Investigation of chemometric calibration performance based on different chemical matrix and signal-to-noise ratio.

The chemometric calibration performance was systematically investigated by two parameters (changing the chemical matrix as well as the signal-to-noise ratio) of the NIR (near-infrared) spectrum. Three different analytes (hexane, cyclohexane, toluene) were selected and heptane was used as a solvent. The degree of spectral difference significantly affected the calibration performance. The largest structural difference between the analyte and the solvent provided the best calibration result for a given signal-to-noise ratio. Additionally, the signal-to-noise ratio of the spectra also directly influenced the calibration performance. Overall, the spectral difference and signal-to-noise ratio were the major factors for governing the chemometric calibration performance, especially in the low-concentration range.     

Independence and graph homomorphisms graph homomorphisms

A graph with n vertices that contains no triangle and no 5-cycle and minimum degree exceeding n/4 contains an independent set with at least (3n)/7 vertices. This is best possible. The proof proceeds by producing a homomorphism to the 7-cycle and invoking the No Homomorphism Lemma. For k ≥ 4, a graph with n vertices, odd girth 2k+1, and minimum degree exceeding n/(k+1) contains an independent set with at least kn/(2k+1) vertices; however, we suspect this is not best possible. © 1993 John Wiley & Sons, Inc.     

Low-order modeling and dynamic characterization of rapid thermal processing

A low-order model of rapid thermal processing (RTP) of semiconductor wafers is derived. The first-principles nonlinear model describes the static and dynamic thermal behavior of a wafer with approximate spatial temperature uniformity undergoing rapid heating and cooling in a multilamp RTP chamber. The model is verified experimentally for a range of operating temperatures from 400° C to 900° C and pressures of 1 Torr and 1 atmosphere in an inert N₂ environment. Theoretical predictions suggest model validity over a still wider range of operating conditions. One advantage of the low-order model over previous high-order and statistical models is that the proposed model contains a small number of fundamental parameters and functions that, if necessary, are easily identifiable. Furthermore, because of reduced computational complexity, the low-order model can be used in real-time predictive applications including signal processing and process control design. In studying and verifying the model, the dynamic behavior of a semiconductor wafer undergoing rapid temperature changes is characterized. Close comparison between theory and experiment in terms of the wafer eigenvalue and dc gain is demonstrated; the strong nonlinear effects of temperature are shown. Convective heat transfer losses are also examined and are shown to increase with radial position on the wafer.     

Irradiation-induced reduction and luminescence properties of Sm doped in BaBPO5

Usually, Sm²⁺ ions could be reduced by heating the materials in reducing atmospheres. Exposure to ionizing radiations is also known to cause Sm³⁺→Sm²⁺ conversion. In this work, BaBPO₅ doped with the samarium ion was prepared by high temperature solid-state reaction. Sm²⁺ ions were obtained by two different reduction methods, i.e., heating in H₂ reduced atmosphere and X-ray irradiation. The measurements of X-ray diffraction (XRD), and scanning electron microscope (SEM) were investigated. It is found that the conversion of Sm³⁺→Sm²⁺ is very efficient in BaBPO₅ hosts after X-ray irradiation. Sm²⁺ ions under these two reduction methods exhibit different characteristics that were studied by measurements of luminescence and decay. The results showed that the luminescence properties of Sm²⁺ ions in BaBPO₅ were highly dependent on the sample preparation conditions.     

Palladium-catalyzed C-N bond formation: synthesis of 1-aryl-1H-pyrazoles from β-bromovinyl aldehydes and arylhydrazines

Cyclic and acyclic β-bromovinyl aldehydes are cyclized with an array of arylhydrazines in toluene at 125 °C in the presence of a palladium catalyst and a phosphorus chelating ligand together with NaO^tBu to give 1-aryl-1H-pyrazoles in moderate to good yields.     

Local chemical distribution and electronic structure of Ge1−xTx DMS single crystals (T=Cr,Mn, Fe)

The spatial concentration distribution and local electronic structure of ferromagnetic Ge_1−xT_x (T=Cr, Mn, Fe) DMS single crystals have been investigated by using scanning photoelectron microscopy (SPEM), X-ray absorption spectroscopy (XAS), and photoemission spectroscopy (PES). It is found that doped T ions in Ge_1−xT_x crystals are chemically phase-separated, suggesting that the observed ferromagnetism arises from the phase-separated T-rich phases in Ge_1−xT_x.     

Thermal properties of poly(styrene) containing brominated aryl phosphate additives

General purpose poly(styrene) is a large volume commodity polymer widely used in a range of applications. For many of these the presence of an additive to impart some flammability resistance is required. Most commonly, brominated aromatics are used for this purpose. As the polymer undergoes combustion these compounds decompose to generate bromine atoms and/or hydrogen bromide which escape to the gas phase and trap flame propagating radicals. While these species are effective in inhibiting flame propagation they present the opportunity for loss of halogen to the atmosphere. For this reason, the use of these compounds is being limited in some parts of the world. Phosphorus compounds, on the other had, impart a flame retarding influence by promoting char formation at the surface of the burning polymer. This prevents heat feedback to the polymer and consequent pyrolysis to generate fuel fragments. The combination of both bromine and phosphorus present in a single compound might generate a superior flame-retarding additive in that both modes of retardancy might be promoted simultaneously. Should this be the case smaller amounts of additive might be necessary to achieve a satisfactory level of flame retardancy. A series of such additives, brominated aryl phosphates, has been synthesized and fully characterized spectroscopically. Blends of these additives, at various levels, with poly(styrene) have been examined by DSC, TG and in the UL-94 flame test. The flammability of the polymer is dramatically diminished by the presence of the additive.     

Structural and electrical characterization of PZT on gold for micromachined piezoelectric membranes

Piezoelectric membranes have been fabricated that incorporate a gold bottom electrode with an adhesion layer of titanium–tungsten (10:90 wt. %). For solution-deposited acetic acid based lead zirconate titanate (HoAc-PZT) with a Zr:Ti ratio of 40:60, the film’s average piezoelectric coefficient, e₃₁, is -5.31 C/m², with a dielectric constant of 814 at 200 Hz, which is similar to values for platinum bottom electrodes. The PZT structure remains columnar on both types of bottom electrodes. Initial fabrication attempts resulted in cracking that initiated in the PZT layer of the structure. X-ray photoelectron spectroscopy was utilized to establish how processing affects diffusion throughout the composite membrane structure. Crack-free membranes were fabricated and tested. This paper discusses the performance properties and piezoelectric fatigue results for these membranes. PACS 77.84.-s; 77.84.Lf     

Conversion estimates for gas-solid reactions: Improved estimates for irreversible systems

Solid conversion has been of much interest to research workers and the Cumulative Gas Concentration Method (CGCM) has been developed to provide bounds for the reactant solid in irreversible systems having power-law type kinetics. This CGCM is used in conjunction with the Pseudo-Steady-State (PSS) assumption and these bounds appear to be good under certain conditions and for long times.

In this work, the PSS condition is not assumed when deriving the bounds on the cumulative gas concentration and the effect of the inclusion of the transient part is analysed. A technique, based on an iterative scheme incorporating the CGCM, is developed to provide improved estimates for the reactant solid.