An analysis of the crystallization behavior of poly(ethylene oxide)/poly(methyl methacrylate) blends by spectroscopic and calorimetric techniques

Infrared spectra in conjunction with calorimetric measurements have been used to follow the crystallization process and microstructural changes of poly(ethylene oxide) (PEO) in poly(ethylene oxide) and poly(methyl methacrylate) (PMMA) blends. We have given particular attention to compositions containing low PEO concentrations. The crystallization behavior and the resultant microstructures of PEO are strongly perturbed by the presence of PMMA. In addition, we found phase separation and trans sequences of PEO to be present, especially at low PEO concentrations.     

Fast Stimulation of Millimeter Wave Waveguide Filters by Boundary Marching Method

The boundary marching method is applied for the analysis of the waveguide bandpass filers. The vector finite element method with the perfectly matched layers (PML) as the matching load is given for parameter extraction of millimeter wave filters. The implementation of the fast boundary marching method is described in detail. The reflection and insertion losses of millimeter wave filters are obtained and compared with those obtained from literature.     

Use of V/III ratio to produce heterostructures in ordered GaInP

Compositional ordering in Ga_0.52 In_0.48 P results in a significant reduction in bandgap energy. The degree of order is known to be a strong function of the input partial pressure of the P precursor during growth due to the effect of this parameter on the surface reconstruction. This raises the possibility of producing heterostructures by simply changing the flow rate of the P precursor during growth. The change in bandgap energy at order/disorder (O/D) heterostructures formed by decreasing the P partial pressure during the OMVPE growth cycle is graded over several thousands of Å when PH₃ is used as the P precursor. Examination of the transmission electron microscope image and the photoluminescence (PL) spectrum reveals that the ordered structure in the lower layer persists far into the upper layer. Similarly, disorder/order (D/O) structures produced in this way yield PL spectra indicative of graded composition at the heterostructure when the P precursor is PH₃. The abruptness is not affected by interruptions in the growth cycle for as long as one hour. Similar heterostructures produced using tertiarybutylphosphine (TBP) as the P precursor are distinctly different. Both D/O and O/D heterostructures can be produced by abruptly increasing the TBP flow rate during the growth cycle. PL studies show two distinct peaks closely corresponding to those observed for single layers grown using these conditions. Surface photoabsorption spectroscopy was used to monitor the transition in surface reconstruction. The change was found to be limited by the dynamics of the mass flow controller. The only difference detected which might explain the difference in behavior between PH₃ and TBP is that atomic force microscopy scans show the layers grown using TBP are covered by monolayer and bilayer (6 Å in height) steps. Growth under similar conditions using PH₃ produces bunched steps, much larger than 6 Å in height.     

Flexibility in the choice of Green's function for the boundaryelement method

Several useful Green's functions are derived for the quasi-static analysis of shielded planar transmission lines by the boundary element method. These newly employed Green's functions satisfy forced boundary conditions in a rectangular region. The integral equation does not have a singular point and the integrand contains only the normal derivative of the electric potential. The present method is proposed to characterize multilayered and multi-conductor structures. Numerical results are presented for a microstrip, a suspended line, and a coplanar waveguide. For the coplanar waveguide, a combined Green's function is also studied. This combined Green's function further reduces the memory size in computation. All of these Green's functions are represented in infinite series. The resulting matrix equation has slowly convergent matrix elements. To reduce the computation time of matrix elements, we split the original series in two parts. The geometric series method is employed to convert one part into a fast convergent form (4 terms). For the other part, only a few terms (less than 20) require computation     

Synthesis and Crystal Structure of CpFe(CO)l(η1-Ph2PCH2P(O)Ph2)

CpFe(CO)I(η¹-Ph₂PCH₂P(O)Ph₂) 2 was obtained in small yield from reaction of [CpFe(CO)]₂[μ-(Ph₂P)₂CH₂] with diiodine in benzene, or prepared in 82% yield on treating CpFe(CO)I(η¹-Ph₂PCH₂PPh₂) 1 with H₂O₂. Compound 2 crystallizes in the space group P2₁/n, with a = 8.441(2) Å, b = 10.054(2) Å, c = 33.343(8) Å, β = 92.33(2)°, Z = 4, V = 2827(1) ų, R_F = 0.057, and R_w = 0.056.     

Nitride-based flip-chip LEDs with transparent Ohmic contacts and reflective mirrors

Nitride-based flip-chip light-emitting diodes (LEDs) with various transparent ohmic contacts and reflective mirrors were fabricated. At 470 nm, it was found that Ni could provide 92% transmittance while Ag could provide 92.4% reflectively. It was also found that the 20-mA forward voltages measured from LEDs with Ni+Ag, Ni+Al, and Ni+Pt were 3.15, 3.29, and 3.18 V while the output powers were 16, 13.3, and 11.6 mW, respectively. Furthermore, it was found that lifetimes of the fabricated flip-chip LEDs were good.     

CPW-fed folded-slot antenna for 5.8 GHz RFID tags

A coplanar waveguide (CPW)-fed capacitive folded-slot antenna is proposed for the radio frequency identification (RFID) application at 5.8 GHz. The antenna is fabricated on a 30/spl times/30 mm substrate. The measured bandwidth and antenna gain are 7.5% and 4.2 dBi, respectively. Radiation patterns are almost omnidirectional in the H-plane. These properties and the compact and uniplanar structure make the antennas suitable for use as RFID tags.     

Can quarks always be confined by a linear potential?

It is demonstrated on the basis of the Dirac equation that quarks cannot be confined by a vector gluon potential of the form(r/r ₀)^a or[ln(r/r ₀]^a, a>0, if the quark-gluon interaction conserves parity. In order to confine quarks with the parity-conserving interaction, the effective gluon potential must be a pseudovector or a scalar. These are shown in a simple Yang-Mills field with theSU(2) group.     

Optical absorption of perdeuterated PMMA and influence of water

The optical absorption coefficient of perdeuterated poly(methyl methacrylate) has been obtained by laser calorimetry at 568.2, 647.1, 676.4, and 752.5 nm. The lowest value of 18 dB/km is obtained at 647.1 nm. The dramatic effect of water uptake by the polymer on the total optical attenuation spectrum in the wavelength range 500–1000 nm has been investigated.