Stable phase-modulated fiber-optic sensors for senior electricalengineering laboratory curricula

A set of fiber-optic sensing experiments that can be performed by senior undergraduates in a fiber optics laboratory is presented. The experiments are based on two stable phase-modulated sensors: a miniaturized Michelson-type fiber-optic interferometer that is relatively insensitive to temperature drifts; and a two-mode fiber used in a differential interferometric sensing scheme. Methods of construction are described, and several possible experiments are presented. These experiments introduce or strengthen the ideas of interference, elliptical-core fibers, and electromagnetic field propagation in fibers     

Apportionment of primary and secondary organic aerosols in southern California during the 2005 study of organic aerosols in riverside (SOAR-1)

Ambient sampling was conducted in Riverside, California during the 2005 Study of Organic Aerosols in Riverside to characterize the composition and sources of organic aerosol using a variety of state-of-the-art instrumentation and source apportionmenttechniques. The secondary organic aerosol (SOA) mass is estimated by elemental carbon and carbon monoxide tracer methods, water soluble organic carbon content, chemical mass balance of organic molecular markers, and positive matrix factorization of high-resolution aerosol mass spectrometer data. Estimates obtained from each ofthese methods indicate that the organic fraction in ambient aerosol is overwhelmingly secondary in nature during a period of several weeks with moderate ozone concentrations and that SOA is the single largest component of PM1 aerosol in Riverside. Average SOA/OA contributions of 70-90% were observed during midday periods, whereas minimum SOA contributions of approximately 45% were observed during peak morning traffic periods. These results are contraryto previous estimates of SOAthroughout the Los Angeles Basin which reported that, other than during severe photochemical smog episodes, SOA was lower than primary OA. Possible reasons for these differences are discussed.     

A compartmental model to analyze ruminal digestion

In contrast to digestion models that include a discrete lag phase, a compartmental digestion model was proposed. It assumed the existence of a lag compartment and a digestion compartment. Substrate present in the digestion compartment was subject to first-order kinetics digestion. Flow of substrate from the lag compartment to the digestion compartment was proposed to be a first-order process and likely was affected by hydration of substrate, bacterial attachment, and colonization. The proposed model was compared with models that assumed the existence of a discrete lag phase. Parameter estimates for these models were obtained either through logarithmic transformation of data or nonlinear regression. Statistically, there was no difference between the compartmental model and the nonlinear model with a discrete lag phase. Differences in parameter estimates between these two models were small. Residual mean squares were higher for the logarithmically transformed models. Differences in parameter estimates between these models and the compartmental model depended on the structure of the experimental data. In a number of cases, the nonlinear parameters of the compartmental model converged to the same value, resulting in a different interpretation of the model. Residual mean squares for predicting rate of disappearance were lowest for the compartmental model.     

Effect of microstructure and temperature on the erosion rates and mechanisms of modified EB PVD TBCs

Thermal barrier coatings (TBCs) have now been used in gas turbine engines for a number of decades and are now considered to be an accepted technology. As there is a constant drive to increase the turbine entry temperature, in order to increase engine efficiency, the coatings operate in increasingly hostile environments. Thus there is a constant drive to both increase the temperature capabilities of TBCs while at the same time reducing their thermal conductivities. The thermal conductivity of standard 7 wt% yttria stabilized zirconia (7YSZ) electron beam (EB) physical vapour deposited (PVD) TBCs can be reduced in two ways: the first by modification of the microstructure of the TBC and the second by addition of ternary oxides. By modifying the microstructure of the TBC such that there are more fine pores, more photon scattering centres are introduced into the coatings, which reduce the heat transfer by radiation. While ternary oxides will introduce lattice defects into the coating, which increases the phonon scattering, thus reducing the thermal conductivity via lattice vibrations. Unfortunately, both of these methods can have a negative effect on the erosion resistance of EB PVD TBCs.This paper compares the relative erosion rates of ten different EB PVD TBCs tested at 90° impact at room temperature and at high temperature and discusses the results in term of microstructural and temperature effects. It was found that by modifying the coating deposition, such that a low density coating with a highly ‘feathered’ microstructure formed, generally resulted in an increase in the erosion rate at room temperature. When there was a significant change between the room temperature and the high temperature erosion mechanism it was accompanied by a significant decrease in the erosion rate, while additions of dopents was found to significantly increase the erosion rate at room and high temperature. However, all the modified coatings still had a lower erosion rate than a plasma sprayed coatings. So, although, relative to a standard 7YSZ coating, the modified coatings have a lower erosion resistance, they still perform better than PS TBCs and their lower thermal conductivities could make them viable alternatives to 7YSZ for use in gas turbine engines.     

Physical and mechanical properties of flame retardant urea formaldehyde medium density fiberboard

Medium density fiberboard (MDF) is one of the widely used wood-based panels to manufacture building components such as furniture units for interior applications. Although MDF is an excellent product it is prone to fire hazard which should be enhanced using flame retardants during its manufacture. Properties of the flame retardant urea formaldehyde (UF) MDF made using a dry process from rubberwood fibers were investigated. Flame retardant chemicals that were evaluated include sodium aluminate, zinc borate and aluminum trihydrate, which were incorporated with rubberwood fibers to manufacture experimental MDF. Four concentration levels, 10%, 15%, 20% and 30% of fire retardants and 15% urea formaldehyde resin based on oven dry fiber weight were used to manufacture experimental panels. Physical and mechanical properties including thickness swelling, water absorption, bending characteristics, and internal bond strength of the samples were determined. Flame retardant properties of the panels were also investigated using a Cabinet Method along with char index, weight loss and size of ellipse area. Finally, thermogravimetry method was employed to analyze thermal properties of the MDF panels. The results showed that thickness swell and water absorption decreased as the flame retardant increased. The MOR was not affected by the flame retardant treatment for boards bonded with urea formaldehyde resin. The internal bond strength showed a small reduction compared with the controls as the flame retardant chemicals increased but not for boards treated with 5% aluminum trihydrate. When the concentration of flame retardant chemicals increased to 30%, the internal bond generally decreased. Char index, area of ellipse and weight loss reduced as the percentage of flame retardant increased. Sodium aluminate showed the best performance in reducing thermal degradation followed by aluminum trihydrate and zinc borate. Aluminum trihydrate cured closely resemble that of the control during the gelation test.     

Determinants of temperature in small coastal embayments of Lake Ontario

Along 25 km of the Lake Ontario shoreline near Toronto, Ontario, small coastal embayments (0.4–32 ha) have been constructed or modified by lake-infilling to restore warmwater fish habitat. The variation in thermal habitat quality for warmwater fishes among these embayments is very high; temperatures range from those found within a small pond to those of much cooler Lake Ontario. Since meteorological conditions and surface heat fluxes are almost identical, the temperature variation among embayments must be caused by differences in bathymetry or exchange with Lake Ontario. However, a previous study on these embayments found paradoxically that temperatures were not strongly associated with channel size or embayment bathymetry. This paper resolves the paradox by showing that flushing times for almost all of the constructed embayments were less than 1 day, and often less than 12 h. With so little time to warm within the embayments, water temperatures of almost all embayments remained very close to the temperatures of the adjacent lake waters. The coldest embayments connected directly to open Lake Ontario and warmer embayments connected to Lake Ontario through other embayments or protected harbors, where the inflowing water from Lake Ontario had already substantially warmed. To allow embayments along the exposed shoreline of Toronto to reach acceptable temperatures for warmwater fish, we use heat budgets to calculate that average summer flushing times must be increased from their current length of 1.5 to 5.5 h to approximately 30 h. Such changes could be achieved through large reductions in the channel cross section.     

Thermal decomposition behavior of poly[3,3-bis(ethoxymethyl) oxetane] and related polyethers

The thermal decomposition behavior of poly[3,3-bis(ethoxymethyl)oxetane] (polyBEMO) was examined and compared to the decomposition of poly(ethylene oxide) (PEO) and poly(tetramethylene oxide) (polyTHF). Differential scanning calorimetric (DSC) studies as a function of heating rates and at constant temperature as a function of time yielded activation energies of 45–50 kcal/mol, characteristic of polyether decomposition. First-order decomposition kinetics were found. The reaction is endothermic, with a heat of decomposition of 18.6 kcal/mol. Effusion mass spectroscopy on polyBEMO showed major peaks at 112, 140, 168, and 174 amu. A mechanism is proposed in which the thermal scission of the ether bonds in both the polymer chain and in the appendanges initiates the decomposition. The main decomposition reaction for polyBEMO can be written as where the appendages and main chain are cleaved in an unknown order.     

Temperature-sensitive mutants of influenza A virus. XIV. Production and evaluation of influenza A/Georgia/74-ts-1[E] recombinant viruses in human adults

The two temperature-sensitive (ts) lesions present in influenza A/Hong Kong/68-ts-1[E] (H3N2 68) virus were transferred via genetic reassortment to influenza A/Georgia/74 (H3N2 74) wild-type virus. A recombinant clone possessing both ts lesions and the shutoff temperature of 38 C of the Hong Kong/68 ts donor and the two surface antigens of the Georgia/74 wild-type virus was administered to 32 seronegative adult volunteers. Thirty-one volunteers were infected, of whom only five experienced mild afebrile upper respiratory tract illness. The wild-type recipient virus was a cloned population that induced illness in five of six infected volunteers. Therfore, the attenuation exhibited by the Georgia/74-ts-1[E] virus could reasonably be assumed to be due to the acquisition of the two ts-1[E] lesions by the Georgia/74 wild-type virus. The serum and nasal wash antibody responses of the ts-1[E] vaccinees were equivalent to those of the volunteers who received wild-type virus. The two ts lesions present in the Hong Kong/68-ts-1[E] virus have now been transferred three times to a wild-type virus bearing a new hemagglutinin, and in each instance the new ts recombination exhibited a similar, satisfactory level of attenuation and antigenicity for adults. It seems likely that the transfer of the ts-1[E] lesions to any new influenza virus will regularly result in attenuation of a recombinat virus possessing the new surface antigens.