Considerations on the methane correction factor and fraction of methane parameters in the IPCC first-order decay model for active aeration landfills.

Understanding the behavior of organic carbon in municipal solid waste landfills is a major challenge for estimating methane (CH4) emissions using the Intergovernmental Panel on Climate Change (IPCC) first-order decay (FOD) model. According to the IPCC guidelines, the default values of CH4 correction factor (MCF) and fraction of CH4 (F) for active aeration landfills are set as 0.4 and 0.5, respectively. However, whether it is reasonable to apply the default values of MCF and F to active aeration landfills is questionable. This study aims to estimate the MCF and develop a method to determine the F value for active aeration landfills. In this investigation, three landfill sites were operated as active aeration landfills to estimate the MCF and the F. The study results indicate that MCF values were lower than the default value of 0.4 provided in the IPCC guidelines under aerobic conditions with a CH4 concentration of less than 5%. According to the carbon balance analyses, there was a mismatch between the theoretical CH4/CO2 ratio based on the F default value of 0.5 and the measured CH4/CO2 ratio. Using the F calculation method proposed in this study, the theoretical CH4/CO2 ratio and the measured CH4/CO2 ratio was calculated equally. The F values during air injection ranged from 0.25 to 0.93 at three landfill sites, suggesting that adapting the F default value of 0.5 for active aeration landfills may lead to significant errors in the estimation of CH4 emissions using the IPCC FOD model.

Alkali-Metal-Intercalated Percolation Network Regulates Self-Assembled Electronic Aromatic Molecules.

In the continuously growing field of correlated electronic molecular crystals, there is significant interest in addressing alkali-metal-intercalated aromatic hydrocarbons, in which the possibility of high-temperature superconductivity emerges. However, searching for superconducting aromatic molecular crystals remains elusive due to their small shielding fraction volume. To exploit this potential, a design principle for percolation networks of technologically important film geometry is indispensable. Here the effect of potassium-intercalation is shown on the percolation network in self-assembled aromatic molecular crystals. It is demonstrated that one-dimensional (1D) dipole pairs, induced by dipole interaction, regulate the conductivity, as well as the electronic and optical transitions, in alkali-metal-intercalated molecular electronic crystals. A solid-solution growth methodology of aromatic molecular films with a broad range of stability is developed to uncover electronic and optical transitions of technological importance. The light-induced electron interactions enhance the charge-carrier itinerancy, leading to a switchable metal-to-insulator transition. This discovery opens a route for the development of aromatic molecular electronic solids and long-term modulation of electronic efficacy in nanotechnologically important thin films.

Is Immediate Postoperative Mechanical Axis Associated with the Revision Rate of Primary Total Knee Arthroplasty? A 10-Year Follow-up Study.

BACKGROUND: Achieving neutral limb alignment during total knee arthroplasty (TKA) has been considered an important determinant in the long-term prosthesis survival. The purpose of this study was to evaluate the association between the immediate postoperative mechanical alignment of the lower limb and the rate of revision TKA by comparing an acceptable mechanical axis group (within ± 3° from neutral alignment) and an outlier group (> 3° deviation from neutral alignment). METHODS: Between 2000 and 2006, clinical and radiographic data of 334 primary TKAs were retrospectively reviewed to determine the 10-year Kaplan-Meier survival rate. Patients were divided into acceptable and outlier groups according to the mechanical axis checked postoperatively within a month. Clinical outcomes were assessed using Hospital for Special Surgery, Knee Society Score, and Western Ontario and McMaster Universities Osteoarthritis Index score preoperatively and at the final follow-up. Postoperative complications and revision rates were also evaluated. RESULTS: The mean change in mechanical axis between the immediate postoperative examination and the last follow-up was greater in the outlier group (1.6 ± 2.7) than in the acceptable group (0.8 ± 2.4). The revision rates were significantly different between the two groups (p = 0.04). At the last follow-up, clinical scores were all improved in both groups compared to each preoperative condition. There were no significant differences in clinical scores between the two groups at the last follow-up. The 10-year Kaplan-Meier survival analysis showed a tendency towards better survival with restoration of neutral mechanical axis. However, the difference was not statistically significant (p = 0.25). CONCLUSIONS: Restoration of neutral limb alignment is a factor that can result in a lower revision rate and higher longevity in TKA. However, there were no significant differences in clinical outcomes between the two groups.

Methods for determining the methane generation potential and methane generation rate constant for the FOD model: a review.

In the first order decay (FOD) model of landfill methane generation, the methane generation potential ( L0) and methane generation rate constant ( k) for both bulk municipal solid waste (MSW) and individual waste components have been determined by a variety of approaches throughout various literature. Differences in the determination methods for L0 and k are related to differences in our understanding of the waste decomposition dynamics. A thorough understanding of the various available methods for determining L0 and k values is critical for comparative study and the drawing of valid conclusions. The aim of this paper is to review the literature on the available determining methods and the ranges for L0 and k values of both bulk MSW and individual waste components, while focusing on understanding the decomposition of waste, including the role of lignin. L0 estimates in the literature are highly variable and have been derived from theoretical stoichiometric calculations, laboratory experiments, or actual field measurements. The lignin concentration in waste is correlated with the fraction of total degradable organic carbon (DOCf) that will actually anaerobically degrade in the landfill. The k value has been determined by precipitation rates, laboratory simulations, aged-defined waste sample, and model fitting or regression analysis using actual gas data. However, the lignin concentration does not correlate well with the k value, presumably due to the impact of lignin arrangement and structure on cellulose bioavailability and degradation rate. In sum, this review summarizes the literature on the measurement of L0 and k values, including the dynamics and decomposition of bulk MSW and individual waste components within landfills.

Estimation of methane emission flux at landfill surface using laser methane detector: Influence of gauge pressure.

The aim of this study was to investigate the possibility of measuring methane emission fluxes, using surface methane concentration and gauge pressure, by analyzing the influence of gauge pressure on the methane emission flux and the surface methane concentration, as well as the correlation between the methane emission flux and surface methane concentrations. The surface methane concentration was measured using a laser methane detector. Our results show a positive linear relationship between the surface methane concentration and the methane emission flux. Furthermore, the methane emission flux showed a positive linear relationship with the gauge pressure; this implies that when the surface methane concentration and the surface gauge pressure are measured simultaneously, the methane emission flux can be calculated using Darcy's law. A decrease in the vertical permeability was observed when the gauge pressure was increased, because reducing the vertical permeability may lead to a reduced landfill gas emission to the atmosphere, and landfill gas would be accumulated inside the landfill. Finally, this method is simple and can allow for a greater number of measurements during a relatively shorter period. Thus, it provides a better representation of the significant space and time variations in methane emission fluxes.

Acceleration of aged-landfill stabilization by combining partial nitrification and leachate recirculation: a field-scale study.

Leachate recirculation for rapid landfill stabilization can result in the accumulation of high-strength ammonium. An on-site sequencing batch reactor (SBR) was therefore, applied to oxidize the ammonium to nitrite, which was then recirculated to the landfill for denitrification to nitrogen gas. At relatively higher ammonium levels, nitrite accumulated well in the SBR; the nitrite was denitrified stably in the landfill, despite an insufficient biodegradable carbon source in the leachate. As the leachate was recirculated, the methane and carbon dioxide contents produced from the landfill fluctuated, implying that the organic acids and hydrogen produced in the acid production phase acted as the carbon source for denitrification in the landfill. Leachate recirculation combined with ex-situ partial nitrification of the leachate may enhance the biodegradation process by: (a) removing the nitrogen that is contained with the leachate, and (b) accelerating landfill stabilization, because the biodegradation efficiency of landfill waste is increased by supplying sufficient moisture and its byproducts are used as the carbon source for denitrification. In addition, partial nitrification using an SBR has advantages for complete denitrification in the landfill, since the available carbon source is in short supply in aged landfills.

Loss of heterozygosity of tumor suppressor genes (p16, Rb, E-cadherin, p53) in hypopharynx squamous cell carcinoma.

OBJECTIVE: Microsatellite alterations, especially those that cause loss of heterozygosity (LOH), have recently been postulated as a novel mechanism of carcinogenesis and a useful prognostic factor in many kinds of malignant tumors. However, few studies have focused on a specific site, hypopharynx. The aim of this study was to evaluate the relationship between LOH and hypopharyngeal squamous cell carcinoma (HPSCC). STUDY DESIGN: Laboratory-based study. SETTING: Integrated health care system. SUBJECTS AND METHODS: Matched normal and cancerous tissues from 30 patients with HPSCC were examined for LOH in 4 tumor suppressor genes (TSGs) (p16, Rb, E-cadherin, and p53) at loci 9p21, 13q21, 6q22, and 17p13, respectively, using microsatellite markers amplified by polymerase chain reaction. The results for each loci were compared with clinicopathological features. RESULTS: Among the 30 cases, 26 (86.7%) exhibited LOH, with the most common alteration being LOH at p53 (52.6%). Significantly higher rates of LOH detection were seen in Rb, p53, and the LOH-high group (cases where 2 or more loci with LOH were found) in cases of lymph node metastasis. Compared with stage I and II carcinoma, tumors of stages III and IV had significantly higher frequencies of LOH in Rb, p53, and the LOH-high group. However, the presence of LOH was not significantly correlated with survival. CONCLUSION: These results suggest that LOH in TSGs such as Rb and p53 may contribute to the development and progression of HPSCC. The presence of LOH in the primary tumor may also be predictive of lymph node metastasis.

Comparison of clinical characteristics between primary and secondary paranasal mucoceles.

PURPOSE: Paranasal sinus mucocele is a benign, expansile mass which can occur as a result of trauma or spontaneous obstruction of a sinus tract. The purpose of this study was to describe and compare the clinical characteristics of primary mucoceles occurring in patients with no previous sinus surgery history or known cause of mucoceles and secondary mucoceles resulting as a complication following endoscopic sinus surgery or the Caldwell-Luc operation. MATERIALS AND METHODS: We performed a retrospective chart review of 33 cases of primary mucoceles and 60 cases of secondary mucoceles which were diagnosed and surgically corrected between 1996 and 2008. RESULTS: The most common presenting symptoms in primary mucoceles were nasal obstruction (19.4%) and rhinorrhea (17.7%). In secondary mucoceles, the most common symptoms were cheek pain (31.7%) and nasal obstruction (18.3%). The most common origins of primary mucoceles were the ethmoid sinus (45.5%) and the maxillary sinus (18.2%). In secondary mucoceles, the maxillary sinus was the most common site (86%), followed by the ethmoid sinus (7.1%). All patients with secondary mucoceles had a history of sinus surgery. CONCLUSION: The maxillary sinus was the most common site of secondary mucoceles while the ethmoid sinus was the most common origin of primary mucoceles. Cases of secondary mucoceles that occurred following sinus endoscopic surgery developed more frequently in the ethmoid sinus than in those following the Caldwell-Luc procedure, therefore, we suggest that the incidence of maxillary sinus mucoceles in the Asian population would decrease as the rate of endoscopic sinus surgery increases.