Porosity control in metal-assisted chemical etching of degenerately doped silicon nanowires

We report the fabrication of degenerately doped silicon (Si) nanowires of different aspect ratios using a simple, low-cost and effective technique that involves metal-assisted chemical etching (MacEtch) combined with soft lithography or thermal dewetting metal patterning. We demonstrate sub-micron diameter Si nanowire arrays with aspect ratios as high as 180:1, and present the challenges in producing solid nanowires using MacEtch as the doping level increases in both p- and n-type Si. We report a systematic reduction in the porosity of these nanowires by adjusting the etching solution composition and temperature. We found that the porosity decreases from top to bottom along the axial direction and increases with etching time. With a MacEtch solution that has a high [HF]:[H(2)O(2)] ratio and low temperature, it is possible to form completely solid nanowires with aspect ratios of less than approximately 10:1. However, further etching to produce longer wires renders the top portion of the nanowires porous.     

Study of LDPE/TiO2 and PS/TiO2 Composites as Potential Substrates for Microstrip Patch Antennas

Low-density polyethylene (LDPE)/titania (TiO₂) and polystyrene (PS)/titania (TiO₂) composite systems have been developed as alternative substrates for microstrip patch antennas (MPA) for handheld devices. Morphological, thermal, and microwave characterizations of these composites have been conducted for different volume fractions of TiO₂ in the polymer matrix. The size of the titania particles was found to be of the order of 0.5 μm, and their distribution in the composite was quite uniform. Composite materials showed an improvement in thermal and microwave properties over the parent polymer. Verification of these composites as potential substrates for MPA was carried out by fabricating simple rectangular patch X-band antennas. Materials with optimized substrate properties were chosen to design the MPA. The patches were designed with 4% volume fraction TiO₂ in the LDPE composite system and 6% volume fraction TiO₂ in the PS composite system. Return loss of ∼18 dB was observed for both systems.     

An Optical Layer Lightpath Management Protocol for WDM AONs

In this work, we propose a control protocol for lightpath management in the optical layer of all-optical networks (AONs). AONs follow a layered structure, as used by various network standards, where each layer communicates with its peer through Protocol Data Units (PDUs). In the context of Open System Interconnection (OSI) Reference Model (RM), a new layer, called optical layer, has been introduced in the AON architecture to manage the lightpath related functions. The optical layer lies in between the physical layer and the data link layer. The objective of this paper is to define a specification for an optical layer protocol for managing lightpaths in AONs. In order to study the dynamics of the optical layer protocol system, we first employ the communicating finite state machine model to represent the protocol. Then a reachability analysis of the model is performed to verify the protocol. This paper shows how the optical layer protocol can be specified formally and made error-free by the step-wise refinement of an initial specification, where validation is done after each refinement.     

mTrust: Call Behavioral Trust Predictive Analytics Using Unsupervised Learning in Mobile Cloud Computing

Filtering spam voice calls are a still major challenge in today’s technology contrary to SMS or email-based spamming. A numerical measure of the trust between users can help us filter calls based on relevance. Given the abundance of user-generated information available from the huge number of online devices, we can harness the power of this data to develop software adapting to user behavior. Existing research works for trust computation face various challenges when it comes to global applicability and understandability of trust values. Our investigation includes detailed surveillance of user call patterns based on the call data available from mobile devices and proposes a novel approach to filter calls that are of higher relevance to users based on their call-trust values. Our implementation realizes the diversity in call patterns of different people due to varying usage and uses classification and clustering algorithms to generate personalized, accurate numerical, and categorical trust values for every user. Categorical trust makes it easier to apply and understand trust ratings on a global scale. The implementation also incorporates a cloud facility to crowd-source trust values from multiple users, in a single database to generate the global trust of a user which can be used for spam filtering on a global scale. A software named “mTrust” is developed in this work for the future generation of a trustworthy mobile cloud network.

     

Quantum-dot cellular automata based reversible low power parity generator and parity checker design for nanocommunication

Quantum-dot cellular automata (QCA) is an emerging area of research in reversible computing. It can be used to design nanoscale circuits. In nanocommunication, the detection and correction of errors in a received message is a major factor. Besides, device density and power dissipation are the key issues in the nanocommunication architecture. For the first time, QCA-based designs of the reversible low-power odd parity generator and odd parity checker using the Feynman gate have been achieved in this study. Using the proposed parity generator and parity checker circuit, a nanocommunication architecture is proposed. The detection of errors in the received message during transmission is also explored. The proposed QCA Feynman gate outshines the existing ones in terms of area, cell count, and delay. The quantum costs of the proposed conventional reversible circuits and their QCA layouts are calculated and compared, which establishes that the proposed QCA circuits have very low quantum cost compared to conventional designs. The energy dissipation by the layouts is estimated, which ensures the possibility of QCA nano-device serving as an alternative platform for the implementation of reversible circuits. The stability of the proposed circuits under thermal randomness is analyzed, showing the operational efficiency of the circuits. The simulation results of the proposed design are tested with theoretical values, showing the accuracy of the circuits. The proposed circuits can be used to design more complex low-power nanoscale lossless nanocommunication architecture such as nano-transmitters and nano-receivers.     

A review of nanofluid preparation,stability, and thermo‐physical properties

This paper represents a comprehensive review on the preparation and stability of nanofluid, the convective heat transfer coefficient and different thermo‐physical properties such as thermal conductivity, specific heat capacity, viscosity, and so on. Here, for each thermo‐physical property, measurement methods, enhancement mechanisms, and criticisms of different studies are also presented. However, based on the available literature, it is concluded that a nanofluid has, in general, better thermo‐physical properties even at a very low particle concentration (typically 1% or less) than conventional heat transfer fluids. The only drawback is high viscosity which leads to a higher pressure drop. At a very low particle concentration, this drawback can be minimized. Three tables are provided for three thermo‐physical properties namely thermal conductivity, specific heat capacity, and viscosity, which can be used as a ready reference for calculating the nanofluid properties.     

Occurrence of Arsenic-contaminatedGroundwater in Alluvial Aquifers from Delta Plains,Eastern India: Options for Safe Drinking Water Supply

Arsenic contamination in groundwater used for drinking purposes has been envisaged as a problem of global concern. Exploitation of groundwater contaminated with arsenic within the delta plains in West Bengal has caused adverse health effects among the population within a span of 8-10 years. The sources of arsenic in natural water are a function of the local geology, hydrology and geochemical characteristics of the aquifers. The retention and mobility of different arsenic species are sensitive to varying redox conditions. The delta plains in West Bengal are characterized by a series of meander belts formed by the fluvial processes comprising different cycles of complete or truncated fining upward sequences (sand-silt-clay). The arseniferous groundwater belts are mainly located in the upper delta plain and in abandoned meander channels. Mineralogical investigations have established that arsenic in the silty clay as well as in the sandy layers occurs as coatings on mineral grains. Clayey sediments intercalated with sandy aquifers at depths between 20 and 80 m are reported as a major source of arsenic in groundwater.Integrated knowledge on geological, hydrologicaland geochemical characteristics of the multi-level aquifer system of the upper delta plain is therefore necessary in predicting the origin, occurrence and mobility of arsenic in groundwater in West Bengal. This would also provide a basis for developing suitable low-cost techniques for safe drinking water supply in the region.