Negative index and mode coupling in all-dielectric metamaterials at terahertz frequencies

We report on the role of the coupling of the modes of Mie resonances in all-dielectric metamaterials to ensure negative effective index at terahertz frequencies. We study this role according to the lattice period and according to the frequency overlapping of the modes of resonance. We show that negative effective refractive index requires sufficiently strong mode coupling and that for even more strong mode coupling, the first two modes of Mie resonances are degenerated; the effective refractive index is then undeterminded. We also show that adjusting the mode coupling leads to near-zero effective index, or even null effective index. Further, we compare the mode coupling effect with hybridization in metamaterials.Comment: 17pages, 10 figure

Métamatériaux "tout-diélectrique" pour le térahertz

Metamaterials are periodic sub wavelength composite structures how may have a negative permeability and / or a negative permittivity. If permittivity and permeability are negative simultaneously, we are in presence of what we called a negative index material, sometimes called “left hand media", capable of negative refraction. By controlling some of these properties, metamaterials allow us to obtained behavior nonexistent in nature. This opens the way to new applications. In this thesis, the use of dielectric materials is justified by the reduction of a major downside: losses. Thanks to the removal of ohmic losses specific to metallic materials. A thorough numerical study of dielectric resonators, basic components of "all-dielectric" metamaterials, was conducted using a finite element commercial software. This study highlighted, at the beginning of the terahertz range, a negative permeability, a negative permittivity and a negative index, for two special ceramics, well known in literature: SrTiO₃ and TiO₂. The parametric studies on these ceramics have allowed to put in clear the key role of the inter-modal coupling in order to obtain a negative index. We have also shown the unconventional nature of inter-modal coupling when the two modes concerned are different: one magnetic, other electric. There are in fact two different coupling regimes: a simple progressive shifting of both resonance modes, and then the apparition of degenerative regime, where both modes are at the same frequency for a long range, something not really common in the literature. In addition to this theoretical contribution, our parametric studies have proposed an alternative to the two resonators paradigm, showing the possibility to design a negative index metamaterial with a single bimodal cell in terahertz range.Les métamatériaux sont des structures composites périodiques sub-longueur d’onde pouvant posséder une perméabilité et/ou une permittivité négative. Si ces deux grandeurs sont négatives simultanément, nous sommes en présence d’un matériau à indice négatif, appelés parfois matériaux « main gauche », capable donc de réfraction négative. Par le contrôle de certaines propriétés de la matière les métamatériaux offrent ainsi des comportements inexistants dans la nature. Ceci ouvre ainsi la voie à de nouvelles applications. Dans cette thèse, l’utilisation de matériaux diélectriques se justifie par la réduction d'un inconvénient majeur, les pertes. On s’affranchie en effet de la limites des pertes ohmiques dans les matériaux métalliques. Une étude numérique approfondie des résonateurs diélectriques, composants de base des métamatériaux « tout-diélectrique », a été menée à l’aide d’un logiciel commercial d’éléments finis. Cette étude a permis de mettre en évidence à l’entrée de la gamme terahertz une perméabilité, une permittivité et un indice de réfraction négatifs, pour deux céramiques particulières : le SrTiO₃ et le TiO₂. Les études paramétriques effectuées sur ces deux céramiques ont permises de mettre en évidente le rôle primordial du couplage inter-modal dans l’obtention d’un indice négatif. Nous avons également montré le caractère non conventionnel du couplage inter-modal lorsque les deux modes sont de nature différente, l’un magnétique, l’autre électrique. Il existe en effet deux régimes de couplage distincts, l’un de simple rapprochement des modes de résonances, l’autre de dégénérescence des modes où ceux-ci restent à la même fréquence sur une large gamme, chose jusqu’alors peu visible dans la littérature. En plus de cet apport théorique, nos études paramétriques ont permis de proposer une alternative au paradigme à deux résonateurs, en montrant la faisabilité d’un métamatériau à indice négatif à l’aide d’une cellule élémentaire bimodale au térahertz

Adiponectin, in contrast to leptin, is not associated with body mass index, waist circumference and HOMA-IR in subjects of a west-African population

Factors associated with plasma levels of adiponectin and leptin were studied in adult subjects without diabetes from Cotonou in Benin (West‐Africa). Seventy (70) men and 45 women were included in the study. Anthropometric variables were measured and a venous blood sample was drawn from each subject, after an overnight fasting period, for measurement of plasma glucose, insulin, leptin, and adiponectin levels. HOMA‐IR was determined to assess insulin resistance. Adiponectin and leptin levels were higher in women than in men (with adiponectin 18.48 ± 12.77 vs.7.8 ± 10.39 μg/mL, P < 0.0001, and leptin 30.77 ± 19.16 vs. 8.66 ± 8.24 ng/mL, P < 0.0001). Fasting insulin level and HOMA‐IR were also higher in the females. Hyperleptinemia was observed in 66,96% of subjects and hypoadiponectinemia was present in 44.35% of subjects. In both men and women, leptin correlated with age (r = 0.2; P = 0.02), BMI (r = 0.572; P < 0.0001), waist circumference (r = 0.534; P < 0.0001), fasting insulin (r = 0.461; P < 0.001), and HOMA‐IR (r = 0.430; P < 0.0001). No significant correlation was observed for adiponectin levels with these variables. Only in women, adiponectin was inversely correlated with fasting glucose (r = −0.423; P < 0.004). These data confirm previous descriptions of leptin but suggest that variations in factors determining serum adiponectin levels observed between ethnicities could also been seen between populations from the same ethnicity

Relationship of orthopedic examination, goniometric measurements, and radiographic signs of degenerative joint disease in cats

<p>Abstract</p> <p>Background</p> <p>Available information suggests a mismatch between radiographic and orthopedic examination findings in cats with DJD. However, the extent of the discrepancy between clinical and radiographic signs of OA in companion animals has not been described in detail. This study aimed to evaluate the relationship between orthopedic examination findings, joint goniometry, and radiographic signs of DJD in 100 cats, in a prospective observational design. Cat temperament, pain response to palpation, joint crepitus, effusion and thickening were graded. Radiographs of appendicular joints and the axial skeleton were made under sedation. Joint motion was measured by use of a plastic goniometer before and after sedation. Associations between radiographic degenerative joint disease (DJD) and examination findings were assessed to determine sensitivity, specificity and likelihood estimations.</p> <p>Results</p> <p>Pain response to palpation was elicited in 0-67% of the joints with DJD, with a specificity ranging from 62-99%; crepitus was detected in 0-56% of the joints and its specificity varied between 87 and 99%; for effusion, values ranged between 6 and 38% (specificity, 82-100%), and thickening, 0-59% (specificity, 74-99%). Joints with DJD tended to have a decreased range of motion. The presence of pain increased the odds of having DJD in the elbow (right: 5.5; left: 4.5); the presence of pain in the lower back increased the odds of spinal DJD being present (2.97 for lumbar; 4.67 for lumbo-sacral).</p> <p>Conclusions</p> <p>Radiographic DJD cannot be diagnosed with certainty using palpation or goniometry. However, negative findings tend to predict radiographically normal joints. Palpation and goniometry may be used as a tool to help to screen cats, mostly to rule out DJD.</p

Adiponectin, in contrast to leptin, is not associated with body mass index, waist circumference and HOMA-IR in subjects of a west-African population

Factors associated with plasma levels of adiponectin and leptin were studied in adult subjects without diabetes from Cotonou in Benin (West‐Africa). Seventy (70) men and 45 women were included in the study. Anthropometric variables were measured and a venous blood sample was drawn from each subject, after an overnight fasting period, for measurement of plasma glucose, insulin, leptin, and adiponectin levels. HOMA‐IR was determined to assess insulin resistance. Adiponectin and leptin levels were higher in women than in men (with adiponectin 18.48 ± 12.77 vs.7.8 ± 10.39 μg/mL, P &lt; 0.0001, and leptin 30.77 ± 19.16 vs. 8.66 ± 8.24 ng/mL, P &lt; 0.0001). Fasting insulin level and HOMA‐IR were also higher in the females. Hyperleptinemia was observed in 66,96% of subjects and hypoadiponectinemia was present in 44.35% of subjects. In both men and women, leptin correlated with age (r = 0.2; P = 0.02), BMI (r = 0.572; P &lt; 0.0001), waist circumference (r = 0.534; P &lt; 0.0001), fasting insulin (r = 0.461; P &lt; 0.001), and HOMA‐IR (r = 0.430; P &lt; 0.0001). No significant correlation was observed for adiponectin levels with these variables. Only in women, adiponectin was inversely correlated with fasting glucose (r = −0.423; P &lt; 0.004). These data confirm previous descriptions of leptin but suggest that variations in factors determining serum adiponectin levels observed between ethnicities could also been seen between populations from the same ethnicity

Assessment of the diversity and abundance of bacterial population and its correlation with medium chain fatty acids production from fermentation of two leachate qualities

The potential of medium chain fatty acids (MCFA) production from two seasonal leachates along with their bacterial community structure were investigated using GC-FID and Illumina high-throughput sequencing during the acid chain elongation process. Significant amounts of MCFA (C6-10) were produced during the experiment, especially with rainy season leachate. The amounts ranged from 1646 mg/l to 22,000 mg/l for C6-C8 and reached 959.65 mg/l for C9 and C10, with optimum values obtained on day 21. Bacterial communities were also different among seasonal samples, with Bacteroidetes, Firmicutes, and Proteobacteria being the most abundant phyla. The relative abundance of Lactobacillus, Clostridium, and Pseudomonas increased during fermentation and showed positive correlations with MCFA with longer chains (C6-C10), demonstrating their probable involvement in the chain elongation process. This study enhances our understanding of the composition, structure and contribution of the bacterial community during the chain elongation process and gives value to leachate from solid waste in sub-Saharan countries

High permittivity processed SrTiO3 for metamaterials applications at terahertz frequencies

High permittivity SrTiO3 for the realization of all-dielectric metamaterials operating at terahertz frequencies was fabricated. A comparison of different processing methods demonstrates that Spark Plasma Sintering is the most effective sintering process to yield high density ceramic with high permittivity. We compare this sintering process with two other processes. The fabricated samples are characterized in the low frequency and in the terahertz frequency ranges. Their relative permittivities are compared with that of a reference SrTiO3 single crystal. The permittivity of the sample fabricated by Spark Plasma Sintering is as high as that of the single crystal. The role of the signal-to-noise ratio in the measurements at terahertz frequency is detailed

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Liver Stiffness Measurement and Biochemical Markers in Senegalese Chronic Hepatitis B Patients with Normal ALT and High Viral Load

Despite the high prevalence of chronic hepatitis B (CHB) in Africa, few studies have been performed among African patients. We sought to evaluate liver stiffness measurement by FibroScan® (LSM) and two biochemical scores (FibroTest®, Fibrometer®) to diagnose liver fibrosis in Senegalese CHB patients with HBV plasma DNA load ≥3.2 log(10) IU/mL and normal alanine aminotransferase (ALT) values.LSM and liver fibrosis biochemical markers were performed on 225 consecutive HBV infected Senegalese patients with high viral load. Patients with an LSM range between 7 and 13 kPa underwent liver biopsy (LB). Two experienced liver pathologists performed histological grading using Metavir and Ishak scoring.225 patients were evaluated (84% male) and LB was performed in 69 patients, showing F2 and F3 fibrosis in 17% and 10% respectively. In these patients with a 7-13 kPa range of LSM, accuracy for diagnosis of significant fibrosis according to LB was unsatisfactory for all non-invasive markers with AUROCs below 0.70. For patients with LSM values below 7 kPa, FibroTest® (FT), and Fibrometer® (FM) using the cut-offs recommended by the test promoters suggested a fibrosis in 18% of cases for FT (8% severe fibrosis) and 8% for FM. For patients with LSM values greater than 13 kPa, FT, FM suggested a possible fibrosis in 73% and 70%, respectively.In highly replicative HBV-infected African patients with normal ALT and LSM value below 13 kPa, FibroScan®, FibroTest® or Fibrometer® were unsuitable to predict the histological liver status of fibrosis