Search

Near-field thermophotovoltaic devices are attractive energy conversion systems. In the present study, three-body near-field thermophotovoltaic systems are designed by introducing an intermediate modulator between thermal emitters and photovoltaic cells. The slab/grating emitter and modulator are made from Ga-doped ZnO, while the slab/grating cell is made from gallium antimonide. The scattering matrix method is used to calculate the radiative exchange between the emitter and the cell. The performances of three-body systems of slab-slab-slab/slab-slab-grating/ grating-grating-grating are investigated. The numerical results show that the output power of the three-slab system is significantly higher than that of the corresponding two-slab system. The output power improvement is attributed to the introduction of the modulator which enables the plasmon polaritons at two GZO surfaces to be coupled. The one-dimensional grating on the surface of the photovoltaic cell can serve as an anti-reflection pattern and improve the conversion efficiency and output power of the three-body system. Grating emitters and modulators can support hyperbolic modes and enhance the radiative heat flux of the whole system. The results prove that the three-body system can provide the possibility to improve the performance of a near-field thermophotovoltaic device.

The paper discusses that IPTV isn't just about delivering digital television over Internet technology; it's about reinventing television to better achieve the goals Sarnoff first articulated decades ago. It's about developing a new medium that's greater than the sum of its parts. It's about creating a video- centric, next-generation Internet accessible on any device, be it mobile phone, computer, or HDTV, at any time and place the consumer chooses. It's about leveraging the Internet's power to better navigate the flood of content flowing our way. And it's about reinventing television advertising from being an unwelcome interruption to being useful, relevant information that can help make our lives more productive and fulfilling.

Toxic Florida red tides of the dinoflagellate Karenia brevis have downstream consequences of 500–1000 km spatial extent. Fish stocks, shellfish beds, and harmful algal blooms of similar species occupy the same continental shelf waters of the southeastern United States, amounting to economic losses of more than 25 million dollars in some years. Under the aegis of the Center for Prediction of Red tides, we are now developing coupled biophysical models of the conditions that lead to red tides and impacted coastal fisheries, from the Florida Panhandle to Cape Hatteras. Here, a nitrogen isotope budget of the coastal food web of the West Florida shelf (WFS) and the downstream South Atlantic Bight (SAB) reaffirms that diazotrophs are the initial nutrient source for onset of red tides and now identifies clupeid fish as the major recycled nutrient source for their maintenance. The recent isotope budget of WFS and SAB coastal waters during 1998–2001 indicates that since prehistoric times of Timacua Indian settlements along the Georgia coast during 1075, ∼50% of the nutrients required for large red tides of >1 μg chl l −1 of K. brevis have been derived from nitrogen-fixers, with the other half from decomposing dead sardines and herrings. During 2001, >90% of the harvest of WFS clupeids was by large ichthyotoxic red tides of >10 μg chl l −1 of K. brevis , rather than by fishermen. After onset of the usual red tides in summer of 2006 and 2007, the simulated subsequent fall exports of Florida red tides in September 2007 to North Carolina shelf waters replicate observations of just ∼1 μg chl l −1 on the WFS that year. In contrast, the earlier red tides of >10 μg chl l −1 left behind off West Florida during 2006, with less physical export, are instead 10-fold larger than those of 2007. Earlier, 55 fish kills were associated with these coastal red tides during September 2006, between Tampa and Naples. Yet, only six fish kills were reported there in September 2007. With little export of red tides and their fish prey during the former year, the computed larger nutrient-sated, fish-fed growth rates of the model’s dinoflagellates also replicate satellite-observed daily increments of K. brevis during fall maintenance in 2006, compared to simulated smaller fish-starved growth rates of decanted red tides during fall 2007. During the last few decades, K. brevis has remained a “prudent predator” of some clupeids, i.e. Spanish sardine, whereas humans have now overfished other Florida stocks of both thread herring and Atlantic shad. Thus, future operational forecasts of the land falls and durations of Florida red tides, from Louisiana to North Carolina, as well as prudent management of regional fisheries of the southeastern United States, require consideration of negelected fish losses, at intermediate trophic levels, to algal predators. Some clupeids are harvested by K. brevis , but these fish are separately supported by a longer parallel diatom-based food chain of calanoid copepods, feeding the zooplanktivores and thence other piscivore fish predators, while intersecting the shorter food chain of just diazotrophs and red tide dinoflagellates, poorly grazed in turn by harpactacoid copepods. The distinct phytoplankton functional groups, different herbivores, as well as zoophagous and piscivore fishes, must all be formulated as explicit state variables of the next set of complex ecological models, cued by satellite data and driven by nested circulation models, within an ecosystem-based management paradigm of commercial and sport harvests of biotic marine resources at higher trophic levels of the WFS and SAB.

The Moderate Resolution Imaging Spectroradiometer (MODIS) semi-analytical (SA) algorithm calculates the spectral absorption properties of surface waters, splitting them into those associated with phytoplankton, aph(λ), colored dissolved organic matter or gelbstoff, ag(λ), and water, aw(λ). The phytoplankton absorption coefficient, aph(675), is then used to derive the concentration of chlorophyll-a, Chlor_a_3. The SA algorithm is designed to respond to variable ratios of aph(λ) to ag(λ) and to wide ranges in the chlorophyll-specific phytoplankton absorption coefficient, a*ph(λ), for a given chlorophyll-a level. In this paper, the SA algorithm is expanded to include environments consistent with strong upwelling zones and high latitudes. Spatial and temporal differences in MODIS Terra chlorophyll-a retrievals are examined between Chlor_a_3 and an empirical algorithm, Chlor_a_2, developed to mimic the performance of the Sea-viewing Wide Field-of-View Sensor (SeaWiFS) OC-4 chlorophyll-a algorithm. The greatest differences observed are for upwelling regions and for southern high-latitude waters during austral spring where Chlor_a_2 values are on average about half of field and Chlor_a_3 values due to lower chlorophyll-specific phytoplankton absorption coefficients typical of this region. Preliminary match-up results indicate strong linearity and good agreement between in situ chlorophyll-a concentrations and MODIS-derived Chlor_a_3 compared to Chlor_a_2.

To improve the microstructure and properties of electron beam welded joints, vacuum or furnace whole post-weld heat-treatment (FWPWHT) should usually be carried out. Electron beam local post-weld heat-treatment (EBLPWHT) is a quite new heat-treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving, and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in the as-welded (AW) and EBLPWHT conditions have been investigated. The results show that the microstructures of different zones of joints in the AW condition are changed by the EBLPWHT procedure, in which the welds from coarse needle martensite are transformed into lath-shaped martensite; and the main structures of the heat-affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of the welded joints can be improved by EBLPWHT in some extent, especially the fracture toughness of the welds, and the fatigue crack resistance of welded joints can be improved significantly. However, more appropriate heat-treatment parameters of EBLPWHT have to be studied in order to improve the mechanical properties of the base metal near to the HAZ.

The purpose of this study is to investigate the effects of the grain boundary misorientation on the radiation-induced segregation (RIS) in 304 stainless steels. There were four test conditions for the specimens: (1) as-received (AR) with enriched Cr at grain boundary, (2) AR + 1 dpa proton irradiation at 450°C, (3) thermally sensitized (SEN), and (4) SEN + 1 dpa proton irradiation at 450°C. The Cr/Ni-concentration profiles were measured by using FEGTEM/EDS and the grain boundary misorientation was determined with the aid of simulated Kikuchi patterns. A delayed Cr depletion compared to no pre-enrichment condition was found at grain boundaries in AR + 1 dpa specimens. The Cr-concentration profile gets narrower and deeper in SEN + 1 dpa specimens. The degree of grain boundary segregation was observed to be higher at random boundaries than special boundaries. The segregation cusps were measured at grain boundaries of Σ 3, Σ 9 and Σ 15 in SEN + 1 dpa 304 stainless steel specimens. From the fitted segregation cusps, it seems that the Cr segregation level at special boundaries in irradiated sensitized 304 stainless steels increases with Σ for values up to Σ =15.

The pervaporation separation of ethylene glycol-water mixtures was carried out over the full range of compositions at temperatures varying from 60 to 80°C, using chemically crosslinked PVA dense membrane which had been developed in our laboratory. A new thermodynamic diffusion coefficient equation is derived based on the modified Vigne equation. Combining Lee-Thodos equations, Wilke-Chang equations, Vrentas-Duda's free volume theory, diffusion equations and swelling equilibrium equations, the permeation fluxes of individual components in ethylene glycol-water mixture through crosslinked poly(vinyl alcohol) (PVA) dense membrane have been calculated and showed to be in agreement with the experimental values.

A composite membrane with a crosslinked PVA dense active layer dip coated on a polyethersulfone support membrane was prepared and evaluated with a pervaporation setup for the separation of a water-ethylene glycol mixture. The effects of preparation conditions including heat-curing temperature and time, dehydration rate, cooling rate, structure of support and crosslinking density of the crosslinked PVA active layer on the separation factor and permeate flux are discussed. Optimum results were obtained with crosslinked PVA membranes containing 3.7 wt% crosslinking agent and 0.05 wt% catalyst, giving a separation factor of 231 and a permeation rate of 383 g/(m2h) for a 82.5 wt% ethylene glycol aqueous solution at 80°C.

While numerous techniques have been successful for scaling the acid strength of Bronsted sites, the situation is not satisfactory at all, for the Lewis acid sites. This is most unfortunate, since Lewis sites are present in most acid catalysts. This contribution aims to show that the simultaneous use of EPR and NMR probes suggests solutions to the problem of scaling the acid strength of Lewis sites. As shown previously, the hyperfine splitting of the EPR spectrum of the aniline radical cation or of the O−2 superoxide ion is a measurement of the strength of the electron acceptor site. Other researchers have suggested the shielding of the 31P nucleus and the shift of its resonance lines in chemisorbed trimethylphosphine (TMP) as a measurement of the Lewis acid strength. The comparison of the scaling obtained on a set of superacids, namely, and in the decreasing order of acidity, the sulfated derivatives of ZrO2, HfO2, Al2O3 and TiO2, by either the EPR or the NMR probes gives interesting information. While very strong Lewis acid centers in sulfated ZrO2 and HfO2 are revealed by 31P downfield shifted resonance lines, no such lines are observed in sulfated Al2O3 or TiO2 or zeolites (such as dealuminated mordenite) which contains strong Lewis acid centers. In the latter samples, the most downfleld shifted line corresponds to that generally assigned to TMPH+. Measurement of 31P relaxation rates suggests that TMP has a more restricted mobility on strong than on weak Lewis sites. They also show that the origin of the relaxation in TMPH+ is ambiguous: either the mobility of TMPH+ is very restricted and/or the extraproton is not as close to the phosphorus as anticipated.

Besides the resonance lines attributable to tetrahedrally (AlIV) and octahedrally (AlVI) coordinated aluminum, the MAS NMR 27Al spectra of transition aluminas obtained from finely divided precursors gibbsite and boehmite have a line which can be assigned to pentacoordinated AI (AlV). This line which is very intense in ex-boehmite aluminas, as compared to ex-gibbsite aluminas, is also observed in the nonframework alumina moieties in acid and dealuminated zeolites. The isotropic chemical shifts of the AlVI, AlV, and AlIV resonance lines are 11.4, 38.3 and 65.6 ppm, respectively, in a field of 11.77 T. Nutation (two-dimensional) spectra of 27Al in these aluminas show a broad distribution of quadrupole coupling constants (QCCs) between ∼2 and ∼5 MHz. A broad range of distortions of the Al coordination shells corresponds to this range of QCCs. To detect electron acceptor sites (or Lewis acid centers), an EPR molecular probe has been adsorbed and the EPR spectra have been recorded before and after introduction of molecular oxygen. With dimethylaniline (DMA) the formation of a radical cation is observed and its concentration is larger on aluminas with AlV than on aluminas without detectable AlV. Molecular O2 which is adsorbed on DMA-treated aluminas, acts as an electron scavenger picking up the electron transferred from DMA to the surface. Moreover, the gzz is in the range expected for O2−, indicating its interaction with an Al nucleus. The surface density in electron acceptor sites with electron affinity ∼−7.1 eV is, at the best, on the order of 0.4 × 1012 spins/cm2. These findings suggest either that strongly distorted shells of pentacoordinated Al are potential Lewis acid centers or that they generate such sites upon thermal activation. Other types of coordination, if sufficiently distorted, may play a similar role.

A metastable b.c.c. (A2) phase with lattice parameter a = (0.280 ± 0.005) nm is obtained upon rapidly solidifying Ni10at.%Zr and Ni8at.%Zr1at.%X (X = Si, Ti, Mo) alloys. The b.c.c. phase is relatively more stable in the ternary alloys. Formation of this metastable phase and the equilibrium phases under rapid solidification conditions are discussed in terms of classical nucleation theory. Upon aging, the b.c.c. phase decomposes into equilibrium phases, the morphology of which is dependent on the aging temperature.

A system for selecting excerpts directly from imaged text without performing optical character recognition is described. The images are segmented to find text regions, text lines and words, and sentence and paragraph boundaries are identified. A set of word equivalence classes is computed based on the rank blur hit-miss transform. This information is used to identify stop words and keywords. Sentences for presentation as part of a summary are then selected based on keywords and on the location of the sentences.

27 Al MAS NMR spectra obtained upon cross-polarization (CP) show that the distorted coordination shells of Al IV and Al V are surface species in small slabs of dehydroxylated alumina. These Al V -rich slabs are present in steamed zeolite as non-framework aluminum or in transition aluminas obtained from ground boehmite. P(CH 3 ) 3 is strongly bound to the Lewis site associated with Al V and this Lewis site is strong, as evidenced by the shift of the 31 P resonance. This shift goes from −51 ppm, in alumina without Al V , to +5 ppm for the Al V −P(CH 3 ) 3 adduct. Furthermore, a thorough kinetic study of the model reaction: 1-butene ↝ cis and trans 2-butene shows that the Lewis sites associated with Al V enhances the cis ↽ trans conversion in transition aluminas. These direct correlations support the earlier indirect evidences that Al V yields strong Lewis sites.

The strength of Lewis acid sites in H-mordenite, HL, HY zeolites and transition alumina was studied by EPR with aniline and N,N-dimethylaniline (DMA) as molecular probes. The following order was established: HM > HL > HY > alumina. Non-framework Al species in zeolites was shown to be an important source of Lewis acidity. Introduction of oxygen after the adsorption of organic reagent resulted in the formation of O2, most probably located on the non-framework Al species. The measurement of the hyperfine splitting constant, Azz, of O2 confirms the above order of acid strength. The effect of zeolite structure on the acid strength of both framework and non-framework Al is discussed.

Apart from technological applications, scientifically amorphous —> crystal transformation is very important in understanding the atomic processes involved. For in-depth understanding of the crystallisation process, it is necessary to employ a combination of a number of experimental techniques. In this investigation, the details of the crystallisation of Ni24Zr76 amorphous alloy has been studied by differential scanning calorimtry (DSC), transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). This amorphous alloy undergoes eutectic crystallisation i.e., it transforms to (α-Zr) + NiZr2 crystals. It is our interest to study the kinetics of the crystallisation as well as the different steps involved in the evolution of equilibrium microstructure.Ribbons of 2-3 mm wide and 25-30 μm thick were produced by melt-spinning technique. Dynamic as well as isothermal crystallisation were studied in a Du-pont DSC 910 cell coupled with computer controlled thermal analyser (TA9900) having system control and data acquisition capabilities.