Analytical formulation of spatiotemporal modulated graphene-based waveguides using Floquet-Bloch theory.

In this work, an analytical model to study graphene-based spatiotemporal modulated structures is developed and verified through comparison with full wave numerical simulations. Graphene is an ideal material for realizing spatiotemporal modulated structures at high frequencies of THz and optics. In this analysis, the electromagnetic response of studied structures is expressed in terms of weighted Floquet-Bloch modes supported by the structure, while graphene is modeled by a spatiotemporal modulated surface current that imposes certain boundary conditions on the modes. The developed analytical technique is a comprehensive tool and can be used for accurate modeling of different kinds of spatiotemporal devices including lossy, guided, and leaky wave structures. To demonstrate the accuracy of the model, two plasmonic waveguides with space and time modulated graphene conductivity are analyzed and their interband and intraband transition between modes are thoroughly investigated. Using the developed analytical model, spatiotemporal modulation phenomena such as mode conversion, wave amplification and nonreciprocal response are explored and discussed for the studied structures.

Detection and Endodontic Treatment of Unusual Anatomic Variations in Second Premolars: A Case Report.

Endodontic treatment of second premolars is challenging due to their complex anatomy and the likelihood of anatomical variations. The current report presents successful treatments of mandibular and maxillary second premolars with different anatomies in a single patient. The first case involved a patient referred from a general practitioner who was unable to complete the root canal treatment of her mandibular second premolar with four root canals. The initial radiograph showed an apical radiolucency, periodontal ligament (PDL) widening, and a fast break suggesting the possibility of root canal branching. With the diagnosis of previous treatment and chronic apical periodontitis, the tooth was successfully retreated with the aid of cone-beam computed tomography (CBCT), a dental operating microscope, and ultrasonic tips. The second case was a maxillary second premolar with Vertucci's type VI root canal morphology, which was not responsive to pulpo-periapical tests. Along with a deep carious lesion and a PDL widening on the initial radiograph, a diagnosis of necrosis with chronic apical periodontitis was made. The root canals were located and treated using a combination of radiography with different angulation and CBCT. Both teeth were clinically and radiographically asymptomatic at the 4-month follow-up session. This case report highlights the importance of thorough preoperative evaluation and the use of advanced technology and techniques in achieving successful endodontic treatment outcomes.

Cross-sectional area of human trunk paraspinal muscles before and after posterior lumbar surgery using magnetic resonance imaging.

PURPOSE: Iatrogenic injuries to paraspinal muscles during the posterior lumbar surgery (PLS) cause a reduction in their cross-sectional areas (CSAs) and contractile densities over time post-surgery. This study aims to quantify such alterations. METHOD: Pre- and postoperative CSAs (~6 months interval) of all paraspinal muscles were measured in six patients undergoing PLS using a 3-T magnetic resonance (MR) scanner to quantify the alterations in geometrical and tissue effective contractile (non-fatty) CSAs of these muscles at all lumbar levels. To examine the presence of any confounding effects on recorded changes within ~7-month period, measurements were also carried out on ten healthy volunteers. RESULTS: In the healthy population, an important (~22%) portion of CSA of the erector spinae (ES) was noncontractile at the lower lumbar levels. Negligible variations over time in both the total geometrical (<1.7% in average) and contractile (<1.2%) CSAs of muscles were observed in the healthy group (i.e., no confounding effect). Following PLS, significant reductions were observed in the geometrical CSA of only multifidus (MF) muscle by ~14 and 11% as well as in its contractile CSA by ~26 and 14% at the L5-S1 and L4-L5 levels, respectively. CONCLUSION: The total CSA of ES at lower lumbar levels shows substantial noncontractile contents in both healthy and patient populations. Biomechanical models of the spine should hence account for the noncontractile contents using only the effective contractile muscle CSAs. Postoperative variations in CSAs of paraspinal muscles may have profound effects on patterns of muscle activities, spinal loading, and stability.