Group-Key Management Model for Worldwide Wireless Mesh Networks

Wireless Mesh Network (WMN) is an upcoming wireless network technology and is mainly used to provide broadband internet in remote locations. It is characterized by minimum fixed infrastructure requirement and is operated in an open medium, such that any user within the range covered by mesh routers may access the network. So a critical requirement for the security in WMN is the authentication of users. However, WMN is far from mature for large-scale deployment in some applications due to the lack of the satisfactory guarantees on security. A wellperformed security framework for WMN will contribute to network survivability and strongly support the network growth or reduction. A key management model to overcome the scalability issue on security aspect for large-scale deployment of WMN i.e. Worldwide WMN is proposed in this work, which aims to guarantee wellperformed key management services and protection from potential attacks. Here, we use a combination of techniques, such as zonebased topology structure, off-line CA, virtual certification authority ) etc

Enhancement of spontaneous emission induced by all-dielectric hyperbolic metamaterial at quasi-Dirac points

We report an all dielectric hyperbolic metamaterial which is sufficiently capable of enhancing spontaneous emission (SE) of a quantum emitter. This hyperbolic metamaterial consists of specially designed dielectric rod based photonic crystal exhibiting Dirac-like and a semi-Dirac cone in its band structure. Rigorous numerical simulation has been done to verify this significant enhancement of SE

Observation of trapped light induced by Dwarf Dirac-cone in out-of-plane condition for photonic crystals

Existence of out-of-plane conical dispersion for a triangular photonic crystal lattice is reported. It is observed that conical dispersion is maintained for a number of out-of-plane wave vectors (k(z)). We study a case where Dirac like linear dispersion exists but the photonic density of states is not vanishing, called Dwarf Dirac cone (DDC) which does not support localized modes. We demonstrate the trapping of such modes by introducing defects in the crystal. Interestingly, we find by k-point sampling as well as by tuning trapped frequency that such a conical dispersion has an inherent light confining property and it is governed by neither of the known wave confining mechanisms like total internal reflection, band gap guidance. Our study reveals that such a conical dispersion in a non-vanishing photonic density of states induces unexpected intense trapping of light compared with those at other points in the continuum. Such studies provoke fabrication of new devices with exciting properties and new functionalities

Design and development of plasmonic hollow core photonic crystal fiber for sensing applications

We report design and fabrication of specialty hollow core photonic crystal fiber for utilizing them in surface plasmon resonance based material sensing. The refractive index of an unknown fluid can be determined by placing it into the hollow core of the fiber. Surface plasmons are generated by replacing air hole of the cladding selectively by silver or gold

Cervical length measurement in nulliparous women at term by ultrasound & its relationship to spontaneous onset of labour

Background & objectives: Data on serial cervical length (CL) measurements in pregnancy at term to predict spontaneous labour onset are scarce and conflicting. This study was conducted to observe CL changes preceding spontaneous onset of labour, by serial transvaginal sonography (TVS) and transabdominal sonography (TAS), in nulliparous Indian women near term. Methods: Only nulliparous women with a singleton foetus in cephalic presentation and who confirmed their gestational age were recruited. Sonographic CL measurements were taken at weekly intervals from 36 wk gestation onwards by a single ultrasonologist. Transabdominal and transvaginal measurements were undertaken using the suitable transducer probes with the women in the supine position. Results: A total of 104 women with spontaneous onset of labour were evaluated. There was substantial variation in CL measurements, both by TVS and by TAS, from 36 to 40 wk gestation, although the two sets of measurements correlated closely. Mean CL changed significantly over the last three weeks before delivery. However, only one-third of the women showed CL change of >5 mm per week in the last three weeks. There was poor correlation between gestational age at delivery and the last measured CL, either by TVS or TAS. Length >3.1 mm, measured by TVS at 38 wk gestation, predicted post-dated pregnancy to a limited extent. Interpretation & conclusions: Inter-individual variations in CL and in CL changes were large. Thus, it was not practical to predict spontaneous onset of labour by sonographic CL measurement near term. Post-dated pregnancy may be predicted with limited success. Further studies should explore other parameters, in addition to CL