M Christophersen | PubMed Health

PubMed2004

Macroporous silicon electrical sensor for DNA hybridization detection.

Macroporous silicon (pore diameter 1-2 microm) was used in an electrical sensor for real time, label free detection of DNA hybridization. Electrical contacts were made exclusively on the back side of the substrate, which allowed complete exposure of the porous layer to DNA. Hybridization of a DNA probe with its complementary sequence produced a reduction in the impedance and a shift in the phase angle resulting from a change in dielectric constant inside the porous matrix and a modification of the depletion layer width in the crystalline silicon structure. The effect of the DNA charge on the response was corroborated using peptide nucleic acid (PNA), an uncharged analog of DNA. The sensitivity and selectivity of the device were characterized and the sensing properties of the porous layer alone were investigated using self-supporting macroporous silicon membranes.

Absorption↗

PubMed2001

Lateral gas transport in soil adjacent to an old landfill: factors governing emissions and methane oxidation.

Field investigations of lateral gas transport and subsequent emissions in soil adjacent to an old landfill in Denmark were conducted during a 1-year period. A significant seasonal variation in the emissions with high carbon dioxide and low methane fluxes in the summer (May to October) was observed. This was attributed to methane oxidation. Diurnal measurements during a drop in barometric pressure showed that the fluxes of landfill gas changed dramatically within a very short time. The concentrations and the soil moisture content in the upper part of the soil profile had significant influence on the fluxes, as did the distance from the landfill border, temperature, barometric pressure and the pressure gradient. Statistical analyses proved that soil moisture described the largest part of the variation. No methane is emitted during the summer. Calculations and isotope analyses showed that very high fractions of the laterally migrating methane were oxidised.

Air Movements↗

PubMed2001

Lateral gas transport in soil adjacent to an old landfill: factors governing gas migration.

Field experiments investigating lateral gas transport in soil adjacent to an old landfill in Denmark during a one-year period were conducted. A significant seasonal variation, with low concentrations of methane and high concentrations of carbon dioxide in the summer, caused by methane oxidation was observed. There was a good correlation between pressure above the barometric pressure and the methane concentration in the soil, indicating that advective flow was the controlling process. This was confirmed by calculations. Diurnal measurement during a drop in barometric pressure showed that lateral migration of landfill gas was a very dynamic system and the concentrations of LFG at a specific place and depth changed dramatically within a very short time. The experiments showed that change in barometric pressure was an important factor affecting gas migration at the Skellingsted landfill in Denmark.

Air Movements↗

PubMed2001

Composition of leachate from old landfills in Denmark.

The Danish counties have performed numerous investigations of old landfills. These investigations have been presented in several reports, but no comprehensive summary of the findings has been carried out. The objective of this study was to evaluate the typical composition of leachates from old smaller landfills by a comprehensive review of the investigations carried out by the counties. In total 106 landfills were selected by criteria avoiding dilution effects. A database was constructed using a standard program. Statistical evaluations showed that the leachate concentrations in general decreased with the age of the landfill, and that the leachate concentrations were lower than found in other similar studies.

Databases, Factual↗

PubMed2001

Lateral gas transport in soil adjacent to an old landfill: factors governing gas migration.

Field experiments investigating lateral gas transport in soil adjacent to an old landfill in Denmark during a one-year period were conducted. A significant seasonal variation, with low concentrations of methane and high concentrations of carbon dioxide in the summer, caused by methane oxidation was observed. There was a good correlation between pressure above the barometric pressure and the methane concentration in the soil, indicating that advective flow was the controlling process. This was confirmed by calculations. Diurnal measurement during a drop in barometric pressure showed that lateral migration of landfill gas was a very dynamic system and the concentrations of LFG at a specific place and depth changed dramatically within a very short time. The experiments showed that change in barometric pressure was an important factor affecting gas migration at the Skellingsted landfill in Denmark.

Atmospheric Pressure↗

PubMed2001

Lateral gas transport in soil adjacent to an old landfill: factors governing emissions and methane oxidation.

Field investigations of lateral gas transport and subsequent emissions in soil adjacent to an old landfill in Denmark have been conducted during a one-year period. A significant seasonal variation in the emissions with high carbon dioxide and low methane fluxes in the summer (May to October) was observed. This was attributed to methane oxidation. Diumal measurements during a drop in barometric pressure showed that the fluxes of landfill gas changed dramatically within a very short time. The concentrations and the soil moisture content in the upper part of the soil profile had significant influence on the fluxes, as did the distance from the landfill border, temperature, barometric pressure and the pressure gradient. Statistical analyses proved that soil moisture described the largest part of the variation. No methane at all emitted during the summer. Calculations and isotope analyses showed that very high fractions of the laterally migrating methane were oxidised.

Atmospheric Pressure↗

PubMed2000

MnSOD expression is increased in metastatic gastric cancer.

BACKGROUND: Manganese superoxide dismutase (MnSOD) catalyzes the scavenging of superoxide radicals in order to protect cells from the damage caused by reactive oxygen species. Previous studies implicate MnSOD in cancer progression, but its role in gastric cancer metastasis is poorly understood. MATERIALS AND METHODS: To determine whether MnSOD expression correlates with gastric cancer metastasis, we compared immunostaining for MnSOD in the primary tumors of gastric cancer patients with (n = 15) and without (n = 9) nodal metastases. These patients were matched for risk factors associated with gastric cancer metastasis, such as tumor site, depth, and grade. MnSOD expression was scored positive (increased) if MnSOD staining of tumor cells was more intense than MnSOD staining in corresponding normal gastric epithelial cells. Statistical analyses were via chi(2) test and Fisher's exact test. RESULTS: MnSOD expression was increased in 14 of the 15 (93%) metastatic tumors, compared to only 4 of the 9 (44%) nonmetastatic tumors (P = 0.015). There was no significant difference in staining when the two groups were compared based on tumor grade (P = 0.70) or depth of tumor cell invasion (T stage) (P = 0.22). CONCLUSIONS: MnSOD expression is upregulated in the primary tumors of gastric cancer patients with lymph node metastases. This finding supports an involvement of MnSOD and possibly the reactive oxygen status of the gastric tumor microenvironment in gastric cancer metastasis.

Adult↗