Addressing the magnetic properties of sub-monolayers of single-molecule magnets by X-ray magnetic circular dichroism

We report on a comparative study of electronic and magnetic properties of Mn6 single-molecule magnets (SMMs) grafted on gold surface. Two derivatives with spin-ground states S=4 and S=12 have been functionalized with 3-tp-CO2- (3-thiophene carboxylate, tpc) ligands and characterized as thick films (TFs) as well as sub-monolayers (sMLs) by synchrotron based techniques. X-ray absorption spectroscopy at the Mn L2,3 edges shows the modification of the spectral lineshape in the sMLs with respect to the TFs suggesting that the local symmetry at the Mn sites changes once the molecules are deposited on gold surface. In spite of this, the expected MnIII oxidation state is preserved. X-ray magnetic circular dichroism (XMCD) spectra show that the total magnetic moment is only given by spin part because of the quenched orbital moment. Moreover, variable temperature and variable field XMCD spectra reveal an effective decrease of the Mn spin moment for both derivatives.     

PCB dechlorination enhancement in Anacostia River sediment microcosms

In situ treatment of PCB contaminated sediments via microbial dechlorination is a promising alternative to dredging, which may be reserved for only the most contaminated areas. Reductive dechlorination of low levels of weathered PCB mixtures typical of urban environments may occur at slow rates. Here, we report that biostimulation and bioaugmentation enhanced dechlorination of low concentration (2.1 mg PCBs/kg dry weight) historical PCBs in microcosms prepared with Anacostia River, Washington, DC, sediment. Treatments included electron donors butyrate, lactate, propionate and acetate (1 mM each); alternate halogenated electron acceptors (haloprimers) tetrachlorobenzene (TeCB, 25 μM), pentachloronitrobenzene (PCNB, 25 μM), or 2,3,4,5,6-PCB (PCB116, 2.0 μM); and/or bioaugmentation with a culture containing Dehalococcoides ethenogenes strain 195 (3 × 10⁶ cells/mL). Dechlorination rates were enhanced in microcosms receiving bioaugmentation, PCNB and PCNB plus bioaugmentation, compared to other treatments. Microcosm subcultures generated after 415 days and spiked with PCB116 showed sustained capacity for dechlorination of PCB116 in PCNB, PCNB plus bioaugmentation, and TeCB treatments, relative to other treatments. Analysis of Chloroflexi 16S rRNA genes showed that TeCB and PCNB increased native Dehalococcoides spp. from the Pinellas subgroup; however this increase was correlated to enhanced dechlorination of low concentration weathered PCBs only in PCNB-amended microcosms. D. ethenogenes strain 195 was detected only in bioaugmented microcosms and decreased over 281 days. Bioaugmentation with D. ethenogenes strain 195 increased PCB dechlorination rates initially, but enhanced capacity for dechlorination of a model congener, PCB116, after 415 days occurred only in microcosms with enhanced native Dehalococcoides spp.     

Crack determination from boundary measurements—Reconstruction using experimental data

In this work we assess the effectiveness of Electrical Impedance Tomography for determining the presence and the location of an interior crack from boundary measurements. Electrical Impedance Tomography uses boundary voltages and currents to image the interior of a region. We collect the data needed for this nondestructive evaluation technique by laboratory experiments and apply two numerical inversion algorithms to the data. Our experiments show that the data collected are sufficient to give good estimates of crack locations and crack sizes.     

Automated merging of software prototypes

As software becomes more complex, more sophisticated development and maintenance methods are needed to ensure software quality. Computer-aided prototyping achieves this via quickly built and iteratively updated prototypes of the intended system. This process requires automated support for keeping track of many independent changes and for exploring different combinations of alternative changes and refinements. This article formalizes the update and change merging process, extends the idea to multiple changes to the same base prototype, and introduces a new method of slicing prototypes. Applications of this technology include automatic updating of different versions of existing software with changes made to the baseline version of the system, integrating changes made by different design teams during development, and checking consistency after integration of seemingly disjoint changes to the same software system.     

Application of ATP bioluminescence method to characterize performance of bioaerosol sampling devices

In this study we developed and tested an adenosine triphosphate (ATP) bioluminescence-based protocol for rapid characterization of bioaerosol sampling devices when collecting bacterial aerosols. Initial calibration of the method was performed using commercially available ATP assays to quantify known bacterial biomass in liquid samples. Here, the relative luminescence units (RLUs) indicative of total ATP content was plotted against total bacterial counts obtained using acridine orange direct count epifluorescence microscopy. The developed calibration curves were used to evaluate the collection performance of a BioSampler (SKC Inc., Eighty Four, PA) when sampling Pseudomonas fluorescens and Bacillus subtilis bacteria at three different sampling flow rates. The average collection efficiency for P. fluorescens and B. subtilis over all flow rates was 69% and 54%, respectively. Collection efficiencies determined by the ATP method for both bacteria at all flow rates agreed well (within 5%) with the acridine orange direct counts. Further, the ATP-based method allowed insights into the losses and fate of particles inside the sampling device. It was determined that a majority of losses occur in sampler's inlet. Such evaluation of losses is very difficult to perform using microscopy or culture-based techniques. Thus, the ATP-based technique could be reliably used as a tool for rapid and detailed evaluation of bioaerosol sampling devices.     

Deposition of Functionalized Cr7Ni Molecular Rings on Graphite from the Liquid Phase

Graphite is a clean substrate and its nanostructures hold great potential for applications. Anchoring large molecules on graphite represents a challenge for several reasons that essentially rise from the planar bonds of the packed honeycomb structure of carbon. Here, a systematic investigation by AFM and XPS on different derivatives of molecular Cr₇Ni rings deposited on highly oriented pyrolytic graphite (HOPG) is reported. Cr₇Ni is emerging as a prototipical example of molecular antiferromagnet on which quantum phenomena and coherence have been demonstrated. For the deposition of Cr₇Ni on HOPG, two strategies are adopted: 1) Cr₇Ni rings are functionalized with extended alkyl/benzene terminations and 2) a self‐assembled monolayer of alkyl chains with sulfonate terminations is deposited and then a cationic Cr₇Ni derivative is used. In both cases the electronic bond with the carbon surface is soft, but the two‐step procedure is efficient, albeit indirect, in sticking molecular Cr₇Ni on HOPG. These strategies can be easily extended to deposit other complex molecular aggregates on graphite from the liquid phase.     

Architectural Re-engineering of Janus using Object Modeling and Rapid Prototyping

This paper describes a case study to determine whether computer-aided prototyping techniques provide a cost-effective means for re-engineering legacy software. The case study consists of developing an object-oriented modular architecture for the existing US Army Janus combat simulation system, and validating the architecture via an executable prototype using the Computer Aided Prototyping System (CAPS), a research tool developed at the Naval Postgraduate School. The case study showed that prototyping can be a valuable aid in the re-engineering of legacy systems, particularly in cases where radical changes to system conceptualization and software structure are needed. The CAPS system enabled us to do this with a minimal amount of coding effort.