Najmul Hassan - Academia.edu (original) (raw)
Papers by Najmul Hassan
2017 13th International Wireless Communications and Mobile Computing Conference (IWCMC), 2017
Modeling of Underwater Wireless Sensor Networks (UWSNs) with a goal of maximum network lifetime a... more Modeling of Underwater Wireless Sensor Networks (UWSNs) with a goal of maximum network lifetime and throughput with minimum energy consumption is a quite difficult task because of limited battery power and harsh underwater environment. Balanced Energy Efficient Rectangular routing protocol (BEER) covers the maximum network area with the mobility of sinks and collects the data from sensor nodes in their transmission range using direct transmission. Sink movement maximizes the throughput and balanced the energy consumption. Simulation results verify that our scheme performs outstanding in terms of network lifetime, stability period and throughput with minimum energy consumption.
Ambient Assisted Living and Enhanced Living Environments, 2017
Energy is an important factor to be considered especially in the cases where implantable nodes ar... more Energy is an important factor to be considered especially in the cases where implantable nodes are used. This is important because it is very difficult to replace the battery of a node placed inside a body. Researchers have been trying to develop energy efficient solutions in order to save energy and to extend the overall network lifetime. This chapter provides a comprehensive overview of Wireless Body Area Network (WBAN) and the energy management challenges. Moreover, heating issues faced by sensor nodes implanted in human body are also discussed. Heat dissipation is mainly due to the transmission and reception of electromagnetic signals to and from other sensor nodes which are part of the same network. The amount of heat dissipation is known as Specific Absorption Rate (SAR) and is measured in W/kg. There is a need to find solutions to reduce it to a level which is not dangerous for human health. High values of SAR results in tissue damage. Thus, the goal of this chapter is to discuss energy management, SAR and safety aspects in implanted wireless body area networks.
Cluster Computing
There are thousands of flights carrying millions of passengers each day, having three or more Int... more There are thousands of flights carrying millions of passengers each day, having three or more Internet-connected devices with them on average. Usually, onboard devices remain idle for most of the journey (which can be of several hours), therefore, we can tap on their underutilized potential. Although these devices are generally becoming more and more resourceful, for complex services (such as related to machine learning, augmented/virtual reality, smart healthcare, and so on) those devices do not suffice standalone. This makes a case for multi-device resource aggregation such as through femto-cloud. As our first contribution, we present the utility of femto-cloud for aerial users. But for that sake, a reliable and faster Internet is required (to access online services or cloud resources), which is currently not the case with satellite-based Internet. That is the second challenge we try to address in our paper, by presenting an adaptive beamforming-based solution for aerial Internet provisioning. However, on average, most of the flight path is above waters. Given that, we propose that beamforming transceivers can be docked on stationery ships deployed in the vast waters (such as the ocean). Nevertheless, certain services would be delay-sensitive, and accessing their on-ground servers or cloud may not be feasible (in terms of delay). Similarly, certain complex services may require resources in addition to the flight-local femto-cloud. That is the third challenge we try to tackle in this paper, by proposing that the traditional fog computing (which is a cloud-like but localized pool of resources) can also be extended to the waters on the ships harboring beamforming transceivers. We name it Floating Fog. In addition to that, Floating Fog will enable several new services such as live black-box. We also present a cost and bandwidth analysis to highlight the potentials of Floating Fog. Lastly, we identify some challenges to tackle the successful deployment of Floating Fog.
Enhanced Living Environments: From models to technologies, 2017
The developments that shaped the twenty/twenty-first century with respect to wireless technologie... more The developments that shaped the twenty/twenty-first century with respect to wireless technologies have had a great influence on quality of life, where wireless body area networks (WBANs) - implantable sensor nodes, more specifically, have recently emerged as a successful initiative for monitoring health remotely, and thus a research challenge. Two concerns that need addressing here are heat dissipation which causes damage to surrounding tissues, and introduction of relay nodes to increase network lifetime, but on the other hand may cause health hazards. There arises a need to find an efficient network topology design to overcome the above-mentioned concerns. This chapter discusses in detail WBAN, its applications, related technologies, energy-aware topology design, efficient relay node placement methods and, last but not least, energy-efficient and thermal-aware routing techniques.
International Journal of Distributed Sensor Networks
High-speed quality Internet provision for aircraft passengers is thought to be one of the major u... more High-speed quality Internet provision for aircraft passengers is thought to be one of the major unresolved challenges for ubiquitous Internet provision. This article aims to resolve the problem of airborne Internet access with high quality of service for modern Internet of things devices. Large remote regions in the ocean along the busy air routes (e.g. Atlantic Ocean) require high-speed, reliable, and low-cost airborne Internet (i.e. Internet provision to the aircraft) to manage various delay- and throughput-sensitive applications. Conventional satellite-based solutions can be an alternate for Internet provision in such far-flung areas; but, such solutions are lacking quality of service (with longer delays and low bandwidth) and are significantly costly. Fortunately, the underwater optical fiber cables deployed across the oceans pass along the same busy air routes. This infrastructure of underwater optical fiber cables can be exploited for Internet backbone providing high quality o...
Journal of Materials Science: Materials in Electronics, 2018
Ti-doped (Cu 0.5 Tl 0.5)Ba 2 (Ca 2−x Ti x)Cu 3 O 10−δ (x = 0, 0.25, 0.50, 0.75, 1.0) superconduct... more Ti-doped (Cu 0.5 Tl 0.5)Ba 2 (Ca 2−x Ti x)Cu 3 O 10−δ (x = 0, 0.25, 0.50, 0.75, 1.0) superconductors have been synthesized by solid state reaction method. The prepared samples are characterized by XRD, electrical resistivity, AC susceptibility and FTIR techniques. XRD analysis showed that the lattice parameters are marginally altered but there is no substantial change with the doping of Ti. All the samples are found with orthorhombic crystal structure following PMMM space group. T c (R = 0) is enhanced with the doping of Ti except for x = 1.0 sample. The magnitude of diamagnetism in the AC-susceptibility measurements is enhanced up to x = 0.5 and decreased beyond. The FTIR measurements show that the apical oxygen phonon modes are softened. The planar oxygen phonon modes are softened but their intensity is raised with the enhanced Ti contents. This softening of the planar oxygen phonon modes may be arising due to the heavier Ti ions (47.9 amu) at the lighter Ca (40.07 amu) sites. Variation in the lattice parameters in the XRD data and shifting of various oxygen phonon modes in the FTIR data show that Ti is incorporated at Ca sites in the unit cell. Increase in the superconducting properties up to certain doping level (x = 0.75) may be arising due to the improved interplane coupling caused by the smaller sized Ti at Ca sites. While the decrease in T c and magnitude of diamagnetism beyond x = 0.75 and x = 0.5 respectively, is attributed to the suppressed density of a particular type of phonons required for optimum superconductivity. This suppression in the density of the desired phonons is brought about by the substitution of heavier Ti ions at the lighter Ca sites. This study signifies the role of electron-phonon interaction in mechanism of high T c superconductivity.
Journal of Materials Science: Materials in Electronics, 2016
Be doped (Cu0.5Tl0.5)Ba2(Ca2−yBey)(Cu2.5Cd0.5)O10−δ (y = 0, 0.1, 0.2, 0.35, 0.5) superconductive ... more Be doped (Cu0.5Tl0.5)Ba2(Ca2−yBey)(Cu2.5Cd0.5)O10−δ (y = 0, 0.1, 0.2, 0.35, 0.5) superconductive samples are synthesized by solid state reaction method at normal pressure. The X-ray diffraction of these samples reveals a suppression in the c-axis length with the enhanced Be contents, reflecting the incorporation of Be at the inter plane Ca sites. The critical temperature Tc (R = 0) and onset temperature of diamagnetism Tc (onset) are found to increase with the increasing Be-contents up to y = 0.2 and decrease beyond this doping level. The room temperature resistivity, ρ(290K), is decreased in y = 0.1 and 0.2 samples, and raised to higher values beyond y = 0.2 in comparison to y = 0 samples. This improvement most likely arises due to the better interplane coupling caused by incorporation of Be at the Ca sites in the unit cell. The magnitude of diamagnetism is suppressed in all the Be-doped samples in comparison to un-doped sample. The FTIR absorption spectra show systematic hardening of the vibrational modes of apical oxygen with the increasing Be concentration. It confirms the incorporation of Be at the interplane Ca sites which results in the enhanced interplane coupling and hence the better superconducting properties in y = 0.1 and 0.2 samples. This hardening of the apical oxygen modes also complements our XRD results. The suppression of superconductivity parameters in samples with higher Be contents, namely y = 0.35 and 0.5, is attributed to the presence of heavier Cd at the Cu planar sites in CuO2/CdO2 planes. Cd atoms suppress the phonon’s population due to anharmonic oscillations it produces. Such anharmonicity is further promoted due to the enhanced interplane coupling caused by Be doping which further suppresses the phonon’s density and hence the superconductivity in the samples with higher Be-contents i.e. y = 0.35 and 0.5. These results stress on the vital role the electron–phonon interactions in the mechanism of superconductivity in cuprate superconductors.
Nanomaterials and Nanotechnology, 2012
Raman scattering investigations based on density functional theory (DFT) calculations were perfor... more Raman scattering investigations based on density functional theory (DFT) calculations were performed to explore the vibrational modes of wurtzite structured CdS nanoparticles (NPs). The calculations were performed to obtain the Raman spectra for the CdS containing 2, 4, 8 and 12 atoms to study the size dependence. Several vibrational modes indicating stretching and bending features related to Cd and S atoms were observed. Modifications of the frequency and intensity of different Raman modes with an increase in number of atoms in NPs are discussed in detail. It is found that the frequency of the CdS symmetric stretching mode of vibration shows a consistent red shift and that of CdS anti-symmetric stretching shows a consistent blue shift with the increase in the number of atoms. Hydrogen atoms were added in order to make the closed shell configuration and saturate the NPs as per the requisite for calculating the Raman spectra. This produced some additional modes of vibration related to hydrogen atoms. The SH stretching mode showed a consistent red shift and the CdH stretching mode showed a consistent blue shift with an increase in the number of atoms in NPs. The results generated are found to be in close agreement with the literature. The observed red shift in different modes is assigned to stimulated Raman stretching and blue shift is ascribed to the coherent anti-stokes Raman scattering.
Physica C: Superconductivity, 2009
Excess conductivities of polycrystalline, as-prepared and oxygen post annealed Mg doped samples h... more Excess conductivities of polycrystalline, as-prepared and oxygen post annealed Mg doped samples have been studied from the resistivity versus temperature data. The logarithmic plots of excess conductivity versus reduced temperatures [(T-Tcmf)/Tcmf] show two cross-over temperatures with three exponents. Except for the as-prepared sample with x=1 all the samples have shown a distinct cross-over from two-dimensional to three-dimensional conductivity in accordance with the 2D, 3D Aslamazov–Larkin equations. Interlayer-coupling strength estimated by using Lawrence–Doniach equations has been observed to increase with higher Mg doping and post-annealing. The improved properties with the higher Mg concentration might be arising from the reduction of the anisotropy along the c-axis. The oxygen post-annealing seems to improve carrier concentration in the conducting CuO2 planes that may be responsible for 2D–3D cross-over of the excess conductivity.
Physica C: Superconductivity, 2007
We have synthesized Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3Ày Ni y O 10Àd (y = 0, 0.5, 1.0, 1.5) superconduc... more We have synthesized Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3Ày Ni y O 10Àd (y = 0, 0.5, 1.0, 1.5) superconductors at normal pressure and studied the enhanced correlation among CuO 2 /NiO 2 planes of Cu 0.5 Tl 0.5 Ba 2 Ca 2Ày Mg y Cu 1.5 Ni 1.5 O 10Àd (y = 0.5, 1.0, 1.5) superconductors by doping Mg at the Ca sites. Surprisingly, we have not observed any substantial depression of critical temperature with Ni doping in Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3Ày Ni y O 10Àd (y = 0, 0.5, 1.0, 1.5) superconductors. The main objective of Mg substitution is to enhance the interplane coupling which may increase the interactions of the spins of Ni atoms in different planes. The increased inter-plane coupling may enhance interactions of the atomic spins with the free carriers and might be a key to understanding the effects of spin scattering and their role in the mechanism of high temperature superconductivity. We have observed a decrease of c-axis length with increased Mg concentration in Cu 0.5 Tl 0.5 Ba 2 Ca 2Ày Mg y Cu 1.5 Ni 1.5 O 10Àd (y = 0.5, 1.0, 1.5) superconductors, showing an enhanced inter-plane coupling. The room temperature resistivity of the samples is decreased and the zero resistivity critical temperature [T c (R = 0)] and the magnitude of diamagnetism are increased with higher Mg doping in Cu 0.5 Tl 0.5 Ba 2 Ca 2Ày Mg y Cu 1.5 Ni 1.5 O 10Àd superconductors. A maximum diamagnetism is observed in the samples when Mg atoms replace 75% of the Ca atoms, which shows that a higher Mg doping concentration enhances the inter-plane coupling which possibly promotes the de-localization of the carriers to the Ni 2+ sites and results in enhanced superconducting properties.
Physica C: Superconductivity, 2009
Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd superconductors Fourier transforms infrared absorption spectroscopy ... more Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd superconductors Fourier transforms infrared absorption spectroscopy (FTIR) X-ray diffraction (XRD) Annealing a b s t r a c t In order to study the higher carrier's doping efficiency of (Cu 0.5 Tl 0.5)Ba 2 O 4Àd charge reservoir layer to the conducting CuO 2 planes we have incorporated Bi in (Cu 0.5 Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd superconductors; the presence of Bi in the charge reservoir layer promotes highest anisotropy to these compounds. For such studies, we have successfully synthesized (Cu 0.25 Tl 0.5 Bi 0.25)Ba 2 Ca 2 Cu 3 O 10Àd , (Bi 0.5 Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd , (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25)Ba 2 Ca 2 Cu 3 O 10Àd and (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25)Ba 2 Ca 2Ày Be y Cu 3 O 10Àd superconductors at normal pressure and studied their superconducting properties. These studies have shown that incorporation of Bi at the charge reservoir layer promoted a decrease in the density of carriers in the conducting CuO 2 planes which in turn suppressed the magnitude of diamagnetism of final compound. The decreased density of the carriers in the CuO 2 planes, which most likely promotes inferior superconducting properties, was replenished by doping of Li in the charge reservoir layer and optimizing their number by post-annealing in oxygen atmosphere. It is observed that Bi doping in (Cu 0.5 Tl 0.5)Ba 2 O 4Àd charge reservoir layer promotes an increase in the c-axis length which in turn increase the anisotropy and decrease the Fermi-vector [k F = (3p 2 N/V) 1/3 ] and Fermi-velocity ½v F ¼ ðpe c D= hÞ of the carriers. We have decreased the c-axis length of Bi doped compounds by doping Be at the Ca sites in (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25)Ba 2-Ca 2Ày Be y Cu 3 O 10Àd superconductors. It is observed from these experiments that Beryllium doping of y = 0.5 has produced excellent superconducting properties in terms of enhancement of T c (R = 0) and magnitude of diamagnetism in this compound. A maximum decrease in the unit cell volume is observed with this Be doping concentration, which enhance k F , v F and superconducting order parameter of the carriers and hence promote the enhancement of superconducting properties. These studies have also shown that the role of density of the carriers in CuO 2 planes is pivotal in the mechanism of superconductivity in these compounds and Bi doping significantly affects them due to its presence in the charge reservoir layer.
Journal of Superconductivity and Novel Magnetism, 2010
... N. Hassan Department of Physics, Hazara University, Mansehra, NWFP, Pakistan ... B. Condens. ... more ... N. Hassan Department of Physics, Hazara University, Mansehra, NWFP, Pakistan ... B. Condens. Matter 430, 378380 (2006) 6. Bahrs, S., Bruchhausen, A., Goñi, AR, Nieva, G., Fainstein, A., Fleischer, K., Richter, W., Thomsen, C.: J. Phys. Chem. ...
Journal of Materials Science: Materials in Electronics, 2010
... NA Khan 4 T. Firdous 4 M. Irfan (&) Materials Science Laboratory, Department of Physics, ... more ... NA Khan 4 T. Firdous 4 M. Irfan (&) Materials Science Laboratory, Department of Physics, Quaid-i-Azam University, Islamabad 45320, Pakistan e-mail: irfanphy@yahoo.com P. Kameli Department of Physics, Isfahan University of Technology, Isfahan 84154, Iran ...
Journal of Applied Physics, 2012
ABSTRACT The effect of oxygen annealing on the excess conductivity of Cu0.5Tl0.25M0.25Ba2Ca2Cu3O1... more ABSTRACT The effect of oxygen annealing on the excess conductivity of Cu0.5Tl0.25M0.25Ba2Ca2Cu3O10−δ (M = K, Na, Li, Tl) samples is investigated. From the analysis of results, we have evaluated the exponents, the coherence length, the crossover temperature, and interlayer coupling strength (J) of the samples. These studies show that the K-doped post-annealed sample has shown narrow transition width with improvement in 2D and 3D conductivities. Oxygen annealing has also enhanced the coherence length and interlayer coupling strength of the material. Na- and Li-doped post-annealed samples have shown increased transition width, poor 2D and 3D conductivities within narrow temperature windows. After annealing, reduction in coherence length and the interlayer coupling strength is also observed. While in Tl-doped sample, oxygen annealing has not caused much deviation in fluctuation induced conductivity (FIC) parameters. The underlying cause of improved behavior of post-annealed K-doped sample is also discussed.
Journal of Applied Physics, 2009
Cu0.5Tl0.5Ba2Ca1.5M1.5Cu4O12− M=0, Be, Mg superconductor samples have been taken for investigatin... more Cu0.5Tl0.5Ba2Ca1.5M1.5Cu4O12− M=0, Be, Mg superconductor samples have been taken for investigating critically the superconducting fluctuations. Using the AslamazovLarkin AL and LawrenceDoniach LD models of excess conductivity, several physical parameters of the ...
Journal of Applied Physics, 2010
... Nawazish Ali Khan,1,a) Najmul Hassan,2 Sana Nawaz,1 Babar Shabbir,1 Sajid Khan,1 and Azhar A.... more ... Nawazish Ali Khan,1,a) Najmul Hassan,2 Sana Nawaz,1 Babar Shabbir,1 Sajid Khan,1 and Azhar A. Rizvi3 1Materials Science Laboratory, Department of Physics, Quaid-i-Azam University, Islamabad, 45320, Pakistan 2Department of Physics, Hazara University Mansehra ...
Journal of Applied Physics, 2013
ABSTRACT Cu0.5Tl0.5Ba2Ca2−xYxCu3O10−δ (x = 0, 0.015, 0.025, 0.05) superconductors samples are syn... more ABSTRACT Cu0.5Tl0.5Ba2Ca2−xYxCu3O10−δ (x = 0, 0.015, 0.025, 0.05) superconductors samples are synthesized at normal pressure. The influence of doped atoms on the superconductivity parameters is investigated by fluctuation induced conductivity analyses of conductivity data. These studies have shown increase in the inter-plane coupling J and coherence length ξc along the c-axis. A decrease in Bc0(T), Bc1(T), Jc(0) and increase in the values of κ, λp.d is observed. The widths of three dimensional conductivity regimes are enhanced whereas two dimensional conductivity regimes are significantly suppressed with the doping of Y+3 at the Ca+2 sites. These studies suggested that doping of Y+3 at Ca+2 improves the inter-plane coupling thereby inducing coherent movement of the carriers in various conducting CuO2 planes.
Journal of Alloys and Compounds, 2010
... [11] A. Poddar, B. Bandyopadhyay, B. Chattopadhyay, Physica C 390 (2003) 120-126. ... [30] P.... more ... [11] A. Poddar, B. Bandyopadhyay, B. Chattopadhyay, Physica C 390 (2003) 120-126. ... [30] P. Sumana, Prabhu, UV Varadaraju, Phy. ... Dr. M. Mumtaz Material Science Laboratory Department of Physics, Quaid-i-Azam University Islamabad Pakistan. ...
IEEE Access, 2019
Maritime networks establish wireless multi-hop networks to provide wireless broadband service at ... more Maritime networks establish wireless multi-hop networks to provide wireless broadband service at sea, connecting various kinds of ships, maritime buoys, and beacons. The maritime networks possess two distinguishing characteristics highly affected by maneuver at sea-dynamic link quality and bandwidth constrained, and dynamic network topology-that warrant specific attention. Unlike land vehicles, maneuver at sea is affected by sea surface movement and wave occlusions, which can cause unstable environment with a high rate of link breakages caused by low link stability, as well as low and highly variable bandwidth. In spite of the need to achieve performance close to high-speed terrestrial wireless broadband service on land, there is only a perfunctory effort to investigate maritime networks. There is an urgent need to refresh the interest to investigate, as well as to further enhance, maritime networks. This paper presents a review of the limited research works of this topic, which revolve around the networking issues in the link, network, and upper layers, in the literature. The objective is to establish a foundation in order to motivate a new research interest in maritime networks. Open issues are also presented to foster new research initiatives in this burgeoning and exciting area. INDEX TERMS Maritime network, ship ad hoc network, wireless network.
2017 13th International Wireless Communications and Mobile Computing Conference (IWCMC), 2017
Modeling of Underwater Wireless Sensor Networks (UWSNs) with a goal of maximum network lifetime a... more Modeling of Underwater Wireless Sensor Networks (UWSNs) with a goal of maximum network lifetime and throughput with minimum energy consumption is a quite difficult task because of limited battery power and harsh underwater environment. Balanced Energy Efficient Rectangular routing protocol (BEER) covers the maximum network area with the mobility of sinks and collects the data from sensor nodes in their transmission range using direct transmission. Sink movement maximizes the throughput and balanced the energy consumption. Simulation results verify that our scheme performs outstanding in terms of network lifetime, stability period and throughput with minimum energy consumption.
Ambient Assisted Living and Enhanced Living Environments, 2017
Energy is an important factor to be considered especially in the cases where implantable nodes ar... more Energy is an important factor to be considered especially in the cases where implantable nodes are used. This is important because it is very difficult to replace the battery of a node placed inside a body. Researchers have been trying to develop energy efficient solutions in order to save energy and to extend the overall network lifetime. This chapter provides a comprehensive overview of Wireless Body Area Network (WBAN) and the energy management challenges. Moreover, heating issues faced by sensor nodes implanted in human body are also discussed. Heat dissipation is mainly due to the transmission and reception of electromagnetic signals to and from other sensor nodes which are part of the same network. The amount of heat dissipation is known as Specific Absorption Rate (SAR) and is measured in W/kg. There is a need to find solutions to reduce it to a level which is not dangerous for human health. High values of SAR results in tissue damage. Thus, the goal of this chapter is to discuss energy management, SAR and safety aspects in implanted wireless body area networks.
Cluster Computing
There are thousands of flights carrying millions of passengers each day, having three or more Int... more There are thousands of flights carrying millions of passengers each day, having three or more Internet-connected devices with them on average. Usually, onboard devices remain idle for most of the journey (which can be of several hours), therefore, we can tap on their underutilized potential. Although these devices are generally becoming more and more resourceful, for complex services (such as related to machine learning, augmented/virtual reality, smart healthcare, and so on) those devices do not suffice standalone. This makes a case for multi-device resource aggregation such as through femto-cloud. As our first contribution, we present the utility of femto-cloud for aerial users. But for that sake, a reliable and faster Internet is required (to access online services or cloud resources), which is currently not the case with satellite-based Internet. That is the second challenge we try to address in our paper, by presenting an adaptive beamforming-based solution for aerial Internet provisioning. However, on average, most of the flight path is above waters. Given that, we propose that beamforming transceivers can be docked on stationery ships deployed in the vast waters (such as the ocean). Nevertheless, certain services would be delay-sensitive, and accessing their on-ground servers or cloud may not be feasible (in terms of delay). Similarly, certain complex services may require resources in addition to the flight-local femto-cloud. That is the third challenge we try to tackle in this paper, by proposing that the traditional fog computing (which is a cloud-like but localized pool of resources) can also be extended to the waters on the ships harboring beamforming transceivers. We name it Floating Fog. In addition to that, Floating Fog will enable several new services such as live black-box. We also present a cost and bandwidth analysis to highlight the potentials of Floating Fog. Lastly, we identify some challenges to tackle the successful deployment of Floating Fog.
Enhanced Living Environments: From models to technologies, 2017
The developments that shaped the twenty/twenty-first century with respect to wireless technologie... more The developments that shaped the twenty/twenty-first century with respect to wireless technologies have had a great influence on quality of life, where wireless body area networks (WBANs) - implantable sensor nodes, more specifically, have recently emerged as a successful initiative for monitoring health remotely, and thus a research challenge. Two concerns that need addressing here are heat dissipation which causes damage to surrounding tissues, and introduction of relay nodes to increase network lifetime, but on the other hand may cause health hazards. There arises a need to find an efficient network topology design to overcome the above-mentioned concerns. This chapter discusses in detail WBAN, its applications, related technologies, energy-aware topology design, efficient relay node placement methods and, last but not least, energy-efficient and thermal-aware routing techniques.
International Journal of Distributed Sensor Networks
High-speed quality Internet provision for aircraft passengers is thought to be one of the major u... more High-speed quality Internet provision for aircraft passengers is thought to be one of the major unresolved challenges for ubiquitous Internet provision. This article aims to resolve the problem of airborne Internet access with high quality of service for modern Internet of things devices. Large remote regions in the ocean along the busy air routes (e.g. Atlantic Ocean) require high-speed, reliable, and low-cost airborne Internet (i.e. Internet provision to the aircraft) to manage various delay- and throughput-sensitive applications. Conventional satellite-based solutions can be an alternate for Internet provision in such far-flung areas; but, such solutions are lacking quality of service (with longer delays and low bandwidth) and are significantly costly. Fortunately, the underwater optical fiber cables deployed across the oceans pass along the same busy air routes. This infrastructure of underwater optical fiber cables can be exploited for Internet backbone providing high quality o...
Journal of Materials Science: Materials in Electronics, 2018
Ti-doped (Cu 0.5 Tl 0.5)Ba 2 (Ca 2−x Ti x)Cu 3 O 10−δ (x = 0, 0.25, 0.50, 0.75, 1.0) superconduct... more Ti-doped (Cu 0.5 Tl 0.5)Ba 2 (Ca 2−x Ti x)Cu 3 O 10−δ (x = 0, 0.25, 0.50, 0.75, 1.0) superconductors have been synthesized by solid state reaction method. The prepared samples are characterized by XRD, electrical resistivity, AC susceptibility and FTIR techniques. XRD analysis showed that the lattice parameters are marginally altered but there is no substantial change with the doping of Ti. All the samples are found with orthorhombic crystal structure following PMMM space group. T c (R = 0) is enhanced with the doping of Ti except for x = 1.0 sample. The magnitude of diamagnetism in the AC-susceptibility measurements is enhanced up to x = 0.5 and decreased beyond. The FTIR measurements show that the apical oxygen phonon modes are softened. The planar oxygen phonon modes are softened but their intensity is raised with the enhanced Ti contents. This softening of the planar oxygen phonon modes may be arising due to the heavier Ti ions (47.9 amu) at the lighter Ca (40.07 amu) sites. Variation in the lattice parameters in the XRD data and shifting of various oxygen phonon modes in the FTIR data show that Ti is incorporated at Ca sites in the unit cell. Increase in the superconducting properties up to certain doping level (x = 0.75) may be arising due to the improved interplane coupling caused by the smaller sized Ti at Ca sites. While the decrease in T c and magnitude of diamagnetism beyond x = 0.75 and x = 0.5 respectively, is attributed to the suppressed density of a particular type of phonons required for optimum superconductivity. This suppression in the density of the desired phonons is brought about by the substitution of heavier Ti ions at the lighter Ca sites. This study signifies the role of electron-phonon interaction in mechanism of high T c superconductivity.
Journal of Materials Science: Materials in Electronics, 2016
Be doped (Cu0.5Tl0.5)Ba2(Ca2−yBey)(Cu2.5Cd0.5)O10−δ (y = 0, 0.1, 0.2, 0.35, 0.5) superconductive ... more Be doped (Cu0.5Tl0.5)Ba2(Ca2−yBey)(Cu2.5Cd0.5)O10−δ (y = 0, 0.1, 0.2, 0.35, 0.5) superconductive samples are synthesized by solid state reaction method at normal pressure. The X-ray diffraction of these samples reveals a suppression in the c-axis length with the enhanced Be contents, reflecting the incorporation of Be at the inter plane Ca sites. The critical temperature Tc (R = 0) and onset temperature of diamagnetism Tc (onset) are found to increase with the increasing Be-contents up to y = 0.2 and decrease beyond this doping level. The room temperature resistivity, ρ(290K), is decreased in y = 0.1 and 0.2 samples, and raised to higher values beyond y = 0.2 in comparison to y = 0 samples. This improvement most likely arises due to the better interplane coupling caused by incorporation of Be at the Ca sites in the unit cell. The magnitude of diamagnetism is suppressed in all the Be-doped samples in comparison to un-doped sample. The FTIR absorption spectra show systematic hardening of the vibrational modes of apical oxygen with the increasing Be concentration. It confirms the incorporation of Be at the interplane Ca sites which results in the enhanced interplane coupling and hence the better superconducting properties in y = 0.1 and 0.2 samples. This hardening of the apical oxygen modes also complements our XRD results. The suppression of superconductivity parameters in samples with higher Be contents, namely y = 0.35 and 0.5, is attributed to the presence of heavier Cd at the Cu planar sites in CuO2/CdO2 planes. Cd atoms suppress the phonon’s population due to anharmonic oscillations it produces. Such anharmonicity is further promoted due to the enhanced interplane coupling caused by Be doping which further suppresses the phonon’s density and hence the superconductivity in the samples with higher Be-contents i.e. y = 0.35 and 0.5. These results stress on the vital role the electron–phonon interactions in the mechanism of superconductivity in cuprate superconductors.
Nanomaterials and Nanotechnology, 2012
Raman scattering investigations based on density functional theory (DFT) calculations were perfor... more Raman scattering investigations based on density functional theory (DFT) calculations were performed to explore the vibrational modes of wurtzite structured CdS nanoparticles (NPs). The calculations were performed to obtain the Raman spectra for the CdS containing 2, 4, 8 and 12 atoms to study the size dependence. Several vibrational modes indicating stretching and bending features related to Cd and S atoms were observed. Modifications of the frequency and intensity of different Raman modes with an increase in number of atoms in NPs are discussed in detail. It is found that the frequency of the CdS symmetric stretching mode of vibration shows a consistent red shift and that of CdS anti-symmetric stretching shows a consistent blue shift with the increase in the number of atoms. Hydrogen atoms were added in order to make the closed shell configuration and saturate the NPs as per the requisite for calculating the Raman spectra. This produced some additional modes of vibration related to hydrogen atoms. The SH stretching mode showed a consistent red shift and the CdH stretching mode showed a consistent blue shift with an increase in the number of atoms in NPs. The results generated are found to be in close agreement with the literature. The observed red shift in different modes is assigned to stimulated Raman stretching and blue shift is ascribed to the coherent anti-stokes Raman scattering.
Physica C: Superconductivity, 2009
Excess conductivities of polycrystalline, as-prepared and oxygen post annealed Mg doped samples h... more Excess conductivities of polycrystalline, as-prepared and oxygen post annealed Mg doped samples have been studied from the resistivity versus temperature data. The logarithmic plots of excess conductivity versus reduced temperatures [(T-Tcmf)/Tcmf] show two cross-over temperatures with three exponents. Except for the as-prepared sample with x=1 all the samples have shown a distinct cross-over from two-dimensional to three-dimensional conductivity in accordance with the 2D, 3D Aslamazov–Larkin equations. Interlayer-coupling strength estimated by using Lawrence–Doniach equations has been observed to increase with higher Mg doping and post-annealing. The improved properties with the higher Mg concentration might be arising from the reduction of the anisotropy along the c-axis. The oxygen post-annealing seems to improve carrier concentration in the conducting CuO2 planes that may be responsible for 2D–3D cross-over of the excess conductivity.
Physica C: Superconductivity, 2007
We have synthesized Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3Ày Ni y O 10Àd (y = 0, 0.5, 1.0, 1.5) superconduc... more We have synthesized Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3Ày Ni y O 10Àd (y = 0, 0.5, 1.0, 1.5) superconductors at normal pressure and studied the enhanced correlation among CuO 2 /NiO 2 planes of Cu 0.5 Tl 0.5 Ba 2 Ca 2Ày Mg y Cu 1.5 Ni 1.5 O 10Àd (y = 0.5, 1.0, 1.5) superconductors by doping Mg at the Ca sites. Surprisingly, we have not observed any substantial depression of critical temperature with Ni doping in Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3Ày Ni y O 10Àd (y = 0, 0.5, 1.0, 1.5) superconductors. The main objective of Mg substitution is to enhance the interplane coupling which may increase the interactions of the spins of Ni atoms in different planes. The increased inter-plane coupling may enhance interactions of the atomic spins with the free carriers and might be a key to understanding the effects of spin scattering and their role in the mechanism of high temperature superconductivity. We have observed a decrease of c-axis length with increased Mg concentration in Cu 0.5 Tl 0.5 Ba 2 Ca 2Ày Mg y Cu 1.5 Ni 1.5 O 10Àd (y = 0.5, 1.0, 1.5) superconductors, showing an enhanced inter-plane coupling. The room temperature resistivity of the samples is decreased and the zero resistivity critical temperature [T c (R = 0)] and the magnitude of diamagnetism are increased with higher Mg doping in Cu 0.5 Tl 0.5 Ba 2 Ca 2Ày Mg y Cu 1.5 Ni 1.5 O 10Àd superconductors. A maximum diamagnetism is observed in the samples when Mg atoms replace 75% of the Ca atoms, which shows that a higher Mg doping concentration enhances the inter-plane coupling which possibly promotes the de-localization of the carriers to the Ni 2+ sites and results in enhanced superconducting properties.
Physica C: Superconductivity, 2009
Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd superconductors Fourier transforms infrared absorption spectroscopy ... more Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd superconductors Fourier transforms infrared absorption spectroscopy (FTIR) X-ray diffraction (XRD) Annealing a b s t r a c t In order to study the higher carrier's doping efficiency of (Cu 0.5 Tl 0.5)Ba 2 O 4Àd charge reservoir layer to the conducting CuO 2 planes we have incorporated Bi in (Cu 0.5 Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd superconductors; the presence of Bi in the charge reservoir layer promotes highest anisotropy to these compounds. For such studies, we have successfully synthesized (Cu 0.25 Tl 0.5 Bi 0.25)Ba 2 Ca 2 Cu 3 O 10Àd , (Bi 0.5 Tl 0.5)Ba 2 Ca 2 Cu 3 O 10Àd , (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25)Ba 2 Ca 2 Cu 3 O 10Àd and (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25)Ba 2 Ca 2Ày Be y Cu 3 O 10Àd superconductors at normal pressure and studied their superconducting properties. These studies have shown that incorporation of Bi at the charge reservoir layer promoted a decrease in the density of carriers in the conducting CuO 2 planes which in turn suppressed the magnitude of diamagnetism of final compound. The decreased density of the carriers in the CuO 2 planes, which most likely promotes inferior superconducting properties, was replenished by doping of Li in the charge reservoir layer and optimizing their number by post-annealing in oxygen atmosphere. It is observed that Bi doping in (Cu 0.5 Tl 0.5)Ba 2 O 4Àd charge reservoir layer promotes an increase in the c-axis length which in turn increase the anisotropy and decrease the Fermi-vector [k F = (3p 2 N/V) 1/3 ] and Fermi-velocity ½v F ¼ ðpe c D= hÞ of the carriers. We have decreased the c-axis length of Bi doped compounds by doping Be at the Ca sites in (Cu 0.25 Tl 0.25 Bi 0.25 Li 0.25)Ba 2-Ca 2Ày Be y Cu 3 O 10Àd superconductors. It is observed from these experiments that Beryllium doping of y = 0.5 has produced excellent superconducting properties in terms of enhancement of T c (R = 0) and magnitude of diamagnetism in this compound. A maximum decrease in the unit cell volume is observed with this Be doping concentration, which enhance k F , v F and superconducting order parameter of the carriers and hence promote the enhancement of superconducting properties. These studies have also shown that the role of density of the carriers in CuO 2 planes is pivotal in the mechanism of superconductivity in these compounds and Bi doping significantly affects them due to its presence in the charge reservoir layer.
Journal of Superconductivity and Novel Magnetism, 2010
... N. Hassan Department of Physics, Hazara University, Mansehra, NWFP, Pakistan ... B. Condens. ... more ... N. Hassan Department of Physics, Hazara University, Mansehra, NWFP, Pakistan ... B. Condens. Matter 430, 378380 (2006) 6. Bahrs, S., Bruchhausen, A., Goñi, AR, Nieva, G., Fainstein, A., Fleischer, K., Richter, W., Thomsen, C.: J. Phys. Chem. ...
Journal of Materials Science: Materials in Electronics, 2010
... NA Khan 4 T. Firdous 4 M. Irfan (&) Materials Science Laboratory, Department of Physics, ... more ... NA Khan 4 T. Firdous 4 M. Irfan (&) Materials Science Laboratory, Department of Physics, Quaid-i-Azam University, Islamabad 45320, Pakistan e-mail: irfanphy@yahoo.com P. Kameli Department of Physics, Isfahan University of Technology, Isfahan 84154, Iran ...
Journal of Applied Physics, 2012
ABSTRACT The effect of oxygen annealing on the excess conductivity of Cu0.5Tl0.25M0.25Ba2Ca2Cu3O1... more ABSTRACT The effect of oxygen annealing on the excess conductivity of Cu0.5Tl0.25M0.25Ba2Ca2Cu3O10−δ (M = K, Na, Li, Tl) samples is investigated. From the analysis of results, we have evaluated the exponents, the coherence length, the crossover temperature, and interlayer coupling strength (J) of the samples. These studies show that the K-doped post-annealed sample has shown narrow transition width with improvement in 2D and 3D conductivities. Oxygen annealing has also enhanced the coherence length and interlayer coupling strength of the material. Na- and Li-doped post-annealed samples have shown increased transition width, poor 2D and 3D conductivities within narrow temperature windows. After annealing, reduction in coherence length and the interlayer coupling strength is also observed. While in Tl-doped sample, oxygen annealing has not caused much deviation in fluctuation induced conductivity (FIC) parameters. The underlying cause of improved behavior of post-annealed K-doped sample is also discussed.
Journal of Applied Physics, 2009
Cu0.5Tl0.5Ba2Ca1.5M1.5Cu4O12− M=0, Be, Mg superconductor samples have been taken for investigatin... more Cu0.5Tl0.5Ba2Ca1.5M1.5Cu4O12− M=0, Be, Mg superconductor samples have been taken for investigating critically the superconducting fluctuations. Using the AslamazovLarkin AL and LawrenceDoniach LD models of excess conductivity, several physical parameters of the ...
Journal of Applied Physics, 2010
... Nawazish Ali Khan,1,a) Najmul Hassan,2 Sana Nawaz,1 Babar Shabbir,1 Sajid Khan,1 and Azhar A.... more ... Nawazish Ali Khan,1,a) Najmul Hassan,2 Sana Nawaz,1 Babar Shabbir,1 Sajid Khan,1 and Azhar A. Rizvi3 1Materials Science Laboratory, Department of Physics, Quaid-i-Azam University, Islamabad, 45320, Pakistan 2Department of Physics, Hazara University Mansehra ...
Journal of Applied Physics, 2013
ABSTRACT Cu0.5Tl0.5Ba2Ca2−xYxCu3O10−δ (x = 0, 0.015, 0.025, 0.05) superconductors samples are syn... more ABSTRACT Cu0.5Tl0.5Ba2Ca2−xYxCu3O10−δ (x = 0, 0.015, 0.025, 0.05) superconductors samples are synthesized at normal pressure. The influence of doped atoms on the superconductivity parameters is investigated by fluctuation induced conductivity analyses of conductivity data. These studies have shown increase in the inter-plane coupling J and coherence length ξc along the c-axis. A decrease in Bc0(T), Bc1(T), Jc(0) and increase in the values of κ, λp.d is observed. The widths of three dimensional conductivity regimes are enhanced whereas two dimensional conductivity regimes are significantly suppressed with the doping of Y+3 at the Ca+2 sites. These studies suggested that doping of Y+3 at Ca+2 improves the inter-plane coupling thereby inducing coherent movement of the carriers in various conducting CuO2 planes.
Journal of Alloys and Compounds, 2010
... [11] A. Poddar, B. Bandyopadhyay, B. Chattopadhyay, Physica C 390 (2003) 120-126. ... [30] P.... more ... [11] A. Poddar, B. Bandyopadhyay, B. Chattopadhyay, Physica C 390 (2003) 120-126. ... [30] P. Sumana, Prabhu, UV Varadaraju, Phy. ... Dr. M. Mumtaz Material Science Laboratory Department of Physics, Quaid-i-Azam University Islamabad Pakistan. ...
IEEE Access, 2019
Maritime networks establish wireless multi-hop networks to provide wireless broadband service at ... more Maritime networks establish wireless multi-hop networks to provide wireless broadband service at sea, connecting various kinds of ships, maritime buoys, and beacons. The maritime networks possess two distinguishing characteristics highly affected by maneuver at sea-dynamic link quality and bandwidth constrained, and dynamic network topology-that warrant specific attention. Unlike land vehicles, maneuver at sea is affected by sea surface movement and wave occlusions, which can cause unstable environment with a high rate of link breakages caused by low link stability, as well as low and highly variable bandwidth. In spite of the need to achieve performance close to high-speed terrestrial wireless broadband service on land, there is only a perfunctory effort to investigate maritime networks. There is an urgent need to refresh the interest to investigate, as well as to further enhance, maritime networks. This paper presents a review of the limited research works of this topic, which revolve around the networking issues in the link, network, and upper layers, in the literature. The objective is to establish a foundation in order to motivate a new research interest in maritime networks. Open issues are also presented to foster new research initiatives in this burgeoning and exciting area. INDEX TERMS Maritime network, ship ad hoc network, wireless network.