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Biomedical subjects

David R Nielsen

Publications and source records attributed to David R Nielsen.

9 recordsLinked to original sources
PubMed2006

Otitis externa: Review and clinical update.

Otitis externa can take an acute or a chronic form, with the acute form affecting four in 1,000 persons annually and the chronic form affecting 3 to 5 percent of the population. Acute disease commonly results from bacterial (90 percent of cases) or fungal (10 percent of cases) overgrowth in an ear canal subjected to excess moisture or to local trauma. Chronic disease often is part of a more generalized dermatologic or allergic problem. Symptoms of early acute and most chronic disease include pruritus and local discomfort. If left untreated, acute disease can be followed by canal edema, discharge, and pain, and eventually by extra-canal manifestations. Topical application of an acidifying solution is usually adequate in treating early disease. An antimicrobial-containing ototopical is the preferred treatment for later-stage acute disease, and oral antibiotic therapy is reserved for advanced disease or those who are immunocompromised. Preventive measures reduce recurrences and typically involve minimizing ear canal moisture, trauma, or exposure to materials that incite local irritation or contact dermatitis.

Acetic Acid↗
PubMed2006

Benzene vapor treatment using a two-phase partitioning bioscrubber: an improved steady-state protocol to enhance long-term operation.

The performance and stability of a two-phase partitioning bioscrubber (TPPB) containing 33% (vol.) n-hexadecane as an immiscible phase was investigated during 30 days of continuous gaseous benzene treatment. Elimination capacities of 141 +/- 12 g/m(3) h were achieved by Achromobacter xylosoxidans Y234 while maintaining >99% removal throughout. A new steady-state operating strategy that limits excessive biomass production by directing substrate consumption to maintenance energy has eliminated the requirement for frequent exchange of liquid contents. Simplifying the operating protocols in this manner has dramatically reduced material costs and rendered the TPPB operational requirements as more comparable (in terms of frequency of required operator inputs) with other vapor-phase bioreactors. The practicality of the proposed simplification to the operating protocol was confirmed by demonstrating that intermediate metabolites were not accumulating in the TPPB, inorganic nutrient requirements were readily predictable, and that high culture viability could be sustained for prolonged cell retention times (30 days).

Achromobacter denitrificans↗
PubMed2006

Direct estimation of the oxygen requirements of Achromobacter xylosoxidans for aerobic degradation of monoaromatic hydrocarbons (BTEX) in a bioscrubber.

The O2 requirements for biomass production and supplying maintenance energy demands during the degradation of both benzene and ethylbenzene by Achromobacter xylosoxidans Y234 were measured using a newly proposed technique involving a bioscrubber. Using this approach, relevant microbial parameter estimates were directly and simultaneously obtained via linear regression of pseudo steady-state data. For benzene and ethylbenzene, the biomass yield on O2, Y(X/O2), was estimated on a cell dry weight (CDW) basis as 1.96 +/- 0.25 mg CDW mgO2(-1) and 0.98 +/- 0.17 mg CDW mgO2(-1), while the specific rate of O2 consumption for maintenance, m(O2), was estimated as 0.041 +/- 0.008 mgO(2) mg CDW(-1) h(-1) and 0.053 +/- 0.022 mgO(2) mg CDW(-1) h(-1), respectively.

Achromobacter↗
PubMed2005

Transient performance of a two-phase partitioning bioscrubber treating a benzene-contaminated gas stream.

The dynamic performance of a prototype, two-phase partitioning bioscrubber in response to fluctuating benzene waste gas feeds has been characterized through a series of spike, step, and shutdown-restart experiments. From stable operation at a nominal loading capacity of 62 +/- 6 g/(m3 h) and removal efficiencies of over 99%, the bioscrubber was subjected to influent benzene concentration step changes and spikes as high as 10- and 20-fold, respectively. The bioscrubber responded rapidly and effectively to all feed concentration spikes and steps, as well as to step changes in the feed flow rate, maintaining nearly undisturbed performance. Although benzene absorption by the two liquid phases was found to dominate the early stages of each transient, Achromobacter xylosoxidans Y234 responded quickly to prolonged disturbances, readily consuming most of the excess absorbed substrate. The results demonstrate that the two-phase partitioning bioscrubber can rapidly acclimate to and recover from fluctuations, ensuring that stable performance can be maintained both during and aftertransients. The presence of n-hexadecane promotes benzene capture in the two-phase system by increasing the absorption driving force, an important characteristic during high intermittent loadings. Rapid recovery from two different shutdown scenarios further demonstrates the practical potential of the two-phase partitioning bioscrubber as a high-performance biotechnology alternative for the treatment of toxic waste gases.

Achromobacter↗
PubMed2005

A restructured framework for modeling oxygen transfer in two-phase partitioning bioreactors.

This communication proposes a mechanistic modification to a recently published method for analyzing oxygen mass transfer in two-phase partitioning bioreactors (Nielsen et al., 2003), and corrects an oversight in that paper. The newly proposed modification replaces the earlier empirical approach, which treated the two liquid phases as a single, homogeneous liquid phase, with a two-phase mass transfer model of greater fundamental rigor. Additionally, newly developed empirical models are presented that predict the mass transfer coefficient of oxygen absorption in both aqueous medium and an organic phase (n-hexadecane) as a function of bioreactor operating conditions. Experimental values and theoretical predictions of mass transfer coefficients in two-phase dispersions, k(L)a(TP), are compared. The revised approach more clearly demonstrates the potential for oxygen mass transfer enhancement by organic phase addition, one of the motivations for employing a distinct second phase in a partitioning bioreactor.

Absorption↗
PubMed2005

Quantifying maintenance requirements from the steady-state operation of a two-phase partitioning bioscrubber.

An innovative method for directly and explicitly quantifying the maintenance energy requirements of pure cultures growing on volatile organic compound (VOC) substrates in a two-phase partitioning bioscrubber is described. Direct evidence of maintenance energy requirements of Achromobacter xylosoxidans Y234 is provided both through observed reductions in the macroscopic biomass-to-substrate yield with decreasing specific growth rates, but more remarkably through achievement of steady-state operation. The data conclusively show that maintenance activities do occur in the two-phase partitioning bioscrubber and clearly illustrate the importance of this phenomenon to the operation of this process, and similar bioreactor systems. While benzene was selected as the principal, sole substrate of interest in this study, ethylbenzene degradation experiments were also subsequently performed to illustrate and confirm the general applicability of the proposed technique, as well as the potential capabilities of the two-phase partitioning bioscrubber for the continuous treatment of waste gases containing various VOCs. The proposed method has been shown to generate maintenance energy estimates that are consistent with those obtained while employing more widely recognized estimation strategies, further validating its capabilities. The proposed steady-state mode also offers key operational advantages in terms of decreased disposal requirements in two-phase partitioning bioscrubbers. (c) 2005 Wiley Periodicals, Inc.

Achromobacter denitrificans↗
PubMed2003

A novel method of simulating oxygen mass transfer in two-phase partitioning bioreactors.

An empirical correlation, based on conventional forms, has been developed to represent the oxygen mass transfer coefficient as a function of operating conditions and organic fraction in two-phase, aqueous-organic dispersions. Such dispersions are characteristic of two-phase partitioning bioreactors, which have found increasing application for the biodegradation of toxic substrates. In this work, a critical distinction is made between the oxygen mass transfer coefficient, k(L)a, and the oxygen mass transfer rate. With an increasing organic fraction, the mass transfer coefficient decreases, whereas the oxygen transfer rate is predicted to increase to an optimal value. Use of the correlation assumes that the two-phase dispersion behaves as a single homogeneous phase with physical properties equivalent to the weighted volume-averaged values of the phases. The addition of a second, immiscible liquid phase with a high solubility of oxygen to an aqueous medium increases the oxygen solubility of the system. It is the increase in oxygen solubility that provides the potential for oxygen mass transfer rate enhancement. For the case studied in which n-hexadecane is selected as the second liquid phase, additions of up to 33% organic volume lead to significant increases in oxygen mass transfer rate, with an optimal increase of 58.5% predicted using a 27% organic phase volume. For this system, the predicted oxygen mass transfer enhancements due to organic-phase addition are found to be insensitive to the other operating variables, suggesting that organic-phase addition is always a viable option for oxygen mass transfer rate enhancement.

Bioreactors↗
PubMed2003

A biochemical analysis demonstrates that the BRCA1 intronic variant IVS10-2A--> C is a mutation.

Sequence analysis of cDNA from an asymptomatic patient belonging to a high-risk breast cancer family carrying the genetic variant BRCA1 IVS10-2A-->C revealed that functional BRCA1 mRNA was derived from only one of the patient's chromosomes. The other chromosome produced an aberrant RNA splicing transcript that deleted exon 11. Analysis of the patient's genomic DNA demonstrated that the chromosome producing the non-functional mRNA carried the genotype BRCA1 IVS10-2A-->C. This transversion disrupts a highly conserved base in the consensus splice acceptor motif. These results support the conclusion that BRCA1 IVS10-2A-->C is a mutation that confers predisposition to breast and ovarian cancer.

Adult↗