Controlled growth of well-aligned GaS nanohornlike structures and their field emission properties

Here, we report the synthesis of vertically aligned gallium sulfide (GaS) nanohorn arrays using simple vapor-liquid-solid (VLS) method. The morphologies of GaS nano and microstructures are tuned by controlling the temperature and position of the substrate with respect to the source material. A plausible mechanism for the controlled growth has been proposed. It is important to note that the turn-on field value of GaS nanohorns array is found to be the low turn-on field 4.2 V/μm having current density of 0.1 μA/cm(2). The striking feature of the field emission behavior of the GaS nanohorn arrays is that the average emission current remains nearly constant over long time without any degradation.     

Real time in vitro measurement of oxygen uptake rates for HEPG2 liver cells encapsulated in alginate matrices

Quantitative non-invasive measurement of critical physiological parameters is necessary to assess the functionality and applicability of tissue engineered matrices. Advancements in fiber optic sensors have made it possible for measuring parameters such as oxygen, glucose, and aminoacids necessary for viable tissue growth. In this study, we have devised an experimental protocol to measure in real time, the oxygen uptake rate (OUR) values for a selected liver cell line (HEPG2) when grown (a) on cover glass slides, and (b) encapsulated within alginate based hydrogel matrices. For both cases, the oxygen uptake rates of HEPG2 cells at selected time points varied in close co-relation with cell proliferation and metabolic activity during the 7-day culture period. This investigation concludes that OUR can be used as an indicative parameter to assess the metabolic activity of cells encapsulated within a matrix. The study also presents a fiber optic sensing technology as a non-invasive diagnostic tool to monitor cell behavior and activity.     

Gap‐coupled designs of star shape microstrip antennas for dual band and wide band circular polarized response

Gap‐coupled designs of star‐shape microstrip antennas for dual band and wide band circular polarized response are proposed. An angular displacement between fed and parasitic patches yields the optimum separation between patch orthogonal resonant modes to yield circular polarized response. In dual band design, axial ratio bandwidth of 8% is obtained whereas wideband design gives axial ratio bandwidth of nearly 29%. Proposed configurations exhibit broadside pattern with peak gain of more than 7 dBi. Resonant length formulations for star shape patch and for their dual and wide band designs are presented. They provide guidelines for redesigning similar antenna at different frequency.     

Modified CAZAC Sequence Based Timing Synchronization Scheme for OFDM System

Wireless Personal Communications - Active queue management schemes are used to reduce the number of dropped packets at the routers. Random early detection uses dropping probability which is...     

Room temperature synthesis of In2S3 micro- and nanorod textured thin films

Thin films of indium sulfide (In₂S₃) micro- and nanorods were successfully prepared by sulfurization of electrodeposited metal indium layers. The films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and UV-vis spectroscopy. From XRD and TEM observations it was concluded that the In₂S₃ nanorods and microrods have ∼50 nm and ∼0.5 μm diameter, respectively. A plausible top-growth mechanism was proposed for the formation of the nanorods in which the hydroxide layer was found to play an important role. The micro- and nanorods showed optical bandgap of ∼2.2 and ∼2.54 eV, respectively. This facile and cost effective method may be extended to fabricate other metal chalcogenide nanostructures on solid substrates.     

Solvothermal synthesis of CdS nanorods: role of basic experimental parameters

CdS nanorods with varying dimensions were synthesized by solvothermal process. It was observed that the anions present with the Cd-salts play an important role in determining the dimensions of the CdS nanorods. The crystalline nature of the sources was found to play a crucial role in determining the phase of the products. The nature of the sulfur source, molar ratio of the precursors, filling fraction of the solvent, and the synthesis temperature play important role in defining the size and shape of the products. By controlling the experimental parameters it was possible to control the dimension of the CdS nanorods within a certain range (diameter of the nanorods could be varied within a wide range from approximately 7 to 100 nm by varying the temperature within 100-250 degrees C). Optical absorption, photoluminescence, and Raman studies of these samples were carried out to characterize the CdS nanorods.     

Multicolor luminescence from transition metal ion (Mn2+ and Cu2+) doped ZnS nanoparticles

Mn and Cu doped ZnS nanoparticles in powder form were prepared by a simple solvothermal route. Particle size and crystal structure of the products were investigated through X-ray diffraction study revealing the formation of cubic ZnS nanoparticles of average diameter 2.5 nm. Particle size was also verified by the high resolution transmission electron microscopic images. Blue emission at approximately 445 nm was observed from the undoped sample, which was attributed to the presence of large surface defects. With increasing doping concentration the defect related emission gradually quenches and subsequently the impurity related emissions appeared. Mn doped samples exhibited orange emission at approximately 580 nm which may be attributed to the transition between (4)T1 and (6)A1 energy levels of the Mn2+ 3d states. Whereas, the Cu doped ZnS nanoparticles exhibited a red shifted strong blue emission at approximately 466 nm which is attributed to the transition of the electrons from the surface states to the 't2' levels of Cu impurities.     

Indirect casting of patient-specific tricalcium phosphate zirconia scaffolds for bone tissue regeneration using rapid prototyping methodology

Bio-composite scaffolds were fabricated by impregnating 10, 20, 30, 40 and 50% ZrO₂ content with the β-TCP matrix to heal load bearing large size bone defects. The composite scaffolds were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and mechanical testing. The in vitro degradation of scaffolds was calculated by immersing the samples in phosphate buffer saline for a period of 21 days. Biocompatibility was evaluated by XTT assay using human Osteosarcoma cell line (MG-63). Results include scaffold surface morphology, overall porosity, phase transformation, bonding, compressive strength, biodegradability and cytotoxicity with an increase in ZrO₂ percentages. The conclusions proved that β-TCP scaffold with 30% ZrO₂ content exhibits the best-required properties for the application in the field of bone tissue regeneration.