Two-Level Multiaccess Schemes for Packet Satellite Systems with Low Duty Factor Terminals

A two-level packet satellite network architecture is proposed to provide efficient communications for a large number of low duty factor terminals. At the first level, disjoint subnets of prioritized users employ a minislotted alternating priorities (MSAP) protocol. At the second level, a time division multiple access (TDMA) or frequency division multiple access (FDMA) uplink, and a time division multiplexed (TDM) or frequency division multiplexed (FDM) downlink is assumed, with the satellite regenerating and reformatting the data appropriately. Examples with a large number of terminals show that the two-level schemes provide superior delay performance over single-level methods for wide ranges of throughput.     

Mechanism synthesis using the workstation environment

Some capabilities of modern engineering workstations and their impact on the mechanism synthesis process are discussed. Specific examples of ongoing work at the University of Minnesota utilizing the Apollo color raster workstation to provide user-friendly general-purpose user-interface tools are presented. The application of these tools to the LINCAGES-4 four-bar linkage synthesis and analysis program and the Minn-Dwell dwell mechanism synthesis program is described. The impact that this environment can have on computer-aided design is assessed     

Direct determination of kerma for a d(48.5) + Be therapy beam

An experimental determination of the neutron kerma ratio between muscle tissue and A-150 plastic was performed at the newly commissioned d(48.5)+ Be therapy facility in Detroit. Low-pressure proportional counters with separate walls made from A-150 plastic, graphite, zirconium oxide and zirconium served to measure ionization yield spectra. The absorbed dose in the wall of each counter was determined and rendered the A-150 and carbon kerma directly, whilst that for oxygen was deduced from differences between the matched metal oxide and metal pair. This enabled the evaluation of an effective kerma ratio as a function of radiation field size and hydrogenous filtration. Although filtration was observed to harden the beam, the application of a single kerma ratio for the various irradiation conditions investigated was found to be appropriate. A neutron kerma ratio of 0.90+/-0.03 was assessed for the Detroit facility, which is lower at the 1sigma level than the 0.95 currently recommended in the dosimetry protocol for high-energy neutron beams.     

Spectral Narrowing of a Varactor-Integrated Resonant-Tunneling-Diode Terahertz Oscillator by Phase-Locked Loop

Spectral narrowing of a resonant-tunneling-diode (RTD) terahertz oscillator, which is useful for various applications of terahertz frequency range, such as an accurate gas spectroscopy, a frequency reference in various communication systems, etc., was achieved with a phase-locked loop system. The oscillator is composed of an RTD, a slot antenna, and a varactor diode for electrical frequency tuning. The output of the RTD oscillating at 610 GHz was down-converted to 400 MHz by a heterodyne detection. The phase noise was transformed to amplitude noise by a balanced mixer and fed back into the varactor diode. The loop filter for a stable operation is discussed. The spectral linewidth of 18.6 MHz in free-running operation was reduced to less than 1 Hz by the feedback.     

Nano-wear mechanism of amorphous carbon thin films

Tribological performance of diamond-like carbon (DLC) overcoat on a magnetic hard disk was evaluated using a contact start stop wear tester. The analysis of worn surfaces suggests that wear of the carbon overcoat took place by a delamination type of wear mechanism at a nanoscale, resulting in the formation of wear particles of about 1.5 nm thick and 30–90 nm wide. This revised version was published online in July 2006 with corrections to the Cover Date.     

Green synthesis of LiZnVO4 nanoparticles and its multiple applications towards electrochemical sensor,supercapacitor, humidity sensing,photoluminescence and antioxidant activities

LiZnVO₄ nanoparticles (NPs) were synthesized by a simple combustion method using Hibiscus Rosa Sinensis leaves as a novel fuel and the prepared NPs were characterized using XRD, FT-IR, morphological analysis by SEM and TEM studies, elemental analysis by EDAX and ICP-MS. XRD data of the synthesized NPs were well-matched with the JCPDS number 038–1332 and it confirms the distorted phenacite structure of LiZnVO₄. FT-IR strengthens the bonding of M-M and M–O in LiZnVO₄. Optical characteristics of LiZnVO₄ NPs were studied by photoluminescence (PL) spectroscopy. Vanadate group of the prepared NPs originates a green emission. Examination of latent finger prints (LFP’s) showed a crystal clear patterns under near UV region (365 nm) as they are the prominent techniques in crime investigations. LiZnVO₄ NPs exhibit a strong antioxidant property and act as a good sensor to detect sodium nitrite analyte at extremely low concentrations with limit of detection of 27.5 nM. Three-electrode system supercapacitor device has been fabricated and examined the performances. Specific capacitance of LiZnVO₄ NPs based supercapacitor was found to be 88.7 F/g at a current density of 0.1 mA. Power density (P_d) and energy density (E_d) were found to be 0.51 W/g and 12.3 Wh/Kg, respectively. This device exhibits a stable CV curves up to the scan rate of 10 V/s. Furthermore, LiZnVO₄ NPs acts as an excellent material towards the humidity sensing with a sensitivity factor, sensitivity and limit of detection of 28.0, 0.3 MΩ/%RH and 5%RH, respectively. All the above studies show the diverse potentiality of LiZnVO₄ NPs.

     

Low-concentration ammonia gas sensing using polyaniline nanofiber thin film grown by rapid polymerization technique

Journal of Materials Science: Materials in Electronics - A thin film of polyaniline (PANI) nanofiber was synthesized by a simple and inexpensive rapid chemical polymerization technique on glass...     

Oxide-based inorganic/organic and nanoporous spherical particles: synthesis and functional properties

Abstract

This paper reviews the recent progress in the preparation of oxide-based and heteroatom-doped particles. Surfactant-templated oxide particles, e.g. silica and titania, are possible candidates for various potential applications such as adsorbents, photocatalysts, and optoelectronic and biological materials. We highlight nanoporous oxides of one element, such as silicon or titanium, and those containing multiple elements, which exhibit properties that are not achieved with individual components. Although the multicomponent nanoporous oxides possess a number of attractive functions, the origin of their properties is hard to determine due to compositional/structural complexity. Particles with a well-defined size and shape are keys for a quantitative and detailed discussion on the unique complex properties of the particles. From this viewpoint, we review the synthesis techniques of the oxide particles, which are functionalized with organic molecules or doped with heteroatoms, the physicochemical properties of the particles and the possibilities for their photofunctional applications as complex systems.