Search

Electric arc furnaces (EAFs) are used for steel production, particularly when recycling scrap material. In EAFs, carbonaceous material is charged with other raw materials or injected into molten slag to generate foam on top of liquid metal to increase energy efficiency. However, the consumption of fossil carbon leads to greenhouse gas emissions (GHGs). To reduce net GHG emissions from EAF steelmaking, the substitution of fossil carbon with sustainable biogenic carbon can be applied. This study explores the possibility of the substitution of fossil material with biogenic material produced by different pyrolysis methods and from various raw materials in EAF steelmaking processes. Experimental work was performed to study the effect of biogenic material utilization on steel and slag composition using an induction melting furnace with 50 kg of steel capacity. The interaction of biogenic material derived from different raw materials and pyrolysis processes with molten synthetic slag was also investigated using a tensiometer. Relative to other biogenic materials tested, a composite produced with densified softwood had higher intensity interfacial reactions with slag, which may be attributed to the rougher surface morphology of the densified biogenic material.

Partial substitution of pulverized coal (PCI) by renewable biocarbon for blast furnace injection is a practical approach to reduce GHGs in the steel production sector. For using biocarbon as feedst...

For a sample of 4378 nearby spiral and S0 galaxies, Yu and Ho (2020) used Fourier analysis of Sloan Digital Sky Survey images to show that the strengths of the spiral arms and the pitch angles of the arms are inversely correlated with central concentration. In the current study, we search for trends in the Yu and Ho (2020) spiral arm parameters with environment and specific star formation rate (sSFR). When comparing galaxies with similar concentrations, we do not find a significant difference in the arm strengths or pitch angles of spiral galaxies in clusters compared to field galaxies. When differences in concentration are taken into account, we also find no significant difference in the parameter f3 for cluster spirals compared to field spirals, where f3 is the normalized m = 3 Fourier amplitude. When concentration is held fixed, both arm strength and pitch angle are correlated with sSFR, but f3 is not. These relations support the suggestion by Davis et al. (2015) of a `fundamental plane' of spiral structure involving pitch angle, bulge stellar mass, and gas surface density. We discuss these results in terms of theories of spiral arm production and quenching in galaxies. To aid comparison with earlier studies based on Galaxy Zoo, we explore how the Yu and Ho (2020) parameters relate to similar parameters measured by Galaxy Zoo (i.e., f3 vs. number of arms, pitch angle vs. winding parameter, and concentration vs. bulge class)., AJ, in press

The state of the interface between slag and carbon determines the slag foaming behavior and thus the effectiveness of carbon in electric arc furnace (EAF) steelmaking. This paper explores the interaction between synthetic slag and carbonaceous materials derived from various sources, including bio-char produced by two different technologies, graphite, coke, and char from tire pyrolysis. Different interfacial phenomena were found between slag and the carbonaceous materials examined. The interactions between bio-char and slag are found to be poor in comparison with other carbonaceous materials. Carbonaceous materials were characterized in terms of their chemical composition and the results obtained suggested that interfacial phenomena were not dominated by ash in the carbonaceous material. The effects of carbon crystalline structure on interaction with slag were evaluated by Raman spectroscopy and X-ray diffraction. Surface properties of the samples were evaluated using scanning electron microscopy, and surface morphology was identified as the principal factor affecting the interaction of slag on carbonaceous particles. The smooth surface of bio-char results in reduced slag foaming. This finding forms the basis for future research on the production of bio-char to be used as a slag foaming agent in EAF steelmaking.

Substitution of pulverised coal injection (PCI) by solid biocarbon fuel has the potential to achieve substantial reduction in GHG emissions associated with blast furnace ironmaking. A systematic ev...

This study compared three methods of removing mineral matter (washing) from coal: jigging coal particles in water using the Roben Jig, the float/sink method using traditional organic liquids (naptha, perchloroethylene, methylene bromide), and a full-sized industrial wash plant. Clean coal composites from six coal types (A, B, C, D, E, and F) were tested. All coals were washed using the Roben Jig and the float/sink method and seams E and F were also washed in an industrial wash plant. In each case, the Roben Jig was capable of producing a clean coal composites with coal quality characteristics (proximate analysis, FSI, S, calorific value, mineral analysis of ash, RoMax) very similar to that of the clean coal samples created by the organic liquids float/sink method and the industrial wash plant sample. The Gieseler fluidity and Ruhr dilatation values were lower in the traditional float/sink method where the coal was exposed to organic liquids. There was very little difference in the Sapozhnikov Y values and small differences in the G Caking Index values. All six coal types were carbonized in a sole-heated oven and CSR was tested. Comparing the CSRs for the clean samples created by the Roben Jig and organic liquids for coals A, B, C, and D, in four out of five cases the CSR from the organic liquids treated samples was higher (differences ranging from 2 to 8 points). Coals E and F were washed using all three methods and the samples prepared in the organic liquids had the highest CSRs (differences ranging from 3 to 7). The clean coal samples from Coal F were carbonized in a moveable wall oven. CSRs ranged from 66.7 to 69.2, with the plant sample having the highest value. ASTM stability values ranged from 51.7 to 57.3 with the lowest value resulting from the organic liquids washed sample.

The effect of organic liquids (white spirit, perchloroethylene and methylene bromide) typically used in float/sink gravity separations (specific gravity 1.4–1.8) on the fundamental properties of a higher-inert Western Canadian metallurgical coal of mvb rank (Romax 1.22) and its resultant coking ability were examined. Over a 6-month period, untreated (control) and treated coal were characterized using a wide range of analyses including elemental chemistry, FTIR spectroscopy, alkali extraction via light transmittance test and thermal rheology, specifically fluidity, Dilatation, FSI and Caking Index G. Exposure to organic liquids was found to have a minor effect on coal chemistry (Ultimate) and oxidation level (Alkali Extraction via Light Transmission Test and FTIR-Spectroscopy). Trends of H/C, O/C, Light Transmittance and FTIR absorbance spectra versus storage time, following initial 1 h exposure to the organic liquids of varying specific gravities, revealed only minor changes, within the scatter/accuracy of the measurements. However, several coal plastic properties were decreased significantly including Gieseler Maximum Fluidity, Dilatation and G Caking Index. Of these, most affected was Maximum Fluidity which underwent an immediate and dramatic decrease of over 80% following organic liquids treatment. Other rheology indicators including FSI and Sapozhnikov were significantly less sensitive in detecting initial stages of degradation in plastic properties. The coking ability of both the untreated and treated coal in perchloroethylene (PCE) organic liquid, s.g. 1.6, after storage for 1 and 6 months was assessed through carbonization trials in both a small-scale sole-heated oven (12.5 kg capacity) and in a pilot-scale movable wall oven (350 kg capacity) at CanmetENERGY Carbonization facility, Ottawa, Canada. The treated samples had appreciably poorer quality ambient (ASTM, IRSID, JIS tumbler tests) and hot (CSR, CRI) coke strength and modified coke structure. Coke ASTM strength for untreated and treated coal at time 1 month was respectively decreased from 62 down to 57 for Stability and from 72 to 67 for Hardness. Similarly, Coke CSR and CRI for untreated and treated coal at time 1 month was respectively decreased from 74 down to 58 and increased from 21 to 29. The treated sample resulted in a lower coke yield, 71%, in comparison with 78% for the untreated sample, produced coke of smaller mean size, 46 mm, than the untreated sample, 53 mm, and generated an appreciably higher fraction of fines (− 12.5 mm), 21%, than untreated sample, 4%. The coke textures from the untreated coal consist of higher carbon forms, mosaic and flow in medium size, compared to those from s.g. 1.6 treated coal of lower carbon forms, very fine and fine mosaic, which renders the coke more reactive to CO2 gasification during CSR test. The higher effective coking rank, 1.2, and Coke Mosaic Size Index, 2.4, of untreated sample relative to that of treated one, 1.1 and 2.2, respectively, supports the better coke quality of the untreated sample. Extension of storage time to 6 months resulted in negligible changes in coke quality showing that the greatest changes occurred within the first month following exposure to organic liquids. Comparison of 1 month untreated and PCE treated mid coking rank Western Canadian (Romax 1.22) and Australian (Romax 1.17) coals show both to undergo comparable decrease in fluidity (50–60%) post treatment with PCE although only the Western Canadian coal leads to lower dilatation. Coke yield is also decreased for the Western Canadian coal and essentially maintained for the Australian coal. Both CSR and CRI are affected negatively and more so for the Western Canadian coal, 16 point drop in CSR and 8 point increase in CRI, relative to the Australian coal, 3 point drop in CSR and 4 point increase in CRI.

Using archival data from the Chandra X-ray telescope, we have measured the spatial extent of the hot interstellar gas in a sample of 49 nearby interacting galaxy pairs, mergers, and merger remnants. For systems with SFR > 1 M(sun)/yr, the volume and mass of hot gas are strongly and linearly correlated with the star formation rate (SFR). This supports the idea that stellar/supernovae feedback dominates the production of hot gas in these galaxies. We compared the mass of X-ray-emitting hot gas Mx(gas) with the molecular and atomic hydrogen interstellar gas masses in these galaxies (M(H2) and M(HI), respectively), using published carbon monoxide and 21 cm HI measurements. Systems with higher SFRs have larger Mx(gas)/(M(H2) + M(HI)) ratios on average, in agreement with recent numerical simulations of star formation and feedback in merging galaxies. The Mx(gas)/(M(H2) + M(HI)) ratio also increases with dust temperature on average. The ratio Mx(gas)/SFR is anti-correlated with the IRAS 60 micron to 100 micron flux ratio and with the Spitzer 3.6 micron to 24 micron. These trends may be due to variations in the spatial density of young stars, the stellar age, the ratio of young to old stars, the initial mass function, and/or the efficiency of stellar feedback. Galaxies with low SFR (, Astronomical Journal, in press

Coal injection is a common practice for coke replacement in current blast furnace (BF) operations. The amount of coal that can be injected and successfully replace large coke is determined by the extent of coal gasification, which is a function of both the combustion environment in the tuyere/raceway region and combustibility of the injected coal. A new carbon type differentiation (CTD) technique was developed at CanmetENERGY for quantifying the amount of unburnt pulverised coal injection (PCI) residue that is carried in the furnace top gas for diagnosing the extent of injected coal gasification. This technique utilises the combustion characteristics of solid carbonaceous material generated during rapid pyrolysis and partial combustion of coal. The CTD technique developed was transferred to ArcelorMittal Dofasco and successfully implemented in the industrial environment. Using this technique, AM Dofasco established a PCI efficiency baseline for each of its three BFs, which will be used as a reference poin...

Substitution of pulverized coal injection by solid biocarbon fuel has the potential to achieve substantial reduction in GHG emissions associated with blast furnace ironmaking. A systematic evaluation was conducted on the performance of solid bio-carbons produced from a single raw biomass source using different pyrolysis technologies. The potential of solid biocarbon in reducing GHG emission of the blast furnace ironmaking process is strongly influenced by its O/C mass ratio. In order to achieve substantial GHG reduction, it is necessary to replace coal injection by solid biocarbon having a low O/C mass ratio. The pyrolysis technology and conditions employed are key parameters influencing O/C mass ratio of the resultant solid biocarbon. Close collaboration between steelmakers and solid biocarbon producers is critical for producing suitable solid biocarbon fuel to replace pulverized coal injection. A successful partnership should pave the way in achieving substantial reduction in GHG emissions of the blast furnace ironmaking process.

Using archived data from the Chandra X-ray telescope, we have extracted the diffuse X-ray emission from 49 equal-mass interacting/merging galaxy pairs in a merger sequence, from widely separated pairs to merger remnants. After removal of contributions from unresolved point sources, we compared the diffuse thermal X-ray luminosity from hot gas (L(X)(gas)) with the global star formation rate (SFR). After correction for absorption within the target galaxy, we do not see strong trend of L(X)(gas)/SFR with SFR or merger stage for galaxies with SFR > 1 M(sun) yr^-1. For these galaxies, the median L(X)(gas)/SFR is 5.5 X 10^39 ((erg s^-1)/M(sun) yr^-1)), similar to that of normal spiral galaxies. These results suggest that stellar feedback in star forming galaxies reaches an approximately steady state condition, in which a relatively constant fraction of about 2% of the total energy output from supernovae and stellar winds is converted into X-ray flux. Three late-stage merger remnants with low SFRs and high K band luminosities (L(K)) have enhanced L(X)(gas)/SFR; their UV/IR/optical colors suggest that they are post-starburst galaxies, perhaps in the process of becoming ellipticals. Systems with L(K) < 10^10 L(sun) have lower L(X)(gas)/SFR ratios than the other galaxies in our sample, perhaps due to lower gravitational fields or lower metallicities. We see no relation between L(X)(gas)/SFR and Seyfert activity in this sample, suggesting that feedback from active galactic nuclei is not a major contributor to the hot gas in our sample galaxies., Astronomical Journal, in press; 43 pages, 24 figures

A mobile system was used for continuous ambient measurements of stable CH4 isotopes (12CH4 and 13CH4) and ethane (C2H6). This system was used during a winter mobile campaign to investigate the CH4 isotopic signatures and the C2H6/CH4 ratios of the main anthropogenic sources of CH4 in the Canadian province of Alberta. Individual signatures were derived from δ13CH4 and C2H6 measurements in plumes arriving from identifiable single sources. Methane emissions from beef cattle feedlots (n = 2) and landfill (n = 1) had δ13CH4 signatures of −66.7 ± 2.4‰ and −55.3 ± 0.2‰, respectively. The CH4 emissions associated with the oil or gas industry had distinct δ13CH4 signatures, depending on the formation process. Emissions from oil storage tanks (n = 5) had δ13CH4 signatures ranging from −54.9 ± 2.9‰ to −60.6 ± 0.6‰ and non-detectable C2H6, characteristic of secondary microbial methanogenesis in oil-bearing reservoirs. In contrast, CH4 emissions associated with natural gas facilities (n = 8) had δ13CH4 signatures ranging from −41.7 ± 0.7‰ to −49.7 ± 0.7‰ and C2H6/CH4 molar ratios of 0.10 for raw natural gas to 0.04 for processed/refined natural gas, consistent with thermogenic origins. These isotopic signatures and C2H6/CH4 ratios have been used for source discrimination in the weekly atmospheric measurements of stable CH4 isotopes over a two-month winter period at the Lac La Biche (LLB) measurement station, located in Alberta, approximately 200 km northeast of Edmonton. The average signature of −59.5 ± 1.4‰ observed at LLB is likely associated with transport of air after passing over oil industry sources located south of the station.

Coke Strength after Reaction (CSR) and the concomitant Coke Reactivity Index (CRI) are useful parameters for assessing the behavior of coke in blast furnace. To measure CSR and CRI of the resultant coke from a particular metallurgical coal or blend, a pilot scale oven test for producing appropriate industrial grade coke for measurements is unavoidable. If the quantity of coal sample available is not sufficient for pilot scale oven test, CSR measurement of the resultant coke is normally not possible. CanmetENERGY has developed a procedure for producing coke to allow CSR measurement involving relatively small amounts of coal sample (∼15 kg). The procedure involves producing semi-coke using the Sole Heated Oven in accordance with ASTM standard D2014-97 (2004). In the Sole Heated Oven test the coal sample is heated only from the bottom (the sole) up to 950 °C with the top of the oven charge rising to 500 °C over a period of 6–7 h. The resulting semi-coke is quenched (either wet or dry) and subsequently reheated to 1100 °C under nitrogen for 1 h. CSR and CRI are measured using the coke produced using this procedure. To demonstrate the validity of CSR and CRI measured using this approach, identical coal blends were carbonized concurrently using the CanmetENERGY pilot scale moveable wall oven (460 mm wide, 350 kg capacity) and the procedures mentioned above. CSR and CRI of the cokes produced by these two approaches were compared. Statistical analysis and coke textual analysis were performed to demonstrate the relevance of this novel approach on CSR determination.

Incorporation of biomass-derived materials in coal blends for cokemaking is one of the strategies that could reduce the levels of greenhouse gas emissions produced by the steelmaking process. Bio-coke refers to the resultant coke prepared with the addition of charcoal to a coal blend. In this work, characteristics of bio-coke gasification by reacting with CO 2 were examined using Thermal Gravimetric Analysis. Bio-coke samples with different levels of charcoal addition to a coal blend were prepared in the CanmetENERGY pilot-scale coke oven. These samples were heated in CO 2 for identification of the minimum gasification temperature. Sample gasification rates at 1000 °C were also measured. It was observed that mineral content plays an important role in the gasification characteristics of the bio-cokes. Those with low mineral content behave very similarly to the reference coke. Higher mineral content bio-coke reacts with CO 2 at a lower temperature. It was found that the gasification characteristics of the bio-cokes are well described by the alkalinity index.

We have used the Galaxy Evolution Explorer (GALEX) ultraviolet telescope to study stellar populations and star formation morphology in a well-defined sample of 42 nearby optically selected pre-merger interacting galaxy pairs. Galaxy interactions were likely far more common in the early universe than in the present; thus our study provides a nearby well-resolved comparison sample for high-redshift studies. We have combined the GALEX near-ultraviolet (NUV) and far-ultraviolet images with broadband optical maps from the Sloan Digitized Sky Survey to investigate the ages and extinctions of the tidal features and the disks. The distributions of the UV/optical colors of the tidal features and the main disks of the galaxies are similar; however, the tidal features are bluer on average in NUV - g when compared with their own parent disks; thus tails and bridges are often more prominent relative to the disks in UV images compared to optical maps. This effect is likely due to enhanced star formation in the tidal features compared to the disks rather than reduced extinction; however, lower metallicities may also play a role. We have identified a few new candidate tidal dwarf galaxies in this sample. Other interesting morphologies such as accretion tails and 'beads onmore » a string' are also seen in these images. We also identify a possible 'Taffy' galaxy in our sample, which may have been produced by a head-on collision between two galaxies. In only a few cases are strong tidal features seen in H I maps but not in GALEX.« less

We describe an ultraviolet spectroscopic survey of interstellar high-velocity cloud (HVC) absorption in the strong 1206.500 Angstrom line of Si III using the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. Because the Si III line is 4-5 times stronger than O VI 1031.926, it provides a sensitive probe of ionized gas down to column densities N(Si III) = 5x10^11 cm^-2 at Si III equivalent width 10 mA. We detect high-velocity Si III over (91+/-4)% of the sky (53 of 58 sight lines), and 59% of the HVCs show negative LSR velocities. Per sight line, the mean HVC column density is = 13.19 +/- 0.45, while the mean for all 90 velocity components is 12.92 +/- 0.46. Lower limits due to Si III line saturation are included in this average, so the actual mean/median values are even higher. The Si III appears to trace an extensive ionized component of Galactic halo gas at temperatures 10^4.0 K to 10^4.5 K indicative of a cooling flow. Photoionization models suggest that typical Si III absorbers with 12.5 < log N(Si III) < 13.5 have total hydrogen column densities N(H) = 10^18 to 10^19 cm^-2 for gas of hydrogen density n(H) = 0.1 cm^(-3) and 10% solar metallicity. With typical neutral fractions N(HI)/N(H) = 0.01, these HVCs may elude even long duration 21-cm observations at Arecibo, the EVLA, and other radio facilities. However, if Si III is associated with higher density gas, n(H) > 1 cm^(-3), the corresponding neutral hydrogen could be visible in deep observations. This reservoir of ionized gas may contain 10^8 M_sun and produce a mass infall rate of 1 M_sun/yr to the Galactic disk., Comment: 23 pages, 6 figures, accepted for ApJ (Nov 10 issue, Vol 705)

Processes involving biomass oxidation are considered to be CO 2 neutral since the replenishing of the biomass by normal growth will remove CO 2 from the atmosphere. Thus the use of charcoal in the production of metallurgical coke, to be used as a reducing agent in the formation of iron, would be a strategy for the reduction of CO 2 in the overall ironmaking process. This paper describes experimental attempts to produce industrial grade coke from coking coal blends to which are added amounts of charcoal up to 10%. Coking experiments were carried out partly in a 30 lb coke oven and partly in a sole heated oven. The influence of blend composition, heating rates and charcoal particle size was investigated. Cokes made using fine charcoal addition (− 60 mesh) were considerably weaker than cokes made from the base blend. This is interpreted to be the effect of the ash constituents in the charcoal which, among other things, contains much higher calcium than the coals used. However, carefully sized fractions of coarse charcoal (− 3/8 + 1/4 in) produced much higher quality coke, possibly the result of a different dispersion of the charcoal mineral components.

Nonmotor symptoms are common in Parkinson disease and can significantly worsen the health and quality of life of the patient and family members. These symptoms can be broadly categorized as sensory, autonomic, cognitive-behavioral, and sleep-related. Clinicians can improve the care of these patients by recognizing and addressing these problems.

We present an empirical assessment of the use of broadband optical colours as age indicators for unresolved extragalactic clusters and investigate stochastic sampling effects on integrated colours. We use the integrated properties of Galactic open clusters as models for unresolved extragalactic clusters. The population synthesis code Starburst99 (Leitherer et al. 1999) and four optical colours were used to estimate how well we can recover the ages of 62 well-studied Galactic open clusters with published ages. We provide a method for estimating the ages of unresolved clusters and for reliably determining the uncertainties in the age estimates. Our results support earlier conclusions based on comparisons to synthetic clusters, namely the (U-B) colour is critical to the estimation of the ages of star forming regions. We compare the observed optical colours with those obtained from Starburst99 using the published ages and get good agreement. The scatter in the (B-V)_observed-(B-V)_model is larger for lower luminosity clusters, perhaps due to stochastic effects., 9 pages, 6 figures, 2 tables, accepted for publication in MNRAS on 7/7/08

We present Spitzer infrared, GALEX UV, and SDSS and SARA optical images of the peculiar interacting galaxy pair Arp 285 (NGC 2856/4), and compare with a new numerical model of the interaction. We estimate the ages of clumps of star formation in these galaxies using population synthesis models, carefully considering the uncertainties on these ages. This system contains a striking example of `beads on a string': a series of star formation complexes ~1 kpc apart. These `beads' are found in a tail-like feature that is perpendicular to the disk of NGC 2856, which implies that it was formed from material accreted from the companion NGC 2854. The extreme blueness of the optical/UV colors and redness of the mid-infrared colors implies very young stellar ages (~4 - 20 Myrs) for these star forming regions. Spectral decomposition of these `beads' shows excess emission above the modeled stellar continuum in the 3.6 micron and 4.5 micron bands, indicating either contributions from interstellar matter to these fluxes or a second older stellar population. These clumps have -12.0 < M(B) < -10.6, thus they are less luminous than most dwarf galaxies. Our model suggests that bridge material falling into the potential of the companion overshoots the companion. The gas then piles up at apo-galacticon before falling back onto the companion, and star formation occurs in the pile-up. A luminous (M(B) ~ -13.6) extended (FWHM ~ 1.3 kpc) `bright spot' is visible at the northwestern edge of the NGC 2856 disk, with an intermediate stellar population (400 - 1500 Myrs). Our model suggests that this feature is part of a expanding ripple-like `arc' created by an off-center ring-galaxy-like collision between the two disks., Accepted by the Astronomical Journal. For color figures and appendix material, go tohttp://www.etsu.edu/physics/bsmith/research/sg/arp285/arp285.html

We have used the Hubble/STIS and FUSE archives of ultraviolet spectra of bright AGN to identify intergalactic Lya absorbers in nearby (z < 0.1) voids. From a parent sample of 651 Lya absorbers, we identified 61 void absorbers located more than 1.4/h_70 Mpc from the nearest L* or brighter galaxy. Searching for metal absorption in high-quality (S/N > 10) spectra at the location of three diagnostic metal lines (O VI 1032, C IV 1548, Si III 1206), we detected no metal lines in any individual absorber, or in any group of absorbers using pixel co-addition techniques. The best limits on metal-line absorption in voids were set using four strong Lya absorbers with N(H I) > 10^{14} cm^-2, with 3-sigma equivalent-width limits ranging from 8 mA (O VI), 7-15 mA (C IV), and 4-10 mA (Si III). Photoionization modeling yields metallicity limits Z < 10^{-1.8+/-0.4} Z_sun, from non-detections of C IV and O VI, some 6 times lower than those seen in Lya and OVI absorbers at z < 0.1. Although the void Lya absorbers could be pristine material, considerably deeper spectra are required to rule out a universal metallicity floor produced by bursts of early star formation, with no subsequent star formation in the voids. The most consistent conclusion derived from these low-z results, and similar searches at z = 3-5, is that galaxy filaments have increased their mean IGM metallicity by factors of 30-100 since z = 3., Accepted for ApJ, 8 pages including Fig 1a,b

Background: Polymorphisms in the glutathione S-transferase pi gene ( GSTP1 ), encoding GSTP1-1, a detoxification enzyme, may increase the risk of Parkinson disease (PD) with exposure to pesticides. Using the Gene PD Study sample of familial PD cases, we explored whether GSTP1 polymorphisms were associated with the age at onset of PD symptoms and whether that relation was modified by exposure to herbicides. Methods: Seven single-nucleotide polymorphisms (SNPs) were genotyped and tested for association with PD onset age in men in three strata: no exposure to herbicides, residential exposure to herbicides, and occupational exposure to herbicides. Haplotypes were similarly evaluated in stratified analyses. Results: Three SNPs were associated with PD onset age in the group of men occupationally exposed to herbicides. Three additional SNPs had significant trends for the association of PD onset age across the herbicide exposure groups. Haplotype results also provided evidence that the relation between GSTP1 and onset age is modified by herbicide exposure. One haplotype was associated with an approximately 8-years-earlier onset in the occupationally exposed group and a 2.8-years-later onset in the nonexposed group. Conclusions: Herbicide exposure may be an effect modifier of the relation between glutathione S-transferase pi gene polymorphisms and onset age in familial PD.

A Victorian lignite, designated Loy Yang low ash, run of mine (LYLA (R)) has been dewatered using mechanical thermal expression (MTE) at 150–200 °C and 6–25 MPa and by hydrothermal dewatering (HTD) at 200–300 °C and the products compared. Total acidity values for all samples as measured by a pyrolysis thermogravimetric Fourier transform infrared (TG–FTIR) method were similar to those measured by barium ion exchange. Stronger (carboxylic) acid values determined by pyrolysis TG–FTIR tended to be lower than ion exchange values, except for the 300 °C HTD sample, for which both methods gave similar values although these were much lower than at all of the other treatment temperatures. Equilibrium moisture contents (EMC) for the MTE products and the 200 °C HTD product were similar to those of the original lignite at relative vapour pressure (RVP) ⩽ 52%, but lower at RVP 92%. EMC values for 300 °C HTD products were all lower than for the original lignite, indicating that processing temperature was the most important factor in determining these properties. CO 2 adsorption surface area was also mainly a function of processing temperature, decreasing with increasing temperature. However, the pore volume as determined by mercury porosimetry was influenced by whether dewatering was effected by MTE or HTD, the mechanical pressure applied in the MTE process resulting in a lower porosity.

This paper attempts to relate oxygen-containing gases H2O, CO2, and CO evolved during pyrolysis of the Argonne premium coals to oxygen-containing functional groups as a function of rank. Our approach to functional group analysis of oxygen-containing species in coal has been to use a pyrolysis technique, thermogravimetric Fourier transform infrared spectroscopy (TG−FTIR), involving thermogravimetric analysis with the measurement of the gaseous decomposition products via IR detection. Under suitable heating conditions, TG−FTIR pyrolysis of a coal sample in a stream of inert gas has been shown to expel quantitatively all of the organic oxygen in the form of H2O, CO2, and CO, and consequently, this technique can be effectively applied for determining the total oxygen content. Focusing on the Argonne premium coals, which cover a wide range in rank between lignite (Ro = 0.25) and low-volatile bituminous (Ro = 1.68), TG−FTIR provided complex pyrolysis profiles of oxygen-containing gases, which yield information ...

A study was undertaken with the aim of finding the best practical way of storing small coal samples in a laboratory setting to limit their extent of oxidation for maintaining good thermal rheological properties. Samples of a Canadian medium-volatile bituminous coal of Cretaceous age (‘as received’ and Chemical changes including O content, O / C, H / O, H / C, Volatile Matter, and Calorific Value; Thermal Rheological changes in Fluidity, Plastic range, Dilatation, Free-Swelling Index and Alkali Light Transmittance. Coke Quality changes in Coke Cake Contraction, Coke Reactivity and Coke Strength indices as well as Coke Optical Textures were also examined. For chemistry related changes, the most obvious ones due to oxidation are in atomic oxygen, which increases, and calorific value, which decreases. Concerning thermal rheology changes, fluidity and dilatation were found to decrease the most whereas Free-Swelling Index and Alkali Light Transmittance do not appear to be sensitive indicators of early stages of oxidation for the examined coal. Pertaining to coke quality, coke cake contraction remains essentially unchanged, Coke Strength after Reaction decreases and Coke Reactivity Index increases, and textures reveal a significant increase in coke inerts. This work has found coal oxidation to be mainly influenced by the storage temperature, with rate of oxidation increasing with temperature, and to a lesser extent by particle size, with oxidation being more likely the smaller the particle size. Of the different storage conditions tested in this investigation, keeping coal at cold temperatures (

Thermogravimetric-Fourier transform infrared (TG-FTIR) studies, using a ramp rate of 30 °C/min, have been used to determine the total acidity and carboxylic acid contents for a range of lignites from the Latrobe Valley coal fields, Vic., Australia, some of which were also studied in water- and acid-washed form. The results are compared with values determined by barium ion-exchange. Total acidities from barium ion-exchange showed good agreement with those determined from the total amount of CO+CO 2 evolved. The carboxylic acid content determined from the amount of CO 2 evolved in pyrolysis showed a good correlation with the concentration of stronger acid functional groups determined by barium ion-exchange, but was lower. The effect of ion-exchange with Na, Mg, Ca and Al on CO, CO 2 , pyrolysis H 2 O and hydrocarbon gas production, as well as on the relative yields of these different gases, was similar to that observed by earlier workers for pyrolysis over much longer run times.

During rapid pyrolysis of coal, TG–FTIR (thermogravimetry – Fourier transform infrared) technique can be effectively used to simultaneously detect and measure the three main O-containing gases, namely H 2 O, CO and CO 2 . Their sum corresponds to the quantitative amount of oxygen in the coal and is, in general, inherently more accurate than the ‘by-difference’ values. In this paper, we first attempt to relate the ‘by-difference’ values for %O reported for the Argonne premium coal samples (lignite to bituminous rank) (Argonne Users Handbook) to those determined from a TG–FTIR examination of the pyrolysis gases evolved. Another objective of the work is to relate the pyrolysis gases (H 2 O, CO and CO 2 ) evolved to oxygen-containing functional groups found in coals as well as the evolution of these functional groups as a function of rank. Correlations are also developed between the TG–FTIR oxygen values and other parameters determined for the Argonne Premium Coals. In particular, comparisons of our results using TG–FTIR with analyses carried out by other workers on functional group analysis of acidic groups are considered.

The natural oxidation/weathering of coal continues to be a subject of interest both scientifically and industrially, in part due to the complexity of the molecular processes at hand as well as to the commercial implications involved. It is widely recognized that coking can be adversely affected by weathering whereas, combustion processes appear to be enhanced as result of oxidation. Combustion techniques are commonly used in the analysis of coal, and organic compounds in general, for the determination of elemental hydrogen, carbon and nitrogen. For oxygen, the method in common practice involves the determination by difference from directly determined values for moisture, ash, sulphur, hydrogen, carbon and nitrogen. This has led us to consider the use of thermogravimetry coupled to gas analysis by infrared spectroscopy (TG-FTIR) to measure organic oxygen in coal directly. Although this technique, developed by Solomon and coworkers, has been extensively used by our group and others, it appears not to have been considered for this particular purpose. Recently, we have shown that TG-FTIR is capable of measuring all the organic oxygen in both fresh and oxidized coal by simultaneous measurement of the three main oxygen-containing gases H2O, CO and CO2 evolved during rapid pyrolysis. This gives us a way of measuring quantitatively the oxygen introduced into the coal matrix during oxidation and at least a partial capability of establishing oxygen speciation. We have found, using TG-FTIR, that the early stages of coal oxidation results in the appearance of O-containing functional groups not present in the original coal. The nature of these functional groups is directly related to the oxidation reaction mechanism. These results will be presented and discussed in detail.

To gain insight into four highly ionized high-velocity clouds (HVCs) discovered by Sembach et al. (1999), we have analyzed data from the Hubble Space Telescope (HST) and Far Ultraviolet Spectroscopic Explorer (FUSE) for the PKS 2155-304 and Mrk 509 sight lines. We measure strong absorption in OVI and column densities of multiple ionization stages of silicon (SiII/III/IV) and carbon (CII/III/IV). We interpret this ionization pattern as a multiphase medium that contains both collisionally ionized and photoionized gas. Toward PKS 2155-304, for HVCs at -140 and -270 km/s, respectively, we measure logN(OVI)=13.80+/-0.03 and log N(OVI)=13.56+/-0.06; from Lyman series absorption, we find log N(HI)=16.37^(+0.22)_(-0.14) and 15.23^(+0.38)_(-0.22). The presence of high-velocity OVI spread over a broad (100 km/s) profile, together with large amounts of low-ionization species, is difficult to reconcile with the low densities, n=5x10^(-6) cm^(-3), in the collisional/photoionization models of Nicastro et al. (2002), although the HVCs show a similar relation in N(SiIV)/N(CIV) versus N(CII)/N(CIV) as high-z intergalactic clouds. Our results suggest that the high-velocity OVI in these absorbers do not necessarily trace the WHIM, but instead may trace HVCs with low total hydrogen column density. We propose that the broad high-velocity OVI absorption arises from shock ionization, at bowshock interfaces produced from infalling clumps of gas with velocity shear. The similar ratios of high ions for HVC Complex C and these highly ionized HVCs suggest a common production mechanism in the Galactic halo., Comment: 38 pages, including 10 figures. ApJ, 10 April, 2004. Replaced with accepted version

We provide an in-depth analysis of the He II and H I absorption in the intergalactic medium (IGM) at redshifts z = 2.3-2.9 toward HE 2347-4342, using spectra from the Far Ultraviolet Spectroscopic Explorer (FUSE) and the Ultraviolet-Visual Echelle Spectrograph (UVES) on the VLT telescope. Following up on our earlier study (Kriss et al. 2001, Science, 293, 1112), we focus here on two major topics: (1) small-scale variability (Delta z = 10^-3) in the ratio eta = N(He II)/N(H I); and (2) an observed correlation of high-eta absorbers (soft radiation fields) with voids in the (H I) Ly-alpha distribution. These effects may reflect fluctuations in the ionizing sources on scales of 1 Mpc, together with radiative transfer through a filamentary IGM whose opacity variations control the penetration of 1-5 ryd radiation over 30-40 Mpc distances. Owing to photon statistics and backgrounds, we can measure optical depths over the ranges 0.1 < tau(HeII) < 2.3 and 0.02 < tau(HI) < 3.9, and reliably determine values of eta = 4 tau(HeII)/tau(HI) over the range 0.1 to 460. Values of eta = 20-200 are consistent with models of photoionization by quasars with observed spectral indices alpha_s = 0-3. Values of eta > 200 may require additional contributions from starburst galaxies, heavily filtered quasar radiation, or density variations. Regions with eta < 30 may indicate the presence of local hard sources. We find that eta is higher in "void" regions, where H I is weak or undetected and 80% of the path length has eta > 100. These voids may be ionized by soft sources (dwarf starbursts) or by QSO radiation softened by escape from the AGN cores or transfer through the "cosmic web". The apparent differences in ionizing spectra may help to explain the 1.45 Gyr lag between the reionization epochs, z(HI) = 6.2 +/-0.2 and z(HeII) = 2.8 +/-0.2., 27 pages, 7 figures, to appear in ApJ

The 3C 273 and RX J1230.8+0115 sightlines probe the outskirts of the Virgo Cluster at physical separations between the sightlines of 200-500 h_70 kpc. We present an analysis of HST STIS echelle and FUSE UV spectroscopy of RX J1230.8+0115 in which we detect five Lyman-alpha absorbers at Virgo distances. One of these absorbers is a blend of two strong metal line absorbers coincident in velocity with the highest neutral hydrogen column density absorber in the 3C 273 sightline ~350 h_70 kpc away. The consistency of the metal line column density ratios in the RX J1230.8+0115 sightline allows us to determine the ionization mechanism (photoionization) for these absorbers. While the low signal-to-noise ratio of the FUSE spectrum limits our ability to model the neutral hydrogen column density of these absorbers, we are able to constrain them to be in the range 10^{16-17} cm^-2. The properties of these absorbers are similar to those of the 3C 273 absorber studied by Tripp et al. However, the inferred line-of-sight size for the 3C 273 absorber is only 70 pc, much smaller than those inferred in RX J1230.8+0115, which are 10-30 h_70 kpc. The small sizes of all three absorbers are at odds with the >~350 h_70 kpc minimum transverse size implied by an application of the standard QSO line pairs analysis. On the basis of absorber associations between these two sight lines we conclude that a large-scale structure filament produces a correlated, not contiguous, gaseous structure in this region of the Virgo Supercluster. These data may indicate that we are detecting overdensities in the large scale structure filaments in this region. Alternatively, the presence of a galaxy 71 h_70 kpc from a 3C 273 absorber may indicate that we have probed outflowing, starburst driven shells of gas associated with nearby galaxies.

Thermogravimetry with Fourier Transform Infrared Analysis (TG-FTIR) has been used to measure the organic oxygen content in a suite of coals of differing rank and compare these with the values determined by difference according to ASTM D3176-89. Two coking coals, one Cretaceous and one Carboniferous, were oxidized at 50 °C to simulate natural weathering and analyzed for their oxygen content by both techniques. Results indicate that the pyrolysis technique is reliable and rapid and is free of the large possible errors inherent in the determination of organic oxygen content by difference.

Since the 1980's discovery of the large (2x10^9 Msun) intergalactic cloud known as the Leo Ring, this object has been the center of a lively debate about its origin. Determining the origin of this object is still important as we develop a deeper understanding of the accretion and feedback processes that shape galaxy evolution. We present HST/COS observations of three sightlines near the Ring, two of which penetrate the high column density neutral hydrogen gas visible in 21 cm observations of the object. These observations provide the first direct measurement of the metallicity of the gas in the Ring, an important clue to its origins. Our best estimate of the metallicity of the ring is ~10% Zsun, higher than expected for primordial gas but lower than expected from an interaction. We discuss possible modifications to the interaction and primordial gas scenarios that would be consistent with this metallicity measurement., Comment: 11 pages, 7 figures, accepted ApJ

We use high-resolution UV spectra of the radio-quiet QSO H1821+643 (z_em = 0.297), obtained with STIS and FUSE, to study the ionization and metallicity of an intervening O VI absorption line system at z(abs) = 0.1212. This absorber has the following notable properties: (1) Several galaxies are close to the sight line at the absorber redshift, including an actively star-forming galaxy at a projected distance of 144 kpc. (2) There is a complex cluster of H I lya absorption lines near the O VI redshift, including at least five components spread over a velocity range of ~700 km/s . (3) The strongest lya line in the cluster appears to be composed of a mildly saturated component with a typical b-value blended with a broad component with b = 85 km/s . (4) The O VI absorption is not aligned with the strongest H I absorption, but instead is well-aligned with the broad component. (5) The only detected species (>4sigma) are O VI and H I despite coverage of strong transitions of other abundant elements. Based on these constraints, we find that the absorption line properties can be produced in collisionally ionized gas with roughly 5.3 < log T < 5.6 and -1.8 < [O/H] < -0.6. However, we find that photoionization is also viable if the pathlength l through the absorbing gas is long enough; simple photoionization models require 85 < l < 1900 kpc and -1.1 < [O/H] < -0.3. We briefly discuss how observations of X-ray absorption lines due to O VII and O VIII could be used, in principle, to break the ionization mechanism degeneracy., To appear in The Astrophysical Journal (Dec. 20, 2001). 25 pgs., 6 figs

We present HST GHRS and STIS observations of five QSOs that probe the prominent high-velocity cloud (HVC) Complex C, covering 10% of the northern sky. Based upon a single sightline measurement (Mrk 290), a metallicity [S/H]=-1.05+/-0.12 has been associated with Complex C by Wakker et al. (1999a,b). When coupled with its inferred distance (5, Comment: 40 pages, 12 figures, 4 tables, LaTeX (aastex.cls). Accepted for publication in The Astronomical Journal. Also available at http://astronomy.swin.edu.au/bgibson/publications.html

Indexers differ in their judgment as to which terms reflect adequately the content of a document. Studies on interindexers' consistency identified several factors associated with low consistency, but failed to provide a comprehensive model of this phenomenon. Our research applies theories and methods from cognitive psychology to the study of indexing behavior. From a theoritical standpoint, indexing is considered as a problem solving situation. To access to the cognitive processes of indexers, three kinds of verbal reports are used. We will present results of an experiment in which four experienced indexers indexed the same documents. It will be shown that the three kinds of verbal reports provide complementary data on strategic behavior, and that it is of prime importance to consider the indexing task as an ill-defined problem, where the solution is partly defined by the indexer him(her)self.Résumé: Afin de mieux cerner l'origine des différences relevées par les études sur la cohérence inter-indexeurs, nous adjoignons les théories et méthodes issues de la psychologie cognitive (spécifiquement celles qui considèrent une tâche comme une situation de résolution de problème) à l'étude des processuscognitifs impliqués lors de l'indexation. Cette approche permet d'identifier les stratégies cognitives élaborées et utilisées par les indexeurs. Afin d'avoir accès à leurs processus cognitifs, trois types de verbalisations sont recueillis. Nous présenterons les résultats d'une expérimentation pour laquelle quatre indexeurs expérimentés ont analysé les mêmes documents. Les résultats avancés démontreront la complémentarité des données issues des trois types de verbalisations et l'importance de considérer l'indexation en tant que problème mal- défini; la solution étant définie en partie par l'indexeur.

We describe a moderate-resolution (20-25 km s-1) Far Ultraviolet Spectroscopic Explorer (FUSE) study of the low-redshift intergalactic medium. We report on studies of seven extragalactic sight lines and 12 Lyβ absorbers that correspond to Lyα lines detected by Hubble Space Telescope (HST)/Goddard High Resolution Spectrograph and Space Telescope Imaging Spectrograph. These absorbers appear to contain a significant fraction of the low-z baryons and were a major discovery of the HST spectrographs. Using FUSE data, with 40 mA (4 σ) Lyβ detection limits, we have employed the equivalent width ratio of Lyβ/Lyα, and occasionally higher Lyman lines, to determine the Doppler parameter b and accurate column densities N for moderately saturated lines. We detect Lyβ absorption corresponding to all Lyα lines with Wλ ≥ 200 mA. The Lyβ/Lyα ratios yield a preliminary distribution function of Doppler parameters, with mean b = 31.4 ± 7.4 km s-1 and median 28 km s-1, comparable to values at redshifts z = 2.0-2.5. If thermal, these b-values correspond to T ≈ 50,000 K, although the inferred Doppler parameters are considerably less than the widths derived from Lyα profile fitting, b/bwidth = 0.52. The typical increase in column density over that derived from profile fitting is Δ log N = 0.3, but ranges up to 1.0 dex. Our data suggest that the low-z Lyα absorbers contain sizable nonthermal motions or velocity components in the line profile, perhaps arising from cosmological expansion and infall.

Partitioning of volatile organic compounds (VOCs) into surfactant micelles affects the apparent vapor−liquid equilibrium of VOCs in surfactant solutions. This partitioning will complicate removal of VOCs from surfactant solutions by standard separation processes. Headspace experiments were performed to quantify the effect of four anionic surfactants and one nonionic surfactant on the Henry's law constants of 1,1,1-trichloroethane, trichloroethylene, toluene, and tetrachloroethylene at temperatures ranging from 30 to 60 °C. Although the Henry's law constant increased markedly with temperature for all solutions, the amount of VOC in micelles relative to that in the extramicellar region was comparatively insensitive to temperature. The effect of adding sodium chloride and isopropyl alcohol as cosolutes also was evaluated. Significant partitioning of VOCs into micelles was observed, with the micellar partitioning coefficient (tendency to partition from water into micelle) increasing according to the following...

A vibrating membrane module currently marketed for filtration applications was evaluated for the separation of volatile organic compounds (VOCs) from aqueous solutions by pervaporation. Preliminary screening experiments with three VOCs, three silicone membranes, and in the presence and absence of a surfactant were performed to determine if further consideration of the vibrating module for a field demonstration project was warranted. The primary process variables studied were vibrational amplitude and liquid flow rate. The vibrations greatly reduced concentration polarization in the system as inferred from an order of magnitude increase in the overall mass transport coefficient. Mass transfer coefficients for the vibrating module compared favorably with those for traditional spiral wound modules.

Absorption due to HeII Ly-alpha has been detected at low resolution in the spectra of four quasars between redshifts z = 2.74-3.29. We assess these observations, giving particular attention to the radiative transfer of the ionizing background radiation, cloud diffuse emission and ionization physics, and statistical fluctuations. We use high-resolution observations of HI absorption towards quasars to derive improved models for the opacity of the intergalactic medium (IGM) and use these models to calculate the HI and HeII photoionization history in both optically-thin and self-shielded clouds, and the average line-blanketing contribution to HeII absorption. The derived ionization rate at z = 2-4, Gamma(HI) = (1-3)x10^-12 s^-1, is consistent with the ionizing background intensity inferred from the proximity effect, but it remains larger than that inferred by N-body hydrodynamical simulations of the Lya absorber distribution. The HeII observations are con- sistent with line blanketing from clouds with N(HI) > 10^12 cm^-2, although a contribution from a more diffuse IGM would help to explain the observed opacity. We compute the expected HeII optical depth and examine the sizable fluc- tuations that arise from variations in the cloud numbers and ionizing radiation field. We assess how HeII absorption constrains the intensity and spectrum of the ionizing radiation and the fractional contributions of the dominant sources (quasars and starburst galaxies). Finally, we demonstrate how high-resolution UV observations can distinguish between absorption from the diffuse IGM and the Lya forest clouds and determine the source of the ionizing background.

We showed previously that antidepressants inhibit GABA-stimulated 36Cl– uptake in rat cerebral cortex. In this study Schild analysis was used to determine if antidepressants are competitive antagonists or allosteric modulators at GABAA receptors. GABA concentration-response curves for 36Cl– uptake in rat cerebral cortex were generated in the absence or presence of different concentrations of the following antidepressants: amitriptyline, amoxapine, mianserin, and also the GABAA receptor antagonist, bicuculline. The pA2 values for amitriptyline, amoxapine, mianserin, and bicuculline were 4.2 ± 0.2, 5.5 ± 0.3, 4.4 ± 0.1 and 6.2 ± 0.6, respectively. The respective Schild slope values were 0.7 ± 0.1, 0.6 ± 0.03, 0.7 ± 0.2 and 1.0 ± 0.3. All slope values for antidepressants differed from unity. The maximum effect produced by GABA to stimulate chloride influx was decreased by both antidepressants and bicuculline. It is concluded that neither the antidepressants studied nor bicuculline are pure competitive GABA antagonists at the GABAA receptor-chloride-ionophore complex in the rat cerebral cortex.

BACKGROUND Nisoldipine, a calcium antagonist, has been reported to improve the quality of grafted rat livers. We thus assessed the protective effect of two calcium antagonists, nisoldipine and nickel, during extended cold ischemia-reperfusion. METHODS Rat livers were isolated and perfused before or after 24 hr of cold ischemia in University of Wisconsin solution (4 degrees C) with or without nisoldipine or nickel. Sinusoidal endothelial cell and hepatocyte functions were measured by hyaluronic acid and taurocholate elimination, respectively. RESULTS Similar alterations in hepatocyte and sinusoidal cell functions were found in all groups after cold ischemia with or without calcium antagonists. In a second set of experiments, liver transplantation was performed in two groups of rats with livers stored under identical conditions with or without nisoldipine. Seven of 12 animals (62.5%) in both groups survived for over 10 days after 24-hr preservation in University of Wisconsin solution. Survival rates were similar in both groups. CONCLUSIONS Calcium antagonists do not appear to have a direct protective effect on sinusoidal endothelial cell and hepatocyte functions, nor on the overall liver preservation after extended cold preservation-reperfusion.

The role of the 190's loop of fructose-1,6-bisphosphatase (Fru-1,6-P2ase) in the allosteric regulation of Fru-1,6-P2ase has been investigated through kinetic studies on three mutant enzymes, Glu-192 → Ala, Glu-192 → Gln, and Asp-187 → Ala. AMP is an allosteric inhibitor, which binds to the regulatory sites and induces the R- to T-state transition; for wild-type Fru-1,6-P2ase AMP inhibition is cooperative with a Hill coefficient of 2.0. The replacement of Asp-187, which forms an interaction across the C1:C2 monomer-monomer interface, with alanine did not change the catalytic efficiency, and it had no effect on the cooperativity of AMP inhibition; however, the apparent dissociation constant for AMP increased more than 4-fold as compared to the value for the wild-type enzyme. The replacement of Glu-192, which forms interactions across the C1:C4 dimer-dimer interface, with Ala and Gln lowered kcat from 21 s−1 for wild-type enzyme to 15 s−1 and 13 s−1, respectively, for the mutant enzymes, while their respective Km values were not changed. However, these replacements did have dramatic effects on AMP inhibition; first, cooperative AMP inhibition was lost; second, the AMP inhibition was biphasic, which can be interpreted as due to AMP binding to two classes of binding sites. The high affinity class of sites corresponds to the regulatory sites, while the low affinity class of sites may be the active sites. The results reported here, combined with the structural and kinetic results from the Lys-42 → Ala enzyme, strongly suggest that the C1:C4 dimer-dimer interface, rather than the C1:C2 monomer-monomer interface, is critical for the propagation of the allosteric signal between the AMP sites on different subunits; in addition, cooperative AMP inhibition is essential for the enzyme to be fully inhibited by the binding of AMP to the allosteric site.