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M J Beck

Publications and source records attributed to M J Beck.

11 recordsLinked to original sources
PubMed2006

Orientation dependence of strained-Ge surface energies near (001): role of dimer-vacancy lines and their interactions with steps.

Recent experiments and calculations have highlighted the important role of surface-energy (gamma) anisotropy in governing island formation in the Ge/Si(001) system. To further elucidate the factors determining this anisotropy, we perform atomistic and continuum calculations of the orientation dependence of gamma for strained-Ge surfaces near (001), accounting for the presence of dimer-vacancy lines (DVLs). The net effect of DVLs is found to be a substantial reduction in the magnitude of the slope of gamma vs orientation angle, relative to the highly negative value derived for non-DVL, dimer-reconstructed, strained-Ge(001) surfaces. The present results thus point to an important role of DVLs in stabilizing the (001) surface orientation of a strained-Ge wetting layer.

Journal Article↗
PubMed2005

Role of strain-dependent surface energies in Ge/Si(100) island formation.

Formation energies for Ge/Si(100) pyramidal islands are computed combining continuum calculations of strain energy with first-principles-computed strain-dependent surface energies. The strain dependence of surface energy is critically impacted by the presence of strain-induced changes in the Ge {100} surface reconstruction. The appreciable strain dependencies of rebonded-step {105} and dimer-vacancy-line-reconstructed {100} surface energies are estimated to give rise to a significant reduction in the surface contribution to island formation energies.

Journal Article↗
PubMed2001

Manganese species migration in soil at the Sabine National Wildlife Refuge, Louisiana.

A modified sequential extraction procedure was employed to speciate the chemical forms of Mn in sediment using flame atomic absorption spectrophotometry. Concentrations were determined in five different fractions for each sample (Mn in the exchangeable form, bound to carbonates, bound to Mn/Fe oxides, bound to organic matter and in the residual form). The determinations were made for sediments obtained from the Sabine National Wildlife Refuge while a marshland reclamation project was being conducted. Sediment samples were taken from Ship Channel dredge spoils (thought to be contaminated), an old reclamation site, a new reclamation site and a reference site. The results indicated that the Ship Channel sediments were not contaminated, but revealed an Mn "pumping" model, which proposes that additional Mn added to a similar site is concentrated near the surface soil layers by environmental conditions, which may be a cause of the observed slow recovery of vegetation at one of the more recently developed sites.

Conservation of Natural Resources↗
PubMed2001

Spatial glutathione and cysteine distribution and chemical modulation in the early organogenesis-stage rat conceptus in utero.

Glutathione (GSH), cysteine, and other low-molecular-weight thiols (LMWT) play a vital role in the detoxication of xenobiotics and endogenous chemicals. Differential alterations of LMWT status in various cell types of the developing embryo may underlie cell-specific sensitivity or resistance to xenobiotics and contribute to embryotoxicity. This study describes the spatial and temporal distribution of LMWTs in rat conceptuses and alterations produced by the non-teratogenic GSH modulator, acetaminophen (APAP). Pregnant female rats were given 125, 250, or 500 mg/kg APAP (po) on gestational day 9. Conceptal LMWT was localized histochemically using mercury orange in cryosections, and GSH and cysteine concentrations were measured by HPLC analysis. Mercury orange histofluorescence revealed a non-uniform distribution of LMWT in untreated conceptal tissues, with strongest staining observed in the ectoplacental cone (EPC), visceral yolk sac (VYS), and embryonic heart. Less intense staining was observed in the neuroepithelium. Following treatment with APAP, tissue-associated LMWT decreased dramatically except in the EPC, while exocoelomic fluid LMWT, and LMWT within embryonic lumens, increased. Exposure to 250 mg/kg APAP decreased embryonic GSH after 6 and 24 h by 46% and 38%, respectively. Acetaminophen (500 mg/kg) decreased embryonic and VYS cysteine content by 54% and 83%, respectively, after 24 h. Acetaminophen alters the spatial distribution of LMWT in rat conceptuses, particularly with respect to cysteine. The mobilization of cysteine following chemical insult may influence the ability of conceptal cells to maintain normal GSH status due to reduced availability of cysteine for de novo GSH synthesis.

Acetaminophen↗
PubMed2000

Comparison of in vitro and in utero ethanol exposure on indices of oxidative stress.

Prenatal ethanol exposure produces neural tube defects and growth retardation in experimental animals. Because ethanol's teratogenic effects may involve oxidative stress and effects may differ in vitro and in utero, glutathione, cysteine and ATP were evaluated in gestational day 10 rat conceptuses exposed to ethanol. Cultured embryos exposed to ethanol (1.5 or 3.0 mg/mL) maintained a concentration-dependent decrease in glutathione of 21 or 35%, respectively, at 6 h; visceral yolk sac (VYS) glutathione (GSH) decreased by 22 or 18%, respectively, at 3 h. Maternal ethanol exposure (4.5 g/kg) decreased glutathione by 30% in embryos and VYSs at 3 h, but values rebounded. Cultured embryonic cysteine decreased after 30 min by 42% with both doses and after 6 h by 32 or 38% with 1.5 or 3.0 mg/mL, respectively. Ethanol (1.5 mg/mL) increased VYS cysteine by 35% after 30 min. In utero ethanol exposure decreased embryonic cysteine by 58% at 3 h. Ethanol (1.5 mg/mL) decreased adenosine triphosphate (ATP) by 30-60% in embryos and VYSs at 30 min. After 6 h, embryonic ATP decreased by 41 and 30% with 1.5 and 3.0 mg/mL, respectively, while VYS ATP decreased by 38% with 1.5 mg/mL. In utero ethanol exposure decreased ATP by 31% at 3 h in VYSs. While decreases in GSH and cysteine were evident earlier in utero than in vitro, values returned to control suggesting embryos exposed in utero respond rapidly to chemical-induced oxidative stress due to maternal protective mechanisms. Differences between in vitro and in utero responses to ethanol have important implications for interpretation of in vitro developmental studies.

Administration, Oral↗
PubMed1994

Molecular diagnostics for polychlorinated biphenyl degradation in contaminated soils.

Molecular diagnostic methods using DNA hybridization with specific gene probes are being developed for the monitoring of microbial populations capable of polychlorinated biphenyl (PCB) degradation in contaminated soils. Evaluation of composite samples from contaminated electrical substation soil by gas chromatography (GC) indicated that the PCBs present in the soil (approximately 200 ppm) resulted from contamination with Aroclor 1248. The PCBs have been weathered or degraded so that the lower molecular weight PCB congeners are no longer present. Microbiological and molecular site characterizations are in progress to determine the abundance of PCB degradative organisms and catabolic genes present. Cloned DNA fragments for the bphC gene (2,3-dihydroxybiphenyl dioxygenase) from the biphenyl/chlorobiphenyl degradative pathways of different organisms were used as gene probes to identify indigenous microorganisms with bphC gene sequences. In colony hybridization experiments, positive signals with the pDA251 gene probe were detected in cultures from both contaminated and uncontaminated soils. The degradative abilities of indigenous microorganisms and an added PCB-degradative bacterial strain were also monitored with [14C]4-chlorobiphenyl mineralization assays and gas chromatography of PCB residues extracted from the soils. Enrichment of the contaminated soil with biphenyl and chlorobiphenyls did not stimulate the indigenous microorganisms to degrade the soil PCB. Nevertheless, enrichment of the contaminated soil with biphenyl and chlorobiphenyl and addition of the PCB-degrading strain Alcaligenes eutrophus GG4202 did result in additional degradation of the soil PCB. The results obtained from these experiments should assist in developing and monitoring a remediation plan for these PCB-contaminated soils.

Biodegradation, Environmental↗
PubMed1993

Bioremediating herbicide-contaminated soils.

Combinations of landfarming and biostimulation were evaluated for remediating pesticide wastes. Various amounts of soil contaminated with alachlor and trifluralin (> or = 100 mg/kg each) and metolachlor and atrazine (> or = 20 mg/kg each) were applied to field plots, and sewage sludge or corn meal was incorporated into designated plots. Plots were also treated with fresh spray mixtures in amounts similar to those applied as contaminated soil. Soil bioactivity and dissipation of parent herbicides were monitored after the treatments. During 100 d, soil dehydrogenase activities were highest in organic-material-amended plots. During the same period, the levels of alachlor had declined by 85-95% in amended, contaminated soil-treated plots and by 75-85% in corresponding unamended plots. In freshly sprayed plots, 95-100% of the initial doses of alachlor had dissipated in amended plots, and 85-95% was lost in corresponding unamended plots. The levels of trifluralin had declined by 70-80% in corn-meal-amended plots and by 60-75% in unamended plots. There were no significant differences between dissipation of trifluralin applied as contaminated soil or fresh sprays.

Biodegradation, Environmental↗
PubMed1992

Efficient fermentation of Pinus sp. acid hydrolysates by an ethanologenic strain of Escherichia coli.

Process conditions for the acid hydrolysis of pine hemicellulose and cellulose have been described which provide a biocompatible sugar solution. By using an improved strain of recombinant Escherichia coli, strain KO11, hydrolysates supplemented with yeast extract and tryptone nutrients were converted to ethanol with an efficiency of 85% to over 100% on the basis of monomer sugar content (approximately 72 g/liter) and with the production of 35 g of ethanol per liter in 48 h. In the process described, approximately 347 liters of ethanol could be produced per dry metric ton of lignocellulose.

Cellulose↗
PubMed1991

Antibody detection using pooled sera and a solid phase system.

The purpose of the study was to evaluate the feasibility of substituting the Immucor Capture-R solid phase (SP) antibody detection system for our routine donor antibody screen. Our routine procedure (RP) used a 12-drop pool of six donor sera and one drop of pooled reagent red cells, with 37 degrees C incubation and indirect antiglobulin test readings. The SP system was used according to the manufacturer's directions except that one drop of the pooled sera (rather than an individual serum) was added to each microwell. In parallel tests of 888 donor pools and of 70 stored sera containing known alloantibodies, results with SP were comparable to results with RP. After implementation of SP for donor antibody detection, 1,135 donor pools were tested. Results with SP appeared satisfactory when compared to previous records. We concluded that Immucor Capture-R system can be used for antibody detection using pooled donor sera.

Journal Article↗