Flame propagation in a gasification channel

In the present study, propagation of a gasification flame through a coal channel is considered. A simplified physical model incorporating all of the main physical factors determining the flame front propagation in a gasification reactor is suggested. It is demonstrated that the flame propagation is governed by the energy balance in the channel. The suggested model is in an agreement with experimental observations obtained in underground gasification of coal (UCG).     

FDTD modeling of scatterers in stratified media

The FDTD technique is well suited for calculating the fields scattered by buried objects when the sources are close enough to the air/ground interface so that they can be incorporated into the solution space. Difficulties arise, however, when the sources are far from the interface since the total fields in the solution space are not all outgoing waves. Using well-known formulas for the fields transmitted and reflected by stratified media, this paper discusses a method whereby the fields scattered by a buried object can be easily calculated by the FDTD technique when the incident field is a plane wave     

Heat and mass transfer in wood during dryingTransfert de chaleur et de masse pendant le sechage du boisWärme- und stoffübertragung bei der trocknung von holzTeплo- и мaccoпepeнoc пpи cyшкe дpeвecины

A model for heat and mass transport in softwood is developed. The model includes liquid transport via capillary action as well as diffusion. The model is unique in that transport properties which in some cases are both not available in the literature and difficult to measure are developed from knowledge of wood structure. Calculated results compared favorably with those determined experimentally. The experimental results represent the first of their kind in that moisture profiles are measured during the drying process using gamma attenuation.     

A study of S-doped TiO<Subscript>2</Subscript> for photoelectrochemical hydrogen generation from water

Sulfur-doped titanium dioxide (TiO₂) was investigated as a potential catalyst for photoelectrochemical hydrogen generation. Three preparation techniques were used: first ballmilling sulfur powder with Degussa P25 powder (P25), second, ball milling thiourea with P25, and third a sol–gel technique involving titanium (IV) butoxide and thiourea. The resulting powders were heat-treated and thin-film electrodes were prepared. In all three cases, the heat-treated powders contained small amounts of S (1–3%). However, Rietveld analysis on X-ray diffraction (XRD) measurements revealed no significant changes in lattice parameters. For the samples prepared using thiourea, X-ray photoelectron spectroscopy (XPS) measurements indicated the presence of N and C in the heat-treated powders in addition to S. In all cases, visible-ultraviolet spectroscopy performed on bulk powders confirmed the extension of absorption into the visible region. However, the same spectroscopic technique performed on thin-film electrodes (∼0.5 μm) suggests that the absorption coefficients were very small in the visible region (≤10⁴ m⁻¹). The first and third methods yielded powders with substantially smaller photocatalytic activity relative to P25 powder in the UV region. The electrodes prepared from powders obtained using the second method yielded photocurrents comparable to those prepared from P25 powder.     

DRYING OF POROUS MATERIALS AT LOW MOISTURE CONTENT

ABSTRACT

Drying experiments were conducted using packed beds of glass beads with initial moisture content near or slightly above the irreducible moisture content. The objective was to validate the vapor phase diffusion coefficient determined in earlier experiments and to quantify the effect of temperature gradient on vapor phase diffusion in the presence of irreducible saturation. The resulls indicate that for isothermal drying the enhancement factor, β, which is the ratio of the diffusion coefficient in the packed bed to that in free space, is slightly less than unity. This is consistent with previous results. However, the results for non-isothermal drying show little effect of temperature gradient for temperature gradients either assisting the concentration gradient or opposing the concentration gradient. This is contrary to the traditional thinking about enhanced vapor diffusion originally proposed by Philip and deVries (1957).     

The Use of HPLC-Derived Phenolic Profiles as a Means of ClassifyingSesbaniaAccessions

Aqueous acetone extracts of mature leaves from 10 accessions of two species of Sesbania plants were prepared and analysed by high-performance liquid chromatography (HPLC). The HPLC phenolic profiles were used to develop a classification rule to distinguish between accessions. Out of the 44 mature leaf samples analysed, 27 had distinctive HPLC phenolic profiles and were successfully assigned to the correct accession. Seedlings of these accessions could be classified to the correct species after 3 months' growth. After 3 months' growth, 8 out of 15 samples could be assigned to the correct accession and, at 6 months, 7 out of 20. However, when accessions with very similar phenolic profiles were grouped together, there was a 100% success rate for classifying the correct accession at 3 months and 80% success rate at 6 months. It was concluded that the method could distinguish between some accessions, or groups of accessions, of Sesbania after 3 months' growth. HPLC phenolic profiling is potentially a relatively rapid, but not uniformly reliable, method for classifying Sesbania accessions.     

Long-term comparisons between two-way satellite and geodetic time transfer systems

Global Positioning System (GPS) observations recorded in the United States and Europe were used to evaluate time transfer capabilities of GETT (geodetic time transfer). Timing estimates were compared with two-way satellite time and frequency transfer (TWSTFT) systems. A comparison of calibrated links at the U.S. Naval Observatory, Washington, D.C., and Colorado Springs, CO, yielded agreement of 2.17 ns over 6 months with a standard deviation of 0.73 ns. An uncalibrated link between the National Institute of Standards and Technology (NIST) and Physikalisch-Technische Bundesanstalt, Braunschweig, Germany, has a standard deviation of 0.79 ns over the same time period.     

Absolute calibration of a geodetic time transfer system

An absolute calibration technique is developed for geodetic Global Positioning System (GPS) receivers. An uncertainty budget for the system (receiver, cables, connectors, antenna) is evaluated, yielding 1.1 ns at each frequency, and 1.6 ns for a two-receiver experiment. Analysis of data on a short baseline yields 0.8 and 1.2 ns agreement on P1 and P2, respectively.     

Optical feedback-induced noise in pigtailed laser diode modules

The sensitivity of commercially available pigtailed laser diode modules to optical feedback, in terms of laser relative intensity noise, is investigated. A pigtailed laser diode model which is based on multimode rate equations, Langevin operators, and optical feedback terms in used to predict that operation in the coherence collapse region can be avoided in high-speed, short-haul, optical data links by trading off optical launch power into the pigtail with decreased laser/fiber coupling efficiency. Experimental results for three pigtailed laser diode modules indicate that with a laser/fiber coupling efficiency of 4%, an external feedback level of between -15 and -17 dB can be tolerated before the laser enters the coherence collapse region. Good correlation between these results and predictions from the numerical model is obtained.<>