Kinetics and mechanisms for reactions of Fe(II) with iron(III) oxides

Uptake of Fe(II) onto hematite (alpha-Fe2O3), corundum (alpha-Al2O3), amorphous ferric oxide (AFO), and a mixture of hematite and AFO was measured. Uptake was operationally divided into adsorption (extractable by 0.5 N HCl within 20 h) and fixation (extractable by 3.0 N HCl within 7 d). For 0.25 mM Fe(II) onto 25 mM iron(III) hematite at pH 6.8: (i) 10% of Fe(II) was adsorbed within 1 min; (ii) 20% of Fe(II) was adsorbed within 1 d; (iii) uptake slowly increased to 24% of Fe(II) during the next 24 d, almost all adsorbed; (iv) at 30 d, the uptake increased to 28% of Fe(II) with 6% of total Fe(II) fixed; and (v) uptake slowly increased to 30% of Fe(II) by 45 d with 10% of total Fe(II) fixed. Similar results were observed for 0.125 mM Fe(II) onto 25 mM iron(III) hematite, except that percent of adsorption and fixation were increased. There was adsorption but no fixation for 0.25 mM Fe(II) onto corundum [196.2 mM Al(III)] at pH 6.8, for 0.125 mM Fe(II) onto 25 mM iron(III) hematite at pH 4.5, and for 0.25 mM Zn(II) onto 25 mM iron(III) hematite at pH 6.8. A small addition of AFO to the hematite suspension increased Fe(II) fixation when 0.25 mM Fe(II) was reacted with 25 mM iron(III) hematite and 0.025 mM Fe(III) AFO at pH 6.8. Reaction of 0.125 mM Fe(II) with 2.5 mM Fe(III) AFO resulted in rapid adsorption of 30% of added Fe(II), followed by conversion of AFO to goethite and a decrease in adsorption without Fe(II) fixation. The fixation of Fe(II) by hematite at pH 6.8 is consistent with interfacial electron transfer and the formation of new mineral phases. We propose that electron transfer from adsorbed Fe(II) to structural Fe(III) in hematite results in oxidation of Fe(II) to AFO on the surface of hematite and that solid-phase contact among hematite, AFO, and structural Fe(II) produces magnetite (Fe3O4). The unique interactions of Fe(II) with iron(III) oxides would be environmentally important to understand the fate of redox-sensitive chemicals.     

Design criteria for nanostructured Li-ion batteries

Extensive experimental research has indicated that active/inactive nanocomposites are promising electrode materials for rechargeable Li-ion batteries. Nanocomposite anode materials allow for capacities between 900 and 4000 mAh g⁻¹ whereas graphitic anodes, which are currently being used by industry, allow for a much lower capacity of 372 mAh g⁻¹. By treating the active sites (which may be comprised of Si, Sn, Al, or Bi) as nanospheres embedded in an inert matrix, linear elastic fracture mechanics are employed in order to develop design criteria for these alternative battery systems, with respect to fracture that results from the large volume expansions that the active sites undergo upon Li-insertion. In particular, the present study: (i) predicts that smaller active site volume fractions are more stable; (ii) Griffith's criterion is used to estimate the crack radius at which cracking will stop; (iii) based on the ultimate tensile strength of the inactive matrix the critical crack length at which the electrode will fracture is calculated; (iv) a theoretical estimation is made for the size of the active sites that will not allow cracks to develop and hence fracture of the electrode will be prevented. Based on the above analysis, Si active sites allow for a greater anode lifetime and therefore are preferred over Sn, furthermore the formulation can be applied to determine the most appropriate matrix materials.     

Microbial reduction of U(VI) at the solid-water interface

Microbial (Geobacter sulfurreducens) reduction of 0.1 mM U(VI) in the presence of synthetic Fe(III) oxides and natural Fe(III) oxide-containing solids was investigated in pH 6.8 artificial groundwater containing 10 mM NaHCO3. In most experiments, more than 95% of added U(VI) was sorbed to solids, so that U(VI) reduction was governed by reactions at the solid-water interface. The rate and extent of reduction of U(VI) associated with surfaces of synthetic Fe(III) oxides (hydrous ferric oxide, goethite, and hematite) was comparable to that observed during reduction of aqueous U(VI). In contrast, microbial reduction of U(VI) sorbed to several different natural Fe(III) oxide-containing solids was slower and less extensive compared to synthetic Fe(III) oxide systems. Addition of the electron shuttling agent anthraquinone-2,6-disulfonate (AQDS; 0.1 mM) enhanced the rate and extent of both Fe(III) and U(VI) reduction. These findings suggest that AQDS facilitated electron transfer from G. sulfurreducens to U(VI) associated with surface sites atwhich direct enzymatic reduction was kinetically limited. Our results demonstrate that association of U(VI) with diverse surface sites in natural soils and sediments has the potential to limit the rate and extent of microbial U(VI) reduction and thereby modulate the effectiveness of in situ U(VI) bioremediation.     

Smooth muscle cells isolated from discrete compartments of the mature vascular media exhibit unique phenotypes and distinct growth capabilities

Heterogeneity of smooth muscle cell (SMC) phenotype and function is rapidly emerging as an important concept. We have recently described that phenotypically distinct SMC subpopulations in bovine pulmonary arteries exhibit unique proliferative and matrix-producing responses to hypoxic pulmonary hypertension. To provide better understanding of the molecular mechanisms contributing to this phenomenon, experimental studies will require a reliable in vitro model. The purpose of the present study was first to determine if distinct SMC subpopulations, similar to those observed in vivo, could be selectively isolated from the mature arterial media, and then to evaluate whether select SMC subpopulations would exhibit heightened responses to growth-promoting stimuli and hypoxia. We were able to reproducibly isolate at least four phenotypically unique cell subpopulations from the inner, middle, and outer compartments of the arterial media. Differences in cell phenotype were demonstrated by morphological appearance and differential expression of muscle-specific proteins. The isolated cell subpopulations exhibited markedly different growth capabilities. Two SMC subpopulations grew slowly in 10% serum and were quiescent in plasma-based medium. The other two cell subpopulations, exhibiting nonmuscle characteristics, grew rapidly in 10% serum and proliferated in plasma-based medium and in response to hypoxia. Certain colonies of the nonmuscle-like cell subpopulations were found to grow autonomously under serum-deprived conditions and to secrete mitogenic factors. Our data, demonstrating that phenotypically distinct cells with enhanced growth potential exist within the normal arterial media, support the idea that these unique cells could contribute selectively to the pathogenesis of vascular disease.     

Field-Scale In-Situ Compliance of Arctic First-Year Sea Ice

This paper presents the experimental results and analysis of the creep recovery and cyclic loading crack-opening-displacement measurements recorded on level first-year sea ice at Barrow, Alaska. This was the third of a three-trip program to track the seasonal evolution of the mechanical and physical properties of first-year S2 sea ice. Seven large-scale in-situ experiments were completed covering a size range of 1:30 with the largest test having dimensions of 30 m × 30 m. The creep recovery response from the largest test specimen is examined in this paper to determine the compliance of a precracked square-plate test geometry via a nonlinear viscoelastic∕viscoplastic formulation. This model is then applied to the cyclic loading, and a monotonic ramp to fracture, to quantify its ability to predict the behavior for a variety of loading paths.     

Characterization of a B cell progenitor present in neonatal bone marrow and spleen but not in adult bone marrow and spleen

The neonatal period marks an important time in mammalian immunologic development, yet it is often ignored in studies of lymphocyte development. We identified a cell population with the phenotype heat stable Ag (HSA)low lin- CD43low that contained B cell progenitors at a high frequency in the neonatal bone marrow and spleen. Although cells with a similar phenotype can be identified in the bone marrow and spleen of adult animals, these populations showed a greatly reduced frequency of B cell progenitors. B lineage cells were detected after 7 days in culture at a frequency of 1:15 when HSAlow lin- CD43low cells from neonatal bone marrow were cultured on stromal cells and IL-7 under limiting dilution conditions. Under similar conditions, the equivalent population in adult bone marrow had a frequency of B cell progenitors that was less than 1:2000. The expression of terminal deoxynucleotidyl transferase in freshly sorted neonatal HSAlow lin- CD43low cells suggested that cells committed to the lymphocyte lineage were present in this population. These data suggested that the HSAlow lin- CD43low population of cells represents a pool of B lineage precursors that may be responsible for filling the immune compartment early in neonatal life.     

Developing explicit risk models for predicting low-back disability: A statistical perspective

Despite extensive research efforts, disability due to work-related low-back disorders continues to pose a significant economic burden to industry, and significant pain and economic loss to workers. Numerous epidemiological studies have been conducted, but many of these studies have resulted in qualitative guidelines rather than explicit quantitative guidelines. Furthermore, there is considerable disagreement and controversy concerning the validity of manual materials handling criteria based on biomechanical, physiological, and psychophysical theory and research. There is a pressing need for epidemiological field evaluation of such criteria, as well as epidemiologically-based models that provide estimates of low-back disability risk given a set of task, workplace and worker characteristics. A critical tool in such investigations is the statistical method chosen to model risk. The statistical appropriateness of previously used methods are reviewed and critiqued. A fairly comprehensive discussion of the statistical models available for modeling disability risk is then presented, with a focus on models that provide explicit estimates of risk. Recent advances in computer speed have significantly advanced the power and flexibility of statistical modeling techniques. These techniques have the potential to provide considerable insight into the etiology of low-back disability and to provide explicit quantitative design criteria for the ergonomics practitioner.Relevance to industryStatistical methods available for modeling the risk of low-back disability are discussed and previous methodologies used are critiqued. The methods discussed will aid researchers conducting epidemiological studies of low-back disorders in industry, and the discussion of these methods will aid practitioners faced with interpreting results of previous studies.     

The transthoracic impedance cardiogram is a potential haemodynamic sensor for an automated external defibrillator

AIMS: The American Heart Association has endorsed the concept of Public Access Defibrillation. However, there have been reports of inappropriate direct current shocks from automatic external defibrillators. The specificity of automatic external defibrillators for shockable rhythms may be improved by the incorporation of a haemodynamic sensor. METHODS AND RESULTS: This study examined the use of four parameters extracted from the impedance cardiogram i.e. Peak dz/dt (the peak of the impedance cardiogram measured from the line dz/dt=0 ohms(-1)), Peak-trough (the peak-to-trough measurement of the impedance cardiogram ohms(-1)), Area 1 (the area under the C wave of the impedance cardiogram above the line dz/dt=0 mohm) and Area 2 (the area under the impedance cardiogram 50 ms on either side of the Peak and above the line dz/dt=0 mohm) as predictors of cardiac output. At 116 cardiac arrest calls the ECG and impedance cardiogram were recorded through two ECG/defibrillator pads placed in an antero-apical position. Nine recordings were rejected for artefact. The rhythm recorded in the remaining 107 calls was asystole (19), ventricular fibrillation (14), agonal rhythm (20), electromechanical dissociation (22), ventricular tachycardia (27) and sinus rhythm (5). These rhythms were divided into those associated with haemodynamic collapse i.e. no pulse -- asystole, ventricular fibrillation, agonal rhythm, electromechanical dissociation and shockable ventricular tachycardia (associated with loss of consciousness, pulselessness or a systolic blood pressure of <80 mmHg) (Group 1) and those associated with a satisfactory cardiac output i.e. non-shockable ventricular tachycardia (conscious with a pulse) and sinus rhythm (Group 2). On univariate analysis each of the four impedance cardiogram parameters were significantly greater in Group 2 than Group 1 (P<0.001). On multivariate analysis the parameters which best differentiated the two groups were Area 1 and Peak-trough. CONCLUSION: Thus the impedance cardiogram is a potential haemodynamic sensor for an automatic external defibrillator.     

Integrating a performance-based approach into practice: a case study

Organizations in both the public and private sectors are increasingly focusing on performance and results, on outcomes rather than on outputs, or on the ends rather than the means to accomplish their mission(s). In the US, the federal government actually embedded this focus in the Government Performance and Results Act, 1993. Since then, US federal government agencies have been in the process of a major shift in their management procedures. The paper illustrates how the US Coast Guard (USCG) is implementing these procedures. USCG missions are clearly defined in 'legal authorities' by the US Congress. These missions in turn are also responding to external public and industry drivers and trends. The USCG is highly dependent on its logistical assets to support its operational units and accomplish its missions. Therefore, the Civil Engineering Program, which is that part of the organization responsible for the most stable and long-lasting assets, namely constructed assets, has been commissioned to create and implement a far-reaching Shore Facility Capital Asset Management system, including Regional Strategic Plans. The design of this integrated system is part of a Framework for Integrated Decision-Making for the USCG as a whole. It is performance based and results oriented. It includes metrics that will allow the USCG to measure objectively and transparently how it performs against the requirements of its missions and strategic goals. All parts of this integrated system are presented, with emphasis on the suitability metrics that most directly link assets to missions.     

LEFM size requirements for the fracture testing of sea ice

The stress-separation curve obtained for the in-situ response of first-year sea ice is used to obtain specimen size requirements for sea ice fracture tests. Issues of notch sensitivity and minimum size requirements for the applicability of linear elastic fracture mechanics are addressed. The role of time dependent deformations in studying sea ice fracture is examined.