublattice
The use of pulse oximetry in evaluation of pulp vitality in immature permanent teeth
Background and aim: The current methods of pulp vitality assessment, either electric or thermal, are of limited use in children. Recently, traumatized and immature teeth may not respond to such methods and because such methods require subjective responses, it may not provide accurate results particularly in children. Pulse oximetry, an atraumatic approach, is used to measure oxygen saturation in vascular system. The aim of this study was to investigate the use of pulse oximetry to evaluate pulp vitality status in immature permanent teeth. Methods and materials: The study was conducted on 329 maxillary central and lateral incisors in children. The negative control group consisted of 10 root filled teeth. Systemic oxygen saturation was first measured on the thumb of the individual using a custom-made sensor. Oxygen saturation values of the teeth were then evaluated. The correlation between oxygen saturation measurement obtained from finger and tooth, and the correlation between oxygen saturation values and stage of root development were analyzed. A further comparison was made between the teeth with open and closed apex. Results: Mean oxygen values recorded in the patient's finger were 97.17, and mean oxygen values in the maxillary central and lateral incisors were 86.77 and 83/92, respectively. There was no significant correlation between blood oxygen levels in the finger and in the teeth. (P > 0.05) There was a significant negative correlation between the stage of root development and the blood oxygen levels in the patients' teeth. (P < 0.05) Mean oxygen values in the teeth with open apex were significantly higher than the teeth with closed apex. (P < 0.001). Conclusion: Vital teeth provided consistent oxygen saturation readings, and non-vital teeth recorded no oxygen saturation values. During tooth development, the oxygen saturation values decreased. These findings confirm that the pulse oximetry is capable of detecting the pulpal blood flow and oxygen saturation. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd
Bilayer graphene Hall bar with a pn-junction
We investigate the magnetic field dependence of the Hall and the bend
resistances for a ballistic Hall bar structure containing a pn-junction
sculptured from a bilayer of graphene. The electric response is obtained using
the billiard model and we investigate the cases of bilayer graphene with and
without a band gap. Two different conduction regimes are possible: ) both
sides of the junction have the same carrier type, and ) one side of the
junction is n-type while the other one is p-type. The first case shows Hall
plateau-like features in the Hall resistance that fade away as the band gap
opens. The second case exhibits a bend resistance that is asymmetric in
magnetic field as a consequence of snake states along the pn-interface, where
the maximum is shifted away from zero magnetic field
Graphene Hall bar with an asymmetric pn-junction
We investigated the magnetic field dependence of the Hall and the bend
resistances in the ballistic regime for a single layer graphene Hall bar
structure containing a pn-junction. When both regions are n-type the Hall
resistance dominates and Hall type of plateaus are formed. These plateaus occur
as a consequence of the restriction on the angle imposed by Snell's law
allowing only electrons with a certain initial angles to transmit though the
potential step. The size of the plateau and its position is determined by the
position of the potential interface as well as the value of the applied
potential. When the second region is p-type the bend resistance dominates which
is asymmetric in field due to the presence of snake states. Changing the
position of the pn-interface in the Hall bar strongly affects these states and
therefore the bend resistance is also changed. Changing the applied potential
we observe that the bend resistance exhibits a peak around the
charge-neutrality point (CNP) which is independent of the position of the
pn-interface, while the Hall resistance shows a sign reversal when the CNP is
crossed, which is in very good agreement with a recent experiment [J. R.
Williams et al., Phys. Rev. Lett. 107, 046602(2011)]
Spectroscopy of snake states using a graphene Hall bar
An approach to observe snake states in a graphene Hall bar containing a
pn-junction is proposed. The magnetic field dependence of the bend resistance
in a ballistic graphene Hall bar structure containing a tilted pn-junction
oscillates as a function of applied magnetic field. We show that each
oscillation is due to a specific snake state that moves along the pn-interface.
Furthermore depending on the value of the magnetic field and applied potential
we can control the lead in which the electrons will end up and hence control
the response of the system
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