Phononic Crystals and Thermal Effects

In this work, we demonstrate a comprehensive theoretical study of one-dimensional perfect and defect phononic crystals. In our study, we investigate the elastic and shear waves with the influences of thermal effects. The numerical calculations based on the transfer matrix method (TMM) and Bloch theory are presented, where the TMM is obtained by applying the continuity conditions between two consecutive sub-cells. Also, we show that by introducing a defect layer in the perfect periodic structures (defect phononic crystals), we obtain localization modes within the band structure. These localized modes can be implemented in many applications such as impedance matching, collimation, and focusing in acoustic imaging applications. Then, we investigate the influences of the incident angle and material types on the number and intensity of the localized modes in both cases of perfect/defect crystals. In addition, we have observed that the temperature has a great effect on the wave localization phenomena in phononic band gap structures. Such effects can change the thermal properties of the PnCs structure such as thermal conductivity, and it can also control the thermal emission, which is contributed by phonons in many engineering structures

Superconductor-Dielectric Photonic Band Gap in Ultraviolet Radiation

Optical properties of a high-temperature superconductor/dielectric (HTcScD) in the UV operation range are theoretically investigated. We have obtained and performed the calculations of optical reflectance and transmittance spectra. The calculated wavelength-dependent reflectance and transmittance for the structure superconductor/dielectric shows that the threshold wavelength is significance by the angle of incidence and the polarization of waves. The variance of the intensity and the bandwidth of the transmission and reflection are strongly dependent on the different thicknesses, different temperatures, and different incident angles as well as we obtained the different band gaps dependent on the thickness of layers. Also we have examined the influence of the increased of the number of periods on the transmittance and reflectance spectra as well as on the band gap positions

Superconducting Quantum Point contacts and Maxwell Potential

The quantization of the current in a superconducting quantum point contact is reviewed and the critical current is discussed at different temperatures depending on the carrier concentration as well by suggesting a constant potential in the semiconductor and then a Maxwell potential. When the Fermi wave length is comparable with the constriction width we showed that the critical current has a step-like variation as a function of the constriction width and the carrier concentration.Comment: 13 pages, 8 figures, some figures are clarified; scheduled to appear in an issue in MPLB Vo.21, (2007

Absorption in One-Dimensional Lossy Photonic Crystal

In this work we have obtained the absorption property in one-dimensional (1D) defective lossy photonic crystals (PCs) composed of double-negative (DNG) and double-positive materials by using transfer matrix method . The considered asymmetric geometric structures contain a defect structure at the center of the host crystal as a photonic-quantum-well (PQW) with two different types of DNG layers. This study investigates the effect of the stack number of the bilayers PQW defect on the number, position, and the rate of the absorption of anti-resonant modes for both types of the DNG defect. The results show that these factors of the anti-resonant modes depend on the types of the DNG metamaterial corresponding to the defect layers. Accordingly, by changing the types of PQW defect, the anti-resonant modes are red-shifted or blue-shifted as a function of the stack number of PQW. Furthermore, the effect of loss factors on the rate of absorption is examined for the two different types of PQW. The results can present helpful information for designing new types of narrowband and multichannel filters at the microwave

Periodic Structure Containing Lossy Metamaterial and Defect Mode

We theoretically investigate the properties of defect mode in one-dimensional lossy metamaterial photonic crystal doped with single-negative materials photonic-quantum-well (PQW). We examine the defect mode as a function of the type of negative index materials (NIMs) and the number of the unit cells of four different defected structures. The results obtained that the parameters; frequency, height, and the number defect modes can be tuned by varying the type of NIM in defect layers, PQW structure, and the unit cells as well in the defected structure. The defect modest end to show a shift in the frequency based on the particular type of NIM and the number of the unit cells. The results can lead to possible information for designing new types of narrow tunable filters at microwave frequency

Group B streptococcal carriage, antimicrobial susceptibility, and virulence related genes among pregnant women in Alexandria, Egypt

Background and aim: Group B Streptococcus (GBS) has emerged as a leading cause of illness and death among neonates. The study was conducted to estimate the prevalence of recto-vaginal carriage of GBS among pregnant women at 35–37 weeks, gestation, to describe GBS antimicrobial susceptibility profile and to investigate selected virulence genes by PCR.Subjects and methods: Two-hundred pregnant women at 35–37 weeks of gestation attending antenatal clinic at Al-Shatby University Hospital were enrolled in the study. Both vaginal and rectal swabs were collected from each subject. Swabs were inoculated onto CHROMagarTM StrepB and sheep blood agar plates. All GBS isolates were subjected to antimicrobial susceptibility testing using disc diffusion. Disc approximation test was performed to detect erythromycin resistance phenotype (MLSB). GBS virulence genes scpB, bac, bca, and rib were identified by PCR.Results: Among the 200 pregnant women, 53 (26.5%) were identified as GBS carriers. All carriers had vaginal colonization (100%), four (7.5%) had combined recto-vaginal colonization. None of the carriers had rectal colonization alone. All isolates (100%) were susceptible to penicillin, ampicillin, ceftriaxone, cefotaxime, cefepime, vancomycin, and linezolid. On the other hand, 43.4%, 28.3%, 22.6%, and 15% of isolates were resistant to levofloxacin, azithromycin, erythromycin, and clindamycin respectively. Out of 12 erythromycin resistant isolates, six isolates had constitutive while two had inducible MLSB resistance. scpB was identified in 100%, rib in 79.2%, and bac in 35.8% of GBS isolates. None of the isolates possessed the bca gene.Conclusion: Introduction of GBS screening in Egyptian pregnant women is recommended. Penicillin or ampicillin is still the antibiotic of choice for intrapartum prophylaxis.Keywords:  Group B streptococci, Rib gene, Penicillin susceptibility, Vaginal carriag

Alternative technique using dual source CT imaging for assessment of myocardial perfusion

AbstractPurposeTo elucidate the diagnostic role of multidetector DSCT for the assessment of myocardial perfusion in correlation with coronary luminal integrity in a single CT scan while both tubes were operated in single energy mode.Methods and materialThirty-five patients were subjected to single acquisition contrast-enhanced, ECG-gated DSCT of the heart at rest. Postprocessing was performed generating two image sets: coronary CT angiographic images (cCTA) and myocardial perfusion images (CTP) for respective correlative assessment of coronary luminal integrity and myocardial perfusion. Perfusion defect was detected subjectively using gray scale images and the color coded first pass and color overlaid late enhancement (color attenuation) images were used for semi-objective evaluation and final objective and quantitative confirmation by density measurement.ResultsSignificant correlation and good agreement between the findings of DSCT myocardial perfusion and the findings of stenosis and its degree on cCTA on a segmental basis is noted with Cohen’s Kappa=0.67 and prevalence and bias adjusted Kappa=0.71 emphasizing the high diagnostic value of DSCT myocardial perfusion as compared to cCTA as the gold reference standard.ConclusionWe propose that comprehensive evaluation of coronary artery morphology and myocardial perfusion in patients with CAD could be achieved by single reproducible non-invasive contrast enhanced CT acquisition using DSCT scanners while operated in single energy mode with high sensitivity, specificity and diagnostic accuracy, it also has the potential to be the first, independent and stand out imaging choice in such field