Deciphering strontium sulfate precipitation via Ostwald's rule of stages: From prenucleation clusters to solution-mediated phase tranformation.

Multiple-step nucleation pathways have been observed during mineral formation in both inorganic and biomineral systems. These pathways can involve precursor aqueous species, amorphous intermediates, or metastable phases. Despite the widespread occurrence of these processes, elucidating the precise nucleation steps and the transformation mechanisms between each step remains a challenging task. Using a suite of potentiometric, microscopic, and spectroscopic tools, we studied the nucleation pathway of SrSO4 as a function of the physico-chemical solution parameters. Our observations reveal that below a threshold supersaturation, nucleation is driven by bound species, akin to the prenucleation cluster model, which directly leads to the formation of the stable phase celestine, SrSO4. At higher supersaturations, this situation is altered, with nucleation dominated by the consumption of free ions. Importantly, this change in nucleation mechanism is coupled to the formation of a hemihydrate metastable phase, SrSO4 · 1/2H2O, which eventually transforms into celestine, adhering to Ostwald's rule of stages. This transformation is a solution-mediated process, also occurring in the presence of a fluid film and is controlled by the physico-chemical parameters of the surrounding environment. It proceeds through the dissolution of the metastable phase and the de novo crystallization of the final phase. Overall, our results reveal that ion association taking place during the prenucleation stage dictates whether the nucleation pathway goes through an intermediate phase or not. This also underlines that although Ostwald's rule of stages is a common process, it is not a prerequisite for mineral formation-even in systems where it can occur.

Scaffolds in a shell-a new approach combining one-photon and two-photon polymerization.

We report on a laser system combining one-photon and two-photon polymerization for precise and fast fabrication of macroscopic three-dimensional structures featuring microscale and nanoscale characteristics. This single-stage process significantly reduces the production time as demonstrated by scaffolds in a shell application. Porous scaffolds with different pore sizes are surrounded by a ring so that cells can be seeded directly to the scaffolds kept in a shell and do not spread over the whole substrate expecting a saving of cell suspension, faster growth on the scaffolds, and a more controllable environment. Compared to a two-photon polymerization process, the ring is fabricated about 500 times faster using one-photon polymerization. The presented hybrid process qualifies for further applications illustrated by a fluidic system.

Exploring dynamic surface processes during silicate mineral (wollastonite) dissolution with liquid cell TEM.

Most liquid cell transmission electron microscopy (LC TEM) studies focus on nanoparticles or nanowires, in large part because the preparation and study of materials in this size range is straightforward. By contrast, this is not true for samples in the micrometre size range, in large part because of the difficulties associated with sample preparation starting from a 'bulk' material. There are also many advantages inherent to the study of micrometre-sized samples compared to their nanometre-sized counterparts. Here, we present a liquid cell transmission electron study that employed an innovative sample preparation technique using focused ion beam (FIB) milling to fabricate micrometre-sized electron transparent lamellae that were then welded to the liquid cell substrate. This technique, for which we have described in detail all of the fabrication steps, allows for samples having dimensions of several square micrometres to be observed by TEM in situ in a liquid. We applied this technique to test whether we could observe and measure in situ dissolution of a crystalline material called wollastonite, a calcium silicate mineral. More specifically, this study was used to observe and record surface dynamics associated with step and terrace edge movement, which are ultimately linked to the overall rate of dissolution. The wollastonite lamella underwent chemical reactions in pure deionized water at ambient temperature in a liquid cell with a 5-µm-spacer thickness. The movement of surface steps and terraces was measured periodically over a period of almost 5 h. Quite unexpectedly, the one-dimensional rates of retreat of these surface features were not constant, but changed over time. In addition, there were noticeable quantitative differences in retreat rates as a function crystallographic orientation, indicating that surface retreat is anisotropic. Several bulk rates of dissolution were also determined (1.6-4.2 • 10-7 mol m-2 s-1 ) using the rates of retreat of representative terraces and steps, and were found to be within one order of magnitude of dissolution rates in the literature based on aqueous chemistry data.

Fabrication of Bragg gratings in planar PMMA: impact of UV dosage and thermal annealing.

We report on the fabrication of planar Bragg gratings in polymer substrates and study the impact of the UV dosage and a subsequent thermal annealing on the reflectivity of the gratings and the full width at half maximum bandwidth of the reflected spectra. In addition, the influence of the grating length is investigated, showing that gratings as short as 4 mm continuously exhibit good reflection properties, facilitating miniaturized sensor designs. Moreover, we highlight that the polymer Bragg gratings exhibit a remarkable stable reflected spectrum for over two years. Finally, the experimentally determined spectral characteristics of the Bragg gratings are compared to simulated results revealing excellent agreement.

Photodiode-based cutting interruption sensor for near-infrared lasers.

We report on a photodiode-based sensor system to detect cutting interruptions during laser cutting with a fiber laser. An InGaAs diode records the thermal radiation from the process zone with a ring mirror and optical filter arrangement mounted between a collimation unit and a cutting head. The photodiode current is digitalized with a sample rate of 20 kHz and filtered with a Chebyshev Type I filter. From the measured signal during the piercing, a threshold value is calculated. When the diode signal exceeds this threshold during cutting, a cutting interruption is indicated. This method is applied to sensor signals from cutting mild steel, stainless steel, and aluminum, as well as different material thicknesses and also laser flame cutting, showing the possibility to detect cutting interruptions in a broad variety of applications. In a series of 83 incomplete cuts, every cutting interruption is successfully detected (alpha error of 0%), while no cutting interruption is reported in 266 complete cuts (beta error of 0%). With this remarkable high detection rate and low error rate, the possibility to work with different materials and thicknesses in combination with the easy mounting of the sensor unit also to existing cutting machines highlight the enormous potential for this sensor system in industrial applications.

Compressive and tensile strain sensing using a polymer planar Bragg grating.

A polymer planar Bragg grating sensor is used for measuring both mechanical compressive and tensile strain. The planar waveguide with integrated Bragg grating is fabricated in bulk Polymethylmethacrylate in a single writing step using combined amplitude and phase mask technique. After butt coupling of a single-mode optical fiber the planar structure can be applied for measuring both mechanical tensile and compressive strain alongside the integrated waveguide without the need of further modifications. In this respect, we particularly report for the first time compressive strain measurements using a polymer Bragg grating. Furthermore, the sensitivity of the sensor against tensile and compressive strain, its reproducibility and hysteresis are investigated and discussed.

Can an ab initio three-body virial equation describe the mercury gas phase?

We report a sixth-order ab initio virial equation of state (EOS) for mercury. The virial coefficients were determined in the temperature range from 500 to 7750 K using a three-body approximation to the N-body interaction potential. The underlying two-body and three-body potentials were fitted to highly accurate Coupled-Cluster interaction energies of Hg2 (Pahl, E.; Figgen, D.; Thierfelder, C.; Peterson, K. A.; Calvo, F.; Schwerdtfeger, P. J. Chem. Phys. 2010, 132, 114301-1) and equilateral-triangular configurations of Hg3. We find the virial coefficients of order four and higher to be negative and to have large absolute values over the entire temperature range considered. The validity of our three-body, sixth-order EOS seems to be limited to small densities of about 1.5 g cm(-3) and somewhat higher densities at higher temperatures. Termwise analysis and comparison to experimental gas-phase data suggest a small convergence radius of the virial EOS itself as well as a failure of the three-body interaction model (i.e., poor convergence of the many-body expansion for mercury). We conjecture that the nth-order term of the virial EOS is to be evaluated from the full n-body interaction potential for a quantitative picture. Consequently, an ab initio three-body virial equation cannot describe the mercury gas phase.

Allylated cyclodextrins as effective affinity materials in chemical sensing of volatile aromatic hydrocarbons using an optical planar Bragg grating sensor.

We report on the application of perallyl-substituted α-, ß- and γ-cyclodextrins to an optical planar Bragg grating refractive index sensor for the effective sensitization of the sensor for airborne volatile aromatic hydrocarbons. Thereby, the emphasis of this work lies on the comparison of the different cyclodextrin types regarding their suitability as affinity material assessed by the sensors sensitivity and response behavior. The opto-chemical sensor device showed an immediate and quick response to the application of the investigated analytes benzene, toluene and m-xylene as well as a linear dependence on the concentration of those analytes. Studies on the sensors sensitivity depending on the applied cyclodextrin types revealed a generally higher sensitivity for the sensor sensitized with perallyl-substituted ß-cyclodextrins. Here, the sensor systems detection limit was found to 60±4 ppm for benzene, 18±3 ppm for toluene and 3.8±0.5 ppm for m-xylene. The response time and recovery time were found to approximately 30s and 40s, respectively, depending on the applied cyclodextrin and the chosen analyte.

Polymer planar Bragg grating sensor for static strain measurements.

We report on a new optical strain sensor based on a polymer planar Bragg grating (PPBG). The sensor consists of commercially available bulk Polymethlymethacrylate with a UV-inscribed optical waveguide as well as a Bragg grating, both of which are fabricated simultaneously in a single writing step. Upon axial strain, the Bragg wavelength reveals a quasi-instantaneous spectral red shift that depends linearly on the mechanical load with a sensitivity of 2.95 pm/µÎµ. The relative reflected intensity of the PPBG remains constant in the investigated load region.

Planar Bragg grating in bulk polymethylmethacrylate.

We report on a one-step writing process of a planar waveguide including a Bragg grating structure in bulk Polymethylmethacrylate (PMMA). A KrF excimer laser and a phase mask covered by an amplitude mask were used to locally increase the refractive index in PMMA and thereby generate simultaneously the planar waveguide and the Bragg grating. Our results show a reflected wavelength of the Bragg grating of about 1558.5 nm in accordance to the phase mask period. The reflectivity of the grating is about 80%. Initial characteristics of the Bragg grating structure towards humidity are investigated.

[Severe overdose in vitamin K antagonist secondary to grapefruit juice absorption]. / Surdosage grave en antivitamine K secondaire à l'absorption de jus de pamplemousse.

Vitamin K antagonists (VKA) are very currently used. Nevertheless, they are known to interact with numerous drugs and foods. Grapefruit juice is known to interact with some drugs metabolized by the enterocytary cytochrome P450 3A4 but its interaction with drugs as VKA that have a good biodisponibility is not clearly demonstrated. We report here the case of a woman treated with VKA in whom massive absorption of grapefruit juice entailed an excessive VKA dosage and a severe haemorrhage.

Contributions of multipolar polarizabilities to the isotropic and anisotropic light scattering induced by molecular interactions in gaseous methane.

The binary isotropic and anisotropic collision-induced light scattering spectra of gaseous methane at room temperature are analyzed in terms of a recent ab initio intermolecular potential and interaction-induced pair polarizability trace and anisotropy models, using quantum line-shapes computations. The translational spectra at relatively low frequencies are determined largely by the effects of bound and free transitions. At intermediate frequencies the spectra are sensitive to both the attractive part of the potential and the short-range part of the polarizability trace and anisotropy. The high frequency wings are discussed in terms of the collision-induced rotational Raman effect and estimates for the dipole-quadrupole polarizability A and the dipole-octopole polarizability E are obtained and checked with recent ab initio theoretical values.

Transport properties of asymmetric-top molecules.

Kinetic theory of gases is extended from linear molecules to asymmetric tops. The integration over the velocity of the centre of mass is carried out explicitly and the results are expressed in a form suitable for classical evaluation. These results can also be employed for spherical and symmetric tops.

Abdominal compartment syndrome and intraabdominal sepsis: two of the same kind?

BACKGROUND: Abdominal compartment syndrome and intra-abdominal hypertension are frequently associated with peritonitis. The aim of this study is to establish the relationship between intra-abdominal hypertension and intra-abdominal sepsis especially in critically ill patients. METHODS: Relevant information was identified through a Medline search (1966-October 2006). The terms used were "intra-abdominal sepsis", "peritonitis", "abdominal compartment syndrome", "intra-abdominal hypertension" and "relaparotomy for sepsis". The search was limited to English- and French-language publications. RESULTS: Only a few clinical trials exist on this specific topic. Further investigations are required to define the incidence of intra-abdominal hypertension in intra-abdominal sepsis, and the prognostic impact of this setting and finally the potential specific treatment. Abdominal compartment syndrome is more likely linked to the abdominal surgery than to peritonitis itself. CONCLUSION: Intra-abdominal pressure monitoring can be valuable in critically ill patients with suspicion of persisting intra-abdominal sepsis after surgical peritonitis treatment.

Abdominal compartment syndrome and intraabdominal sepsis: two of the same kind?

BACKGROUND: Abdominal compartment syndrome and intra-abdominal hypertension are frequently associated with peritonitis. The aim of this study is to establish the relationship between intra-abdominal hypertension and intra-abdominal sepsis especially in critically ill patients. METHODS: Relevant information was identified through a Medline search (1966-October 2006). The terms used were "intra-abdominal sepsis", "peritonitis", "abdominal compartment syndrome", "intra-abdominal hypertension" and "relaparotomy for sepsis". The search was limited to English- and French-language publications. RESULTS: Only a few clinical trials exist on this specific topic. Further investigations are required to define the incidence of intra-abdominal hypertension in intra-abdominal sepsis, and the prognostic impact of this setting and finally the potential specific treatment. Abdominal compartment syndrome is more likely linked to the abdominal surgery than to peritonitis itself. CONCLUSION: Intra-abdominal pressure monitoring can be valuable in critically ill patients with suspicion of persisting intra-abdominal sepsis after surgical peritonitis treatment.

Body mass index, weight gain, and risk of endometrial cancer.

Excess weight near the time of diagnosis is a well-established risk factor for endometrial cancer; less is known about the influence of weight at earlier periods of a woman's life or weight gain in adulthood. In a case-control study in western New York State, interviews were conducted with 232 incident endometrial cancer cases, diagnosed between 1986 and 1991, and 631 community controls. Body mass index at 16 years of age and 20, 10, and 2 years before interview and changes in body mass index between these time periods were examined. While being relatively heavy at 16 years of age was associated with slightly increased risk [adjusted odds ratio (OR) = 1.28, 95% confidence interval (CI) = 0.84-1.96], large gains over the entire period from 16 years of age to 2 years ago (OR = 3.45, CI = 2.13-5.57) and high body mass index close to the time of diagnosis (OR = 3.21, CI = 2.01-5.15) were associated with greater risk. Differences in mean body mass index between cases and controls increased over time.