On the qualitative behaviors of solutions of third order nonlinear differential equations

We present some new results about oscillation and asymptotic behavior of solutions of third order nonlinear differential equations of the form

(r₂(t)(r₁(t)y^′)^′)^′+p(t)y^′+q(t)f(y(g(t)))=0.     

Optical and structural properties of MOVPE grown GaxIn1−xAs/InP strained multiple quantum well atructures

This paper presents a study of the structural and optical properties of strained GaInAs/ InP multiple quantum well (MQW) structures fabricated by LP-MOVPE. The composition of the Ga _x In_1−x As films ranged fromx = 0.17 tox = 1.0 and was determined by sputtered neutral mass spectrometry (SNMS) on thick layers. The structures of the MQW samples with well widths from 1.5 to 5 nm were investigated by high resolution x-ray diffraction (HR-XRD). Simulations of the diffraction patterns showed that transition layers of approximately 2 monolayer (ML) thickness with high lattice mismatch exist at the interfaces. Photoluminescence (PL) measurements indicate well widths of a multiple of a monolayer with local variations of one monolayer. The PL peak energies vary smoothly with the Ga concentration. These results were confirmed by optical absorption measurements.     

Electromigration-induced damage in bamboo Al interconnects

Depletion and hillock formation were examined in-situ in a scanning electron microscope (SEM) during electromigration of bamboo Al interconnect segments. Hillocks formed directly at the anode ends of the segments by epitaxial addition of Al at the bottom Al/TiN interface. Depletion occurred nonuniformly from the cathode end and stopped once the distance between the leading void and the hillock reached the critical length for electromigration at the given current density. A modified equation for the drift velocity is proposed, which includes the effect of nonuniform depletion and predicts that interconnects with nonuniform depletion are more reliable than those with uniform depletion.     

Dual-Antenna RF CMOS Front-End for Interferer Removal in Ultra-Wideband Systems

Many ultra-wideband (UWB) systems are challenged by strong jammers and narrowband interferers. Using two antennas, we demonstrate a robust UWB radio frequency (RF) front-end design in a 0.25 μm mixed-signal complementary metal oxide semiconductor (CMOS) technology. The proposed realization is capable of adaptively removing a high-power, narrowband interferer early in the receiver chain avoiding front-end saturation and preserving UWB signal power. The early interferer removal resulting in interferer-free demodulation is based on the least mean squares (LMS) algorithm and achieved through a novel combiner low-noise amplifier and noise optimized filtering. Circuit level RF simulations of the proposed circuitry indicate a maximum improvement in signal-to-interference ratio of 39.6 dB.     

Intentional ρ-type doping by carbon in metalorganic MBE of GaAs

We report on the intentional ρ-type doping of GaAs layers grown in an UHV system from molecular beams of arsine (AsH₃) and mixtures of frimethyl gallium (TMG) and friethyl gallium (TEG). The entire doping range between 10¹⁴ cm^-3 (growth from pure TEG) and 10²⁰ cm^-3 (growth from pure TMG) can be covered by using mixtures of TMG and TEG. As revealed by SIMS and photoluminescence (PL) carbon is the dominant acceptor in the layers. Comparison of the Hall mobility and of the PL spectra shows that the quality of our films equals that of the best LPE and MBE grown ρ-type GaAs layers.     

Simultaneous growth of self-patterned carbon nanotube forests with dual height scales

In this study, we report on a unique, one-step fabrication technique enabling the simultaneous synthesis of vertically aligned multi-walled carbon nanotubes (VA-MWCNTs) with dual height scales through alcohol catalyzed chemical vapor deposition (ACCVD). Regions of VA-MWCNTs with different heights were well separated from each other leading to a self-patterning on the surface. We devised a unique layer-by-layer process for application of catalyst and inhibitor precursors on oxidized Si (100) surfaces before the ACCVD step to achieve a hierarchical arrangement. Patterning could be controlled by adjusting the molarity and application sequence of precursors. Contact angle measurements on these self-patterned surfaces indicated that manipulation of these hierarchical arrays resulted in a wide range of hydrophobic behavior changing from that of a sticky rose petal to a lotus leaf.     

DEVELOPMENT OF SYNERGISTIC HEAT STABILIZERS FOR PVC FROM ZINC BORATE-ZINC PHOSPHATE

The importance of flame-retardant and smoke-suppressed poly(vinyl chloride) (PVC) compositions is increasing gradually in the polymer industry since PVC releases smoke and toxic gases (hydrogen chloride, HCl) during heating at temperatures above 140°C with the result of dehydrochlorination reaction. In this study, the synergistic effects of zinc borate (ZB)-zinc phosphate (ZP) on the thermal stability of PVC were investigated using thermal techniques. The induction and stability time values of PVC plastigels were obtained at 140° and 160°C. The results revealed that PVC plastigels having only ZP and ZB retarded dehydrochlorination of PVC compared with the unstabilized sample. However, the plastigels with both ZB and ZP had a superior synergistic effect on char formation of PVC. Since the induction periods of the samples having both ZB and ZP were higher than those of the unstabilized samples having only ZB or only ZP, the synergistic effect was observed.     

Packet Reservation Window Multiple Access for Microcellular Voice/Data Transmission

We propose a new packet reservation multiple access (PRMA) scheme for the joint transmission of voice and data traffics in a microcellular medium. The collision resolution protocol within the system is based on a modification of the window random access algorithm, which has superior properties compared to the conventional slotted Aloha. The proposed algorithm, which we call packet reservation window multiple access (PRWMA), works in distinct modes for voice and data without prioritization, and the user performs slightly different operations depending on the information type. Simulation results show that PRWMA outperforms PRMA by a significant margin in terms of voice user capacity.