NMR Instabilities in Highly Magnetised Liquid Helium Solutions

Spin dynamics have been shown to be dramatically altered in anisotropic samples when the internal dipolar field dominates the external static field gradients. In recent NMR experiments on laser polarised liquids (He or Xe), spectral clustering and precession instabilities have been observed. Early analyses have suggested the generic nature of these effects, and tentatively addressed their existence in bulk systems. We report here on NMR experiments conducted in spherical samples of laser-polarised liquid helium mixtures (0.5–10% ³ He in ⁴ He at 1–2K). We focus on the relative influence of magnetisation density and applied field gradients on FID signals induced by 90° tipping pulses. Numerical simulations are used to study the effects of distant dipolar couplings on local and global magnetisation. A discussion of the features of FID and spin echo signals is presented.     

NMR Time Reversal Experiments in Highly Polarised Liquid 3He-4He Mixtures

Long-range magnetic interactions in highly magnetised liquids (laser-polarised ³He-⁴He dilute mixtures at 1 K in our experiment) introduce a significant non-linear and non-local contribution to the evolution of nuclear magnetisation that leads to instabilities during free precession. We recently demonstrated that a multi-echo NMR sequence, based on the magic sandwich pulse scheme developed for solid-state NMR, can be used to stabilise the magnetisation against the effect of distant dipolar fields. Here, we report investigations of echo attenuation in an applied field gradient that show the potential of this NMR sequence for spin diffusion measurements at high magnetisation densities.      

Mine Closure of Pit Lakes as Terminal Sinks: Best Available Practice When Options are Limited?

In an arid climate, pit lake evaporation rates can exceed influx rates, causing the lake to function as a hydraulic terminal sink, with water levels in the pit remaining below surrounding groundwater levels. We present case studies from Western Australia for two mines nearing closure. At the first site, modelling indicates that waste dump covers for the potentially acid forming (PAF) material would not be successful over the long term (1,000 years or more). The second site is a case study where PAF management is limited by the current waste rock dump location and suitable cover materials. Pit lake water balance modelling using Goldsim software indicated that both pit lakes would function as hydraulic terminal sinks if not backfilled above long-term equilibrium water levels. Poor water quality will likely develop as evapoconcentration increases contaminant concentrations, providing a potential threat to local wildlife. Even so, the best current opportunity to limit the risk of contaminant migration and protect regional groundwater environments may be to limit backfill and intentionally produce a terminal sink pit lake.     

Fluid flow through dentin–self-etch resin interface during long term in vitro aging

This work aimed at characterizing the interface between dentin and the resin-infiltrated dentin made following the etching procedure that prepares for the bonding of tooth-colored restorations. The non-destructive measurement of fluid flow through the dentin–self-etch resin interface was followed repeatedly during a two year aging period. Two self-etch adhesive systems were selected for experiments on the evolution of permeability and evaluation of infrared spectral changes following the 24 month aging period. The adhesives contained water and a co-solvent, namely acetone for iBond, and t-butanol for Xeno V. For both adhesive systems, the permeability decreased during the first 3 months after etching, reaching values of ? 66.9 and ? 70.5% for iBond and Xeno V, respectively. Afterwards, the fluid flow slowly increased but still remained below 50% of the initial value following the 2-year aging period. The slow degradation of the resin–dentin interface, attributed to water impregnated collagen hydrolysis, is evidenced by these variations in fluid flow, and is also noted by the increase in water-related infrared absorption bands at 3300 cm^? 1 and at 1600 cm^? 1. The results are discussed in terms of co-solvent hydrophobicity, evaporation rate and viscosity together with resin infiltration depth and affinity for water.     

Hybrid Dual-Mode Frequency Synthesis for Cognitive Multi-radio Front-Ends

This paper investigates a novel approach to reconfigurable frequency synthesis for flexible radio transceivers in future cognitive multi-radios. The frequency range covered by the proposed multi-radio synthesizer corresponds to the frequency bands of the most diffused wireless communication standards operating in the radio band ranging from 800 MHz to 6 GHz. A hybrid phase locked loop (PLL) based frequency synthesizer is proposed here and a novel switching protocol is presented and validated on an experimental evaluation board. The proposed architecture combines fractional and integer PLL modes of operation along with a switched loop filter topology. Compared to standard PLL techniques, the proposed configuration provides great flexibility options and moreover, it offers relatively low circuit complexity and low power consumption. The proposed architecture provides reconfigurability of the loop bandwidth, frequency resolution, phase noise and settling time performance and hence, it can adapt itself to diverse requirements given by the concerned wireless communication standards.     

Design support tools to sustain climate change adaptation at the local level: A review and reflection on their suitability

For mid-latitude cities, higher summer temperatures due to climate change are a cause for concern because they aggravate the urban heat island phenomenon and reduce thermal comfort inside buildings. By acquiring the appropriate knowledge and skills, architects and urban designers can become key actors in adaptation to climate change. Two workshops bringing together architects and urban designers provided evidence of deficiencies in this area. We hypothesize that a design support tool (DST) focused on the issue of adaptation of mid-latitude cities to rising summer temperatures could help improve knowledge and skills of professionals in the field. The first section presents the results taken from a review and classification of DSTs, which highlight the tools' features that are likely to reach this goal. Tools of the “hybrid” category seem most appropriate. To verify this, seven DSTs were selected and tested by fourteen students enrolled in a graduate-level architecture design studio. The second section presents the results from this test, including an analysis of the final projects, a web-based questionnaire and two focus groups. The relevance of hybrid approaches is established, but the results bring into question the capacity of a single DST to meet the individual and multiple needs of professionals.     

Parametric imaging for characterizing focal liver lesions in contrast-enhanced ultrasound

The differentiation between benign and malignant focal liver lesions plays an important role in diagnosis of liver disease and therapeutic planning of local or general disease. This differentiation, based on characterization, relies on the observation of the dynamic vascular patterns (DVP) of lesions with respect to adjacent parenchyma, and may be assessed during contrast-enhanced ultrasound imaging after a bolus injection. For instance, hemangiomas (i.e., benign lesions) exhibit hyper-enhanced signatures over time, whereas metastases (i.e., malignant lesions) frequently present hyperenhanced foci during the arterial phase and always become hypo-enhanced afterwards. The objective of this work was to develop a new parametric imaging technique, aimed at mapping the DVP signatures into a single image called a DVP parametric image, conceived as a diagnostic aid tool for characterizing lesion types. The methodology consisted in processing a time sequence of images (DICOM video data) using four consecutive steps: (1) pre-processing combining image motion correction and linearization to derive an echo-power signal, in each pixel, proportional to local contrast agent concentration over time; (2) signal modeling, by means of a curve-fitting optimization, to compute a difference signal in each pixel, as the subtraction of adjacent parenchyma kinetic from the echopower signal; (3) classification of difference signals; and (4) parametric image rendering to represent classified pixels as a support for diagnosis. DVP parametric imaging was the object of a clinical assessment on a total of 146 lesions, imaged using different medical ultrasound systems. The resulting sensitivity and specificity were 97% and 91%, respectively, which compare favorably with scores of 81 to 95% and 80 to 95% reported in medical literature for sensitivity and specificity, respectively.     

Engineering stability into Escherichia coli secreted Fabs leads to increased functional expression

The recombinant expression of immunoglobulin domains, Fabs and scFvs in particular, in Escherichia coli can vary significantly from antibody to antibody. We hypothesized that poor Fab expression is often linked to poor intrinsic stability. To investigate this further, we applied a novel approach for stabilizing a poorly expressing anti-tetanus toxoid human Fab with a predisposition for being misfolded and non-functional. Forty-five residues within the Fab were chosen for saturation mutagenesis based on residue frequency analysis and positional entropy calculations. Using automated screening, we determined the approximate midpoint temperature of thermal denaturation (TM) for over 4000 library members with a maximum theoretical diversity of 855 unique mutations. This dataset led to the identification of 11 residue positions, primarily in the Fv region, which when mutated enhanced Fab stability. By combining these mutations, the TM of the Fab was increased to 92 degrees C. Increases in Fab stability correlated with higher expressed Fab yields and higher levels of properly folded and functional protein. The mutations were selected based on their ability to increase the apparent stability of the Fab and therefore the exact mechanism behind the enhanced expression in E.coli remains undefined. The wild-type and two optimized Fabs were converted to an IgG1 format and expressed in mammalian cells. The optimized IgG1 molecules demonstrated identical gains in thermostability compared to the Fabs; however, the expression levels were unaffected suggesting that the eukaryotic secretion system is capable of correcting potential folding issues prevalent in E.coli. Overall, the results have significant implications for the bacterial expression of functional antibody domains as well as for the production of stable, high affinity therapeutic antibodies in mammalian cells.     

Surface characterization and reactivity of a nitrogen atomized 304L stainless steel powder

The oxide layer on the surface of the particles of a nitrogen atomized 304L stainless steel powder was quantitatively characterized using X-ray photoelectron spectroscopy (XPS), secondary-ion microprobe (IMP) analysis, selective reduction of surface iron oxide by hydrogen, and chemical analysis for total oxygen, all as a function of particle size. The composition and thickness of the oxide layer do not depend significantly on particle size. A 5.8-nm-thick outer layer made of MnO and Fe₂O₃ islands covers a 2.4-nm-thick inner layer of Cr₂O₃. The reaction of the powder with O₂ impurity in either H₂ or N₂ exhibits different kinetics and mechanism in both cases. In H₂, a selective oxidation of the alloying elements Mn, Cr, and Si takes place above 400 °C with a parabolic isothermal rate law. In N₂, iron also is oxidized, isolated Fe₂O₃-rich microcrystals form over a Cr₂O₃-rich uniform underlayer, and the isothermal kinetics are accelerated.     

Cdk2 activity is dispensable for the onset of DNA replication during the first mitotic cycles of the sea urchin early embryo

Earlier work reported the important role of Cdk2 as a regulator of DNA replication in somatic cells and in Xenopus extracts. In the present report we analyze in vivo the involvement of Cdk2 in DNA replication during early embryogenesis using the first mitotic cycles of sea urchin embryos. Unfertilized Sphaerechinus granularis eggs are arrested after the second meiotic cytokinesis. Fertilization resumes the block and induces DNA replication after a short lag period, making sea urchin early embryo a good model for studying in vivo the onset of DNA replication. We show that Cdk2 as well as its potential partner cyclin A are present in the nucleus in G1 and S phase and therefore available for DNA replication. In accordance with data obtained in Xenopus egg extracts we observed that Cdk2 kinase activity is low and stable during the entire cycle. However, in contrast with this in vitro system in which Cdk2 activity is required for the onset of DNA replication, the specific inhibition of Cdk2 kinase by microinjection of the catalytically inactive Cdk2-K33R or the inhibitor p21(Cip1) does not prevent DNA replication. Because olomoucine, DMAP, and emetine treatments did not preclude DNA synthesis, neither cyclin A/Cdk1 nor cyclin B/Cdk1 kinase activities are necessary to replace the absence of Cdk2 kinase in promoting DNA replication. These data suggest that during early embryogenesis Cdks activities, in particular Cdk2, are dispensable in vivo for the initiation step of DNA replication. However, the specific localization of Cdk2 in the nucleus from the beginning of M phase to the end of S phase suggests its involvement in other mechanisms regulating DNA replication such as inhibition of DNA re-replication and/or that its regulating role is achieved through a pathway independent of the kinase activity. We further demonstrate that even after inhibition of Cdk activities, the permeabilization of the nuclear membrane is required to allow a second round of DNA replication. However, in contrast to Xenopus egg extracts, re-replication can take place in the absence of DMAP-sensitive kinase.