The role of dynamical polarization of the ligand-to-metal charge transfer excitations in the ab initio determination of effective exchange parameters

The role of the bridging ligand on the effective Heisenberg coupling parameters is analyzed in detail. This analysis strongly suggests that the ligand-to-metal charge transfer excitations are responsible for a large part of the final value of the magnetic coupling constant. This permits us to suggest a variant of the difference dedicated configuration interaction (DDCI) method, presently one of the most accurate and reliable for the evaluation of magnetic effective interactions. This method treats the bridging ligand orbitals mediating the interaction at the same level than the magnetic orbitals and preserves the high quality of the DDCI results while being much less computationally demanding. The numerical accuracy of the new approach is illustrated on various systems with one or two magnetic electrons per magnetic center. The fact that accurate results can be obtained using a rather reduced configuration interaction space opens the possibility to study more complex systems with many magnetic centers and/or many electrons per center.

Evaluation of the MIT-Scan-T2 for Non-Destructive PCC Pavement Thickness Determination Final Report, July 2008

The MIT-Scan-T2 device is marketed as a non-destructive way to determine pavement thickness on both HMA and PCC pavements. PCC pavement thickness determination is an important incentivedisincentive measurement for the Iowa DOT and contractors. The thickness incentive can be as much as 3% of the concrete contact unit price and the disincentive can be as severe as remove and replace. This study evaluated the potential of the MIT device for PCC pavement thickness quality assurance. The limited testing indicates the unit is sufficiently repeatable and accurate enough to replace core drilling as the thickness measurement method. Further study is needed to statistically establish the single user and multi-user/device precision as well as establish an appropriate sampling protocol and PWL specification.

Determination of four sequential stages during microautophagy in vitro.

Microautophagy is the transfer of cytosolic components into the lysosome by direct invagination of the lysosomal membrane and subsequent budding of vesicles into the lysosomal lumen. This process is topologically equivalent to membrane invagination during multivesicular body formation and to the budding of enveloped viruses. Vacuoles are lysosomal compartments of yeasts. Vacuolar membrane invagination can be reconstituted in vitro with purified yeast vacuoles, serving as a model system for budding of vesicles into the lumen of an organelle. Using this in vitro system, we defined different reaction states. We identified inhibitors of microautophagy in vitro and used them as tools for kinetic analysis. This allowed us to characterize four biochemically distinguishable steps of the reaction. We propose that these correspond to sequential stages of vacuole invagination and vesicle scission. Formation of vacuolar invaginations was slow and temperature-dependent, whereas the final scission of the vesicle from a preformed invagination was fast and proceeded even on ice. Our observations suggest that the formation of invaginations rather than the scission of vesicles is the rate-limiting step of the overall reaction.

Determination of entrance loss coefficients for pre-cast reinforced Concrete Box Culverts, December 2012

There is an increased interest in constructing Pre-Cast (PC) Twin and Triple Reinforced Concrete Box (RCB) culverts in Iowa due to the efficiency associated with their production in controlled environment and decrease of the construction time at the culvert sites. The design of the multi-barrel PC culverts is, however, based on guidelines for single-barrel cast-inplace (CIP) culverts despite that the PC and CIP culverts have different geometry. There is scarce information for multiplebarrel RCB culverts in general and even fewer on culverts with straight wingwalls as those designed by Iowa DOT. Overall, the transition from CIP to PC culverts requires additional information for improving the design specifications currently in use. Motivated by the need to fill these gaps, an experimental study was undertaken by IIHR-Hydroscience & Engineering. The goals of the study are to document flow performance curves and head losses at the culvert entrance for a various culvert geometry, flow conditions, and settings. The tests included single-, double- and triple-barrel PC and CIP culverts with two span-to-rise ratios set on mild and steep slopes. The tests also included optimization of the culvert geometry entrance by considering various configurations for the top bevel. The overall conclusion of the study is that by and large the current Iowa DOT design specifications for CIP culverts can be used for multi-barrel PC culvert design. For unsubmerged flow conditions the difference in the hydraulic performance curves and headloss coefficients for PC and CIP culverts are within the experimental uncertainty. Larger differences (specified by the study) are found for submerged conditions when the flow is increasingly constricted at the entrance in the culvert. The observed differentiation is less important for multi-barrel culverts as the influence of the wingwalls decreases with the increase of the number of barrels.

Single-step extraction of fluconazole from plasma by ultra-filtration for the measurement of its free concentration by high performance liquid chromatography.

High performance liquid chromatography (HPLC) is the reference method for measuring concentrations of antimicrobials in blood. This technique requires careful sample preparation. Protocols using organic solvents and/or solid extraction phases are time consuming and entail several manipulations, which can lead to partial loss of the determined compound and increased analytical variability. Moreover, to obtain sufficient material for analysis, at least 1 ml of plasma is required. This constraint makes it difficult to determine drug levels when blood sample volumes are limited. However, drugs with low plasma-protein binding can be reliably extracted from plasma by ultra-filtration with a minimal loss due to the protein-bound fraction. This study validated a single-step ultra-filtration method for extracting fluconazole (FLC), a first-line antifungal agent with a weak plasma-protein binding, from plasma to determine its concentration by HPLC. Spiked FLC standards and unknowns were prepared in human and rat plasma. Samples (240 microl) were transferred into disposable microtube filtration units containing cellulose or polysulfone filters with a 5 kDa cut-off. After centrifugation for 60 min at 15000g, FLC concentrations were measured by direct injection of the filtrate into the HPLC. Using cellulose filters, low molecular weight proteins were eluted early in the chromatogram and well separated from FLC that eluted at 8.40 min as a sharp single peak. In contrast, with polysulfone filters several additional peaks interfering with the FLC peak were observed. Moreover, the FLC recovery using cellulose filters compared to polysulfone filters was higher and had a better reproducibility. Cellulose filters were therefore used for the subsequent validation procedure. The quantification limit was 0.195 mgl(-1). Standard curves with a quadratic regression coefficient > or = 0.9999 were obtained in the concentration range of 0.195-100 mgl(-1). The inter and intra-run accuracies and precisions over the clinically relevant concentration range, 1.875-60 mgl(-1), fell well within the +/-15% variation recommended by the current guidelines for the validation of analytical methods. Furthermore, no analytical interference was observed with commonly used antibiotics, antifungals, antivirals and immunosuppressive agents. Ultra-filtration of plasma with cellulose filters permits the extraction of FLC from small volumes (240 microl). The determination of FLC concentrations by HPLC after this single-step procedure is selective, precise and accurate.

Temperature-dependent turnovers in sex-determination mechanisms: a quantitative model.

Sex determination is often seen as a dichotomous process: individual sex is assumed to be determined either by genetic (genotypic sex determination, GSD) or by environmental factors (environmental sex determination, ESD), most often temperature (temperature sex determination, TSD). We endorse an alternative view, which sees GSD and TSD as the ends of a continuum. Both effects interact a priori, because temperature can affect gene expression at any step along the sex-determination cascade. We propose to define sex-determination systems at the population- (rather than individual) level, via the proportion of variance in phenotypic sex stemming from genetic versus environmental factors, and we formalize this concept in a quantitative-genetics framework. Sex is seen as a threshold trait underlain by a liability factor, and reaction norms allow modeling interactions between genotypic and temperature effects (seen as the necessary consequences of thermodynamic constraints on the underlying physiological processes). As this formalization shows, temperature changes (due to e.g., climatic changes or range expansions) are expected to provoke turnovers in sex-determination mechanisms, by inducing large-scale sex reversal and thereby sex-ratio selection for alternative sex-determining genes. The frequency of turnovers and prevalence of homomorphic sex chromosomes in cold-blooded vertebrates might thus directly relate to the temperature dependence in sex-determination mechanisms.

A new method for the determination of plutonium and americium using high pressure microwave digestion and alpha-spectrometry or ICP-SMS

Plutonium and americium are radionuclides particularly difficult to measure in environmental samples because they are alpha-emitters and therefore necessitate a careful separation before any measurement, either using radiometric methods or ICP-SMS. Recent developments in extraction chromatography resins such as Eichrom (R) TRU and TEVA have resolved many of the analytical problems but drawbacks such as low recovery and spectral interferences still occasionally occur. Here, we report on the use of the new Eichrom (R) DGA resin in association with TEVA resin and high pressure microwave acid leaching for the sequential determination of plutonium and americium in environmental samples. The method results in average recoveries of 83 +/- 15% for plutonium and 73 +/- 22% for americium (n = 60), and a less than 10% deviation from reference values of four IAEA reference materials and three samples from intercomparisons exercises. The method is also suitable for measuring Pu-239 in water samples at the mu Bq/l level, if ICP-SMS is used for the measurement.

Determination of picogram levels of midazolam, and 1- and 4-hydroxymidazolam in human plasma by gas chromatography-negative chemical ionization-mass spectrometry.

Midazolam is a widely accepted probe for phenotyping cytochrome P4503A. A gas chromatography-mass spectrometry (GC-MS)-negative chemical ionization method is presented which allows measuring very low levels of midazolam (MID), 1-OH midazolam (1OHMID) and 4-OH midazolam (4OHMID), in plasma, after derivatization with the reagent N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide. The standard curves were linear over a working range of 20 pg/ml to 5 ng/ml for the three compounds, with the mean coefficients of correlation of the calibration curves (n = 6) being 0.999 for MID and 1OHMID, and 1.0 for 4OHMID. The mean recoveries measured at 100 pg/ml, 500 pg/ml, and 2 ng/ml, ranged from 76 to 87% for MID, from 76 to 99% for 1OHMID, from 68 to 84% for 4OHMID, and from 82 to 109% for N-ethyloxazepam (internal standard). Intra- (n = 7) and inter-day (n = 8) coefficients of variation determined at three concentrations ranged from 1 to 8% for MID, from 2 to 13% for 1OHMID and from 1 to 14% for 4OHMID. The percent theoretical concentrations (accuracy) were within +/-8% for MID and 1OHMID, within +/-9% for 4OHMID at 500 pg/ml and 2 ng/ml, and within +/-28% for 4OHMID at 100 pg/ml. The limits of quantitation were found to be 10 pg/ml for the three compounds. This method can be used for phenotyping cytochrome P4503A in humans following the administration of a very low oral dose of midazolam (75 microg), without central nervous system side-effects.

Determination of the critical period of weed control in corn using a thermal basis

Field studies were conducted over 3 years in southeast Buenos Aires, Argentina, to determine the critical period of weed control in maize (Zea mays L.). The treatments consisted of two different periods of weed interference, a critical weed-free period, and a critical time of weed removal. The Gompertz and logistic equations were fitted to relative yields representing the critical weed-free and the critical time of weed removal, respectively. Accumulated thermal units were used to describe each period of weed-free or weed removal. The critical weed-free period and the critical time of weed removal ranged from 222 to 416 and 128 to 261 accumulated thermal units respectively, to prevent yield losses of 2.5%. Weed biomass proved to be inverse to the crop yield for all the years studied. When weeds competed with the crop from emergence, a large increase in weed biomass was achieved 10 days after crop emergence. However, few weed seedlings emerged and prospered after the 5-6 leaf maize stage (10-20 days after emergence).

A highly sensitive LC-tandem MS assay for the measurement in plasma and in urine of salbutamol administered by nebulization during mechanical ventilation in healthy volunteers.

The new-generation nebulizers are commonly used for the administration of salbutamol in mechanically ventilated patients. The different modes of administration and new devices have not been compared. We developed a liquid chromatography-tandem mass spectrometry method for the determination of concentrations as low as 0.05 ng/mL of salbutamol, corresponding to the desired plasma concentration after inhalation. Salbutamol quantification was performed by reverse-phase HPLC. Analyte quantification was performed by electrospray ionization-triple quadrupole mass spectrometry using selected reaction monitoring detection ESI in the positive mode. The method was validated over concentrations ranging from 0.05 to 100 ng/mL in plasma and from 0.18 to 135 ng/mL in urine. The method is precise, with mean inter-day coefficient of variation (CV%) within 3.1-8.3% in plasma and 1.3-3.9% in urine, as well as accurate. The proposed method was found to reach the required sensitivity for the evaluation of different nebulizers as well as nebulization modes. The present assay was applied to examine whether salbutamol urine levels, normalized with the creatinine levels, correlated with the plasma concentrations. A suitable, convenient and noninvasive method of monitoring patients receiving salbutamol by mechanical ventilation could be implemented. Copyright © 2011 John Wiley & Sons, Ltd.

Determination of trimipramine and its demethylated and hydroxylated metabolites in plasma by gas chromatography-mass spectrometry.

A gas chromatographic-mass spectrometric (GC-MS) method has been developed, for the determination of trimipramine (TRI), desmethyltrimipramine (DTRI), didesmethyltrimipramine (DDTRI), 2-hydroxytrimipramine (2-OH-TRI) and 2-hydroxydesmethyltrimipramine (2-OH-DTRI). The method includes two derivatization steps with trifluoroacetic acid anhydride and N-methyl-N-(tert.-butyldimethyl silyl)trifluoroacetamide and the use of an SE-54 capillary silica column. The limits of quantitation were found to be 2 ng/ml for DTRI and 4 ng/ml for all other substances. Besides, methods have been optimized for the hydrolysis of the glucuronic acid conjugated metabolites. This specific detection method is useful, as polymedication is a usual practice in clinical situations, and its sensitivity allows its use for single-dose pharmacokinetic studies.

Circulating EM66 is a highly sensitive marker for the diagnosis and follow-up of pheochromocytoma.

We have previously demonstrated that measurement of tissue concentration of the novel secretogranin II-derived peptide EM66 may help to discriminate between benign and malignant pheochromocytomas. The aim of the present study was to characterize EM66 in plasma and urine of healthy volunteers and pheochromocytoma patients, in order to further evaluate the usefulness of this peptide as a circulating marker for the management of the tumors. HPLC analysis of plasma and urine samples demonstrated that the EM66-immunoreactive material coeluted with the recombinant peptide. In healthy volunteers, plasma and urinary EM66 levels were, respectively, 2.6 (1.9-3.7) ng/ml and 2.9 (1.9-4.6) ng/ml. In patients with pheochromocytoma, plasma EM66 levels were 10-fold higher than those of healthy volunteers (26.9 (7.3-44) ng/ml), and returned to normal values after removal of the tumor. In contrast, urinary EM66 levels were not significantly different from those of healthy volunteers (3.2 (2.2-3.9) ng/ml). Measurement of total or free plasma metanephrines and 24 hr urinary metanephrines in our series of patients revealed that these tests, taken separately, are less sensitive than the EM66 determination. Pheochromocytes in primary culture secreted high levels of EM66, suggesting that the chromaffin tumor was actually responsible for the increased plasma peptide concentrations in the patients. These data indicate that EM66 is secreted in the general circulation and that elevated plasma EM66 levels are correlated with the occurrence of pheochromocytoma. Thus, EM66 is a sensitive plasma marker that should be considered as a complementary tool in the management of pheochromocytoma.

A fully validated method for the determination of arsenic species in rice and infant cereal products

A full validation of inorganic arsenic (iAs), methylarsonic acid (MA), and dimethyl arsinic acid (DMA) in several types of rice and rice-based infant cereals is reported. The analytical method was developed and validated in two laboratories. The extraction of the As species was performed using nitric acid 0.2 % and hydrogen peroxide 1 %, and the coupled system liquid chromatography-inductively coupled plasma-mass spectrometry (LCICP-MS) was used for speciation measurements. Detection limit (DL), quantification limit, linearity, precision, trueness, accuracy, selectivity, as well as expanded uncertainty for iAs, MA, and DMA were established. The certified reference materials (CRMs) (NMIJ 7503a, NCS ZC73008, NIST SRM 1568a) were used to check the accuracy. The method was shown to be satisfactory in two proficiency tests (PTs). The broad applicability of the method is shown from the results of analysis of 29 samples including several types of rice, rice products, and infant cereal products. Total As ranged from 40.1 to 323.7 μg As kg1. From the speciation results, iAs was predominant, and DMA was detected in some samples while MA was not detected in any sample.

Smart instrumentation for determination of ligament stiffness and ligament balance in total knee arthroplasty.

Ligament balance is an important and subjective task performed during total knee arthroplasty (TKA) procedure. For this reason, it is desirable to develop instruments to quantitatively assess the soft-tissue balance since excessive imbalance can accelerate prosthesis wear and lead to early surgical revision. The instrumented distractor proposed in this study can assist surgeons on performing ligament balance by measuring the distraction gap and applied load. Also the device allows the determination of the ligament stiffness which can contribute a better understanding of the intrinsic mechanical behavior of the knee joint. Instrumentation of the device involved the use of hall-sensors for measuring the distractor displacement and strain gauges to transduce the force. The sensors were calibrated and tested to demonstrate their suitability for surgical use. Results show the distraction gap can be measured reliably with 0.1mm accuracy and the distractive loads could be assessed with an accuracy in the range of 4N. These characteristics are consistent with those have been proposed, in this work, for a device that could assist on performing ligament balance while permitting surgeons evaluation based on his experience. Preliminary results from in vitro tests were in accordance with expected stiffness values for medial collateral ligament (MCL) and lateral collateral ligament (LCL).